1
|
Higgins SI, Banerjee S, Baudena M, Bowman DMJS, Conradi T, Couteron P, Kruger LM, O'Hara RB, Williamson GJ. Reassessing the alternative ecosystem states proposition in the African savanna-forest domain. THE NEW PHYTOLOGIST 2024; 243:1660-1669. [PMID: 38982706 DOI: 10.1111/nph.19911] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2024] [Accepted: 05/26/2024] [Indexed: 07/11/2024]
Abstract
Ecologists are being challenged to predict how ecosystems will respond to climate changes. According to the Multi-Colored World (MCW) hypothesis, climate impacts may not manifest because consumers such as fire and herbivory can override the influence of climate on ecosystem state. One MCW interpretation is that climate determinism fails because alternative ecosystem states (AES) are possible at some locations in climate space. We evaluated theoretical and empirical evidence for the proposition that forest and savanna are AES in Africa. We found that maps which infer where AES zones are located were contradictory. Moreover, data from longitudinal and experimental studies provide inconclusive evidence for AES. That is, although the forest-savanna AES proposition is theoretically sound, the existing evidence is not yet convincing. We conclude by making the case that the AES proposition has such fundamental consequences for designing management actions to mitigate and adapt to climate change in the savanna-forest domain that it needs a more robust evidence base before it is used to prescribe management actions.
Collapse
Affiliation(s)
- Steven I Higgins
- Plant Ecology, University of Bayreuth, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Swarnendu Banerjee
- Dutch Institute for Emergent Phenomena, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, PO Box 94240, 1090 GE, Amsterdam, the Netherlands
- Copernicus Institute of Sustainable Development, Utrecht University, 3508 TC, Utrecht, the Netherlands
| | - Mara Baudena
- National Research Council, Institute of Atmospheric Sciences and Climate (CNR-ISAC), 10133, Torino, Italy
- National Biodiversity Future Center (NBFC), 90133, Palermo, Italy
| | - David M J S Bowman
- Fire, Centre, School of Natural Sciences, University of Tasmania, 7005 Sandy Bay, Hobart, Tas., Australia
| | - Timo Conradi
- Plant Ecology, University of Bayreuth, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Pierre Couteron
- AMAP, University of Montpellier, IRD, CNRS, INRAE, CIRAD, 34394, Montpellier, France
| | - Laurence M Kruger
- Organization for Tropical Studies, PO Box 33, Skukuza, 1350, South Africa
| | - Robert B O'Hara
- Department of Mathematical Sciences, Norwegian University of Science and Technology, Trondheim, N-7491, Norway
| | - Grant J Williamson
- Fire, Centre, School of Natural Sciences, University of Tasmania, 7005 Sandy Bay, Hobart, Tas., Australia
| |
Collapse
|
2
|
Biancari L, Aguiar MR, Saiz H, Gross N, Le Bagousse-Pinguet Y, Eldridge DJ, Maestre FT. Upper boundary on tree cover at global drylands. THE NEW PHYTOLOGIST 2024; 242:836-840. [PMID: 38362948 DOI: 10.1111/nph.19598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 01/28/2024] [Indexed: 02/17/2024]
Affiliation(s)
- Lucio Biancari
- IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, CONICET, Buenos Aires, C1417DSE, Argentina
- Cátedra de Ecología, Departamento de Recursos Naturales y Ambiente, Facultad de Agronomía, UBA, Buenos Aires, C1417DSE, Argentina
| | - Martín R Aguiar
- IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, CONICET, Buenos Aires, C1417DSE, Argentina
- Cátedra de Ecología, Departamento de Recursos Naturales y Ambiente, Facultad de Agronomía, UBA, Buenos Aires, C1417DSE, Argentina
| | - Hugo Saiz
- Departamento de Ciencias Agrarias y Medio Natural, Escuela Politécnica Superior, Instituto Universitario de Investigación en Ciencias Ambientales de Aragón (IUCA), Universidad de Zaragoza, Huesca, 50009, Spain
- Institute of Plant Sciences, University of Bern, Bern, 3013, Switzerland
| | - Nicolas Gross
- Université Clermont Auvergne, l'Institut national de recherche pour l'agriculture, l'alimentation et l'environnement, VetAgro Sup, Unité Mixte de Recherche 212 Ecosystème Prairial, Clermont-Ferrand, F-63000, France
| | | | - David J Eldridge
- Centre for Ecosystem Science, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia
| | - Fernando T Maestre
- Instituto Multidisciplinar para el Estudio del Medio "Ramon Margalef", Universidad de Alicante, Carretera de San Vicente del Raspeig s/n, Alicante, 03690, Spain
- Departamento de Ecología, Universidad de Alicante, Carretera de San Vicente del Raspeig s/n, Alicante, 03690, Spain
| |
Collapse
|
3
|
O'Keefe K, Nippert JB, Keen RM, McCulloh KA. Contrasting shrub and grass hydraulic responses to experimental drought. Oecologia 2024; 204:931-941. [PMID: 38607552 DOI: 10.1007/s00442-024-05543-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Accepted: 03/07/2024] [Indexed: 04/13/2024]
Abstract
Whole-plant hydraulics provide important information about responses to water limitation and can be used to understand how plant communities may change in a drier climate when measured on multiple species. Here, we measured above- and belowground hydraulic traits in Cornus drummondii, an encroaching shrub within North American tallgrass prairies, and Andropogon gerardii, a dominant C4 grass, to assess the potential hydraulic responses to future drought as this region undergoes woody expansion. Shelters that reduced precipitation by 50% and 0% were built over shrubs and grasses growing in sites that are burned at 1-year and 4-year frequencies. We then measured aboveground (Kshoot), belowground (Kroot), and whole-plant maximum hydraulic conductance (Kplant) in C. drummondii and Kroot in A. gerardii. We also measured vulnerability to embolism (P50) in C. drummondii stems. Overall, we show that: (1) A. gerardii had substantially greater Kroot than C. drummondii; (2) belowground hydraulic functioning was linked with aboveground processes; (3) above- and belowground C. drummondii hydraulics were not negatively impacted by the rainfall reductions imposed here. These results suggest that a multi-year drought will not ameliorate rates of woody expansion and highlight key differences in aboveground and belowground hydraulics for dominant species within the same ecosystem.
