Assessing changes in semi-natural and agricultural vegetation extent around Sorbas, south east Spain.

Spain’s membership of the European Union (EU) has brought obligations and opportunities under the Common Agricultural Policy (CAP). The CAP provides subsidies for the planting of tree crops, such as olives and almonds, and has resulted in the development of extensive plantations on previously abandoned and unproductive land. In semi arid Almeria, such development typically begins with mechanised clearance of the native, semi-natural vegetation, which is dumped or burned. This study uses airborne imagery from 1982, 1996 and 2001 to examine the changing status of vegetation in undeveloped areas near to the town of Sorbas in Almeria province, a region where extensive clearance for tree crops has been occurring for at least a decade. Initial estimates made from the imagery were surprising, with the density of semi natural vegetation in certain areas seeming to have increased during the five-year interval. Shrub counts made from aerial photography indicated a significantly increased shrub density in parts of the study area. Further analysis of NDVI images from the two later dates, in conjunction with detailed Digital Elevation Models (DEMs) revealed an apparently significant increase in vegetation, mainly on north, east and west facing slopes. Virtually no change was detected on south facing slopes. A series of hypotheses was assessed to account for this change. Recent climate records for the area show no significant change in rainfall patterns, although there is substantial inter-annual variation. Fire recovery was also considered, but municipality records indicate that the area has not been burnt since at least 1977, when municipal logging of detailed fire records began. Recovery of maquis/matorral vegetation is expected to be significantly quicker than this. Anecdotal evidence suggested the potential importance of changes in grazing patterns and, upon further investigation, the number of goats recorded as being grazed in the Sorbas area was found to have fallen significantly since the 1960s, despite the total for Almeria province remaining effectively the same. In an attempt to validate results from the airborne data, a set of large (15m x 15m) quadrats, initially surveyed in 1997/98 for a different project, was resurveyed in April 2003. No statistically significant change in vegetation density was detected, though this may be due to the small sample size (many quadrats could not be precisely re-located), a change in survey personnel, and the inherent subjectivity in assessing ground cover. If the apparent vegetation succession is validated and if, as suspected, the semi-natural vegetation sequesters more carbon than the agricultural crops, then the EU would appear to be subsidising the destruction of what might be a substantial European carbon sink.