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Revista de Biología Tropical, ISSN: 2215-2075, Vol. 69(3): 1079-1097, July-September 2021 (Published Sep. 27, 2021)
Floristic composition, structure and environmental characterization of
Cyathea costaricensis population in a remnant cloud forest in Mexico
Miguel Olvera-Vargas
1*
; https://orcid.org/0000-0002-7290-1639
Blanca L. Figueroa-Rangel
1
; https://orcid.org/0000-0002-5869-5277
Christiam Solís Robles
2
; https://orcid.org/0000-0002-1341-1605
1. Departamento de Ecología y Recursos Naturales, Centro Universitario de la Costa Sur, Universidad de Guadalajara,
Av. Independencia Nacional # 151. Autlán de Navarro, Jalisco, México; molvera@cucsur.udg.mx (*Correspondence),
bfrangel@cucsur.udg.mx
2. Centro Universitario de la Costa Sur, Universidad de Guadalajara, Av. Independencia Nacional # 151, Autlán de
Navarro, Jalisco, México; sorch94@gmail.com
Received 10-VI-2021. Corrected 26-VIII-2021. Accepted 17-IX-2021.
ABSTRACT
Introduction: Tree ferns are significant components of temperate, tropical and subtropical forests, contributing
to shape complex forest stand structures.
Objectives: 1) to describe the population structure of Cyathea costaricensis in a remnant cloud forest of West-
central Mexico; 2) to characterize and relate the floristic composition and the structure of the most important tree
species associated to the C. costaricensis population and; 3) to describe the environment where C. costaricensis
occurs.
Methods: We estimated the Importance Value Index (IVI) to select the most important canopy-dominant species
associated to C. costaricensis; we constructed height and Diameter at Breast Height (DBH) frequency distribu-
tions for those selected species according to IVI as well as for C. costaricensis population; we computed the
asymmetry of the frequency distributions through the coefficient of skewness and the probability density func-
tion via the Kernel density estimation. We tested for differences between canopy-dominant tree species and C.
costaricensis population structure by the non-parametric Wilcoxon rank sum test.
Results: C. costaricensis individuals presented the smallest heights and intermediate DBH sizes as compared
with the canopy-dominant species, with statistically significant differences for height but not for DBH according
to the Wilcoxon test. Most of the tree fern individuals were located in uneven terrains and over the base slope
of the terrain; canopy openness and Total Radiation Under the Canopy values were similar to those reported for
Cyathea species elsewhere.
Conclusions: We confirm the hypothesis of comparable structure between the canopy-dominant species and the
C. costaricensis population only for DBH; on the contrary, for trunk height, there were statistically significant
differences; the small heights of C. costaricensis suggest their coexistence in the understory through sheltering
from the taller canopy-dominants. Mostly all individuals of C. costaricensis were confined to local environmen-
tal conditions, particularly to physiography.
Key words: tree ferns; population structure; canopy species composition; reversed J-shaped; height categories;
local environment.
Olvera-Vargas, M., Figueroa-Rangel, B. L., & Solís Robles, C.
(2021). Floristic composition, structure and environmental
characterization of Cyathea costaricensis population in
a remnant cloud forest in Mexico. Revista de Biología
Tropical, 69(3), 1079-1097. https://doi.org/10.15517/rbt.
v69i3.47359
https://doi.org/10.15517/rbt.v69i3.47359
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Revista de Biología Tropical, ISSN: 2215-2075 Vol. 69(3): 1079-1097, July-September 2021 (Published Sep. 27, 2021)
Tree ferns in some forest communities
are important elements in the development of
complex forest structure over time (Fedrigo
et al., 2019). They inhabit a variety of forest
ecosystems as prominent components of tem-
perate and tropical understories, contributing
significantly to the total basal area and stem
density (Bystriakova et al., 2011; Shepherd
et al., 2019). Several tree ferns: Alsophila
tricolor (Colenso) R. Tryon, A. engelii R.M.
Tryon, Cyathea caracasana (Klotzsch) Domin
are known to be negatively stand density
dependent; such negative density dependence
and strong environmental filtering, may affect
the establishment of tree fern seedlings and
saplings, particularly when they occur near
conspecific adult tree ferns (Brock et al., 2020;
Chacón-Labella et al., 2014).
