Abstract
The debate on ecological and climatic benefits of planted forests at the sensitive dry edge of the closed forest belt (i.e. at the ‘xeric limits’) is still unresolved. Forests sequester atmospheric carbon dioxide, accumulate biomass, control water erosion and dust storms, reduce river sedimentation, and mitigate small floods. However, planting trees in areas previously dominated by grassland or cropland can dramatically alter the energy and water balances at multiple scales. The forest/grassland transition zone is especially vulnerable to projected drastic temperature and precipitation shifts and growing extremes due to its high ecohydrological sensitivity. We investigated some of the relevant aspects of the ecological and climatic role of forests and potential impacts of climate change at the dryland margins of the temperate-continental zone using case studies from China, the United States and SE Europe (Hungary). We found that, contrary to popular expectations, the effects of forest cover on regional climate might be limited and the influence of forestation on water resources might be negative. Planted forests generally reduce stream flow and lower groundwater table level because of higher water use than previous land cover types. Increased evaporation potential due to global warming and/or extreme drought events is likely to reduce areas that are appropriate for tree growth and forest establishment. Ecologically conscious forest management and forestation planning should be adjusted to the local, projected hydrologic and climatic conditions, and should also consider non-forest alternative land uses.
Highlights
Forest steppe is the grassland-forest transition zone where forest ecosystems largely depend on locally accessible water
The aim of this study is to present a range of views and arguments which should underline the complexity of factors influencing the decisions about maintaining/increasing forest cover in the ‘forest steppe’ zone, and emphasize the necessity to strengthen research in an ecological zone, which has received relatively moderate attention in the past
Forests provide multiple ecological benefits, forestation on watersheds previously used by agriculture or covered by grassland can reduce stream flow due to higher water use and may have serious disadvantages for water management and sustainable development
Summary
Forest steppe (open woodland) is the grassland-forest transition zone where forest ecosystems largely depend on locally accessible water. Water availability determines forest ecosystem structure and function, and relatively small changes in the soil moisture balance may lead to considerable ecological shifts (Ryan and Vose 2012). The aim of this study is to present a range of views and arguments which should underline the complexity of factors influencing the decisions about maintaining/increasing forest cover in the ‘forest steppe’ zone, and emphasize the necessity to strengthen research in an ecological zone, which has received relatively moderate attention in the past. We examine two main thematic fields: (1) the hydrological significance of forest cover in the drylands, and (2) the vulnerability of these forests under climate change and their potential in mitigating projected effects. We present and discuss results and experiences from three selected regions with comparable ecological conditions, in China, in the United States, and in continental SE Europe (Hungary)
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