2
Tropical Dry Forest Ecological Succession
in Mexico: Synthesis of a Long-Term Study
Mauricio Quesada, Mariana Álvarez-Añorve, Luis Ávila-Cabadilla,
Alicia Castillo, Martha Lopezaraiza-Mikel, Silvana Martén-Rodríguez,
Victor Rosas-Guerrero, Roberto Sáyago, Gumersindo Sánchez-Montoya,
José Miguel Contreras-Sánchez, Francisco Balvino-Olvera, Sergio Ricardo
Olvera-García, Sergio Lopez-Valencia, and Natalia Valdespino-Vázquez
CONTENTS
2.1 Introduction .................................................................................................. 17
2.2 Ecosystem Structure and Composition .................................................... 19
2.2.1 Species Richness .............................................................................. 20
2.2.2 Species Density ................................................................................ 21
2.2.3 Species Composition ....................................................................... 21
2.2.4 Vegetation Structure ........................................................................ 24
2.3 Phenology ..................................................................................................... 27
2.3.1 Leaing ............................................................................................... 27
2.3.2 Flowering and Fruiting ................................................................... 27
2.4 Successional Changes in Vertebrate Communities ................................. 28
2.4.1 Birds ................................................................................................... 28
2.4.2 Bats ..................................................................................................... 28
2.5 Human Dimensions .................................................................................... 29
2.6 Conclusions and Recommendations .........................................................30
2.1 Introduction
The current status and rates of conversion of mature tropical forests indicate
that these habitats will eventually disappear, leaving behind a complex landscape matrix of agricultural ields and forest patches under different levels of
succession. Tropical dry forests (TDFs) are not an exception, and the current
management derived from human activities will clearly result in the complete loss of this habitat worldwide (Quesada and Stoner 2004; Miles et al.
2006; Quesada et al. 2009). The TDFs have been extensively transformed and
occupied by urban and agricultural areas at signiicantly higher rates than
17
© 2014 by Taylor & Francis Group, LLC
Downloaded by [Silvana Marten] at 18:05 02 February 2014
18
Tropical Dry Forests in the Americas
tropical rainforests (Murphy and Lugo 1986a). Therefore, understanding
tropical succession in the context of ecological and human dimensions represents one of the major challenges to promoting and developing conservation
and management programs for this threatened ecosystem.
Few studies have analyzed ecological succession in TDFs, indicating contrasting results; in some cases, a relatively faster structural recovery is found
for this system than for other tropical systems (i.e., Ceccon et al. 2002; Ruiz
et al. 2005; Vieira and Scariot 2006), but in others, a slower process is found in
TDFs than in wet forests in terms of plant growth and other developmental
features (Ewel 1977; Murphy and Lugo 1986a). However, the interpretation
of succession is not clear because the recovery of species richness and the
composition are dependent on structural change (Sheil 2001; Ceccon et al.
2002; Pascarella et al. 2004; Ruiz et al. 2005; Toledo and Salick 2006; Quesada
et al. 2009; Alvarez-Añorve et al. 2012). In addition, some studies claim that
TDFs are relatively simple and small in structure and composition, and that
they recover predominantly through coppicing after disturbance (Ewel 1977;
Murphy and Lugo 1986a; Chazdon et al. 2007). However, Quesada et al. (2009,
2011) challenge this view, as the predominant mode of reproduction in TDFs
is through a wide variety of sexual systems in which seeds are mainly produced via outcrossing. If coppicing or asexual reproduction were the main
drivers of regeneration, changes in species composition along secondary
succession would not be expected. Several studies that analyze a chronosequence have found differences in species composition in TDFs. Therefore, the
regeneration of TDFs is expected to be slow and very susceptible to human
disturbance because the growth rate of many tree species is slow, reproduction is highly seasonal, and most plants are mainly outcrossed and dependent on animal pollination (Bawa 1974, 1990; Frankie 1974; Murphy and Lugo
1986a; Hamrick and Murawski 1990; Bullock 1995; Jaimes and Ramirez 1999;
Cascante et al. 2002; Fuchs et al. 2003; Quesada et al. 2001, 2004, 2009). Another
important aspect to consider in the process of regeneration is the functional
recovery of the community, which identiies groups of plants and animals
that exhibit similar responses to environmental conditions and have similar
effects on dominant ecosystem processes that are associated with successional stages (Gitay and Noble 1997; Lebrija-Trejos et al. 2010; Alvarez-Añorve
et al. 2012; Avila-Cabadilla et al. 2012). Only a few studies have simultaneously evaluated TDF succession in loristic, structural, and functional terms.
