Function, effects, and management of forest roads
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.
References (65)
- et al.
The effect of human activity on the structure and composition of a tropical forest, Puerto Rico
For. Ecol. Manage.
(1994) - et al.
The effects of road design and harvest intensity on forest damage caused by selective logging: Empirical results and a simulation model for the Bosque Chimanes, Bolivia
For. Ecol. Manage.
(1993) - et al.
Rates and patterns of deforestation in the Philippines: Application of geographic information systems analysis
For. Ecol. Manage.
(1993) - et al.
Impacts of disturbance initiated by road construction in a subtropical cloud forest in the Luquillo Experimental Forest, Puerto Rico
For. Ecol. Manage.
(1998) - et al.
Importance Of Rural Roads As Source Areas For Runoff In Mountainous Areas Of Nothern Thailand
J. Hydrol.
(1997) - et al.
Modelling road surface sediment production using a vector geographic information system
Earth Surface Processes and Landforms
(1998) - et al.
Effects of roadside disturbance on substrate and vegetation properties in arctic tundra
Ecol. Appl.
(1997) - Barrow, C.J., 1991. Land Degradation. Cambridge University Press, Cambridge, p....
- et al.
Survey of native prairie on railroad rights-of-way in Minnesota
Transp. Res. Rec. (Washington)
(1981) - Bliss, L.G., 1990. Arctic ecosystems: patterns of change in response to disturbance. In: Woodwell, G.M. (Ed.), The...
Roads, land use, and deforestation: a spatial model applied to Belize
The World Bank Econ. Rev.
Abolishing virginity
J. Trop. Ecol.
Threats to wilderness ecosystems: impacts and research needs
Ecol. Appl.
Some general principles of landscape and regional ecology
Landscape Ecol.
Roadside soils: A corridor for invasion of xeric scrub by nonindigenous plants
Nat. Areas J.
The distribution and abundance of organisms as a consequence of energy balances along multiple environmental gradients
Oikos
An integrated approach to the ecology and management of plant invasions
Conser. Biol.
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