Moose, fire and forest ecology

Robert Frost quotes the 17th Century proverb “good fences make good neighbors” in his Mending Wall poem. He questions why fences make good neighbors, asking what he was walling in or walling out, and to whom he may be giving offence by building a wall. He concludes his musings by asking “Why do they make good neighbors? Isn’t it/Where there are cows?” — an apt nod to the prevalence of our moose neighbors roaming the Kenai Peninsula. Hidden in forgotten pockets of forest and old burn areas across the Kenai National Wildlife Refuge and the Chugach National Forest are a series of mainly rectangular high-walled fenced-in plot structures, offending hungry moose eyeing the birch growth inside. 


Why were these grand and durable structures, intended to keep moose out, constructed in the first place? The interactions of fire, climate, moose browse, and tree regeneration make a dynamic ecological story across the Kenai Peninsula. In the 1960s, when moose densities were high in the aftermath of the big 1947 burn, several of the moose exclosures 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. 

Seventeen of these structures exist in varying states of repair. An interest in relocating and documenting the structures began in the mid-1990s with our former Refuge ecologist, Dr. Ed Berg. Documenting some of the sites was an intriguing mix of talking to locals and long-time staff members, reviewing limited old records, and serendipitous discovery by staff doing other field work. In a few locations, existing records were difficult to interpret as roads have been widened or changed, trails re-routed, or streams have migrated. Of the seventeen documented sites, several in challenging terrain have not been revisited in many years, and one has collapsed. Most are in sturdy enough shape to last for many more years, but the two selected for reconstruction were in the worst condition, with eminent breaching potential by moose. 

The Refuge’s Youth Conservation Corps crew spent two days repairing these structures, one located along the Russian Falls trail and the other near Quartz Creek. Built in approximately 1970 and in 1960, respectively, both exclosures were compromised structurally, with whole sides falling over and willow growth overtopping and crushing side walls. The exclosure along the Russian Falls trail is perhaps the most visible to the public, with an unmarked but maintained gravel trail to the structure, and an interpretive sign explaining the difference in growth rates for birch with and without browsing. Crew leaders and members installed new structural posts, added side support beams, replaced cross-bars, and installed new wire fencing. Crew members also took turns assisting biology staff in measuring the vegetation diversity in a series of meter-sized plots both inside and outside the fence to directly compare differences. 

What’s growing inside either of the repaired exclosures was dramatically different, ecologically speaking, from the forest outside of the fences. Inside the Quartz Creek fence is a thick and abundant tall birch forest, with huge willows overtopping the sides of the exclosures. Just outside is 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 shows a more subtle contrast, but inside the fence were tall, healthy birches, while just outside are 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. While all exclosures have not yet been revisited, the 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 more recently burned (1994, 2002) so we can assess how browsing moose change post-fire vegetation composition and structure. Future vegetation monitoring needs on the Kenai will incorporate paired unexclosed and exclosed plots. 

Conversion from spruce (which is highly flammable when mature) to hardwood forests (which are relatively fire resistant when mature) 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 such as 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 in response to exotic species of insect defoliators, invasive plants, and earthworms on the Refuge. 

Preserving the legacy of the plots, and maintaining the structures, is a component in understanding the long term interactions of our wildlife, vegetation, and fire ecology on the Kenai, as well as keeping our Refuge and Forest history alive. And although, as Frost informs his neighbor, “My apple trees will never get across/And eat the cones under his pines,” the moose are more than happy to enjoy a birch sapling snack or a fresh willow branch in all the tasty expanses outside the fence.  

Dr. Elizabeth “Libby” Bella is an ecologist at Kenai National Wildlife Refuge. You can find more information about the Refuge at or


An Outdoor View: Getting along with bears

Author’s note: The Clarion first published this column on Aug. 11, 2006. It has been edited it for brevity. — LP

Read more