Observe globally, think locally: advice to park managers about global climate change.

Park managers need to write realistic natural resources management plans that incorporate projections about the near future--that is, what the environments they manage will be like in the next five to 50 years. Unfortunately, publications addressing such phenomena as global climate change tend to emphasize management policy for landscape-level systems, without offering much advice to onsite park managers.

I don't pretend to be able to advise how every important issue should be addressed in a natural resource management plan. I offer only an opinion about how to approach the major changes likely to affect parks in the future, such as global climate change and the spread of invasive exotics. (Note: I use the word "park" in the broad sense to refer to national and state parks, national wildlife refuges, military bases and training ranges, and miscellaneous government lands that require moderate to substantial management of natural resources.)

A Complication: What are the Goals?

One goal of most park managers is to maintain at least part of the lands and waters they manage in as natural condition as possible. Of course, "natural" can be defined many different ways. For the purposes of this article, I'll say that, in the absence of such recent changes as global climate change and the introduction of exotic species, a natural biotic community is self-sustaining, at least to the extent that under normal circumstances few species would be added or lost to the landscape.

Change is now a constant. Global climate change and the introduction of exotics have begun to alter the environment of nearly all parks. Note, however, that typical natural resource management plans emphasize specific biotic communities, presumably under the assumption that the existing range of environmental conditions will persist. But as conditions change, the biotic communities present at a site might not be able to persist. Furthermore, the change may not be toward any biotic community that exists today. Indeed, although most Pleistocene species other than the very large animals persisted into the present, they apparently combined in ways such that the Pleistocene communities have no modern analogues.

Because from a geological perspective, communities change, you might conclude that there's no "correct" biotic community for any site. There are, however, two fundamental differences between modern biotic communities and those that predated humans: the rate of climatic change is more rapid than typical, and humans have introduced many more barriers to effective colonization than would have occurred in prehistory. It seems likely that, in the near future, nomadic or migratory species that originally occurred in some areas will be effectively excluded from those same areas by fences or other barriers. Note also that, as our parks become more isolated, their ecologies will come to resemble those of islands, and they'll become islands of habitat. Many species won't be able to survive in fragmented habitats without human intervention. Furthermore, because the species that are able to colonize islands are a nonrandom subset of the original biota, it seems likely that the more isolated parks of the future will spin away on divergent ecological trajectories unless colonization is enhanced by human agency.

Consider, for example, ponderosa pine forest, such as occurs at the Fort Tuthill Recreation Area, located in Flagstaff; Ariz., and managed by the U.S. Air Force. Environmental Protection Agency climate-change models. predict that the Flagstaff area will become warmer and that there will be more precipitation. A simplistic management prescription for Fort Tuthill would be to manage as though the park will become similar to adjacent areas that are warmer and wetter.

Unfortunately, none of the large patches of natural habitat near Fort Tuthill are warmer and wetter. Douglas fir forest occurs at a higher elevation and is wetter but colder. Pinyon-juniper woodland, which is dominated by several species in the genera Pinus and duniperus, occurs at a lower elevation and is warmer but drier. Thus, if the climate changes dramatically in the direction predicted, there will be no large biotic community nearby to replace the ponderosa pine. If the vegetation in the vicinity of Fort Tuthill does eventually attain the appearance of an old-growth community, it's unlikely to correspond to any existing biotic community in Arizona, but will instead be a hodgepodge of species from several sites.

Hence, as the environment changes, the management goals become moving targets. If ponderosa pine forest goes away, what should we put in its place? More generally, what do we do if rapid changes in the environment cause the biotic community to come apart at the seams?

I don't have a simple answer, but suggest that an important psychological step is to free ourselves from a typological approach to defining a biotic community. We can speak, for example, about "pinyon-juniper woodland" and "alpine tundra," and can describe the ecological processes and species compositions associated with them. We can tolerate some fuzziness in these classifications, and are used to the idea that the boundaries of biotic communities can shift, especially at their edges. Note, however, that the mature assemblage of organisms that eventually occupies a site may not conform to an existing, named community. Of course, the advantage to using the typological approach is that it provides a built-in management goal: to maintain the ecosystem so as to preserve the structure and function of the given, named community.

