RESUMEN
Globally, grasslands are shaped by grazing and fire, and grassland plants are adapted to these disturbances. However, temperate grasslands have been hotspots of land-use change, and how such changes affect interrelations between herbivory, fire and vegetation are poorly understood. Such land-use changes are widespread on the Eurasian steppe, where the dissolution of the Soviet Union in 1991 triggered the abandonment of cropland and pasture on globally relevant scales. Thus, to determine how relationships between plant functional composition, grazing and fire patterns changed after the Soviet Union dissolved, we studied a 358,000 km2 region in the dry steppe of Kazakhstan, combining a large field dataset on plant functional traits with multi-scale satellite data. We found that increases in burned area corresponded to decreases in livestock grazing across large areas. Furthermore, fires occurred more often with high cover of grasses with high leaf dry matter content and thus higher flammability, whereas higher grazing pressure favoured grazing-tolerant woody forbs and ruderal plants with high specific leaf area. The current situation of low grazing pressure represents a historically exceptional, potentially non-analogue state. We suggest that the dissolution of the Soviet Union caused the disturbance regime to shift from grazer to fire control. As grazing and fire each result in different plant functional compositions, we propose that this led to widespread increases in grasses and associated changes in steppe plant community structure. These changes have potentially occurred across an area of more than 2 million km2 , representing much of the world's largest temperate grassland area, with globally relevant, yet poorly understood implications for biodiversity and ecosystem functions such as carbon cycling. Additionally, future steppe management must also consider positive implications of abandonment ('rewilding') because reverting the regime shift in disturbance and associated changes in vegetation would require grazing animals to be reintroduced across vast areas.
Asunto(s)
Ecosistema , Incendios , Animales , Pradera , Herbivoria , Plantas , PoaceaeRESUMEN
Fine-scale vegetation cover is a common variable used to explain animal occurrence, but we know less about the effects of fine-scale vegetation heterogeneity. Theoretically, fine-scale vegetation heterogeneity is an important driver of biodiversity because it captures the range of resources available in a given area. In this study we investigated how bird species richness and birds grouped by various ecological traits responded to vegetation cover and heterogeneity. We found that both fine-scale vegetation cover (of tall trees, medium-sized trees and shrubs) and heterogeneity (of tall trees, and shrubs) were important predictors of bird richness, but the direction of the response of bird richness to shrub heterogeneity differed between sites with different proportions of tall tree cover. For example, bird richness increased with shrub heterogeneity in sites with high levels of tall tree cover, but declined in sites with low levels of tall tree cover. Our findings indicated that an increase in vegetation heterogeneity will not always result in an increase in resources and niches, and associated higher species richness. We also found birds grouped by traits responded in a predictable way to vegetation heterogeneity. For example, we found small birds benefited from increased shrub heterogeneity supporting the textual discontinuity hypothesis and non-arboreal (ground or shrub) nesting species were associated with high vegetation cover (low heterogeneity). Our results indicated that focusing solely on increasing vegetation cover (e.g. through restoration) may be detrimental to particular animal groups. Findings from this investigation can help guide habitat management for different functional groups of birds.
Asunto(s)
Biodiversidad , Aves , Ecología , Ecosistema , Árboles , Animales , FenotipoRESUMEN
Improving biodiversity conservation in fragmented agricultural landscapes has become an important global issue. Vegetation at the patch and landscape-scale is important for species occupancy and diversity, yet few previous studies have explored multi-scale associations between vegetation and community assemblages. Here, we investigated how patch and landscape-scale vegetation cover structure woodland bird communities. We asked: (1) How is the bird community associated with the vegetation structure of woodland patches and the amount of vegetation cover in the surrounding landscape? (2) Do species of conservation concern respond to woodland vegetation structure and surrounding vegetation cover differently to other species in the community? And (3) Can the relationships between the bird community and the woodland vegetation structure and surrounding vegetation cover be explained by the ecological traits of the species comprising the bird community? We studied 103 woodland patches (0.5 - 53.8 ha) over two time periods across a large (6,800 km(2)) agricultural region in southeastern Australia. We found that both patch vegetation and surrounding woody vegetation cover were important for structuring the bird community, and that these relationships were consistent over time. In particular, the occurrence of mistletoe within the patches and high values of woody vegetation cover within 1,000 ha and 10,000 ha were important, especially for bird species of conservation concern. We found that the majority of these species displayed similar, positive responses to patch and landscape vegetation attributes. We also found that these relationships were related to the foraging and nesting traits of the bird community. Our findings suggest that management strategies to increase both remnant vegetation quality and the cover of surrounding woody vegetation in fragmented agricultural landscapes may lead to improved conservation of bird communities.