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

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 5 years between 1991 and 2021. General linear models were developed to explain variation in change over the 30 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.