Alvarez-Añorve et al. (2012) found that plant functional traits along
succession change from those that maximize heat dissipation in early
successional stages to those that enhance light acquisition and water use in
late successional stages. This study suggests that the functional recovery of
TDFs could take longer than inferred when the process is evaluated from just
a loristic and/or structural perspective, but more studies from other tropical
regions are required to corroborate patterns of functional succession. In
addition, the variation in vertebrate guild assemblages is associated with the
variation in landscape habitat attributes under different successional stages.
© 2014 by Taylor & Francis Group, LLC
Tropical Dry Forest Ecological Succession in Mexico
19
TABLE 2.1
Downloaded by [Silvana Marten] at 18:05 02 February 2014
Tropi-Dry Plot Abbreviations and Age of Abandonment in 2004 and 2009
Successional Stage
Plots
Age in 2004 (Years
of Abandonment)
Initial (pastures)
Early
Intermediate
Late
P1-P3
E1-E3
I1-I3
L1-L3
0
3–5
8–12
>50
Age in 2009 (Years of
Abandonment)
5
8–10
13–17
>55
Avila-Cabadilla et al. (2012) found that nectarivore bats tend to be associated with TDF patches, whereas frugivore bats are associated with riparian
forests. This probably relects the prevalence of species that produce nectar
resources for bats in dry forests, and of species which produce fruits that
are eaten and dispersed by bats in riparian forests. In conclusion, the main
mechanisms of succession and regeneration of TDFs still remain unexplored,
and more efforts are required to understand the ecological processes of these
important ecosystems.
The main goal of this synthesis is to understand the successional process
underlying the natural regeneration of TDFs for the development of
conservation strategies in the Chamela–Cuixmala Biosphere Reserve region,
which is located along the central Paciic coast of Mexico (Figure 1.2). Little is
known about the regeneration process of these forests, and our study is one of
the few that provides basic and applied ecological information on the succession in TDFs in Mexico. To characterize TDF successional patterns, we assessed
the successional changes in vegetation attributes (i.e., structure, species composition), ecosystem functioning (i.e., functional traits, herbivory, phenology),
and fauna diversity and abundance in a highly diverse Mexican TDF. For this
purpose, we performed a ive-year study in a chronosequence that represented
four TDF successional stages: initial, early, intermediate, and late (Table 2.1).
We also conducted socio-ecological research to understand the changes in
land-use history and their effects on succession and forest regeneration of
TDFs (see Chapter 21 for an in-depth comparative study). We emphasize the
need to integrate ecological knowledge with the human dimension as a tool
that supports sound conservation, management, and understanding of TDFs.
2.2 Ecosystem Structure and Composition
Between 2004 and 2009, vegetation structure and species composition of
the plots were compared among the different successional stages. Changes
in the chronosequence were compared within plots, between successional
stages, and over the course of the ive-year study (Table 2.1). The study design
and methods are detailed in Chapter 1.
© 2014 by Taylor & Francis Group, LLC
Tropical Dry Forests in the Americas
20
In general, species richness increased with successional age (Figure 2.1), and
intermediate stage plots showed similar species richness than did late successional plots. This parameter differed signiicantly among successional
stages during both years (Kruskal–Wallis x2(2004) = 9.46, df = 3, p = 0.024;
x2(2009) = 8.08, df = 3, p = 0.044) (Figure 2.1). In 2004, pastures and early
stages had a signiicantly lower species richness than intermediate and late
stages. These results indicate that management practices used in the chronosequence plots left many species of late successional stages standing in
the intermediate plots. In 2009, early, intermediate, and late successional
stages were similar to each other; only pastures differed from all the other
three successional stages. During the same, pastures (5 years old by 2009)
also showed high intra-stage variations, suggesting higher stochasticity in
early stages. The lowest species richness occurred at site P3, which is dominated by trees and shrubs of the genus Mimosa (Leguminosae) and that
is surrounded by other pastures. In contrast, the highest species richness
occurred at site P2, which is surrounded by secondary forests that could
facilitate the regeneration of several species. In general, from 2004 to 2009,
the highest increase in species richness occurred in pastures, whereas there
was no signiicant change in intermediate and late successional plots. Plots
that are 8 years old and older present similar species richness, indicating a
relatively rapid regeneration and recovery. This suggests an important role
20
I1 I2 I2
P2
L1 L1
E3
E2
16
L2 L2 L3
I3
I1
Species richness
Downloaded by [Silvana Marten] at 18:05 02 February 2014
2.2.1 Species Richness
L3
I3
E1
E3
E1
12
P1
8
P1
E2
P2
4
P3
P3
0
Sampling sites
FIGURE 2.1
Species richness of Tropi-Dry plots under different successional stages for years 2004 (circles)
and 2009 (triangles). Species richness was rariied at 23 individuals. P1-P3 = pastures,
E1-E3 = early successional plots, I1-I3 = intermediate successional plots, and L1-L3 = late successional plots.