In preserved areas, combined with under-
story shade, some tree fern species (Cyathea
caracasana) can enter a “persistence mode
until a canopy gap opens above them; subse-
quently, they begin a rapid growth, producing
spores and seedling recruitment (Arens, 2001).
The recruitment of tree ferns may be controlled
by environmental filters, including forest can-
opy disturbances that create gaps and edges,
which in turns modify local niche conditions
(Bernabe et al., 1999; Brock et al., 2018a).
Sun-light, temperature, humidity, small-scale
physiographic variations, are among the most
important environmental determinants for their
occurrence (Mendoza-Ruiz & Ceja-Romero,
2014). Many tree fern species thrive well
along stream banks, soils rich in organic mat-
ter and over more exposed sites with direct
sunlight; others like Cyathea sinuata Hook.
& Grev. (synonymous of Alsophila sinuata)
succeed well even on rocky stream side banks
(Ranil et al., 2017).
Tree ferns facilitate regeneration of cer-
tain species (Gaxiola et al., 2008); hence they
have an important influence on the regenera-
tion niche of potentially dominant tree species
through macro-litter fall and shading with
effects on nutrient cycling. A number of tree
ferns species are recognized as keystone spe-
cies for their role in casting deep shade on forest
floor environment, acting as a differential eco-
logical filter on regeneration processes (Forbes
et al., 2016). The ecological relevance of tree
ferns has been documented in several regions
of the world, particularly in the understory as
crucial factors determining forest structure,
through the release of shade-intolerant conifers
from angiosperm competition (Brock et al.,
2020). But also, tree ferns can affect succes-
sional processes around their neighborhood
by inhibiting the growth of understory species
through the release of allelochemicals (Negrão
et al., 2017), in some cases, inhibiting and
slowing forest succession (Brock et al., 2018b).
Tree ferns are important components of cloud
forests in Mexico (Hernández-Álvarez et al.,
2019; Ruiz Coyoahua, 2020), however, eco-
logical information on these vascular plants has
been largely restricted to taxonomic descrip-
tions (Mendoza-Ruiz & Ceja-Romero, 2014)
and to assess species richness (Ramírez-Bara-
hona et al., 2011). Cloud forest is a community
included in the humid forest ecosystems of
Mexico, mostly located between 1 000 to 3 000
m.a.s.l. (Villaseñor, 2010) where high humid-
ity, due to cloud condensation, is common. In
Mexico, one of the most important tree fern
genera is Cyathea; it contains approximately
10 species under different conservation catego-
ries, mostly growing in sub-tropical, tropical
and cloud forests (Ruiz Coyoahua, 2020). One
of these tree fern species is Cyathea costari-
censis (Mett. ex Kuhn) Domin, a Mesoameri-
can endemic species distributed from Western
Mexico to Western Panama (Mickel & Smith,
2004); although it is tagged as an Endangered
species according to the Mexican Red List
NOM-059-SEMARNAT-2010 (Secretaría del
Medio Ambiente y Recursos Naturales, 2010),
there is no documented studies on its ecology.
Accordingly, this study seeks to answer: how
tree ferns coexist with the canopy-dominant
shade-tolerant species of a remnant cloud forest
in West-Central Mexico? Therefore, the objec-
tives in the present study were: 1) to describe
the population structure of C. costaricensis in a
remnant cloud forest of West-Central Mexico;
we hypothesized that C. costaricensis is an
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important element beneath the canopy of domi-
nant trees with a typical behavior of a shade-
tolerant species, thus its diameter and height
frequency distribution will be characterized by
a reversed J-shape showing a gradual lessen-
ing of individuals as its diameter and height
category increase; 2) to characterize and relate
the canopy floristic composition including the
structure of the most important tree species,
to C. costaricensis population structure; we
hypothesized that the canopy-dominant species
and the C. costaricensis population, will show
a similar structural pattern due to their shade-
tolerance behavior; 3) to describe the environ-
ment where C. costaricensis occurs, we expect
that sun-light related variables should explain
the presence of this species in our study area.
