Distribution , Ecology and Population Structure of Euphorbia monchiquensis , an Endemism in Southern Portugal

Euphorbia monchiquensis is, within the widespread and euryoecious E. paniculata- complex, an acidophilous subspecies, endemic in Southern Portugal. To evaluate the vulnerability of this taxon vis-a-vis disturbance and landuse changes, we studied the actual distribution, the population size, the ecological requirements and the coenological value of this taxon in the Serra de Monchique, a mountainous region in the Algarve Hinterland. Data sampling was between April and July 2001. The quite constant branching system of this half shrubby spurge allows to determine the age of the indivuduals from the plant architecture and therefore to study the demographic structure in a non-destructive way. 1618 individuals, clustered in 46 populations, have been registered in the Serra. 88% were in flower. Euphorbia monchiquensis is rare relative to its overall distribution. It shows a bimodal altitudinal and coenological pattern. The majority of the populations are concentrated in the most humid mid altitudes and on the luv-ward northwestern side of the Serra. A few populations occur in the dry lowlands, linked to riverine shrublets. The plant depends on a good water supply but does not need shadowing. Within its limited bioclimatic niche, the spurge has a certain capacity of recolonisation and is not extremely sensitive to disturbance. Humid forests of the Euphorbio monchiquensis-Quercetum canariensis are just one of the preferred sociological situations. The coenological spectrum includes pure cork oak forests, Castanea sativa coppices, Eucalyptus-afforestations, mantle communities (Lonicero-Rubetum, Rubo- Nerietum), Origanion virentis fringes, abandoned meadows and roadside verges. It was in this kind of secondary habitats with intermittent disturbance, that most of the juvenile plants could be stated. Only very few plantlings were found. Most of the recorded populations are well balanced in their medium age classes, others are overaged. A correlation between habitat qualities, the reproductive effort and the regeneration efficiency could not be found. Four inflorescence- -morphotypes can be distinguished. The inflorescence architecture becomes more complex with increasing age. Euphorbia monchiquensis is not an extremely endangered, but a vulnerable species. It can be threatened by the process of Eucalyptus afforestation and by the spontaneous spread of Acacia dealbata. To give a reliable answer to the extinction risk, further aspects of its life cycle, seed bank characteristics, and reproductive behaviour have to be studied.