Management of Western Forests and Grasslands
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This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. USE OF MONTANE MEADOWS BY BIRDS Fred B. Samson Assistant Leader Missouri Cooperative Wildlife Research Unit U. S. Fish and Wildlife Service 112 Stephens Hall, University of Missouri Columbia, MO 65211 ABSTRACT Montane meadows comprise about 3.2 million ha under the jurisdiction of the U. S. Forest Service, the Bureau of Land Management, and state and private ownership. Relatively few species of birds breed on montane meadows, but meadows serve as important foraging,areas for avian communities associated with nearby riparian or forest habitats. Recommendations for management of montane meadows include: (1) care should be exercised in grazing or other land-use prescriptions such as fire, considering their apparent accelerative effect on meadow succession; (2) information is needed on the effect of meadow size on the diversity of breeding and foraging birds to fully predict the effect of land use changes; and (3) detailed studies involving marked individuals rather than singing male counts are needed to ensure accurate estimates of densities and essential habitat needs of breeding birds. KEYWORDS: montane meadows, meadow succession, nongpme wildlife management, avian ecology. In successfully occupying higher elevations, birds have accommodated a complex of environmental conditions--extensive solar radiation particularly in the ultraviolet spectrum, reduced air and oxygen pressure, intense night cooling by reradiation of heat, low atmospheric humidity, persistent wind, and, in winter, deep snowpack (Brinck 1974). Thus, high montane avifaunas are generally poor in species; populations often are small, reflecting low primary productivity; and densities vary from locale to locale (Dorst 1974). The severe environment, however, has not precluded extensive resource development and recreational use by man (Turner and Paulsen 1976, Johnson 1979), and, in some regions of the world, the montane is the most endangered of all ecosystems (Eckholm 1975). Importantly, the distribution, abundance and ecological relationships of most montane avian communities are not well known. The purpose of this report is to review avian use of a western U. S. montane ecotype--the montane meadow--emphasizing (1) a description of vegetation, 113 (2) geographic distribution, (3) local distribution, and (4) population characteristics important to management. MONTANE MEADOWS The meadow as a principal type of vegetative physiognomy consists of ''dense grassland, usually rich in forbs, with grasses having broad and soft blades, and occurring in relatively moist habitats" (Daubenmire 1968:251). In the western United States, montane meadows vary in size from a few to several hundred hectares, lie interspersed as "islands" among subalpine forests of lodgepole pine (scientific names in Appendix 1), quaking aspen, Douglas-fir, Englemann spruce-subalpine fir, and ponderosa pine and generally are located on gentle slopes, broad or rounded ridges, or along streams, rivers, or other water sources. Within this broad description, meadows are reported as "wet," those along small streams with dense and diverse grass, forb and shrub vegetation, or "dry," often a transition between wet and forested areas but sustaining a dense mixture of grasses and forbs with scattered pines or aspen stands (Patton and Judd 1970, Austin and Perry 1979). Western montane plant communities, however, are difficult to characterize, since western mountain ranges differ geologically, climatically, and biologically. For example, the Olympic Mountains were produced by two periods of diastrophism (Kuramoto and Bliss 1970), and the high Cascades are constructed of extrusive volcanics (Price 1978). Total annual precipitation ranges from over 500 em in the Olympic Mountains to less than 50 em in the Intermountain Region. The complex plant communities on mountain meadows comprise several hundred species of sedges, grasses, forbs, and small shrubs and reflect a number of factors--climate, site and edaphic conditions, surface age, mountain mass, and different historic immigration routes (Chabot and Billings 1972). Fortunately, detailed ecological studies that include flora of subalpine meadows are available for the Great Basin (Hayward 1945, 1952, Ellison 1954, Lewis 1970, Cronquist et al. 1977), the Pacific Northwest (Merkle 1951, Fonda and Bliss 1969, Kuramoto and Bliss 1970, Hitchcock and Cronquist 1973), the Sierra Nevada (Mooney et al. 1962, Chabot and Billings 1972) , and the Rocky Mountains (Costello 1944, Hurd 1961, Patton 1963, Mehringer et al. 1977). In contrast to plant communities, the dynamics of individual sedge, grass, or forb populations on mountain meadows have not been extensively investigated (Scott and Billings 1964, Gorham and Somers 1973, Johnson and Caldwell 1975, Thilenius 1975, Briggs 1978). It is known that "floral aspects of mountain grasslands differ markedly from one year to another and production of viable seed by individual plant species probably varies even more" (Turner and Paulsen 1976:5). Presumably this variation is influenced by microclimate and annual variation in moisture and temperature. These factors also influence total herbage produced on meadows which, in a study in Apache National Forest, Arizona, varied from 834 to 17 41 kg per 0.4 ha on a wet meadow versus 19 to 131 kg per 0. 