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Severely degraded high mountain vegetation recovers under different levels of wild herbivore grazing pressure, 1991-2021

James Kirkpatrick , Kerry Bridle

Abstract

Context. It is important to understand the way in which wild herbivore grazing affects decadal vegetation dynamics after cessation of unnatural disturbances, especially in a context of climate change. Aims. We investigated the decadal effects of different grazing regimes on treeless subalpine vegetation recovery from stock grazing and burning on sites of different environmental character and initial state. Methods. At each of four sites, two fenced areas that excluded mammalian herbivores, two that allowed in only rabbits and two grazed control plots were monitored every five years between 1991 and 2021. General linear models were developed to explain variation in change over the thirty years in different cover types. The years in which peak and trough values occurred were also determined, as were the incidence and direction of differences between treatments in sites and years. Key results. There was marked variation in change over 30 years between the sites and lifeforms. Exclusion of mammalian herbivores increased the slow rate of revegetation. There was little effect from rabbits by themselves. Unexpectedly, the cover of both short and tall herbs was not promoted by grazing exclusion. Short term climatic variation affected some cover types, with many peaks and troughs in the dry year of 2001, but it was not possible to disentangle decades scale climate change effects from the process of recovery after disturbance. Conclusions. The slight increase in revegetation rates in the absence of native herbivores and rabbits does not justify culling. Restoration interventions appear to be unnecessary. The prospect of increasing fire incidence and deer numbers suggests that it is desirable to continue monitoring the plots.

BT23085  Accepted 15 April 2024

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