Deer are some of the most abundant mammals in the woods. So does this large amount of deer lead to a negative effect on the environment around them? Norwegian scientists have shown that this is not the case, but rather the converse is true.
In a study that took place in a northern forest in Norway, it was found that moderate to fairly high densities of red deer lead to a larger number of understory species richness as compared to smaller densities of red deer.
With the deer consuming a large quantity of woody species, it leads to a further dispersal and assemblage of the low-growing species. The deer’s periodic heavy consumption will allow plant diversity to increase. However, if the deer decide to become too picky and allow the herbivory-resisitant species to become the dominant species, the diversity will fall.
Through Hegland, Lilleeng, and Moe’s study, one type of geographical location and one type of plant species (bilberry) was observed to eliminate any extraneous variables. In the seven different plots sampled over ten years (2001-2011), it was found that the deer consistently consumed the bilberry at a much higher rate than species growing higher than it.
To fully test this, these scientists set permanent one-by-one meter plots that would lie flat on the ground, which would be inside a larger nine-by-nine meter macroplot. This macroplot would be set in an area known for deer grazing.
These plots would show the species richness of plants by classifying them in eight different categories based on the type of species.
Samples were then taken three times in the 10-year period (2001, 2006, and 2011) and measured for the deer herbivory intensity in the samples’ respective area. They were classified on a scale from 0-4 to show their browsing level with 0 having no browsing, and 4 being more than 75% of the bilberry being consumed.
Through the use of the intermediate disturbance hypothesis, a relationship was formed to predict the richness of the species. It would be found that the species should be at the highest level when the frequency of a disturbance is at the intermediate level.
This theoretical approach turned out to be a good basis for the study as the results proved to find an intermediate level of disturbance having positive outcomes for the low-growing plant species.
The low-growing species in the woods had a clear advantage to diversify itself than did the higher-growing woody species. Increasing the density of the deer in the area would only further help the lower growing species, still not benefiting the higher growing species.
The higher density of deer, just as predicted, increased in the total richness of species as well as richness within the low-growing species. It should be noted that this is not the case when the levels of high densities become artificial; the unimodal trend does not hold true.
In conclusion it was found that there is a relationship between the density of deer and species richness as well as abundance of lower growing plant species in the woods. Therefore the abundance of deer in the woods is not harmful to the environment, but actually helpful.
This raises an interesting thought, however. If deer were allowed to graze freely without population control, the forests’ plant species could possibly be changed in the future, as low-growing plant species would become so dominant as compared to the high-growing species. This has not occurred, but it does provide a rationale for population control of the deer if there is an interest in conserving the plant species that grow at a higher level.
Hegland, S., Lilleeng, M., & Moe, S. (2013). Old-growth forest floor richness increases with red deer herbivory intensity. Forest Ecology and Management, 310(15 Dec), 267-274. Retrieved from http://www.sciencedirect.com/science/article/pii/S0378112713005586