caracterizaciÓn de la inflamabilidad de especies...

CARACTERIZACIÓN DE LA INFLAMABILIDAD DE ESPECIES LEÑOSAS EN EL

CHACO SEMIÁRIDO DE ARGENTINA, A PARTIR DEL ANÁLISIS DE RASGOS

FUNCIONALES

AUTOR: ANA CAROLINA SANTACRUZ GARCÍA

DIRECTOR: DRA. SANDRA BRAVO

UNIVERSIDAD DISTRITAL FRANCISCO JOSE DE CALDAS

FACULTAD DE MEDIO AMBIENTE Y RECURSOS NATURALES

MAESTRÍA EN MANEJO USO Y CONSERVACIÓN DEL BOSQUE

BOGOTA

2018

Nota de Aceptación

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Firma de la Directora

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Firma del Jurado

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Firma del Jurado

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Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,

a partir del análisis de rasgos funcionales

DEDICATORIA

A quienes extraño con el alma y adoro con mi vida:

A quienes nunca se han cansado de creer en mí y

han estado siempre presentes, mi par de

viejitos: Bertha y Alberto

A quienes son mi motor, mi principal motivación día a día, mi par de fotocopias:

Sofi y mi Negra

A mi abue, simplemente por ser tan peculiar como solo

puede ser él

A mis amigos de siempre, los que creyeron que este día

llegaría y a los que no, también...

A los amigos que he ido

haciendo día a día, a medida que avanza esta

travesía

A quién siempre persevero, tuvo infinita paciencia y me

apoyo a terminar este proyecto y emprender otros más, mi directora de tesis:

Sandra

Y sobre todo, a Dios, a la virgen y a la vida por la luz y la fuerza que me brindan

cada día...



TABLA DE CONTENIDO

RESUMEN…………………………………………………………………………………….. 1

ABSTRACT…………………………………………………………………………………….. 2

I. INTRODUCCIÓN GENERAL…………………………………………………… 3

II. CAPÍTULO I: “Flammability characterization of woody species in semiarid Chaco

region, Argentina, through functional traits analysis” ………………………..…. 7

Abstract…………………………………………………………………………..….7

Resumen……………………………………………………………………………..9

Highlights…………………………………………………………………………..11

1. Introduction……...…………………………………………………………….12

2. Material and methods……………………………………………………….…14

2.1 Study area……………………………………...………………………….14

2.2 Functional traits of plant flammability……………………………..…….18

2.3 Seasonal variations of flammability……………………..………………..18

2.4 Statistical data analysis……………………………………………………19

3. Results……………………………………………………………………..…..19

3.1 Disturbance effects……...…………………………………………...……19

3.2 Interspecific variation of flammability…………………………… ……...22

3.3 Seasonal variations of flammability……………………………………... 23

4. Discussion……………………………………………………………………..27

5. Conclusions……………………………………………………………………31

6. Acknowledgements…………………...……………………...………………..32

III. CONCLUSIONES GENERALES…………………………………………...…….33

IV. RECOMENDACIONES GENERALES………………………………………..…34

V. REFERENCIAS…………………………………………………………………...35



INDICE DE TABLAS

Table 1.Botany family, foliar phenology and growth habit for the studied species……………16

Table 2.Average (A) and Standard Deviation (SD) for six flammability functional traits evaluated

in eleven native species from Western Chaco region, Argentina, during three sampling dates for

fire season (June, August and October) in forest with different disturbance history. CF= Forest

under closure, without disturbances over three last decades, considered as reference condition;

DF=Disturbed forest with fires and roller chopper applications. References: TDMC=Twig dry-

matter content (mg*g-1); TDT= Twig drying time (days); LDMC=Leaf dry-matter content (mg*g-

1); TMC= Twig moisture content (%); FMC=Foliar moisture content (%); DR =Number of

ramifications orders; FD=1 to 5 categories following Pérez-Harguindeguy et al. 2013…..……21



INDICE DE FIGURAS

Figure 1. Study sites localization in (A) American Chaco Region, (B) Santiago del Estero

Province included in South extreme of American Chaco Region, (C) Sampling sites localization

at Experimental Ranch Francisco Cantos belonging to the National Institute of Agricultural

Technology (INTA)……………………………………………………………………………..14

Figure 2. Temperatures (continuous line), monthly rains (vertical bars) and average dates of the

first and last frosts in the Experimental Ranch “Francisco Cantos”, INTA EEA Santiago del

Estero. The rectangle indicates fire season in the Chaco region’s central zone. Climatic data period

1981-1990, EEE Meteorological Observatory Santiago del Estero, INTA. Source: Kunst & Bravo,

2003………………………………………………………...…………………………………..15

Figure 3. Study sites: (A) Satellite image of the Experimental Ranch “Francisco Cantos”

belonging to the National Institute of Agricultural Technology (INTA), Argentina, (B) Control

plot, a forest under closure, without disturbances over three last decades (C) Disturbed plot,

disturbed forests with fires and roller chopper applications…………………….……………….17

Figure 4. Flammability degree (FD) in native woody species from Western Chaco region,

Argentina, during three sampling dates along fire season (June, August and October) in forests

with different disturbance history. CF= Forest under closure (without disturbances over three last

decades, considered as reference condition) DF=Disturbed forest with fires and roller chopping

with management goal. Different letters indicates significant differences between sampling dates,

according to LSD Fisher, Tukey and Di Rienzo, Guzmán, Casanoves (DGC) pair-wise

comparison procedure with α: 0,05, n=66 individuals by site each sampling

date………………………………………………………………………………………..…….20

Figure 5.Flammability degree (FD) in native woody species from Western Chaco region,

Argentina, following Pérez Harguindeguy et al. (2013). Same letters indicate no significant

differences between species, according to LSD Fisher pair-wise comparison procedure with α:



0,05, n=66 individuals. References: 1=S. gilliesii; 2=L. divaricata; 3=C. microphylla; 4=S.

lorentzii; 5=S. johnstonii 6=M. spinosa; 7=C. ehrenbergiana; 8=A. quebracho-blanco; 9= A.

emarginata; 10= S. mistol; 11=C. praecox……………………………………………………………..22

Figure 6.Dendrogram resulting from cluster analysis (Ward method and Euclidean distance) for

eleven native woody species from Western Chaco region, Argentina; based on six functional traits

related to flammability, foliar persistence and growth habit. References: SG=Senegalia gilliesii;

AQB=Aspidosperma quebracho-blanco; AE=Atamisquea emarginata; CM=Condalia

microphylla; LD=Larrea divaricata; SJ=Schinus johnstonii; MS=Maytenus spinosa; CE=Celtis

ehrenbergiana; SL=Schinopsis lorentzii; CP=Cercidium praecox; SM=Sarcomphalus

mistol……………………………………………………………………………...……..………23

Figure 7. Average flammability degree of 11 native woody species from Western Chaco region,

Argentina, at different sampling date along fire season (May to October) and rain season

(December to March). Same letters indicate no significant differences in flammability degree,

according to LSD Fisher pair-wise comparison procedure withα: 0,05, n=66

individuals…………………………………………………………………………….….……..24

Figure 8.Principal Component Analysis (PCA) of functional traits associated to flammability,

foliar persistence and growth habit for eleven natives woody species in Semiarid Chaco Region

(General trend). The ordination was based on six functional traits in six individuals per species.

FD=Flammability degree; LDMC=Leaf dry-matter content; TDMC=Twig dry-matter content;

DR=Degree of ramification; TDT=Twig drying time; PCO1= First principal coordinate,

represents growth habit; PCO2= Second principal coordinate, represents foliar persistence.

References: 1. S. gilliesii; 2. A. quebracho-blanco; 3. A. emarginata; 4. C. ehrenbergiana; 5. C.

microphylla; 6. L. divaricata; 7. M. spinosa; 8. C. praecox; 9. S. lorentzii; 10. S. johnstonii; 11.

