How Will Climate Change Affect Community Stability?

There’s a great deal of concern and uncertainty over the patterns and causal mechanisms that underlie community grassland change in response to climate change (Ratajczak & Ladwig 2019). Experimental work is needed to better understand the potentially synergistic effects of global change stressors on stability of grasslands. In the recent Editor’s Choice article in Journal of Ecology, Qian Wu and colleagues investigated the impact of two particular stressors, warming and N addition on community stability in a decade-long field experiment set in desert steppe grassland of northern China.

Overall, this study is important as it shows that decreased stability of grasslands due to anthropogeneic environmental changes are likely to compromise the critical ecosystem functions and services provided by this biome. That community stability was affected through effects on the dominant species also highlights the important role that these species have on community stability as shown in some other recent studies in Journal of Ecology (e.g., Liu et al 2019, Smith et al 2019). Research to understand the mechanisms through which these changes occur will allow the development of mitigation policies. The Editors welcome submission of similar novel studies to Journal of Ecology.

Below, authors Qian Wu and Goudong Han describe the highlights of their study.

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The desert steppe is a transitional ecotone between grasslands and desert. It is an important and unique part of the Eurasian temperate steppe, and is considered to be a fragile ecosystem in the face of global change (e.g. global warming and increased nitrogen deposition). The desert steppe plays a crucial role in carbon sequestration, biodiversity, animal husbandry and regional economic development. Therefore, it is important to understand how desert steppe responds to projected warming and increased nitrogen deposition, including their potential interactive effects on ecosystem functions.

The stability of an ecosystem represents its ability to maintain consistent properties in the face of temporal variation in environmental conditions. However, how stability of the desert steppe responds to the combination of warming and increased nitrogen deposition remains unknown. In this study, we made a first attempt to investigate the long-term impacts of warming and nitrogen addition on plant community stability in a species-poor Stipa breviflora desert steppe in Inner Mongolia, northern China.

At the experimental site, warmed plots were heated continuously for 24 hours a day throughout the year, starting from May 2006. Heating was done using an infrared radiator. Nitrogen was applied once prior to a rainfall event in about the third week of June in the form of NH₄NO₃, at a rate of 10 g N m^-2 yr^-1. A visual estimate of canopy coverage of each species was made in August at the peak of the growing season from 2006 to 2015. We quantified the stability of the whole community, dominant, common and rare species as the ratio of mean plant coverage and its temporal standard deviation in each plot over the decade of the experiment.

We found that long-term warming and nitrogen addition had additive, negative effects on plant community stability. Warming decreased species richness whereas nitrogen addition reduced species asynchrony. Furthermore, the stability of different plant functional groups was altered by warming or nitrogen addition. A warming-induced decrease in species richness was not a significant driver of decreased community stability, which was instead driven by the decreased stability of dominant species under warming. On the other hand, a nitrogen-induced decrease in community stability was ascribed to both decreased stability of dominant and common species and decreased asynchronous population dynamics under nitrogen addition.

This study suggests that warming and increased nitrogen deposition, two important components of global environmental change, may combine to threaten plant community stability in arid grassland ecosystems, while also highlighting the different mechanisms associated with the similar effects of climate warming and increased nitrogen deposition on grassland community stability. These findings, combined with the reported adverse effects of ongoing anthropogenic environmental changes on the stability of other ecosystems, point to the need for immediate interventions to mitigate projected future global environmental changes, in order to conserve the stability of natural ecosystem functions and services provided for humanity.

Qian Wu Inner Mongolia Agricultural University, China & University of Alberta, Canada
Guodong Han Inner Mongolia Agricultural University, China

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You can read the full article on Journal of Ecology: Additive negative effects of decadal warming and nitrogen addition on grassland community stability by Wu et al.