Forest exclosures AN EXPERIMENTAL APPROACH TO UNDERSTANDING BROWSING BY MOOSE AND DeeR Photo © Stephen DeStefano by Stephen DeStefano, Ed Faison, Justin Compton, and Dave Wattles The peculiar fences hikers may encounter in certain areas of Massachusetts are part of a long term experiment to study the impacts of moose and deer on the forest habitats of southern New England... If you have been out hiking in the past An Experimental Approach couple of years on parts of the Quabbin or Ware River watersheds, or perhaps in Experimentation has been called the the Harvard Forest, you may have come foundation of science. In an experiment, upon some mysterious, relatively large the scientist strives to isolate or manipu- fenced areas in small clearings located late the variable or factor of interest while out in the woods. These fenced areas controlling, or holding constant, other are square in shape, about 66 feet on a variables. In this way, the researcher side (20 meters by 20 meters), and their can see how that main factor affects 8-foot-tall fences are supported by 4x4 the outcome of the experiment without cedar or pressure-treated posts. You interference from other variables. For may also have noticed that each site has example, an agricultural scientist can a pair of these fenced areas, exactly the conduct an experiment to determine if same in size and design, except for one a new formula of fertilizer will produce detail: the fencing on one has been held 2 higher yields of corn. He or she will apply feet off the ground (a “Partial Exclosure”) the old, the new, and maybe even no fertil- while the fencing on the other goes right izer to various patches or plots in a field. down to the ground (a “Full Exclosure”). At the same time, all other variables, such So, what’s up with these fenced areas, as sunlight, soil type, and water, will be or “experimental exclosures” as we call constant for all the patches. In this case, them, out in the middle of the woods? the question of interest is: “Does this new Let us explain. fertilizer improve corn yield?” 14 The plots getting the new fertilizer are to carefully define both the questions be- the “treatment” plots, while the plots ing asked and the design used to try to getting the old or no fertilizer are the answer those questions. And the results “controls.” At harvest, the researcher can be more definitive, because compar- compares treatment to controls, and if ing a treatment to a control can yield an the patches with the new fertilizer pro- unequivocal answer. duce significantly more bushels of corn, Despite the importance and strength then it can be concluded that the new of well-thought-out experiments in fertilizer had a positive effect on corn advancing scientific knowledge, experi- yield. What’s more, an estimate can be mentation is rare in wildlife studies. Most made of how much more corn – by the wildlife research is “observational” and bushel or the pound – can be grown with “descriptive,” that is, biologists simply this new fertilizer. study animals and observe and describe Experiments can quickly get compli- their behavior, habitat use, movements, cated far beyond our simple corn-yield numbers, density, reproduction, or sur- example. Disputable components of good vival. Experimental manipulations and study design include randomization, application of treatments and controls replication, interspersion of plots, sample are uncommon, largely because of the size, statistical models, assumptions, and logistics involved. Wild, free-ranging analysis. But experimentation, if it can animals pose all sorts of challenges to be carried out successfully, can be very researchers, and so, in most cases, obser- effective because it forces the researcher vational studies are the best we can do. Photo © Dave Small An aerial view, taken in winter, of two of the experimental exclosures constructed within the Quabbin Reservation. The results of this experiment will provide invaluable data on the effects of having the “ecological driving force” that is the Moose return to our forest ecosystems, and also allow its impacts to be compared with those that are associated with the White-tailed Deer. 15 Despite their limitations, observational Amherst; Harvard Forest; the Highstead studies are extremely valuable and form Foundation; and Great Mountain Forest the foundation of what is known about (the latter two in Connecticut). wildlife populations. People in southern New England have But if an experimental approach is at long been interested in white-tailed deer all possible, it can add a new dimension and their role in forest ecosystems, but to our constant search for knowledge now a larger species of deer is among us: on wild animals and their interactions the North American moose. The moose with their environment. In 2007, we has returned to southern New England af- had an opportunity to begin such an ter a long absence, and is now widespread experiment thanks to the support of the and fairly common in the woodlands Massachusetts Division of Fisheries & of central and western Massachusetts, Wildlife (DFW) and the Department of extending south into Connecticut. There Conservation and Recreation, and addi- is much that we would like to know, and tional collaborations with the USGS Co- are learning, about moose in our state operative Research Unit; the U.S. Forest (see the No. 4, 2009, issue of Massachu- Service; the University of Massachusetts- setts Wildlife). Among the questions we Photo © Bill Byrne The Moose diet is roughly 90% woody browse; a single adult may consume as much as 40-60 pounds of buds and twigs each day. Compare that to the diet of the White-tailed Deer, which is composed of 60% woody browse. While white-tails are more numerous than Moose, both species are capable of altering forest ecology. The exclosure experiment will provide data on how the feeding activities of these two species compare, and allow us to make predictions about how our forests are likely to change under their combined influence. 16 Photo © Mass.Coop.Unit At each of eight sites there is a full exclosure that excludes all ungulates; a partial exclosure that excludes Moose, but not deer; and one or two “controls” that do not have any fencing at all. Here, a White-tailed Deer, its image captured by a remote, infra-red camera, is shown within a partial exclosure. have is how are moose interacting with the onset of European settlement in their forest habitat now that they have North America. During the early phases returned to southern New England? of European settlement, some of these ungulate species may have at first benefit- Moose and Browsing ted by the changes wrought by the early Historically, New England was occupied settlers. Creating openings in the forest by a host of “ungulates” – hoofed animals and setting back plant succession, as well that feed on a variety of vegetation, some as eliminating major predators such as of which were “browsers” because they wolves and cougars, would at first create feed primarily on the buds, twigs, and boom times for some of these species. leaves of woody shrubs and trees, others However, European settlers also used considered “grazers” because they feed large numbers of these animals for food, on grasses and other herbaceous growth, and land clearing became so extensive and still others adopting a mix of both that all of these species, with the excep- strategies. Elk, woodland caribou, moose, tion of the white-tailed deer, were entirely and white-tailed deer at one time lived extirpated from southern New England. in the region we now call New England. At one point, even the white-tail was re- The interactions of these herbivores with duced to remnant populations numbering their environment evolved over the mil- only in the hundreds. During the time of lennia, the animals developing strategies market hunting (which has long since that improved their foraging efficiency been banned in the United States) they and the plants developing defenses (such fell to what was probably their lowest as certain chemical compounds) to help numbers in many centuries. cope with being eaten. But the moose has made a comeback in As we well know, however, the diver- southern New England. Moose are also sity of large animals and the character among the most voracious of browsers, of the landscape changed quickly with Continued, page 20 17 Exclosures, cont. from Page 17 ing) browsing in the exclosure, which is with about 90% of their diet being com- the treatment. prised of woody browse (compare that to We have done something else to add to 60% for white-tailed deer). It takes a lot the value of this experiment, however. of vegetative material to feed that large We have essentially created a second body (most adult moose weigh between treatment by creating a second fenced 600-1,200 pounds), with an individual plot. The only difference between the eating as much as 40-60 pounds of buds two fenced plots is that we have held a day. There is no question that moose the fencing 2 feet off the ground in the affect the structure and composition of second plot to allow deer, but not moose, forests and are what ecologists call an access to the food within. Deer are able “ecological driving force.” Most people to crawl under fences and brush that are who care about Massachusetts’ wildlife a lot closer to the ground than this, but welcome the moose back to its place we wanted to give them as free access among the native fauna of our state. A to these partial exclosures as possible, question at this point, however, is how while at the same time keeping moose might we expect forests to change now out.