© 2014 by Taylor & Francis Group, LLC
Tropical Dry Forest Ecological Succession in Mexico
21
of the surrounding landscape attributes of the vegetation matrix in the successional process of this system.
Species density differed signiicantly among successional stages and
increased with successional age (ANOVA 2004 F(3,8) = 19.4, p = 0.0004;
ANOVA 2009 F(3,8) = 12.4, p = 0.002) (Figure 2.2). In 2004, similar to species
richness, pastures and early stages were signiicantly different from intermediate and late stages. In 2009, only pastures differed from other successional
stages. The density parameter appears to be useful in differentiating
successional stages as well as in predicting temporal dynamics from the
chronosequence due to the following reasons: (1) Density showed a gradual
increase along succession. (2) There were signiicant differences among
successional stages. (3) Early successional plots of the year 2009 (8–10 years
old) showed similar values to intermediate successional plots of the year
2004 (8–12 years old). (4) Pastures of the year 2009 (5 years old) showed similar values to early successional plots of the year 2004 (3–5 years old).
2.2.3 Species Composition
Species composition was analyzed by means of a nonmetric multidimensional scaling (NMDS) method that was based on a Bray–Curtis dissimilitude matrix (Figure 2.3). The scores of the axis that explained most of the
variation (synthetic variable) were used to compare the successional stages
60
I1
L3 L3
I3
50
I2
E3 I1
Species density
Downloaded by [Silvana Marten] at 18:05 02 February 2014
2.2.2 Species Density
E2
40
I2
I3
L1 L1
L2
L2
E1
30
P2
20
10
E1
P1
P1
E3
E2
P2
P3
P3
0
Sampling sites
FIGURE 2.2
Species density of Tropi-Dry plots under different successional stages for years 2004 (circles)
and 2009 (triangles). P1-P3 = pastures, E1-E3 = early successional plots, I1-I3 = intermediate
successional plots, and L1-L3 = late successional plots.
© 2014 by Taylor & Francis Group, LLC
Tropical Dry Forests in the Americas
22
2004
1.2
P1
0.8
Axis 2
I3
0.4
P2
0
E1
L1
L2
E3
I1
E2
–0.4
L3
–0.8
–1.5
–1
0
Axis 1
–0.5
0.5
1
1.5
2009
1.5
P1
1
L1
0.5
Axis 2
Downloaded by [Silvana Marten] at 18:05 02 February 2014
I2
L2
0
I2
I3
I1
L3
E3
P3
P2
–0.5
E2
–1
–1.5
–1.5
E1
–1
–0.5
0
0.5
1
1.5
2
2.5
3
Axis 1
FIGURE 2.3
Nonmetric multidimensional scaling (NMDS) of the species composition under different successional stages for years 2004 and 2009. Plots are presented according to their successional
stage: circles = pastures, triangles = early, squares = intermediate, and diamonds = late.
in compositional terms. In 2004, pastures and early successional plots signiicantly differed from intermediate and late successional stages (Pillai test
F(3,7) = 3.25, p = 0.032). In contrast, in 2009, species composition did not differ
among the successional stages, suggesting that this parameter became similar to late successional stages in a short period of time (Pillai test F(3,7) = 1.51,
p = 0.237). However, pastures showed great variations in this parameter, and
these variations could be masking real differences in the species composition of this successional stage. The great variations among the pastures of
the year 2009 (5 years old) again suggest higher stochasticity in the assembly
of early successional communities. Stochasticity can be inluenced by landscape attributes, as pastures that are separated from the rest of the sites in
the analysis are surrounded by pastures; whereas P2, the pasture that is closest to early successional plots in the analysis, is surrounded by secondary
© 2014 by Taylor & Francis Group, LLC
Tropical Dry Forest Ecological Succession in Mexico
23
0.8
0.6
0.4
0.2
n)
ea
-L
3
(m
L
L2
-L
3
L1
-L
2
L1
n)
I(
m
ea
-I3
I2
-I3
I1
-I2
I1
n)
E
(m
ea
-E
3
E2
-E
3
E1
E1
-E
2
0
P1
-P
2
Bray–Curtis dissimilitude index
2004
1
Pair of sampling sites
2009
1
Bray–Curtis dissimilitude index
Downloaded by [Silvana Marten] at 18:05 02 February 2014
forests (Figure 2.3). Intermediate successional plots of 2009 (13–17 years old)
appear more grouped than those in 2004 (Figure 2.3), suggesting a rapid
homogenization of plot species composition.