S. mistol…………………………………………………………………………………………………….25

Figure 9.Principal Component Analysis (PCA) of functional traits associated to plant

flammability, foliar persistence and growth habit, for eleven native woody species from Western



Chaco region, Argentina, at different sampling dates during fire season (A) May; (B) October;

and rain season (C) December; (D) March. The ordination was based on six functional traits in

six individuals per species. FD=Flammability degree; LDMC=Leaf dry-matter content;

TDMC=Twig dry-matter content; DR=Degree of ramification; TDT=Twig drying time; PCO1=

First principal coordinate, represents growth habit; PCO2= Second principal coordinate,

represents foliar persistence. References: 1. S. gilliesii; 2. A. quebracho-blanco; 3. A. emarginata;

4. C. ehrenbergiana; 5. C. microphylla; 6. L. divaricata; 7. M. spinosa; 8. C. praecox; 9. S.

lorentzii; 10. S. johnstonii; 11. S. mistol…………………………………………………………26



1

RESUMEN

El conocimiento sobre las estrategias de las plantas para adaptarse y tolerar las perturbaciones

ambientales es un propósito fundamental para promover la conservación de la biodiversidad, en

el actual escenario de cambio climático. Nuestro objetivo fue evaluar la inflamabilidad de

especies nativas del Chaco semiárido desde un enfoque funcional, analizando variaciones

estacionales y el efecto de los disturbios. Se evaluaron ocho rasgos funcionales, 6 de ellos

vinculados a la inflamabilidad y dos referidos a persistencia foliar y hábito de crecimiento, en

once especies leñosas nativas de la región. Los mismos se compararon en bosques con diferente

historia de disturbios (BDHF): clausura y con disturbios como el fuego y rolados. Los resultados

indicaron que el 80% de la cobertura vegetal del Chaco Semiárido tiene grado de inflamabilidad

(GI) de media a elevada. Los rasgos funcionales de mayor influencia en la inflamabilidad fueron

el contenido de materia seca en ramas y hojas (CMSR y CMSH), la fenología foliar y el hábito

de crecimiento. La especie con mayor GI (Muy Alta) es Senegalia gilliesii, un arbusto de

arquitectura ramificada y elevado CMSR y CMSH, mientras que las especies con menor GI

(Media), se caracterizan por ser especies arbóreas con bajo CMSR. Se identificaron 2 picos de

inflamabilidad uno a finales de la temporada de fuego y otro al final de la temporada de lluvias,

relacionados a la fenología foliar y las condiciones climáticas durante la temporada de fuego. No

se encontraron diferencias significativas en la inflamabilidad de las especies en BDHF. Esto

representa un avance significativo para el estudio de la inflamabilidad de combustibles en bosques

chaqueños y contribuirá a mejorar las actividades de gestión de combustibles, prevención y

extinción de incendios.



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ABSTRACT

Knowledge about plant strategies for adapting and tolerating the environmental disturbances is a

fundamental purpose to promote biodiversity conservation, in the current climate change

scenario. Our objective was to evaluate the flammability of native species from Western Chaco

region through a functional approach, analysing seasonal variations and the effects of disturbances

on flammability. We evaluated eight functional traits, six of them related to flammability and two

referred to growth habit and foliar persistence, in eleven native woody species of the region. Those

traits were compared in forest with different disturbance history (FDDH): closure and

disturbances as fire and roller chopper applications. The 80 % of plant cover from Western Chaco

region forests have Medium to High flammability degree (FD). Functional traits more incident

on flammability were twig and leaf dry-matter content (TDMC and LDMC), foliar persistence

and growth habit. The unique species with Very High FD was Senegalia gilliesii, a shrub with

complex architecture and high TDMC and LDMC. Lowest flammability species (Medium FD)

were tree species with low TDMC. We identified two flammability peaks, one at the end of fire

season and the other at the end of rainy season, related to foliar persistence and climatic conditions

during fire season. There were no significant differences in the FD for studied species in FDDH.

These results represent a significant advance for fuels flammability studies in the Chaco region

and it will contribute to improve the activities of fuel management, prevention and firefighting.



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I. INTRODUCCIÓN GENERAL

Los incendios forestales se han convertido en un fenómeno recurrente que afecta la

dinámica poblacional de los ecosistemas tropicales; se estima que aproximadamente el 50% de

la superficie global actualmente afectada por el fuego corresponde a áreas tropicales. A

pesar de ello, las causas y efectos sobre la vegetación no han sido estudiados con profundidad en

gran parte de los países tropicales y subtropicales de Latinoamérica (Neri, Rodríguez y Contreras,

2009). El conocimiento sobre el comportamiento del fuego y sobre las características y

propiedades de los combustibles forestales es fundamental para el planeamiento de

estrategias preventivas y de las actividades de restauración de áreas quemadas. Es así como

instituciones como el INTA (Instituto Nacional de Tecnología Agropecuaria), emplean los datos

proporcionados por investigaciones de esta naturaleza, para la elaboración de manuales,

protocolos y capacitaciones con el fin de mitigar los efectos del fuego y la ocurrencia y

propagación de incendios forestales (Instituto Nacional de Tecnología Agropecuaria [INTA]

2014).

El fuego no constituye una amenaza a los ecosistemas, por el contrario, es un proceso natural

de los mismos (Agee, 1993); sin embargo, su recurrencia ha aumentado a causa del cambio

climático y de cambios en el uso de la tierra. Los factores antropogénicos como la transformación

y degradación de zonas forestales ocasionada por la expansión de la frontera agrícola, la

sobreexplotación de los recursos naturales y la deforestación, entre otras, han conducido a la

alteración de los regímenes naturales del fuego, lo que se ha convertido en una problemática a

nivel mundial aún en grandes áreas boreales y tropicales (Neri, Rodríguez y Contreras, 2009;

Conafor, 2012).

Los combustibles forestales son uno de los factores determinantes en la severidad y

recurrencia de los fuegos. Se define como combustibles forestales a “(…) cualquier

sustancia o compuesto susceptible de encenderse y mantener un proceso de combustión”.

Están constituidos por materia orgánica, abarcando tanto la biomasa de las plantas vivas y como



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sus restos muertos; éstos combustibles al interactuar con el tiempo atmosférico y las

condiciones topográficas conducen el fuego, cuya intensidad, velocidad y dirección de

propagación puede variar de acuerdo a la disponibilidad y distribución espacial de estos

combustibles (Conafor, 2012).

Un rasgo determinante del comportamiento del fuego es la inflamabilidad, la cual es un aspecto

clave para las tareas de gestión de incendios forestales. La gestión forestal preventiva considera

la necesidad del manejo de combustibles atendiendo a las características que le son propias,

con el fin de reducir los efectos ecológicos, sociales y económicos de los grandes incendios

(CREAF, 2003). La inflamabilidad se entiende como la capacidad de un combustible para entrar

en ignición y sostener el fuego. Esta considera cuatro aspectos: la combustibilidad que hace

referencia al calor desprendido durante la ignición, la ignitabilidad, que aborda la facilidad de un

material para entrar en ignición, la consumibilidad, que consiste en la proporción de un

combustible que entró en combustión y la sostenibilidad que analiza la duración de la

combustión (Anderson, 1970; Martin et al., 1994). Estos componentes de la inflamabilidad se

encuentran en estrecha relación con el contenido de agua de hojas, ramillas y ramas y con la

arquitectura del canopeo (Cornelissen et al., 2003; Pérez Harguindeguy et al., 2013) y es

considerado un concepto complejo, ya que puede ser analizado a escala individual como de

comunidad (Pausas y Moreira 2012).

Algunos trabajos han puesto énfasis en el efecto de los rasgos foliares sobre la

inflamabilidad de los combustibles, estudiando entre otros el contenido de humedad y tamaño de

las hojas, área foliar específica y resistencia de la lámina en diferentes especies (Gill et al., 1996;

Blackhall et al., 2012). Otros, se han enfocado en los aspectos bioquímicos vinculados a la

inflamabilidad de los combustibles como la presencia de resinas, aceites, terpenoides

considerados promotores del fuego (Ormeño et al., 2008; Zhao et al., 2012), y otros compuestos

como la presencia de sales de calcio, fosfatos de amonio, sulfatos de amonio, silicatos, entre otros,



5

que parecen actuar como retardantes del fuego y podrían contribuir como elemento de

prevención (Liodakis et al., 2006; Scarff y Westoby, 2008).

Pausas y Moreira (2012), han sugerido que la inflamabilidad puede variar acorde a la recurrencia

de fuego y que en sitios con una baja frecuencia de estos eventos las especies son menos

inflamables y de menor densidad específica, lo que contribuye reducir el tiempo de residencia

del fuego.

