Plant diversity patterns on a mosaic landscape
April 28, 2019
Biodiversity loss has been attributed to a number of factors, two major ones being the conversion of natural landscapes to human-dominated systems, such as agricultural and urban areas, and fragmentation of natural habitats. The outcome of these processes can be landscape mosaics which are characterized by variations in configuration (i.e., patch size, shape and arrangement in space) and composition (i.e., land use types).
Miedema et al. (2019) examined how the diversity of plant functional traits might be affected by landscape configuration and composition. Plant functional traits are the physiological, structural, and behavioural characteristics that determine how plants respond to and interact with their habitat and there is evidence that measures of functional diversity are useful indicators of human impacts on biodiversity and ecosystems.
The assemblage of functional traits in a plant community can be divergent or convergent in response to landscape factors. Trait divergence occurs when species are sufficiently dissimilar that they can coexist, leading to a broader range of traits in a community, whereas trait convergence is where the surrounding habitat determines which plants can survive due to the adaptive qualities of their traits. Miedema et al. (2019) hypothesized that variable landscape composition and configuration would favour plant communities exhibiting a pattern of trait divergence.
To test their hypothesis, Miedema et al. (2019) drew on plant species and functional trait data from 13 forest sites in the Credit Valley watershed of southern Ontario. This watershed comprises various habitat and land use systems and is a region with a highly dense and fast-growing human population.
Landscape factors that may be influencing functional traits that were included in the analyses were, for composition, agricultural, urban, and natural lands and, for configuration, the diversity, density, and shape of patches and indices of patch cohesion and landscape division. Measures were determined at 1- and 10-km radiuses around each plant sampling site and analyses were performed using all landscape factors together and also each individually.
Plant functional traits selected for the analyses were those relevant to how a plant functions in a habitat or ecosystem and how it completes its life cycle; these included maximum height, seed weight, root depth, leaf area, leaf shape, leaf nitrogen content, growth rate, plant age of maturity, and Raunkiaer life form.
The results of the study showed trait divergence rather than convergence as dominating the plant communities, meaning that there was greater functional trait diversity than would be expected if traits emerged at random. Divergence was observed at both the 1-km and 10-km scales when the landscape factors were considered together. Traits of plant maturity, leaf area, maximum height, seed weight, root depth, and growth rate were found to be driving the divergence.
Trait divergence was also observed when landscape factors were considered individually, but this was the case only for agricultural land at the 1-km scale and both agricultural and natural land at the 10-km scale. As far as landscape configuration factors, the main drivers of trait divergence differed depending on the scale and factor under consideration. This variability suggests that landscape factors each had their own unique effects on particular functional traits.
Miedema et al. (2019) propose three non-mutually exclusive mechanisms to explain the trait divergence they observed in the Credit Valley watershed forests: limiting similarity, niche availability, and disturbance. In the first instance, limiting similarity, plant species could coexist over time as species differentiate in how and/or what resources they acquire. Second, niche availability, could be a mechanism given that the watershed has many habitat niches, each potentially catering to a different species’ requirements for completing its life cycle. Finally, disturbances in the environment could prevent any one species from dominating a community, thereby favouring diversity.
The insights provided from this study on the effects of landscape factors on plant functional trait assembly could be used to support the creation and management of healthier and more resilient ecosystems, particularly in regions characterized by landscape mosaics.
Read the full article here (open access):
Miedema LJ, Capmourteres V and Anand M. 2019. Impact of land composition and configuration on the functional trait assembly of forest communities in southern Ontario. Ecosphere. 10(3):e02633.