Predatory insects have their advantages: if it’s not just bark beetles or other plant pests, then an abundance of insects is obviously advantageous for a forest, reports a Chinese-German-Swiss research team in the journal Nature Ecology & Evolution. And to promote insect diversity, a species-rich mixed forest is ideal. The team writes that forest management that promotes predatory insects and a species-rich tree population could lead to plants binding more of the greenhouse gas carbon dioxide.
Many tree species lead to a species-rich insect community, which in turn is good for the growth of the plants. This ecological triple jump not only makes a correspondingly oriented forestry interesting, but also underlines the importance of species protection in the climate crisis. Scientists not involved in the study praise the work. What is special about the work is the realization that the positive effect of plant diversity on forest productivity “is also due to the fact that with increasing plant diversity, herbivorous insects are controlled more strongly by predatory insects,” says Wolfgang Weisser, Chair of Terrestrial Ecology at the Technical University of Munich.
It also needs insects that eat the herbivores
The experiment in which the data was collected is unique in the world, says the biologist. A good 14 years ago, several dozen test fields, each with 400 trees, were planted in the eastern Chinese province of Jiangxi. The fields differ, there are different monocultures as well as more varied stocks with up to 24 species. Year after year, the number of insect species and how much biomass the trees produce are recorded there. The data now presented were measured between 2015 and 2022 in the field laboratory.
Accordingly, more insects lead to more growth. However, there are differences depending on the composition of insect populations. As expected, too many herbivores have a detrimental effect on the biomass development of the trees. However, if predators or parasites attacking herbivores are plentiful, tree growth increases. So much for the observation. The group writes that it remains to be clarified whether there is a causal connection and which mechanisms work by.
On the other hand, thanks to the large number of different forest plots, it is clear that species-rich mixed forest has a positive effect on the insect population, says Weisser. In order to determine the effect of the insects, a way would have to be found to colonize plots with different mixtures of insects, “that is logistically almost impossible”. But he sees no reason why the results from China should not also be transferrable to European forests.