MATERIALS AND METHODS
Study site: We carried out this research
in a remnant cloud forest which contains a
unique ancient flora of Pleistocene origin,
mainly dominated by Acer binzayedii Y.L.
Vargas-Rodr., Podocarpus reichei J. Buch-
holz & N.E. Gray and Abies religiosa (Kunth)
Schltdl. & Cham. (Del Castillo-Batista et al.,
2018; Vargas-Rodríguez et al., 2012). The
study area is located over the East-Southeast
zone in Talpa de Allende Jalisco, Mexico
(between the coordinates (20º13’46.28” N &
104º44’2.69” W), at 1 798 m.a.s.l.), within
the tributary Talpa watershed. Annual aver-
age precipitation extends from 1 600 to 1 800
mm and temperature from 16 to 22 ºC. This
floristic zone is characterized by a complex
biogeographical history that combines Holarc-
tic, Tropical, Pantropical and Asian-American
elements as a result of the convergence of the
Nearctic and the Neotropic biogeographical
zones (Vázquez-García et al., 2000).
Data collection method: First, we con-
ducted a field exploration on the whole area
covered by the relict cloud forest in the study
area where we observed Cyathea costaricensis
individuals (around 3 ha); in a second stage, we
census all individuals of Cyathea costaricensis
present in the study area.
Vegetation characterization: Field-work
explorations revealed that Cyathea costaricen-
sis population in the study area has a fragment-
ed and rather small population size. Therefore,
we established seven circular plots (500 m
2
each). In each plot, all C. costaricensis indi-
viduals were counted, identified and their total
height and diameter at breast height (DBH;
measured at 1.30 m height above the forest
floor) were measured. Tree species ≥ 5 cm
DBH, co-occurring with C. costaricensis, were
also recorded by species, DBH and height.
When necessary, we removed any obstacle (e.g.
lichens, dead material, creeper plants, etc.) that
might impede an accurate DBH measurement.
All individuals were identified during the field-
work to species level according with the speci-
mens deposited in the ZEA Herbarium of the
Department of Ecology and Natural Resources
of the Centro Universitario de la Costa Sur,
University of Guadalajara; the scientific spe-
cies names were cross-checked according to
Tropicos.org database (Tropicos.org, 2021).
Environment characterization: In each
plot, we recorded the following variables: ele-
vation (m.a.s.l.); slope inclination (as a indica-
tive of soil moisture and depth due to surface
runoff) measured in the steepest down-slope
of the terrain; aspect expressed as azimuth in
degrees from 0 to 360° and then transformed
into a continuous variable according to Beers
et al. (1966); topography, visually evaluated in
two categories, even and uneven terrains (Table
1); stones and rocks (a visual evaluation of the
amount of this material covering the surface of
the plot; both assessed into five categories) and
canopy strata (a visual assessment of the num-
ber of vertical strata formed by crown of the
trees, evaluated in four categories) (Table 1).
The environmental characterization was carried
out following the criteria proposed by Olvera-
Vargas et al. (1996). We also assessed the light
environment using hemispherical photographs
following the protocol proposed by Zhang et al.
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(2005). For this purpose, we took three hemi-
spherical photographs within each 500 m
2
plot,
one at the upper slope, one at the middle and
one at the lower. We used a Nikon Coolpix 990
digital camera and a Nikon Fish-eye Converter
FC-E8 0.21×lens attached to a self-leveling tri-
pod mount. For hemispherical image analysis,
we used WinSCANOPY (Regent Instruments
Inc., 2005) considering the following variables:
canopy openness (CO), canopy gap fraction
(CGF), leaf area index (LAI), photosynthetic
photon flux density (PPFDu), total radiation
over the canopy (TROC), total radiation under
the canopy (TRUC), direct radiation (DiR) and
diffuse radiation (DfR) (Table 1). We recorded
the date and the time of the day in which each
photo was taken. We used this information as
input during image analysis in WinSCANOPY.
