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Plant responses to fire in a Mexican arid shrubland

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Background Fire responses of species in arid environments have only been scarcely studied. We studied four species ( Dasyliron lucidum Zucc., Juniperus deppeana Steud., Echinocactus platyacanthus Link & Otto, and Agave potatorum Zucc.) in the Tehuacán-Cuicatlán Biosphere Reserve, Mexico. The objectives were to describe and quantify survival and resprouting, as well as the factors determining them, for the selected species. Six months after a 330 ha wildfire in 2014, 32 plots were established on three transects. Forest dasometric and fire severity variables were recorded. Logistic regression was utilized to obtain mortality and resprouting probability models, as well as linear regression to detect relationships among post- and pre-fire variables. Results All species had high survival rates (74.5 to 97.7%). All surviving D. lucidum individuals resprouted apically. For J. deppeana , the probability of mortality was directly related to fire scar height on the trunk and inversely related to its diameter, whereas the probability of crown recovery was inversely related to the proportion of the tree height scorch. For E. platyacanthus, necrosed height was directly related to plant height. There was a positive relationship between basal area and the emission of new leaves for the A. potatorum . Conclusions In the different species, several traits that allowed high fire survival rates were observed ( e.g., thick cortex or bark, fleshy non-flammable leaves, flammable leaves that reduce fire intensity, high volume to surface ratio). Many of these were primarily linked to drought resistance. All species gain fire resistance or tolerance as they increase in size. We concluded that the studied arid ecosystem of Mexico can withstand an altered or a base fire regime.
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O R I G I N A L R E S E A R C H Open Access
Plant responses to fire in a Mexican arid
shrubland
Dante Arturo Rodríguez-Trejo
1*
, Juli G. Pausas
2
, and Andrés Gelacio Miranda-Moreno
1
Abstract
Background: Fire responses of species in arid environments have only been scarcely studied. We studied four
species (Dasyliron lucidum Zucc., Juniperus deppeana Steud., Echinocactus platyacanthus Link & Otto, and Agave
potatorum Zucc.) in the Tehuacán-Cuicatlán Biosphere Reserve, Mexico. The objectives were to describe and
quantify survival and resprouting, as well as the factors determining them, for the selected species. Six months after
a 330 ha wildfire in 2014, 32 plots were established on three transects. Forest dasometric and fire severity variables
were recorded. Logistic regression was utilized to obtain mortality and resprouting probability models, as well as
linear regression to detect relationships among post- and pre-fire variables.
Results: All species had high survival rates (74.5 to 97.7%). All surviving D. lucidum individuals resprouted apically.
For J. deppeana, the probability of mortality was directly related to fire scar height on the trunk and inversely
related to its diameter, whereas the probability of crown recovery was inversely related to the proportion of the
tree height scorch. For E. platyacanthus, necrosed height was directly related to plant height. There was a positive
relationship between basal area and the emission of new leaves for the A. potatorum.
Conclusions: In the different species, several traits that allowed high fire survival rates were observed (e.g., thick cortex
or bark, fleshy non-flammable leaves, flammable leaves that reduce fire intensity, high volume to surface ratio). Many of
these were primarily linked to drought resistance. All species gain fire resistance or tolerance as they increase in size.
We concluded that the studied arid ecosystem of Mexico can withstand an altered or a base fire regime.
Keywords: arid zones, fire ecology, fire traits, Mexico
Resumen
Antecedentes: Las respuestas al fuego de especies en ambientes semiáridoshansidopocoinvestigadas.Nosotros
estudiamos cuatro especies (Dasyliron lucidum Zucc., Juniperus deppeana Steud., Echinocactus platyacanthus Link & Otto,
yAgave potatorum Zucc.) en la Reserva de la Biosfera Tehuacán-Cuicatlán, México. Los objetivos fueron describir y
cuantificar la supervivencia y el rebrote, así como los factores que las determinan, para las especies seleccionadas. Seis
meses después de un incendio de 330 ha en 2014, se establecieron 32 sitios sobre tres transectos. Se registraron variables
dasométricas y de severidad del fuego. Se usó regresión logística para obtener modelos probabilísticos de mortalidad y
rebrote, así como regresión lineal para detectar relaciones entre las variables previas y posteriores al fuego.
(Continued on next page)
© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.
