The importance of local habitat fragmentation versus landscape composition for biodiversity conservation and ecosystem services in agricultural landscapes

• Unité de recherche: ART
• Numéro de projet: 08.33.01.05
• Titre du projet anglais: The importance of local habitat fragmentation versus landscape composition for biodiversity conservation and ecosystem services in agricultural landscapes
• Titre court: FRAGMENT

Mots-clé (Anglais)

orchard, spiders, bugs, land snails, farmland birds

Description succincte (Anglais)

The loss and fragmentation of semi-natural habitats are a major threat to biodiversity in agricultural landscapes. Through the loss of biodiversity, important ecosystem services such as the biological control of pest insects can also be reduced. As habitat loss and fragmentation usually occur together, most existing studies have examined only their combined effect. While habitat loss has large, consistently negative effects on biodiversity, not much is known about the effect of fragmentation per se. Based on the small number of relevant empirical studies, it appears even that positive effects of habitat fragmentation on biodiversity would prevail.

Objectifs du projet (Anglais)

The proposed study will differentiate between the effect of local fragmentation and landscape composition on biodiversity and pest control in agricultural landscapes. The following hypothesis will be tested:

(i) The amount of semi-natural habitats in the surrounding landscape has large, positive effects on local biodiversity, especially for species and groups with high rates of aerial dispersal (e.g. fully winged plant- and leafhoppers, ballooning spiders).

(ii) Local fragmentation has negative effects mainly on habitat specialists with low dispersal abilities (e.g. land snails, flightless plant- and leafhoppers, cursorial spiders).

The proposed project will be one of the first that differentiates between the effects of local habitat fragmentation and landscape-scale habitat loss on biodiversity and ecosystem services. This is also of practical relevance, as the Swiss by-law on ecological quality (ÖQV) currently supports farmers for connecting semi-natural habitats. The main emphasis, however, is the scientific interest of the research question and the added value to landscape ecological research.

Procédure/Etat des travaux (Anglais)

We will test these hypothesis using two focal habitats in agricultural landscapes as models: traditional orchards and sown wildflower strips. Other semi-natural habitats, which can provide source populations of flora and fauna for the focal habitats will be considered as well. In a paired sampling design, we will select landscape situations which have a similar amount of semi-natural habitat within a 500 m radius of the focal habitat. In one member of the pair, the focal habitat (orchard, wildflower strip) will be isolated 100 m or more from the nearest semi-natural habitat, and in the other member of the pair the focal habitat will be well connected to semi-natural habitats. We will repeat this paired sampling along a gradient from low to high amounts of semi-natural habitats. Vascular plants, land snails (Stylommathophora, Mesogastropoda), grasshoppers (Orthopteroidea), plant- and leafhoppers (Hemiptera: Auchenorrhyncha), spiders (Araneae), solitary bees and birds will be investigated as biodiversity indicators. Diversity, community composition and density of the different taxa and ecological groups will be analysed with respect to local fragmentation and landscape composition. In addition to the biodiversity indicators, exclusion experiments will be conducted in the field to quantify the influence of spiders on apple aphids (Homoptera: Aphididae).

In 2007, biodiversity and landscape parameters will be investigated in 30 traditional fruit orchards in north-eastern Switzerland. Of the 30 orchards, 15 are isolated (no semi-natural habitats in a 100 m radius around the orchards) and 15 are well connected to semi-natural habitats. The 15 orchards of each group are distributed along a gradient from a low to a high share of habitats within a 500 m radius.

In 2008 the same sampling design will be repeated for flower strips. In 2009 the data will be analysed and published.