Persistence of Desertified Ecosystems: Explanations and Implications

Whitford, Walter G.; Martinez-Turanzas, Gustavo; Martinez-Meza, Ernesto

doi:10.1007/978-94-009-1635-7_23

Cited by 13 publications

(15 citation statements)

References 25 publications

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“…1). This result agrees with findings from the Patagonian Steppe and the Chihuahuan Desert (Reynolds et al 1999, Yahdjian et al 2006, Yahdjian and Sala 2008 but disagrees with regional modeling results (Burke et al 1997) and local experiments (Whitford et al 1995). There are three compatible explanations for this phenomenon; substrate limitation, location in the soil profile of the bulk of mineralization in the upper layers, or the simultaneous increase of gross mineralization and immobilization along the precipitation gradient.…”

Section: Discussionsupporting

confidence: 60%

“…Biogeochemical simulation models predict that net N mineralization increases with increasing moisture along precipitation gradients in semiarid to mesic ecosystems (Burke et al 1997), mostly driven by climatic controls and increasing N pools. At the local scale, some studies report that mineral N concentration decreases with increasing water availability (Fisher et al 1987) and some report the opposite pattern (Whitford et al 1995). Other studies show that net N mineralization does not differ between dry or wet soils (Schimel and Parton 1986, Reynolds et al 1999, Yahdjian et al 2006, or across precipitation gradients in the Great Plains (McCulley et al 2009).…”

Section: Introductionmentioning

confidence: 99%

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Water controls on nitrogen transformations and stocks in an arid ecosystem

Reichmann¹,

Sala²,

Peters³

2013

Ecosphere

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Abstract. Following water, nitrogen (N) is the most frequent limiting factor to aboveground net primary production in arid ecosystems. Increased water availability can stimulate both plant nitrogen uptake and microbial nitrogen mineralization, but may also stimulate losses from the ecosystem. Here, we assess the effect of water availability on nitrogen stocks and transformations in an arid ecosystem. We conducted a field experiment with five levels of precipitation input (À80%, À50%, ambient, þ50%, þ80%) and two levels of N fertilization (ambient or 10 gÁm À2 Áyr À1 NH 4 NO 3 ) in a desert grassland of the Chihuahuan Desert. We measured in situ net N mineralization, plant N uptake, foliar N, N leaching under grass-rooting zone, and soil N availability during two years. Our results showed that increased water availability did not affect net N mineralization, but there was higher plant N uptake than with drought. Soil inorganic N pools were 2-4 times lower with increased water availability compared to drought conditions. N leaching below grass-rooting zone was higher in dry than wet conditions because of higher available N. Increased water availability differentially affected N species significantly reducing the NO 3 :NH 4 ratio. The accumulation of inorganic N during drought was the result of a decoupling between microbial and plant activity, and suggests that the cycling of N is more open in dry years than in wet years.

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Section: Discussionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Water controls on nitrogen transformations and stocks in an arid ecosystem

Reichmann¹,

Sala²,

Peters³

2013

Ecosphere

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“…The local soil surface gradient is a direct manifestation of the vegetation type, particularly due to the characteristics of the canopy as discussed earlier. Shrubs with dense canopies are more able to capture aeolian sediments, which increases the size of the soil mound beneath the canopy leading to a steep local slope gradient (Whitford et al, 1995;Aguiar and Sala, 1999;Reynolds et al, 1999). Large shrub soil mounds and associated high local slope gradients are typical of the mesquite shrub that has a canopy typically four times as dense as that of the creosotebush (Reynolds et al, 1999).…”

Section: Runoff Characteristicsmentioning

confidence: 98%

“…Nonetheless grassland productivity remains closely linked with rainfall (Stephens and Whitford, 1993). N/A Stemflow accounts for between 16 and 25 % of intercepted rainfall, entering the soil at the root crown and contributing to the tight cycling of nutrients (Whitford et al ., 1995).…”

Section: Rootsmentioning

confidence: 99%

Vegetation controls on small‐scale runoff and erosion dynamics in a degrading dryland environment