When we analyzed the Bray–Curtis dissimilitude values between the plots,
we observed a greater dissimilitude between pasture plots than between plots
of other successional stages (Figure 2.4). This suggests that pastures present higher beta diversity than older successional stages. Intra-successionalstage beta diversity should decrease with a decrease along succession in
dissimilitude between the plots of a given successional stage. This trend is
0.8
0.6
0.4
0.2
P1
-P
2
P1
-P
3
P2
-P
3
P
(m
ea
n)
E1
-E
2
E1
-E
3
E2
-E
3
E
(m
ea
n)
I1
-I2
I1
-I3
I2
-I3
I(
m
ea
n)
L1
-L
2
L1
-L
3
L2
-L
3
L
(m
ea
n)
0
Pair of sampling sites
FIGURE 2.4
Bray–Curtis dissimilitude values between Tropi-Dry plots (open bars) and mean Bray–
Curtis dissimilitude values among all the plots of a given successional stage (solid bars) in
two different years (2004 and 2009). P1-P3 = pastures, E1-E3 = early successional plots, I1-I3 =
intermediate successional plots, and L1-L3 = late successional plots.
© 2014 by Taylor & Francis Group, LLC
24
Tropical Dry Forests in the Americas
consistent in both years (2004 and 2009). The higher beta diversity in pastures
reinforces the idea of greater stochasticity in the assembly of early successional communities, resembling what has been found in other successional
models (Leishman and Murray 2001), where stochastic and niche processes
dominate early successional stages and only niche processes dominate late
successional stages. In these models, both processes have an impact on the
community’s assembly in the early stages, but deterministic forces dominate
the late stages.
Downloaded by [Silvana Marten] at 18:05 02 February 2014
2.2.4 Vegetation Structure
Vegetation structure was analyzed through principal component analysis
(PCA) (Figure 2.5), which allowed for the ordination of plots in terms of four
variables (basal area, number of stems, number of individuals, and number of species). Principal components (i.e., PC1, PC2) that explained most of
the variation were used to compare different successional stages through
ANOVAs and post hoc Tukey’s mean separation tests. In 2004, intermediate
and late successional plots appeared grouped and separated from the rest of
the plots, indicating that structural traits are similar among themselves but
different from pastures and early successional stages. In 2009, in contrast,
late successional plots appeared grouped along PC1, but there was no clear
separation among successional stages along this axis. Intermediate successional plots appeared separated from the rest of the plots along PC2. Most
variations in PC2 were accounted for by the number of individuals and the
number of species, and parameters were highest in intermediate successional
stages. Accordingly, in 2004, ANOVA tests showed signiicant differences in
structural traits among successional stages (F(3,8) = 9.835, p = 0.005). Tukey’s
test showed that intermediate and late successional plots were similar among
themselves but different from pastures, whereas pastures were different
from all the other successional stages. In 2009, ANOVAs showed no differences among successional stages in PC1 (F(3,8) = 1.22, p = 0.365), but signiicant
differences among the stages were detected in PC2 (F(3,8) = 4.33, p = 0.043).
Tukey’s test indicated that, along this axis, intermediate successional plots
were similar to late successional plots but different from pastures and early
successional plots (which were also similar to each other).
From 2004 to 2009, when the percentage of change in structural variables was analyzed, again, the greatest changes occurred in pastures and
early successional plots. The early successional plot E1, however, showed
a small increase compared with other early successional sites, probably
as a consequence of the high mortality of woody individuals that was
caused by an invasion of Ipomoea lianas. This mortality reduced the net
increase in structural traits. The intermediate successional plot I2 also
experienced Ipomoea invasion and high mortality, which is relected in a
net reduction in the values of structural traits. In contrast, site I3, which
was the youngest intermediate plot, showed the greatest increase during
© 2014 by Taylor & Francis Group, LLC
Tropical Dry Forest Ecological Succession in Mexico
25
2004
2
E1
Axis 2
1
E3
0
P3
P2
I3
P1
I1
L3
E2
–1
–4
–3
–2
0
–1
L2
1
2
3
Axis 1
2009
3
L2
2
L1
Axis 2
Downloaded by [Silvana Marten] at 18:05 02 February 2014
L1
I2
1
E2
0
L3
P1
I1
P3
I2
–1
–2
–3
E1
–2
–1
P2
I3
E3
0
Axis 1
1
2
3
FIGURE 2.5
Principal component analysis (PCA) of the vegetation structure of four successional stages for
years 2004 and 2009 in the region of Chamela, Jalisco, Mexico. In 2004, PC1 accounted for 86%
of the variation; in 2009, PC1 accounted for 40%, and PC2 accounted for 34% of the variation.
Plots are presented according to their successional stage: circles = pastures (P1-P3), triangles =
early (E1-E3), squares = intermediate (I1-I3), and diamonds = late (L1-L3).
this successional stage. These cases constitute an example of site-speciic
effects that can determine particular successional trajectories in different
sites of the same region.
