Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. ‘harkens a eee a eee Bureau of Biolozical Survey | | United States Department of Agriculture -* | | Wildlife Rescarch and Management Leafict BS-132 Washincton, D. C. 7 April 1939 ! ——_ re SOME CALIFORNIA WILDLIFE-FOREST RELATIONSHIPS 1/ By E, E. Horn, Biologist, Scction of Wildlife Surveys Division of Wildlife Rescarch Contonts Pago | Page Effects of forest-wildlife inter- Wildlife affccts type of forest. 3 Seance, gota. G6 flees orege% 1 Results on California study Type of forest affects wildlife 2 areasos) Ge setae he ee eS 3 ee ee EFFECTS OD #OREST-WILDLIFS INTERACTIONS Forests, with their diversity of conditions, are the homes of nu- merous forms of wildlife. They are, indeed, communities of interrelated living organisms. The lives of the forest plants and animals are so close- ly interwoven that it is impossible for one of them to function without influencing others, These interactions largely determine the naturo of the biotic commnity. The animals in any community depend, directly or indirectly, woon plants for food and, in many instances, for shelter. The type of vescta- tion available for food and cover detormines, in part, the species of an- imals that can exist on an area, All animals display preferences, in these respects, that may or may not prevail to an exclusive extent. The results are twofold: (1) If an animal is unadaptable to a given environment and re- quires a definite type of food or cover, plants may be an important factor in determining its abundance and distribution. In such circumstances there will be a somewhat constant ratio between the abundance of host plats and that of guest animals, though over a long period of time the numbers of doth may fluctuate greatly. (2) If the animal is highly adaptable, changing readily from one food to another and maintaining its numbers, it is likely to exert a mariced influence upon the plant community. ee ee ee ee 1/ Revised from paper presentod at the Third North American Wildlife Conforcnce, Baltimoro, Md., Fobruary, 1938 (Trans., ppe 376-380, 19358). TYPE OF FOREST AFFECTS WILDLIFE Compared with other parts of a dense forest, the floor is prac- tically devoid of animal life. Few animals can utilize it for a per- manent home. Food is scarce, and shelter is scant. On such a forest the only forms present in any abundance are those capable of arboreal life. Chickadees (Penthestes), nuthatches (Sitta), pine squirrels (Tamiasciurus) , evay squirrels (Sciurus), ahd a few chipmunks (Eutamias) frequent the treetops, The more-open forests, as those of the ponderosa pine (Pinus ponderosa) of the West, are more hospitable to wildlife. Ex- cept in dense reproduction thickets, the trees are so spaced that some light reaches the forest floor. Grasses and herbaceous vegetation thrive in proportion to the openness of the canopy. Here small rodents exist in somewhat greater abundance, and birds and the larger mammals, includ- ing the fur bearers and deer, in notably largernumbers. The sugar pine- fir type of the Sierra Nevadas seems intermediate in wildlife carrying Capacity. In this kind of forest in Califomia, sugar pine (Pinus lambertiana) is not reproducing on many large areas. Instead, white fir (Abies concolor) and incense cedar (Libocedrus decurrens) predom- inate in the reproduction. On any forest, disturbances of catastrophic proportions, as burn- ing or cutting, cause abrupt changes in the biotic community. This was observed in California forests. Following logging on the sugar pine-fir type, the ground cover increased rapidly. Herbaceous species, as grasses, shrubs, and especially bur-clover (Chamaebatia foliolosa), grew abundant - ly, the bur-clover forming a tenacious mat on the ground. The habitat was vastly improved for small rodents and micc (Peromyscus sp. and Microtus mordax), and chipmunks increased from 10 to 50 fold. As such an arca grows up to browse species, decr (Qdocoilcus hemionus) find it suitable for summer pasture. Winter range of deer in tnis area is more of a restrictive factor than summer range, and manage- ment that produces additional summer range should also provide the sup- plementary winter range that will inevitably be needed. In a few years, many of the cut-over areas support a large population of Beechey ground squirrels (Citellus beecheyi beecheyi). The statement is often made that this species is extending its range to higher clevations. In the Stanislaus National Forest, Calif., these squirrels did increase on cut-over areas, either by migration to a habitat made suitable for oc- cCupancy by the cutting, or by the breeding of relict populations. In either event, the result was a noticeable increase in this highly adapt- able rodent. Because the Beechey ground squirrel is food for certain predators, its increase may be followed by enlargement of the population of the carnivores, especially when other habitat factors are favorable. WILDLITE AFFECTS TYPE OF FOREST Rodents, especially mice and chipmunks, show a decided preference for seeds of some pines, and studies show that among those produced in the California forests the preference was in the following order; Sugar Jeffrey (Pinus jeffreyi), and poaderosa pines, and after these, white fi and incense cedar, ‘The last nemed is eaten in small quantities, Though the preference was in the order of sced size, that is not the deciding factor, as the relative acecptability was the same when tne seeds were reduced to a paste by grinding. Fossibly the chemical composition of the seed may play an important pact. Cutting decreases the supply of sugar pino sced, and the utiliza- tion of the seeds by rodents is high. As 2 result, nearly all the secds are taken each year, Tho.fcew that are left to germinate find severe and often fatal competition with bur-clover and other plants that increased so markedly after logging operations. As white fir seed is abundant and only partially consumed by ro- dents, it reproduces far more readily than does the sugar pine. Incense cedar seed is eaten in small quantities by rodents and reproduces well. As a result of these conditions the suzar pine is not regenerating and is being replaced by the less commercially valuable white fir and incense