Impact of Selective Logging on Phenology in Amazon Rain-Forests

Alexander Koltunov, University of California, Davis, akoltunov@ucdavis.edu
Susan L Ustin, University of California, Davis, slustin@ucdavis.edu (Presenting)

Selective logging (SL) in the Brazilian Amazon was recently shown in analyses of Landsat ETM+ data to be occurring at rates of about 12000-20000 sq. km per year, thus indicating the central role of selective logging in tropical forest disturbance.



There has been no previous systematic study of forest phenology following selective logging, while phenological changes are known to provide an integrated signal of altered ecosystem functionality. In contrast to deforestation that typically follows a significantly different phenological trajectory than the previous forest, rapid closure of relatively small canopy gaps following selective logging may appear similar to natural regeneration phenomena in forests. As a result, forest biospheric processes and functions, may seem unaffected.





We investigated the assumption that no significant change in forest function follows SL by analyzing a time-series of MODIS data at 1-km scale in logged forests in Mato Grosso, Brazil. The area studied is nearly 670000 sq. km and is characterized by a large number of small SL events that occurred between 1999 and 2000. Using time series of MODIS EVI and NDWI, we show that even low levels (5-10%) of canopy damage cause significant and long-lasting (> 3 years) changes in forest phenology. Partial clearing impedes forest green-up in the dry season, progressively dehydrates the canopy, induces overall seasonal deficits in canopy moisture and greenness, and influences green-up season timing. Given the large and constantly increasing geographic extent of selective logging throughout Amazonia, phenological disturbances may have far-reaching impacts on carbon and water fluxes, nutrient dynamics, and other functional processes in Amazon forests.