In general, late successional plots showed low rates of change for most
variables, and most of them showed decreases in the number of individuals
and species, indicating mortality of woody individuals. Meteorological data
of the Chamela Biological Station over the last 20 years indicate an increase
in the number of dry days per year, which could be related to an increase
in vegetation mortality (unpublished data). The main structural changes
occurred in basal area and stem number, mainly due to increases in stem
number and not increases in the number of individuals (as this parameter
decreased in most cases). This idea was analyzed through a hierarchical
© 2014 by Taylor & Francis Group, LLC
Downloaded by [Silvana Marten] at 18:05 02 February 2014
26
Tropical Dry Forests in the Americas
partitioning analysis, a statistical technique that determines how much of
the variation in a given variable (basal area in this case) is explained by other
correlated variables (number of stems, number of individuals, etc.). This
analysis showed that 93% of the changes in basal area from 2004 to 2009
were explained by changes in stem number (54%), followed by changes in
the number of individuals (44%).
The analysis of the ecological succession of a chronosequence of TDFs in
Mexico showed that during the irst year of the study (2004), pastures and
early successional stages were similar to each other but different from later
successional stages in terms of species richness, density, and composition. In
terms of vegetation structure, early successional stages were similar to intermediate and late stages, as all these stages had an equivalent total basal area.
However, this result relects the high number of small stems derived from
the resprouting and recruitment of juveniles in early successional stages.
Thus, a casual interpretation of results for total basal area could lead to an
underestimation of the time required for structural recovery. Based on what
has been stated earlier, the contribution of distinct stem diametric classes to
the total basal area should be evaluated. This would enable a more accurate
assessment of the vegetation structure at iner scales.
Five years later, in 2009, the four successional stages still differed in most
of the variables evaluated, however in a more complex way. Pastures (5 years
old in 2009) maintained their distinctness in terms of all the variables analyzed, although they were more similar to early successional stages in terms
of species density and structure. Early stages of succession became more
similar to later stages in terms of species richness and composition, whereas
intermediate and late stages generally remained similar to each other (see
results above, Figures 2.1 and 2.3). The increasing similarity in species composition with the advancement of succession is likely the result of a strong
effect of deterministic factors. In contrast, stochastic factors, which appear to
be important in explaining intersite variations in pastures, become less relevant in later stages of succession. It is of particular importance to state that
the composition and structure of intermediate and late successional stages
are similar from the beginning to the end of the chronosequence study, indicating that management practices that occurred in the intermediate stages
maintained many species and trees in disturbed areas.
Although it appears that species composition is similar between intermediate and late successional stages, less frequent and rare species are not
likely to be similar in both stages. For instance, other studies have demonstrated that beta diversity is high in mature TDFs in the region (Lott and
Atkinson 2002; Balvanera et al. 2002), creating a heterogeneous landscape. In
addition, the most diverse plant community of Chamela–Cuixmala, which is
found in the canopy stratum (lianas, orchids, and bromeliads), is likely to be
one of the communities that is most affected by disturbance, although this
idea has not been assessed in the context of succession. However, a study of
epiphyte-host networks in the Chamela–Cuixmala region in Mexico showed
© 2014 by Taylor & Francis Group, LLC
Tropical Dry Forest Ecological Succession in Mexico
27
Downloaded by [Silvana Marten] at 18:05 02 February 2014
that the assembly of these commensalistic interactions is determined by the
host-species abundance, species spatial overlap, host size, and wood density (Sáyago et al. 2013). Only the host plant communities of late successional
stages are capable of supporting the unique, diverse canopy plant community of Chamela–Cuixmala. Further work on the succession of TDFs should
include an analysis of all canopy-level strata. Meanwhile, it is important to
interpret results from vegetation analyses with caution and to critically evaluate apparent similarities among successional stages that may relect different underlying processes or causes.
2.3 Phenology
Phenological data were collected during four years (2006–2010) for a total of
695 individuals who belonged to 90 species. Results for this part of the study
are presented in detail in Chapter 7 by Lopezaraiza et al.; next, we present a
summary of the major indings of this study.
2.3.1 Leafing
All successional sites showed a distinct and consistent leaing pattern both
within and across years. The months with the highest proportion of individuals with no leaves were April, May, and June. During the drier months,
the proportion of individuals and species with no leaves was higher in the
late successional sites. During the greener months, there was no difference
among successional stages in the proportion of individuals or species with
50%–100% leaves. In the late successional sites, a higher proportion of individuals had no leaves for ive or more months in a year; whereas at early
and intermediate sites, a higher proportion of individuals maintained their
leaves for six or more months per year. Thus, in general, individuals keep
their leaves for longer at the early and intermediate sites.
