1
|
Mtsetfwa FP, Kruger L, McCleery RA. Climate change decouples dominant tree species in African savannas. Sci Rep 2023; 13:7619. [PMID: 37165034 PMCID: PMC10172338 DOI: 10.1038/s41598-023-34550-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Accepted: 05/03/2023] [Indexed: 05/12/2023] Open
Abstract
To understand how two dominant African savanna trees will continue to respond to climate changes, we examined their regeneration niche and adult tree distributions. Specifically, we wanted to (1) determine if distributional patterns were shifting, (2) predict future distributions under different climate change scenarios and (3) evaluate the realism of predicted future distributions. We randomly placed 40 grids into 6 strata across a climate gradient in the kingdom of Eswatini. Within these grids, we sampled adult and seedling marula (Scelerocarya birrea) and knobthorn (Senegalia nigrecens) trees and used the data to model their abundance. Next, we quantified shifts in distributional patterns (e.g., expansion or contraction) by measuring the current and projected areas of overlap between seedling and adult trees. Finally, we predicted future distributions of abundance based on predicted climate conditions. We found knobthorn seedlings within a small portion of the adult distribution, suggesting it was unlikely to track climate changes. Alternatively, finding marula seedlings on and beyond one edge of the adult distribution, suggested its range would shift toward cooler climates. Predicted future distributions suggest suitable climate for both species would transition out of savannas and into grasslands. Future projections (2041-2070) appeared consistent with observed distributions of marula, but knobthorn predictions were unrealistic given the lack of evidence for regeneration outside of its current range. The idiosyncratic responses of these species to climate change are likely to decouple these keystone structures in the coming decades and are likely to have considerable cascading effects including the potential rearrangement of faunal communities.
Collapse
Affiliation(s)
- Fezile P Mtsetfwa
- Department of Wildlife Ecology and Conservation, School of Natural Resource and Environment, University of Florida, Gainesville, FL, USA
- School of Animal Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Laurence Kruger
- Organisation for Tropical Studies, Skukuza, South Africa
- Biology Department, University of Cape Town, Cape Town, South Africa
| | - Robert A McCleery
- Department of Wildlife Ecology and Conservation, School of Natural Resource and Environment, University of Florida, Gainesville, FL, USA.
| |
Collapse
|
2
|
Donaldson JE, Holdo R, Sarakikya J, Anderson TM. Fire, grazers, and browsers interact with grass competition to determine tree establishment in an African savanna. Ecology 2022; 103:e3715. [PMID: 35388482 DOI: 10.1002/ecy.3715] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Accepted: 02/10/2022] [Indexed: 11/11/2022]
Abstract
In savanna ecosystems, fire and herbivory alter the competitive relationship between trees and grasses. Mechanistically, grazing herbivores favor trees by removing grass, which reduces tree-grass competition and limits fire. Conversely, browsing herbivores consume trees and limit their recovery from fire. Herbivore feeding decisions are in turn shaped by risk-resource trade-offs that potentially determine the spatial patterns of herbivory. Identifying the dominant mechanistic pathways by which fire and herbivores control tree cover remains challenging, but is essential for understanding savanna dynamics. We used an experiment in the Serengeti ecosystem and a simple simulation driven by experimental results to address two main aims: (1) determine the importance of direct and indirect effects of grass, fire and herbivory on seedling establishment; and (2) establish whether predators determine the spatial pattern of successful seedling establishment via effects on mesoherbivore distribution. We transplanted tree seedlings into plots with a factorial combination of grass and herbivores (present/absent) across a lion kill-risk gradient in the Serengeti, burning half of the plots near the end of the experiment. Ungrazed grass limited tree seedling survival directly via competition, indirectly via fire, and by slowing seedling growth, which drove higher seedling mortality during fires. These effects restricted seedling establishment to below 18% and, in conjunction with browsing, resulted in seedling establishment dropping below 5%. In the absence of browsing and fire, grazing drove a 7.5-fold increase in seedling establishment. Lion predation risk had no observable impact on herbivore effects on seedling establishment. The severe negative effects of grass on seedling mortality suggests that regional patterns of tree cover and fire may overestimate the role of fire in limiting tree cover, with regular fires representing a proxy for the competitive effects of grass.