El Chaco semiárido de Argentina es una de las regiones donde el fuego y las inundaciones

constituyen los disturbios más frecuentes, responsables ambos del modelado del paisaje de

bosques, sabanas y pastizales (Bucher, 1982). Entre pastizales y sabanas, algunos corresponden

a formaciones de origen edáfico y otros de carácter antropogénico, producto del uso del

fuego desde tiempos precolombinos (Bravo et al., 2001; Kunst y Bravo, 2003 ;Torella yAdámoli;

2005). Los incendios se originan en pastizales y sabanas dominadas por especies altamente

inflamables como Elionurus muticus, Schinus molle y algunas latifoliadas herbáceas como Lippia

turbinata y Aloyssia gratissima. En los bosques del Chaco que han sido sobreexplotados o

sobrepastoreados, las especies arbóreas y arbustivas de madera dura coexisten con distintos

grados de dominancia, lo que crea diferentes situaciones de susceptibilidad a la ocurrencia y

propagación de incendios.

Como otras regiones semiáridas de América, los incendios podrían ser considerados una amenaza

para la conservación de la biodiversidad, de la estructura y funcionamiento de los bosques

(Kennard y Putz 2005). Sin embargo, hay antecedentes que sugieren una elevada capacidad de

resistencia al fuego de las especies de leñosas nativas del Chaco (Pinard y Huffman, 1997; Bravo

et al., 2001; 2006; 2008, 2014, Kennard y Putz 2005) lo que podría indicar una evolución bajo

condiciones de fuegos recurrentes. Sin embargo, no existen muchos antecedentes sobre la

influencia de rasgos morfológicos y estructurales sobre la inflamabilidad de los combustibles en

bosques del Chaco semiárido. Jaureguiberry (2012) analizó este carácter como rasgo funcional,

entre especies de leñosas y herbáceas nativas del Chaco seco de Argentina, determinando una



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estrecha correlación entre la inflamabilidad y la altura de la planta y la forma de crecimiento.

Estudios a nivel de comunidad son muy interesantes, sobre todo en bosques discetáneos

multiespecíficos como los del Chaco. Las características climáticas de la región chaqueña

Argentina, caracterizada por un clima semiárido marcadamente estacional, produce

seguramente variaciones en la inflamabilidad de combustibles a lo largo del año (Kunstet al,.

2012, 2014). Por ello, la valoración de cambios estacionales en los rasgos morfológicos y

estructurales vinculados a la inflamabilidad es otra demanda de información básica, en la temática

de la ecología de fuego.

El propósito de este trabajo es evaluar la inflamabilidad de once especies leñosas nativas de

bosques del Chaco semiárido mediante la estimación de rasgos funcionales, analizar cambios

estacionales en la inflamabilidad de los combustibles vegetales y evaluar el efecto de los

disturbios en la inflamabilidad. Estos resultados se encuentran en el Capítulo I del presente trabajo

y podrían contribuir en la gestión futura de los bosques chaqueños, ya que permitirán comprender

el comportamiento del fuego en estos ambientes y mejorar las tareas de control.



7

II. CAPÍTULO I

FLAMMABILITY CHARACTERIZATION OF WOODY SPECIES IN SEMIARID

CHACO REGION, ARGENTINA, THROUGH FUNCTIONAL TRAITS ANALYSIS

Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de

Argentina, a partir del análisis de rasgos funcionales

Ana Carolina Santacruz-García1, Sandra Bravo2

Abstract

The increasing tendency of wildland fires in the tropics have generated the urgent need of

knowledge about species flammability as an important input for risks management and prevention

plans of fires. The present work characterized the flammability of native species from Chaco

region through functional traits, analysed its seasonal variability and the effects of disturbances

on flammability. We selected eleven native woody species considering their representation within

native forests. A set of eight functional traits, six of them related to flammability (leaf dry-matter

content –LDMC-, twig dry-matter content -TDMC-, twig moisture content –TMC-, foliar

moisture content –FMC-, degree of ramification –DR- and twig drying time –TDT-) and two

describing growth habit and foliar persistence were evaluated at first time along fire season (May

to October) and then considering also rainy seasons within Chaco region. The 80 % of plant cover

from Western Chaco region forests have Medium to High flammability degree (FD) and the

functional traits more closely related to plant flammability were TDMC, LDMC, foliar

persistence and growth habit. The highest flammable species was Senegalia gilliesii, a shrub with

high DR and high LDMC and TDMC. The lowest plant flammability was observed in Cercidium

praecox, a tree species, with herbaceous and low LDMC. There was seasonal variability on plant



8

flammability with two peaks, at March and October but fuel desiccation was greater at the last

date accompanied by the lowest TDT. Flammability peaks at March could be related to high

foliation period and high LDMC in perennial species. There were no significant differences in

species flammability among forests with different disturbance history. Our results provide

valuable information that will contribute to improve efficiency of prevention activities, and

evaluations of fire behaviour.

Keywords

Disturbance effects, flammability, functional traits, seasonal variations.

1Consejo Nacional de Investigaciones Científicas y Técnicas CONICET and Instituto de Silvicultura y Manejo de Bosques –INSIMA.

Universidad Nacional de Santiago del Estero –UNSE. Belgrano 1912, Santiago del Estero (Capital),

[email protected]. Corresponding author.

2 Instituto de Silvicultura y Manejo de Bosques –INSIMA. Universidad Nacional de Santiago del Estero –UNSE. Belgrano 1912,

Santiago del Estero (Capital), Argentina, [email protected]

mailto:[email protected]

mailto:[email protected]



9

Resumen

El aumento de incendios forestales en los trópicos ha generado la necesidad de información básica

sobre características y comportamiento de combustibles para fortalecer los planes de prevención

de incendios. El conocimiento de la inflamabilidad de las especies se considera una valiosa

información para la determinación de la vulnerabilidad de las comunidades vegetales, la

prevención de incendios y en la restauración de áreas afectadas. El presente trabajo caracterizó la

inflamabilidad de once especies de leñosas nativas del Chaco semiárido a través de rasgos

funcionales, analizó su variación estacional y los efectos de los disturbios en la inflamabilidad.

Se seleccionaron once especies considerando su representatividad dentro de los bosques nativos

de la región de estudio y se evaluaron seis rasgos funcionales relacionados con la inflamabilidad

(contenido de materia seca en hojas –CMSH-, contenido de materia seca en ramas –CMSR-,

contenido de humedad en ramas –CHR-, contenido de humedad foliar –CHF-, grado de

ramificación –GR- y tiempo de secado de las ramas –TSR-) y dos que describen el hábito de

crecimiento y la fenología foliar. Se midieron atributos funcionales inicialmente a lo largo de la

temporada de fuego (mayo a octubre) y luego se considero la temporada de lluvias dentro de la

región chaqueña. El 80% de las especies que representan la cobertura vegetal del Chaco, se

caracterizan por tener inflamabilidad de Media a Muy Alta. Los rasgos funcionales de mayor

efecto sobre la inflamabilidad fueron CMSR, CMSH, fenología foliar y hábito de crecimiento. La

especie de mayor inflamabilidad fue Senegalia gilliesii, un arbusto con alto GR y alto CMSH y

CMSR. La especie con menor inflamabilidad fue Cercidium praecox, una especie arbórea, con

hojas herbáceas y bajo CMSH. Hubo variaciones estacionales en la inflamabilidad, y se

registraron dos picos, uno en marzo y otro en octubre. Sin embargo; la desecación de los

combustibles es mayor ésta última fecha en coincidencia con el menor TSR. El pico de

inflamabilidad en marzo podría estar relacionado con la foliación plena de todas las especies

estudiadas y con el alto CMSH en especies perennes. No se identificaron diferencias significativas

en la inflamabilidad de las especies en bosques con diferente historia de disturbios al menos con

los rasgos considerados en este estudio. Nuestros resultados proporcionan información valiosa



10

que contribuirá a mejorar la eficiencia de las actividades de prevención y las evaluaciones de

comportamiento del fuego.

Palabras clave: Efecto por disturbios, inflamabilidad, rasgos funcionales, variaciones

estacionales.



