Importance of overstorey attributes for understorey litter production and nutrient cycling in European forests

Background:In contrast with the negligible contribution of the forest understorey to the total aboveground phytobiomass of a forest,its share in annual litter production and nutrient cycling may be more important.Whether and how this functional role of the understorey differs across forest types and depends upon overstorey characteristics remains to be investigated.Methods:We sampled 209 plots of the FunDivEUROPE Exploratory Platform,a network of study plots covering local gradients of tree diversity spread over six contrasting forest types in Europe.To estimate the relative contribution of the understorey to carbon and nutrient cycling,we sampled non-lignified aboveground understorey biomass and overstorey leaf litterfall in all plots.Understorey samples were analysed for C,N and P concentrations,overstorey leaf litterfall for C and N concentrations.We additionally quantified a set of overstorey attributes,including species richness,proportion of evergreen species,light availability(representing crown density)and litter quality,and investigated whether they drive the understorey’s contribution to carbon and nutrient cycling.Results and conclusions:Overstorey litter production and nutrient stocks in litterfall clearly exceeded the contribution of the understorey for all forest types,and the share of the understorey was higher in forests at the extremes of the climatic gradient.In most of the investigated forest types,it was mainly light availability that determined the contribution of the understorey to yearly carbon and nutrient cycling.Overstorey species richness did not affect the contribution of the understorey to carbon and nutrient cycling in any of the investigated forest types.

Understorey species distinguish late successional and ancient forests after decades of minimum human intervention: A case study from Slovenia

The main species composition drivers in temperate deciduous forests are environmental conditions, a stand?s age and the site history, e.g., the succession stage and past land use, as well as disturbance regime and current management. We compared plant species diversity and composition in late successional and ancient forests, cooccurring on the same small river island applying species accumulation curves and nonmetric multidimensional scaling, respectively. Given the island?s geomorphological characteristics, we expected these to be very similar before human intervention in the past. The forests experienced differing disturbance regimes in the past, while over the last 30 years, human intervention has been the same and reduced to a minimum. The ancient forest in this study had two major characteristics defining it as old, mature forest: continuity of presence for more than 200years and specific composition. The late successional forest experienced major disturbance in the 20th century and was allowed natural regeneration by bordering on the ancient forest, representing a potential species pool,and by decades of minimum human intervention. Our results showed that, even though there was no difference in species richness, we could still detect differences between the forests, particularly in the abundance and species composition of the understorey, among which geophytes had the most indicative importance. To make our results useful on a broader scale, we composed from the literature a species list of plants indicative for ancient forest and tested its application. These results are important for distinguishing between old and mature secondary stands and particularly for identifying old forest stands, which should be conserved and, in the case of fragmented landscapes, included in a network connecting forest fragments.

Plant growth in a fragmented forest is a consequence of top-down and bottom-up processes, but not their interaction

Aims Habitat loss and fragmentation are the leading causes of global biodiversity decline.How fragmentation(leading to edge effects,increased isolation and declining habitat size)interacts with top-down processes like vertebrate herbivory,an important driver of vegetation structure and composition in many ecosystems,is poorly quantified.Interactions between fragmentation and changes in her-bivory may exacerbate their individual influences on plant growth,with implications for management of native plant communities within fragmented landscapes.We examined the effects of habitat fragmentation on herbivore activity,and also how both fragmen-tation and mammalian herbivory influence growth of understorey plant species.Methods This study was conducted at the Wog Wog habitat fragmentation experiment,located in south-eastern New South Wales,Australia.We use herbivore exclusion plots across an experimentally frag-mented landscape to assess the interactive effects of fragmenta-tion and herbivory on the growth of four plant species that vary in growth form and rarity in the landscape.Important Findings We observed species-specific responses to both herbivory and fragmentation,but no additive or interactive effects between these drivers.We show that a reduction in herbivore activity within frag-ments does not correspond with an increase in plant growth,even for the most palatable species.Rather,top-down processes continue to operate across the fragmented landscape.Although changes in habitat conditions within fragments appear to negatively influence both plant growth and mammalian herbivore activity,it is likely that alterations to bottom-up effects(i.e.fragmentation)may be more important than top-down effects(i.e.herbivores)for the spe-cies under investigation.The species-specific response of plants to herbivory or fragmentation may have implications for temporal and spatial population persistence in fragmented landscapes and ulti-mately fragment vegetation structure.