Preserving the Status Quo?

Thus, one management alternative is to struggle to maintain the status quo by attempting to sustain the original species composition of a site despite environmental changes. The likelihood of success of this tactic depends on the time scale involved and the normal variability of the biotic community in question. Over the short term, climate change can often be ignored if the magnitude of the change doesn't exceed the variation that normally occurs from year to year. Also, some management practices, such as removing invasive exotics, are beneficial to many biotic communities, not just the contemporary one.

In the long term, however, the human-initiated changes in the environment could exceed the tolerance limits of many of the species present at the site; reversing the trend in global climate change is beyond the means of any single park manager. Of course, there are things that a society could do to alleviate global climate change. Nevertheless, there are enough case studies to confirm the general trend of species displacement from parks, and the problems resulting from global climate change will probably not be solved soon. Meanwhile, we have parks to manage.

Generalized Management Goals

Assuming that global climate change and other modern phenomena will shred our existing biotic communities, we will need to develop new management goals to replace those that are generated automatically by the now obsolete typological classification of biotic communities. Perhaps we should ascertain characteristics common to most healthy, old-growth communities, and strive to enhance those characteristics. Let's look at six key such characteristics.

High Species Richness: Although there are bound to be exceptions, evidence suggests that in most circumstances, high species richness stabilizes ecosystem processes. Therefore, maintaining or increasing species richness ought to be a goal for the park manager. Furthermore, species that are being squeezed out of their old homes by climate change will need new places-perhaps including your park--to go to. Also, not all potential colonizing species are likely to survive, so if a large species pool is present at the onset of the transition to a new climate, you're less likely to end up with a species-poor community at maturity. Of course, invasive exotics shouldn't count toward species richness. Allowing new but non-exotic species to colonize your parcel will often be the simplest way to maintain high species richness, but preserving the structure of the abiotic environment (e.g., prevention of erosion preserves the soil horizons) enhances the persistence of the species already present.

Species Slow to Reach Reproductive Maturity: Colonization of your park by species adapted to the new climate could occur so quickly that only species that are rapid colonizers, and that reproduce quickly, might become established. Species that colonize slowly, aren't good at crossing obstacles to dispersal and take a long time to reach sexual maturity might never get an opportunity to become established.

Some species are such poor colonizers that they're unlikely to become established on extremely isolated islands, including habitat islands. These slow-reproducing and slow-maturing species might be important for several reasons. For one, they're often large individuals that provide food, shelter, nesting cavities, etc., that aren't provided by smaller species. For another they often buffer environmental variables, such as the shrubs and trees that shade sun-sensitive baby saguaro cacti.

Therefore, it might sometimes be appropriate to coddle some species to even the competitive playing field. For example, suppose that few seeds of a tree species that was well adapted to the new climate survived the gauntlet of human-initiated dispersal obstacles. If the seed germinated at your site and the seedling was about to be overtopped and killed by fast-growing herbs, you might consider removing the competitors.

Invasive Exotics: One goal that would be almost universally applicable under any climatic regime would be to suppress or eradicate invasive exotics. More often than not, global climate change might facilitate the spread of invasive exotics, because warm climates favor greater species richness, including the species richness of exotics. For example, Hawaii and Florida have many more invasive exotics than Alaska, despite the much greater size of Alaska. Equally important, invasives often have good dispersal abilities, which allow them to keep up with rapidly moving climate envelopes.

At some point, as species move around to track climate change, we'll be faced with the problem of deciding what's native and what's exotic. Clearly, species that originated on another continent and only recently arrived at our sites are exotic. But what about species whose range extended only slightly? Is every species new to your park an exotic?

I don't have any hard-and-fast rules that determine if a species is exotic. One criterion to determine this would be how prevalent the species is nearby If the only reason a species occurs on neighboring property and not yours is that a wall separates the parcels, then a humanmade barrier is probably preventing what would otherwise be a natural colonization of your park; in other words, it's not necessarily an exotic. In fact, if we don't occasionally allow new species to encroach on our property, there will be no way to maintain high species richness as climate change extirpates some species locally Species need to move around to survive.

