The aim of our study was to identify the most important ecological factors influencing the breeding density of chukar partridges (Alectoris chukar) in Southeastern Bulgaria. Identified habitats were divided into two categories:1) natural habitats with an extant population of the species, and 2) habitats in which it was absent. In each habitat, annual precipitation, lowest elevation in the habitat, Paliurus cover, grazing livestock per 100 ha, shrub height, shrub density, bedrock type, percentage of pastures, percentage of agriculture, percentage of wetlands, percentage of rocks, presence/absence of buildings, presence/absence of highways, plant
species composition, plant layer coverage, and chukar breeding pairs were measured. We have found several habitat variables that probably affect the density of nesting chukar partridge. These are: 1) grazing intensity, 2) percentage of rock outcrops, 3) percentage of grasslands, 4) shrub cover, and 5) elevation. Grazing intensity and rock outcrop presence, together with the elevation gradient, influence the breeding pair distribution and abundance most significantly. Our study has confirmed only three types of habitats that the chukar currently prefers to nest in. Unknown factors probably changed the other sites in a way that they are no longer suitable for the species’
existence and reproduction.
Photosynthetic pathway types (C3 and C4 species) and their dynamics along grazing gradient were determined for 42 plant species in 30 genera and 13 families from the Songnen grassland, Northeastern China. Of the total, 10 species in 9 genera and 4 families had C4 photosynthesis; 32 species in 21 genera and 12 families had C3 photosynthesis. The proportion of C4 species in total plants and C4/C3 increased with grazing intensity, and peaked in overgrazed plot. Most of the increased C4 species (6 of 10) along the grazed gradient were annual grasses and halophytes. This indicated that the C4 species had greater capacity to tolerate environmental stresses (e.g. drought and saline) caused by animal grazing in the Songnen grassland, Northeastern China.