Conventional wisdom says that grazing deer are enemies to fledgling trees and plants, but have we been wrong all this time? New research suggests we might have been.
The latest study, published this month in the journal Proceedings of the Royal Society B, saw researchers test the effects of allowing foraging white tailed deer access to plots of land where young saplings are growing. Traditionally, white tailed deer’s numbers are restricted in such areas — often times through the use of controlled culls — because it was feared that the voracious eaters would damage the fledgling trees.
However, more recently, this wisdom has been called into question. Researchers had previously observed that by allowing deer into grassland areas, those areas would then produce a more diverse range of plants. Ecologists therefore wanted to test whether the results could be repeated in a different setting and whether it would give them insight into why this might happen.
The researchers, a team from the Smithsonian, chose a Maryland forest as their setting and planted 140 3x3 plots of saplings that were all a year old. A proportion of those plots contained only one sapling selected from fifteen species. Others contained fifteen saplings but they were all from the same species.
The researchers then tested what would happen when they left the area alone for the white tailed deer to roam through or, in some plots, what happened if they prevented the deer from accessing the saplings.
What they found might at first sound counter intuitive. After three years, the researchers discovered that the plots with higher diversity were the ones the deer had grazed. The researchers believe that the deer acted, in a sense, as instinctual gardeners. The tended to favor nibbling the faster and more hardy species of saplings. This stopped those saplings from outpacing their slower and less ruddy counterparts, meaning that they couldn’t strangle or simple muscle out their competition. In effect, the deer disadvantaged the hardy plants and therefore created more of a balance in what was able to grow.
Unsurprisingly, in the areas where the deer weren’t allowed to graze, a monoculture quickly took hold where only the fastest-growing species flourished. This, the researchers suggested, might be what would happen if we continued under the misapprehension that deer are always bad for cultivating young trees and plants.
Said John Parker, one of the researchers involved in the study: “Seeing a positive effect was really surprising. If we protect plants from browsing, maybe we’re eliminating the very factor that makes diversity work.”
So could our quick-cull mentality actually be causing less diversity and not more? Well, this study certainly gives us pause. However, we can’t say for certain that this phenomena will hold up on a wider scale. We know, for instance, that restricting deer from accessing certain areas when the deer populations have boomed — usually thanks to a lack of predators — is sometimes necessary because the deer will quickly graze the land to a state where very few young saplings of any kind survive. That, by the way, is not to advocate culling in any way but rather to emphasize that some kind of action is sometimes necessary.
The question seems to be about balance: what is the threshold where deer numbers are beneficial to diversity and at what point are their numbers antagonistic? Parker and his research team have recently planted a new forest containing as many as 24,000 trees. They expect to be able to gather meaningful data for many years and probably decades, to really see whether the effect holds up on a much wider scale and answer those kinds of questions.
What should we take from this research in the meantime, though? The research highlights how difficult ecology can be and how subtle influences from seemingly hostile species can actually play an important part in maintaining an eco-system’s balance.
This research, then, demonstrates in quite stark terms the limits of our knowledge when it comes to attempting to manipulate biodiversity and how, even when we think we are doing good, in the absence of a more complete understanding, drastic measures like culling and severely restricting grazing access might actually be bad for the habitats we are trying to maintain and save.
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