* Correspondence: dantearturo@yahoo.com
1
División de Ciencias Forestales, Universidad Autónoma Chapingo, km. 38.5
carretera México-Texcoco, C.P. 56230, Chapingo, Estado de México, Mexico
Full list of author information is available at the end of the article
F
ire Ecolog
y
Rodríguez-Trejo et al. Fire Ecology (2019) 15:11
https://doi.org/10.1186/s42408-019-0029-9
(Continued from previous page)
Resultados: Todas las especies tuvieron una alta supervivencia (74.5a97.7%).TodoslosindividuossobrevivientesdeD.
lucidum rebrotaron del ápice. En J. deppeana, la probabilidad de mortalidad estuvo directamente relacionada con la altura
de la cicatriz de quemado sobre el tronco e inversamente relacionada con el diámetro, mientras que la probabilidad de
recuperación de la copa estuvo inversamente relacionada con la proporción de la altura del árbol afectada por el fuego.
Para E. platyacanthus,laalturadedeshidrataciónestuvodirectamenterelacionadaconlaalturadelaplanta.Sehallóuna
relación positiva entre el área basal y la emisión de nuevas hojas en A. potatorum.
Conclusiones: En las diferentes especies, se observaron varios caracteres que les permitieron una elevada tasa de
supervivencia (como corteza o córtex gruesos, hojas carnosas no inflamables, hojas inflamables que reducen la intensidad
del fuego y una alta relación volumen:superficie). Muchos de estos caracteres son primariamente adaptaciones a la
sequía. Todas las especies ganaron resistencia o tolerancia al fuego conforme incrementaron su tamaño. Concluimos que
el ecosistema árido de México estudiado se puede sostener en un régimen de fuego alterado o base.
Introduction
Fire and, more specifically, fire regimes have been a force
that has shaped plants (Keeley et al. 2011), so many plant
species in fire-prone ecosystems have adaptive strategies to
persist under recurrent wildfires. Examples of ecosystems
for which there is a good understanding of these strategies
are the Mediterranean ones (Keeley et al. 2012)andsa-
vannas (Dantas et al. 2013, Charles-Dominique et al. 2015).
However, little is known about fire tolerance strategies in
arid ecosystem species where fire frequency is low due to
fuel discontinuity and low fuel loadings (Bond 1983).
Therefore, in these ecosystems, many species may not have
evolved strategies for survival or regeneration in the face of
fire and, consequently, they may be very sensitive to the
current anthropogenic fire regime. However, in arid ecosys-
tems, fires do occur, whether due to natural or human
causes, and there is evidence of many plants surviving fire.
For succulent plants in arid zones, mainly cacti, mor-
phological characteristics may serve as fire survival
mechanisms. In this context, Thomas (1991) proposed
that the following characteristics would help plants to
survive fire: protection of the apical meristem with pilos-
ities; compaction at the base of the leaves (rosetted); and
insulation of the vascular tissue, thanks to a thick cortex.
Bond (1983) showed that the degree of coverage of the
persistent dead leaves on the Aloe ferox Mill. Stem is
negatively related to post-fire mortality due to leavesin-
sulating properties. Likewise, the protection of apical
meristems, and thick and highly suberised bark confer
fire tolerance in some succulent plants (e.g., Kumara pli-
catis [L.] G. Rowley in South Africa; Cousins et al.
2016). The low flammability of succulent plants has also
been proposed as an adaptive mechanism for surviving
low-intensity fire regimes (Pausas et al. 2017).
In species similar to those that we studied, physical traits
in succulent plants give them some degree of survival in
the case of fires. For example, there is evidence of some
survival (between 3 and 50%) in Dasylirion leiophyllum
Engelm. ex Trel. and D. wheeleri S. Watson ex Rothr. after
non-severe fires (Ahlstrand 1982, Wright and Bailey 1982,
Thomas and Goodson 1992,Tesky1993a,b). In Ferocactus
wislizenii Britton & Rose (SY = Echinocactus wislizenii
Engelm.), older individuals have a thick cortex that insulates
the vascular cambium from a fires lethal temperatures, and
its apical meristem is relatively high on the stem. Hence, in-
dividuals >30 cm in height normally survive fires, while
shorter individuals reach mortalities of 75% (Humphrey
1974, Matthews 1994). Regarding the Agave species, there
is little information about their post-fire response; in some
locations, scorching of >50% of the leaves results in the
death of the plant, but in others, all the leaves may have
been scorched but the plant nonetheless recovers (Kittams
1973,Thomas1991).
