In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodivers...In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodiversity, and increase soil erosion, potentially triggering abrupt and rapid changes in ecosystem condition. Alternate stable state theory provides a framework for understanding this type of dynamic. In the Sanjiangyuan atop the Qinghai-Tibetan plateau (QTP), grassland degradation has been accompanied by irruptions of native burrowing animals, which has accentuated the loss of ground cover. Severely degraded areas of alpine meadows are referred to as 'Heitutan'. Here, using the framework of alternate stable state theory, we describe the proximate and ultimate drivers of the formation of Heitutan on the QTP, and we assess prospects for recovery, in relation to the degree of biophysical alteration, of these alpine meadows. Effective rehabilitation measures must address the underlying causes of degradation rather than their symptoms. Heitutan degradation is not uni-causal. Rather it reflects different mechanisms operating at different spatio-temporal scales across this vast region. Underlying causes include overly aggressive exploitation of the grasslands (e.g. overgrazing), amplification of grazing and erosion damage by small mammals when outbreaks occur, and/or climate change. Given marked variability in environmental conditions and stressors, restorative efforts must vary across the region. Restoration efforts are likely toyield greatest success if moderately and severely degraded areas are targeted as the first priority in management programmes, before these areas are transformed into extreme Heitutan.展开更多
Process interactions on catenas have supported grazing adapted ecosystems and sustained biodiversity values in the source zone of the Yellow River in western China for millennia.In recent decades,anthropogenic disturb...Process interactions on catenas have supported grazing adapted ecosystems and sustained biodiversity values in the source zone of the Yellow River in western China for millennia.In recent decades,anthropogenic disturbance and climate change have threatened the integrity of these systems,impacting upon environmental values and their capacity to sustain local livelihoods.Collaborations between local experts and a team of international researchers during a workshop and field excursion to this area in July 2019 developed a cross-disciplinary,process-based model of alpine meadow catenas.This paper relates the contemporary health of these grassland-wetland systems to their‘best achievable state’under prevailing boundary conditions,differentiating stages of degradation and recovery in relation to climate and land use changes.Recovery is underway for alpine meadow catenas at Maqin.Reduced land use pressures(stocking rates)and longer growing seasons have enhanced grasslandwetland conditions.However,recovery prospects are limited for local areas of extremely degraded grasslands(heitutan),as breached abiotic thresholds have resulted in soil and nutrient loss and reduced capacity for water retention.While lagomorphs and rodents act as ecosystem engineers when alpine meadows are in a healthy state,irruptions locally increase the proportion of bare ground and inhibit recovery potential.Management options that support recovery of alpine meadows are presented for differing stages of degradation.展开更多
基金supported by Special Fund for Agroscientific Research in the Public Interest(201203041)the National Natural Sciences Foundation of China(41161084)International Science & Technology Cooperation Program of China(2011DFG93160,2011DFA20820)
文摘In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodiversity, and increase soil erosion, potentially triggering abrupt and rapid changes in ecosystem condition. Alternate stable state theory provides a framework for understanding this type of dynamic. In the Sanjiangyuan atop the Qinghai-Tibetan plateau (QTP), grassland degradation has been accompanied by irruptions of native burrowing animals, which has accentuated the loss of ground cover. Severely degraded areas of alpine meadows are referred to as 'Heitutan'. Here, using the framework of alternate stable state theory, we describe the proximate and ultimate drivers of the formation of Heitutan on the QTP, and we assess prospects for recovery, in relation to the degree of biophysical alteration, of these alpine meadows. Effective rehabilitation measures must address the underlying causes of degradation rather than their symptoms. Heitutan degradation is not uni-causal. Rather it reflects different mechanisms operating at different spatio-temporal scales across this vast region. Underlying causes include overly aggressive exploitation of the grasslands (e.g. overgrazing), amplification of grazing and erosion damage by small mammals when outbreaks occur, and/or climate change. Given marked variability in environmental conditions and stressors, restorative efforts must vary across the region. Restoration efforts are likely toyield greatest success if moderately and severely degraded areas are targeted as the first priority in management programmes, before these areas are transformed into extreme Heitutan.
基金funded by the Qinghai Science and Technology Department(Grant No.2020-ZJ-904)the National Natural Sciences Foundation of China(Grant No.31872999)+4 种基金the 111 Project(Grant No.D18013)Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK1002)Changjiang Scholars and Innovative Research Team in University,MOE(Grant No.IRT_17R62)local authorities for their support for this workUniversity of Auckland for their commitment to the Three Brothers Project。
文摘Process interactions on catenas have supported grazing adapted ecosystems and sustained biodiversity values in the source zone of the Yellow River in western China for millennia.In recent decades,anthropogenic disturbance and climate change have threatened the integrity of these systems,impacting upon environmental values and their capacity to sustain local livelihoods.Collaborations between local experts and a team of international researchers during a workshop and field excursion to this area in July 2019 developed a cross-disciplinary,process-based model of alpine meadow catenas.This paper relates the contemporary health of these grassland-wetland systems to their‘best achievable state’under prevailing boundary conditions,differentiating stages of degradation and recovery in relation to climate and land use changes.Recovery is underway for alpine meadow catenas at Maqin.Reduced land use pressures(stocking rates)and longer growing seasons have enhanced grasslandwetland conditions.However,recovery prospects are limited for local areas of extremely degraded grasslands(heitutan),as breached abiotic thresholds have resulted in soil and nutrient loss and reduced capacity for water retention.While lagomorphs and rodents act as ecosystem engineers when alpine meadows are in a healthy state,irruptions locally increase the proportion of bare ground and inhibit recovery potential.Management options that support recovery of alpine meadows are presented for differing stages of degradation.
