The causes and consequences of disturbance and recovery in tropical forests are poorly known, due in large part to the lack of annual tree rings and the sparseness of long-term observations in most tropical forests. This study combines novel remote sensing technologies with careful reconstructions of forest history to understand disturbance and recovery in rain forests that differ substantially in climate and soil fertility across the Hawaiian Islands. High-precision remote measurements will yield a detailed and very broad-scale view of the structure and chemistry of these forests, and this information will be used to identify patterns of disturbance and recovery across landscapes. These patterns will be checked and refined using on-the-ground measurements of site histories (based on pollen profiles dated using lead isotopes), soil fertility, and biological diversity.
Tropical forests contribute substantially to carbon fluxes from terrestrial ecosystems, to climate, and to many other aspects of global biogeochemistry and diversity. Their dynamics are known to depend strongly upon their disturbance regimes, which in turn depend on differences among tropical forests in climate and soil fertility. The interplay between remote and on-the-ground measurements proposed here should yield new information on the dynamics of Hawaiian forests; should identify mechanisms that also operate (with modifications) in more complex continental tropical forests; and should provide new tools for understanding the dynamics of forests everywhere.
Knowing the patterns, causes, and consequences of disturbance in tropical forests is important for understanding their evolution and functioning, as well as their role in sequestering carbon and in regulating our climate system. Forest disturbances can range in size and type, from small-scale treefall events to large-scale losses via fire and severe weather events. Our understanding of tropical forest disturbances over large geographic areas has been difficult to achieve due to difficulties in reconstructing stand dynamics caused by the lack of annual tree rings and the sparseness of long-term observations. To improve our knowledge in this critically important ecological research area, we determined the interactions between landscape-level nutrient availability and disturbance dynamics in montane tropical forests of Hawaii. The Carnegie Airborne Observatory LiDAR (Light Detection and Ranging) and Visible and Infrared Imaging Spectrometer (VSWIR) were used to develop highly detailed geographic information on forest structure and canopy chemistry (http://cao.ciw.edu). This information was used to develop landscape-level maps of potential disturbance/regeneration dynamics for forest landscapes differing in underlying soil fertility and climate conditions. The findings indicated that soil fertility mediates the rates, sizes and spatial characteristics of forest canopy gap dynamics, and pointed to the critical need for large-area samples to obtain reliable estimates of ecosystem dynamics. The effects of invasive species on forest canopy three-dimensional structure, biomass and functional traits were also mapped and analyzed over large forested areas throughout Hawaii. This effort yielding new insight to the way that invasive species fill ecological niches, or where they replace native species following disturbance and/or via niche-based competition. The project also greatly advanced the field of airborne and satellite remote sensing of ecosystem structural, functional and compositional properties. The results of the project were published in top-ranked, peer-reviewed research journals. Project References Asner, G. P., R. F. Hughes, P. M. Vitousek, D. E. Knapp, T. Kennedy-Bowdoin, J. Boardman, R. E. Martin, M. Eastwood, and R. O. Green. 2008a. Invasive plants transform the 3-D structure of rainforests. Proceedings of the National Academy of Sciences 105:4519-4523. Asner, G.P., M.O. Jones, R.E. Martin, D.E. Knapp, and R.F. Hughes. 2008b. Remote sensing of native and invasive species in Hawaiian forests. Remote Sensing of Environment 112:1912-1926. Asner, G.P., D.E. Knapp, T. Kennedy-Bowdoin, M.O. Jones, R.E. Martin, J. Boardman, and R.F. Hughes. 2008c. Invasive species detection in Hawaiian rainforests using airborne imaging spectroscopy and LiDAR. Remote Sensing of Environment 112:1942-1955. Asner, G.P., R.F. Hughes, J. Mascaro, A.L. Uowolo, D.E. Knapp, J. Jacobson, T. Kennedy-Bowdoin, and J.K. Clark. 2011. High-resolution carbon mapping on the million-hectare Island of Hawaii. Frontiers in Ecology and Environment 9:434-439. Asner, G.P., R.F. Hughes, T.A. Varga, D.E. Knapp, and T. Kennedy-Bowdoin. 2009a. Environmental and biotic controls over aboveground biomass throughout a tropical rain forest. Ecosystems 12:261-278. Asner, G.P., R.E. Martin, D.E. Knapp, and T. Kennedy-Bowdoin. 2009b. Effects of Morella faya tree invasion on aboveground carbon storage in Hawaii. Biological Invasions 3:477-494. Féret, J.-B. and G. P. Asner. 2012a. Semi-supervised methods to identify individual crowns of lowland tropical canopy species using imaging spectroscopy and LiDAR. Remote Sensing 4:2457-2476. Féret, J.-B., and G.P. Asner. 2012b. Tree species discrimination in tropical forests using airborne imaging spectroscopy. IEEE Transactions on Geoscience and Remote Sensing doi:10.1109/ TGRS.2012.2199323 Kellner, J. R. and G. P. Asner. 2009. Convergent structural responses of tropical forests to diverse disturbance regimes. Ecology Letters 12:887-897. Kellner, J., G. Asner, P. Vitousek, M. Tweiten, S. Hotchkiss, and O. Chadwick. 2011. Dependence of Forest Structure and Dynamics on Substrate Age and Ecosystem Development. Ecosystems 14:1156-1167. Litton, C.M., C.P. Giardina, J.K. Albano, M.S. Long, and G.P. Asner. 2011. The magnitude and variability of soil-surface CO2 efflux increase with temperature in Hawaiian tropical montane wet forest. Soil Biology and Biochemistry 43:2315-2323. Somers, B. and G.P. Asner. 2012a. Hyperspectral time series analysis of native and invasive species in Hawaiian rainforests. Remote Sensing 4:2510-2529. Somers, B. and G. P. Asner. 2012b. Invasive Species Mapping in Hawaiian Rainforests Using Multi-Temporal Hyperion Spaceborne Imaging Spectroscopy. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing:1-9. Vitousek, P.M., G.P. Asner, O.A. Chadwick, and S. Hotchkiss. 2009. Landscape-level variation in forest structure and biogeochemistry across a substrate age gradient in Hawaii. Ecology 90:3074-3086. Vitousek, P. M., C. M. D'Antonio, and G. P. Asner. 2010a. Invasions and ecosystems: vulnerabilities and the contribution of new technologies. Pages 277-288 Fifty Years of Invasion Ecology. Wiley-Blackwell. Vitousek, P. M., M. A. Tweiten, J. Kellner, S. C. Hotchkiss, O. A. Chadwick, and G. P. Asner. 2010b. Top-down analysis of forest structure and biogeochemistry across Hawaiian landscapes. Pacific Science 64:359-366.
