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Degradation Gradient (degradation + gradient)
Selected AbstractsOn the importance of patch attributes, environmental factors and past human impacts as determinants of perennial plant species richness and diversity in Mediterranean semiarid steppesDIVERSITY AND DISTRIBUTIONS, Issue 1 2004Fernando T. Maestre ABSTRACT Richness and diversity of perennial plant species were evaluated in 17 Stipa tenacissima steppes along a degradation gradient in semiarid SE Spain. The main objective of the study was to evaluate the relative importance of historical human impacts, small-scale patch attributes and environmental factors as determinants of perennial plant species richness and diversity in S. tenacissima steppes, where vegetation is arranged as discrete plant patches inserted on a bare ground matrix. Partial least squares regression was used to determine the amount of variation in species richness and diversity that could be significantly explained by historical human impacts, patch attributes, and environmental factors together and separately. They explained up to 89% and 69% of the variation in species richness and diversity, respectively. In both cases, the predictive power of patch attributes models was higher than that of models consisting of abiotic characteristics and variables related to human impact, suggesting that patch attributes are the major determinants of species richness and diversity in semiarid S. tenacissima steppes. However, patch attributes alone are not enough to explain the observed variation in species richness and diversity. The area covered by late-successional sprouting shrubs and the distance between consecutive patches were the most influencing individual variables on species richness and diversity, respectively. The implications of these results for the management of S. tenacissima steppes are discussed. [source] Role of habitat degradation in determining fish distribution and abundance along the lowland Warta River, PolandJOURNAL OF APPLIED ICHTHYOLOGY, Issue 1 2007A. Kruk Summary The distribution and abundance of fish collected in 1996,1998 are compared in three river sections X, Y and Z in the 808-km-long Warta River, Poland. The upper section, X, was least human-modified, the middle section, Y, was the most polluted by industry and regulated, and the downstream section, Z, was moderately disturbed. The differences between X and Y in concentrations of dissolved oxygen, volatile phenols and nitrite nitrogen, and in the index of availability of hiding places, were highly significant because these parameters were several times worse in the Y section; in the Z section they assumed intermediate values. Although the abundance of certain fish species was changing along the downstream river gradient (i.e. differed the most between X and Z), both the Kohonen artificial neural network (SOM) and assemblage indices showed the biggest differences between X and Y, thus confirming the crucial role of the degradation of aquatic environment in shaping fish assemblages. The latter result ensued from the reaction of the rheophilic burbot, stone loach, gudgeon, chub and dace, which were most abundant in X, almost absent in Y and reoccurring in Z (although less numerous when compared with X). The opposite was recorded for mud loach, tench, ide and silver bream, which were most abundant in the degraded section Y, probably because of weak competition with the almost-absent rheophils. The abundance of two generalists, roach and pike, was similar in all three sections, i.e. changed neither along the downstream nor in the degradation gradient. [source] The response of Phragmites australis to harvesting pressure in the Muzi Swamp of the Tembe Elephant Park, South AfricaLAND DEGRADATION AND DEVELOPMENT, Issue 5 2004J. A. Tarr Abstract Phragmites australis (Cav.) Trin. ex Steud. has been harvested in the Muzi Swamp in Maputaland, South Africa for generations. Over the last ten years, however, a flourishing trade in this reed has developed. Concern has now been expressed that at the current levels of utilization the ecological integrity of the Muzi Swamp is being compromised, and that the current harvesting rates are not sustainable in the long term. The hypothesis was put forward that a degradation gradient exists with the most severe degradation occurring the closest to where community members enter the park, and the least degradation the furthest from this point. The results of this study, however, show no distinct degradation gradient. Yet the overall condition of the reeds in the harvesting area is poorer than in the non-utilized area. Expansion of the current harvesting area, coupled with adaptive harvesting systems and yearly monitoring will improve the quality of the reeds within the harvesting area without affecting the harvesting quotas. Copyright © 2004 John Wiley & Sons, Ltd. [source] Ecohydrological effects of grazing-induced degradation in the Patagonian Monte, ArgentinaAUSTRAL ECOLOGY, Issue 5 2009ALEJANDRO JORGE BISIGATO Abstract Water-limited ecosystems have undergone rapid change as a consequence of changing land use and climate. The consequences of these changes on soil quality and vegetation dynamics have been documented in different regions of the world. In contrast, their effects on soil water, the most limiting resource in these environments, have received less attention, although in recent years increasing efforts have been made to relate grazing, soil water and vegetation functioning. In this paper, we present the results of field observations of plant phenology and soil water content carried out during two successive years at four sites along a degradation gradient caused by grazing in the Patagonian Monte, Argentina. We also developed a simplified soil water balance model to evaluate how changes in plant cover could affect water balance. Our field observations showed that the soil water content in the soil layer where roots of grasses are abundant (0,25 cm) was higher and the growing cycles were longer in degraded than in preserved sites. Similarly, our modelling approach showed that the deep soil (depth > 10 cm) was wetter in the degraded than in the preserved situation. Simulation also suggested a switch from transpiration to a direct evaporation dominance of water losses with degradation. Although reductions in plant cover related to grazing degradation were associated with a decrease in annual transpiration, the simulated soil water loss by transpiration was higher during summer in the degraded than in the well preserved situation. Thus, our field observations seem to be a consequence of ecohydrological changes causing an accumulation of water in the soil profile during the cold season and its transpiration during summer. In conclusion, our results showed that changes in plant cover caused by grazing disturbance can alter the soil water balance, which in turn can affect vegetation function. [source] Assessment of European streams with diatoms, macrophytes, macroinvertebrates and fish: a comparative metric-based analysis of organism response to stressFRESHWATER BIOLOGY, Issue 9 2006DANIEL HERING Summary 1. Periphytic diatoms, macrophytes, benthic macroinvertebrates and fish were sampled with standard methods in 185 streams in nine European countries to compare their response to degradation. Streams were classified into two main stream type groups (i.e. lowland, mountain streams); in addition, the lowland streams were grouped into four more specific stream types. 2. Principal components analysis with altogether 43 environmental parameters was used to construct complex stressor gradients for physical,chemical, hydromorphological and land use data. About 30 metrics were calculated for each sample and organism group. Metric responses to different stress types were analysed by Spearman Rank Correlation. 3. All four organism groups showed significant response to eutrophication/organic pollution gradients. Generally, diatom metrics were most strongly correlated to eutrophication gradients (85% and 89% of the diatom metrics tested correlated significantly in mountain and lowland streams, respectively), followed by invertebrate metrics (91% and 59%). 4. Responses of the four organism groups to other gradients were less strong; all organism groups responded to varying degrees to land use changes, hydromorphological degradation on the microhabitat scale and general degradation gradients, while the response to hydromorphological gradients on the reach scale was mainly limited to benthic macroinvertebrates (50% and 44% of the metrics tested correlated significantly in mountain and lowland streams, respectively) and fish (29% and 47%). 5. Fish and macrophyte metrics generally showed a poor response to degradation gradients in mountain streams and a strong response in lowland streams. 6. General recommendations on European bioassessment of streams were derived from the results. 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