Data analysis: Confidence intervals at 95
% were computed by plot for all quantitative
environmental variables while the mode was
computed for qualitative variables. Confidence
intervals were also estimated for DBH, height
and basal area for Cyathea costaricensis and all
canopy-dominant species. In order to establish
the relative ecological importance of each spe-
cies to the overall forest community dominance,
we first calculated the Importance Value Index
(IVI) (Etherington et al., 1987). This index
represents the sum of relative density (number
of individuals per species/total number of indi-
viduals all species), relative frequency (number
of plots in which species appear/total number
of plots) and relative basal area (total basal
area per species/total basal area all species).
To further describe the tree canopy-dominant
species composition, we selected those species
whose IVI were higher than 70 %. We first
computed quartiles for height and DBH for
the most important species and display them
using box and whisker plots. We analyzed size
frequency distributions for C. costaricensis and
for the canopy-dominant species with the high-
est IVI. For DBH, we used histograms with 5
cm intervals. For height categories, we used the
approach by Pérez-Paredes et al. (2014); these
authors used the following categories in their
study with Cyathea fulva (M. Martens & Gale-
otti) Fée: Juveniles: individuals < 3 m height;
Intermediate: individuals 3-7 m height; Mature:
individuals > 7 m height; we decided to apply
the same height categories since C. costaricen-
sis and C. fulva have relatively similar growth
in terms of maximum height of their stems. To
further compare height class frequency dis-
tribution of C. costaricensis with height class
frequency distribution of the species with the
highest IVI, at plot level, we constructed histo-
grams using the following height intervals (in
meters): < 3, 3-7, 7-11, 11-15, 15-19, 19-24,
24-27, > 27. We also estimated total basal area
by height class for C. costaricensis in order to
discern the contribution in basal area by each
height sizes. The coefficient of skewness (g
1
)
was computed for both height and DBH fre-
quency distributions to assess symmetry. A g
1
= 0 indicates a symmetric distribution. A g
1
< 0
indicates a negative asymmetry skewed to the
left, while a g
1
> 0 indicates a positive asym-
metry skewed to the right. We estimated the
coefficient of skewness following the Wright
et al. (2003) metric approach:
Where: n, xi, x, and s represent the number of
individuals, the logarithm of DBH or height
for individual i, the mean of the xi, and the
standard deviation (Std) of the xi, respectively.
In order to compare height and DBH
sizes of C. costaricensis with the tree canopy-
dominant species with the highest IVI, a kernel
probability density function was computed and
plotted, one for C. costaricensis and one for
the canopy-dominant species with the high-
est IVI. The shape of the kernel probability
density function does not rely on the number
of class intervals subjectively chosen and it
is built on the individuals’ location of all data
(Węglarczyk, 2018); those characteristics were
suitable as we want to compare dissimilar
sizes for height and DBH of C. costaricensis
and its canopy-dominant species. Shapiro-Wilk
normality test was applied to test the normality
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TABLE 1
Environmental variables recorded in the study plots with Cyathea costaricensis following Olvera-Vargas et al. (1996)
Variable name Acronym
Acronym for
categorical
variables
Measurement units
or names for
categorical variables
Variable Description
1. Elevation Elev Metres above sea
level
Distance above sea level measured with
a Suunto altimeter.
2. Slope inclination Slope Percentage Percentage of slope terrain inclination
measured in the steepest down-slope.
3. Aspect Aspect Degrees Azimuth of dominant direction of
downward-facing slope-inclination.
Log-transformed into a continuous
variable.
4. Topography Top A measure of the terrain evenness.
Top1 Even terrain Continuous and homogeneous terrain
inclination.
Top2 Uneven terrain Discontinuous and heterogeneous
terrain inclination.
5. Rocks Rck Rck0 Absence Visual evaluation of the amount of rocks
covering the surface of the plot.
Rck1 Hardly visible
Rck2 Scarce
Rck3 Moderate
Rck4 Abundant
6. Stones Sto Sto0 Absence Visual evaluation of the amount of
stones covering the surface of the plot.
Sto1 Hardly visible
Sto2 Scarce
Sto3 Moderate
Sto4 Abundant
7. Canopy strata CStr CStr1 One vertical stratum Visual assessment of the number
of vertical strata formed by the tree
crowns. Shrubs were not considered for
this assessment.
