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Sobek S., Tscharntke T., Scherber C., Schiele S.,
Steffan-Dewenter, I. Canopy vs. understory:
Does tree diversity affect bee and wasp
communities and their natural enemies across
Article in Forest Ecology and Management · August 2009
Impact Factor: 2.66 · DOI: 10.1016/j.foreco.2009.04.026
CITATIONS READS5 authors, including:
Teja Tscharntke Christoph Scherber Georg-August-Universität Göttingen University of Münster 433 PUBLICATIONS 27,111 CITATIONS 122 PUBLICATIONS 2,331 CITATIONS
SEE PROFILE SEE PROFILEIngolf Steffan-Dewenter University of Wuerzburg 215 PUBLICATIONS 16,991 CITATIONS SEE PROFILE All in-text references underlined in blue are linked to publications on ResearchGate, Available from: Christoph Scherber letting you access and read them immediately. Retrieved on: 18 May 2016 Göttinger Zentrum für Biodiversitätsforschung und Ökologie − GÖTTINGEN CENTRE ECOLOGY −
Chapter 4: Canopy vs. understory: How does tree diversity affect cavity-nesting bee and wasp communities and their natural enemies across forest strata? 87
Chapter 5: Sapling herbivory, herbivores and predators across a semi-natural tree diversity gradient in Germany’s largest connected deciduous forest 107
Introduction Biodiversity & forest ecosystems in a changing world Biodiversity research has become a key subject in modern ecology. Throughout the last decade, a plethora of studies has been conducted to elucidate the status quo and distribution of global biodiversity (Gaston 2000), to determine major threats (Purvis & Hector 2000), to link biodiversity with ecosystem functioning and services (Loreau et al. 2001, Hooper et al. 2005, Kremen 2005, Balvanera et al. 2006), and to stop biodiversity loss by applying appropriate conservation measures (Perfecto et al. 1997, Rundlöf et al. 2008). What is biodiversity, and why has it recently gained major attention of scientists around the globe?
The term “biodiversity” combines different perceptions of variety among organisms.
According to the United Nations’ “Convention on Biological Diversity” (1992), it includes ecological diversity (=niche diversity), organismic diversity, and genetic diversity among individuals (Noss & Cooperrider 1994, Schellnhuber et al. 1999). The UN conference on the environment and development in Rio de Janeiro (1992) also acknowledged biodiversity as a natural resource, and determined its conservation as a keystone task for future sustainable development (Haila & Kouki 1994).
Biodiversity offers goods and services that are impossible to be replaced by man alone. If society remains unable to establish sustainability and fails in stopping the current biodiversity decline, ecosystem services such as pollination, provision of clean air and soil, biocontrol of pest outbreaks, continuity of biogeochemical cycles etc. will be lost (Ehrlich & Ehrlich 1992).
Besides these apparent driving forces of the environment, biodiversity also has economic implications and serves as resource for food, industrial production (e.g. timber, medical goods), and recreation (Ehrlich & Ehrlich 1992).
Forest ecosystems, in tropical as well as in temperate regions, are believed to house the major proportion of global biodiversity (Carnus et al. 2006). As a result of global change, extensive timber logging, and conversion of forest to arable land for biofuel production, pristine forest habitats decline rapidly. According to the 2005 report of the Food and Agriculture Organisation of the United Nations (FAO), approximately 7.3 million hectares of forest are lost each year. Worldwide, only 30 % of surface area is still covered by natural or planted forest, and especially Central Europe exhibits only a minute fraction of large-scale forest habitats (FAO 2005). In Germany, although 30 % of land surface is forested, the proportion of old-growth natural forest equals zero (FAO 2005).
With the majority of pristine forest habitats already vanished and with prospect to future losses, it is of immediate importance to identify the contribution of the remaining forest habitats to global diversity and ecosystem functioning. Since the late Holocene, European beech (Fagus sylvatica L.) and other deciduous trees should be naturally predominant in Central Europe (Tinner & Lotter 2006). Instead, for many years conifers have primarily been reforested (Puumalainen et al. 2003), and only recently sustainable forestry tries to reestablish a greater abundance and variety of deciduous tree species. For Central Europe and Germany in particular, the scope should thus lie on the last semi-natural deciduous forest habitats, which are scarce and widely scattered across a landscape otherwise dominated by agricultural land use.
Research on animal and plant communities in forest habitats has a long tradition in ecology, but nevertheless, blank spots remain on the map of global forest diversity. Although numerous examinations in tropical rainforests have illustrated that especially insects in the forest canopy are prime contributors to global biodiversity (Erwin 1982, Erwin 1988, Stork 1988, Novotny & Basset 2005, Dial et al. 2006), canopy research in temperate deciduous forests in Central Europe has long been neglected, and only a handful of published studies on a limited selection of arthropod taxa exists. (Kampichler & Teschner 2002, Goßner & Bräu 2004, Goßner & Ammer 2006, Goßner et al. 2007, Müller & Goßner 2007).
