Causes and consequences of woody plant encroachment into western North American grasslands

Auken, O. W. Van

doi:10.1016/j.jenvman.2009.04.023

Cited by 540 publications

(409 citation statements)

References 94 publications

(191 reference statements)

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“…The phenomenon of shrub encroachment (i.e. the expansion of woody vegetation into former grasslands [99]), a key land-cover change affecting drylands worldwide, has multiple effects on ecosystem structure and functioning [100]. Although this phenomenon has not been found to significantly affect ecosystem attributes such as biodiversity at the global scale [100], it may either enhance or reduce plant species richness at local and regional scales [97,101].…”

Section: Global Environmental Change Effects On Drylandsmentioning

confidence: 99%

It is getting hotter in here: determining and projecting the impacts of global environmental change on drylands

Maestre

Salguero‐Gómez

Quero

2012

Phil. Trans. R. Soc. B

271

209

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Drylands occupy large portions of the Earth, and are a key terrestrial biome from the socio-ecological point of view. In spite of their extent and importance, the impacts of global environmental change on them remain poorly understood. In this introduction, we review some of the main expected impacts of global change in drylands, quantify research efforts on the topic, and highlight how the articles included in this theme issue contribute to fill current gaps in our knowledge. Our literature analyses identify key under-studied areas that need more research (e.g. countries such as Mauritania, Mali, Burkina Faso, Chad and Somalia, and deserts such as the Thar, Kavir and Taklamakan), and indicate that most global change research carried out to date in drylands has been done on a unidisciplinary basis. The contributions included here use a wide array of organisms (from micro-organisms to humans), spatial scales (from local to global) and topics (from plant demography to poverty alleviation) to examine key issues to the socio-ecological impacts of global change in drylands. These papers highlight the complexities and difficulties associated with the prediction of such impacts. They also identify the increased use of long-term experiments and multidisciplinary approaches as priority areas for future dryland research. Major advances in our ability to predict and understand global change impacts on drylands can be achieved by explicitly considering how the responses of individuals, populations and communities will in turn affect ecosystem services. Future research should explore linkages between these responses and their effects on water and climate, as well as the provisioning of services for human development and well-being.

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Section: Global Environmental Change Effects On Drylandsmentioning

confidence: 99%

It is getting hotter in here: determining and projecting the impacts of global environmental change on drylands

Maestre

Salguero‐Gómez

Quero

2012

Phil. Trans. R. Soc. B

271

209

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“…Both types of dominance shift in savannas are often associated with disturbances such as overgrazing or frequent fires. Generally, such dominance shifts are induced by any process or factor that either weakens the grass’s competitive abilities (e.g., through overgrazing; Ward, 2005), increases germination and recruitment rates of the competing species (Synodinos et al., 2015; Van Auken, 2009), or strengthens their seedlings (e.g., higher rainfalls, elevated CO 2 ; Bond & Midgley, 2000; Kulmatiski & Beard, 2013). …”

Section: Introductionmentioning

confidence: 99%

A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses

Wagner

Richter

Joubert

et al. 2018

Ecology and Evolution

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The characteristic vegetation structure of arid savannas with a dominant layer of perennial grass is maintained by the putative competitive superiority of the C4 grasses. When this competitive balance is disturbed by weakening the grasses or favoring the recruitment of other species, trees, shrubs, single grass, or forb species can increase and initiate sudden dominance shifts. Such shifts involving woody species, often termed “shrub encroachment”, or the mass spreading of so‐called increaser species have been extensively researched, but studies on similar processes without obvious preceding disturbance are rare. In Namibia, the native herbaceous legume Crotalaria podocarpa has recently encroached parts of the escarpment region, seriously affecting the productivity of local fodder grasses. Here, we studied the interaction between seedlings of the legume and the dominant local fodder grass (Stipagrostis ciliata). We used a pot experiment to test seedling survival and to investigate the growth of Crotalaria in competition with Stipagrostis. Additional field observations were conducted to quantify the interactive effect. We found germination and growth of the legume seedlings to be facilitated by inactive (dead or dormant) grass tussocks and unhindered by active ones. Seedling survival was three times higher in inactive tussocks and Crotalaria grew taller. In the field, high densities of the legume had a clear negative effect on productivity of the grass. The C4 grass was unable to limit the recruitment and spread of the legume, and Crotalaria did outcompete the putative more competitive grass. Hence, the legume is able to spread and establish itself in large numbers and initiate a dominance shift in savannas, similar to shrub encroachment.

