This article below was written by Jens Hilke and printed in the winter edition of Natural Heritage Harmonies, a publication of the Vermont Department of Fish and Wildlife. The regional, or valley, perspective of habitat fragmentation underscores the importance of the MRV’s Forests, Wildlife, Communities Project.
Several years ago, I was involved in a project to reshoot a series of aerial photos of washed out bridges and flooded buildings taken just after the 1927 flood . Our team logged many hours in a small Cessna flying the river valleys of Vermont trying to capture the same angles that a photographer had used some eighty years prior so that we could document the changes seen in the landscape, creating a matched pair of “then and now” photos. Flying affords an incomparable macro perspective. Terrain details blur and you’re left with a mosaic of towns and forests and farmland. The more we looked at the photos and then at the distant terrain out the plane window, the more history blurred as we imagined how clearing for farming in the 1800s led to the flooding and erosion seen in 1927, and how those fields have grown up into today’s varied habitats.
So, when we ask the question “what is good quality fish and wildlife habitat on our land,” we should begin by “looking out the plane window”—adopting the birdseye view of the mosaic and patterns of forests and fields, as well as the history of an ever changing landscape.
A few landscape patterns jump out immediately. We are likely to see broad expanses of forests that haven’t been developed. They are bordered by roads and buildings but include continuous mixes of natural communities, from evergreen and deciduous forests to meadows, streams and wetlands. I call these areas contiguous habitat blocks and use them to represent biological diversity. The mix of varied topography, climate and physical features (such as bedrock), produces niches in which more wildlife species can find homes.
So, bigger blocks of contiguous habitat generally have more species diversity than smaller blocks. This gives us a sense of biological diversity based simply on the size of the blocks. It isn’t an absolutely comprehensive measure since there are many rare species and significant natural communities that fit in small parcels. But this landscape perspective gives us a quick and easy sense of where diversity might be greatest.
Now these blocks often include working forests, and lands important for recreation and other values compatible with wildlife habitat. So we’re not defining lands that are free from human use, but simply lands that aren’t developed.
In many places in Vermont we see isolated forest “islands” surrounded by development and agriculture. This forest fragmentation is a problem of both reducing the size of the forest patches as well as degrading the quality. We’re still losing wildlife habitat as development continues to isolate forest blocks and as development creeps into forest blocks, hiding under the canopy but still reducing habitat quality.
Landscape context is important. There is no minimum or maximum number of acres to define contiguous habitat. Instead consider the size of the contiguous habitat block as well as all the associated species of plants and animals, within the context of the level of fragmentation in the region. Habitat configuration also has an impact. For example, an area of forest habitat that is highly irregular in shape, with a high degree of forest edge may be less functional for some species than forest habitat of the same acreage with a regular shape. So as these contiguous blocks become more isolated and have more edge, they become less diverse and functional.
We can see from our birdseye view that many of our forests or contiguous habitat blocks are often connected by narrow bands of greenspace. Sometimes these “connecting lands” follow river corridors, sometimes they are upland. Connecting lands (corridors) may include roads, lightly developed lands or even less suitable lands but still allow wildlife species to cross between big blocks of forests and wetlands. On this landscape scale, this connectivity function is incredibly important, effectively increasing the size of habitat blocks. Even though it might be clear that these connections aren’t as good quality habitat as the bigger blocks, they are incredibly important functionally.
At a landscape scale, we often look at the needs of far-ranging species such as black bear or moose as representatives for a variety of the smaller-ranging species that live within the bear’s home range. If we manage enough land in a way that allows for these far-ranging species to survive, we’ve also allowed for the host of smaller-ranging, often lesser-known, species within that block.
As we look at our birdseye view, we must keep in mind that it is the history of the land use that has helped form this mosaic. For example, some of today’s white pine stands were badly eroded sheep pasture in the 1800s and prior to that they were likely mixed hardwoods. This serves to remind us that the landscape is constantly changing, reacting to people’s decisions for hundreds of years now. Our mosaic is in large part a pattern of our own making and has shown many other patterns over the land’s long history. The land use decisions we make today, that improve or degrade wildlife habitat quality, will be clearly visible in the patterns of our landscape tomorrow.