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Highlights

- Native woody species from Western Chaco have medium to high flammability degree.

- The LDMC, the foliar persistence and growth habit influence species flammability.

- Foliar functional traits influence the seasonal variation of plant flammability.



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1. Introduction

The flammability of plant is defined as the propensity to burn and it represents a significant

functional trait especially in fire prone ecosystems such as those developed under Mediterranean

climate (Pausas et al. 2004; Pausas & Moreira, 2012). As a global tendency, wildfires are

increasing even in those ecosystems (rainforest, jungles) where they were no frequent

disturbances (FAO, 2016)

The vegetation structure and plant leaf traits are the main variables considered in fire behavior

models. Moisture content of branches, twigs and leaves influence plant flammability through the

drying-time of fuels. Expected flammability will be greater with high dry-mass content leaves

and low diameter twigs, which contribute to the fast fire propagation under dry atmospheric

conditions (low air humidity and standing winds) (Bradstock, 2016). Other plant attributes closely

related to plant flammability are volatile oils, waxes and resins contents, canopy architecture and

degree of ramification (Ormeño, 2008; Blackhall et al., 2012; Burger & Bond, 2015; Wyse et al.,

2016).

The common methods to plant flammability assessment involve measurements of small pieces of

plants under laboratory conditions. However, the entire plant flammability could vary broadly of

these assessments. As an alternative to these methods, a functional approach has been postulated

by Cornelissen et al. (2003) considering plant attributes related to flammability such as leaf and

twig moisture content, the dry matter content of twigs and leaves, ramification degree, among

others. This approach proposes five plant flammability categories considering variations ranks of

attributes related to plant flammability. More recently, Pérez-Harguindeguy et al., (2013)

following this approach, recommended the use of a low technology device (Jaureguiberry et al.,

2011) and functional attributes, to assign five categories of plant flammability obtained by

average (rounded to one decimal) of the each class scores. These flammability classes consider



13

quantitative and qualitative traits obtained by measuring standardized methods. The selected traits

are relatively easy to measure, closely related to flammability determined at laboratory (Pérez-

Harguindeguy et al., 2013).Therefore this combination of traits allow good estimation of plant

flammability at field and it has been checked in other studies on this issues (Jaureguiberry, 2012;

Wyse et al., 2106). This estimation are valuable for fuel management plans destined to as fire

forest prevention and extinction activities.

The native vegetation of Chaco region comprises a mosaic of forests, grasslands, savannas and

shrublands, where fire has been a frequent ecological event, at least during the last two centuries

(Morello & Adamoli 1974; Prado, 1993; Bravo et al., 2001),). These vegetation units currently

are experimenting strong changes in land uses and disturbances regimes (Tálamo & Caziani,

2003; Grau et al., 2005; 2014; Gasparri & Grau, 2009, Bravo et al., 2010). Chaco forests are

considered as a high priority conservation area (Dinerstein et al. 1995, Torrella et al., 2015).The

continuity of grasslands, savannas and forests in Chaco region represents wide contact surfaces

of different types and fuel models and land uses. Elionurus muticus Spreng. (aibe), is the grass

species dominant in these open areas with values of plant cover among 30 to 90%. This species

propagates easily wildfires and fires initiated by farmers. Its flammability has been attributed to

a high content of citral terpenes in its foliage and a high rate of fine fuel production(Burkart, 1969;

Bravo et al., 2001; Kunst et al., 2012). Fires can propagate into forests according environmental

conditions and fuel moisture content (Argañaraz et al., 2016).

The objectives of this work were to characterize the flammability of eleven native woody species

from Argentine Chaco region through functional traits, to evaluate the seasonal variability and

the effects of disturbances on plant flammability.



14

2. Material and methods

2.1 Study area

The study area was located in Argentine Western Chaco region (Fig. 1). This region is

characterized by a seasonal semiarid climate, with the most rainfall concentrated from October to

March. The average temperature of the coldest month (July) is 10.6 ºC and the average

temperature of the hottest month (January) is 26.1 ºC (Boletta et al., 2006). The Western Chaco

region includes the South American heat polo with maximum temperatures of hottest month

above 47 ºC (GTZ, 2006).

Figure 1. Study area and sites localization in (A) American Chaco Region, (B) Santiago del Estero Province

included in South extreme of American Chaco Region, (C) Sampling sites localization at Experimental

Ranch Francisco Cantos belonging to the National Institute of Agricultural Technology (INTA).

C

A B



15

The average annual precipitation is 574 mm (annual series from 1934-2000, INTA climatic

record). The dry season extends from May to October, with a notably diary thermal variation and

strong deficit moisture, increasing over dry season.(Fig.2)The fire season coincides with dry

season in Western Chaco region, but some fires can occur out it under unusual environmental

conditions or human activities such as residues burns in urban-rural interfaces

Figure 2. Temperatures (continuous line), monthly rains (vertical bars) and average dates of the first and

last frosts in the Experimental Ranch “Francisco Cantos”, INTA EEA Santiago del Estero. The rectangle

indicates fire season in the Chaco region’s central zone. Climatic data period 1981-1990, EEE

Meteorological Observatory Santiago del Estero, INTA. Source: Kunst & Bravo, 2003.

The sampling sites were located in the Experimental Ranch “Francisco Cantos”, belonging to the

National Institute of Agricultural Technology (INTA), Santiago del Estero, Argentina (28°03’S

64°15’E) (Fig. 1). This Experimental Ranch has an extension approximated of 8000 has and

contents patches of forests, grasslands and savannas typical of Chaco region, in good conservation

state.

Aspidosperma quebracho-blanco Schltdl. (quebracho blanco) and Schinopsis lorentzii (Griseb.)

Engl. (quebracho colorado) are the two dominant tree species of the upper stratum reaching over

20m height. The medium forest strata can reach 7 to 12m height and are common Prosopis nigra

Griseb (algarrobo negro), Sarcomphalus mistol (Griseb.) Hauenschild (mistol), Cercidium

praecox (R. et P.) Harms (brea) and Geoffroea decortican sGillies ex Hook. &Arn, (chañar).In



16

the understory are common several Acacia, Celtis and Prosopis species, Atamisquea emarginata

Miers ex Hook.&Arn(atamisqui), Moya spinosa Griseb.(abreboca),accompanied by juvenile

individuals of S. lorentzii and A. quebracho-blanco (Brassiolo, 2005).In the herbaceous layer, the

most common grass species are Trichloris crinite (Lag.) Parodi, Trichloris pluriflora E. Fourn.,

Pappophorum pappiferum (Lam.) Kuntze, Setaria leiantha Hack., and Gounia spp among others

broad leaf species (INTA,2015).

The woody species selected for this study were: A. quebracho-blanco and S. lorentzii, dominant

of upper forest stratum; S. mistol, C. praecox and Celtis ehrenbergiana,representing medium

forest stratum and C. atamisquea, Schinus spp., Larrea divaricata Cav., M. spinosa, Senegalia

gilliesii Steud.,and Condalia microphylla Cav.,typical of understory. The species selection took

account floristic inventories of the study area (Araujo et al. 2008) and the criteria of the most

abundant species defined by those that, together, make up about 70- 80% of the standing biomass

of the community (Cornelissen et al., 2003). The Table 1 shows botany family, growth habit and

foliar persistence for species selected for this study due to this traits will be used in discussions

about plant flammability. Names of species are according to classification system of Darwinion

Institute, National University of La Plata, Argentina. The foliar persistence was assigned

following botany descriptions of species by Palacio & Roger (2016).

Table 1. Botany family, foliar phenology and growth habit for the studied species.

Species Botany Family Growth Habit Foliar Persistence

Aspidosperma quebracho-blanco Schltdl. Apocynaceae Tree Perennial

Atamisquea emarginata miers Ex Hook.

&Arn.= Capparis atamisquea Kuntze Capparaceae Shrub Perennial

Celtis ehrenbergiana (Klotzsch) Liebm Celtidaceae Shrub Deciduous

Cercidium praecox (R. Et P.) Harms. Fabaceae Tree Deciduous

Condalia microphylla Cav. Rhamnaceae Shrub Perennial

Larrea divaricata Cav. Zygophyllaceae Shrub Perennial

Maytenus spinosa (Griseb.) Lourteig &

O´Donell= Moya spinosa Griseb. Celastraceae Shrub Deciduous

Sarcomphalus mistol (Griseb.)

