|OKIN, GREGORY - University Of California|
Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2009
Publication Date: 3/15/2010
Citation: Okin, G.S. 2010. The contribution of brown vegetation to vegetation dynamics. Ecology. 91(3):743-755.
Interpretive Summary: An important component to monitoring changes in the earth’s land surface is the observation of change in vegetation. Seasonal and annual changes in vegetation are both typical and extreme, but we need to understand these normal changes if we are going to detect more substantial changes in response to altered climatic patterns that may occur in the future. This study, funded in part by the National Science Foundation, used remotely sensed data collected from sensors abound the Earth Orbiting System satellite to examine vegetation dynamics across the southwestern United States from 2000-2006. One question address by this study was what is the importance of green and non-green (non-photosynthetic) vegetation in these dynamics over time, much of the southwestern U.S. is dominated vegetation that is “brown” much of the year, and this study was designed to identify the importance of brown vegetation in characterizing these vegetation dynamics. Most studies in the past have focused on green vegetation, and this emphasis may not be appropriate for deserts. Desert areas are 5% of the U.S. land over 25% of the world’s land surface. This study determined that detection of vegetation changes in these deserts and needs to include monitoring of brown vegetation to appropriately characterize the arid lands.
Technical Abstract: Indices of vegetation dynamics that include both green vegetation (GV) and non-photosynthetic vegetation (NPV), that is, brown vegetation, were applied to MODIS surface reflectance data from 2000 to 2006 for the southwestern United States. These indices reveal that the cover of NPV, a measure of vegetation brownness and a component of ecosystems worldwide, is highly variable in both space and time in the study region. In the more mesic regions of the study area, the timing of peaks in NPV appears to result from simple senescence of GV at the end of the growing season. In these regions, the amplitude of GV cyclicity dominates the total vegetation signal. In contrast, in arid and semiarid regions, the amplitude of cyclicity of NPV dominates the total vegetation signal, showing the vegetation of these regions to be unexpectedly dynamic. Shrublands of southwestern United States exhibit temporal behavior in which the annual peak in NPV cover precedes the annual peak in GV cover by a few months. Several explanations for this behavior are offered. This study shows the importance of vegetation indices that include NPV, or vegetation brownness, in understanding terrestrial ecosystem dynamics, as well as the response to change for these ecosystems.