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Monitoring Mediterranean ecosystem changes: the ground flora of olive groves subject to different management practices

Monitoring Mediterranean ecosystem changes: the ground flora of olive groves subject to different management practices

Land use change has been identified as a major contributor to loss of biodiversity, and models of global biome change predict that mediterranean-type ecosystems will probably experience large losses by the end of the twenty-first century. Olive groves represent one of the iconic landscapes of the Mediterranean, but in recent decades have undergone rapid land use change. Intensification of olive cultivation across the Mediterranean has been heavily subsidised by the European Union Common Agricultural Policy: in Crete production of olive oil increased by more than 600% between 1968 and 1999. There is a need to establish the impact of changes in cultivation practices on the biodiversity of olive groves and shrubland communities both at the local scale, by means of ground-based fieldwork, and at the landscape and regional scales by means of remote sensing. In this way the longer term effects of agricultural intensification and abandonment of more marginal land can be evaluated.

Bare ground beneath intensive olive cultivation with irrigation pipes
Image as described adjacent

In this project, detailed floristic surveys were made of 95 quadrats from sites representing traditional olive cultivation and semi-abandoned olive-groves and non-olive sclerophyllous shrub communities. TWINSPAN and ordination analysis identified four vegetation communities: olive with herbaceous taxa, olive with sclerophyllous shrub taxa, and two different sclerophyllous shrub communities. The ground flora of the olive-herbaceous communities is quite distinctive from those dominated by shrubs. In addition to grasses, the herbaceous taxa include many ruderal species, such as Reichardia tingitana, Papaver rhoeas, Tordylium apulum and Oxalis pes-caprae. Compared with the sclerophyllous shrub communities, species richness is lower in the olive-shrub communities, probably as a result of the dominance of tall shrubs (2-3 m) such as Anthyllis hermanniae and Phlomis fruticosa. The sclerophyllous shrub communities are dominated by lower growing species such as Sarcopoterium spinosum, with an average height of 0.25-0.30 m. The herbaceous taxa found in sclerophyllous shrub communities are more characteristic of open ground conditions, and also include a number of orchid species, such as Serapias parviflora, Orchis tridentata and Ophrys scolopax. The difference between the drier south-facing and north-facing sclerophyllous shrub communities is evident in the dominance of Thymus capitatus and the presence of Phlomis cretica and Euphorbia characias representing the shrubs in the drier sites, with Sarcopoterium spinosum dominant on the north-facing sites.

Olive-shrub communities - invasion by Anthyllis hermanniae
Image as described adjacent

Canonical correspondence analysis established the relationships between vegetation (species presence and cover abundance) and environmental factors. The olive-herbaceous communities tend to be located at lower elevations, on flatter ground and on soils developed on limestone with a higher pH and greater percentages of calcium carbonate. The olive-shrub communities are more likely to be located on south-facing slopes and at higher elevations than the olive-herbaceous communities, but at below average elevations for all sites in the study. The two different sclerophyllous shrubland communities are differentiated by elevation and aspect into sites typical of south-facing drier slopes, and higher elevation, north-facing slopes.

Olive-herbaceous communities
Image as described adjacent

The ordination results indicate that environmental variables explain about 60% of the species-environment relationships. The remaining variation in species composition is interpreted to be the result of different cultivation practices: the olive-herbaceous communities represent traditional management practices, while the olive-shrub communities represent semi-abandoned olive cultivation. Continued intensification of olive cultivation, especially through the clearance of 'weeds' is likely to increase the threat to the herbaceous taxa of the ground flora of the traditionally managed, low-input but labour intensive olive groves, and to the insect, bird and mammal fauna through removal of their breeding and feeding resources. Semi-abandonment of more marginal and unproductive groves results in encroachment by shrubs, in particular Anthyllis hermanniae, and a reduction in herbaceous diversity because of increased shade. This could increase the risk of fire, as many of the shrub species are inflammable. In addition a more visually homogeneous landscape is developing.

Newly planted olive grove created through bulldozing older groves
Image as described adjacent

The lower elevation, drier sclerophyllous shrubland communities are found in highly fragmented uncultivated land. In places these areas are being bulldozed to create new intensive groves, increasing habitat fragmentation. The higher elevation, north-facing areas of shrubland appear to be more extensive and continuous.

South-facing sclerophyllous shrubland communities
Image as described adjacent

Detailed floristic surveys such as these are difficult to achieve across an island like Crete, which is topographically very diverse time-consuming and they also need to be repeated on seasonal and annual bases to monitor biodiversity change. However, the work presented here can be used in conjunction with remote sensing and GIS to begin the identification of areas of olive cultivation most vulnerable to intensification or abandonment. Integrating further data on distributions of rare or vulnerable species will aid in the production of conservation management plans for plant and animal taxa.

Publications and conference presentations

  • Allen HD, Randall RE, Amable, GS & Devereux, BJ (2006) The impact of changing olive cultivation practices on the ground flora of olive groves in the Messara and Psiloritis regions, Crete, Greece Land Degradation and Development 7, 249-273
  • Allen HD, Randall RE, Amable, GS & Devereux, BJ (2005) The typology of olive cultivation: integrating lidar with vegetation field data Second Biennial Conference of the, International Biogeography Society, Shepherdstown, WV, USA 5-9 January 2005
  • Allen HD, Randall RE, Amable, GS & Devereux, BJ (2004) 3-dimensional structural characteristics and biodiversity patterns of Cretan olive groves: preliminary results from field surveys and airborne LiDAR and VIS/NIR imaging 30th Congress of the International Geographical Union, Glasgow, August 2004

Funding

A British Ecological Society Small Project Grant (2004: 2268) supported some of the field work costs of this project.