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.