Function, effects, and management of forest roads

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Abstract

We propose a unified approach to the management and analysis of the function and effects of roads on forested rural landscapes. The approach is based on considering roads as ecosystems (techno-ecosystems) and conducting analyses of road ecology prior to making policy or management decisions. An ecosystem approach to road issues has four advantages: (1) allows for the analysis of all types of roads irrespective of geographic location; (2) provides a holistic framework for analyzing all aspects of roads from their alignment to their operation and decommissioning as well as all road functions irrespective of value judgment; (3) provides a holistic focus to their management; and (4) supplements landscape management approaches based on spatial concepts. We present five precautions to be considered when evaluating road ecosystems: (1) identify the type of road under consideration; (2) differentiate the effects and conditions of individual road segments from those of road networks; (3) be explicit about what phase of road development the argument applies because different phases of development have different effects on the landscape; (4) ascertain the age of the road and evaluate the degree of landscape adjustment to the road and vice versa; and (5) not to prejudge human-induced changes in landscapes as automatically good or bad for the ecology or economy of a region. This ecosystem focus and guiding principles are applied to several issues that road policy and management activities must address.

Introduction

Roads are a critical component of civilization. Developing and maintaining the economic activity that is vital for the quality of modern life would be difficult without roads. Roads provide access for people to study, enjoy, or contemplate natural ecosystems. In fact, the development of human civilization has benefited from transportation systems that evolved from foot trails to complex highway systems (Chisholm, 1990, Grubler, 1994). Building and maintaining roads have become controversial, however, because of public concerns about their short- and long-term effects on the environment and the value that society now places on roadless wilderness (Cole and Landres, 1996, Williams, 1998). Opposition to road building and pressure to decommission roads in rural landscapes will continue to increase as roadless areas decrease in relation to roaded ones.

Decisions about road alignment, building, maintenance, or decommissioning are complex because of the many tradeoffs involved. One example is the quote below expressed for rural roads through tropical forests. Another example might be the tradeoff between access to roads for recreation and research with the potential effects of that access on biodiversity. Roads have been evaluated from physical, biological, and socioeconomic points of view, often under only one set of criteria in isolation from others. Such an approach is useful for identifying issues, but it can lead to conflict and flawed policy because it may play one set of values against another. For example, a road that is justified only by economic criteria at the expense of ecological ones – or vice versa – is likely to be questioned by advocates of the missing criteria. A unified approach to alignment, constructing, maintaining, and decommissioning roads is needed to optimize resource use.

The focus of much of the ecological literature on roads is on their deleterious effects (Scheidt, 1967, Forman, 1995a, Forman et al., 1997). Typically, the effects of roads on a wide variety of parameters are compiled to demonstrate their harmful consequences. The listings are usually collected from various parts of the world e.g., the Arctic (Bliss, 1990, Auerbach et al., 1997), Belize (Chomitz and Gray, 1996)1, United States (Furniss et al., 1991, Miller et al., 1996, Forman et al., 1997), Bolivia (Gullison and Hardner, 1993), the Amazon (Turner and Meyer, 1994), the Philippines (Liu et al., 1993), Thailand (Ziegler and Giambelluca, 1997), Puerto Rico (Patterson Zucca, 1978, Olander et al., 1998), St. John, US Virgin Islands (MacDonald et al., 1997, Anderson and MacDonald, 1998), or Europe (Reck and Kaule, 1993), and then combined, as if all of the effects will happen regardless of environmental conditions, use, or engineering and design considerations. Are road effects universal or are there patterns or differences that can be used to improve road policy and management? Are any desired ecological effects associated with roads or are all effects negative?

Part of the problem with evaluating ecological effects of roads is that their ecological benefits are hard to confirm (Lyon, 1984) and all ecological changes tend to be interpreted as negative. For example, the positive effects of road runoff on plant growth in low rainfall areas is deemed negative to slow growing, drought-adapted plants, or due to alien species that take advantage of the increased moisture (Huey, 1941). Moreover, though road effects change over time, they start with a ‘negative balance’ because of the high impact of construction activities (Lyon, 1984). Few studies explore the long-term aspects of road ecology or consider available management opportunities (Lyon, 1984, Furniss et al., 1991, LaFayette et al., 1996, Olander et al., 1998). Evaluating the ecological effects of roads requires rigorous analysis and an understanding of the ecology of roads, that is, the interplay between all of the living components, the function of roads, and the environmental factors that regulate processes along the road corridor (Forman et al., 1997).

