Population Dynamics of Big-leaf Mahogany in the Brazilian Amazon
Natural plant populations expand and contract in response to ever-changing physical and biological factors such as climate, topography and soils, disturbances that open growing space, competition between plants of the same and other species, and predators. Different stages of the life cycle may experience different opportunities and constraints on growth and survival, presenting ecologists who model population dynamics with densely complex puzzles to solve. For high-value tropical timber species occurring at extremely low densities on the landscape, such as mahogany, piecing the demographic puzzle together may require decades of work in hundreds or thousands of hectares of forest.
The Mahogany Project seeks to understand what makes big-leaf mahogany 'tick' in southeast Amazonia by monitoring vital rates for all stages of its life cycle, from seeds to senescent adults, across temporal and spatial scales relevant to each life phase. After fifteen years (1995 - 2009) of annual censuses of over 600 trees and many thousands of seedlings and saplings scattered across nearly 5000 hectares of forest, Forest Service sponsored research has developed a demographic model that can be used to simulate both short- and long-term population responses to forest management practices such as minimum diameter felling limits, commercial tree retention rates, and vine cutting. Long-term growth and mortality rates by mahogany at five sites in the Brazilian Amazon indicate that a few, ultra-fast-growing individuals contribute disproportionately to observed population structures. Identifying those individuals and the life-long conditions they experience may hold the key to the sustained management and conservation of surviving natural populations of the world's most valuable tropical timber species.