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    ABSTRACT: Aim  Species in the tropics respond to global warming by altitudinal distribution shifts. Consequences for biodiversity may be severe, resulting in lowland attrition, range-shift gaps, range contractions and extinction risks. We aim to identify plant groups (growth forms, families, endemic status) with higher than average risks.Location  South Ethiopian highlands.Methods  Based on observational data from mainly unexplored and remote mountain regions, we applied a published model to project the consequences of an upward shift of thermal site conditions on the altitudinal distribution of 475 plant species. Annual average temperature increases of up to 5 °C were evaluated. Differences between groups of species were analysed by a permutation procedure and Generalized Linear Models.Results  Because of a limited regional species pool, even mild warming is projected to create strong potential risks concerning lowland attrition, i.e. the net loss of species richness because of upward range shifts in the absence of new species arriving. Likewise, many species are expected to face range-shift gaps, i.e. the absence of an overlap between future and current altitudinal ranges already under mild warming scenarios. Altitudinal contractions and mountain-top extinctions will potentially become important when warming exceeds 3.5 °C. Mean area per species is projected to decline by 55% for the A2 emissions scenario (+4.2 °C until 2100) because of the physical shape of the mountains. Higher than average vulnerability is expected for endemic species as well as for herbs and ferns. Plant families that are especially threatened are identified.Main conclusions  Lowland biotic attrition and range-shift gaps as predicted by a simple model driven by shifts of isotherms will result in novel challenges for preserving mountain biodiversity in the inner tropics. Whereas contractions of occupied area are expected to threaten endemic and already endangered species in particular, we suggest that conservation priorities can be identified based on simple prognostic models even without precise regional warming scenarios.
    Full-text · Article · Jun 2010 · Diversity and Distributions
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    ABSTRACT: Questions: Do growth forms and vascular plant richness follow similar patterns along an altitudinal gradient? What are the driving mechanisms that structure richness patterns at the landscape scale?Location: Southwest Ethiopian highlands.Methods: Floristic and environmental data were collected from 74 plots, each covering 400 m2. The plots were distributed along altitudinal gradients. Boosted regression trees were used to derive the patterns of richness distribution along altitudinal gradients.Results: Total vascular plant richness did not show any strong response to altitude. Contrasting patterns of richness were observed for several growth forms. Woody, graminoid and climber species richness showed a unimodal structure. However, each of these morphological groups had a peak of richness at different altitudes: graminoid species attained maximum importance at a lower elevations, followed by climbers and finally woody species at higher elevations. Fern species richness increased monotonically towards higher altitudes, but herbaceous richness had a dented structure at mid-altitudes. Soil sand fraction, silt, slope and organic matter were found to contribute a considerable amount of the predicted variance of richness for total vascular plants and growth forms.Main Conclusions: Hump-shaped species richness patterns were observed for several growth forms. A mid-altitudinal richness peak was the result of a combination of climate-related water–energy dynamics, species–area relationships and local environmental factors, which have direct effects on plant physiological performance. However, altitude represents the composite gradient of several environmental variables that were interrelated. Thus, considering multiple gradients would provide a better picture of richness and the potential mechanisms responsible for the distribution of biodiversity in high-mountain regions of the tropics.
    Full-text · Article · Mar 2010 · Journal of Vegetation Science
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    ABSTRACT: This study evaluated changes in land cover in the Chemoga watershed, headwater to the Blue Nile. Two sets of aerial photographs (1957 and 1982) and a multispectral Spot image (1998) were used as inputs to produce 3 GIS-based land cover maps of the area. The results show that during the last 41 years, forest cover increased at a rate of about 11 ha per annum in the 36,400-ha watershed. Woodlands and shrublands decreased between 1957 and 1982 but increased between 1982 and 1998, approximately to their previous levels. Farmland and settled areas gained from the other cover types (13% increase) in the first period but lost around 586 ha (2% decrease) in the second. Grassland and degraded land decreased, accounting for 4.8% of the total area of the watershed in 1982 and 3.5% in 1998, as against 9.6% in 1957. Riverine trees suffered the greatest destruction, shrinking by 79% over the 4 decades; much of this decline was due to cultivation. Marshlands increased in the first period and decreased in the second. A new pond emerged amid the marshlands between 1982 and 1998. Population growth and the associated demand for land and trees was the major driving force behind the changes. This study shows that the deforestation trend was reduced and even partly reversed in the area because local people planted trees as a source of fuel and income. This trend ought to be encouraged through appropriate interventions—in particular by promoting planting of local species rather than eucalyptus—to increase not only economic but also ecological benefits. Indeed, the current state of land cover and its dynamics have environmental implications at the local scale and beyond. Hence, environmental management for sustainable development requires interregional and international cooperation.
    Preview · Article · Jan 2009 · Mountain Research and Development
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