Species richness, diversity and human activities in an elevation gradient of a high-ecosystem in Lagunas Huascoaltinas, Atacama Region, Chile (original) (raw)
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The relationship between species richness, diversity and grazing frequency along an altitudinal gradient (1900-3400 m) of an Andean ecosystem indicates that there is an intense human pressure on vegetation use. To identify the vascular flora and its conservation, 20 sites were sampled in two visits during 2006. We identified 79 taxa, including 62.03% native species, 22.78% adventitious and 8.86% endemic (the remaining 6.33% was identified only at the genus level). Some genera were underrepresented. We also observed latitudinal limits (Alstremeria andina), monotypic genera (Geoffroea, Kurzamra, Phragmites, Tessaria and Salix) and monogeneric families (Buddlejaceae, Ephedraceae, Equisetaceae, Malesherbiaceae, Salicaceae and Oxalidaceae). Moreover, we found differences in the species distribution patterns during periods of grazing use and identified statistically significant differences in the species richness (p < 0.001), diversity (p = 0.010) and grazing frequency ( p = 0.047).
Background:Understanding the role of livestock grazing on plant diversity can be improved by an accurate measurement of diversity at all hierarchical scales due to the changeability of diversity components in space. Aims:We evaluated the effects of grazing on plant species diversity at different scales of all common and rare species in two regions that have different climatic conditions (arid vs. semi-arid). Methods:In each region, we collected abundant data of plant species from a nested sampling design that consisted of local (80 plots) and regional (16 sites) scales. We partitioned total species diversity (γ) into within plots (αl), among plots (βl) and among sites (β2) using the additive partitioning. Results: Diversity among sites contributed the most to total diversity for all and rare plant species in both regions. In addition,α1andβ1diversities in ungrazed areas were greater than those in grazed areas for all and common species in both climates. Conclusion: Abandonment of grazing after 10 years resulted in significant regeneration of common species at the local scale, with no change in rare species. We conclude that low grazing intensity is likely to be an important tool for conservation of plant diversity in which all scales should be considered.
Variations in species and functional plant diversity along climatic and grazing gradients
Ecography, 2006
. Variations in species and functional plant diversity along climatic and grazing gradients. Á Ecography 29: 801 Á810. Different components of biodiversity may vary independently of each other along environmental gradients giving insights into the mechanisms that regulate species coexistence. In particular, the functional diversity (FD) or the presence of rare or endemic species in natural assemblages do not necessarily increase with species diversity. We studied if different components of plant species diversity (species richness, Simpson diversity, evenness) varied similarly to FD (measured as a generalization of the Simpson index) and rarity along grazing intensity and climatic gradients. Plots under different sheep grazing regimes (high and low intensity, abandonment) were surveyed in five locations along a climatic gradient in north-eastern Spain, from semiarid lowland to moist upland locations. Variation in species diversity, functional diversity and rarity followed different patterns. Species diversity was lowest in waterstressed environments (arid locations and southern aspects) and increased with grazing more makedly in humid locations. The FD was comparable between the most speciespoor and species-rich locations and decreased with grazing in the moistest location, i.e. where species diversity markedly increased. The FD did not show a strong correlation with species richness nor with the Simpson index and less specious communities could show the highest functional diversity. The rarest species in the region were more frequently found in the abandoned areas, which held the lowest species diversity. Consequently, the mechanisms that enhance the diversity of species do not necessarily support a functional differentiation among those species or the maintenance of rare species in a region. We hypothesize that the degree of dependence of functional diversity on species diversity might be mostly related to the amplitude of the species' traits pool and on how species partition the niche space available.
Agriculture
Grasslands and pastures are extensively studied due to their geographic variation, species richness, ecological functioning, and economic importance. They are vital components of land use in many parts of the world. The impact of grassland management on species diversity and species composition has also been widely discussed, but results have been contradictory. It is well known that the relationship between species richness and the sampled area is perhaps one of the most consistent rules in plant ecology. This relationship is particularly important in biodiversity studies as it helps to predict richness at larger scales. Additionally, species richness is also influenced by absolute plant abundance, spatial patterns, and the degree of species mixing. However, species richness also depends on absolute plant abundance, spatial patterns, and the degree of mixing species. To assess this relationship, we analyzed the impact of cattle grazing on species richness at a sampling scale in the...