2.3.2 Flowering and Fruiting
General patterns of lowering and fruiting at the community level show
peaks at different times of the year. This may be due to differences in community composition and species abundance among plots, as well as due to the
differences in the local physical environment. Almost every month, at least
one species is lowering or fruiting, with large variation among sites. The
most consistent lowering peak across sites and years occurs at the end of the
dry season and at the beginning of the rainy season, around the months of
June and July. There are other lowering peaks at different times for various
sites at the end of the rainy season and at the beginning of the dry season.
© 2014 by Taylor & Francis Group, LLC
28
Tropical Dry Forests in the Americas
Downloaded by [Silvana Marten] at 18:05 02 February 2014
At the early and intermediate successional sites, some individuals lowered
for three to ive months in a year; whereas at the late successional sites, individuals were only recorded lowering for one or two months in a year. In
contrast, at the early successional sites, individuals were recorded with fruits
for approximately three months in a year; whereas at the intermediate and
late sites, some individuals were recorded with fruits for 4 to 10 months in
a year. Thus, individuals tend to lower longer at early successional stages,
whereas they ripen or bear fruits longer at late successional stages.
2.4 Successional Changes in Vertebrate Communities
In this study, we analyzed mainly bird and bat communities along successional stages.
The chapter by Nassar et al. (Chapter 11) and the studies by Avila-Cabadilla
et al. (2009, 2012) describe the main indings of this section in detail.
2.4.1 Birds
In total, we captured 2,775 individuals of 84 different species. The most
abundant species were Vireo lavoviridis (12.3%), Passerina lechanclerii (11.29%),
Cyanocompsa parellina (11.03%), and Columbina passerina (9.4%). Fifty-one
species were considered rare, because they occurred at low abundance
(<0.5% of total captures). When comparing bird species richness and diversity
among successional stages, the stages did not differ signiicantly in terms of
rareied species richness (Kruskal–Wallis tests x2 = 3.77, p = 0.28) and rareied
Shannon diversity indices (x2 = 1.33, p = 0.72). However, bird species composition differed between late successional plots and the remaining successional
stages when analyzed through NMDS. Species composition among plots that
were evaluated through the Morisita index showed a gradient of similarity
along successional stages, where pastures were more similar to early successional sites, and intermediate sites were more similar to late successional
sites. A comparison of plots through rank-abundance curves showed some
species that occurred exclusively in particular successional stages. These species could potentially be considered indicator species. In general, our results
suggest that the mosaic of secondary forests characterizing this region plays
an important role in the maintenance of bird species biodiversity.
2.4.2 Bats
We documented the changes in the structure of bat assemblages among the
secondary successional stages of Chamela–Cuixmala TDF over 42 nights
of sampling and captured 606 phyllostomid bats belonging to 16 species.
© 2014 by Taylor & Francis Group, LLC
Downloaded by [Silvana Marten] at 18:05 02 February 2014
Tropical Dry Forest Ecological Succession in Mexico
29
In general, the late stage had the highest species richness, sustaining all
16 species, followed by the intermediate site with nine species, and the pasture with four species. Species found within any successional stage were a
combination of species found at the previous stage as well as additional species. Bat diversity and abundance did not differ signiicantly among early,
intermediate, and late stages. However, nectarivores were more abundant in
early stages than in late stages, likely as a consequence of differences in food
availability. Our results suggest that areas of forest that are recognized as
late successional are the most important reservoirs of species richness.
We also evaluated variations in the occurrence of phyllostomid bat assemblages in different successional stages and variations in relation to habitat
attributes at local (vegetation structure complexity) and landscape levels
(percentage of forest cover, mean patch area, and diversity of patch types).
We found that frugivore abundance was mainly explained by variations
in the amount of riparian vegetation, whereas nectarivore abundance was
mainly explained by variations in the amount of dry forest vegetation. These
results relect that fruit resources for bats mainly occur in the riparian habitat, whereas bat loral resources are mainly found in the dry forest habitat.
We conclude that the preservation of the riparian vegetation is crucial for
the conservation of bat diversity and the important ecological interactions in
which bats are involved in TDF-transformed landscapes.
2.5 Human Dimensions
Humans have inhabited the coast of Jalisco for thousands of years (Mountjoy
2008). Before the Spaniards’ arrival, indigenous communities had low impacts
on the ecosystems of the region and even during early colonial times, the
region remained relatively undeveloped (Rodríguez 1991). Eventually, the
colonists directed the conversion of indigenous people’s lands into extensive
Haciendas that were dedicated to cattle ranching and agriculture, which led
to land disputes that lasted over centuries. The coast of Jalisco was characterized by the presence of extensive Haciendas. Today, the Chamela–Cuixmala
Biosphere Reserve is surrounded by Ejidos (see Chapter 21). During the
1950s, the federal law of Mexico promoted the colonization of the Paciic
coast. This policy sparked TDF transformation in the Jalisco coastal region
and land-ownership conlicts that have lasted until the present day. For many
decades, government policies considered forested areas as useless lands,
promoting the destruction and conversion of TDFs into pastures for cattle
ranching and agricultural ields. Over time, governmental policies did not
produce the expected results. On the contrary, TDFs have been cleared and
fragmented, and local families have not accomplished digniied livelihoods.