Hauenschild Rhamnaceae Tree Deciduous

Schinopsis lorentzii (Griseb.) Engl. Anacardiaceae Tree Deciduous

Schinus johnstonii f.A. Barkley Anacardiaceae Shrub Perennial

Senegalia gilliesii Steud.) Seigler &

Ebinger = Acacia gilliesii Steud. Fabaceae Shrub Deciduous



17

Sampling sites were selected employing satellite images and a record of recent land uses of

Experimental Ranch of INTA. Sampling sites were located in forests with two different

disturbance histories: a) disturbed forests (DF) with by wildfires and roller chopping applications

to control of shrub encroachment and improve the pasture growth for livestock (Kunst et al. 2012)

and, b) forests under closure (CF) without disturbances over three last decades (Fig. 3). Past fire

events were detected by fires scars, charred barks and carbonized woods on soil. The roller

chopping was informed as low severity event by personnel of Experimental Ranch. The study

was performed in 2015 – 2016 and a 150 x 150 m plot was delimited in each sampling sites. The

control and disturbed plots were emplaced about 4000 m of distance among them. In each

sampling sites, six mature and healthy individuals from each species were selected for this study

(Palacio & Roger, 2016)

Figure 3. Study sites: (A) Satellite image of the Experimental Ranch “Francisco Cantos” belonging to the

National Institute of Agricultural Technology (INTA), Argentina, (B) Control plot, a forest under closure,

without disturbances over three last decades (C) Disturbed plot, disturbed forests with fires and roller

chopper applications.

A

B

C

B C



18

2.2 Functional traits of plant flammability

The variables related to flammability considered in this work were: leaf dry-matter content

(LDMC), twig dry-matter content (TDMC), foliar moisture content (FMC), twig moisture

content (TMC),twig drying time (TDT) and degree of ramification (DR). Measures were made

following Pérez-Harguindeguy et al. (2013), tacking account the functional approach of this

work. The foliar persistence and growth habit were considered as other explicative variables in

the statistical analysis.

The LDMC and TDMC assessments were made in two twigs with diameter <2.5 cm and 20 cm

length, extracted from each individual. The FMC, TMC and TDT assessments were made on the

same material and for the last variable we took account time (days) until reach constant weight.

The fresh weight of samples was recorded using a balance Sartorius with 0.001 g. Then, material

was dried in controlled temperature oven at 40°C, until reach constant weight. The LDMC and

TDMC (mg. g-1) were assessed by ratio among oven-dry mass (mg) and water-saturated fresh

mass (mg). The degree of ramification was used as a predictor of canopy architectural complexity.

We measured the number of nodes and/or branches along a 1 m length branch segment (from the

top to bottom) and we categorized values obtained in a scale from 0 (no branches) to 5 (four or

more orders of ramifications). Values obtained of each variable considered were used to assign a

flammability category of each species. Each flammability category was calculated as average

class value (rounded to 1 decimal) of overall traits considered in this work, identifying five

flammability categories (From 1 to 5).In this work, we considered the three (3), four (4) and five

(5) flammability degree, from Perez- Harguindeguy et al. (2013), as categories named as Medium,

High and Very High flammability.

2.3 Seasonal variations of flammability

The seasonal variations of flammability of species selected were studied considering the fire

season in Western Chaco region from Argentina (Fig. 2; Kunst & Bravo, 2003). At first step, the



19

assessments were carried out in three dates along fire season: June, August and October. Along

fire season the vegetation experiments changes in plant moisture content and phenological state

due to its extended duration (six months). This fact can modify the fuel conditions for fire

propagation (Kunst & Bravo 2003; Bravo et al., 2014). The sampling was carried out in both

types of forests (CF and DF), testing simultaneously disturbance effects. In a second step, we

studied the annual variation of flammability among species, selecting March. May, October and

December as sampling dates. These dates allowed us to analyze seasonal changes in functional

attributes of species closely related to flammability (Fig. 2).

2.4 Statistical data analysis

For assessment of disturbances effects on flammability, data were analyzed through a general

lineal model (GLM) using sampling site and fire date as fixed effects. When the study area was

delimitated to disturbed forest (DF), a generalized linear mixed model (GLMM) was performed

to the assessment of seasonal variations of plant flammability, using Poisson distribution and fire

date and species as fixed effects. A Cluster Analysis was performed, including growth habit and

foliar persistence, using Ward method and Euclidean distance, in order to establish flammability

groups. Correspondence analysis were performed to identify associations between categorical

traits and flammability groups. Principal Component Analysis (PCA) were used to determine the

association between FD and LDMC, TDMC, FMC, TMC and TDT. To incorporate growth habit

and foliar persistence in the PCA, a principal coordinates analysis were performed before. The

statistical software used was Infostat/2017 (InfoStat Group, Universidad Nacional de Córdoba,

Argentina) with a α= 0.05.

3. Results

3.1 Disturbance effects

The Table 2 shows the average of six functional attributes evaluated during three sampling dates

along fire season (June, August and October) in the eleven woody species studied. Results



20

considering LDMC, TDMC, FMC, TMC, TDT and DR, did not indicate significant differences

in the FD between sites with different disturbance history in neither sampling date. The 63.64 %

of species studied showed FD High and Very High according the categories given by Pérez

Harguindeguy et al. (2013). There were significant differences in the flammability throughout the

fire season (Fig. 4). Flammability degree increased from August to October, without significant

differences among these sampling dates. These preliminary results guided the selection of DF as

study area of plant flammability of native woody species and encouraged the study about seasonal

variations in functional attributes on a wider temporal framework.

Figure 4. Flammability degree (FD) in native woody species from Western Chaco region, Argentina, along

fire season (June, August and October) in forests with different disturbance history. CF= Forest under

closure (without disturbances over three last decades, considered as reference condition) DF=Disturbed

forest with fires and roller chopping with management goal. Different letters indicates significant

differences between sampling dates, according to LSD Fisher, Tukey and Di Rienzo, Guzmán, Casanoves

(DGC) pair-wise comparison procedure with α: 0,05, n=66 individuals by site each sampling date.

CF DF

June August October0,00

1,00

2,00

3,00

4,00

5,00

FD

BC

A A

C

AB ABC

A A

C

AB A

CF DF

Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina, a partir del análisis de rasgos funcionales

21

Table 2. Average (A) and Standard Deviation (SD) for six flammability functional traits evaluated in eleven native species from Western Chaco region, Argentina, during three

sampling dates for fire season (June, August and October) in forest with different disturbance history. CF= Forest under closure, without disturbances over three last decades,

considered as reference condition; DF=Disturbed forest with fires and roller chopper applications. References: TDMC=Twig dry-matter content (mg*g-1); TDT=Twig drying

time (days); LDMC=Leaf dry-matter content (mg*g-1); TMC= Twig moisture content (%); FMC=Foliar moisture content (%); DR=Number of ramifications orders; FD=1 to 5

categories following Pérez-Harguindeguy et al. 2013.

