The meaning of sustained yield in use of rangelands
Sustained yield is the threshold for the propeι- use of renewable natural resources. Its application to rangelands without loss of their fot·est character and their disassociation froιn tl1e protective uιnbrella of the forest low can ensure theiι- constant availability for grazing and for other multifunctional and environιnental roles. Moreover, it can allow fιxing the stocking rate at the productive potential of rangelands, with or without improveιnent. Pι-erequisites for its use in practice are its legal authorization, the conψulsory preparation of grazing prograιns within broad forest ιnanageιnent plans and the control of its applications.
Rangelands of the prefecture of Drama and their management problems
Rangelands constitute 33% of the whole prefecture of Drama and cover 115.000 ha. The majority of them (60%) are found on the ιnountains and hilly zones. From these areas only 86200 ha are suitable for range development. Pωductivity and range condition of the rangelands located on the ιnountains and subalpine zones are higher than in the lower zones. The funds. for improveιnent of rangelands are usually limited and ιnainly spent for infrastructure access roads, watering points, etc.). All rangelands are public lands but the right ofuse belongs to the village coιnmunities which practice free and uncontrolled grazing. The application of controlled use faces less technical and more social and political problems. Although the grazing pressure has been reduced in the last few years, the application of proper use is still difficult to be iιnpleιnented.
Analysis of two indexes water use efficiency in Dactylis glomerata L
The instaneous and the intrinsic water use efficiency were analysed in order to study the mechanisms of water use optimization in Dactylis glomerata L. during the growing season. Net assimilation rate(A), transpiration rate (E) and stomatal conductance (gs) were measured in the leaf of Dactylis glomerata L. and the instantaneous (A/E) and intrinsic water use efficiency(A/gs) were calculated by A, E, gs. In the early stages of biological cycle of Dactylis glomerata L and until May the A/E was higher than A/gs. Early in summer when the water deficit was higher the two indexes seem to be similar. Our results provide indications of water use efficiency optimization during the dry season, decreasing and maintaining more or less the value of gs constant.
Invasibility of three native plant communities tο the establishment of the plant invader Oxalis pes-caprae L.
Although some invasive plants are cosmopolitan, not all ecosystems are invaded to the same degree. Yet, there is little experimental work on how ecosystem resistance to invasion at the establishment phase differs among ecosystems. We conducted a field experiment to examine establishment of the plant invader Oxalis pes-caprae in coastal dunes, shrublands and herbaceous understory of olive groves in Lesbos. We selected thirty (30) observational stations, ten per native plant community. Each station consists of a pair of plots: the invaded plot and the reference one. In each invaded plot, we sowed a hundred bulbs of O. pes-caprae, measured the number of seedlings of the plant invader and estimated local species richness, diversity and evenness of native plant communities. In addition, we recorded not only the geographical longitude, the geographical latitude and the elevation in each observational station, but also precipitation and mean temperature for the period between sowing and sampling. Local species richness and vegetation structure were not a good predictor for seedling establishment in costal dunes and herbaceous understory of olive groves. All abiotic factors did not determine the ecosystem invasibility of native plant communities. Finally, we found out that differences in local species richness and diversity of shrublands were only associated to differences in establishment rates of plant invader. Consequently, we concluded that any species poor shrublands are more susceptible to the invasion of the plant invader O. pes-caprae.
