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Moose Exclosure Plots

Seventeen high-walled, fenced-in plot structures exist in varying states of repair across the Kenai National Wildlife Refuge and the adjacent Chugach National Forest. These durable structures were installed to better understand the interactions of fire, climate, moose browse, and tree regeneration. Of the seventeen documented sites, several have not been revisited in many years, and one has collapsed. Most are still sturdy enough to last for many years, and two were reconstructed in 2012.

The presence of exclosures on the Kenai NWR and the Chugach NF provides a unique opportunity to directly compare various stages of post-fire succession with and without moose herbivory. Historical records suggest that moose were not abundant (and perhaps not even present) on the peninsula before human-caused fires late in the nineteenth century. In the 1960s, when moose densities were high in the aftermath of the big 1947 burn, several of the structures were installed as a long-term experiment to understand differences in hardwood and shrub growth between non-browsed and browsed sites. Later construction, in post-1969 burn areas and in the 1980s, reflected a desire to continue to understand the role of fire interacting with browse in determining forest composition and structure.

Vegetation data collection showed that forest structure inside of and outside of the two exclosures that were repaired in 2012 was dramatically different, ecologically speaking. Inside the Quartz Creek fence was a thick and abundant tall birch forest, with huge willows overtopping the sides of the exclosures. Just outside was a dark spruce forest, with small willow patches. Interestingly, the wildflower and small shrub diversity was greater on the outside, probably due to openings in the spruce cover offering more light to the forest floor. The Russian Lakes fence showed a more subtle contrast, but inside the fence were tall, healthy birches, while just outside were heavily browsed seedlings and saplings, and shorter birches mixed in with spruce. The forest floor inside included a dense mat of low shrubs and mosses, while the exterior had a thinner mat of sparse moss and various small shrubs and wildflowers.

By revitalizing data collection inside and outside the plots, we’ll have a set of data to illustrate forest structure and composition differences directly tied to a specific disturbance – moose herbivory. We also have the opportunity to integrate information on another disturbance - the well-studied fire history regime on the Kenai. Herbivory by large moose populations has a substantial effect on the hardwood component of forest vegetation. Plots constructed in post-1969 burn areas may show differences in forest succession between browsed and un-browsed plots. We have also established unexclosed plots on parts of the Refuge in more recently burned areas (1994, 2002) so we can assess how browsing moose change post-fire vegetation composition and structure. Quantifying the role of moose herbivory in the succession process is important because its impact probably depends on the scale of the disturbance. Large burn areas like that of 1947 and 1969 can initiate dramatic increases in moose abundance, followed by a positive feedback of intensified herbivory which further increases the population. Smaller burns may not stage this feedback, as they experience less herbivory and a better developed hardwood stage of succession. Future vegetation monitoring needs on the Kenai will incorporate paired unexclosed and exclosed plots.

Tree-ring studies may also be used to detect changes in moose populations, as reflected by changing degrees of hardwood browsing. In one old sampled birch stand (the Bufflehead Birch stand), for example, trees are more than 200 years old. The trees grew rapidly in the sapling stage, as shown by wide growth rings. Birch saplings today in the Refuge generally have very narrow growth rings, due to intense browsing. By examining birch (and willow) stands of different ages, we may be able to document reduced growth due to increasing moose populations in the last century, as the historical record suggests.

Conversion from spruce (late stage forests are highly flammable) to hardwood forests (early stage forests are relatively fire resistant) is the expected trajectory after an intense fire that burns down to mineral soil, but our fire regimes are likely changing as our climate warms. Understanding past regeneration potential for birch and other hardwood species like cottonwood and quaking aspen will help us understand future successional pathways that will likely change not only because of a warming climate, but in unexpected and sometimes synergistic ways to response to exotic species of insect defoliators, invasive plants, and earthworms on the Refuge. Planning the distribution of early-successional areas is a challenge that will evolve as we study the current forest dynamics through a changing climate lens. Maintenance of the structures is a component in understanding the long term interactions of our wildlife, vegetation, and fire ecology on the Kenai.

Last Updated: Dec 19, 2012
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