Another criterion is compatibility--new species that act invasively and extirpate other species should be controlled. Sometimes the only way to acquire funds to control these species might be to have them declared "exotic," even if they naturally occur in the same country. Certainly, there are cases where the introduction of species from another part of the same country contributed to the endangerment of local species, including the Bonneville cutthroat trout and the Apache trout. Introducing an aquatic species into a watershed where it didn't previously occur is clearly risky.

Communities Extending Across Boundaries: The slow colonization rate of some species, and the prevalence of human barriers to dispersal, suggest that one of our goals should be to maintain as much connectivity as possible with other natural areas. This will allow species to naturally disperse into our site, and conversely, from our site to our neighbors'. It might often be possible to work out easements or agreements with our neighbors to maintain habitat corridors. This, of course, requires that we're familiar with our neighbors' property and how it's managed.

To chart the dispersal of movement of species in and out of your park, visit your neighbors frequently and ask them about what's happening to the species on their parcels, including what new species are immigrating. One way to gauge the justification for facilitating the entry of a new species into your park is to note how quickly and successfully it colonizes your neighbors' parcels. If a native species is colonizing your neighbor's parcel and doing so without any apparent ill effects to the biotic community, it seems reasonable to allow said species to colonize your own parcel, or perhaps even to deliberately introduce it. Preserving the Quality of the Abiotic Component of the Ecosystem: We should expect greater isolation of parks in the near future, with all of the attendant problems. This combination of problems will often preclude letting nature take its course to solve problems. Thus, it might be advisable to mitigate erosion brought about by climate change, simply because not to do so would result in great loss of species and ecosystem function.

Critics may assume nature can always take care of it own. If we accept this line of thinking, then whatever happens in a park could be considered, by definition, natural, and therefore acceptable. I disagree. For one thing, global climate change is at least partly caused by human technological activities. Furthermore, we should also consider the small size of our managed parcels in relation to the size and connectivity of natural habitat under natural conditions. For example, 1,000 years ago in North America, only a small fraction of the landscape would be disturbed by erosion, catastrophic fires, tornadoes, etc., at any given time. Species removed from a site by a catastrophe could simply recolonize from a nearby site. The healing of these scars would be accomplished with reasonable alacrity, and there would be no permanent damage to large areas.

Isolation also hampers the maintenance of a natural fire regime, because humanmade barriers preclude the natural spread of a fire into your parcel. In many cases, artificially ignited, prescribed fires may result in a more "natural" fire regime than waiting for the rare lightning strike to reach your park. A small park that's the only local home for many species could be irrevocably damaged by a single catastrophic event, or by failure of the park manager to initiate nature-mimicking processes such as prescribed fire. If the surrounding landscape isn't a natural habitat, then it's unlikely that it will heal a disturbance to its original condition, or to maintain a natural fire regime. Under these circumstances, human intervention would be necessary to initiate an effective therapy. Self-sustaining Community: Parks don't manage themselves. If nothing else, managers have to manage people to make sure that humans don't interfere with the natural processes that occur in the parks. Nevertheless, excessive efforts to maintain the resilience and integrity of a biotic community should be circumspect, as they might indicate that human activities prevent natural ecosystem processes from occurring. Late pre-Columbian biotic communities can serve as a benchmark against which to measure North American management interventions. Although Native Americans modified their environments to some extent by the use of fire, hunting, etc., this management required no money or external energy (fossil fuels or electricity). Indeed, even the fires set by Native Americans consumed fuel that was originally part of the ecosystem.

Change Happens

A typical park is an island containing one or more biotic communities, surrounded by something else (something that's often not natural habitat). At one time, however, it was surrounded by even more extensive natural habitat. In that distant past, changes in the environmental conditions in the general vicinity of the park would bring about changes in the biota, changes that might initiate at one point and then spread. Each species would move or change at its own rate, and the resulting species composition might not be exactly like any other biotic community elsewhere. But the habitat would be continuous--barring geographic barriers to dispersal, any species suited to the new climate in the park could eventually immigrate.

We might therefore be inclined to accelerate the dispersal process and move new species into our parks in anticipation of their eventual natural colonization. Although I don't categorically disapprove of this practice, there's an important point to consider before embarking on this course of action: How confident are we that we know the environmental changes that will take place in our parcel? If we're fairly confident about the direction and magnitude of the environmental changes happening in our park, it might be reasonable to try to convert the site to a biotic community made up of species adapted to the new climate.

