Reversal of desertification: The role of physical and chemical soil properties

Allington, Ginger R.H.; Valone, Thomas J.

doi:10.1016/j.jaridenv.2009.12.005

Cited by 66 publications

(59 citation statements)

References 50 publications

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“…Reversibility is suggested by a few recent studies, showing a recovery from desertification when the external pressure (grazing, in most cases) has been removed [30][31][32][33][34]. Some evidence for linearity are suggested in Figure 2, where the desertification process of the Sahara during the mid-Holocene is traced through the eolian dust record of Site 658C [35].…”

mentioning

confidence: 88%

Stochastic desertification

Weissmann¹,

Shnerb²

2014

EPL

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The process of desertification is usually modeled as a first order transition, where a change of an external parameter (e.g. precipitation) leads to a catastrophic bifurcation followed by an ecological regime shift. However, vegetation elements like shrubs and trees undergo a stochastic birth-death process with an absorbing state; such a process supports a second order continuous transition with no hysteresis. We present a numerical study of a minimal model that supports bistability and catastrophic shift on spatial domain with demographic noise and an absorbing state. When the external parameter varies adiabatically the transition is continuous and the front velocity renormalizes to zero at the extinction transition. Below the transition one may identify three modes of desertification: accumulation of local catastrophes, desert invasion and global collapse. A catastrophic regime shift occurs as a dynamical hysteresis, when the pace of environmental variations is too fast. We present some empirical evidence, suggesting that the mid-holocene desertification of the Sahara was, indeed, continuous.PACS numbers: 87.10. Mn,87.23.Cc,64.60.Ht,05.40.Ca The catastrophic bifurcation and its statistical mechanics analog, the first order transition, play a central role in the physical sciences. In these processes a tiny change in the value of an external parameter leads to a sudden jump of the system from one phase to another. This change is irreversible and is accompanied by hysteresis: once the system relaxed to its new phase, it will not recover even when the external parameters are restored.The relevance of these processes to the ecology of population and communities has been established while ago [1]. Recently, there is a growing concern about the possible occurrence of regime shifts in ecological systems [2][3][4][5]. The anthropogenic changes of local and global environmental parameters from habitat fragmentation to the increasing levels of CO2 in the atmosphere -raise anxiety about the possibility of an abrupt and irreversible catastrophe that may be destructive to the functions and the stability of an ecosystem [6]. This concern triggered an intensive search for empirical evidence that may allow one to identify an impending tipping point, where the most popular suggestion is to use the phenomenon of critical slowing down [5,[7][8][9][10][11]. Other suggested early warning indicators, especially for sessile species, deal with spatial patterns and the level of aggregation [4,12,13] Of particular importance is the process of desertification, which is considered as an irreversible shift from the "active" vegetation state to the "inactive" bare soil state, resulting from an increased pressure (e.g., overgrazing, declines in precipitation). As drylands cover about 41% of Earth land surface, desertification affects about 250 million people around the world [14]. Various models show that, when the vegetation state has a positive feedback, like an increased runoff interception or reduced evaporation close to vegetation pa...

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confidence: 88%

Stochastic desertification

Weissmann¹,

Shnerb²

2014

EPL

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“…Snyman (2004) concludes from the lack of climax grasses in the soil seed bank and their very low abundance in deteriorated vegetation that arid and semiarid rangelands reach a threshold of degradation, beyond which spontaneous recovery over the short-term is excluded. This is linked to sufficient infiltration rates supporting grass establishment (Allington and Valone, 2010), which are, however, reduced by prominent bare patches at DEG that are prone to crusting (Dreber and Esler, 2011).…”

Section: Evaluation Of the Restoration Potentialmentioning

confidence: 99%

“…In arid and semiarid ecosystems, recovery processes in degraded rangelands are slow and stochastic (Call and Roundy, 1991;Visser et al, 2004), and the time span for improvement might last several decades (Allington and Valone, 2010;Wiegand and Milton, 1996), which is beyond what is relevant for management. Both the time needed and the lack of a promising natural restoration potential at DEG to support species which are common to sustainably managed rangelands, point towards the need for active interventions.…”

