Clarifying the effect of biodiversity on productivity in natural ecosystems with longitudinal data and methods for causal inference

Causal effects of biodiversity on ecosystem functions can be estimated using experimental or observational designs - designs that pose a tradeoff between drawing credible causal inferences from correlations and drawing generalizable inferences. Here, we develop a design that reduces this tradeoff and revisits the question of how plant species diversity affects productivity. Our design leverages longitudinal data from 43 grasslands in 11 countries and approaches borrowed from fields outside of ecology to draw causal inferences from observational data. Contrary to many prior studies, we estimate that increases in plot-level species richness caused productivity to decline: a 10% increase in richness decreased productivity by 2.4%, 95% CI [-4.1, -0.74]. This contradiction stems from two sources. First, prior observational studies incompletely control for confounding factors. Second, most experiments plant fewer rare and non-native species than exist in nature. Although increases in native, dominant species increased productivity, increases in rare and non-native species decreased productivity, making the average effect negative in our study. By reducing the tradeoff between experimental and observational designs, our study demonstrates how observational studies can complement prior ecological experiments and inform future ones

Chronic fertilization and irrigation gradually and increasingly restructure grassland communities

Scientists have known for over a century that resource addition can lead to species loss from plant communities. Recent studies have also shown that resource addition can substantially restructure communities by altering their functional and taxonomic composition—even when species richness remains unchanged. Understanding which aspects of community structure are impacted by different resources and over which timescales will provide insight for management decisions and may also elucidate which measures can act as early warning indicators for subsequent changes in the community. Here, we take advantage of a long‐term factorial experiment to understand how grassland plant communities respond to a decade of nitrogen fertilization (14 g N·m−2·yr−1) and irrigation (25 mm water/week during the growing season). After 10 yr, fertilization and irrigation decreased species richness by 22% and 9%, while functional richness decreased by 31% and 41%. Abundance‐weighted functional distance between treatments and controls increased by 55% and 24%, respectively. We expected that abundance‐weighted measures would shift before presence–absence‐based measures, but found limited evidence for this. Instead, our results suggest that species gains, which can occur quickly because they require the addition of only one individual, may serve as early indicators for subsequent community restructuring in the opposite direction. Overall, both chronic nitrogen fertilization and irrigation tended to have gradual and increasing impacts on community structure, but the magnitude of these effects varied greatly depending on the aspect of community structure investigated. Further study will be needed to determine the extent to which our results can be generalized to other resources or sites in order to develop management strategies to maintain both taxonomic and functional trait diversity in the face of chronic resource changes

Clarifying the effect of biodiversity on productivity in natural ecosystems with longitudinal data and methods for causal inference

Abstract Causal effects of biodiversity on ecosystem functions can be estimated using experimental or observational designs — designs that pose a tradeoff between drawing credible causal inferences from correlations and drawing generalizable inferences. Here, we develop a design that reduces this tradeoff and revisits the question of how plant species diversity affects productivity. Our design leverages longitudinal data from 43 grasslands in 11 countries and approaches borrowed from fields outside of ecology to draw causal inferences from observational data. Contrary to many prior studies, we estimate that increases in plot-level species richness caused productivity to decline: a 10% increase in richness decreased productivity by 2.4%, 95% CI [−4.1, −0.74]. This contradiction stems from two sources. First, prior observational studies incompletely control for confounding factors. Second, most experiments plant fewer rare and non-native species than exist in nature. Although increases in native, dominant species increased productivity, increases in rare and non-native species decreased productivity, making the average effect negative in our study. By reducing the tradeoff between experimental and observational designs, our study demonstrates how observational studies can complement prior ecological experiments and inform future ones

Publisher Correction: Clarifying the effect of biodiversity on productivity in natural ecosystems with longitudinal data and methods for causal inference (Nature Communications, (2023), 14, 1, (2607), 10.1038/s41467-023-37194-5)

The original version of this Article contained errors in the Methods section ‘Target causal effect’, in which terms were omitted from the mathematical definitions of the causal effect and average causal effect. These sentences incorrectly read “The causal effect of a change in richness from R′ to R″ on productivity P in plot i is defined as [(R″) − (R′)], where Pi(R″) is the potential productivity outcome when R = R″ and P(R′) is the potential productivity outcome when R = R′ (R′ ≠ R″).” and “The average causal effect of a change in biodiversity from R′ to R″ across all plots is [(R″) − P(R′)], where E[·] is the expectation operator.”. The correct version states “[Pi(R′′) − Pi(R′)]” in place of “[(R″) − (R′)]”, “Pi (R′)” in place of “P (R′)”, and “E[Pi(R′′) − Pi(R′)]” in place of “[(R″) − P(R′)]”. This has been corrected in both the PDF and HTML versions of the Article

Species loss due to nutrient addition increases with spatial scale in global grasslands