In arid ecosystems, non-succulent woody plants (trees
and shrubs) also show some fire resistance. For example,
Juniperus deppeana Steud. is considered fire resistant
due to its high crown and relatively thick bark (Kittams
1973, Tirmenstein 1999); it shows low mortality even if
it is burned by relatively severe fires (Rodríguez-Trejo
1996,2014). This species has the ability to resprout after
a fire from root-crown, lignotuber, and epicormic buds
(Rodríguez-Trejo 2014, Pausas 2017). Fire scars on old
trees show that they can survive large number of fires
throughout their lives, although prescribed burns every
3 to 7 years can eliminate them (Moir 1982, Tirmenstein
1999). Other American species of that genus (e.g.,
Juniperus virginiana L., J. monosperma [Engelm.] Sarg.,
J. osteosperma [Torr.] Little, J. occidentalis Hook.,J.
flaccida Schltdl.) exhibit less fire resistance since they
have thin bark, their buds are small, and they lack the
ability to resprout (Miller 2000, Rodríguez-Trejo 2014).
In Mexican ecosystems, the role of fire is very noticeable
(Rodríguez-Trejo 2008,2014; Jardel-Pelaez et al. 2014;
Pausas 2016), and many species in different types of eco-
systems show strategies to persist in the face of fire. It is
estimated that, in half of the 32 types of ecosystems, spe-
cies with adaptive fire strategies prevail (Rodríguez-Trejo
2008,2014). However, little is known about strategies in
Rodríguez-Trejo et al. Fire Ecology (2019) 15:11 Page 2 of 9
arid areas, which constitute a very important part of the
countrys biodiversity. The fire ecology in arid zones has
received little attention worldwide and minimal attention
in Mexico. To help fill this knowledge gap, we have studied
four species (Dasyliron lucidum Zucc., Echinocactus platya-
canthus Link & Otto, Agave potatorum Zucc., and Juni-
perus deppeana) with highly contrasting morphological
characteristics in the Tehuacán-Cuicatlán Biosphere Re-
serve, where fires are common at present (CONANP
2013). The three former species were chosen for their dom-
inance in the rosetophilous shrubland (Fig. 1), while the lat-
ter species was dominant in the juniper forest. Specifically,
the objectives of this research were to describe and quantify
survival and resprouting, as well as the factors that deter-
mine them, for the four selected species; among the factors,
forest dasometric and fire severity variables were consid-
ered. Our research will help us to understand the effect of
fires on the diversity of these arid ecosystems.
Methods
Study area
The Tehuacán-Cuicatlán Biosphere Reserve covers
490 187 ha in the states of Puebla and Oaxaca, Mexico. The
study area hosts 21 ecosystem types; more than 3000 species
of vascular plants, of which 12% are endemics, and 180 fam-
ilies have been recorded there, roughly representing 10% of
vascular plant types for Mexico (CONANP 2013). One of
the most important vegetation types there is the xeric shrub-
land, which covers 25% of the area. Of the four types of
shrublands existing in the reserve, the one that covers the
largest area is the rosetophilous shrubland (14.3% of the
reserves total area, CONANP 2013), which includes Dasylir-
ion lucidum stands (Rivera and Solano 2012). The study area
was located amongst these stands, and also included
Echinocactus platyacanthus and Agave potatorum on the
slopes. Juniperus deppeana dominated the lower flat areas.
The study area was in an area of low mountains aligned
from southwest to northeast, reaching 2400 to 2500 m
a.s.l., surrounded by flat areas (around 2350 m a.s.l.). The
area was formed by Cretacic sedimentary rocks. On the
hills, the soils were litosols (CONANP 2013). The data
from the meteorological station at Cuesta Blanca, Munici-
pality of Palmar de Bravo, showed a mean temperature of
11.5 °C and mean annual precipitation of 392 mm (for the
period 2000 to 2014), falling mostly during the summer;
the extreme annual precipitation levels were 133.2 mm
(for 2005) and 569.5 mm (for 2008) (CICESE-CONACYT
2018). We visually estimated a surface fuel load of 2 to 4 t
ha
-1
(no succulent plants were included).