Note, however, that climate change analyses are poor predictors of change at the local level, and are less certain about changes in precipitation than about temperature. More reliable, but still the result of extrapolation, are predictions based upon local weather information compiled over several years.

These extrapolations emphasize species rather than communities, because climate change is expected to disrupt or eliminate existing species assemblage and replace them with others. Because the various species in a community have different tolerances for different environmental variables, the resulting mix of species may belong to a new community that doesn't even have a name yet.

As our parks increasingly become islands of natural habitat, the island edges become vulnerable to invasive edge species. Studies in the tropics indicate that edge effects can extend so far into natural habitat that only large parks will retain an intact community of species characteristic of undisturbed habitat; these species are commonly referred to as habitat interior specialists. The problems caused by invasion of edge species are likely to increase in the future, and their control should be considered part of the cost of doing business to maintain a park. The brown-headed cowbird is just one example of an edge-frequenting species that has been known to decrease population sizes of species that inhabit forest interiors, and many parks now engage in some level of cowbird control.

A Burning Question

Another goal would be to prevent catastrophic fires. That's not necessarily the same thing as suppressing all fires. Many biotic communities are fire-tolerant or even require periodic fires. However, we should keep in mind that the species mixes that result from global climate change might be something completely new, something with no counterpart in our existing biotic communities. In that case, we don't always know what sort of fire regime is appropriate. My suggestion is to evaluate the abundance of fire-tolerant and fire-dependent plants, and to plan prescribed burns for sites that would be likely to burn anyway under the new climate. We should, however, exclude exotics from the list of fire-tolerant species, because repeated burning of fire-dependent exotics could enhance their invasion. It might seem arbitrary to designate a community as either a "burn" or "non-burn" community, but many parks use photographs taken regularly at the same location--photo-points--to help them decide when and how much to burn.

In the absence of prescribed burns, fuel reduction by mechanical means may be necessary to prevent wildfires. Indeed, fuel reduction may be necessary even if prescribed burns are accepted as beneficial for the site, if the previous biotic community has a heavy fuel load. For example, if global climate change would eventually result in the creation of a warmer, non-forested association at a site that now has cool forest, then the standing dead wood that remains from the forest could fuel a catastrophic wildfire.

Endangered Species 

As the local climate changes, the suitability of any given site as appropriate habitat for a species could also change. Over a short term, these changes would be so minor that they wouldn't alter the effectiveness of recovery plans for endangered or threatened species. Over the long term, however, existing plans might become obsolete. Perhaps the most important activity with regards to endangered species and climate change is monitoring. By monitoring I mean not only the endangered species, but also the biotic community as a whole. Obviously, if habitat quality for an endangered species improves, the recovery process could be accelerated. However, if habitat deteriorates beyond a certain point, maintaining the species on site will fail.

At this point, the park manager might, perhaps justifiably, approach the relevant agencies and request that the agencies reevaluate the land manager's responsibilities. Because climate change is beyond the control of an individual park manager, it might be reasonable to alter the recovery plan so as to exclude major responsibilities for the park manager. The manager might need to make a strong case based not only on weather data for his or her own site, but perhaps recorded changes in the biotic community as well.

Practical Ecological Monitoring

The importance of biological monitoring is greater than ever. We need to know what's happening to our biotic communities as a result of the processes mentioned above, and to be able to justify our management actions. For example, global climate models might suggest that invasive plants will become more of a problem, but until you document their occurrence at or near your park, you won't be able to program funds to remove them. Ideally, biological surveys would be undertaken frequently to keep abreast of changes in the species abundance and composition.

Unfortunately, most park managers don't anticipate increasing revenue and staff for ecological monitoring and biological surveys. So we're left with the problem of doing more with less. For example, in early 2002, and even before the advent of a gigantic forest fire, the Arizona State Parks were forced by budget shortfalls to close several parks. Many park systems exist on similar slender budgets, and simply won't be able to afford expensive and grandiose analyses. Furthermore, some funding must always be allocated for other needs, such as requirements to monitor endangered species.