cedar. Apparently regeneration of the sugar pine occurs only at widely Separated periods. Provably reproduction is the result of coincidence of a heavy seed crop and a low seed-catine animal population in a year followed by conditions suitable for germination of seedlings. Farrow, in his work on rabbits in Engiand, found good indications that these animals have been responsible for the change of many areas from forest to’ grassland. ‘There is a strong possibility, likewise, that in California some sugar pine-fir-incense cedar associations may give way to fir-cedar because of activities of seed-eating rodents. RESULTS ON CALIFORNIA STUDY AREAS The effects of changes in forest composition are far reaching. Opening forests by burning or cutting increases food and shelter for many animals. Shrubs valuable for deer food thrive, more edges are created, and the deer increase. In 1924, during the outbreak of foot-and-mouth disease, 22,000 deer were kilied in one of the efforts to stamp out th malady. Before and after the deer were killed, lumbering opened large portions of the forest, so that the habitat became very favorable. e range. If this proves truc, over-grazing of the winter rango will follow. As the cut-over aroas grow up to forest treos, conditions for deer on t! Summer range also will becomc lcss favorable. Good browse species may than Show the effocts of ovor-grazing and finally disappear. The secd-oating rodents, by limiting sugar pine reproduction and permitting relative in- { [ex] ! crease of fir and cedar, may contribute to a more closed forest that will be disastrous to.the deer population. The proper ratio of summer to winter range could be regulated, however, by continued logging and opening of timber areas. - A thousand-acre experimental burn on the Lassen National Forest, Calif., had the following effects upon wildlifey Ss Deer loft the area before the fire and returned in increasing numbers the year after, attracted, no doubt, by new sprouting shrubs and. increased annual vegetation. 2, All rabbits, chiefly cottontails (Sylvilagus), were killod, a the few survivors moved off immediately after the firo, Many carcasses were found. 3, Chipmunks were markedly reduced bet not extirpated. Breeding stocks survived in some of the rocky outcroppings, 4, Mice of the genus Peromyscus, although markedly reduced in mun bers, survived the hottest fire, This was indicated by the fact that 2 days after the fire, adults and their litters of young were caught in traps in the center of the burned areca. Doubtless these mice escaped the heat by going into deeper burrows. After the fire, two generations of young Peromyscus were produced, thus augmenting the population of these secd-eating eee There was ~ @ good seed crop of ponderosa, Jeffrey, and even sugar pine, and seed was well scattered over the bucn, Mice were mumerous enough, however, to pick up most of the seed, so that only a small Peet remained to germinatée Brush of the kinds that ordinarily follow firé (Arctostaphylos, Ceanothus, and Prums) has made good growth, producing compotition for the conifer scodlings. If this growth continues it will result in dense growth favor- able to timber production but of limited value to game. Sced consumption by rodents greatly reduces the mumber of seedlings that might spring.up on brushfields after a burn. Burns discourage rabbits for several years. Perhaps lack of pro- tective cover is the factor responsible, for the rabbit-food supply is improved in quality, quantity, and diversity by the burns. In 1935 a small experimental burn was immediately planted to ponderosa pine, using the forester’s 1-1 stock, ard an adjoining unburned area also was. planted. Rabbits clipped 68 nercent of the plants on the green brush area and. only 23 percent of tho burned area, In the spring of 1937 the areas wore intor~ planted, and the results in clipped seedlings were ‘16 perecnt on tho burned area and 61 percent on the green brush area, In many sections of the Cali- fornia pine forests, rabbits cause considerable damage to seedlings and planted stock of pine by cutting off and eating the young trees. Some seedlings are killed, while others are retarded in growth, the terminal bud being taken out, following which, in time, one of the laterals becomes « 2 = the leader. Recovery from repeated clipping by rabbits produces badly de- formed, bushy trees. Much of this damage can be avoided by planting burned areas the first season following the burn, As noted, the opening of large forest areas by cither burning or cutting results in an increased population of small rodents. These pvro- vide quarry for predatory birds and mammals, which thon may also increase, Subscquent depredations of some of these predators on game specics is only incidental, but the incidence of game in their food is greater as their numbers increase. |The rodents, as buffer species, serving as a staple food supply for the predators, act to increase the predator population and therefore the predation on certain game specics. Whether this in- creased predation is scrious depends upon whctncr the game-predator ratio is altered. The response of animals to habitat changes makes it possible to increase desired species by proper management. If the habitat is made more suitable, wildlife increases, and conversely, if less suitable, wildlife decreases. Response varies in proportion not only to habitat change but also to animal adaptability. It is possible to take advantage of these relations to bring about ecological control of certain undesir- able species of animals. Evon here the ability of the animal to mect altered conditions will determine whether the practice is feasible and Compatible with other uses of the land area. For example, burning of the Manzanita-Ceanothus brushfields of northern California discourages rabbits and thus cuts down the loss of planted pine stock. It results, also, in an increase of seed-eating mice and tends to prevent natural pine regener- ‘ation. Forest-management planning also should consider less conspicuous but equally far-reaching ccological relationships, so that the grcatcst uses can be made of both the forest and the wildlife resources. A ay i Y 4 ~ we Ronn ey Ae ROMP RUT ahh) AS. ie BU Sy i Me ye AGL as