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“…and creosote shrubland (Larrea tridentata) encroaching across the Rio Grande basin and piñon-juniper woodland (Pinus edulis-Juniperus monosperma) encroaching downslope in the Los Piños mountains. These vegetation changes are characteristic of those occurring across large extents of the semiarid basin and range landscape of the southwestern U.S. [Eldridge et al, 2011;Van Auken, 2009]. The criteria used in the selection of the sites were (a) each site must be characteristic of an end-member vegetation state over the two monitored ecotones; (b) sites must be of comparable area, dimensions, and slope to allow comparison between monitored rainfallrunoff relationships; (c) sites must be located on a planar interfluve slope; and (d) at the two ecotones, sites selected as being representative of end-member vegetation states must be as close as possible, thus minimizing variation in geology, soil characteristics, and meteorological variables.…”

Section: Study Sitesmentioning

confidence: 91%

“…At the SNWR (Figure 1), as with the observed encroachment across the southwestern U.S., evidence suggests that human settlement over the last 150 years caused the current episode of change, attributed primarily to grassland degradation by cattle grazing and fire suppression, between 1936and 1973[U.S. Fish and Wildlife Service, 2014, exacerbated by periods of drought [Buffington and Herbel, 1965;Peters et al, 2006;Van Auken, 2009]. Aerial photos provide evidence for the enlargement of woody clusters into grasslands [Gosz, 1992], and biogeochemical studies suggest the previous presence of grasslands in areas now dominated by woody vegetation [Turnbull et al, 2008b;Puttock et al, 2012].…”

Section: Study Sitesmentioning

confidence: 93%

“…Observations from the grass-woody vegetation transitions occurring in drylands across the southwestern U.S. suggest that the competitive ability of grass species is being reduced, allowing woody species to encroach and that ecosystems are adjusting to a change in current or historic controls on vegetation patterns [Archer, 1995]. Cited drivers of woody encroachment include climate [Seager et al, 2007], atmospheric CO 2 [Higgins and Scheiter, 2012], fire [Yu and D'Odorico, 2014], and animal activity, particularly grazing [Van Auken, 2009], and it is generally recognized that encroachment results from a combination of both climatic and land use drivers [Peters et al, 2013].…”

Section: Introductionmentioning

confidence: 99%

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Woody plant encroachment into grasslands leads to accelerated erosion of previously stable organic carbon from dryland soils

et al. 2014

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Drylands worldwide are experiencing rapid and extensive environmental change, concomitant with the encroachment of woody vegetation into grasslands. Woody encroachment leads to changes in both the structure and function of dryland ecosystems and has been shown to result in accelerated soil erosion and loss of soil nutrients. Covering 40% of the terrestrial land surface, dryland environments are of global importance, both as a habitat and a soil carbon store. Relationships between environmental change, soil erosion, and the carbon cycle are uncertain. There is a clear need to further our understanding of dryland vegetation change and impacts on carbon dynamics. Here two grass-to-woody ecotones that occur across large areas of the southwestern United States are investigated. This study takes a multidisciplinary approach, combining ecohydrological monitoring of structure and function and a dual-proxy biogeochemical tracing approach using the unique natural biochemical signatures of the vegetation. Results show that following woody encroachment, not only do these drylands lose significantly more soil and organic carbon via erosion but that this includes significant amounts of legacy organic carbon which would previously have been stable under grass cover. Results suggest that these dryland soils may not act as a stable organic carbon pool, following encroachment and that accelerated erosion of carbon, driven by vegetation change, has important implications for carbon dynamics.

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Causes and consequences of woody plant encroachment into western North American grasslands

Cited by 540 publications

References 94 publications

It is getting hotter in here: determining and projecting the impacts of global environmental change on drylands

It is getting hotter in here: determining and projecting the impacts of global environmental change on drylands

A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses

Woody plant encroachment into grasslands leads to accelerated erosion of previously stable organic carbon from dryland soils

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Causes and consequences of woody plant encroachment into western North American grasslands

Cited by 540 publications

References 94 publications

It is getting hotter in here: determining and projecting the impacts of global environmental change on drylands

It is getting hotter in here: determining and projecting the impacts of global environmental change on drylands

A dominance shift in arid savanna: An herbaceous legume outcompetes local C4 grasses

Woody plant encroachment into grasslands leads to accelerated erosion of previously stable organic carbon from dryland soils

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A dominance shift in arid savanna: An herbaceous legume outcompetes local C₄ grasses