Roadside Ecology

Michael Brereton NRS 534 Final White Paper Roadside Ecology There are very few species in the recent history of our planet Earth that have made such a lasting impact on the surface of the world as us. Human activity has left the landscape of our planet forever changed as we continue to expand our territory to fit our exponentially growing population. One of the signs of a rapidly growing civilization is the road. Whether paved or dirt, roads are used by humans to transport ourselves great distances at the cost of our natural surroundings. Roads are a major driver of habitat fragmentation, a term used in ecology to describe the fracturing or dividing of a natural landscape type by an impassible barrier. The creation of roads clears large areas of land and reduces forest cover, furthering an ever-growing loss of habitat for arboreal species to human growth. The constant mowing of roadsides allow invasive exotic species to colonize. Roads can reduce the range for foraging and hunting animals, and those who dare to cross risk death by vehicle. Roads can also change the physical aspect of an environment, causing greater risk to pollution and flooding. In order to continue living in harmony with the flora and fauna of our natural surroundings, we must employ new ideas and technologies to our roads. The study of road ecology will provide the answers we need to have safer roads for both ourselves and our natural world. Road ecology sits at the crossroads between many different scientific fields, including invasion ecology, hydrology, stream ecology, soil science, and many more. But just what is “road ecology”. One of the first, if not the first, mention of this term can be found in a paper by Richard Forman and Lauren Alexander in 1998 called “Roads and their Major Ecological Effects”. While the paper does not give a clear definition for the term, the concept is introduced as the study of the effects of roads and their surrounding areas on ecosystems. A key contribution of this paper is its discussion of the “road-effect zone”. This illustration is the result of Forman and Alexander’s accumulated research into the effects of roads on various features of the natural environment. According to them, actions such as salting or paving roads can lead to aquatic leaching within 50 meters of the road, sediment pollution and invasion of cleared areas by exotic plant species can have an impact around 1 kilometer from the road. Many impacts of roads are discussed in this paper, including invasive species, hydrology, sediment leaching, and drastic habitat change. One of the major problems of roads that are discussed in the literature I have found is the creation of edge or barrier effects. Many plants and animals depend on large areas to reproduce, forage, and hunt. For example, a study done on small mammals in the Czech Republic showed that roads negatively impact on two vole and one mouse species. These rodents were inhibited by the roads and could not pass safely, significantly reducing their range and ability to forage. However, the ability of these small mammals to cross was found to be directly related to the width of the road, Michael Brereton NRS 534 Final White Paper as animals were more likely to make it across thin roads (Rico et al, 2007). Eastern hognose snakes (Heterodon platirhinos) have also been observed to change their movement behavior based on roads, only crossing roads with no pavement (Blouin- Demers and Robston, 2013). The barrier effect can even lead to severe population-wide effects on a species. Genetic diversity can be significantly reduce if a population becomes isolated due to barriers. A 2003 study of shows that major road construction can lead to loss of genetic variability and gene flow in Swiss ground beetles (Keller and Largiader, 2003). This can have disastrous consequences on species that already have shrinking numbers or low reproductive numbers. As said by Shaffer and Samson (1985), “Fragmentation may be more critical than area as a determinant of extinction probabilities”, when considering species with low reproduction. Areas affected by fire and drought are more likely to suffer loss of species due to the fragmentation as resources become quite thin for animals surrounded by impassable roads (Andrews, 1990). While roads themselves produce unsafe barriers to animals populations, vegetation can also be affected. The effects of roadways on nested land cover types in the northern Great Lakes have been quantified and discussed in a paper by Saunders et al (2002). In this paper, the effects of roads on eight major land cover types are analyzed and presented. The edge effect provided by the roads creates patches of forest on the Wisconsin landscape, and these units are distinguishable via satellite.The patch type, density, and abundance were all affected, with patch size decreased and patch abundance increasing. This change in forest connectivity is shocking, and it is noteworthy that of the 78,752 km2 analyzed in the