Section: Evaluation Of the Restoration Potentialmentioning

confidence: 99%

Species, functional groups and community structure in seed banks of the arid Nama Karoo: Grazing impacts and implications for rangeland restoration

Dreber

Oldeland

Rooyen

2011

Agriculture, Ecosystems & Environment

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Please cite this article in press as: Dreber, N., et al., Species, functional groups and community structure in seed banks of the arid Nama Karoo: Grazing impacts and implications for rangeland restoration. Agric. Ecosyst. Environ. (2011) The regeneration potential of grazing-affected Nama Karoo vegetation was evaluated by comparing soil seed banks of different microsites across a fence-line contrast in arid Namibia. Seed banks under low and high grazing pressure reflected the condition of the standing vegetation in terms of composition, community structure and species abundance distributions. However, a close concordance between vegetation and seed bank was restricted to the herbaceous and grassy vegetation within the inter-shrub matrix. The divergence of seed bank communities across the fence-line was low at community level but high at the level of species abundances. Continuous severe grazing increased the abundance of small-seeded, prostrate forbs with round seeds and favored unpalatable, annual grasses over palatable, perennial grasses. Microsites provided a source of small-scale variation in seed bank community composition and were dissimilar between the rangelands.Results indicated an advanced divergence in the vegetation at the degraded site with seed banks of species common under sustainable grazing being drastically reduced. Their low abundance, even in safe sites, suggests that long-distance dispersal is one of the main limiting factors for natural re-establishment after disturbance. The inertia in recovery of Namibian degraded rangelands through seed limitation can be overcome only by active species introduction.

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“…Possibly the most successful species to colonize disturbed areas has been D. viscosa, which has a great ability to germinate in eroded soil [40], generating organic matter and preventing the germination of other species [57]. In the absence of trampling, soil aggregate stability increases, which enhances infiltration, reduces erosion, and may promote nutrient accumulation and soil retention [58,59].…”

Section: Soil Recoverymentioning

confidence: 99%

Recovery of Vegetation Cover and Soil after the Removal of Sheep in Socorro Island, Mexico

Ortiz-Alcaraz

Maya

Cortés‐Calva

et al. 2016

Forests

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Abstract:For over 140 years, the habitat of Socorro Island in the Mexican Pacific has been altered by the presence of exotic sheep. Overgrazing, jointly with tropical storms, has caused soil erosion, and more than 2000 hectares of native vegetation have been lost. Sheep eradication was conducted from 2009 to 2012. Since then, the vegetation has begun to recover passively, modifying soil properties. The objective of our study was to verify that this island was resilient enough to be recovered and in a relatively short time scale. To confirm our hypothesis, we analyzed changes in the physical-chemical properties of the soil and vegetation cover, the last one in different times and habitats after sheep eradication. The change in vegetation cover was estimated by comparing the normalized difference vegetation index (NDVI) between 2008 and 2013. In sites altered by feral sheep, soil compaction was assessed, and soil samples were taken, analyzing pH, electrical conductivity, organic carbon, total nitrogen, phosphorus, calcium, and magnesium. After a year of total sheep eradication, clear indications in the recovery of vegetation cover and improvement of soil quality parameters were observed and confirmed, specifically compaction and nitrogen, organic carbon, phosphorus, and calcium. The results seem to support our hypothesis.

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Reversal of desertification: The role of physical and chemical soil properties

Cited by 66 publications

References 50 publications

Stochastic desertification

Stochastic desertification

Species, functional groups and community structure in seed banks of the arid Nama Karoo: Grazing impacts and implications for rangeland restoration

Recovery of Vegetation Cover and Soil after the Removal of Sheep in Socorro Island, Mexico

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