Introduction
A growing road network can have several large impacts on wildlife habitats such as a decrease in populations through collisions and population isolation. Even at low road density it still affects the environments around it sometimes having different effects for either side of the road. These can then also overlap with effects of other roads nearby. This makes it hard to truly assess the response the animals will have. Nevertheless, it is still important to understand how the populations will react to ensure their well-being even when the road networks continue to grow.
The population decreases are due to collisions with cars and a general avoidance of habitats near roads. Animals don’t have a choice but to live in habitats near roads if the network continues to grow, therefore it is critical to understand their behaviour and responses towards them.
There might be a threshold regarding the response of animals to road density which depends on favourable habitat, road network design and the effects roads have on wildlife. Instead of experiments which are difficult to conduct since it is only achievable with a limited number of species, a movement-based simulation model was created. Such a model has two advantages, it takes the animal’s starting point and potential obstacles into account and it also furthers the results in studies of animal movement. Elk were a good species to base the model on because their mortality rate is quite high when it comes to roads and they seem to avoid habitats near roads. However, the elk also show a variety of responses towards road densities.
Methods, Materials and Study Area
The study area was situated in the lower foothills, natural subregion of the Rocky Mountains of Alberta and encompassed about 2800km2. The elk were in areas with a road density of 0.13- 0.88 km/km2. The focus lay on gravel roads that were open throughout the year. For the development of the model movement behaviour was added until the 95% confidence interval for simulated and real elk overlapped. To verify the model, 100 actual locations of elk were chosen as starting points and then the movement was simulated every two hours. The simulation included Simple Random Walk, State-Based Random Walk and Habitat-Biased Random Walk models.
Results of the study
There was almost no area that wasn’t effect by a road density of 1.6 km/km2. The risk of elk mortality increased when the road network grew bigger. The habitat accessibility dropped after the main road was developed and road density increased.
Discussion
The three observations that were provided by the simulation were that a potential threshold of road density could be between 0.25 km and 0.5 km of road/km2, if the road density goes above 1.25 km of road/km2 then the mortality risk continuously increases and a density of 1.6 km/km2 would saturate the landscape. A bigger percentage of elk would inhabit an area with a lot of road density when being protected from hunting. In areas where hunting was not restricted the elk would avoid road areas much more. One example would be the Banff National Park where the elk are protected, they are near roads more often because they associate it with more positive traits than negative such as protection aginst predation.
There is a chance that with the increase of road density the range of response will grow too. The movement-based model used in this project showed great use in the project by isolating the effects of landscape context vs. road network design. The design of the road network can play an important role for the accessibility to forage habitats but it can also not provide any benefits. For example if there are many forage areas and the roads move away from the patches, then the elk could move from patch to patch without encountering many roads. However, if there aren’t many forage habitats then the road design doesn’t have much influence on the mortality rate. When a road went through a clearcut or went adjacent to it the whole forage patch would mostly not be used again by the elk. The simulations showed that the design of the road is the reason for up to 60-80% difference in the road density. This means that it is possible to still expand the road service while at the same time making sure the ecosystem isn’t effected. Reducing the road density but also simple changes in the design could already help wildlife and reduce the mortality risk. The model is a good way of showing which road network design could be beneficial to wildlife populations. However, reducing the density would still be a more effective tool and that in order to protect populations in the future additional action needs to be undertaken such as completely road-less areas.
Conclusion
The development of road networks throughout the environment has a large impact on the wildlife populations surrounding them. They either reduce the population numbers as a result of collisions or they isolate groups due to the avoidance of roads. A movement-based model showed that the design of the roads can already have a positive impact on the animals, however, it is still important to include the reduction of road density and completely road-less areas.