Michaelides

Lister

Wainwright

et al. 2009

Hydrological Processes

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Abstract:This paper investigates the controls of vegetation on runoff and erosion dynamics in the dryland environment of Jornada, New Mexico, USA. As the American southwest has seen significant shifts in the dominant vegetation species in the past 150 years, an understanding of the vegetation effects on hydrological and erosional processes is vital for understanding and managing environmental change. Small-scale rainfall simulations were carried out to identify the hydrological and erosional processes resulting from the grassland and shrubland vegetation species. Results obtained using tree-regression analysis suggested that the primary vegetation control on runoff and erosion is the shrub type and canopy density, which directly affects the local microtopographic gradient of mounds beneath the shrubs. Significant interactions and feedbacks were found to occur among the local mound gradient, crust cover, soil aggregate stability and antecedent soil moisture between the different vegetation species for both the runoff and erosion responses. Although some of the shrub species were found to produce higher sediment yields than the grass species, the distinguishing feature of the grassland was the significantly higher enrichment in the fine sediment fraction compared to all other surface cover types. This enrichment in fines has important implications for nutrient movement in such environments.

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“…In the southwestern U.S., the duration and timing of available soil water may be a key variable involved in many kinds of transitions (Whitford et al 1995, Devine et al 1998 Reynolds et al 1999, Dodd et al 2000. Transitions may be due to threshold (non-linear) changes in the availability of soil water over time due to shifts in runoff patterns (e.g., percolation thresholds; Davenport et al 1998) , Ludwig et al 2000, Kuehl et al 2001.…”

Section: Using Models: Proximate Variables Indicators and Predictinmentioning

confidence: 99%

Development and use of state-and-transition models for rangelands

Bestelmeyer¹,

Brown²,

Havstad³

2003

REM

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State-and-transition models have received a great deal of attention since the introduction of the concept to range management in 1989. Nonetheless, only recently have sets of state-and-transition models been produced that can be used by agency personnel and private citizens, and there is little guidance available for developing and interpreting models. Based upon our experiences developing models for the state of New Mexico, we address the following questions: 1) how is information assembled to create site-specific models for entire regions, 2) what ecological issues should be considered in model development and classification, and 3) how should models be used? We review the general structure of state-and-transition models, emphasizing the distinction between changes among communities within states (pathways) that are reversible with changes in climate and "facilitating practices" (e.g. grazing management), and changes among states (transitions) that are reversible only with "accelerating practices" such as seeding, shrub control, or the recovery of soil stability and historical hydrologic function. Both pathways and transitions occur, so these models are complementary. Ecological sites and the climatically-defined regions within which they occur (land resource units) serve as a framework for developing and selecting models. We illustrate the importance of clearly delineating ecological sites to produce models and describe how we have dealt with poorly-delineated sites. Producing specific models requires an understanding of the multiple ecological mechanisms underlying transitions. We show how models can represent and distinguish alternative and complementary hypotheses for transitions. Although there may be several mechanisms underlying transitions, they tend to fall within discrete categories based upon a few, fundamental ecological processes and their relation- Dyksterhuis (1949) that is based on the successional theory of Clements (1916) and the edaphic polyclimax concept of Tansley (1935). This model emphasized the return of disturbed communities to a competitively-determined climax state and has been a guiding principle in range management (Westoby 1980). Upon recognizing an undesirable trend in plant community composition, managers could respond by reducing or redistributing grazing pressure and effect a return to desirable conditions. An important reason for the success of this model is that it provided a method to measure and compare land condition against the expectations of the model (i.e., the similarity index), thus providing a concrete link between theoretical expectations and management response.Rangeland managers have long recognized that semiarid grasslands can transform into shrub-dominated states that cannot be returned to grassland through grazing management (Laycock 1991), contrary to applications of the succession-retrogression model. Assuming that a single, competition-defined equilibrium plant community should exist for each site, alternative states, and the rangelands in whic...

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Persistence of Desertified Ecosystems: Explanations and Implications

Cited by 13 publications

References 25 publications

Water controls on nitrogen transformations and stocks in an arid ecosystem

Water controls on nitrogen transformations and stocks in an arid ecosystem

Vegetation controls on small‐scale runoff and erosion dynamics in a degrading dryland environment

Development and use of state-and-transition models for rangelands

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