Plant Species and Functional Types’ Diversity in Relation to
In arid and semi-arid rangelands, grazing as one of the natural or human induced processes has direct and indirect effects on structure and dynamics of plant community and ecosystems. A study was done to analyze the effects of grazing on plant species diversity and Plant Functional Types’ (PFTs) diversity of arid and semi-arid rangelands. We analyzed plant richness and diversity data from 75 sampling plots located in five bioclimatic zones of Khabr National Park containing a total of 73 plant species. Ward's hierarchical clustering was then used to cluster all plant species into eight PFTs according to the chosen traits. For each site, grazing intensity was estimated in three classes (low grazing, medium and high grazing intensities). We found that as grazing intensity increased, total species richness and diversity were decreased. Considering PFTs as total showed the same pattern for species; however, each PFT diversity and richness didn’t display a significant different response to grazing. Looking at each PFT relative cover change in different grazing intensities showed that PFT1 and PFT8 were grazing sensitivities while PFT6 and PFT7 benefited from grazing and their relative cover increased consistently in response to the increased grazing intensity. PFT3 and PFT4 had the highest relative cover rates in moderately grazed areas. PFT2 and PFT5 had a complicated response to grazing and their relative cover was the minimum at moderately grazed sits. This finding may imply that grazing has completely negative impacts on the community structure and it seems that it reduces plant species and functional types’ diversity and richness. It can be also concluded that the analyses on PFTs level possibly give more insight into the grazing response of plant community in arid and semi-arid rangelands than those on species level but there is a need for further studies.
Cattle grazing effects on annual plants assemblages in the Central Monte Desert, Argentina
Journal of Arid Environments, 2009
Plant assemblages' dynamics have been studied to evaluate the influence of different environmental factors. The aim of our work was to assess the effect of a disturbance in the form of livestock grazing on annual plants, in a South American desert. We tested the exclusion of cattle grazing by comparing the composition of annual plants in three major vegetation types within a MaB Reserve in the Monte Desert of Argentina, with those of an adjacent grazed field. Sampling was conducted in two consecutive years that differed in precipitation. We established three sampling sites within each vegetation type at the reserve and the grazed field. Transects were set to assess plant cover, abundance, and richness. Theoretically, changes in diversity are explained by changes in one of its components: species richness. Species richness of annual plants was not different between the grazed and ungrazed sites. However, plant cover and diversity were lower in grazed sites, whereas abundance increased. Owing to a strong species-specific effect, we propose that it is evenness the main parameter involved in diversity dynamics in the heterogeneous vegetation mosaic of the Monte desert. Finally, vegetation types (spatial heterogeneity) and rainfall regime (temporal heterogeneity) greatly interacted with grazing effects. We endorse the idea that rapid responses of annual plant assemblages to changes in rainfall conditions coupled with herbivore control, might result in a restoration pathway for degraded arid landscapes.
Effects of grazing intensity on plant richness and diversity: a meta-analysis
Oikos, 2018
Most of our knowledge of the effect of grazing on grassland structure is based on grazed-ungrazed contrasts. The effects of grazing in the most common scenario, where grazing intensity varies from low to high grazing intensity, are less known. The objectives of this paper were to 1) quantify the effect of stocking rates on species richness and diversity of grasslands worldwide , and 2) evaluate the response under different environmental and experimental conditions. We conducted a meta-analysis of experiments with at least two levels of controlled stocking rates and evaluated their effect on species richness and diversity. The results showed that the response of richness and diversity to either reducing or increasing stocking rate from a moderate level mostly fell within the range ± 25% or ± 5 species. Mean response of species richness and diversity to increasing stocking rate from moderate to high levels was negative. Mean response to lowering stocking rate from moderate levels was not different from zero. However, overall, species richness significantly decreased as stocking rate increased. The response of richness and diversity to stocking rate was not related to mean precipitation, productivity or aridity. However, the most negative responses of richness to stocking rate were larger in arid, low productivity systems than in subhumid and humid systems. The effects of grazing on richness and diversity found in this review were smaller than the effects on species composition shown by the literature. Thus, grazing drastically changes species composition, but the net change of species and diversity is much smaller.