Collapse
Affiliation(s)
| | - Ricardo Holdo
- Odum School of Ecology, University of Georgia, Athens, GA, USA
| | | | - T Michael Anderson
- Department of Biology, Wake Forest University, Winston Salem, North Carolina, USA
| |
Collapse
|
3
|
Ngarega BK, Masocha VF, Schneider H. Forecasting the effects of bioclimatic characteristics and climate change on the potential distribution of Colophospermum mopane in southern Africa using Maximum Entropy (Maxent). ECOL INFORM 2021. [DOI: 10.1016/j.ecoinf.2021.101419] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
|
4
|
Stevens N. What shapes the range edge of a dominant African savanna tree, Colophospermum mopane? A demographic approach. Ecol Evol 2021; 11:3726-3736. [PMID: 33976771 PMCID: PMC8093671 DOI: 10.1002/ece3.7377] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 01/25/2021] [Accepted: 02/18/2021] [Indexed: 11/11/2022] Open
Abstract
Climate is widely assumed to be the primary process that limits the distribution ranges of plants. Yet, savannas have vegetation not at equilibrium with climate, instead its structure and function are shaped by interactions between fire, herbivory, climate, and vegetation. I use the rich literature of a dominant African savanna woody plant, Colophospermum mopane, to demonstrate that climate and disturbance interact with each demographic stage to shape this species range limits. This synthesis highlights that climate-based predictions for the range of C. mopane inadequately represents the processes that shape its distribution. Instead, seed bank depletion and rainfall limitation create a demographic bottleneck at the early seedling stage. The legacy of top-kill from disturbance changes tree stand architecture causing a critical limitation in seed supply. Exposure to top-kill at all demographic stages causes a vigorous resprouting response and shifts tree architecture from that of 1-2 stemmed tall trees to that of a short multi-stemmed shrub. The shorter, multi-stemmed shrubs are below the height threshold (4 m) at which they can produce seeds, resulting in shrub-dominated landscapes that are effectively sterile. This effect is likely most pronounced at the range edge where top-kill-inducing disturbances increase in frequency. The proposed mechanistic, demographic-based understanding of C. mopane's range limits highlights the complexity of processes that interact to shape its range edges. This insight serves as a conceptual model for understanding the determinants of range limits of other dominant woody savannas species living in disturbance limited ecosystems.
Collapse
Affiliation(s)
- Nicola Stevens
- Environmental Change InstituteSchool of Geography and the EnvironmentUniversity of OxfordOxfordUK
| |
Collapse
|
5
|
Factors affecting survival of seedling of Afzelia africana, a threatened tropical timber species in West Africa. Trop Ecol 2021. [DOI: 10.1007/s42965-021-00160-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
|
6
|
Lenton TM, Kohler TA, Marquet PA, Boyle RA, Crucifix M, Wilkinson DM, Scheffer M. Survival of the Systems. Trends Ecol Evol 2021; 36:333-344. [PMID: 33414020 DOI: 10.1016/j.tree.2020.12.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 11/26/2020] [Accepted: 12/04/2020] [Indexed: 02/07/2023]
Abstract
Since Darwin, individuals and more recently genes, have been the focus of evolutionary thinking. The idea that selection operates on nonreproducing, higher-level systems including ecosystems or societies, has met with scepticism. But research emphasising that natural selection can be based solely on differential persistence invites reconsideration of their evolution. Self-perpetuating feedback cycles involving biotic as well as abiotic components are critical to determining persistence. Evolution of autocatalytic networks of molecules is well studied, but the principles hold for any 'self-perpetuating' system. Ecosystem examples include coral reefs, rainforests, and savannahs. Societal examples include agricultural systems, dominant belief systems, and economies. Persistence-based selection of feedbacks can help us understand how ecological and societal systems survive or fail in a changing world.
Collapse
Affiliation(s)
- Timothy M Lenton
- Global Systems Institute, University of Exeter, Exeter, EX4 4QE, UK.
| | - Timothy A Kohler
- Department of Anthropology, Washington State University, Pullman, WA 99164-4910, USA; Santa Fe Institute, Santa Fe, NM 87501, USA; Crow Canyon Archaeological Center, Cortez, CO 81321, USA
| | - Pablo A Marquet
- Santa Fe Institute, Santa Fe, NM 87501, USA; Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile; Instituto de Ecología y Biodiversidad (IEB), Centro de Cambio Global UC, Laboratorio Internacional de Cambio Global (LINCGlobal), Santiago, Chile
| | - Richard A Boyle
- Global Systems Institute, University of Exeter, Exeter, EX4 4QE, UK
| | - Michel Crucifix
- Université Catholique de Louvain, Earth and Life Institute, Louvain-la-Neuve, Belgium
| | - David M Wilkinson
- School of Life Sciences, University of Lincoln, Lincoln, LN6 7DL, UK; Classics and Archaeology, University of Nottingham, Nottingham, NG7 2RD, UK
| | - Marten Scheffer
- Aquatic Ecology and Water Quality Management, Wageningen University, 6700AA Wageningen, The Netherlands
| |
Collapse
|