Wind born(e) landscapes: the role of wind erosion in agricultural land management and nature development

Wind has played an important role in the geological development of the north-western Europe. Various aeolian deposits such as inland dunes, river dunes, cover sands, drift sands and coastal dunes, form the base of large areas in our present landscape. The role of wind erosion in today's north-west European landscapes is, besides in coastal dunes, mainly related to arable fields (on light sandy soils), and to some active remnants of the inland drift-sand areas. In both latter cases there is an urgent need to manage the wind-erosion process. The aim of this PhD thesis is to develop management tools and strategies to control unwanted and wanted wind erosion.On arable land the main objective of managing the wind erosion process is to minimize the on- and off-site damage by reducing erosion risk. The extent, frequency, intensity of wind erosion events, and thereby their on-site and off-site effects, is controlled by soil characteristics, climate and human activities. Field surveys in areas with light sandy soils in four European countries showed that the erosion risk on agricultural land on light sandy soils is controlled by the cropping system, openness of the landscape and farmers practices. Scenario runs with the WEELS wind erosion model give insight into the general change in erosion risk per month. The simulations point to major changes in erosion risk for changes in a wind-break network, but relatively small changes in erosion risk for the tested cropping systems and climate-change scenario's. With this information, the possible consequences for on-site and off-site damage can be estimated, and from this estimation, additional (policy) measures for controlling wind erosion can be formulated for the region in question. There are enough effective land-management techniques available to minimise the erosion risk to an acceptable level. Voluntary measures based on good agricultural practice work well in a cropping system with high valuable crops and farmers financial benefit from control measures. However, additional policy measures such as mandatory measures and subsidies are needed in case of cropping systems with low or negative net profits and in case of high risk for off-site damage for instance in the period after harvesting when the soil is not longer protected by a crop.Inland drift-sand areas, on the contrary suffer from a lack of wind erosion activity. In the remnant active drift-sand areas with nature as main land-use type, which were saved from the large scale forestation schemes at the begin of the twentieth century, an ecologically high valuable vegetation and fauna developed. The role of wind erosion as main landscape differentiating process has changed to a local process with limited impact on the further development of the drift-sand areas. The general trend is an ongoing reduction of wind erosion activity and further colonisation of the drift sands by vegetation. This development  addresses the reduced openness of the landscape, change in land-use, the limited size of the remainder open drift-sand areas, the relative high nitrogen-deposition and the invasion by exotic plant species. Without sufficient erosion activity the drift-sand pioneer vegetation turns into a grass dominated vegetation and eventually in forest. To maintain the positive interaction between erosion and the pioneer vegetation in the remaining active drift-sand areas, it is necessary to keep the active (bare) areas open (process management). In practice several tillage techniques are used by the terrain managers. Of these the beach-sand cleaner and the rotary cultivator proved to be most effective to reactivate drift sand areas with a pioneer vegetation cover. At the same time the complete top soil needs to be removed to set back the succession (pattern management) in parts of the areas covered with higher succession stages. This can go hand in hand with reactivation of wind erosion on locations in order to slow down the succession rate. In that case the treated area should be at least 5 to 10 ha to guarantee a positive impact of erosion on the surrounding area. Other criteria are: the presence of a sufficient amount of erodible sand and an optimum erosive wind force.