@article {131927, title = {Compositional variation in grassland plant communities}, journal = {ECOSPHERE }, volume = {14}, year = {2023}, month = {06/2023}, pages = {e4542}, abstract = {

Human activities are altering ecological communities around the globe. Understanding the implications of these changes requires that we consider the composition of those communities. However, composition can be summarized by many metrics which in turn are influenced by different ecological processes. For example, incidence-based metrics strongly reflect species gains or losses, while abundance-based metrics are minimally affected by changes in the abundance of small or uncommon species. Furthermore, metrics might be correlated with different predictors. We used a globally distributed experiment to examine variation in species composition within 60 grasslands on six continents. Each site had an identical experimental and sampling design: 24 plots x 4 years. We expressed compositional variation within each site-not across sites-using abundance- and incidence-based metrics of the magnitude of dissimilarity (Bray-Curtis and Sorensen, respectively), abundance- and incidence-based measures of the relative importance of replacement (balanced variation and species turnover, respectively), and species richness at two scales (per plot-year [alpha] and per site [gamma]). Average compositional variation among all plot-years at a site was high and similar to spatial variation among plots in the pretreatment year, but lower among years in untreated plots. For both types of metrics, most variation was due to replacement rather than nestedness. Differences among sites in overall within-site compositional variation were related to several predictors. Environmental heterogeneity (expressed as the CV of total aboveground plant biomass in unfertilized plots of the site) was an important predictor for most metrics. Biomass production was a predictor of species turnover and of alpha diversity but not of other metrics. Continentality (measured as annual temperature range) was a strong predictor of Sorensen dissimilarity. Metrics of compositional variation are moderately correlated: knowing the magnitude of dissimilarity at a site provides little insight into whether the variation is driven by replacement processes. Overall, our understanding of compositional variation at a site is enhanced by considering multiple metrics simultaneously. Monitoring programs that explicitly incorporate these implications, both when designing sampling strategies and analyzing data, will have a stronger ability to understand the compositional variation of systems and to quantify the impacts of human activities.

}, doi = {10.1002/ecs2.4542}, author = {Bakker, Jonathan D. and Price, Jodi N. and Henning, Jeremiah A. and .. and Sankaran, M and al et} } @article {128076, title = {Overcoming the coupled climate and biodiversity crises and their societal impacts.}, journal = {Science}, volume = {380}, year = {2023}, month = {2023 Apr 21}, pages = {eabl4881}, abstract = {

Earth{\textquoteright}s biodiversity and human societies face pollution, overconsumption of natural resources, urbanization, demographic shifts, social and economic inequalities, and habitat loss, many of which are exacerbated by climate change. Here, we review links among climate, biodiversity, and society and develop a roadmap toward sustainability. These include limiting warming to 1.5{\textdegree}C and effectively conserving and restoring functional ecosystems on 30 to 50\% of land, freshwater, and ocean "scapes." We envision a mosaic of interconnected protected and shared spaces, including intensively used spaces, to strengthen self-sustaining biodiversity, the capacity of people and nature to adapt to and mitigate climate change, and nature{\textquoteright}s contributions to people. Fostering interlinked human, ecosystem, and planetary health for a livable future urgently requires bold implementation of transformative policy interventions through interconnected institutions, governance, and social systems from local to global levels.

}, keywords = {Biodiversity, Climate Change, Conservation of Natural Resources, Ecosystem, Fresh Water, Humans, Urbanization}, issn = {1095-9203}, doi = {10.1126/science.abl4881}, author = {P{\"o}rtner, H-O and Scholes, R J and Arneth, A and Barnes, D K A and Burrows, M T and Diamond, S E and Duarte, C M and Kiessling, W and Leadley, P and Managi, S and McElwee, P and Midgley, G and Ngo, H T and Obura, D and Pascual, U and Sankaran, M and Shin, Y J and Val, A L} } @article {77444, title = {Frost maintains forests and grasslands as alternate states in a montane tropical forest-grassland mosaic; but alien tree invasion and warming can disrupt this balance}, journal = {JOURNAL OF ECOLOGY}, volume = {108}, year = {2020}, month = {01/2020}, pages = {122-132}, abstract = {

1. Forest-grassland mosaics, with abrupt boundaries between the two vegetation types, occur across the globe. Fire and herbivory are widely considered primary drivers that maintain these mosaics by limiting tree establishment in grasslands, while edaphic factors and frosts are generally considered to be secondary factors that reinforce these effects. However, the relative importance of these drivers likely varies across systems. In particular, although frost is known to occur in many montane tropical mosaics, experimental evidence for its role as a driving factor is limited.

