Saturday, 25 May 2013

Should traditional management practices be reintroduced into preserves?

For many of us, the term "nature preserve" tends to conjure up an image of a wild landscape that is either unmanaged or only lightly managed, and is undisturbed save for the quiet footfalls of the occasional hiker. While it's true that this picture does reflect conditions in a number of contemporary preserves, it wouldn't have been so accurate when these areas were first protected; further, this scenario may be just as "unnatural" as the highly disturbed, homogeneous landscapes that preserves are created to prevent.

Why? Because humans have been managing the land for thousands (in some places, tens of thousands) of years, and many of the species impacted by our activities have adapted to thrive under some level of environmental disturbance. In places where humans had little or no effect, other animals and processes have played a similar managerial role, keeping some species in check and allowing others to thrive. Many contemporary preserves lack these sorts of disturbance, and may be the poorer for it.

Cattle grazing, mowing, and haying are all traditional management techniques that may improve biodiversity in nature preserves. Further research is needed to understand potential drawbacks of these methods, and to compare them to alternatives.

This is an issue that has previously been addressed by botanists, historians, and anthropologists (for example, in M. Kat Anderson's Tending the Wild), but has not received much serious consideration from conservationists. A recent review in Biological Conservation, however, seeks to synthesize the existing literature and highlight the myriad ways in which traditional land management techniques might contribute to biodiversity and ecosystem stability in nature preserves.

Author Beth Middleton, of the United States Geological Survey, begins by pointing out that disturbances are a fact of life in all ecosystems. Things like wildfires, extreme storms, and grazing animals help shape habitats by killing off or reducing the growth of some organisms, thus allowing others to gain or keep a foothold. Early human management techniques (including periodic burning of meadows, grazing of small herds of cattle, wood cutting, and haying) may have had similar environmental effects by mimicking the effects of non-anthropogenic disturbances. More recently, however, we have generally attempted to protect parks and preserves from all such perturbations--thus potentially allowing dominant species to become so successful that they exclude other organisms. This is particularly problematic when the excluded organisms are protected species.

Some human disturbances mimic natural processes more than others. On the shores of this subterranean Californian soda lake, the more moderate management practices of indigenous Americans were replaced by more intense disturbances such as road and building construction.

Middleton is quick to stress that use of traditional management in preserves is a complex issue. For one thing, it may be difficult to convince people that their local nature preserve should be open to grazing by cattle, or that it is a good idea to allow loggers to periodically cut down a few trees. (In fact, Australian conservationists argued against these ideas in a recent essay posted on The Conversation.)

That said, a wide range of international studies suggest that traditional management could have major benefits. Low levels of cattle grazing, for example, have been found to promote biodiversity, and, in particular, to help rarer species thrive; this may be mediated by reductions in shrubby growth and dispersal of seeds in cattle dung. Some preserves have been created out of areas that were once heavily managed (for example, land that had previously been communally farmed by citizens of the former USSR). In these sites, maintenance of some level of disturbance can prevent macrophytes from encroaching and preventing the growth and persistence of smaller vegetative species. Middleton notes that the benefits of disturbance extend not just to plants, but also species that depend on vegetation for sustenance and shelter--including, for example, both insects and the organisms that feed upon them.

Fencing around Lake Nakuru, Kenya, excludes cattle and ensures that all resources can be utilized by native ungulates. Elsewhere in Kenya, the pattern is reversed, and in some places both types of animal can be found together.
Reintroduction of traditional management techniques is no simple matter, and Middleton describes the need for additional research. Particularly tricky is figuring out whether certain habitats were maintained by a single disturbance or an interaction between multiple different perturbations. In North America, for instance, prairies were impacted by both bison grazing and wildfires. While cattle might be adequate stand-ins for bison, the ecosystem might look quite different from its prehistoric form without the action of periodic fires. Further, cattle might have different grazing patterns than bison and could therefore have unanticipated side effects--such as inadvertently damaging insect populations by eating larvae attached to the vegetation. The impacts of reintroductions are likely to be influenced by a myriad of factors, including soil quality, plant growth patterns, humidity, and rainfall. Managers would probably need to rotate herds between different sites, and use fences to prevent overgrazing and physical damage. Another solution might be temporary introductions, where domestics like cattle and goats are brought in just long enough to nibble away any problematic woody vegetation--after which they are removed from the habitat.

A number of preserves have already successfully experimented with traditional grazing practices; non-livestock solutions such as haying and light mowing have also been advocated (for the protection of orchids in Europe, for example). For each of these techniques, it will be important to understand how much management is useful, and whether these practices are maximally beneficial at certain times or places. Biodiversity may peak just after mowing, for instance, but then decrease again as the grasses rebound to their original growth; meadows and fens may benefit more from traditional management than, say, wooded areas.

Some environmental disturbances are more extreme than others; both the geography and vegetation of the Mojave National Preserve have been significantly impacted volcanic activity.

The bottom line, says Middleton, is that we need to determine "what constitutes a natural disturbance, and how important [these are] in maintaining biodiversity in worldwide ecosystem types." We need additional studies examining the effects of small-scale cutting, grazing, and prescribed fire efforts, and we need to compare the outcomes of these practices with conditions from "prehistoric, indigenous, traditional agriculturalist, and contemporary times." Middleton argues that, rather than selecting regional-specific techniques for each preserve, we should create a global toolbox of techniques that can be used anywhere that management is needed. Once that has been achieved and we have a firm grasp on the science, we'll need to tackle the equally difficult task of convincing the public that these methods can protect biodiversity and preserve the integrity of natural areas.

Note: Some concepts/points that are not specifically attributed to B.A. Middleton may have been inspired by ideas from Kat Anderson's Tending the Wild.

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Middleton, B.A. 2013. Rediscovering traditional vegetation management in preserves: trading experiences between cultures and continents. Biological Conservation 158:271-279.

All photos by Flickr user specialagentCK.

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