Climate Change Is Likely to Alter Future Wolf – Moose – Forest Interactions at Isle Royale National Park, United States

Nathan R De Jager,Matthew J Duveneck,Jason J Rohweder

doi:10.3389/fevo.2020.543915

Abstract

We evaluated how climate change and variable rates of moose browsing intensity, as they relate to wolf predation, might impact the forests of Isle Royale National Park, MI USA by conducting a simulation modelling experiment. The experiment consisted of contrasting three different scenarios of wolf management and with a static (current conditions) and changing climate (high emissions). Our results suggest that the interactive effects of wolf predation and climate change are likely to be temporally variable and dependent on biogeographic and forest successional processes. During the first 50 years of simulations, when the effects of climate change were minor, higher simulated rates of predation by wolves reduced moose population densities, resulting in greater forest biomass and higher carrying capacities for moose. However, over the longer term, early successional and highly palatable aspen and birch forests transitioned to late successional spruce and fir forests, regardless of climate or predation intensity. After 50 years, the effects of climate change and predation were driven by effects on balsam fir, a late successional species that is highly palatable to moose. High-intensity predation of moose allowed balsam fir to persist over the long term but only under the current climate scenario. Climate change caused a reduction in balsam fir and the other boreal species that moose currently feed on, and the few temperate species found on this isolated island were unable to compensate for such reductions, causing strong declines in total forest biomass. The direct effects of moose population management via reintroduction of wolves may become increasingly ineffective as the climate continues to warm because the productivity of boreal plant species may not be sufficient to support a moose population at all, and the isolation of the island from mainland temperate tree species may reduce the likelihood of compensatory species migrations.

Highlights

Today’s natural resource management agencies are tasked with anticipating how the effects of their decisions are likely to play out over the long term in the face of climate change
We addressed the following questions: (1) How does predation by wolves influence moose population dynamics and the effect of moose browsing on patterns of forest succession and productivity with and without climate change? (2) Are northern hardwood forests able to replace boreal forests as the climate warms and does this phenomenon depend on rates of wolf predation? (3) In general, can Isle Royale support both a healthy forest and a moose population over the long-term in the face of climate change, and how much does the answer depend on the rate of predation by wolves?
Past research has indicated that wolf predation can play a significant role in reducing and/or redistributing the intensity of moose browsing across the island (Vucetich et al, 2011; Peterson et al, 2014) and that reductions to moose browsing intensity would be expected to change rates of forest succession (Pastor and Naimen, 1992; Pastor et al, 1993; Pastor and Danell, 2003)

Summary

Introduction

Today’s natural resource management agencies are tasked with anticipating how the effects of their decisions are likely to play out over the long term in the face of climate change. Management agencies often use a variety of techniques to locally reduce herbivore populations (e.g., re-introducing predators or conducting controlled harvests) when their populations grow large enough to affect forest resources in ways that cause conflicts with other land management objectives (Demarais et al, 2012). While such actions can have important effects on the plant communities that these animal populations rely on (Terborgh et al, 1999; Ripple and Beschta, 2012), so too can climate change (Iverson et al, 2008). Will population management actions continue to be effective as the climate warms? Will population management actions become increasingly important? More generally, will the ecosystems that currently support large mammalian herbivore populations continue to do so in the future, with or without population management?

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Conclusion