Species Site TDMC TDT LDMC TMC FMC DR FD

A SD A SD A SD A SD A SD A SD A SD

A. quebracho-blanco CF 619,74 209,13 2 1 504,68 58,06 38,03 20,91 49,53 5,81 4,33 0,58 3,9 0,6

DF 469,66 48,90 2 2 557,64 24,17 53,03 4,89 44,24 2,42 4,33 0,58 3,8 0,3

A. emarginata CF 603,61 36,82 3 0 524,07 31,97 39,64 3,68 47,59 3,20 4,33 1,15 3,6 0,1

DF 495,96 54,01 3 2 511,87 23,07 50,40 5,40 48,81 2,31 3,67 1,53 3,5 0,3

C. ehrenbergiana CF 671,72 161,66 2 1 466,86 101,23 32,83 16,17 53,31 10,12 3,33 1,15 3,7 0,2

DF 550,99 166,25 1 1 484,37 106,92 44,90 16,62 51,56 10,69 3,33 1,15 3,6 0,5

C. praecox CF 645,08 98,99 4 1 421,00 0,00 35,49 9,90 57,90 0,00 3,67 0,58 3,6 0,5

DF 568,71 43,28 3 1 301,66 0,00 43,13 4,33 69,83 0,00 4,00 0,00 3,6 0,4

C. microphylla CF 575,85 246,44 2 1 507,29 46,37 42,41 24,64 49,27 4,64 5,33 2,08 3,8 0,6

DF 585,86 15,45 3 1 485,49 19,22 41,41 1,55 51,45 1,92 4,67 1,53 3,4 0,3

L. divaricata CF 512,14 108,38 2 1 515,98 32,59 48,79 10,84 48,40 3,26 5,33 0,58 3,6 0,3

DF 415,52 79,33 3 1 508,58 67,96 58,45 7,93 49,14 6,80 4,67 1,15 3,5 0,3

M. spinosa CF 593,58 37,73 3 2 546,10 22,50 40,64 3,77 45,39 2,25 3,33 1,15 3,6 0,3

DF 592,53 33,16 3 2 559,25 18,70 40,75 3,32 44,07 1,87 4,33 1,53 3,8 0,4

S. mistol CF 692,66 186,56 2 1 459,05 10,06 30,73 18,66 54,10 1,01 4,00 1,00 3,7 0,6

DF 563,01 126,95 2 1 470,66 52,31 43,70 12,70 52,93 5,23 4,00 1,73 3,6 0,4

S. lorentzii CF 576,44 92,75 3 0 467,40 20,27 42,36 9,27 53,26 2,03 4,00 1,00 3,5 0,4

DF 585,71 88,74 3 1 491,36 24,34 41,43 8,87 50,86 2,43 3,67 1,15 3,5 0,3

S. johnstonii CF 568,69 16,35 2 1 509,71 28,68 43,13 1,63 49,03 2,87 6,00 0,00 3,6 0,3

DF 518,95 78,59 2 1 519,93 30,76 48,11 7,86 48,01 3,08 5,00 1,73 3,7 0,2

S. gilliesii CF 567,57 68,84 2 1 516,99 71,28 43,24 6,88 48,30 7,13 5,67 0,58 3,8 0,2

DF 592,45 137,35 3 1 481,19 19,09 40,76 13,74 51,88 1,91 4,67 0,58 3,7 0,0



22

3.2 Interspecific variation of flammability

Flammability degree varied among 3,3 in C. praecox and 4,1 in S. gilliessi. )The 63.64 % of

species studied presented FD values are included in High to Very High flammability categories

according to Pérez-Harguindeguyet al. (2013). ANOVA did not indicated significant differences

in FD among eleven studied species, considering exclusively LDMC, TDMC, TDT, TMC, FMC

and DR (Fig. 5). A Cluster Analysis including the three FD categories assigned (Medium, High

and Very High), growth habit and foliar persistence of species studied allowed us a better

identification the three functional species groups with different flammability (Fig. 6).

Figure 5. Flammability degree (FD) in native woody species from Western Chaco region, Argentina,

following Pérez Harguindeguy et al. (2013). Same letters indicate no significant differences between

species, according to LSD Fisher pair-wise comparison procedure with α: 0,05, n=66 individuals.

References: 1=S. gilliesii; 2=L. divaricata; 3=C. microphylla; 4=S. lorentzii; 5=S. johnstonii-,

6=M.spinosa; 7=C. ehrenbergiana; 8=A. quebracho-blanco;9= A.emarginata; 10= S. mistol; 11=C.

praecox.

Medium flammability species are characterized by tree growth habit, herbaceous and perennial

leaves, with low dry-matter content. High flammability species are characterized by shrubby

growth habit, perennial and coriaceous leaves, with high leaf dry-matter content. Senegalia

gilliesii was the unique species with Very High flammability degree, with shrubby growth habit,

high degree of ramification, and high leaf and twig dry-matter content (Fig. 6)

1 2 3 4 5 6 7 8 9 10 110,00

1,00

2,00

3,00

4,00

5,00

FD

A

A AA A A A A A A

A

A

A AA A A A A A A

A



23

Figure 6. Dendrogram resulting from cluster analysis (Ward method and Euclidean distance) for eleven

native woody species from Western Chaco region, Argentina; based on six functional traits related to

flammability, foliar persistence and growth habit. References: SG=Senegalia gilliesii; AQB=Aspidosperma

quebracho-blanco; AE=Atamisquea emarginata; CM=Condalia microphylla; LD=Larrea divaricata;

SJ=Schinus johnstonii; MS=Maytenus spinosa; CE=Celtis ehrenbergiana; SL=Schinopsis lorentzii;

CP=Cercidium praecox; SM=Sarcomphalus mistol.

3.3. Seasonal variations of flammability

The analysis of generalized linear mixed model (GLMM) considering LDMC, TDMC, FMC,

TMC, TDT and DR showed significant differences in flammability along the year with two peaks

observed at March and October, without significant differences among them. The October peak

coincided with the maximum value of flammability observed in Chaco region fire season and

with the lowest values of drying time of leaves and twigs (Fig. 7). The lowest FD values

corresponded to May and December, without significant differences among them (Fig. 7).

0,00 1,52 3,04 4,56 6,09

SG

AQB

AE

CM

LD

SJ

MS

CE

SL

CP

SM



24

Figure 7. Average flammability degree of 11 native woody species from Western Chaco region, Argentina,

at different sampling date along fire season (May to October) and rain season (December to March). Same

letters indicate no significant differences in flammability degree, according to LSD Fisher pair-wise

comparison procedure withα: 0,05, n=66 individuals.

The Principal Component Analysis (PCA) of functional traits associated to flammability (LDMC,

TDMC, TDT and DR), and the two first coordinates of the Principal Coordinate Analysis for

foliar persistence and growth habit traits, explained for the two first axes the 75% of the data

variability, and showed that TDMC and growth habit (tree or shrub) are the functional traits more

incident on flammability (Fig. 8). In the Principal Coordinates Analysis, the PCO1 axis separated

tree growth habit species from shrub growth habit species. The PCO2 separated perennial species

from deciduous species. FMC and TMC were not considered in this analysis in order to avoid

redundancy in the PCA, owing to the strong association to LDMC and TDMC.

The first component principal (PC1) explained the 47,6% of variability and separated species

according their growth habit, considering the flammability groups established (Fig. 6). PC1

separated Medium flammability group, conformed by tree species from High and Very High

flammability groups, conformed by shrubby species. The second component principal (PC2)

explained the 28,4% of variability and separated species according their foliar persistence.

Regardless of season, general trend indicated that the more incident functional traits on

March May October December0,00

1,00

2,00

3,00

4,00

5,00

FD

A

C

AB

BC

A

C

AB

BC



25

flammability were TDMC, LDMC and DR, followed by growth habit, foliar persistence and

TDMC (Fig. 7).

Figure 8. Principal Component Analysis (PCA) of functional traits associated to flammability, foliar

persistence and growth habit for eleven natives woody species in Semiarid Chaco Region (General trend).

The ordination was based on six functional traits in six individuals per species. FD=Flammability degree;

LDMC=Leaf dry-matter content; TDMC=Twig dry-matter content; DR=Degree of ramification;

TDT=Twig drying time; PCO1= First principal coordinate, represents growth habit; PCO2=Second

principal coordinate, represents foliar persistence. References: 1. S. gilliesii; 2. A. quebracho-blanco; 3. A.

emarginata; 4. C. ehrenbergiana; 5. C. microphylla; 6. L. divaricata; 7. M. spinosa; 8. C. praecox; 9. S.

lorentzii; 10. S. johnstonii; 11. S. mistol

According to seasonal variations of functional attributes considered in this study, on May the

more flammable species were S. gilliesii, M. spinosa and L. divaricata (Fig 9 A). On October,

the more flammable species were A. emarginata, M. spinosa, S. johnstonii and L. divaricata (Fig

9 B). All them are shrubs with perennial and coriaceous leaves, and both sampling dates

corresponded to the Chaco region fire season. On December more flammable species were S.

gilliesii and C. microphylla and this period coincided with the beginning of rainy season in the

region. At this sampling date, the degree of ramification (DR), leaf dry-matter content (LDMC)

and growth habit (GH) were the most important functional traits on flammability (Fig 9 C). On

March, S. gilliesii, C. microphylla and A. emarginata. were the most flammable species (Fig. 9

-5,00 -2,50 0,00 2,50 5,00

CP 1 (47,6%)

-5,00

-2,50

0,00

2,50

5,00

CP

2 (

28

,4%

) 1

2

3

4

5

6

7

8 9

10

11

LDMC

TDMC

TDT

DR

FD

PCO1

PCO2

1

2

3

4

5

6

7

8 9

10

11

LDMC

TDMC

TDT

DR

FD

PCO1

PCO2



26

D) and TDMC, LDMC and DR were the more determinant traits of plant flammability. At least

60% of the information (variances) contained in the data were retained by the first two principal

components.