For example, in the Ejido Ley Federal de la Reforma Agraria, 70% of Ejido’s
© 2014 by Taylor & Francis Group, LLC
Downloaded by [Silvana Marten] at 18:05 02 February 2014
30
Tropical Dry Forests in the Americas
young men migrate to the Americas in search of job opportunities. These
migrants send a monthly stipend to their families, and this has become the
most important source of income along the coast of Jalisco.
When we query the local population on their perceptions of policy outcomes, the opinion of local Ejidatarios is that government policies only favor
those who are in better economic positions or investors who are interested
in developing the coast for tourism. The current Coast of Jalisco Land Use
Planning Program—a program that enhances social development and
biological conservation in the region—prohibits clearing land for agriculture and favors private investment (Castillo et al. 2009). Most Ejidatarios
disagree with these policies. Our analysis also reveals that, although the
conservation of TDFs is clearly necessary to preserve biodiversity and ecosystem services, many local people are in conlict with conservation policies.
Local and federal governments have favored land concessions to national
and foreign investors to develop large-scale tourism projects that promote
socioeconomic injustice and environmental damage. People recognize the
need to create policies that regulate large-scale exploitation of TDFs and
coastal resources by a few stakeholders and to preserve TDF habitats and
ecosystem services.
2.6 Conclusions and Recommendations
Our study showed that secondary TDF succession is not a simple, unidirectional linear sequence of change in functional groups/species composition. In general, the analysis of the ecological succession of a chronosequence
of TDFs in Mexico showed that, after ive years, pastures maintained their
distinctness in terms of all composition and structure variables analyzed,
although they were more similar to early successional stages in terms of species density and structure. Early stages of succession became similar to later
stages in terms of species richness and composition, whereas intermediate
and late stages remained similar to each other. The increasing similarity in
species composition with the advancement of succession is likely the result of
strong deterministic factors. The composition and structure of intermediate
and late successional stages are similar from the beginning to the end of the
chronosequence study, indicating that management practices in the intermediate stages maintain many species and trees in disturbed areas. Although
it seems that species composition is similar between intermediate and late
successional stages, the high beta diversity found in the plant communities
of the TDFs of Mexico indicates that less frequent and rare species may not
be similar in both stages, and a more heterogeneous landscape should be
found at a larger scale. Further research should identify the main parameters
involved in TDF succession to develop models of recruitment dynamics of
© 2014 by Taylor & Francis Group, LLC
Downloaded by [Silvana Marten] at 18:05 02 February 2014
Tropical Dry Forest Ecological Succession in Mexico
31
key dry forest plant species that facilitate the process of succession following
natural or human-induced disturbances.
One component of TDFs for which an assessment of succession has not
been conducted is found in the canopy stratum (lianas, orchids, and bromeliads), which encompasses the most diverse plant community of the
Chamela–Cuixmala region. Changes in vegetation attributes in this forest
stratum are likely to differ greatly with succession. Speciically, a decrease
in species composition in early and intermediate successional stages would
be expected due to a reduction in host species abundance, host size, and
wood density (Sáyago et al. 2013). Apparently, only the host plant communities of late successional stages are capable of supporting the canopy plant
community of the Chamela–Cuixmala TDFs. Further work on the succession
of TDFs should include an analysis of all canopy-level strata. Meanwhile, it is
important to interpret results from vegetation analyses with caution and to
critically evaluate apparent similarities among successional stages that may
relect the different underlying processes or causes.
Another important aspect to be considered in the process of ecological succession is the functional response of the community, in which certain groups
of plants and animals respond in a similar fashion to environmental conditions and are associated with particular successional stages. Preliminary
data from our study in Mexico indicate that certain plant groups that share
speciic plant functional traits are more likely to be represented in a particular successional stage. For example, groups of plants in early successional
stages that are more exposed to high temperatures and solar radiation tend
to maximize heat dissipation more than plants from late successional stages,
which tend to enhance more light acquisition and water use. Therefore, the
functional recovery of TDFs might be more complex than inferred by just
analyzing loristic and/or structural components of the community. In addition, the variations in animal community assemblages also seem to be associated with different successional stages. Our studies show that bird and
bat guilds tend to be more associated with certain habitats under certain
successional stages. More studies from other tropical regions are required to
corroborate patterns of functional succession. In conclusion, the main mechanisms of succession and regeneration of TDFs still remain unexplored, and
more efforts are required to understand the ecological processes of these
important ecosystems.
