Abstract

Floristic surveys and diversity indices are often applied to measure tree species diversity in mixed tropical forest remnants. However, these analyses are frequently limited to the overall results and do not allow to evaluate the spatial variability distributions of tree diversity, leading to develop additional tools. This study aimed to estimate the spatial variability of tree diversity and map their spatial patterns in a Brazilian mixed tropical forest conservation area. We used indices to measure the tree species diversity (dbh≥10 cm) in 400 sampling units (25mx25m) from a continuous forest inventory. Semivariograms were fitted to estimate spatial dependences and punctual kriging was applied to compose maps. Mean diversity values were constant in the continuous inventories, indicating a forest remnant in an advanced stage of ecological succession. On the other hand, tree diversity presented spatial patterns identified by geostatistics, in which the dynamics were composed of heterogeneous mosaics spatially influenced by tree species with different ecological features and densities, gap dynamics, advancement of forest succession, mortality, and Araucaria angustilofia's cohorts.

Highlights

  • Over the past century, intensive human exploitation has caused severe logging and biodiversity loss in native mixed tropical forests in the Southern region of Brazil (Behling and Pillar 2007)

  • Floristic surveys and diversity indices are the most widely used tools to evaluate the conservation status of these mixed tropical forest remnants (Sonego et al 2007, Ribeiro et al 2013, Polisel et al 2014). These measures are fundamental for the evaluation of forest landscapes, such as: Shannon’s index (1948), which assumes individuals are randomly sampled and all species are represented in a sample; Simpson’s index (1949), a robust measure that considers the probability of any two individuals belonging to the same species; and Margalef’s index (1958), which indicates species diversity as the ratio between the number of species and the logarithm of the total number of individuals in a sample. These analyses have often been limited to the overall results of floristic compositions, whose approaches do not allow us to evaluate the spatial variability of tree diversity

  • Data transformations ln ( xi ), ln ( xi +1), and xi were evaluated for Shannon’s and Simpson’s indices that showed negatively-skewed distributions. These transformations did not provide the appropriate normality condition and, the original data were used (Table II), since normal distribution is not an assumption required for applying geostatistical analysis, in which it is recommended to avoid the biased influence of a few high values on the kriging interpolator in positively-skewed data distributions

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Summary

Introduction

Intensive human exploitation has caused severe logging and biodiversity loss in native mixed tropical forests in the Southern region of Brazil (Behling and Pillar 2007). Floristic surveys and diversity indices are the most widely used tools to evaluate the conservation status of these mixed tropical forest remnants (Sonego et al 2007, Ribeiro et al 2013, Polisel et al 2014) These measures are fundamental for the evaluation of forest landscapes, such as: Shannon’s index (1948), which assumes individuals are randomly sampled and all species are represented in a sample; Simpson’s index (1949), a robust measure that considers the probability of any two individuals belonging to the same species; and Margalef’s index (1958), which indicates species diversity as the ratio between the number of species and the logarithm of the total number of individuals in a sample. This context leads, to a search for additional tools for modeling spatial patterns, such as geostatistical analyses based on the theory of regionalized variables, in which a spatial function is applied to measure a spatial phenomenon (Webster and Oliver 2007), aiming to compose maps, sampling procedures, and local interventions

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