Establishing a new road segment or road network on a landscape is equivalent to adding a new ecosystem to the existing one. Although road ecosystems are human creations like railroad or powerline rights of way, they have natural analogs in riverine and riparian corridors. Treating roads and other human-created corridors as ecosystems might be used in developing methods for analyzing and evaluating them in the context of their surrounding landscapes. Naiman and Décamps (1997) proposed terminology and formalized an ecological approach for studying ecosystem interfaces using riparian corridors as examples. Much of what they discuss applies to road corridors, but differences exist between roads and riparian corridors. For example, the nature, frequency, and intensity of material exchanges across the interfaces differ in roads and riparian zones. Nevertheless, a unified ecological approach to roads and road networks is useful in making decisions about road management issues and can provide a mechanism in developing consensus among stakeholders.

In this paper we treat roads as ecosystems and propose a unified ecosystem approach to road management. We focus attention on roads in forested landscapes but the principles discussed can also be applied to nonforested lands.

Section snippets

Roads as ecosystems

Roads can be defined as ecosystems because they occupy ecological space (sensu Hall et al., 1992), have structure, support a specialized biota, exchange matter and energy with other ecosystems, and experience temporal change. Road ecosystems are built and maintained by people (techno-ecosystems sensu Haber, 1990). Road ecosystems are characterized by open fluxes of energy and matter and a predominance of respiration over photosynthesis, i.e., they are subsidized heterotrophic systems. The road

Factors that influence the function of roads

The environmental gradients believed to be most important in describing the ecological space in which roads function as ecosystems are shown in Fig. 2. The gradients are arrayed hierarchically from the most general to the most detailed. An advantage of this approach is that it does not compare roads on the basis of geographic space (eastern roads with western, tropical with temperate) and avoids lumping roads as if they all behaved in the same way. Instead, this approach allows analysis or

Management implications

An ecosystem approach to road issues has four advantages. First, it allows for analysis of all types of roads irrespective of geographic location, i.e., either latitudinal or elevational position. Roads are compared by their location in ecological space. Second, it provides a holistic framework for analyzing all aspects of roads from their alignment to their operation and decommissioning as well as all road functions irrespective of value judgment. Third, it provides a holistic focus to road

Fragmentation

Roads fragment the landscape and affect populations and communities. However, the evaluation of the effects of roads on fragmentation is difficult for three reasons: (1) different types of roads as well as different levels of road use and maintenance pose different barriers to organisms, (2) different species or groups of organisms have different thresholds of tolerance to dispersal barriers, and (3) the size threshold for normally functioning community fragments is not known, but expected to

Market and non-market economics

Chomitz and Gray (1996) developed a land-use model to explore the tradeoff between economic development and deforestation in rural Belize. They observed that the conditions through which the road was passing, i.e., low human population density and nutrient-poor soils, resulted in a lose-lose situation for both the economic and the environmental aspects of the road. Soil quality, land tenure regulations, and intended uses of the road became important determinants on deciding whether placing a

Conclusions

In summary, roads are a challenge to scientists and managers because they are complex ecosystems that traverse the landscape and affect its function at both local and regional scales. Traditionally, road analysis has been narrowly focused both geographically and ecologically. We propose that roads be analyzed as ecosystems using environmental gradient analysis to distinguish between road segments in different sectors of the landscape or across latitudes and elevation. Such an ecological

Acknowledgements

This work was done in cooperation with the University of Puerto Rico. We thank several anonymous reviewers and the following colleagues for their suggestions to improve the manuscript: S. Brown, C. Domı́nguez Cristóbal, W. Edwards, D. Ryan, F.N. Scatena, F. Swanson, and J. Wunderle.

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