Effects of grazing intensity in grasslands of the Espinal of central Chile
Journal of Vegetation Science, 2006
Question: How is grazing intensity associated with species and morpho-functional traits (MFTs) composition, productivity and richness of annual dominated grasslands? Have native and exotic species similar associations to this gradient? Location: Anthropogenic grassland in the Espinal vegetation in the sub-humid area of the mediterranean type climate region of Chile (35°58' S, 72º17' W). Methods: Data were obtained from a long-term (eight years) experiment with six stocking rates (1 to 3.5 sheep/ha). Detrended Correspondence Analysis (DCA) and regression analysis were used to determinate the relationship between grazing intensity and biomass, richness, abundance and traits of the species. Results: The first DCA axis was related to grazing intensity and explained most of the floristic variation (69.3%); the abundance of some non-native species, e.g. Vulpia megalura were highly correlated with this axis. In the DCA for MFTs the first axis explained 87% of the variance and was also related to grazing intensity; the abundance of small size plants and shallow roots increased with grazing intensity. The relative abundance of grasses and composites, but not of legumes, changed with stocking rate: as grazing intensity increased composites became the predominant species to the detriment of grasses. The above-ground biomass measured in exclusion cages declined with increasing grazing pressure. The richness of exotic species was greater compared to native ones at low stocking rates, but they converge to similar values at higher stocking rates. However, the relative abundance of exotic species was greater than 75% in all stocking rates. Conclusions: Grazing intensification has large effects in the structure of grassland in central Chile. With grazing intensities greater than 1 sheep/ha species characteristics change; evolving in a few years (6-8) towards a similar community regardless of the stocking rate. The overgrazed community has more native than exotic species richness, possibly due to greater defence traits against herbivory of this group of species.
Effect of grazing on plant patterns in arid ecosystems of Patagonian Monte
Ecography, 2005
Our objective was to assess the relationship between the spatial patterning of perennial grasses (total, grazed, and non-grazed) and shrub patches in rangelands under different grazing pressures of the Patagonian Monte. We selected three grazed paddocks with the usual stocking rate for the area, where previous studies showed that a piosphere formation is common. At each paddock, we analysed the grain of heterogeneity at sites located at two distances from the single watering point (near, far), using high-resolution aerial photographs. At these sites, we also assessed in the field the density, size, cover, and spatial patterning of grazed and non-grazed perennial grasses and shrub patches. The grain of heterogeneity of shrub patches was coarser in sites near the watering point than in those distant from it, as a consequence of the increase in size of both, bare soil and shrub patches. Field sampling showed that a coarse grain of heterogeneity relative to fine-grained sites resulted from changes in species composition, increased bare soil areas and reduced perennial grass cover. In coarse-grained sites, lower perennial grass cover resulted from lower density and/or smaller size of grass bunches than in finegrained sites. We did not find significant differences among sites in the proportion of perennial grazed grasses. Since the density and cover of perennial grasses was higher in fine-than in coarse-grained sites, we suggested that fine-grained sites are more important as feeding stations than coarse-grained sites. The consequences of this differential use could lead to degradation of fine-grained sites and to higher homogeneity in spatial plant structure and floristic composition within paddocks with respect to the condition observed at present, increasing the size of the highly degraded zone within the piosphere. At the patch level, we found that at about one third of the sampled transects, both total and non-grazed perennial grasses were spatially aggregated with shrub patches. However, in most transects grazed perennial grasses were indifferently distributed in relation with shrub patches, showing that grazers display high selectivity of foraging sites at macro level (i.e. high and low grazing pressure sites at the paddock level), but random occupancy of vegetation units (randomness in the distribution of grazed perennial grasses at the patch level). The intensity of the positive association between non-grazed grasses and shrub patches was higher in fine-grained than in coarse-grained sites and may be attributed to higher protection against herbivores associated to denser shrub patches in fine-relative to coarse-grained sites. We concluded that a feedback exists between the spatial distribution of species preferred by grazers and the spatial patterning of use of these species.