Population and community dynamics of tropical rain forest canopy trees
Kellner, James Robert
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A challenge in tropical forest ecology has been integrating across tree life stages and spatial scales to understand the drivers of population and community dynamics. Here I use data from satellite and aircraft remote sensing to quantify population dynamics and canopy height changes throughout two lowland Neotropical rain forest landscapes. In the first section, develop an unbiased remote sensing approach to map and monitor rain forest canopy trees using high resolution satellite observations and Bayesian statistical modeling. I show using time series observations from satellite remote sensing between 2002 and 2007 for the rain forest canopy tree Tabebuia guayacan throughout 15.4 km of tropical moist forest in Panama that precise estimation of survival, recruitment, and realized population growth is achievable using remote observations. Patterns in adult population dynamics were associated with historical land use and the frequency of canopy disturbance, and mediated by changes to rates of adult recruitment. Temporal variability in recruitment throughout the landscape indicates that regional processes are influencing adult population dynamics in rain forest canopy trees. The results demonstrate the feasibility of making remote measurements of canopy tree population dynamics throughout large areas, including measurement of demographic rates that are not obtainable in the field. In a separate study I combine LiDAR remote sensing with field measurements of canopy height to quantify the structure and dynamics of an old-growth Neotropical rain forest in the Atlantic lowlands of Costa Rica. Persistent disturbance figures prominently in the dynamics of this forest. Forty-one percent of the old-growth landscape had net canopy height changesduring 8.5 years. Most gaps in the forest canopy were small, and individual gap sizes and neighbor distances followed power-laws with slopes that were indistinguishable between years. Gap sizes were unbiased with respect to topographic slope and soil Phosphorus. Despite substantial dynamics, the analysis demonstrates consistency in characteristics of forest disturbance at large spatial scales, and suggests that changes in canopy height were very close to the steady-state equilibrium expectation. These findings challenge the view that Neotropical forests are undergoing structural degradation in response to global changes, and provide evidence of the necessary conditions for selection for long-distance dispersal.