Interaction among human interference, climate and the viability and dynamics of contracted acacia populations in the Eastern Sahara

There are two main factors driving environmental change in arid lands, climate variability and human interference. ACACIA will focus on these factors' effect upon the dynamics and viability of an essential resource, namely tree populations of Acacia torti lis, in a short- and long-term perspective. Contrary to most research on environmental changes in arid lands, ACACIA will focus on the arid core, i.e. the desert environment, and interactions with the nomadic populations inhabiting these desert rangelands . The seemingly counterintuitive question ?Does traditional nomadic land-use increase the viability of contracted tree populations? will be raised. This is seen in relation to the long-term desiccation of Sahara that started 5500 BP. Already at that time nomadic pastoralism was established in the area, and ACACIA will document and study the scientific content of traditional ecological knowledge (TEK) among present generations of nomads, and to what degree TEK is affected by the current trends of change in these societies. Nomads have through millennia adapted to the climatic variability in the desert. The past savannah forest of the Holocene wet period has now contracted. Isolated and possibly relict tree populations are both valuable and vulnerable. Incr eased stress, caused by change in land-use and/or climate, can reduce their viability. At the same time they might represent unique genetic diversity which can be of high value for conservation in a more extreme climate. ACACIA will therefore study the ge netic diversity of these populations. Further, ACACIA will apply stable carbon and oxygen isotopic analysis combined with 14c dating from acacia wood to achieve a better understanding of the climate variability in this extreme environment, and thereby of ecological and socio-economic change. Since these trees can become several centuries old, this approach can contribute climatic information over the recent past for an area where such data at present is lacking.