CStr2 Two vertical strata
CStr3 Three vertical strata
CStr4 No discernible
vertical stratums
8. Canopy openness CO Percentage
9. Canopy gap fraction CGF Percentage
10. Leaf area index LAI (m
2
m
-2
)
11. Photosynthetic photon
flux density under the
canopy
PPFDu (μmol/s-m
2
)
12. Total radiation over the
canopy
TROC (MJ/m
2
day)
13. Total radiation under the
canopy
TRUC (MJ/m
2
day)
14. Direct radiation DiR Percentage
15. Diffuse radiation DfR Percentage
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of height and DBH class frequency distribu-
tion for C. costaricensis and for the canopy-
dominant species with the highest IVI. To test
for differences between the canopy-dominant
species and the C. costaricensis population
structure, using DBH and height as indicators
of structural behavior, the non-parametric Wil-
coxon rank sum test was estimated for DBH
and height; the Wilcoxon test compares two
independent groups when data are not nor-
mally distributed (MacFarland & Yates, 2016).
Descriptive statistics and hypothesis tests (Sha-
piro-Wilks and Wilcoxon) were estimated in R
software-v.3.6 (R Core Team, 2018); for the
coefficient of skewness, we used the e1071
library and for graphs, the ggplot2 library.
RESULTS
Floristic composition and structural
characterization: We recorded a total of 333
individuals 5 cm of DBH distributed in 27
species, 24 genera and 24 families. Cyathea
costaricensis was represented by 62 individu-
als, representing 18.61 % of the total number
of individuals, followed by Carpinus tropicalis
(Donn. Sm.) Lundell (50 individuals), Podo-
carpus reichei (with 38), Clusia salvinii Donn.
Sm (with 32), Conostegia volcanalis Standl. &
Steyerm. (with 23) and Acer binzayedii (with
23). In contrast, 18 species were present with
fewer than ten individuals. Quercus (3 spe-
cies) was the most diverse genus, followed by
Eugenia (2 species). Considering those spe-
cies with 3 individuals, Acer binzayedii Y.L.
Vargas-Rodr. was the species with the biggest
DBH and Eugenia crenularis Lundell with the
smallest DBH; the tallest species corresponded
to Quercus uxoris McVaugh and the smallest
height to Cyathea costaricensis (Table 2).
IVI results revealed that 10 species, out
of the 27 recorded in the study plots, contrib-
uted with > 70 % to the total dominance in the
community; Cyathea costaricensis showed the
second higher IVI value (127 %) only after
Carpinus tropicalis (135 %); A. binzayedii
and P. reichei attained similar IVI’s (around
118 %); these dominant species were followed
by Quercus nixoniana S. Valencia & Lozada-
Pérez (100 %), Clusia salvinii (99 %), Conoste-
gia volcanalis (95 %), Clethra fragrans L.M.
González & R. Delgad. (93 %), Quercus uxoris
(83 %) and Ilex brandegeeana (75 %). The
remaining of the species reported IVI’s with
less than 50 % (Fig. 1).
Cyathea costaricensis, Carpinus tropicalis
and Podocarpus reichei were the most frequent
species, recorded in the seven plots, while 11
species with frequencies around 14 % were
present in only one plot. The same three species
with the highest relative frequency, were also
the most abundant. Acer binzayedii (around
26 %) and Carpinus tropicalis (21 %) were
the most dominant species according to their
relative basal area, while 21 species contrib-
uted with less than 5 % (Fig. 1). Trunk height
was variable among the ten species with the
highest IVI. Cyathea costaricensis showed the
smallest mean height, even smaller than those
shade-tolerant species commonly found in the
understory in our study area such as Clusia
salvinii and Conostegia volcanalis; the largest
mean heights were reported for Quercus uxo-
ris and Acer binzayedii; this last species also
showed the tallest individuals, with tree heights
up to 40 m. In terms of stem height, Carpinus
tropicalis and Quercus nixoniana showed the
greatest variation (Fig. 2A, Table 2). In terms
of DBH, C. costaricensis displayed an interme-
diate mean size when compared with the rest
of the species; highest values for DBH corre-
sponded to A. binzayedii, Q. uxoris, C. tropica-
lis and Q. nixoniana in that order of magnitude;
the highest DBH variation corresponded to A.
binzayedii and the lowest variation to C. cos-
taricensis (Fig. 2B, Table 2).