2. We used replicated in situ transplant and warming experiments to examine the role of microclimate (frost and freezing temperatures) and soil in influencing germination and seedling survival of both native forest trees and alien invasive Acacia trees in grasslands of a tropical montane forest-grassland mosaic in the Western Ghats of southern India.

3. Seed germination of both native and alien tree species was higher in grasslands regardless of soil type, indicating that germination was not the limiting stage to tree establishment. However, irrespective of soil type, native seedlings in grasslands incurred high mortality following winter frosts and freezing temperatures relative to native seedlings in adjoining forests where freezing temperatures did not occur. Seedling survival through the tropical winter was thus a primary limitation to native tree establishment in grasslands. In contrast, alien Acacia seedlings in grasslands incurred much lower levels of winter mortality. Experimental night-time warming in grasslands significantly enhanced over-winter survival of all tree seedlings, but increases were much greater for alien Acacia than for native tree seedlings.

4. Synthesis. Our results provide evidence for a primary role for frost and freezing temperatures in limiting tree establishment in grasslands of this tropical montane forest-grassland mosaic. Future increases in temperature are likely to release trees from this limitation and favour tree expansion into grasslands, with rates of expansion of non-native Acacia likely to be much greater than that of native trees. We suggest that studies of frost limitation to plant establishment are needed across a range of tropical ecosystems to re-evaluate the general importance of frost as a driver of vegetation transitions in the tropics.

}, doi = {10.1111/1365-2745.13239}, author = {Joshi, AA and Ratnam, J and Sankaran, M} } @article {85905, title = {Nutrients cause grassland biomass to outpace herbivory.}, journal = {Nat Commun}, volume = {11}, year = {2020}, month = {2020 11 27}, pages = {6036}, abstract = {

Human activities are transforming grassland biomass via changing climate, elemental nutrients, and herbivory. Theory predicts that food-limited herbivores will consume any additional biomass stimulated by nutrient inputs ({\textquoteright}consumer-controlled{\textquoteright}). Alternatively, nutrient supply is predicted to increase biomass where herbivores alter community composition or are limited by factors other than food ({\textquoteright}resource-controlled{\textquoteright}). Using an experiment replicated in 58 grasslands spanning six continents, we show that nutrient addition and vertebrate herbivore exclusion each caused sustained increases in aboveground live biomass over a decade, but consumer control was weak. However, at sites with high vertebrate grazing intensity or domestic livestock, herbivores consumed the additional fertilization-induced biomass, supporting the consumer-controlled prediction. Herbivores most effectively reduced the additional live biomass at sites with low precipitation or high ambient soil nitrogen. Overall, these experimental results suggest that grassland biomass will outstrip wild herbivore control as human activities increase elemental nutrient supply, with widespread consequences for grazing and fire risk.

}, issn = {2041-1723}, doi = {10.1038/s41467-020-19870-y}, author = {Borer, E T and Harpole, W S and Adler, P B and Arnillas, C A and Bugalho, M N and Cadotte, M W and Caldeira, M C and Campana, S and Dickman, C R and Dickson, T L and Donohue, I and Eskelinen, A and Firn, J L and Graff, P and Gruner, D S and Heckman, R W and Koltz, A M and Komatsu, K J and Lannes, L S and MacDougall, A S and Martina, J P and Moore, J L and Mortensen, B and Ochoa-Hueso, R and Olde Venterink, H and Power, S A and Price, J N and Risch, A C and Sankaran, M and Sch{\"u}tz, M and Sitters, J and Stevens, C J and Virtanen, R and Wilfahrt, P A and Seabloom, E W} } @article {62920, title = {Ants, fire, and bark traits affect how African savanna trees recover following damage}, journal = {BIOTROPICA}, year = {2019}, month = {07/2019}, abstract = {

Bark damage resulting from elephant feeding is common in African savanna trees with subsequent interactions with fire, insects, and other pathogens often resulting in tree mortality. Yet, surprisingly little is known about how savanna trees respond to bark damage. We addressed this by investigating how the inner bark of marula (Sclerocarya birrea), a widespread tree species favoured by elephants, recovers after bark damage. We used a long-term fire experiment in the Kruger National Park to measure bark recovery with and without fire. At 24\ months post-damage, mean wound closure was 98, 92, and 72\%, respectively, in annual and biennial burns and fire-exclusion treatments. Fire exclusion resulted in higher rates of ant colonization of bark wounds, and such ant colonization resulted in significantly lower bark recovery. We also investigated how ten common savanna tree species respond to bark damage and tested for relationships between bark damage, bark recovery, and bark traits while accounting for phylogeny. We found phylogenetic signal in bark dry matter content, bark N and bark P, but not in bark thickness. Bark recovery and damage was highest in species which had thick moist inner bark and low wood densities (Anacardiaceae), intermediate in species which had moderate inner bark thickness and wood densities (Fabaceae) and lowest in species which had thin inner bark and high wood densities (Combretaceae). Elephants prefer species with thick, moist inner bark, traits that also appear to result in faster recovery rates.

