Biome-scale woody encroachment threatens conservation potential and sustainability of U.S. rangelands

Rangelands of the United States provide ecosystem services that sustain biodiversity and rural economies. Native tree encroachment is a recognized and long-standing conservation challenge to these landscapes, but its impact is often overlooked due to the slow pace of tree invasions and the positive public perception of trees. Here we show that tree encroachment is a dominant change agent in U.S. rangelands; tree cover has increased by more than 77,000 km2 over 30 years, and more than 25% of U.S. rangelands are now experiencing sustained tree cover expansion. Further, we use machine learning methods to estimate the potential herbaceous production (forage) lost to tree encroachment. Since 1990 roughly 300 Tg of herbaceous biomass has been lost, totaling some $5 billion in foregone revenue to agricultural producers. These results suggest that tree encroachment is similar in scale and magnitude to row-crop conversion, another primary cause of rangeland loss in the U.S. Prioritizing conservation efforts to prevent tree encroachment in rangelands can bolster ecosystem and economic sustainability of these landscapes, particularly among privately-owned lands threatened by land-use conversion.

Drainage ditches enhance forest succession in a raised bog but do not affect the spatial pattern of tree encroachment

The study was conducted in the raised bog Kusowo (Baltic region, West Pomerania, Poland). Along a transect line crossing two open mires affected by forest succession we analysed tree age distribution. One of those mires had been drained in the past years and still retained some open ditches, while the other one was located far from the ditches. Every 10 meters along the transect line one tree was drilled at the root collar in order to determine its age. We also conducted phytosociological analyses and short-term water level measurements in the sample plots. We expected faster tree encroachment in the undisturbed part of the open mire. The results showed, that there were no significant differences in water table level and in soil moisture indicator values between the formerly drained and undisturbed open mire. There were also no statistically significant differences in tree encroachment between the disturbed and undisturbed mires. Location and the age distribution of the trees suggest that changes in the tree growth conditions cannot be directly explained by the general decreasing of water level in the bog, although periods following drainage works were associated with more numerous establishment of young trees, in the drained part of the bog as well as in the part not directly affected by drainage ditches.

Benefits of conservation-driven mowing for the EU policy species Gladiolus palustris Gaudin in mountain fen meadows: a case-study in the European Alps

The sword lily Gladiolus palustris Gaudin is protected on European level and listed in Annexes II and IV of the EC Habitat Directive 92/43/EEC. It grows in nutrient-poor, calcareous meadows in central and eastern Europe. Tree encroachment in montane meadows of the European Alps as a result of recent land use changes and the abandonment of traditional farming practices threaten the survival of this species. Conservation-driven mowing is considered a feasible conservation measure for maintaining high species diversity in abandoned semi-natural grasslands. To assess the effects of ten years of biennial mowing on a grassland community in the Dolomiti Bellunesi National Park, Italy (Site of Community Importance, Natura 2000 network), ten 25 m2 plots were established whereby four plots were placed in the mowed area, four in the non-mowed area and two in a small non-mowed patch of grassland inside the mowed area. In each plot the following variables were recorded, total percentage of plant cover, percentage cover of woody species, percentage cover of herbaceous species, percentage cover and number of flowering ramets of G. palustris and a complete list of species and their percentage abundance. Mowed plots showed a higher species richness than non-mowed plots. The number of G. palustris flowering ramets and percentage cover increased manifold in mowed plots compared to non-mowed plots. The resumption of mowing for conservation purposes undertaken by the managing authority halted the process of tree encroachment and avoided a drastic change in plant composition. Periodic mowing (every second or third year) was demonstrated to be a cost-effective conservation measure in non-productive grasslands to keep grasses at bay in favour of forbs of high conversation value.