For the latest post in our Toward prediction in the restoration of biodiversity series, Chad Zirbel turns to tallgrass prairies to examine the role of plant traits in predicting restoration outcomes. Chad and colleagues’ paper, Plant functional traits and environmental conditions shape community assembly and ecosystem functioning during restoration, is available in the Journal of Applied Ecology.

Two of the major goals of restoration are to return biodiversity and ecosystem functioning (e.g. nutrient cycling, erosion control, pollinator resources, etc.) to degraded ecosystems. The outcomes of these restorations vary widely from successes to failures. To date, we still do not have a good understanding of what causes variation in biodiversity and ecosystem function in sites undergoing restoration.

Purple gian Hyssop (Agastache scrophulariifolia) in a restored prairie at the Edward Lowe foundation. Cassopolis, Michigan, USA. Photo by Chad Zirbel.

Our study took place in 29 tallgrass prairies in southwestern Michigan that were restored from former agricultural land by sowing native prairie seeds. These restored prairies are managed with prescribed fire and are planted across a range of conditions, from dry sandy soils to soils with higher organic matter content and water holding capacity. They also vary in the landscape that surrounds each restoration, from sites that are primarily surrounding by agriculture to those surrounded by forest and other grasslands. Furthermore, these sites have different past land use histories with some sites being restored directly from tillage while others were allowed to fallow for some period of time before being restored. Here, we were interested in understanding whether or not these environmental conditions matter for the distribution of plant traits, and, in turn, if the traits and environmental conditions explain variation among sites in ecosystem functions.

At each of these sites we measured environmental conditions, plant community composition, plant functional traits, and a series of ecosystem functions including: above and below ground plant biomass production, decomposition rate, seed predation rate, arthropod predation rate, and pollinator resource availability. These functions relate to resource fluxes across trophic levels and different types of ecosystem services such as provisioning (aboveground plant biomass), supporting (above and belowground biomass, decomposition), and cultural (pollinator resource availability).

We found that environmental conditions predicted plant traits. For example, sites restored directly from tillage (as opposed to those allowed to fallow) supported taller species with larger seeds suggesting that more competitively dominant and less weedy species established at these sites. Site age and fire frequency were both negatively related to traits that are related to growth rate. This suggests that older, more frequently burned sites support species that grow more slowly and are more competitive. Interestingly, this describes many of the species targeted for prairie restoration.

Chad next to a compass plant (Silphium laciniatum). Photo by Maddy Cleary.

We also found that both plant traits and environmental conditions predicted ecosystem functioning, but these relationships varied among the measured functions. For example, the frequency of plants that are animal pollinated increased, and fire frequency decreased, the abundance of flowers available to pollinators. Vegetative height increased decomposition rate. Soil moisture and fire frequency both increased, while site age decreased, above-ground plant biomass production. Prairie restoration has been suggested as a way to increase both pollinator resources and produce cellulosic biofuels. Here we show the functions underlying each of these can be increased but by different traits and environmental conditions.

Our results suggest that both traits and environment play an importation role in shaping ecosystem function during restoration, and the importance of each depends on the function of interest. Because of this, variation in environmental conditions will be necessary to promote multiple ecosystem functions across restored landscapes. An approach to restoration based on plant traits can aid interpretation of variable outcomes through insights into the ways restored communities form and provide ecosystem functions.

The full article, Plant functional traits and environmental conditions shape community assembly and ecosystem functioning during restoration, is a part of the Special Feature, Toward prediction in the restoration of biodiversity and available in read in the Journal of Applied Ecology.

Read other blogs from the series: