David Tilman

Plant diversity effects on community productivity often increase over time. Whether the strengthening of diversity effects is caused by temporal shifts in species-level overyielding (i.e., higher species-level productivity in diverse communities compared with monocultures) remains unclear. Here, using data from 65 grassland and forest biodiversity experiments, we show that the temporal strength of diversity effects at the community scale is underpinned by temporal changes in the species that yield. These temporal trends of species-level overyielding are shaped by plant ecological strategies, which can be quantitatively delimited by functional traits. In grasslands, the temporal strengthening of biodiversity effects on community productivity was associated with increasing biomass overyielding of resource-conservative species increasing over time, and with overyielding of species characterized by fast resource acquisition …

Two of the major factors that control the composition of herbaceous plant communities are competition for limiting soil resources and herbivory. We present results from a 14-year full factorial experiment in a tallgrass prairie ecosystem that crossed nitrogen (N) addition with fencing to exclude white-tailed deer, Odocoileus virginianus, from half the plots. Deer presence was associated with only modest decreases in aboveground plant biomass (14% decrease; −45 ± 19 g m−2) with no interaction with N addition. N addition at 5.44 and 9.52 g N m−2 year−1 led to increases in biomass. There were weak increases in species richness associated with deer presence, but only for no or low added N (1 and 2 g N m−2 year−1). However, the presence of deer greatly impacted the abundances of some of the dominant perennial forb species, but not the dominant grasses. Deer presence increased the abundance of the forb …

Future economic growth will affect societal well-being and the environment, but is uncertain. We describe a multidecadal pattern of gross domestic product (GDP) per capita growth rising, then declining, as regions become richer. An empirically fitted differential-equation model and an integrated assessment model—International Futures—accounting for this pattern both predict 21st-century economic outlooks with slow growth and income convergence compared to the Shared Socioeconomic Pathways, similar to SSP4 (“Inequality”). For World Bank income groups, the differential-equation model could have produced, from 1980, consistent projections of 2100 GDP per capita, and more accurate predictions of 2010s growth rates than the International Monetary Fund’s short-term forecasts. Both forecasts were positively biased for the low-income group. SSP4 might therefore represent a best-case—not worst-case …

In their letter, Muzzioli et al.(1) raise two main points: 1) the diffuse relationship between nutrition and environment in figure 4 of ref. 2, introduces the possibility for trade-offs between these outcomes and 2) the functional unit that should be used report nutrition and environmental impacts of food products. Both have been discussed in depth in ref. 2 and elsewhere (3).On the first point: The diffuse relationship between nutrition and environment shown in figure 4 is the reality of the food environment in which many of us live. Whilst there is a general trend for more nutritious foods to be more sustainable across the thousands of food products many of us are fortunate to be able to choose between, there are many outliers to this trend (eg, table condiments, desserts, etc). This builds on findings in previous analyses focusing on commodities (4) or diets (5, 6), which despite their small sample size (often< 15 data points) also …

Mounting evidence suggests that plant–soil feedbacks (PSF) may determine plant community structure. However, we still have a poor understanding of how predictions from short‐term PSF experiments compare with outcomes of long‐term field experiments involving competing plants. We conducted a reciprocal greenhouse experiment to examine how the growth of prairie grass species depended on the soil communities cultured by conspecific or heterospecific plant species in the field. The source soil came from monocultures in a long‐term competition experiment (LTCE; Cedar Creek Ecosystem Science Reserve, MN, USA). Within the LTCE, six species of perennial prairie grasses were grown in monocultures or in eight pairwise competition plots for 12 years under conditions of low or high soil nitrogen availability. In six cases, one species clearly excluded the other; in two cases, the pair appeared to coexist. In …

Rates of species colonisation and extirpation are increasing in plant communities world‐wide. Colonisation could potentially help compensate for, or compound, resident diversity loss that results from global environmental change. We use a multifactorial seed addition grassland experiment to examine relationships between plant colonisation, resident species diversity and key community assembly factors over 3 years. By manipulating colonist seed rate, imposing disturbance and examining abundance and diversity impacts of 14 formerly absent sown colonists in communities that varied in successional stage and time since agricultural abandonment, we were able to disentangle effects of global change factors (species introduction, novel disturbance and land use change) that are usually confounded. Evidence suggested that cover abundance of sown colonists was most strongly influenced by successional …

Highly productive agriculture is essential to feed humanity, but agricultural practices often harm human health and the environment. Using a nitrogen (N) mass-balance model to account for N inputs and losses to the environment, along with empirical based models of yield response, we estimate the potential gains to society from improvements in nitrogen management that could reduce health and environmental costs from maize grown in the US Midwest. We find that the monetized health and environmental costs to society of current maize nitrogen management practices are six times larger than the profits earned by farmers. Air emissions of ammonia from application of synthetic fertilizer and manure are the largest source of pollution costs. We show that it is possible to reduce these costs by 85% ($21.6 billion per year, 2020$) while simultaneously increasing farmer profits. These gains come from (i …

To determine which types of plant traits might better explain ecosystem functioning and plant evolutionary histories, we compiled 42 traits for each of 15 perennial species in a biodiversity experiment. We used every possible combination of three traits to cluster species. Across these 11,480 combinations, clusters generated using tissue %Ca, %N and %K best mapped onto phylogeny. Moreover, for the 15 best combinations of three traits, 82% of traits were chemical, 16% morphological and 2% metabolic. The diversity‐dependence of ecosystem productivity was better explained by the %Ca, %N and %K clusters: compared to adding a new species at random, adding a species from an absent cluster/clade better‐explained gains in productivity. Species number impacted productivity only when all clusters were present. Our results suggest that tissue elemental chemistry might be more phylogenetically conserved and …