Fires are not common in the reserve. During the
period 2013 to 2016, 26 forest fires were recorded, with
an average affected area of 33.3 ha (ranging from 1 to
330 ha), all on shrubland. Although the records are in-
complete, the main cause of fire was related to livestock
raising, and fires occurred in spring (CONANP 2013;
CONANP, Tehuacán, Puebla, Mexico, unpublished re-
port: reporte de incendios forestales [20132018]). No
data on fire regime were available for the study area but,
according to the authorsobservations, the rosetophilous
shrublands, dominated by Yucca L. species experienced
relatively frequent spring surface fires (from every few
years to every few decades). This regime is considered a
Fig. 1 Landscape view of the rosetophylous shrubland in the study zone on the Tehuacán-Cuicatlán Biosphere Reserve, state of Puebla, Mexico,
in November 2014, six months after fire. Note the dominance of Dasylirion lucidum. In the background, note the juniper forest in the bottom of
the valley. Photo credit: Dante Arturo Rodríguez-Trejo
Rodríguez-Trejo et al. Fire Ecology (2019) 15:11 Page 3 of 9
base fire regime, because despite it includes natural and
human-ignited fires it maintains the integrity of the
ecosystem. Where Dasylirion species were present, the
fire regime included passive crown fires. CONANP
(2013) points out that there were no reports of fires of
natural origin in the reserve. In any case, we could not
discard the possibility of natural fires given the long re-
turn periods (decades to centuries) that typify this type
of shrubland in the United States (USFS 2012a,2012b).
Species
We considered four species: Dasylirion lucidum (Aspar-
agaceae), Juniperus deppeana (Cupressaceae), Echinocac-
tus platyacantus (Cactaceae), and Agave potatorum
(Asparagaceae). The three former species populate rocky
limestone slopes with shallow and sandy soils. J. dep-
peana is a common tree species that usually grows on
flat, deep, alluvial soils or on low slopes (Lesur 2011).
Except for Juniperus deppeana, the species are endemic.
Echinocactus platyacanthus is at risk, and under special
protection. All species provide some use to the local
population (as ornamental and medicinal plants, for
wood, or for making beverages).
Sampling
In April 2014, a human-ignited wildfire occurred in the com-
munity of San Sebastián Coacnopalan, Municipality of
Palmar de Bravo, within the Tehuacán-Cuicatlán Biosphere
Reserve, state of Puebla, Mexico, on rosetophilous shrubland
of Dasylirion lucidum on the hillsides, and Juniperus dep-
peana on the lower and flat parts. The fire covered 330 ha,
mostly with an intense, passive crown fire (by which each in-
dividuals crown burns independently of the other crowns) in
Dasylirion lucidum (M. Palma Martínez, Reserva de la Bios-
fera Tehuacán-Cuicatlán, Comisión Nacional de Áreas Nat-
urales Protegidas, Tehuacán, Puebla, México, personal
communication.)
Six months after the fire, a total of 32 plots were estab-
lished on three transects in the affected area: two transects,
each 240 m in length, with 12 plots sampled every 20 m;
and one transect 160 m in length, with 8 plots also sampled
every 20 m. Each plot consisted of a central point from
which four quadrants (128 quadrants in total) were placed.
From that point, the distance to the closest individual (of
any of the four species) in each quadrant was measured.
One of the transects (12 plots, 48 quadrants) was estab-
lished in the stands of Dasylirion lucidum with Agave pota-
torum, between 2300 and 2400 m a.s.l., with SW and NE
aspects; another transect was settled in stands of Juniperus
deppeana (2250 m a.s.l., flat); and one more, selectively
chosen for its patches of Echinocactus platyacanthus (with
8 plots, 32 quadrants, SW aspect, between 2300 and 2400
m a.s.l.). For each individual of the four species considered,
the following variables were recorded, according to the
plantlifeform:height,diameteratbreastheightandatthe
base, and crown diameter. In addition, for each individual,
theseverityofthefire(damagetotrunkandcrown)was
evaluated. We recorded whether each was alive or dead, its
stem char height, its lethal crown scorch height, the per-
centage of lethal crown scorch, and its scorch (necrosed)
height. The scorched surface and green surface were re-
corded for Echinocactus platyacanthus. For A. potatorum,
we measured: rosette diameter, proportion of leaves with
>50% dehydration, number of dead leaves, number of leaves
with <50% dehydration, and number of new leaves.
Data analysis
Means and intervals of density, diameter, and height
were calculated, as well as mortality. To calculate the
probability of mortality and resprouting, logistic
mixed-model regression was used (Hosmer and Leme-
show 2000). The dasometric and fire severity (damage to
trunk and crown) variables obtained in the sampling
were used as independent variables individually and in
combinations. These variables were considered with
fixed effects, while the quadrants were considered with
random effects. The R program (R Core Team 2017)was
used for modeling. In addition, linear regression was
used to relate recovery variables to dasometric and fire
severity variables.
Results
Dasylirion lucidum
Dasylirion lucidum was the most abundant species in
the study area (Table 1). All individuals were fully
scorched; that is, the whole height of the stem and all
the foliage were burned. The average height at the base
of the lowest (among 1 to 3 rosettes per individual)
post-fire rosette was 0.6 m, but some were 0.06 m high,
which showed how easily the leaves were reached by sur-
face fires. However, survival rate reached 97.7%. This
high survival rate did not lead to any modeling of this
variable (Fig. 2a).
All surviving Dasylirion lucidum had vigorous,
well-developed green rosettes, a product of the survival
of the apical bud (often termed apical resprouting); the
average crown area was 0.6 m
2
(SD = 0.44). Plant height
(H, assuming that it was the same as before the fire) had
a direct relationship with crown area (Sc) six months
after fire; that is, taller plants generated a larger crown
when resprouted (Fig. 3; Eq. 1;R
2
= 0.56, P< 0.0001).
Sc ¼0:09062 þ0:77356 Hð1Þ
Only 9.3% of individuals exhibited basal resprouts, and
those had between 1 and 2 of them, with an average of
1.3 resprouts per individual. Many individuals flowered
Rodríguez-Trejo et al. Fire Ecology (2019) 15:11 Page 4 of 9
after the fire, but so did the Dasylirion lucidum that
were outside the burned area. Therefore, no relationship
was found between fire and flowering.
Juniperus deppeana
Juniperus deppeana had a low density, although it was
the tallest species in the study area (Table 1). The crown
diameter was between 0.9 and 12 m (mean = 4.36 m, SD =
2.05); 25.5% of the trees were recorded as dead after the fire.
Technical personnel of the reserve reported no evident tree
mortality in this area prior to fire. Stem char height reached
from 0.15 to 5.8 m, with an average of 2.61 m (SD = 1.23). Le-
thal crown scorch height reached up to 5.8 m, with an average
of 3.14 m (SD = 1.31). The percentage of crown recovery
ranged from null to 90%, with an average of 37.6% (SD = 34.6;
Fig. 2b).
Of the surviving trees, 55.2% showed some sign of
resprouting at the base of the trunk, with an average of
5.3 resprouts per tree (among those that resprouted). The
resprouts were 2 to 50 cm long, with a mean of 17.8 cm.
Regarding the probability of mortality, the most robust
model was with the explanatory variables stem char
height and diameter at breast height. The probability of
mortality (P
M
) increased with scar height on the trunk
(T), and with the reduction in the diameter at breast
height (D; Fig. 4; Eq. 2; Table 2).
PM¼1
1þexp −−1:70058 þ2:06797 T0:27006 DðÞ
ð2Þ
The probability of resprouting (P
R
) had an inverse relation-
ship with scorch height (A
A
; expressed as a percentage of the
Table 1 Main characteristics of the four species studied on the Tehuacán-Cuicatlán Biosphere Reserve, state of Puebla, Mexico, in
November 2014, indicating the number of individuals studied (n), the density (individuals per 100 m
2
), the post-fire height (mean,
standard deviation, and range; m), the diameter (basal for Dasylirion lucidum, of rosette for A. potatorum, of the body for Echinocactus
platyacanthus, and at breast height for Juniperus deppeana [mean and standard deviation; cm]), and the mortality (in percentage of
individuals)
Species nDensity (plants per 100 m
2
) Height (m) Height range (m) Diameter (cm) Diameter range (cm) Mortality (%)
Dasyliron lucidum 34 28.6 0.91±0.41 0.32 to 1.85 20.4±5.89 9 to 33 2.3
Agave potatorum 30 17.6 0.27±0.11 0.05 to 0.47 32.7±14.3 11 to 70 10.0
Echinocactus platyacanthus
a
20 2.1 0.67±0.25 0.21 to 1.40 47.8±12.4 28 to 78 4.8
Juniperus deppeana
b
47 1.8 4.22±1.47 0.85 to 6.30 22.0±10.7 5 to 55 25.5
a
Within the colonies and patches that it forms
b
In the low valleys where it is found
Fig. 2 aDasylirion lucidum showing crown recovery after fire. The
tips of the leaves look burned or dehydrated because they were
beginning to emerge at the time of the fire. bSome Juniperus
deppeana dead after the fire and others with epicormic resprouts. c
Dehydration and growth of green tissue between the tubers (ribs) of
Echinocactus platyacanthus.dAgave potatorum and Agave peacockii
Croucher after fire. Photos were taken six months after fire on the
Tehuacán-Cuicatlán Biosphere Reserve, state of Puebla, Mexico, in
November 2014. Photo credit for photos a,c, and d: Dante Arturo
Rodríguez-Trejo. Photo credit for photo b: José Daniel Luna-Fontés
Fig. 3 Relationship between the height of the plant and the resprouted
crown area six months after fire on the Tehuacán-Cuicatlán Biosphere
Reserve, state of Puebla, Mexico, in November 2014. Each point
represents a sampled individual
Rodríguez-Trejo et al. Fire Ecology (2019) 15:11 Page 5 of 9
height of the tree). As the proportion of the affected height
increased, with respect to the height of the tree, the likeli-
hood of crown recovery decreased (Fig. 4;Eq.3;Table2).
