The Structure and Dynamics of Tropical Forests In Relation to Climate Variability

• Main Author: Dong, Shirley Xiaobi
• Other Authors: Moorcroft, Paul R
• Language: en_US
• Published: Harvard University 2011
• Online Access: http://nrs.harvard.edu/urn-3:HUL.InstRepos:5112895

Although trends and changes in environmental forcing over tropical regions have been recognized, the question remains: how do tropical forests respond to current and future global climate change? Results from long-term studies of permanent forest plots have reported different, and in some cases opposing, trends in tropical forest dynamics in response to climate variability. Researchers remain divided as to whether tropical forests are likely to become net carbon sources or net carbon sinks under ongoing climate change. In this thesis, I use both empirical field measurement data analyses and mathematical modeling approaches to study the structure and dynamics of tropical forests in relation to climate variability. I examine tree growth rates calculated from long-term plot censuses with 5-year intervals and dendrometer band measurements with 3- or 6-month intervals to analyze changes in trees’ growth responses to differences in the mean climate forcing at different sites and to temporal variation in precipitation, temperature and solar radiation at different locations. The results reveal new information about relationships between tree growth and climate variability and offer plausible explanations for conflicting trends in tree growth rates observed across different tropical forests over time. In the modeling studies, I use an integral projection model combined with allometric scaling theories to relate tree demographic rates to differences in forest structure. The ability of this model to predict steady-state stem size-frequency distributions of the forests provides the opportunity to gain insights into the demographic history of the forest. I then develop a new dynamic scaling theory that incorporates the two-way interaction between tree demography and forest structure. It can predict the transient, time-dependent dynamics of forest demography and structure as forests reach their steady-state equilibrium, and can capture the characteristic timescales for these processes. This dynamic scaling theory can also be applied in non-equilibrium situations, such as the dynamics of forest re-growth following natural or human disturbances, or transient changes in forest demography and size distributions following climate change.