study, only 205 km2 were found to be original undisturbed land. In addition to fracturing forest land cover, road edges have introduced changes that affect natural selection of plants. The appearance of mowed or cleared roadsides has created a disadvantage for many native plant species who are not very tolerant of frequent disturbance. A study done in southern Utah confirmed that large paved roads create significant edge effects up to 200m from the road and reduce both the abundance and diversity of native plants (Belnap and Gelbard, 2003. The same study noted that the richness of exotic species was 50% greater in paved roads compared to smaller four-wheel-drive tracks, further cementing the idea that paved road create more disturbance. Despite the threat of exotic species, some native plants can reap benefits from edge effects. One study in England showed that healthland plants, specifically heath and grasses, actually increased their growth in response to being in close proximity to the road (Angold, 1997). This study also suggests that the size of the road and frequency of traffic may directly increase to the amount of disturbance taking place. Eutrophication from the road is identified as a source of increased growth, as nitrogen from the car exhaust provides nutrition for certain heather and grass species (Angold, 1997). Michael Brereton NRS 534 Final White Paper This type of chemical disturbance reminds us that not only do roads disturb the ecological structures along their edges, but the physical and chemical components of these environments. Roads can also greatly affect the hydrology and geomorphology of an area. Paved roads create impervious surface layers, which have been observed to significantly alter the flow of water within an environment. Impervious surface creates a shift in the flow of water from subsurface flow to almost exclusively surface runoff (Shuster et al, 2005). This causes redistribution of water resources at a level much more related to the slope of an area, as rainwater flows downhill along the surface of the road without permeation. This surface effect also means that flooding can result from smaller precipitation events than in environments with less impervious surface (Shuster et al, 2005). The altered balance between peak flood levels in response to roads is also confirmed by Jones et al (2000). Jones et al (2000) reviews the effects of roads on hydrology and geomorphology in roadside streams. The paper concludes that roads can serve as both the source and sink for flood debris depending on their location and can increase both the magnitude and frequency of debris flows from rain (Jones et al, 2000). An increase in severe flooding can change the disturbance level in an environment and hinder the growth and recovery of riparian zones and stream ecosystems (Jones et al, 2000). The redistribution of water flow and increase in flood intensity shows the powerful effect of roads on both the biological and physical aspects. With the threat of road-related environmental disturbance looming, what can the scientific world do? How are we to protect our precious ecosystems from barrier effects and fragmentation-caused extinction. One major breakthrough in road ecology is the concept of the wildlife corridor. These natural throughways provide wildlife the opportunity to cross high traffic roads without the danger of being struck by a vehicle. The danger of vehicular death on animals is summarized by both Forman and Alexander (1998) and Andrews (1990), as well as Rico et al (2007) in relation to small European mammals. However, the location and design of these corridors can greatly affect their success. In a 1993 study, the effects of road corridor design on Australian marsupial species are discussed. The amount of vegetation within the corridors affected the populations of these marsupials, as these species are herbivorous (Lindenmayer and Nix, 1993). The connectivity between the corridors along the road also played a major part in species survival, as well as the location of the corridors in relation to slope. For each wildlife corridor, the foraging and movement patterns of the species being conserved must be considered (Lindenmayer and Nix, 1993). The conclusion of this paper and many other studies on Australian mammals and roadsides were used to produce the blueprint for an Australian wildlife underpass project called East Evelyn Underpass Project (Goosem et al, 2001). This project helped created four large underpasses on East Evelyn Road in Queensland, Australia. These underpasses, while providing safe passage across a major road, also consider the foraging and movement Michael Brereton NRS 534 Final White Paper patterns of local animal species, such as goannas, cassowaries, and tree kangaroos (Goosem et al, 2001). In a follow-up report in 2003, Miriam Goosem confirmed that the underpasses were successful in reducing the animal mortality count along Evelyn Road (Goosem, 2003).

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