Vegetation-Microclimate Feedbacks in Woodland-Grassland Ecotones. D'Odorico, P.; He, Y.; Collins, S.; De Wekker, S. F. J.; Engel, V.; and Fuentes, J. D. 22(4):364–379.
Vegetation-Microclimate Feedbacks in Woodland-Grassland Ecotones [link]Paper  doi  abstract   bibtex   
[Aim] Climatic conditions exert a strong control on the geographic distribution of many woodland-to-grassland transition zones (or 'tree lines'). Because woody plants have, in general, a weaker cold tolerance than herbaceous vegetation, their altitudinal or latitudinal limits are strongly controlled by cold sensitivity. While temperature controls on the dynamics of woodland-grassland ecotones are relatively well established, the ability of woody plants to modify their microclimate and to create habitat for seedling establishment and growth may involve a variety of processes that are still not completely understood. Here we investigate feedbacks between vegetation and microclimatic conditions in the proximity to woodland-grassland ecotones. [Location] We concentrate on arctic and alpine tree lines, the transition between mangrove forests and salt marshes in coastal ecosystems, and the shift from shrubland to grassland along temperature gradients in arid landscapes. [Methods] We review the major abiotic and biotic mechanisms underlying the ability of woody plants to alter the nocturnal microclimate by increasing the temperatures they are exposed to. [Results] We find that in many arctic, alpine, desert and coastal landscapes the presence of trees or shrubs causes nocturnal warming thereby favouring the establishment and survival of woody plants. [Main conclusion] Because of this feedback, trees and shrubs may establish in areas that would be otherwise unsuitable for their survival. Thus, in grassland-woodland transition zones both vegetation covers may be (alternative) stable states of the landscape, thereby affecting the way tree lines may migrate in response to regional and global climate change. [Excerpt: Conclusions] Positive feedbacks between the encroachment of woody plants and land surface-atmosphere interactions in former grasslands occur as a function of changes in albedo, surface roughness and heat storage which accompany shifts in canopy architecture. The density and height of stems, leaf morphology, total leaf area and the vertical leaf area distributions are examples of architectural properties of the canopy that are likely to influence the degree of coupling between the canopy air mass and the overlying or surrounding atmosphere (Geiger, 1965; Bonan, 2002). In most cases (e.g. arctic and alpine tree lines) the warming effect is due to the ability of the canopy to reduce nocturnal radiative cooling. However, in the case of arid grassland-shrubland transition zones the feedback mechanism is not controlled by canopy architecture but by the ability of some desert shrubs to eliminate grass cover from their surroundings (Báez & Collins, 2008), thereby increasing the bare soil fraction in shrub-dominated areas. The different thermal properties of grass and bare soil surfaces determines a difference in soil heat fluxes between the two land covers, which explains the higher nocturnal temperature in the shrubland. Several environmental factors also regulate the strength of microclimate feedbacks in woodland-grassland transition zones, including solar angles and the land surface aspect, wind speed, cloudiness, photosynthetically active radiation, air humidity and topography. [] In this review we have shown that these feedbacks have been documented across a wide range of arid, coastal, alpine and arctic grassland-woodland transitional communities. Recent studies have shown that, when integrated spatially, the microclimatic alterations caused by woody plant encroachment may have implications for larger-scale climates (e.g. Bonan et\,al., 1992; Beltrán-Przekurat et\,al., 2008), and global carbon cycles (Archer et\,al., 2001; Chmura et\,al., 2003; Chapin et\,al., 2005).
@article{dodoricoVegetationmicroclimateFeedbacksWoodlandgrassland2013,
  title = {Vegetation-Microclimate Feedbacks in Woodland-Grassland Ecotones},
  author = {D'Odorico, Paolo and He, Yufei and Collins, Scott and De Wekker, Stephan F. J. and Engel, Vic and Fuentes, Jose D.},
  date = {2013-04},
  journaltitle = {Global Ecology and Biogeography},
  volume = {22},
  pages = {364--379},
  issn = {1466-822X},
  doi = {10.1111/geb.12000},
  url = {https://doi.org/10.1111/geb.12000},
  abstract = {[Aim]

Climatic conditions exert a strong control on the geographic distribution of many woodland-to-grassland transition zones (or 'tree lines'). Because woody plants have, in general, a weaker cold tolerance than herbaceous vegetation, their altitudinal or latitudinal limits are strongly controlled by cold sensitivity. While temperature controls on the dynamics of woodland-grassland ecotones are relatively well established, the ability of woody plants to modify their microclimate and to create habitat for seedling establishment and growth may involve a variety of processes that are still not completely understood. Here we investigate feedbacks between vegetation and microclimatic conditions in the proximity to woodland-grassland ecotones.

[Location]

We concentrate on arctic and alpine tree lines, the transition between mangrove forests and salt marshes in coastal ecosystems, and the shift from shrubland to grassland along temperature gradients in arid landscapes.

[Methods]

We review the major abiotic and biotic mechanisms underlying the ability of woody plants to alter the nocturnal microclimate by increasing the temperatures they are exposed to.

[Results]

We find that in many arctic, alpine, desert and coastal landscapes the presence of trees or shrubs causes nocturnal warming thereby favouring the establishment and survival of woody plants.

[Main conclusion]

Because of this feedback, trees and shrubs may establish in areas that would be otherwise unsuitable for their survival. Thus, in grassland-woodland transition zones both vegetation covers may be (alternative) stable states of the landscape, thereby affecting the way tree lines may migrate in response to regional and global climate change.

[Excerpt: Conclusions]

Positive feedbacks between the encroachment of woody plants and land surface-atmosphere interactions in former grasslands occur as a function of changes in albedo, surface roughness and heat storage which accompany shifts in canopy architecture. The density and height of stems, leaf morphology, total leaf area and the vertical leaf area distributions are examples of architectural properties of the canopy that are likely to influence the degree of coupling between the canopy air mass and the overlying or surrounding atmosphere (Geiger, 1965; Bonan, 2002). In most cases (e.g. arctic and alpine tree lines) the warming effect is due to the ability of the canopy to reduce nocturnal radiative cooling. However, in the case of arid grassland-shrubland transition zones the feedback mechanism is not controlled by canopy architecture but by the ability of some desert shrubs to eliminate grass cover from their surroundings (Báez \& Collins, 2008), thereby increasing the bare soil fraction in shrub-dominated areas. The different thermal properties of grass and bare soil surfaces determines a difference in soil heat fluxes between the two land covers, which explains the higher nocturnal temperature in the shrubland. Several environmental factors also regulate the strength of microclimate feedbacks in woodland-grassland transition zones, including solar angles and the land surface aspect, wind speed, cloudiness, photosynthetically active radiation, air humidity and topography.

[] In this review we have shown that these feedbacks have been documented across a wide range of arid, coastal, alpine and arctic grassland-woodland transitional communities. Recent studies have shown that, when integrated spatially, the microclimatic alterations caused by woody plant encroachment may have implications for larger-scale climates (e.g. Bonan et\,al., 1992; Beltrán-Przekurat et\,al., 2008), and global carbon cycles (Archer et\,al., 2001; Chmura et\,al., 2003; Chapin et\,al., 2005).},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13928385,~to-add-doi-URL,arid-region,boreal-forests,climate,ecological-zones,ecology,feedback,forest-resources,grasslands,habitat-suitability,mangrove-forests,meadows,microclimate,mountainous-areas,temperate-mountain-system,tree-line,tundra},
  number = {4}
}
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