Structural variation by plot: The num-
ber of individuals for C. costaricensis varied
among plots, with plot 2 showing the highest
number of individuals (N= 18), followed by
plot 5 (N= 12), whilst the lowest number (N=
4) was present in plots 1 and 4; the smallest
mean for DBH, height and basal area cor-
responded to plot 2 and the highest to plot 6
(Table 3).
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TABLE 2
List of species present in the remnant cloud forest in west-central Mexico
Species Family Acronym N DBH Ht BA
Cyathea costaricensis (Met. ex
Kuhn) Domin
Cyatheaceae Cycos 62 11.32 ± 0.96 6.01 ± 0.48 0.03 ± 0.004
Carpinus tropicalis (Donn. Sm)
Lundell
Betulaceae Catro 50 17.76 ± 3.14 13.81 ± 2.28 0.09 ± 0.03
Podocarpus reichei J. Buchholz
& N.E. Gray
Podocarpaceae Porei 38 11.20 ± 2.74 9.09 ± 1.90 0.04 ± 0.02
Clusia salvinii Donn. Sm.
Clusiaceae Clsal 32 10.45 ± 1.95 7.21 ± 0.90 0.03 ± 0.01
Acer binzayedii Y.L.Vargas-
Rodr.
Sapindaceae Acbin 23 25.03 ± 10.27 15.28 ± 4.30 0.26 ± 0.20
Conostegia volcanalis Sandl. &
Steyerm.
Melastomataceae Covol 23 9.05 ± 1.69 7.28 ± 1.39 0.021 ± 0.008
Quercus nixoniana S. Valencia
& Lozada-Pérez
Fagaceae Qunix 19 17.11 ± 6.70 15.00 ± 4.55 0.10 ± 0.07
Clethra fragrans L.M. González
& R. Delgad.
Clethraceae Clfra 16 10.87 ± 2.40 9.88 ± 2.60 0.03 ± 0.01
Quercus uxoris McVaugh
Fagaceae Quuxo 13 20.68 ± 8.87 15.69 ± 5.43 0.14 ± 0.11
Zinowiewia concinna Lundell
Celastraceae Zicon 9 9.04 ± 2.23 9.33 ± 3.28 0.02 ± 0.009
Ilex brandegeeana Loes.
Aquifoliaceae Ilbra 7 10.62 ± 7.40 9.21 ± 5.16 0.03 ± 0.04
Eugenia crenularis Lundell
Myrtaceae Eucre 6 8.26 ± 3.41 9.00 ± 4.19 0.017 ± 0.013
Juglans major (Torr.) A.Heller
Juglandaceae Jumaj 6 15.05 ± 6.91 13.00 ± 9.29 0.05 ± 0.05
Inga laurina (Sw.) Willd.
Fabaceae Inlau 5 12.08 ± 6.58 11.3 ± 5.61 0.037 ± 0.04
Magnolia pacifica A. Vázquez
Magnoliaceae Mapac 3 13.5 ± 6.57 13.33 ± 15.17 0.04 ± 0.04
Prunus cortapico Kerber ex
Koehne
Rosaceae Prcor 3 13.76 ± 11.28 12.33 ± 6.23 0.05 ± 0.17
Quercus laurina Bonpl.
Fagaceae Qulau 3 9.36 ± 1.0 7.33 ± 3.79 0.019 ± 0.004
Dendropanax arboreus (L)
Decne. & Planch.
Araliaceae Dearb 2 * * *
Myrsine coriacea (Sw.) R. Br.
ex Roem. & Schult.
Myrtaceae Mycor 2 * * *
Perrottetia longistylis Rose
Dipentodontaceae Pelon 2 * * *
Saurauia serrata DC.
Actinidiace Saser 2 * * *
Symplocos citrea Lex. Ex La
Llave & Lex
Symplocaceae Sycit 2 * * *
Cordia prunifolia I.M. Johnst.
