Plant Traits, Functional Diversity, and Ecosystem Services
Published on 13 May 2014 in Sustainability and Communities , Ecosystems and biodiversity
Introduction
The protection of biodiversity is seen increasingly within the context of ecosystem service delivery, but understanding how biodiversity controls the delivery of ecosystem functions and processes, and hence final ecosystem services, is not straightforward. Developing this understanding is essential if we are to manage the environment for both nature conservation and ecosystem service delivery.
One approach to understanding how biodiversity might regulate ecosystem functions is through the concept of “functional traits”. These are the characteristics of species – in plants these might be leaf or root construction costs or morphological features – that regulate ecosystem functions such as productivity, decomposition and carbon sequestration. Plant functional traits might provide a more accurate description of the functioning found within ecosystems than measures of species presence. We include arable cropping systems within this understanding of ecosystems.
For example, adding species to a community may have little impact on how it functions if the species are – in terms of their traits – all the same. Only the addition of species with different traits would lead to a change in how the system functions. If this is the case then functional identity or functional diversity rather than species diversity might be the key component of biodiversity that really drives ecosystem function and service delivery.
Recent research at the James Hutton Institute has considered how plant traits and functional diversity may affect ecosystem processes, both in the short (within a growing season in crop systems) and long-term (from years to decades through decomposition processes).
Key Points
- The extent to which different “levels” of biodiversity can control ecosystem functions, and hence ecosystem services, may depend upon the identity of species or the range of functional trait variation that they offer.
- In order to monitor biodiversity and infer the likely consequences of biodiversity change for ecosystem services, it may be as important to monitor functional diversity as it is to monitor more commonly-assessed measures of biodiversity such as species or habitat richness.
Research Undertaken
In a recent greenhouse-based study we constructed artificial plant communities to examine the relative roles of genetic diversity and species diversity in regulating a key ecosystem function – the production of plant biomass (that is, primary production). The plant communities were constructed by combining different levels of weed species diversity with different levels of barley genetic diversity (using different commercial barley varieties). This study found that:
- Weed species diversity had a much larger effect on productivity than did barley genetic diversity. To put it another way, adding or removing a single weed species from the community had a proportionately bigger effect on productivity than adding or removing one of the barley varieties.
- The relatively greater role of species diversity can be explained by examining the functional traits of the plants involved. In particular – and perhaps unsurprisingly – the changes in species diversity were associated (on average) with bigger changes in functional traits.
- Although these results may at first seem obvious, to the best of our knowledge this is the first study to explicitly compare the relative effects of species and genetic diversity on plant productivity, and to interpret their effects through the concept of plant functional traits.
Other research has focussed on how plant traits control tissue decomposition. Leaf decomposition in grasslands appears to be tightly linked to the leaf dry matter content (the ratio between the mass of dried and fresh leaves). Whilst this is a simple measure, it reflects the relative investment of leaf resources into structural materials and the speed of plant growth: slow growing plant tissues tend to have higher dry matter content. Leaf litters from individual species or mixtures of litter with high leaf dry matter content – that is, those with a high investment in structural tissue that is less readily broken down – decay more slowly than leaf litters with a lower dry matter content. The same applies below-ground; root litter decomposition is highly correlated to specific root area (the area of root surface per unit mass). Hence the key ecosystem function of decomposition appears to be controlled by the functional traits of the dominant species, and diversity has only a limited effect.
Policy Implications
Current policies – for example the Scottish Biodiversity Strategy and associated 2020 Challenge for Scotland’s Biodiversity – describe how biodiversity is important for society because it underpins the delivery of ecosystem services and associated goods and benefits. This research work helps us to better understand how different elements of biodiversity (genetic and species diversity, functional identity and diversity) can contribute to ecosystem service delivery.
However, the fact that certain kinds of biodiversity do not contribute as much to a particular ecosystem function shouldn’t be used to argue that these components of biodiversity are not as important. For example, we found a weaker role for genetic diversity in the control of biomass production by the whole plant community, but genetic diversity might be very important for other ecosystem properties and services, for example long-term stability in crop systems or the conservation of rare and endangered species.
In future we need to understand what plant or animal traits are associated with the delivery of a far wider suite of ecosystem services, and how these traits are themselves controlled by interactions between species and by other factors such as land management and climate change. Our aim is to see whether we can map ecosystem services based on the distribution and abundance of plant species and their associated traits across large geographic areas. If possible, this would allow us to produce ecosystem service maps by using existing data on the traits of plant species, and on plant species distributions. Research on this particular issue is currently underway as part of the Ecosystem Services Theme of the Strategic Research Programmes, and will be delivering results within the coming year.
Authors
Professor Rob Brooker, James Hutton Institute rob.brooker@hutton.ac.uk
Professor Robin Pakeman, James Hutton Institute
Dr Alison Karley, James Hutton Institute
Professor Adrian Newton, James Hutton Institute
Dr Christian Schoeb, Institute of Evolutionary Biology and Environmental Studies, University of Zurich
Topics
Sustainability and Communities , Ecosystems and biodiversity
