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Figure 1. Linear regression for density of Guarea guidonia vs. Canopy Cover before and after the storm Jeanne. Figure 2. Linear regression for density of Guarea guidonia vs. Understory Cover before and after the storm Jeanne. A. procera Density. G. Guidonia Density. Canopy Cover (Before). - PowerPoint PPT Presentation
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Effect of a Tropical Storm in a Urban Secondary Forest in Humacao, Puerto RicoCintrón Sol Taína 1,, Carmen Zayas 1, Natalia Piñeiro 1, Joel Soto 2 y Denny S. Fernández 1
1. Department of Biology, University of Puerto Rico at Humacao2. Departament of Education, University of Puerto Rico at Cayey
IntroductionThe secondary forests have been object of study
by many years. These are from the disturbances caused
by anthropogenic impact and natural disturbances as
they are it the natural land slidings, fires and hurricanes.
These forests have an important ecological value
because optimal conditions for the viability of the
recolonization of native species recover the productivity
of the place after a disturbance providing.
A great percentage of the tropic forests could be
considered like secondary forest. In Puerto Rico most of
the forests they are secondary forests. This its by the
high deforestation that underwent the primary forests in
century 19 because the conducted agricultural activity in
those time. In century 20, with the change of an
agricultural society to an industrialist, they are managed
to recover these forests in great proportions of territories
previously of deforested by agriculture. The secondary
forest at University of Puerto Rico at Humacao is
product from the abandonment of the sugar cane
plantation in the Southeast, an important lands in the
agricultural industry at this time.
Initially in this study we pretend to observed how
the canopy affects the regeneration of the understory
and if exist competition between two species of native
and exotic trees. These data were collected during the
summer of 2004, on September of this year after the
tropical storm Jeanne we collect the data necessary to
observe the effect of this storm on the canopy and the
understory of the forest.
MethodologyThe study area has an extension of 1.5 hectare and
we placed there five transects. These transects were
separated 30 m from each other, and aligned North-South.
In the transects we located 6 to 7 points, 20 m apart,
starting from the South end; thus we managed to sample a
total of 33 points. In each point we located two 1 x 1 m
plots, at 0.5 m from the reference point. In these parcels we
measure the density of seedlings of Guarea guidonia and
Albizia procera. For each 1 x 1 m plot we measured the
canopy cover using a densiometer, and the understory
cover of the ground by eye estimation.
On each point we delimited a circle of three meter
radius to measure the density of larger trees with a DBH
equal or greater than 5 cm and smaller ones (with a DBH of
less than 5 cm), and the density of fallen trees inside this
perimeter. In order to estimate the density of trees near
each point we measure the distance to the closest tree on
each of the four.
Processed data were analyzed using standard
statistical packages to compare variables and estimators
before and after the storm, and to test for correlations
between pairs of variables. Geostatistics procedures
(semivariance and krigging) were used to create
interpolation maps for the area.
Results
The results in the table 1 showed the T-test value and the
Wilcoxon test value. Most of the measured variables they
show a significant value. This suggests there was a reduction
in the canopy cover (T-test = .00001****, Wilcoxon
= .00001****) and the understory (T-test = .0268*, Wilcoxon
= .00231*). In table 2 we can observe the results of the
regressions, this regressions suggest that the density of
Albizia procera seedlings don’t depend of each other variable.
But for Guarea guidonia in the figure 1 it is possible to be
observed the relationship between their seedlings and the
canopy cover before and after the storm. Figure 3 are the
maps from the geostatistical analysis and reveal variations in
the heterogeneity of this forest.
Measured Variables Paired T-test Wilcoxon
Tree Density 0.0057** 0.0047**
Albizia procera seedlings density 0.0005*** 0.0009***
Guarea guidonia seedlings density 0.0016** 0.0002***
Understory cover 0.0268* 0.0231*
Canopy cover 0.00001**** 0.00001****
Small tree density 0.8267 0.5434
Big tree density 0.1555 0.0034**
Circular of Big and Small Tree 0.2565 0.5026
Canopy Cover P-ValueGuarea guidonia seedlings density after storm 0.0007***
Guarea guidonia seedlings density before storm 0.0027**
Albizia procera seedlings density after storm 0.537
Albizia procera seedlings density before storm 0.0962
Understory P-ValueGuarea guidonia seedlings density before storm 0.00001****
Guarea guidonia seedlings density after storm 0.1747
Albizia procera seedlings density before storm 0.7212
Albizia procera seedlings density after storm 0.095
Tree Density
Circular of Big and Small Tree P-ValueGuarea guidonia seedlings density before storm 0.0082**
Guarea guidonia seedlings density after storm 0.0396*
Albizia procera seedlings density before storm 0.7715
Albizia procera seedlings density after storm 0.1206
Small tree density P-ValueGuarea guidonia seedlings density before storm 0.4978
Guarea guidonia seedlings density after storm 0.4565
Albizia procera seedlings density before storm 0.2167
Albizia procera seedlings density after storm 0.4314
Big tree density P-ValueGuarea guidonia seedlings density before storm 0.7811
Guarea guidonia seedlings density after storm 0.9834
Albizia procera seedlings density before storm 0.533
Albizia procera seedlings density after storm 0.5209
Fallen Tree P-ValueGuarea guidonia seedlings density after storm 0.7627
Albizia procera seedlings density after storm 0.7175
Circular density Guarea guidonia tree P-ValueGuarea guidonia seedlings density before storm 0.9167
Albizia procera seedlings density before storm 0.7272
Circular density Albizia procera tree P-ValueGuarea guidonia seedlings density before storm 0.7716
Albizia procera seedlings density before storm 0.4423
Circular Density of Big Tree P-ValueGuarea guidonia seedlings density after storm 0 .0836
Albizia procera seedlings density after storm 0.4847
Circular Density of Small Tree P-ValueGuarea guidonia seedlings density after storm 0.00001****
Albizia procera seedlings density after storm 0.252
Table 2. Regression Analysis for measured variables. *P < 0.05; ** P < 0.01; *** P < 0.001; **** P < 0.00001
Guarea guidoniaGuarea guidonia
Albizia Albizia proceraprocera
Acknowledgments
Thanks are given to Camille Battaglia and Noel Rivera for their
colaraboration in the field and to ADVANCE IT for the financial support.
Table 1. Statistical Analysis for each measured variables.
*P < 0.05; ** P < 0.01; *** P < 0.001; **** P < 0.00001
Discussion
Figure 1. Linear regression for density of Guarea guidonia vs. Canopy Cover before and after the storm Jeanne
Figure 2. Linear regression for density of Guarea guidonia vs. Understory Cover before and after the storm Jeanne
A. procera A. procera DensityDensity
G. Guidonia Density
Canopy Cover
(Before)
Canopy Cover (After)
Figure 3. Maps from the geostatistical analyses. a) distribution for Guarea guidonia density in the forest. b) distribution for Albizia procera density c) Canopy Cover before the storm Jeanne d) Canopy cover after the storm Jeanne. (The measurements are given in percentage)
a) b)
c) d)
It’s clear that the tropical storm Jeanne has a effect on the canopy and understory cover. After the storm the canopy cover was reduced significantly and as a results the density of G. guidonia seedling also was reduced because this plant grow under few light condition. The decrease of overall canopy with the lost of the foliage increases the understory cover. This phenomena promote the colonization and growth of other species that are pioneers trees. Also accelerated the growth of advanced regeneration of the forest. In conclusion the tropical storm Jeanne has effect on the canopy and understory cover and this atmospherics phenomena cause frequents changes in the forest dynamic.
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