Collapse
Affiliation(s)
- Kimberly O'Keefe
- Department of Biological Sciences, St. Edward's University, Austin, TX, 78704, USA.
- Department of Botany, University of Wisconsin, Madison, WI, 53706, USA.
| | - Jesse B Nippert
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA
| | - Rachel M Keen
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA
- Department of Ecology and Evolutionary Biology, Kansas Biological Survey, The University of Kansas, Lawrence, KS, 66047, USA
| | | |
Collapse
|
4
|
Wigley BJ, Coetsee C, February EC, Dobelmann S, Higgins SI. Will trees or grasses profit from changing rainfall regimes in savannas? THE NEW PHYTOLOGIST 2024; 241:2379-2394. [PMID: 38245858 DOI: 10.1111/nph.19538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Accepted: 12/19/2023] [Indexed: 01/22/2024]
Abstract
Increasing rainfall variability is widely expected under future climate change scenarios. How will savanna trees and grasses be affected by growing season dry spells and altered seasonality and how tightly coupled are tree-grass phenologies with rainfall? We measured tree and grass responses to growing season dry spells and dry season rainfall. We also tested whether the phenologies of 17 deciduous woody species and the Soil Adjusted Vegetation Index of grasses were related to rainfall between 2019 and 2023. Tree and grass growth was significantly reduced during growing season dry spells. Tree growth was strongly related to growing season soil water potentials and limited to the wet season. Grasses can rapidly recover after growing season dry spells and grass evapotranspiration was significantly related to soil water potentials in both the wet and dry seasons. Tree leaf flushing commenced before the rainfall onset date with little subsequent leaf flushing. Grasses grew when moisture became available regardless of season. Our findings suggest that increased dry spell length and frequency in the growing season may slow down tree growth in some savannas, which together with longer growing seasons may allow grasses an advantage over C3 plants that are advantaged by rising CO2 levels.
Collapse
Affiliation(s)
- Benjamin J Wigley
- Plant Ecology, University of Bayreuth, Universitaetsstrasse 30, 95447, Bayreuth, Germany
- School of Natural Resource Management, Nelson Mandela University, George Campus, George, 6530, South Africa
- Savanna Node, Scientific Services, SANParks, Skukuza, 1350, South Africa
| | - Corli Coetsee
- School of Natural Resource Management, Nelson Mandela University, George Campus, George, 6530, South Africa
- Savanna Node, Scientific Services, SANParks, Skukuza, 1350, South Africa
| | - Edmund C February
- Department of Biological Sciences, University of Cape Town, HW Pearson Building, University Ave N, Rondebosch, Cape Town, 7701, South Africa
| | - Svenja Dobelmann
- Department of Remote Sensing, Institute of Geography, Julius-Maximilians-Universitaet Wuerzburg, 97074, Wuerzburg, Germany
| | - Steven I Higgins
- Plant Ecology, University of Bayreuth, Universitaetsstrasse 30, 95447, Bayreuth, Germany
| |
Collapse
|
5
|
Wilcox KR, Chen A, Avolio ML, Butler EE, Collins S, Fisher R, Keenan T, Kiang NY, Knapp AK, Koerner SE, Kueppers L, Liang G, Lieungh E, Loik M, Luo Y, Poulter B, Reich P, Renwick K, Smith MD, Walker A, Weng E, Komatsu KJ. Accounting for herbaceous communities in process-based models will advance our understanding of "grassy" ecosystems. GLOBAL CHANGE BIOLOGY 2023; 29:6453-6477. [PMID: 37814910 DOI: 10.1111/gcb.16950] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Accepted: 06/01/2023] [Indexed: 10/11/2023]
Abstract
Grassland and other herbaceous communities cover significant portions of Earth's terrestrial surface and provide many critical services, such as carbon sequestration, wildlife habitat, and food production. Forecasts of global change impacts on these services will require predictive tools, such as process-based dynamic vegetation models. Yet, model representation of herbaceous communities and ecosystems lags substantially behind that of tree communities and forests. The limited representation of herbaceous communities within models arises from two important knowledge gaps: first, our empirical understanding of the principles governing herbaceous vegetation dynamics is either incomplete or does not provide mechanistic information necessary to drive herbaceous community processes with models; second, current model structure and parameterization of grass and other herbaceous plant functional types limits the ability of models to predict outcomes of competition and growth for herbaceous vegetation. In this review, we provide direction for addressing these gaps by: (1) presenting a brief history of how vegetation dynamics have been developed and incorporated into earth system models, (2) reporting on a model simulation activity to evaluate current model capability to represent herbaceous vegetation dynamics and ecosystem function, and (3) detailing several ecological properties and phenomena that should be a focus for both empiricists and modelers to improve representation of herbaceous vegetation in models. Together, empiricists and modelers can improve representation of herbaceous ecosystem processes within models. In so doing, we will greatly enhance our ability to forecast future states of the earth system, which is of high importance given the rapid rate of environmental change on our planet.
