More clutter for more biodiversity

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The branch bundles were placed in these tubes to see which beetle species hatch
The branch bundles were placed in these tubes to see which beetle species hatch from them. Photo: BFH-HAFL
It may look chaotic, but deadwood in the forest does have a function. It has a decisive influence on biodiversity. Researcher Elena Haeler has shown in a study that not only the quantity but also the distribution of deadwood in the habitat plays an important role.

Until now, research into deadwood has mainly focused on the amount of wood present. The distribution of the wood in the habitat has often been overlooked. Austrian forest scientist Elena Haeler - a research associate at BFH-HAFL at the time of the study - and her Swiss research colleagues wanted to change this. They investigated how the distribution of deadwood influences species diversity, with a focus on beetles.

The researchers placed four different bundles of branches at 69 locations in the Sihlwald forest near Zurich. The bundles consisted of one, three, six or twelve branches. These bundles were hung from trees 1.3 m above the ground for one year and colonized by beetles whose larvae developed in the wood. The results showed that the larger the bundle of branches, the more beetle species were found in it. What was surprising, however: ’Taken together, the three small branch bundles harbored just as many different species as the largest, even though fewer branches were examined,’ summarizes Elena Haeler. ’We assume that heterogeneity in a small area could play a certain role,’ says Haeler. However, further studies are needed to prove this hypothesis.

A good distribution of deadwood

The heterogeneity of deadwood can be increased by a scattered distribution. Even if the wood is only a few meters apart, there are small differences in the environment such as light, temperature and humidity. ’This can create different habitats for different species. The species that first live in a piece of wood also influence which other species can occur there later,’ says Elena Haeler. For example, the first colonizers can bring along fungi that could be necessary for certain subsequent species. However ideally the deadwood is distributed: This cannot compensate for the fact that there is generally too little deadwood in the forest. More deadwood is needed, for example by leaving the treetops of felled trees lying around - preferably from different tree species. Haeler’s conclusion: ’In order to promote the greatest possible diversity of organisms, the forest should not be cleared and the wood should be left spatially distributed in the forest.