Biotic homogenization can decrease landscape/scale forest multifunctionality (2016) von der Plas et al., Proceedings of the National Academy of Sciences of the United States of America, 113

The Crux

Any ecosystem performs a multitude of functions, benefiting both the species that live in it and the humans who interact with it, from litter decomposition to resistance of drought to timber production. As such, maintaining high levels of ecosystems is a well-studied concept, and it has been posited that high levels of biodiversity increase the levels functions an ecosystem can perform, or its multifunctionality.

But while the word biodiversity is recklessly bandied about these days, scientifically it’s a somewhat vague term. At an ecosystem level, you may have patches of very high local (or alpha) diversity, but the turnover of species between patches (beta diversity) might be quite low. The variation in types of biodiversity may influence your ecosystem multifunctionality. For instance, patches of high alpha diversity might lead to high levels of functionality in some patches, but little functionality elsewhere, whereas high levels of beta diversity may lead to low levels of functionality, but many functions. This paper investigates relationships between different biodiversity levels and ecosystem multifunctionality.

How it Works

The experiment used 209 forest plots taken from across the whole of Europe, maximising species diversity whilst attempting to minimise other environmental factors, so that the study was not biased by higher presence of any individual species. They measured the effectiveness of 16 different ecosystem functions, from wood decomposition to tree regeneration to bird diversity, and measured both the number of functions that exceeded a certain performance level threshold, and the total level of functionality of all functions.

What They Found Out

High levels of beta diversity increased the number of functions that exceeded a certain threshold, regardless of what that threshold was, and this was more or less consistent regardless of which country it occurred in. High levels of alpha diversity only helped when the threshold was low, and actually detracted from multifunctionality when the threshold grew higher.

Did You Know: Metapopulations Biodiversity may vary greatly within one ecosystem, so it follows that certain species will only be able to colonise certain regions of an ecosystem. These separate populations form a metapopulation. Some populations within this population will flourish, and they will have a constant stream of emigration. These source populations contrast with sink populations, that cannot sustain a population independently and rely on immigration from other populations. A metapopulation will be better able to survive if the separate populations are well-connected.

Problems

It can often be difficult to qualify functionalities, especially across such a wide landscape. It is also worth noting that the functions used here do not relate to humans, and although the takeaway messages below may seem to make very clear-cut suggestions, the fact is that forest managers often have to make allowances for anthropogenic needs.

So What?

Whilst biodiversity is the calling cry of many a conservationist today, this study indicates that how you define biodiversity affects the results of its implementation. Rather than simply trying to introduce as many native species as possible in order to increase ecosystem functioning, managers may be better off creating a variety of monocultures throughout an ecosystem. An increase i this type of diversity may provide more functions at a high level. However if lower levels of functionality are acceptable, then the preferred option may be to promote high levels of diversity on a wide scale, giving rise to many functionalities within one region.