Abstract:The Chihuahuan desert of New Mexico, USA, has changed in historical times from semiarid grassland to desert shrublands dominated by Larrea tridentata and Prosopis glandulosa. Similar displacement of perennial grasslands by shrubs typifies desertification in many regions. Such structural vegetation change could alter average values of net primary productivity, as well as spatial and temporal patterns of production. We investigated patterns of aboveground plant biomass and net primary production in five ecosyste… Show more
“…Yet, RUE trend analysis counts with several methodological problems. First, the fundamental postulation that there is a linear correlation with zero intercept between rainfall and NPP (Houérou, 1984) seems hardly applicable outside arid and semi-arid areas as forest and perennials are less responsive to rainfall as compared to annual vegetation (Huenneke et al, 2002). Second, low correlation between NDVI time series and NPP introduces considerable uncertainty (Bai & Dent, 2007) in interpretation of RUE data (Wessels, 2009).…”
This study compares the results of two nationwide land degradation assessments for Senegal. The first approach is based on expert judgments, the second on trend analyses of Rainfall Use Efficiency (RUE). The comparison yields some interpretable results for extreme negative RUE slope values with maximum degrees of land degradation as indicated by experts, yet, overall, the correlation between both approaches proves to be low and without clear sign. As RUE trend analysis suffers from several inherent methodological problems and expert judgments are found to be consistent we consider expert opinions as the preferable option for a nation-wide land degradation assessment in Senegal. Yet, we argue that methodological improvements would increase the explanatory power of the expert approach and consolidate its position in a policy making framework.
“…Yet, RUE trend analysis counts with several methodological problems. First, the fundamental postulation that there is a linear correlation with zero intercept between rainfall and NPP (Houérou, 1984) seems hardly applicable outside arid and semi-arid areas as forest and perennials are less responsive to rainfall as compared to annual vegetation (Huenneke et al, 2002). Second, low correlation between NDVI time series and NPP introduces considerable uncertainty (Bai & Dent, 2007) in interpretation of RUE data (Wessels, 2009).…”
This study compares the results of two nationwide land degradation assessments for Senegal. The first approach is based on expert judgments, the second on trend analyses of Rainfall Use Efficiency (RUE). The comparison yields some interpretable results for extreme negative RUE slope values with maximum degrees of land degradation as indicated by experts, yet, overall, the correlation between both approaches proves to be low and without clear sign. As RUE trend analysis suffers from several inherent methodological problems and expert judgments are found to be consistent we consider expert opinions as the preferable option for a nation-wide land degradation assessment in Senegal. Yet, we argue that methodological improvements would increase the explanatory power of the expert approach and consolidate its position in a policy making framework.
“…These two broad categories of regional landscapes cover more than one-third of China's mainland. These areas are important on the landatmosphere interaction process because of their unique energy budget (high sensible heat flux), and increasing aridification and desertification Fu and Wen, 2002;Huenneke et al, 2002). At the same time, the semi-arid areas are more sensitive to climate change and land use, and the extent and distribution of arid and semi-arid areas are subject to modification because of land use and water utility (Fu and Wen, 2002).…”
Based on 3 years of the eddy covariance (EC) observations on degraded grassland and cropland surfaces in a semi-arid area of Tongyu (44 • 25 N, 122• 52 E, 184 m a.s.l.), Northeast China, seasonal and annual variations of water, energy and CO2 fluxes have been investigated. The soil moisture in the thin soil layer (at 0.05, 0.10 and 0.20 m) clearly indicates the pronounced annual wet-dry cycle; the annual cycle is divided into the wet (growing season) and dry seasons (non-growing season). During the growing season (from May to September), the sensible and latent heat fluxes showed a linear dependence on the global solar radiation. However, in the non-growing season, the latent heat flux was always less than 50 W m −2 , while the available energy was dissipated as sensible, rather than latent heat flux. During the growing season in 2003-05, the daily average sensible and latent heat fluxes were larger on the cropland surface than on the degraded grassland surface. The cropland ecosystem absorbed more CO2 than the degraded grassland ecosystem in the growing season in 2003-05. The total evapotranspiration on the cropland was more than the total precipitation, while the total evapotranspiration on the degraded grassland was almost the same as the total annual precipitation in the growing season. The soil moisture had a good correlation with the rainfall in the growing season. Precipitation in the growing season is an important factor on the water and carbon budget in the semi-arid area.Key words: water, energy and flux, semi-arid area, eddy covariance, seasonal and annual variation Citation: Liu, H. Z., G. Tu, C. B. Fu, and L. Q. Shi, 2008: Three-year variations of water, energy and fluxes of cropland and degraded grassland surfaces in a semi-arid area of northeastern China.
“…For example Smith et al (2009) droughts on amazon forests (Lewis et al, 2011). Direct examples of the impact of natural hazards like landslides and droughts on ecosystem services include mostly impacts on ecosystem processes and functioning, namely soil quality, carbon cycling, primary productivity and climate regulation (Guariguata, 1990;Huenneke et al, 2002;Hilton et al, 2011 The impacts of post-disaster reconstruction can also exacerbate existing environmental problems in a country, as noted by a UNEP assessment two years after the 2004 Asian tsunami. Reported impacts of the reconstruction process on the environment include, for example, pollution of ground and surface water and over-extraction of fuel wood used to prepare burnt clay bricks for the reconstruction of houses (UNEP, 2007).…”
Section: Negative Impact Of Natural Hazards On Ecosystemsmentioning
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