}, doi = {10.1111/btp.12683}, author = {Wigley, BJ and Coetsee, C and Kruger, LM and Ratnam, J and Sankaran, M} } @article {53175, title = {Dry-forest tree species with large seeds and low stem specific density show greater survival under drought}, journal = {JOURNAL OF TROPICAL ECOLOGY}, volume = {35}, year = {2019}, month = {01/2019}, pages = {26-33 }, author = {Krishnan, L and Barua, D and Sankaran, M} } @article {67829, title = {Soil net nitrogen mineralisation across global grasslands.}, journal = {Nat Commun}, volume = {10}, year = {2019}, month = {2019 Oct 31}, pages = {4981}, abstract = {

Soil nitrogen mineralisation (N), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net N) varies with soil properties and climate. However, because most global-scale assessments of net N are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net N across 30 grasslands worldwide. We find that realised N is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential N only weakly correlates with realised N, but contributes to explain realised net N when combined with soil and climatic variables. We provide novel insights of global realised soil net N and show that potential soil net N data available in the literature could be parameterised with soil and climate data to better predict realised N.

}, issn = {2041-1723}, doi = {10.1038/s41467-019-12948-2}, author = {Risch, A C and Zimmermann, S and Ochoa-Hueso, R and Sch{\"u}tz, M and Frey, B and Firn, J L and Fay, P A and Hagedorn, F and Borer, E T and Seabloom, E W and Harpole, W S and Knops, J M H and McCulley, R L and Broadbent, A A D and Stevens, C J and Silveira, M L and Adler, P B and B{\'a}ez, S and Biederman, L A and Blair, J M and Brown, C S and Caldeira, M C and Collins, S L and Daleo, P and di Virgilio, A and Ebeling, A and Eisenhauer, N and Esch, E and Eskelinen, A and Hagenah, N and Hautier, Y and Kirkman, K P and MacDougall, A S and Moore, J L and Power, S A and Prober, S M and Roscher, C and Sankaran, M and Siebert, J and Speziale, K L and Tognetti, P M and Virtanen, R and Yahdjian, L and Moser, B} } @article {66083, title = {Strong but opposing effects of associational resistance and susceptibility on defense phenotype in an African savanna plant}, journal = {OIKOS}, year = {2019}, month = {08/2019}, abstract = {

The susceptibility of plants to herbivores can be strongly influenced by the identity, morphology and palatability of neighboring plants. While the defensive traits of neighbors often determine the mechanism and strength of associational resistance and susceptibility, the effect of neighbors on plant defense phenotype remains poorly understood. We used field surveys and a prickle-removal experiment in a semi-arid Kenyan savanna to evaluate the efficacy of physical defenses against large mammalian herbivores in a common understory plant, Solanum campylacanthum. We then quantified the respective effects of spinescent Acacia trees and short-statured grasses on browsing damage and prickle density in S. campylacanthum. We paired measurements of prickle density beneath and outside tree canopies with long-term herbivore-exclusion experiments to evaluate whether associational resistance reduced defense investment by decreasing browsing damage. Likewise, we compared defense phenotype within and outside pre-existing and experimentally created clearings to determine whether grass neighbors increased defense investment via associational susceptibility. Removing prickles increased the frequency of browsing by ~25\%, and surveys of herbivory damage on defended leaves suggested that herbivores tended to avoid prickles. As predicted, associational resistance and susceptibility had opposing effects on plant phenotype: individuals growing beneath Acacia canopies (or, analogously, within large-herbivore exclosures) had a significantly lower proportion of their leaves browsed and produced ~ 70{\textendash}80\% fewer prickles than those outside refuges, whereas plants in grass-dominated clearings were more heavily browsed and produced nearly twice as many prickles as plants outside clearings. Our results demonstrate that associational resistance and susceptibility have strong, but opposing, effects on plant defense phenotype, and that variable herbivore damage is a major source of intraspecific variation in defense phenotype in this system.

}, doi = {10.1111/oik.06644}, author = {Coverdale, TC and McGeary, IJ and O{\textquoteright}Connell, RD and Palmer, TM and Goheen, JR and Sankaran, M and Augustine, DJ and Ford, AT and Pringle, RM} } @article {36271, title = {Nitrogen fixation ability explains leaf chemistry and arbuscular mycorrhizal responses to fertilization }, journal = {PLANT ECOLOGY }, volume = {219}, year = {2018}, month = {04/2018}, pages = {391-401 }, doi = {10.1007/s11258-018-0803-9 }, author = {Tiruvaimozhi, YV and Varma, V and Sankaran, M} }