PR¼1
1þexp 2:584 0:041 AA
ðÞ
ð3Þ
Echinocactus platyacanthus
Echinocactus platyacanthus was not abundant. It had
the largest stem diameter of the four species (Table 1).
The average individual coverage of this cactus reached
0.19 m
2
(SD = 0.24; Fig. 2c). Cactus mortality was 4.8%.
However, at the time of evaluation, the vigor of these
plants was poor. New green tissues were observed in the
inner part between the ribs of all the surviving cacti,
representing 5% of the surface of the plants. No resprouts
of any kind were found. The maximum and minimum
scorch heights were 1.30 m and 0.13 m, respectively, with
the mean equal to 0.53 m (SD = 0.25). Thus, an average of
89.1% of the height of these cacti was necrosed by the fire.
Plant height (H) was positively related to the average
necrosed height (H
N
;Eq.4;R
2
=0.87;P< 0.0001).
HN¼0:12114 þ0:96543 Hð4Þ
Agave potatorum
Agave potatorum was a relatively abundant species
(Table 1). Its average mortality was 10%. Almost all living
A. potatorum individuals sprouted and continued to
sprout new leaves from the plants central axis. On aver-
age, there were 27.3 dead leaves, including partial leaves,
per individual. However, it was not possible to discern
how many of these died directly as a result of the fire and
how many from natural or other causes before the fire.
There was an average of four leaves with 50% fire dam-
age, as well as 4.4 leaves with <50% fire damage, per plant.
The average number of new leaves (not affected) was 10.1.
There was post-fire shoot resprouting in only 3.3% of the
individuals (Fig. 2d). A linear trend was observed in which
as the agaves were larger (with a greater basal area, BA),
they sprout a greater number of new leaves (NL)inthe
center (Fig. 5;Eq.5;R
2
=0.64;P< 0.0001).
NL ¼0:91003 þ0:04995 BA ð5Þ
Discussion
Different species have different traits that confer survival
in the face of fire (Table 3). Such strategies are not
Fig. 4 Probability of mortality and probability of crown recovery of Juniperus deppeana six months after fire on the Tehuacán-Cuicatlán Biosphere
Reserve, in November 2014. Mortality is a function of the height of the fire scar and the diameter, and crown recovery is determined by the
proportion of the tree that was scorched by fire. See Table 2for details. D = diameter at breast height
Table 2 Summary of the mixed models for mortality and crown
recovery for Juniperus deppeana in the study sites on the
Tehuacán-Cuicatlán Biosphere Reserve, state of Puebla, Mexico, in
November 2014. The last column provides the intercept and
coefficients of the fixed effects for the final model. See also Fig. 4
AIC Chi-square Pvalue Coeff
Mortality
Null 56.364 1.700
Fire scar height 47.393 10.970 0.00092 2.067
Diameter 32.538 16.855 0.00004 0.270
Crown recovery
Null 1075.6 2.584
Scorch height 834.3 243.3 <0.00001 0.041
Rodríguez-Trejo et al. Fire Ecology (2019) 15:11 Page 6 of 9
exclusive responses to fire, as many serve primarily to
withstand drought. Traits such as succulent leaves, high
volume to surface ratio (approximately 2 versus 0.02 in
broadleaf trees), and a thick cuticle (up to 20 μm, com-
pared to up to 6 μm in broad-leaved trees) (Nobel 1998)
decrease flammability and facilitate fire resistance in
Agave species. The bulk at the base of the fleshy leaves
also increases the volume to surface ratio and can help in-
sulate the apical meristem and the caudex of the agave
from high temperatures during fires. This characteristic is
also observed in rosethophilous arborescent species, such
as Aloe ferox Mill. In South Africa, whose dry leaves insu-
late the stem from the heat of combustion because they
are not very flammable (Bond 1983). It should be
added that, in Agave, the external leaves are the old-
est and with the highest volume to surface ratio, en-
abling them to act as a barrier that insulates these
plants from the heat they receive during fires, par-
ticularly if the outermost layers of leaves tend to be
raised. The tips of the leaves usually dehydrate the
most compared to the rest of the leaf, but the tips re-
cover after damage from fire. It can be expected that
Agave species with thicker, longer, and more abundant
leaves receive less damage from fire, which increases
their chances of survival (Fig. 4d). In addition,
Thomas (1991) and Gucker (2006)reportthatAgave
lechuguilla Torr. has sufficient root depth (10 cm,
according to Nobel and Quero 1986) to survive a
fires lethal temperatures, although we do not know
this factor for A. potatorum of the study area.
