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Fauna responses to climate change

Fauna sampling in the six sites was carried out for 5-6 days per site in the period April 29 to July 23 2003. The sampling time for each site was chosen to correspond to late spring or early summer and to coincide with the beginning of the drought treatment. In each plot of the VULCAN sites 5 subplots (1260cm2) were selected. Composition, cover, age and height of the vegetation were used as basis for choosing the position of subplots emphasizing similarity between plots. A specially designed non-destructive suction method was used to sample the fauna on plants and soil surface. Within each subplot leaves and stems of all plants and an area of the soil/litter surfacewere systematically sucked by a mouthpiece connected to a fauna-trap and a vacuum-cleaner.

Animals dropping from the plants during suction were sampled in plastic boxes placed under the plants before suction. A 10 cm deep soil sample (surface area 25cm2) was collected within each subplot and the soil fauna extracted by a standard high-gradient extraction method at the Mols Laboratory.

Additional samplings were carried out in similar vegetation outside the experimental plots for comparison of the suction sampling method with conventional methods. The large material was sorted and the animals were counted to the level of larger taxonomic groups (classes, orders, families) and for selected taxa (Collembola, oribatid mites) to species level. Biomass was as a first approximation calculated by employing average values borrowed from the literature of individual weights representative for broad taxonomic groups.

A more precise and site-specific measure of average individual weight representative of important fauna groups is being worked out based on microscopic measurements of body length and width. Comparisons of faunal abundance show several examples of significant differences between sites and between treatments within sites for broad fauna categories such as total invertebrates, total insects, plant feeders and detritus/microbial feeders (mainly soil fauna) as well as whole fauna groups such as Acari (mites), Collembola (springtails), leaf hoppers (cicadas), plant bugs, aphids, wasps, ants and spiders. Whether the responses of population density to manipulated drought and warming were negative, positive or non-significant depended on taxonomic group and site.

The statistically significant comparisons showed that most individual taxonomic groups responded negatively in all sites to both types of climatic manipulations whereas opposite reactions in different sites were demonstrated for the composite assemblies of taxa: total insects, total fauna, plant feeders and detritus/microbial feeders.

The cover percentage of individual plant species within subplots interacted with the treatments so that in some cases opposite effects on fauna populations were observed depending on vegetation type. Detailed analysis of the microarthropod taxa Acari and Collembola further demonstrated that different species may respond differently to the manipulations resulting in altered species composition and diversity due to the treatments.

On the other hand, examples of opposite reactions of the same species in different sites were also observed. Biodiversity of Collembola (number of species) was lower in the drought treatment than in the control in the British, Dutch, Hungarian and Spanish site, but higher in the Danish and Italian sites. The species number in the warming treatment was equal to the control in the British and the Dutch sites, lower in the Hungarian and Spanish sites and higher in the Danish and Italian sites.

The distribution between sites and treatments of crude biomass estimates based on average individual weights borrowed from the literature differed in composite taxa considerably from distributions based on abundance values because of a large variety in size found between the fauna groups composing these taxa. Less crude biomass estimates based on measurement of the actual size distribution within the fauna groups is still in progress. It can be concluded that the arthropod fauna as a whole and several taxonomic and trophic fauna groups as well as a number of microarthropod species responded significantly to both the warming- and the drought treatment but that the response pattern is complex depending on site and vegetation quality within sites.

The observed responses of the fauna cannot immediately lead to conclusions about the effect on plant growth and survival. No examples of ongoing pest attack were observed at the sampling occasions in 2003 whereas consequences for the Calluna vegetation of earlier attacks of heather beetles were recorded in the Danish and Dutch site.5 mauscripts are planned for international scientific journals. A current PhD-project. The effect of stress on biodiversity (S. Bahrndorff 2004-2006) is based on the VULCAN fauna studies and includes plans for resampling in the Danish and Spanish sites.

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Mols Laboratory, Strandkaervej 6-8
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