Ecology,growth and management of black locust(Robinia pseudoacacia L.),a non-native species integrated into European forests

Black locust(Robinia pseudoacacia L.),a species native to the eastern North America,was introduced to Europe probably in 1601 and currently extends over2.3×10~6 ha.It has become naturalized in all sub-Mediterranean and temperate regions rivaling Populus spp.as the second most planted broadleaved tree species worldwide after Eucalyptus spp.This wide-spreading planting is because black locust is an important multipurpose species,producing wood,fodder,and a source of honey as well as bio-oil and biomass.It is also important for carbon sequestration,soil stabilization and re-vegetation of landfills,mining areas and wastelands,in biotherapy and landscaping.In Europe,black locust is drought tolerant so grows in areas with annual precipitation as low as 500-550 mm.It tolerates dry,nutrient poor soils but grows best on deep,nutrient-rich,well-drained soils.It is a fast-growing tree and the height,diameter and volume growth peak before the age of 20.It mostly regenerates vegetatively by root suckers under a simple coppice system,which is considered the most cost-effective management system.It also regenerates,but less frequently,by stool sprouts.Its early silviculture in production forests includes release cutting to promote root suckers rather than stool shoots,and cleaning-respacing to remove low-quality stems,reduce the number of shoots per stool,and adjust spacing between root suckers.In addition,early,moderate and frequent thinning as well as limited pruning are carried out focusing on crop trees.The species is regarded as invasive in several European countries and its range here is expected to expand under predicted climate changes.

Douglas-fi r(Pseudotsuga menziesii(Mirb.)Franco)in Europe:an overview of management practices

Douglas-fir(Pseudotsuga menziesii(Mirb.)Franco),one of the most commercially important tree species in western North America and one of the most valuable timber trees worldwide,was introduced to Europe in 1827.It became a major species for aff orestation in Western Europe after WWII,currently grows in 35 countries on over 0.83 million ha and is one of the most widespread nonnative tree species across the continent.A lower sensitivity to drought makes Douglas-fi r a potential alternative to the more drought-sensitive Norway spruce so its importance in Europe is expected to increase in the future.It is one of the fastest growing conifer species cultivated in Europe,with the largest reported dimensions of 2.3 m in diameter and 67.5 m in height.Pure stands have high productivity(up to 20 m 3 ha−1 a−1)and production(over 1000 m 3 ha−1).The species is generally regenerated by planting(initial stocking density from less than 1000 seedlings ha−1 to more than 4000 ha−1),using seedlings of European provenance derived from seed orchards or certifi ed seed stands.As the range of end-uses of its wood is very wide,the rotation period of Douglas-fi r is highly variable and ranges between 40 and 120 years.When the production of large-sized,knotfree timber is targeted,thinnings are always coupled with pruning up to 6 m.There is an increasing interest in growing Douglas-fi r in mixtures and managing stands through close-to-nature silviculture,but the species’intermediate shade tolerance means that it is best managed through group selection or shelterwood systems.

Diversity and surge in abundance of native parasitoid communities prior to the onset of Torymus sinensis on the Asian chestnut gall wasp(Dryocosmus kuriphilus) in Slovenia,Croatia and Hungary

Since the rapid spread of the Asian chestnut gall wasp(ACGW) throughout south-east Europe in the last few years,the possibilities of its control have been increasingly investigated.Due to constraints in available suppression measures in forest stands,biological control is recognized as the most suitable action to lower the abundance of the new invasive pest.Torymus sinensis,as a specialized parasitoid chalcid wasp of ACGW,was introduced to suppress the pest in Italy in 2005,and later in Croatia,Hungary(2014) and Slovenia(2015).We investigated the native parasitoid complex associated with ACGW in Slovenia,Croatia and Hungary over 8 years of sampling.We found 41 species of native parasitoids,eight of which are the first records on ACGW in Europe,adding up to a total of 51 species known to parasitize ACGW.These findings represent a large complex of cynipid-parasitoid fauna.Moreover,the abundance of native parasitoid populations on ACGW have demonstrated a temporal surge between the invasion of a new alien host(ACGW) and the onset of its specialized parasitoid,T.sinensis.Our results indicate that the introduced parasitoid acts as a very successful biocontrol of ACGW,outcompeting native parasitoids.This outcome should be considered as beneficial through the maintenance of ecological balance in affected forest ecosystems.