Reducing habitat fragmentation by minor rural roads through traffic ...

134 C.F. Jaarsma, G.P.A. Willems / Landscape and Urban Planning 58 (2002) 125–135Half of this percentage can be attributed to MRRs,according Derckx (1995).Lower traffic flows do not necessarily lead to fewerroad kills. Huijser et al. (1998) discussed this ideathat higher traffic flows do not always lead to moreroad kills, because a bigger barrier effect can, in fact,prevent species from attempting to cross the road.Conversely, lower traffic flows, leading to a smallerbarrier effect, might in fact encourage species to tryto cross the road more frequently, resulting in moreroad kills.Nevertheless, according Forman and Alexander(1998), road kills have only a minimal impact onthe overall population size. Once you minimise theeffects of road kills, the barrier effects can beincreased and vice verse. Greater disturbance has agreater impact on the fauna than either the road kills orthe destruction of suitable habitat, because this impactaffects far more animals within a larger area.Fragmentation does not automatically lead to adecrease of biodiversity. The new spatial heterogenitythat results can provide space for new species. Formany species the landscape is not an archipel ofhabitat islands, but rather a mosaic of different ecotopesin a characteristic pattern (RMNO, 1990).Finally, the impacts of (de-)fragmentation on theecology and the concept of the TCRA can also affectthe local inhabitants and outdoor recreationists eitheron bike or foot. They may feel themselves safer and/orare less hampered by noise and emissions. For farmers,road crossings with cattle or tractor can becomeeasier. Thus, an improvement of the liveability of localresidents and recreationists can go hand in hand withde-fragmentation of habitat.7. ConclusionThe concept of the TCRA was developed for TheNetherlands (Jaarsma, 1997), a small industrialisedcountry with a dense population and a dense rural roadnetwork. The idea behind rural traffic calming thatincludes the concentration of through traffic on alimited number of rural highways and leaving theminor roads to smaller flows of rural bound traffic,is believed to be equally relevant in other countries.The relevancy is greatest where present diffuse trafficflows are hampering local people, recreationists, and/or the fauna. To implement the concept alternativeroutes within the region must be available, usuallyafter adaptation of existing roads. In countries with adense public road network, such alternatives are generallyavailable.The concept of TCRA was developed to improverural traffic safety (Jaarsma, 1994). The concept hasalso proven useful for reducing habitat fragmentationalong MRRs (Jaarsma and van Langevelde, 1997). Toreduce the habitat fragmentation of the complementingroads, such as the rural highways and motorways,various engineering and design solutions are available.These include fences, green bridges, and underpasses.Finally, by decreasing the current concentration ofdiffuse flows on the minor roads in favour of a limitednumber of major roads, the effects of the large-scalesolutions for the fragmentation of habitat will beincreased.AcknowledgementsThe authors are grateful to their colleague ChrisBaltjes for preparing and executing the GIS presentationsand the calculation of the acreage in both pilotstudies. Furthermore, we like to thank Donna Isaac,research fellow at the Land Use Planning Group, forcorrecting and improving the language of the paper.ReferencesCuperus, R., Kanters, K.J., Schaik, A.W.J., 1993. Infrastructuur encompensatie van natuurwaarden: aard en achtergrond vancompenserende natuurwaarden (infrastructure and compensationof nature values: type and background of compensatingnature values). Ontsnipperingsreeks deel 18, Dienst Weg-enWaterbouwkunde/CML RU-Leiden, Leiden, The Netherlands(in Dutch).de Wit, T., 2000. Handbook on traffic engineering measures for(secondary) rural roads. In: Jaarsma, C.F., Michels, Th. (Eds.),Proceedings of the Third International Workshop on SecondaryRural Roads. Report 00-07 CROW, Ede, pp. 115–133.Derckx, H., 1995. Dassen op weg (badgers on their way).Landschap 12, 39–44 (in Dutch).Dutch Ministry of Agriculture and Fisheries, 1969. Plattelandswegennota(report for minor rural roads). Hague, Staatsuitgeverij(in Dutch).Forman, R.T.T., Godron, M., 1986. Landscape Ecology. Wiley,New York.Forman, R.T.T., Alexander, L.E., 1998. Roads and their majorecological effects. Annu. Rev. Ecol. Syst. 29, 207–231.