Given these constraints, a cost-effective approach would be to preferentially monitor sites that are expected to be most subject to change. Instead of monitoring the best stands of plants, the ones in the most pristine and undisturbed portion, monitor the most heavily disturbed, the ones most subject to desiccation, road traffic, cattle grazing, etc. Instead of monitoring water flow in the large stream or river, monitor the small tributaries that feed them; they're more likely to dry up first. Look for invasive exotics on the edge of the forest, rather than in the center. Put up a portable weather station near the edge of the park, not in the pristine center. Count the puddle ducks in the temporary ponds, not in the big lake. And so on. This sort of monitoring may be less aesthetically appealing, but it's more indicative of trends relevant to resource management.

Some work on problems of global climate change involves producing elaborate models of the expansion and contractions of species' geographic ranges. I don't deride such work, and consider it complementary to my advice. However, conservation biology is a crisis discipline, and we must often make tactical decisions before we're confident of the sufficiency of the data. Because most park managers won't have detailed, site-specific prescriptions for managing the consequences of global climate change soon, what I offer are first-aid guidelines. Park managers need to consider potential problems that could arise because of global climate change, implement monitoring to gather data and then take concrete action based upon reasonable extrapolations.

BIOLOGICAL INTUITION

Park managers should use their ecological and management knowledge to formulate back-up plans for contingencies related to issues such as global climate change and the influx of invasive exotics. Periodically, they should ask themselves questions such as, "Is the local climate getting warmer? If so, what changes should I expect in my park? If so, what management actions should I take?"

For example, the Environmental Protection Agency climate predictions for Arizona call for higher temperatures and more precipitation. These conditions are a recipe for the production of mosquitoes, potentially including species that are disease vectors. So what should the park manager do? I can suggest several actions, not mutually exclusive.

Check published sources of information--newspapers often carry articles about dengue fever, malaria and other mosquito-borne diseases. Another action would be to determine empirically if the conditions under which the threat occurs are likely to occur near the park in the near future. If, for example, the mosquitoes are not freeze-tolerant, a slight warming of the climate might not be enough to allow colonization of a cold site. If, however, conditions seem hospitable to the species in question, some mosquitoes in the park could be trapped to see if they're potential disease vectors. If the species is a potential disease vector and the discovery is made when the species is still at low density, several steps could be taken to greatly reduce the likelihood that the species will become permanently established. By contrast, eradicating a well-entrenched population of mosquitoes is, at best, difficult.

As another example, suppose a park manager discovers a few individuals of an unfamiliar plant species. She might simply ignore them, but if the species is an invasive exotic, or a threatened or endangered species, she could lose valuable time in addressing management concerns. On the other hand, if she let the future color her thought process, she might anticipate that global climate change and the spread of invasives will introduce new species to her turf.

HARVESTED SPECIES

In addition to managing natural biotic communities, many park managers are also stewards of timber, fisheries and huntable wildlife. Most of the processes that threaten natural biotic communities also threaten exploited species. Global climate change could move the local temperature outside of the tolerance limits of the exploited species, exotic species could choke them out and so on. As you might expect, some of the same recommendations apply to exploited species as to natural biotic communities, including monitoring marginal portions of habitat for change, and removal of exotics where feasible.

A normal response to the impracticality of harvesting a particular species would be to search for another species to exploit that could be grown on the same site. Note, however, that if a particular site is clearly becoming unsuitable for the perpetuation of the current type of exploitation, then one alternative that should be considered is returning the site to a "natural" condition. Indeed, if this situation occurs on federal land, any major action to address the change in use of the land should be analyzed by the Environmental Impact Analysis Process as described in the National Environmental Policy Act.

Thus, land that can no longer sustain a harvest of the original species could be used to establish a mix of wild species and processes that maximize biodiversity conservation. We could manage with specific goals in mind, such as maintaining or increasing the species richness, improving ecosystem function by removal of exotics and restoring pre-exploitation hydrological regimes, and so on.

Cris Cristoffer is a natural resources planner at Luke Air Force Base in Arizona. His primary research interest is in developing gestalts of natural communities and how they function, so that their pasts can be revealed and their futures preserved. He has a special interest in comparing the evolution and ecology of certain taxa of organisms. He can be reached as [e-mail].