Another important process to consider in ecological succession is related to
plant phenology. Phenological differences encountered among successional
stages might be related to biophysical parameters in which early successional
stages should show high canopy openness (high light transmission) and low
Leaf Area Index as a consequence of their low vegetation density and plant
cover. This, in turn, should be relected in low water availability, high light
availability, and high temperature. Some of these environmental events have
been proposed to trigger phenological patterns in plants. Leaf lushing is
a phenological process that is directly associated to primary productivity.
© 2014 by Taylor & Francis Group, LLC
Downloaded by [Silvana Marten] at 18:05 02 February 2014
32
Tropical Dry Forests in the Americas
The timing of leaf lushing is similar in all successional stages, but early and
intermediate stages appear to retain leaves longer than do late successional
stages. In addition, early successional stages also maintain lowers all year
round with higher peaks of fruiting as well. It seems that plants in early
successional stages are capable of using high light environments with high
water eficiency and are very effective at temperature regulation. Extended
patterns of lowering phenology in early successional stages are likely to
maintain pollinators, particularly bees and butterlies, for long periods of
time. Future research should be designed to study how intraspeciic variation in the frequency, duration, amplitude, and synchrony of lowering may
affect the reproductive success and genetic structure of plant communities
in relation to the regeneration capacity of the different successional stages.
Finally, our study showed that human settlements have transformed a
part of the landscape surrounding the Biosphere Reserve, but a high percentage of mature and successional forest is still found in fragments and
continuous patches, which are owned by the communal land ownership of
Ejidos. Although this Biosphere Reserve is still surrounded by an almost
continuous forest, this important protected area of Mexico may turn into
an island in less than 50 years at the current rate of deforestation, especially
if trends related to Ejidos lands, private ranches, and urban developments
far from the Biosphere Reserve are maintained (Sánchez-Azofeifa et al.
2009a). Ejidos encompass 70% of the territory located in the vicinity of the
Biosphere Reserve, and the remaining land is divided between tourist developments and private properties. Ejidos are also characterized by poverty,
high levels of illiteracy, migration, and limited access to secure employment. Agricultural production is the main economic activity, but it cannot
secure peasant families’ livelihoods. Although peasants recognize the services provided by TDFs, such as cooler climate, shade, and plant and animal
species for family consumption, they are proud of their pasture ields and
economic activities that are aimed at creating jobs and reducing migration to
the Americas. Consequently, the conservation and restoration of TDFs is not
perceived as a necessary activity, as has been found in interviews carried out
in this study. As a communal tenure forum, Ejidos have a social organization
that helps the conduction of collective activities such as forest exploitation.
Their organization is also positioned with the local social institutions with
which a regional conservation and development plan can be formulated and
implemented.
New strategies for the preservation and restoration of TDFs should
promote conservation via payment for environmental services. Among the
most important environmental services are (1) pollination of crops by wild
pollinator species, a service that is particularly important for temporal crops
grown in riparian habitats; (2) protection of watersheds and aquifers, a service that helps prevent natural disaster and ensures availability of one of
the most essential and endangered natural resources—water; and (3) carbon
sequestration by mature and regenerating forests, a service that provides a
© 2014 by Taylor & Francis Group, LLC
Downloaded by [Silvana Marten] at 18:05 02 February 2014
Tropical Dry Forest Ecological Succession in Mexico
33
healthy environment for tourists and local communities, while contributing to a reduction in the impacts of global climate change. Consequently,
to accomplish the goal of promoting conservation through environmental
services, we propose the creation of a “Red de Areas Ejidales Protegidas”
(Ejidos’ protected areas network) in the region surrounding the Chamela–
Cuixmala Biosphere Reserve (Sánchez-Azofeifa et al. 2009a). In this network,
Ejidos will commit to protect land within their property, and the government
and the Biosphere Reserve will commit to pay for environmental services
and to provide technical assistance and training for alternative ecosystem
management strategies. For this to be implemented, the government agency
that is responsible, along with the Biosphere Reserve, should accept a leading
role in the construction of a payment form that improves peasant families’
livelihoods and secures the long-term maintenance of TDFs and associated
habitats. Promotion of environmental educational programs and training
activities for the Ejidos should be implemented to modify the way in which
they perceive and value TDFs. Furthermore, a continuous communication
exchange between the Ejidos and the Biosphere Reserve should be enforced.
Research groups and institutions would also play an important role in terms
of providing information for evaluating the services provided by the Ejidos’
reserves. Schemes similar to those developed in countries such as Costa
Rica (Sánchez-Azofeifa et al. 2007) may be used as an initial template. The
implementation of economic schemes under programs for payment of environmental services will be a very dynamic way of pragmatically enforcing
sustainable development, conservation, and management in tropical rural
Mexico.
© 2014 by Taylor & Francis Group, LLC