Perennial Vegetation Cover Research Articles

The effect of land use change on soils and vegetation over various lithological formations on Lesvos (Greece)

The effect of land use change, from arable to abandoned pasture, on soil properties and vegetation establishment was studied in hilly areas of the island of Lesvos. The main purpose of this study was to establish key indicators or land parameters that can be used for defining environmentally sensitive areas to desertification. 106 soil sites were selected in fields cultivated or non-cultivated for 40–45 years and measurements related to protection from land degradation after abandonment, such as fertility status (organic matter content, pH, cation exchange capacity (CEC), exchangeable potassium and sodium), water storage capacity (soil water retention characteristics, soil depth), erosion resistance (soil aggregate stability), and vegetation characteristics (plant species, extent of vegetation cover) were conducted. The selected sites were located on a variety of parent materials such as volcanic lava, pyroclastics, ignimbrite, schist-marble, and shale. The obtained data indicated that soil pH, and CEC were slightly affected after abandonment as compared to the cultivated soils. Levels of exchangeable sodium and potassium were higher in cultivated soils. Organic matter content and soil aggregate stability were greatly enhanced in most of the abandoned soils. Physical characteristics of the parent material greatly influenced the establishment of the natural vegetation. A critical minimum soil depth of 25–30 cm was measured. On more shallow soils, the associated natural perennial vegetation cover was rapidly reduced, under the prevailing climatic conditions of the study area. Reduction of vegetation cover was related to the parent material. Perennial vegetation was not supported at all on soils below a crucial depth, ranging from 4 to 10 cm, depending on the parent material. This study showed that soil depth is the most important parameter which has to be considered in planning land use change from arable to unmanaged pasture under the soil and climatic conditions of the study area.

Does Nest Placement Affect the Fate or Productivity of California Gnatcatcher Nests?

I monitored 384 California Gnatcatcher (Polioptila californica) nests at five study areas in western Riverside County, California, from 1992 through 1995. Overall, 78.9% of the nesting attempts failed (52.9% from nest predation), and 21.1% fledged young. Vegetation measurements were taken at 207 of 384 nest locations and at 207 randomly selected locations within gnatcatcher territories. Nest placement was not random in that gnatcatchers placed their nests in locations with greater cover and height of perennial vegetation, increased horizontal structural homogeneity, and increased vertical structural homogeneity relative to random locations. The volume of gnatcatcher nest shrubs was lower than that of random shrubs, and concealment was higher at nests than at random shrubs. Nevertheless, variables that differed significantly between nests and random locations were not significantly associated with nesting success, nest predation, nest abandonment, or productivity. The use of specific perennial shrub species as nest substrates was not proportional to the availabilities of the shrub species within the study areas, yet I found no relationship between nesting success and the species of nest shrub. Nesting success appeared to be unrelated to the abundance of perennial shrubs at four of five study areas. My results suggest that factors affecting the fate of California Gnatcatcher nests operate at scales larger than the nest site or nest patch.

International borders and range ecology: The case of Bedouin transborder grazing

Recent research suggests that, under unconstrained human circumstances, pastoral nomads within arid environments have at their disposal means of evading ecological stress that could impel them to cause damage to their grazing and land resources. The Israeli-Egyptian border has imposed a severe constraint upon the range management strategy of the Bedouin whose traditional territory it bisects. The border forced them to exert an increased pressure upon local resources. Considerable damage was thus caused to the perennial vegetation cover (both macrophytes and microphytes) and to the structure of sand dunes on the Egyptian side of the border, with opposite effects on the Israeli side to which the Bedouin had no access. This case study adds a further dimension to the discussion of range management by pastoral nomads in arid and semi-arid areas.

De-awning of Agropyron spicatum cultivator for use as an understory grass on erosive sites

South-facing, semi-arid slopes supporting sagebush (Artemisia tridentata) with scant understory are difficult sites for establishment of perennial vegetative cover in Central Washington. Blue-bunch wheatgrass (Agropyron spicatum) is the most ubiquitous, widely distributed native perennial where exotic annuals are a competitive problem. It can be found as an understory associate or in open stands.Secar is a cultivar, of A. spicatum developed in the Pacific Northwest. Unfortunately, the percent germination of secar seed has been found to be low. It was suspected that a possible inhibitor exists in the awn and mechanical removal may result in earlier and greater germinative ability for increased establishment on Conservation Reserve Program lands.It was found that total germination was not significantly affected by temperature treatment but an apparent difference in rate was determined. A significant increase in germination occurred with awn removal. Specific location of an inhibitor(s) was not statistically apparent. Key words: Agropyron spicatum, germination, seedling vigor, reseeding

The Population Dynamics of Vulpia Fasciculata: A Nine-Year Study

(1) The population dynamics of Vulpiafasciculata were monitored on the fixed dunes of two dune systems in North Wales over a nine-year period. During the first four years of the study the number of individuals on each plot varied little, but the numbers then declined rapidly to extinction. (2) The decline in abundance was associated with an increase in the cover of perennial vegetation and a decline in the cover of bare sand. There was no evidence to link the decline in V.fasciculata to changes in climate at the edge of the species' range or to increased levels of herbivory and granivory. (3) The fecundity of individuals varied between years but generally increased with the decline in density. The negatively density-dependent relationship between fecundity and density measured over time was consistent with the relationship determined in one year by the manipulation of densities. (4) A seed transplant experiment demonstrated that the decline in V.fasciculata, whilst associated with an increase in the abundance of perennials, could not be related directly to resource competition. Rather the decline was associated with a decrease in the local movement of surface-blown sand and an increase in mortality amongst the seedlings which germinated on the sand surface. (5) A population model was used to relate the abundance of V. fasciculata to environmental conditions and in particular to the cover of bare sand. It is predicted that populations can only be expected to persist where the percentage of bare sand remains greater than 50%.