Boranginaceae Copru 1 * * *
Eugenia culminicola McVaugh
Myrtaceae Eucul 1 * * *
Persea hintonii C.K. Allen
Lauraceae Pehin 1 * * *
Pinus herrerae Martínez
Pinaceae Piher 1 * * *
Styrax radians P.W. Fritsch
Styracaceae Strad 1 * * *
N = Total number of individuals; DBH = Mean diameter at breast height (cm); Ht = Mean tree height (m.); BA = Mean
Basal Area (m
2
/ha). Confidence intervals (95 %) for DBH, Ht and BA. *Parameter estimation confidence intervals were not
computed as only two individuals were present.
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Height class frequency distribution pre-
sented an unbalanced pattern at plot level. The
coefficient of skewness, g1 was > 0 in all plots,
revealing a positive asymmetry; their values
were near to 1.0 in five (1, 2, 3, 6 and 7) of the
seven plots exhibiting very irregular patterns in
their distributions; on the contrary, plots 4 and
5 with higher g1values; the 2 words have to be
separated (2.75 and 2.35 respectively), showed
a reversed J-shaped with individuals mainly
concentrated over the smallest height classes
(between 7 to 11 m height) (Fig. 3). The high-
est number of C. costaricensis individuals were
in the intermediate height category in all plots,
while only plots 2 and 3 showed individuals in
the three height categories (mature, intermedi-
ate and juveniles). The tallest individuals corre-
sponded to A. binzayedii, Carpinus tropicalis,
Quercus uxoris and Q. nixoniana in all plots,
while Clusia salvinii and Conostegia volca-
nalis were also recurrent with small values in
height (Fig. 3).
DBH class frequency distribution was
moderately characterized by the classic
J-shaped in plots 2, 4 and 5; this represents a
large number of small- to middle diameter size
classes of intermediate to shade tolerant spe-
cies. The coefficient of skewness (g1) revealed
that all the studied plots showed positive asym-
metry, reinforcing that individual over smaller
DBH classes dominated the plots (Fig. 4).
Most of the species contained individuals
in 10, 15 and 20 cm DBH classes; C. cos-
taricensis individuals were also concentrated in
these DBH classes in the seven plots. Only few
old-growth trees (corresponding to A. binzaye-
dii, C. tropicalis, Q. uxoris and Q. nixoniana)
were recorded with diameters higher than 40
Fig. 1. Importance Index Value (IVI) of the species present in the remnant cloud forest in West-central Mexico. Percentage
values are displayed in descending order for IVI, Relative Basal Area (BA), Relative Density and Relative Frequency.
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Revista de Biología Tropical, ISSN: 2215-2075, Vol. 69(3): 1079-1097, July-September 2021 (Published Sep. 27, 2021)
cm. In certain plots, some of the species with
the highest IVI, were represented in all DBH
categories; for instance, A. binzayedii and
Carpinus tropicalis in plot 1, Q. uxoris and
Clethra fragrans in plot 3, Clusia salvinii in
plot 5 (Fig. 4).
Structural comparison of Cyathea cos-
taricensis with canopy dominant species:
Heights for C. costaricensis ranged from 2.0 to
10.5 m with marked differences in number of
individuals by height class. The intermediate
class reported the highest number of individu-
als (N= 43), followed by the mature class (N=
15) and the juvenile class (N= 4). The highest
contribution in basal area (1.060 m
2
) was esti-
mated for the intermediate class (Fig. 5A). The
coefficient of asymmetry (g1) was very close to
zero (g1= 0.06) representing a symmetric distri-
bution; however, results from the Shapiro-Wilk
Fig. 2. Box and whisker plots representing quartiles for A. Height and B. DBH of the species with Importance Index
Values > 70 %.
TABLE 3
Structural variables for Cyathea costaricensis by plot in the remnant cloud forest, West-central Mexico
Plot Number of individuals Mean DBH (cm) Mean Height (m) Mean Basal Area (m
2
/plot)
1 4 12.4 6.5 0.013
2 18 8.7 4.7 0.006
3 8 10.0 5.6 0.009
4 4 12.1 6.1 0.012
5 12 13.5 6.9 0.014
6 9 13.6 7.1 0.015
7 7 11.6 6.3 0.011
CI 8.8 ± 3.64 11.32 ± 0.96 6.01 ± 0.48 0.011 ± 0.001
CI = confidence intervals at 95 %.