On the other hand, the dry leaves of Dasylirion lucidum
on the stem are highly flammable (Rodríguez-Trejo 2014),
but when burned quickly they probably generate low fire
intensity at the base, and the apical bud survives (Gagnon
et al. 2010,Pausasetal.2017). Along with the short height
of this species, the dry leaves provide vertical continuity
so that the surface fire reaches the crowns of these plants.
Recovery is achieved by the growth of the original bud
(apical resprouting). As a consequence, almost all individ-
uals survived.
Thermal insulation of the vascular cambium by bark or
cortex is another characteristic that allows survival in many
species (Wright and Bailey 1982,Pausas2015). According
to Dickison (2000), the genus Dasylirion has a type of cam-
bium called a thickening ring. The cortex and the perennial
base of the leaves provide heat insulation to this tissue. The
relatively thick bark of Juniperus deppeana provides resist-
ance to fire (Kittams 1973,Tirmenstein1999), but resist-
ance is reduced in both dry years (Steuter and Wright
1983) and in the drier environments of its natural range.
During dry years, moisture limitation can reduce productiv-
ity, vigor, and the regenerative capacity of fire-damaged tis-
sues, such as their photosynthetic ability. In very dry
environments, productivity is reduced, which should result
in thinner trees with thinner bark and, therefore, with re-
duced vascular cambium protection. Even the lowest crown
can facilitate a higher level of damage during a fire.
Damage caused by fire in some species can increase mor-
tality months and years after its passage. In Juniperus dep-
peana,thehigherthedamagetothetrunkandthesmaller
thediameter,thegreatertheprobabilityofmortality.Like-
wise, the higher that the level of damage to the crown is,
the less the resprouting. In several temperate-zone species,
for example Quercus crassifolia Humb & Bonpl, the greater
that the damage to the crown is, the better the resprouting
of the base (Juárez-Bravo et al. 2012), because when the
crown is affected, auxins, phytohormones that inhibit
resprouting, are eliminated, while the cytokinins in the root
stimulate this resprouting response (Miller 2000). The
scarce resprouting of Juniperus deppeana maybedueto
Fig. 5 Direct relationship between the basal area of the agaves and
the emission of new leaves after fire on the Tehuacán-Cuicatlán
Biosphere Reserve, state of Puebla, Mexico, in November 2014
Table 3 Main characteristics that confer fire resistance or fire tolerance to the four species studied on the Tehuacán-Cuicatlán
Biosphere Reserve, state of Puebla, Mexico, in November 2014. Empty cells = No.
Trait D. lucidum E. platyacanthus A. potatorum J. deppeana
Thick cortex or bark Yes Yes Yes
Fleshy, non-flammable leaves Yes
Protected apical buds Yes Yes Yes
Flammable leaves that reduce fire intensity Yes
High volume to surface ratio Yes Yes
Bank of buds on the stem and root crown Yes
Rodríguez-Trejo et al. Fire Ecology (2019) 15:11 Page 7 of 9
the limited moisture in the study area, which reduces prod-
uctivity, recovery from damage, and resprouting.
The thick cortex in the cactus not only prevents dehy-
dration, but it also helps it resist fire. The cortex of
Echinocactus platyacanthus insulates phloem and cam-
bium from the heat of the fire. As the cactus grows, its
apical meristem becomes higher and the base of the ribs
develops a bark (Thomas 1991, Matthews 1994). For
some Dasylirion species, such as Dasylirion lucidum,
if the fire causes cambial death, it can cause the
death of individuals, although some are considered
more sensitive, such as Dasylirion wheeleri (Ahlstrand
1982,Tesky1993b).