4 ha on a dry forest floor (Patton and Judd 1970). Investigations of the interplay of man~elated and natural factors affecting succession on montane meadows have suggested those that influence tree invasion to be most important (Fig. 1). In a thorough review of the impact of grazing (records from 1914-1975) on tree invasion of subalpine meadows in the Wind River Mountains, Wyoming, Dunwiddie (1977) suggested moderate grazing by cattle results in extensive tree establishment because of reduced competition from a mat of meadow vegetation (Fig. 1). Furthermore, cessation of grazing historically coincided with lack of invasion of trees. Dunwiddie (1977) also pointed to the possible importance of· changing climate on the extension of trees into formerly treeless areas, results similar to those of Fonda and Bliss (1969), Franklin et al. (1971), Douglas (1972), and Mehringer et al. (1977). Fire, another natural factor, may create openings for meadows (Patton 1963), but several microenvironment variables determine whether trees reinvade (Kuramoto and Bliss 1970). Despain (1973:350), also working in Wyoming, states "caution should be exercised when interpreting the existence of grasslands 114 or parks in otherwise heavily timbered Soil/Site forests as indicating fire.'' Rather, Properties herbaceous cover, soil properties, and patterns.in snow accumulation appear I \ significant in maintaining open Snow Herbaceous mountain meadows. Pack Mat ~ Open / ( Meadow '\ Fire Grazing ~ Conifer _/ Invasion Recreational Long Term Development Climate Change / Meadow "" Loss Figure I.--Generalized schematic representation of vegetative succession on montane meadows (following Despain 1973, Dunwiddie 1977, Weaver and Dale 1978, and others). DISTRIBUTION OF BIRDS ON ALPINE MEADOWS Recent studies of montane avian distribution consider mountains ecologically similar to islands, i.e., rising from generally level low-lying areas with their colonization dependent upon conditions and history of the surrounding environment (Brinck 1974, Johnson 1975, Behle 1978, Brown 1978, Thompson 1978). Among hypotheses proposed to explain variation in number of bird species from place to place, the theory of island biogeography (MacArthur and Wilson 1967) has produced good predictions of species numbers, incorporating the size of the area studied and the degree of isolation between similar habitats (Fig. 2). Thompson (1978), working in central Montana, has shown that area of a mountain in the Sweet Grass Hills can predict the number of summer resident bird species. Brown (1978:209) reported "insular area is the single variable that accounts for most of the variability in both bird and mammal species diversity" in the Great Basin (Fig. 3). Similarly, in the Great Basin, Johnson (1975) reported mountain area, inasmuch as area and habitat variety are closely correlated, was important in imposing limits on the distribution of birds. 115 Productivity l & Mortality Competitors Sex and I Age Ratios l Habitat Vari~ty I Food I I Habitat Struct·u re J Behavior I Isolation Density 1 Minimum Area I J Area t- t- - - Population ,... Geographic Local - Distribution t- Characteristics ~ Distribution ~ 1- r- Figure 2. Summary of factors important in avian geographic and local distribution and in management of populations on montane meadows. 20 S = 2.526 A0 ·165 r = 0.701 10 en w 0 • w D.. en u. 5 0 a: w m • ~ :::::>z 2 1 ~----~--------~-------L------~--------~------~----- 25 250 25,000 AREA ABOVE 2280 m ELEVATION (Km 2) Figure 3. Figure redrawn following Brown(l978.:215) with dots representing individual montane "islands" in the Great Basin. The relationship between montane area and number of bird species is significant (r = 0.701, P<.Ol). In addition to mountain area, isolation between mountains or mountain ranges is proposed as an influence on avian distribution (Fig. 2). For example, Johnson (1975: 549) pointed out that historically the northern three-toed woodpecker "probably used mountain top forests as a stepping stone along an area from the Wasatch Mountains through the Pine Valley Mountains of