In the present study, we try to fill these blanks by relating diversity and function of canopy and understory insect communities to a semi-natural tree diversity gradient ranging from simple beech to mixed deciduous forest stands located in the Hainich National Park (Thurinigia, Germany).
The research conducted for this thesis was placed within the framework of the DFG (German Research Foundation) Research Training Group (“Graduiertenkolleg”) 1086, “The role of biodiversity for biogeochemical cycles and biotic interactions in temperate deciduous forests”.
The multidisciplinary programme was aimed to link the work of 14 PhD students, who independently examined various topics of temperate forest biodiversity and ecosystem functioning. A complete list of all parameters investigated can be found in Leuschner et. al.
(in press), subprojects included:
Abiotic stand characteristics, biogeochemical cycles, and productivity Stand structure and abiotic conditions are primarily set by the tree species present in the canopy layer. Analyses included soil moisture, soil carbon and nutrient content, local stand climate, and management history. Biogeochemical processes were examined and modelled from the soil up to the canopy, including rainfall precipitation and water cycling, nutrient fluxes, sap flow and canopy transpiration, litter decomposition, soil respiration, and primary plant production (stem increment, leaf and fine root production, etc.).
Biotic stand characteristic and interactions Again, focus was laid on examining animal and plant communities from the soil up to the high canopy. Investigations ranged from analysing abundance and diversity of mycorrhizal fungi, herb layer plants, tree seedlings, and full-grown trees to soil mesofauna (oribatid mites), macrofauna (earthworms, ground beetles, isopods, spiders, snails), and canopy arthropods. Results for the latter including beetles, true bugs, bees and wasps are described in detail in chapter 2 to 4 of the present thesis. Biotic interactions like parasitsm, herbivory of tree seedlings, and the abundance of herbivores and predators, as well as their functional relationships, are presented in chapter 4 and 5.
Economic evaluation As mentioned earlier in this chapter, biodiversity offers services and goods of high economic impact and monetary value. Hence, to make the multidisciplinary survey complete, the willingness-to-pay for insurance values maintained by diverse forest stands (e.g. biocontrol of pest outbreaks) was investigated in a choice experiment and by random interviews.
All investigations were conducted in the the Hainich National Park. The park was established in 1997 and is located in the federal state Thuringia (Germany) in temperate Central Europe.
It is described as Germany’s largest connected semi-natural deciduous forest, and covers a total area of 16,000 ha (Nationalpark Hainich; http://www.nationalpark-hainich.de). In the past, the region belonged to the territory of the former German Democratic Republic, and has been used for many years as a military training site by Russian occupants. The latter ensured that most of the forest remained unmanaged for at least 40 years. In 1997, 7,600 ha have been put under permanent conservation and been declared National Park. In 2005, 12 permanent research plots were set-up in the north-eastern part of the conservation zone close to the village Weberstedt, establishing a semi-naturally grown tree diversity gradient ranging from simple beech to mixed forest stands with up to 9 broadleaved tree species (Fig. 1.1 & Fig 1.2).
Fig. 1.1. Simple beech stand in the Hainich National Park in spring 2008 (photo: C. Scherber).
Fig. 1.2. Species-rich forest stand in the Hainich National Park in spring 2005 (photo: S. Schiele).
The tree species composition of the Hainich National Park is highly exceptional, and unlike other forest habitats in Germany, conifers are a minority group and frequently logged to regain a late successional stage of semi-natural deciduous forest. One can find many stands dominated by European beech (Fagus sylvatica L.), other tree species like lime (Tilia sp.) and ash (Fraxinus excelsior L.) also appear frequently, and the mix is enriched with species like hornbeam (Carpinus betulus L.), maple (Acer campestre L., Acer platanoides L., Acer pseudoplatanus L.), cherry (Prunus avium L.), oak (Quercus robur L.) and elm (Ulmus glabra Huds.). Even the rare service tree (Sorbus torminalis L.) is present, and in total a maximum of 14 different tree species per hectare has been reported (Mölder et al. 2006).
Insects in the forest canopy and understory Insects are the predominant taxon in terrestrial ecosystems by means of species richness, individual abundance, and biomass (Kremen 1993), and are of great importance for conservation management (Pearce & Venier 2006, Underwood & Fisher 2006). Estimations of global faunal diversity are closely interlinked with investigations on insect species richness, abundance, and host specifity (e. g. Erwin 1982, Erwin 1988, Erwin 1991, Longino 1994, Stork 1988), most of which have focused on forest canopy habitats in the tropics.