In Ferocactus wislizenii, insects, drought, and browsing
by rodents, lagomorphs, and livestock interact with fire
to determine mortality. The loss of spines by fire in
these cacti eliminates their defense against herbivores,
and herbivores tend to consume more plants with suc-
culent tissues in drier years. Therefore, fire, drought, and
damage by herbivores affect survival (Thomas 1991).
Drought adaptations such as spines and apical pubes-
cence of columnar and biznaga cacti protect apical meri-
stem from excessive heating and frost damage. Spines
and pubescence can reduce the temperature at this area
by about 14 °C (Nobel 1998). If a fire eliminates spines
and apical pubescence in Echinocactus platyacanthus,
more damage and post-fire mortality can be expected.
In some cases, the plants studied were located next to
or in stony areas where fuel load was low. This helped to
reduce the fires intensity and severity, as in many arid
zones (Thomas 1991), and makes a refuge for some plants
(refugia strategy, Pausas 2019). It must also be taken into
account that 2014 was a wet year, with precipitation of
559.6 mm, while the precipitation for 2012 and 2013 was
357.2 and 485 mm, respectively (precipitation data from
CICESE-CONACYT 2018). Such higher humidity avail-
ability may have facilitated post-fire resprouting and sur-
vival in the studied species. Drier years may show weaker
and slower post-fire responses and lower survival.
Conclusions
In conclusion, most plants studied survive after a fire
(mortality <30%, Table 1), although with different mech-
anisms (Table 3), and all gained fire resistance or toler-
ance as they increased in age and size. Therefore, it
seems that this arid ecosystems of Mexico resist a cer-
tain fire regime. To what extent an increase in fire activ-
ity may reduce resilience remains to be studied.
However, it seems that very frequent fires, particularly
during dry years, may increase mortality, especially in
cacti and Agave. Less frequent fires may not increase the
intensity or severity of fires or fire-related mortality very
much because of the low precipitation that limits prod-
uctivity and fuel accumulation.
Acknowledgements
The authors thank the Tehuacán-Cuicatlán Biosphere Reserve (CONANP) and
biologists F. Reyes-Flores and M. Palma-Martínez, officials of the Reserve, for
their logistical support. We thank G. Mendoza-Ángeles, J.D. Luna-Fontés, J.
Rupit-Morteno, and E. Palafox for their support in the field. The authors thank R.
Paradice for the translation (Spanish to English) of the manuscript and technical
editing of the Spanish to English translation. We thank the anonymous peer-
reviewers for their thoughtful work that helped to improve ours.
Funding
Funding for this study was provided in part by Fondo Mexicano para la
Conservación de la Naturaleza, USDA Forest Service, US Agency for
International Development, Universidad Autónoma Chapingo (Ajusco Project
on Fire Ecology, Fire Management and Restoration of Burnt Areas), and
FOCSEC Project (PROMETEO/2016/21), on the role of fire and aridity in plant
communities.
Availability of data and materials
Please contact corresponding author for data requests.
Authorscontributions
DART conceived and designed the experiment, coordinated the field work,
conducted field sampling, performed statistical analysis, and participated in
the writing of the manuscript and technical editing of the Spanish to English
translation. JGP participated in field work, performed statistical analysis, and
participated in the writing of the manuscript, and in the technical editing of
the English to Spanish translation of it. AGMM was responsible for species
identification, and helped with the writing of the manuscript and technical
editing of the Spanish to English translation. All authors read and approved
the final manuscript.
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
PublishersNote
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
Author details
1
División de Ciencias Forestales, Universidad Autónoma Chapingo, km. 38.5
carretera México-Texcoco, C.P. 56230, Chapingo, Estado de México, Mexico.
2
Centro de Investigaciones sobre Desertificación, Consejo Superior de
Investigaciones Científicas (CIDE-CSIC), Carretera CV-315, km. 10.7, 46113
Montcada, Valencia, Spain.
Received: 7 August 2018 Accepted: 28 January 2019
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The frequency of disturbances is an important factor contributing to the megabiodiversity of Mexico, and fire is a prominent disturbance in this region. Here I briefly summarise important aspects of fire ecology in Mexico and introduce a new book for fire science in this country: Incendios de la vegetación (Vegetation fires) by D. Rodríguez-Trejo. The book covers many fire topics including fire ecology, fire behaviour, fire management, fire history and the anthropology of fire, and provides a basis for sustainable vegetation management in the region; it also advocates for the use of fire as a management tool. The message is that the biodiversity of Mexico, and therefore its management, cannot be understood without considering fire.
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