Biology Reference
In-Depth Information
Explanatory Variables
Because a number of patch and landscape-scale environmental variables may af-
fect the structure of tree assemblages in tropical forests [8], [52], we also consid-
ered the effects of soil type, distance to the nearest forest edge, forest fragment
size, the spatial distribution of plots (i.e. plot location in the landscape), and the
amount of forest cover retained in the surrounding landscape (hereafter forest
cover) as independent variables for the frequency of reproductive traits in the
tree assemblages. Forest cover is positively correlated with overall connectivity
between patches [53] and was quantified as the percentage of forest within a 1-km
width buffer set from the border of each fragment. Patch and landscape metrics
were quantified using a combination of three Landsat and Spot images acquired
in 1989, 1998, and 2003, a set of 160 aerial photos (1:8,000) taken from com-
missioned helicopter overflights on April 2003, a soil map by IBGE [36], and a
soil map provided by the Usina Serra Grande Agriculture Office. Analyses were
conducted using ArcView 3.2 and Erdas Imagine 8.4.
Functional Diversity of Reproductive Traits
Here we operationally define a functional group as a set of tree species within the
same category of reproductive trait, i.e. a set of species sharing a life-history trait as
previously adopted elsewhere [1]. To calculate the functional diversity of reproduc-
tive traits in forest fragment and control plots, we used Shannon's (log base 2) and
Simpson's indices [54]. We used both indices to elucidate the contribution of both
the richness of categories and the evenness to diversity scores (note that the use of
evenness-based indices for estimating functional diversity has been recommended
by some authors [55]-[57]). We calculated these indices twice for each of the 20
plots: first, using categories as the equivalent of species, and the number of tree spe-
cies within each category as the equivalent of individuals; and second using catego-
ries as the equivalent of species and the number of individual within each category.
Statistical Analysis
Differences in (1) the average percentage of species and individuals within each
category of reproductive trait, and in (2) the average functional diversity of repro-
ductive traits between the control area and fragments were compared with t or
Mann-Whitney tests [58]. General linear models (GLM) were used to detect any
effect of explanatory variables on the frequency of traits in tree assemblages by
first examining the effects of habitat type (fragments vs. control plots), soil type
and distance to the nearest edge considering all 20 plots in the two habitats, and
then the effects of forest fragment size and surrounding forest cover considering
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