The anthropogenic impacts on tropical forest ecology and dynamics
Author(s)
Cazzolla Gatti, Roberto
Date Issued
June 17, 2013
Type
Doctoral Thesis
Abstract
The first aim of this Ph.D. thesis is to investigate the impact of selective logging, which alter forest
dynamics and cause loss of functional species, and could seriously affect tropical forests under a
changing climate. I carried out researches on African tropical forests trying to find a significant
answer to this issue.
My findings suggest that the vertical structure of the logged forest are not largely different from
those of a primary forest, while a remarkable difference in forest density, synthesized in some
indicators, together with a concomitant invasion by vines, climbers and other weeds is pointed out. I
show that the effects on species richness and biomass are greater than those expected from the
simple removal of commercial species, implying that selective logging, unless it is practiced very
carefully at very low harvest intensities, may significantly reduce the biomass density of a tropical
forest for time scales spanning decades, and possibly longer, seriously diminishing the aboveground
carbon storage and richness of the forest.
Then, I present a simple deterministic model that describes the dynamics of tropical rainforest
subject to selective logging to understand how and why weeds displace native species. I argue that
the selective removal of tallest tropical trees carries out gaps of light that allow weeds, vines and
climbers to prevail on native species, inhibiting the possibility of recovery of the original
vegetation.
The second aim of this Ph.D. thesis is to understand the relations between forest structure,
productivity and biodiversity. By studying tropical forest of Africa and of the Earth I tried to shed
light on competing hypothesis and to develop a unified theory which could explain the relations
between forest structure, niche volume, climate and biodiversity. Ishow that there is a global
positive correlation between forest canopy height and biodiversity and that it follows a latitudinal
gradient. I combined the species pool size and the fractal nature of ecosystems to clarify some
general patterns of this gradient.
Finally, for the third purpose of the Ph.D. researches, I compared growth trends of old trees born in
the pre-industrial age (17th century) with those of younger trees born in the modern age (20th
century) to evaluate the changing forests behavior under a modified atmospheric chemistry. I show,
as preliminary results, that the Sapele and Ayous species (African tropical forests) increased their
growth trends during the last century (from 1900).
Additional information
Dottorato di ricerca in Ecologia forestale
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