PARENT SESSION
Contributed Oral Session 29: Climate Dynamics: Arid Land Responses to Variability in Rainfall
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal
Corona - spy photos for change detection of arboreal vegetation in an arid cultural landscape.
Andersen, Gidske*,1, 1 Department of Biology, University of Bergen, Bergen, Norway
ABSTRACT- Arid landscapes are homelands to indigenous populations and managed throughout history to provide diverse resources for following generations. Trees are main multipurpose landscape elements and the backbone in nomadic lifestyle. In the hyperarid, mountainous desert landscape of Eastern Desert of Egypt, they grow under optimal conditions in wadis. Their density is, however, decreasing, due to commercial energy production. Despite significant focus on arid land degradation, the degree and long-term consequence is not well known because reliable detailed historical data has so far been scarce. In 1995 data from the first generation U.S. photo-reconnaissance satellite, CORONA, covering large parts of the globe between 1960 and 1972, were declassified. These high-resolution, panchromatic panorama images represent a potential for detailed, long-term environmental change analyses. In this study images from 1965, with a best resolution of 2.7 m, are compared with field data from 2003 in order to quantify the changes in the arboreal wadi vegetation, i.e. Acacia tortilis ssp. and Balanites aegyptiaca. The change analysis shows that: 1) all detectable individuals (Canopy Area > 6m2) present in 2003 were present in 1965, and already then of considerable size. This indicates that growth is slow and age of trees high. 2) Approximately 50 % of interpreted individuals have disappeared in the period studied. 3) Among sites there is large difference in number of individuals disappeared, ranging from approximately 10 to 70 %. 4) Regarding population size the trend for half of the sites is negative, i.e. they are showing a higher rate of mortality than of recruitment. In this estimate all smaller individuals (CA =< 6m2) are considered recruited in the period, which overestimates recruitment. Sources of error influencing change analysis of this kind are discussed, however, overall trends of change in the arid arboreal vegetation remains also when such errors are accounted for.
Key words: Acacia tortilis, change analysis, CORONA images, arid cultural landscapes