A combined grazing and fire management may reverse woody shrub encroachment in desert grasslands     

Wang  Guan  Li  Junran  Ravi  Sujith 《Landscape Ecology》2019,34(8):2017-2031

Context

Fire and controlled grazing have been widely adopted as management interventions to counteract woody shrub proliferation in many arid and semiarid grassland systems. The actual intensity of grazing and fire, along with the timing of the interventions, however, are difficult to determine in practice.

Objectives

This study aims to establish model simulations to access the long-term landscape changes under different land management scenarios.

Methods

We developed a cellular automata model to evaluate landscape dynamics in response to scenarios of grazing, fire, time of intervention, and initial coverage of grasses and shrubs.

Results

With current grazing intensity and fire suppression, the landscape may shift to a shrub-dominated landscape in 100–150 years. An appropriate combination of grazing and fire management could help maintain over 50% of grass cover and reduce the shrub cover to less than 2%, keeping the landscape highly reversible. Even using 1% grazing intensity and periodic fire once a year, the management tools should be implemented in 60 years, otherwise, they may lose effectiveness and the vegetation transition to grasslands would become impossible.

Conclusions

This study highlighted that the reintroduction of fire not only directly removes shrubs but also reallocates soil water and resources among different microsites, which may accelerate grass recovery and suppress shrub regrowth, potentially reversing the shrub invasion process. The combined grazing and fire management plans should be carried out before a threshold time depending on the chosen management tools.

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Post-fire resource redistribution and fertility island dynamics in shrub encroached desert grasslands: a modeling approach     

Sujith Ravi  Paolo D’Odorico 《Landscape Ecology》2009,24(3):325-335

A common form of land degradation in desert grasslands is associated with the relatively rapid encroachment of woody plants, a process that has important implications on ecosystem structure and function, as well as on the soil hydrological and biogeochemical properties. Until recently this grassland to shrubland transition was thought to be highly irreversible. However recent studies have shown that at the early stages of shrub encroachment in desert grasslands, there exists a very dynamic shrub–grass transition state with enough grass connectivity between the shrub islands to allow for fire spread. In this state fire could play a major role in determining the dominance of grasses and their recovery from the effects of overgrazing. Using a spatially explicit cellular automata model, we show how the patch-scale feedbacks between fires and soil erosion affects resource redistribution and vegetation dynamics in a mixed grass–shrub plant community at landscape to regional scales. The results of this study indicate that at its early stages, the grassland-to-shrubland transition can be reversible and that the feedbacks between fire and soil erosion processes may play a major role in determining the reversibility of the system.  相似文献   

Interactions Between Soil Erosion Processes and Fires: Implications for the Dynamics of Fertility Islands     

Sujith Ravi  Paolo D’Odorico  Travis E. Huxman  Scott L. Collins 《Strength and Conditioning Journal》2010,63(3):267-274

Shrub encroachment in arid and semiarid rangelands, a worldwide phenomenon, results in a heterogeneous landscape characterized by a mosaic of nutrient-depleted barren soil bordered by nutrient-enriched shrubby areas known as “fertile islands.” Even though shrub encroachment is considered as a major contributor to rangeland degradation, little is known about mechanisms favoring the reversibility of the early stages of this process. Here we synthesize the interactions between fires and soil erosion processes, and the implications of these interactions for management of rangelands. The burning of shrub vegetation develops relatively high levels of soil hydrophobicity. This fire-induced water repellency was shown to enhance the soil erodibility in and around burned shrub patches. The fire-induced enhancement of local-scale soil erosion results from changes in the interparticle bonding forces between the soil grains, thus altering the way moisture is retained in the soil. It has been shown—with a number of wind-tunnel studies, field-scale manipulative experiments, microtopographic measurements, and isotopic tracer studies—how the fire-erosion interactions affect the dynamics of fertility islands. Further we propose a new conceptual model of resource “island” dynamics that explains some of the findings previously reported in the literature on the interactions between aeolian processes and arid-land vegetation. In particular, we highlight the ability of fires to enhance the erodibility of nutrient-rich soils accumulated under the shrubs favoring the redistribution of soil resources, thereby contributing to the reversibility of the early stages of shrub encroachment.  相似文献   

Highly pathogenic avian influenza virus infection in chickens but not ducks is associated with elevated host immune and pro-inflammatory responses     

Suresh V Kuchipudi  Meenu Tellabati  Sujith Sebastian  Brandon Z Londt  Christine Jansen  Lonneke Vervelde  Sharon M Brookes  Ian H Brown  Stephen P Dunham  Kin-Chow Chang 《Veterinary research》2014,45(1)

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