Figure 9.Principal Component Analysis (PCA) of functional traits associated to plant flammability, foliar

persistence and growth habit, for eleven native woody species from Western Chaco region, Argentina, at

different sampling dates during fire season (A) May;(B) October; and rain season (C) December; (D)

March. The ordination was based on six functional traits in six individuals per species. FD=Flammability

degree; LDMC=Leaf dry-matter content; TDMC=Twig dry-matter content; DR=Degree of ramification;

TDT=Twig drying time; PCO1= First principal coordinate, represents growth habit; PCO2= Second

principal coordinate, represents foliar persistence. References: 1. S. gilliesii; 2. A. quebracho-blanco; 3. A.

emarginata; 4. C. ehrenbergiana; 5. C. microphylla; 6. L. divaricata; 7. M. spinosa; 8. C. praecox; 9. S.

lorentzii; 10. S. johnstonii; 11. S. mistol

-4,00 -2,00 0,00 2,00 4,00

CP 1 (36,2%)

-4,00

-2,00

0,00

2,00

4,00

CP

2 (

25

,3%

)

12

3

4

56

7

8

9

10

11 LDMC

TDMC

TDT

DR

FD

PCO1

PCO2

12

3

4

56

7

8

9

10

11 LDMC

TDMC

TDT

DR

FD

PCO1

PCO2

March

-4,00 -2,00 0,00 2,00 4,00

CP 1 (39,8%)

-4,00

-2,00

0,00

2,00

4,00

CP

2 (

26

,6%

)

1

2

3

4

5

6

79

10

11

LDMC

TDMC

TDT

DRFD

PCO1

PCO2

1

2

3

4

5

6

79

10

11

LDMC

TDMC

TDT

DRFD

PCO1

PCO2

May

-4,00 -2,00 0,00 2,00 4,00

CP 1 (38,8%)

-4,00

-2,00

0,00

2,00

4,00

CP

2 (

33

,1%

)

2

3

4

5

6

7

10

11

LDMC

TDMC

TDT

DR

FD

PCO1

PCO2

2

3

4

5

6

7

10

11

LDMC

TDMC

TDT

DR

FD

PCO1

PCO2

October

-4,00 -2,00 0,00 2,00 4,00

CP 1 (32,6%)

-4,00

-2,00

0,00

2,00

4,00

CP

2 (

26

,5%

)

1

2

3

45

6

7

8 9

1011

LDMC

TDMC

TDT

DR

FD

PCO1

PCO2

1

2

3

45

6

7

8 9

1011

LDMC

TDMC

TDT

DR

FD

PCO1

PCO2

December

A

C D

B



27

4. Discussion

The set of woody species studied represent 80 % of plant cover from Western Chaco region forests

(Araujoet al., 2008).The percentage of species with High or Very High flammability (63,64%)

suggests the Chaco forests could be considered a fire-prone vegetation type. Even though

functional traits considered in this work are directly related to plant flammability (Kunst et al.

2012; Pérez Harguindeguy et al. 2013; Burger & Bond 2015), multiple morphological and

biochemical traits (Diaz et al., 2013) contribute to enhance the plant ignitability, fire spread rate

and combustion rate modifying its behavior as fuel. Landi et al. (2017) informed that forest cover

is less flammable than grassland and shrublands in Chaco region attributing that to fine fuel

availability and fuel desiccation. Some aspects usually does no considered determinant on plant

flammability as growth habit and foliar persistence seem influencing the response of plant as fuel

during wildland fire.

The lack of significant differences in plant FD among sites with different disturbance history

could be related to the short time period considered in this analysis (only 3 decades under closure

in CF),to the plant community heterogeneity or low severity of disturbances within DF. Blackhall

et al., (2012) communicated that foliar flammability properties such as leaf moisture, leaf size,

and specific leaf area and leaf strength varied according time since last fire. Carbone & Aguilar

(2016) found differences in foliar area and, specific foliar area in perennial herbs from Argentine

Chaco Serrano, in areas with different fire frequency. Therefore, it is probable that foliar traits

analyzed in our work be less sensible to changes promoted by disturbances or these were low

severity events. Rosenblun (2015) considered that plant communities and fire regimes

heterogeneity make it difficult to discerner what result from fire suppression, which generating

the need to stand level studies to better management decisions. Time from the last fire and low

severity roller chopper applications could not represent an enough environmental pressing to

promote changes in flammability traits analyzed. Tálamo et al.,(2013) informed a high resilience



28

of native vegetation from Argentine Chaco region to common disturbances as logging, wildfires

and livestock. Therefore, null or slight changes in plant flammability traits could be expected, at

least in this preliminary approach.

Nevertheless, the seasonal variation of flammability along Western Chaco region fire season

observed in our work, with an increasing tendency at end of this season, agreed with data from

experimental fires to study effects of fuel moisture content (Kunst et al., 2014), and to assess the

fire severity on tree species within the same study area (Bravo et al., 2014).High severity fires are

expected at fire season end due to lower moisture content of fuels than early fire season (Kunst

& Bravo, 2003). These results suggest that variables considered in our work may be useful to

detect seasonal variations in plant flammability but could be less sensible to changes promoted

by disturbances.

The absence of significant differences in the FD among species studied (Fig. 5) in ANOVA could

be attributed to the set of functional traits used for its characterization (LDMC, TDMC, FMC,

TMC, TDT and DR) and the analysis of FD as categorical variable. The standard methods for

measurement and the categories of plant flammability proposed by Pérez Harguindeguy et

al.(2013) using quantitative and qualitative variables allowed us to assign categories 3, 4 and 5 to

the species studied which we named as Medium, High and Very high FD species. The inclusion

of growth habit and foliar persistence in the Cluster Analysis improved the identification of three

species functional groups with different FD. These category names were reaffirmed through field

observations of fire behavior during experimental burns in native forests from the same study

area, where differences in flammability, spread rate and intensity have been observed among some

species studied.(Kunst et al., 2012; Bravo et al., 2014-, Ledesma et al., 2018. Liodakis

and Kakardakis (2006) found also three different categories of plant flammability in seven

dominant Mediterranean plant species from wildland/urban interfaces in Athens, Greece

considering the ignition delay time, heat content, combustion duration and mass residues as



29

analysis variables. These authors named flammability categories as FD categories identified in

our study.

Species from same plant community can differ strongly in flammability traits, fire resistance,

tolerance and postfire regeneration strategies (Burger & Bond, 2015). The Medium FD species

group included to S. lorentzii and S. mistol, two of the three more important tree species of canopy

and medium stratum of Chaco forests, respectively (Araujo et al., 2008). High FD species

included shrubby species with perennial sclerophyllous foliage (high dry matter content leaves),

open canopy with high density of low diameter twigs. The unique species identified as Very High

DF species, S. gilliessi, has caducifolious foliage but the plant architecture seems promoting its

ignitability. The shrub-vegetation types are one of the more relevant landscape units of

Mediterranean climate areas. Shrublands from New Zealand, Australia and South Africa are

particularly propensity to fire recurrence (Anderson et al., 2015). The combination of traits such

low plant height, fine-branching and dense canopy, perennial leaves with high dry matter content

could be related to high flammability of shrub species studied (Allen, 2008).