Collapse
Affiliation(s)
- Kevin R Wilcox
- University of North Carolina Greensboro, Greensboro, North Carolina, USA
- University of Wyoming, Laramie, Wyoming, USA
| | - Anping Chen
- Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado, USA
| | - Meghan L Avolio
- Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland, USA
| | - Ethan E Butler
- Department of Forest Resources, University of Minnesota, St. Paul, Minnesota, USA
| | - Scott Collins
- Department of Biology, University of New Mexico, Albuquerque, New Mexico, USA
| | - Rosie Fisher
- CICERO Centre for International Cimate Research, Forskningsparken, Oslo, Norway
| | - Trevor Keenan
- Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Nancy Y Kiang
- NASA Goddard Institute for Space Studies, New York, New York, USA
| | - Alan K Knapp
- Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado, USA
| | - Sally E Koerner
- University of North Carolina Greensboro, Greensboro, North Carolina, USA
| | - Lara Kueppers
- Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Guopeng Liang
- Department of Forest Resources, University of Minnesota, St. Paul, Minnesota, USA
| | - Eva Lieungh
- Natural History Museum, University of Oslo, Oslo, Norway
| | - Michael Loik
- Department of Environmental Studies, University of California, Santa Cruz, California, USA
| | - Yiqi Luo
- School of Integrative Plant Science, Cornell University, Ithaca, New York, USA
| | - Ben Poulter
- Biospheric Sciences Lab, NASA GSFC, Greenbelt, Maryland, USA
| | - Peter Reich
- Department of Forest Resources, University of Minnesota, St. Paul, Minnesota, USA
- Hawkesbury Institute for the Environment, Western Sydney University, Penrith, New South Wales, Australia
| | | | - Melinda D Smith
- Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado, USA
| | - Anthony Walker
- Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Ensheng Weng
- NASA Goddard Institute for Space Studies, New York, New York, USA
- Center for Climate Systems Research, Columbia University, New York, New York, USA
| | - Kimberly J Komatsu
- University of North Carolina Greensboro, Greensboro, North Carolina, USA
| |
Collapse
|
6
|
Belovitch MW, NeSmith JE, Nippert JB, Holdo RM. African savanna grasses outperform trees across the full spectrum of soil moisture availability. THE NEW PHYTOLOGIST 2023; 239:66-74. [PMID: 36967595 DOI: 10.1111/nph.18909] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 03/20/2023] [Indexed: 06/02/2023]
Abstract
Models of tree-grass coexistence in savannas make different assumptions about the relative performance of trees and grasses under wet vs dry conditions. We quantified transpiration and drought tolerance traits in 26 tree and 19 grass species from the African savanna biome across a gradient of soil water potentials to test for a trade-off between water use under wet conditions and drought tolerance. We measured whole-plant hourly transpiration in a growth chamber and quantified drought tolerance using leaf osmotic potential (Ψosm ). We also quantified whole-plant water-use efficiency (WUE) and relative growth rate (RGR) under well-watered conditions. Grasses transpired twice as much as trees on a leaf-mass basis across all soil water potentials. Grasses also had a lower Ψosm than trees, indicating higher drought tolerance in the former. Higher grass transpiration and WUE combined to largely explain the threefold RGR advantage in grasses. Our results suggest that grasses outperform trees under a wide range of conditions, and that there is no evidence for a trade-off in water-use patterns in wet vs dry soils. This work will help inform mechanistic models of water use in savanna ecosystems, providing much-needed whole-plant parameter estimates for African species.
Collapse
Affiliation(s)
| | | | - Jesse B Nippert
- Division of Biology, Kansas State University, Manhattan, KS, 66506, USA
| | - Ricardo M Holdo
- Odum School of Ecology, University of Georgia, Athens, GA, 30601, USA
- School of Animal Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, 2050, South Africa
| |
Collapse
|