Reed, Rebecca A., Julia Johnson-Barnard, and William L. Baker. 1996. Contribution of Roads to Forest Fragmentation in the Rocky Mountains. Conservation Biology. Vol. 10, No. 4, pages 1098-1106.

RELEVANT TO:

FORESTS/LOGGING/RESTORATION

MOTORIZATION

SPECIES

HABITAT LINKAGES

DESCRIPTION OF DOCUMENT

This document provides evidence on the contribution of roads and clearcuts to forest fragmentation. The authors quantify fragmentation due to roads in a 30,213-hectare section of the Medicine Bow-Routt National Forest in southwestern Wyoming with several indices of landscape structure using a geographic information system (GIS). The paper presents the results of their GIS analysis on the landscape, primarily roads and clearcuts. Results indicate that roads add to forest fragmentation more than clearcuts by dissecting large patches into smaller pieces and by converting forest interior habitat into edge habitat. The document presents interpretation of patch-related effects, edge-related effects, and applications to forest management.

MAJOR FINDINGS

Fragmentation is defined by the authors as a change in landscape structure that typically, but not universally, includes smaller patch sizes, smaller patch perimeter lengths, greater distances between patches, more edge habitat, and less interior habitat (i.e., habitat not affected by human-created boundaries). Roads precipitate fragmentation by dissecting previously large patches into smaller ones, and in so doing they create edge habitat in patches along both sides of the road, potentially at the expense of interior habitat.
Fragmentation affects animal populations in a variety of ways, including decreased species diversity and lower densities of some animal species in the resulting smaller patches (Arnold, et al. 1995, etc.).
Roads cut existing patches of forest into two or more patches. The effect of roads on edge habitat was examined in the study by placing 50- and 100-meter depth-of-edge influences along the roads on each map created. These edge depths were chosen because Vaillancourt (1995) found that edge effects in terms of edge species habitat were evident approximately 50 meters or more into the surrounding forest habitat in this area of Wyoming.
The results of this study indicate:

Clearcuts, roads, and area-of-edge influences created by clearcuts and roads affect 42% of the study area and 62% of the loggable area (20,201 hectares of land that is legally available for logging in the study area), assuming a 100-meter depth-of-edge influence.
The amount of edge created by roads in the study area is 1.54 times that created by clearcuts assuming a 50-meter depth-of-edge influence.
If a 100-meter depth-of-edge influence is assumed, the amount of edge created by roads is almost 2 times that created by clearcuts .
Roads cause a degree of fragmentation even greater than that caused by clearcutting alone.

These landscape structure measurements demonstrate a clear pattern of fragmentation of the landscape by roads and a greater fragmentation effect from roads than clearcuts. The number of patches approximately tripled due to road dissection even in a landscape that had heavy clearcut activity. The implications of decreasing mean patch area are manifested largely in the substantive increase in the ratio of area-of-edge influence to interior area. Such trends indicate a significant reduction in the amount of interior forest habitat available to requisite interior species such as pine martens and brown creepers in this area, or gray wolves or northern spotted owls in areas to the north and west.
Larger distances between suitable interior habitat patches may make migration between patches more difficult for individuals in a population and could ultimately lead to isolation of subpopulations within patches or small areas of the landscape, possibly endangering the survival of species (Saunders et al 1991).
The concern with the introduction of edges onto landscapes results from potentially detrimental microclimatic and biological changes, relative to intact forest, which occur along the edges (Noss and Cooperrider 1994). Edge habitat along roads and clearcuts experience microclimatic changes, including increased evaporation, temperature, and incident solar radiation; and decreased available soil moisture (Kapos 1989, etc.). Road edges tend to exist long-term (as compared with clearcuts) and be disturbed more frequently.
Road edges increase pollution (Santelmann and Gormam 1988), soil erosion (Hodgson and Dixon 1989, etc.), noise (Reijnen et al 1995), direct vehicular fatalities (Wilkens 1982, etc.), disturbance by human activity (Stankey 1980, etc.), and exotic weed introductions (Amor and Stevens 1976, etc.), and may induce population changes (McLellan and Shackleton 1988, etc.) in the vegetation and animal communities included in the areas of edge influence. These factors combine to create particularly deleterious habitat situations, and endanger the existence and perpetuation of all native species (interior and edge species alike) on the landscape.
Applications to forest management include:

The authors recommend a forest-wide program of systematic obliteration and revegetation of roads. This measure would reclaim land for a variety of resources, including wildlife and timber production.
Not only should existing old, little-used logging roads be revegetated, but road obliteration and revegetation should become part of the overall harvesting process.
Timber harvests should be planned to minimize impact on the landscape and exacerbation of the current landscape fragmentation problem on the forest.
An adequate assessment of present and future fragmentation in forests subject to timber harvest should include an analysis of 1) harvested and roaded area, 2) the edge created by these activities, and 3) the dissection of patches by roads.
Roads must be mapped as accurately as possible, for example by using global positioning systems. Otherwise road lengths and the impacts of roads on the landscape may be significantly underestimated.
A cumulative effects analysis of proposed roads and effectively closed roads over several decades should become part of the environmental assessment process required of extractive activities.

QUESTIONS THIS RAISES FOR THE THREE FORESTS

Have the Three Forests documented landscape-level (i.e. the Forest) fragmentation caused by roads? Has a cumulative effects analysis been completed that applies a 50- or 100-meter depth-of-edge influence?
Do the Three Forests have any evidence to believe that negative impacts of habitat fragmentation caused by roads are any different than the southwestern Wyoming forests of this study?
Have the Forests documented increased prevalence of exotic weeds and soil erosion along forest roads?
Do the Three Forests have accurate maps of where all (Forest Service designed and user-created) roads occur?
Do the Three Forests currently have an active program of road closure and obliteration/revegetation?

VI. Forest Management Significance

Each of the Three Forests should analyze the potential area of edge effect reduction offered by closure/revegetation of various categories of roads, e.g.: old logging roads; unnecessary roads bisecting otherwise large contiguous habitat; unnecessary draw-bottom roads; and all user-created roads.
It is important to maintain large roadless habitat.