Bond & Van Vilgen (1996) considered that water content and drying rates of plant parts are one

of the most important properties affecting flammability at level both individual plants and the

entire plant community. The study of seasonal variation of plant flammability tacking account a

wider temporal framework showed the highest flammability values at October (the end of fire

season within Chaco region) and March (the end of rainy season). Antecedents about fire behavior

in Western Chaco region (Kunst et al., 2014; Bravo et al., 2010; 2014) and Chaco Serrano

(Argañaraz et al, 2016) referred the importance of fuel availability and fuel desiccation level in

fire recurrence and severity. However, the maximum FD values obtained in our work (October

and March) did not differ significantly among them and coincided respectively, with the minimum

and maximum moisture content of fuels from Chaco region (Kunst et al., 2014). Our results



30

suggest that different factors could contribute to plant flammability at different climatic seasons

(fire and rainy) at community level.

In fact, the first PCA analysis regardless season, showed the influence of TDMC and DR on

species FD (Fig.7). In both two sampling dates along fire season (May and October) also TDMC

and LDMC were the factors more closely related to FD. The influence of LDMC on FD during

fire season (in coincidence dryness season in Chaco region) could be related to the percentage of

perennials among species studied (45%) and the short time period without leaves in caducifolious

species.. The greater variability of data explained when PCO1 (growth habit) and PCO2 (foliar

persistence) were added to PCA, agreed with functional traits of species groups of High and Very

high FD in Cluster Analysis. According to that, shrubby growth habit and coriaceous and

perennial leaves are the more flammable combination of traits during Chaco region fire season.

Flammability is expected to be greater with lower moisture content and high leaf dry matter

content (Cornelissen et al., 2003). The shrubby species architecture promote the air flux

indispensable to hold the combustion (Dickinson & Johnson, 2001) and this growth habit

represent to the 55 % of species studied (Table 1). The community level analysis suggests a high

flammability of shrubby stratum of Chaco forests. The high FD observed on March are closely

related to TDMC and LDMC in coincidence to maximum foliation of caducifolious species and

woody growth modules fully differentiated. Low diameter twigs and fully expanded leaves

present a high ratio surface/volume, facilitating the fast loss of humidity of tissues, and fuel

desiccation, in coincidence with hot winds and high air temperatures characterizing summers in

Chaco region. These considerations are very important to fire prevention activities which always

were concentrated on dry climate period in Chaco region. Argañaraz et al. (2016) considered de

LDMC is a strong indicator of fire danger for Argentine Chaco Serrano, with a seasonal variation

related to the annual precipitation.

The influence of growth habit and foliar traits seems be confirmed in results of Cluster Analysis

that allowed identifying three groups with different flammability among studied species. Medium



31

flammability species included tree deciduous species with herbaceous foliage. These species loss

the foliage during the most fire season and recover it at ending of this season, in coincidence with

October flammability peak. High flammability species included shrubby species with

sclerophyllous foliage (high dry matter content leaves) and open canopy with high density of low

diameter twigs. These traits contribute to fast dehydrating in dry environmental conditions,

increasing the ignitability. Blackhall et al. (2012) informed that shrublands in Northwest

Patagonia are dominated by species with high foliar flammability. In our work, Senegalia gilliesii

was the unique species with Very High flammability and it is characterized by a deciduous leaves

and a shrubby growth habit, notably sclerophyllous. These result reaffirmed the importance of

TDMC, DR and LDMC on plant flammability since dry matter content has a strong effect on

heat release rate (Madrigal et al., 2012). Carbone & Aguilar (2016) determined a LDMC

increasing in three herbaceous species, in different fire frequency scenarios of Chaco Serrano,

Argentina. Blackhall et al. (2012) considered that initial burns create a positive feed-backs

towards increased fire occurrence since promotes the replacement of fire-resistance forests by

shrublands dominated by resprouting species.

5. Conclusions

Our results represent a significant advance in fire ecology knowledge from Argentine Chaco

region. The functional approach using traits related to plant flammability allowed to identify

species groups with different FD and a seasonal variation of FD beyond the fire season in Western

Chaco region. As well, the results indicated the importance of growth habit and foliar persistence

on flammability of native woody species of Chaco forests. The functional traits considered in this

work did not allow us to identify significant differences in plant flammability among species and

among forests with different recent disturbance history. These aspects will be considered in future

studies with other traits considered also related to plant flammability as foliar area, specific foliar

area and biochemical flammable compounds (terpenes, tannins, and essential oils, among others).



32

6. Acknowledgements

Authors are grateful with authorities of Universidad Nacional de Santiago del Estero (UNSE) and

Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) for funding our research

and providing support for equipment. Special acknowledgement to Universidad Distrital

Francisco José de Caldas, (UDFJC) Bogotá, Colombia, for supporting our work and scientific

assistance of reviewers. To the assistant personnel and colleagues from Cátedra de Botánica

General, FCF, UNSE for help to field work and to Engineers Ana Belén Cisneros and Jaime

Andrés Herrán, and Dr Pedro Jaureguiberry for advising us during the statistical data analysis

and whole investigation.



33

III. CONCLUSIONES GENERALES

-El 63,64% de las especies evaluadas tienen inflamabilidad de elevada (Corresponden al 80% de

la cobertura vegetal del Chaco Semiárido), lo cual podría explicar la adaptación y resistencia de

las especies chaqueñas al fuego y la recurrencia de éste disturbio en la región.

-Los rasgos foliares son indicadores de inflamabilidad, al estar relacionada directamente la

biomasa foliar con la cantidad de combustible fino. Las especies con alto grado de inflamabilidad

se caracterizan por tener bajo porcentaje de humedad y alto contenido de materia seca en hojas y

ramas, siendo el contenido de materia seca en ramas y hojas (TDMC y LDMC) los rasgos con

mayor incidencia en la inflamabilidad. El contenido de materia seca se asocia directamente con

la resistencia de la planta a los disturbios, entre más alto sea éste rasgo indica mayor adaptación

y tolerancia a factores ambientales como fuego y sequía.

-El hábito de crecimiento es un factor determinante en el grado de inflamabilidad de una especie,

se encontró que las especies arbustivas tienen mayor grado de inflamabilidad que las especies

arbóreas, lo cual remarca la importancia de la arquitectura de la canopia en la inflamabilidad de

las especies.

-Hay una variación estacional en la inflamabilidad que podría estar relacionada a la fenología

foliar sumada a las condiciones climáticas durante la temporada de fuego. Los meses con mayor

grado de inflamabilidad (marzo y octubre) coinciden con los meses de mayor expansión foliar en

la región chaqueña. No obstante, la inflamabilidad es mayor en octubre, debido a las condiciones

de sequía en la que se encuentran los combustibles vegetales al estar finalizando la temporada de

fuego.

-El conocimiento sobre las estrategias de adaptación de las especies al fuego, proporciona

información valiosa sobre el rol de éste disturbio en las comunidades vegetales. La susceptibilidad

o la tolerancia de las comunidades al fuego influye directamente en los cambios en la

biodiversidad del ambiente afectado.



34

IV. RECOMENDACIONES GENERALES

El conocimiento sobre las estrategias de adaptación de las especies al fuego, proporciona

información valiosa sobre el rol de éste disturbio en las comunidades vegetales. Por esta razón,

se considera importante para estudios posteriores evaluar el contenido de hojarasca y el porcentaje

de ramas muertas. La proporción de biomasa muerta debajo de la planta durante la estación seca

es crítica para la inflamabilidad (Pérez-Harguindeguy et al., 2013). El material vegetal muerto

contribuye a bajas tasas de acumulación de agua, incidiendo directamente en la inflamabilidad de

la planta. Otros rasgos importantes a considerar son el área foliar y el área foliar específica, ya

que estos son indicadores de la adaptación y resistencia de las especies a factores ambientales

disturbantes.

Otra línea de investigación interesante es la composición bioquímica de las especies, compuestos

como resinas, aceites esenciales y terpenos, contribuyen marcadamente a la inflamabilidad de las

especies. El estrés producido por los incendios, sobre la mayor parte de las comunidades vegetales

promueve la síntesis y/o liberación de metabolitos secundarios, muchos de ellos volátiles, que

predisponen a la vegetación a nuevos eventos de características similares o aún de mayor

severidad.

Evaluar la respuesta metabólica y los rasgos funcionales propuestos, puede contribuir a la

interpretación del comportamiento de las especies frente al fuego, a nivel de poblaciones y

comunidades. La producción de información básica para determinar la vulnerabilidad de las

coberturas vegetales a incendios es una demanda de gran importancia para la gestión de

recursos naturales.



35

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