Assessment Of Land Use Change Research Articles

A preliminary synthesis of major scientific results during the SALSA program

The objective of this paper is to provide an overview of the primary results of the Semi-Arid Land–Surface–Atmosphere (SALSA) Program in the context of improvements to our overall understanding of hydrologic, ecologic, and atmospheric processes and their interactions in a semi-arid basin. The major findings and future research needs associated with the different core components of the program are emphasized. First, remote-sensing investigations are discussed, especially those directed toward taking full advantage of the capabilities of the new generation of satellites (ERS2/ATSR2, VEGETATION, LANDSAT7, NASA-EOS). Second, we discuss parameterization of the water and energy fluxes in arid and semi-arid regions, with special emphasis on methods to aggregate these fluxes from patch scale to grid scale. Third, we address the issues related to grassland ecology and competition for water between native grass and invasive mesquite species. Fourth, findings related to the interactions between surface water, ground water, and vegetation in a semi-arid riparian system are discussed. Next, an assessment of land use and land cover change over the entire basin over a quarter century is reviewed. Finally, unsolved issues and the needs for further research are outlined.

Bracken Distribution in Great Britain: Strategies for its Control and the Sustainable Management of Marginal Land

Abstract Bracken is often perceived as a widespread and increasing land management problem. The pollen record of a wide range of sites in Great Britain suggests that the current abundance of bracken is less than or, at worst, equivalent to maximum historical levels. Recently gathered data also suggest that bracken cover is declining. Results of risk assessments of land use change, and experimental and modelling investigations into the effects of climate change are synthesized. This synthesis suggests that there is the potential for increased bracken dominance in northern Britain, spread into new areas at high altitudes, and possible spread into areas with reduced grazing. However, this must be set against any changes in the extent of other vegetation types at the expense of bracken. There is now a long history of bracken control, both in Great Britain and globally. Conventional methods of control (cutting, asulam application) are well understood, but many control attempts do not result in long-term success, as control is often not followed by aftercare. Bracken control is just one part of the process to ensure a sustainable use of resources and to maintain biodiversity. A coherent strategy for bracken control is put forward, a necessary part of which includes the restoration of vegetation and subsequent land management which takes into account an understanding of bracken ecology.

Canopy transpiration from a boreal forest in Sweden during a dry year

Estimation of areal evapotranspiration is crucial for the parameterization of the soil-vegetation-atmosphere interface in climate models and for the assessment of land-use changes on water resources. Present knowledge on how areal forest evapotranspiration depends on forest species composition and age is insufficient. In this study, transpiration of 50- and 100-year-old coniferous stands was estimated on the basis of sap-flow measurements on 24 trees, 12 in each stand. The measured samples represented the size distribution of Pinus sylvestris and Picea abies trees. Daily canopy transpiration ( E Q) was scaled from individual tree flow rates using the quotients of stem circumferences of the sample trees to those of the stands. E Q was used in a rearranged Penman equation to deduce a potential canopy conductance, valid for non-limiting soil-water conditions, from a period when soil-water storage was not limiting transpiration. This enabled quantification of the seasonal transpiration deficit, which in both stands reached at least one fifth of the total potential transpiration over the growth season. The estimated fluxes of E Q were low with a maximum daily value of about 2.8 mm in the 50-year-old stand. For dry-weather days, E Q was well correlated to daily sums of stand evapotranspiration estimated from eddy-correlation measurements. Responses to drought were species specific. Transpiration in pines from the 50-year-old stand was less affected by drought relative to spruce or older pine trees, which was also reflected by stem increment during the season.