Long term prevention of disturbance induces the collapse of a dominant species without altering ecosystem function.

Qiang Yu,Hao Yang,Zhengwen Wang,Melinda Smith,Xingguo Han,Honghui Wu,Fumei Lü,Dan F B Flynn

doi:10.1038/srep14320

Abstract

Limitation of disturbances, such as grazing and fire, is a key tool for nature reserve management and ecological restoration. While the role of these disturbances in shaping ecosystem structure and functioning has been intensively studied, less is known about the consequences of long-term prevention of grazing and fire. Based on a 31-year study, we show that relative biomass of the dominant grass, Leymus chinensis, of grasslands in northern China declined dramatically, but only after 21 years of exclusion of fire and grazing. However, aboveground net primary productivity (ANPP) did not decline accordingly due to compensatory responses of several subdominant grass species. The decline in dominance of L. chinensis was not related to gradually changing climate during the same period, whereas experimentally imposed litter removal (simulating fire), mowing (simulating grazing), fire and moderate grazing enhanced dominance of L. chinensis significantly. Thus, our findings show that disturbances can be critical to maintain the dominance of key grass species in semiarid grassland, but that the collapse of a dominant species does not necessarily result in significant change in ANPP if there are species in the community capable of compensating for loss of a dominant.

Highlights

Litter decreased species richness and evenness[14]
The expectation is that if the exclusion of grazing and fire does not favor dominant species and/or strongly modifies biogeochemical processes, the ecosystem impacts of the disturbance prevention can be large and potentially nonlinear, if disturbance is excluded over the long-term and in tandem with other global change drivers, such as climate change[22]
Our study addresses the following questions: (1) Whether dominance of L. chinensis, plant community structure, and ecosystem functioning changes gradually or abruptly during long-term (30 + y ears) exclusion of two key disturbances – fire and grazing? and (2) Does the shift of dominant species result in significant change in ecosystem function? Our expectation was that long-term exclusion of disturbances would negatively impact dominance by L. chinensis over time, and that this decline in dominance would alter plant community structure and negatively impact aboveground net primary productivity (ANPP)

Summary

Introduction

Litter decreased species richness and evenness[14]. our understanding is limited concerning the long-term (e.g., > 30 years) impacts of removal of disturbances on plant community dynamics and ecosystem function for ecosystems in which disturbances are integral to their structure and function. The expectation is that if the exclusion of grazing and fire does not favor dominant species and/or strongly modifies biogeochemical processes, the ecosystem impacts of the disturbance prevention can be large and potentially nonlinear, if disturbance is excluded over the long-term and in tandem with other global change drivers, such as climate change[22]. It remains unclear whether ecosystem structure and function changes gradually (linearly) or abruptly (nonlinearly) after long-term prevention of disturbance and whether shifts in abundance of dominant species drive these dynamics. The goal of our research was to document these dynamics and assess potential mechanisms underlying the expected decline in L. chinensis dominance

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Conclusion