The effects of altered nutrient supplies and herbivore density on species diversity vary with spatial scale, because coexistence mechanisms are scale dependent. This scale dependence may alter the shape of the species–area relationship (SAR), which can be described by changes in species richness (S) as a power function of the sample area (A): S = cAz, where c and z are constants. We analysed the effects of experimental manipulations of nutrient supply and herbivore density on species richness across a range of scales (0.01–75 m2) at 30 grasslands in 10 countries. We found that nutrient addition reduced the number of species that could co-occur locally, indicated by the SAR intercepts (log c), but did not affect the SAR slopes (z). As a result, proportional species loss due to nutrient enrichment was largely unchanged across sampling scales, whereas total species loss increased over threefold across our range of sampling scales.Fil: Seabloom, Eric W.. University of Minnesota; Estados UnidosFil: Batzer, Evan. University of California at Davis; Estados UnidosFil: Chase, Jonathan M.. German Centre For Integrative Biodiversity Research; AlemaniaFil: Stanley Harpole, W.. German Centre For Integrative Biodiversity Research; Alemania. Martin-universität Halle-wittenberg; Alemania. Helmholtz Zentrum Für Umweltforschung; AlemaniaFil: Adler, Peter B.. State University of Utah; Estados UnidosFil: Bagchi, Sumanta. Indian Institute Of Science; IndiaFil: Bakker, Jonathan. University of Washington; Estados UnidosFil: Barrio, Isabel C.. Agricultural University Of Iceland; IslandiaFil: Biederman, Lori. Iowa State University; Estados UnidosFil: Boughton, Elizabeth H.. Archbold Biological Station; Estados UnidosFil: Bugalho, Miguel N.. Universidade Nova de Lisboa; PortugalFil: Caldeira, Maria C.. Universidade Nova de Lisboa; PortugalFil: Catford, Jane A.. King's College London; Reino UnidoFil: Daleo, Pedro. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Eisenhauer, Nico. Universität Leipzig; Alemania. German Centre For Integrative Biodiversity Research; AlemaniaFil: Eskelinen, Anu. Helmholtz Zentrum Für Umweltforschung; Alemania. German Centre For Integrative Biodiversity Research; AlemaniaFil: Haider, Sylvia. Martin-universität Halle-wittenberg; Alemania. German Centre For Integrative Biodiversity Research; AlemaniaFil: Hallett, Lauren M.. University of Oregon; Estados UnidosFil: Svala Jónsdóttir, Ingibjörg. University of Iceland; IslandiaFil: Kimmel, Kaitlin. Johns Hopkins University; AlemaniaFil: Kuhlman, Marirose. Mpg Ranch; Estados UnidosFil: MacDougall, Andrew. University of Guelph; CanadáFil: Molina, Cecilia Denisse. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Moore, Joslin L.. Monash University; AustraliaFil: Morgan, John W.. La Trobe University; AustraliaFil: Muthukrishnan, Ranjan. Indiana University; Estados UnidosFil: Ohlert, Timothy. University of New Mexico; Estados UnidosFil: Risch, Anita C.. Swiss Federal Institute for Forest, Snow and Landscape Research WSL; SuizaFil: Roscher, Christiane. Helmholtz Zentrum Für Umweltforschung; Alemania. German Centre For Integrative Biodiversity Research; AlemaniaFil: Schütz, Martin. Swiss Federal Institute for Forest, Snow and Landscape Research WSL; SuizaFil: Sonnier, Grégory. Archbold Biological Station; Estados UnidosFil: Tognetti, Pedro Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Virtanen, Risto. University of Oulu; IslandiaFil: Wilfahrt, Peter A.. University of Minnesota; Estados UnidosFil: Borer, Elizabeth. University of Minnesota; Estados Unido

Extreme drought impacts have been underestimated in grasslands and shrublands globally.

Climate change is increasing the frequency and severity of short-term (~1 y) drought events-the most common duration of drought-globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function-aboveground net primary production (ANPP)-was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought

Species loss due to nutrient addition increases with spatial scale in global grasslands

Abstract The effects of altered nutrient supplies and herbivore density on species diversity vary with spatial scale, because coexistence mechanisms are scale dependent. This scale dependence may alter the shape of the species–area relationship (SAR), which can be described by changes in species richness (S) as a power function of the sample area (A): S = cAz, where c and z are constants. We analysed the effects of experimental manipulations of nutrient supply and herbivore density on species richness across a range of scales (0.01–75 m²) at 30 grasslands in 10 countries. We found that nutrient addition reduced the number of species that could co-occur locally, indicated by the SAR intercepts (log c), but did not affect the SAR slopes (z). As a result, proportional species loss due to nutrient enrichment was largely unchanged across sampling scales, whereas total species loss increased over threefold across our range of sampling scales

Extreme drought impacts have been underestimated in grasslands and shrublands globally

Altres Ajuts: Fundación Ramón Areces grant CIVP20A6621Climate change is increasing the frequency and severity of short-term (~1 y) drought events-the most common duration of drought-globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function-aboveground net primary production (ANPP)-was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought

Extreme drought impacts have been underestimated in grasslands and shrublands globally

Climate change is increasing the frequency and severity of short-term (~1 y) drought events—the most common duration of drought—globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function—aboveground net primary production (ANPP)—was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought