Scholarly Work - Ecology

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Ecological effects of weather modification: effect of late snow melt on Festuca idahoensis meadows
(1974) Weaver, T.
Diversity, cover and productivity of Festuca idahoensis meadows become progressively lower as one moves: (1) from deep-soil to shallow-soil sites, or (2) from sites that melt out in mid-May to sites that melt in late May or early June. Changes in species composition are also obvious on late melting sites. Changes associated with different melt dates are probably due to the shorter growing season of the late melting sites. Winter weather modification programs are expected to add snow, postpone melt, shorten the growing season and degrade these meadows in proportion to the amount of snow they add. Especially if the snow is deposited in drifts, the 10-15% increases in snowfall probably achievable will have small effects on the "target area" while returns to the "service area" might be considerable.
Pinus albicaulis in Central Montana: Environment, Vegetation and Production
(1974-07) Weaver, T.; Dale, D.
Nineteen apparently climax, non-krumholz, whitebark pine (Pinus albicaulis) forests were sampled at 2490-2930 m in the Rocky Mountains of S-Central Montana. The understory of these forests is strongly dominated by Vaccinium scoparium (median cover 40% +). Mature stands (200 + years old), with trees 12 m high, had basal areas of 14-24 m2/ha and had merchantable volumes of 195 m3/ha. Whitebark stands usually occur on soils of igneous origin. The growing season in a typical stand has 3 wet months with over 80 mm of rain and 3 dry months with less than 50 mm of rain; average maximum temperatures in this period rose to 20 C while average minimum temperatures Jell below 0 C.
Trampling Effects on Vegetation of the Trail Corridors of North Rocky Mountain Forests
(1974-08) Dale, D.; Weaver, T.
The management of trails should be based on knowledge of the effects of humans on them; most of the available information has been reviewed by Speight (1973), Stankey & Lime (1973), and Liddle (1975). Observations of existing trails suggest the following conclusions. (1) Vegetation cover is reduced by trampling and some plants are more resistant to trampling than others (Speight 1973; Liddle 1975; Dale & Weaver 1974; Davidson & Fox 1974). (2) Trail width increases linearly with increasing slope, wetness, roughness and the logarithm of the number of users (Bayfield 1973; Dale & Weaver 1974), but decreases linearly with the logarithm of the roughness of trailside vegetation and terrain (Bayfield 1973). Vegetation more than 2 m from the edge of a trail is often little effected (Dale & Weaver 1974). (3) Trail depths depend on compaction and erosion and therefore on climate, vegetation type, soil and substrate type, slope, and type of user (Helgath 1975; Dale & Weaver 1974). (4) Soil compaction is usually greater, i.e. bulk densities average 02-06 g cm-3 greater, in trampled areas than in untrampled areas. Several experimental studies .have shown the quantitative effects of wear on vegetation (Bell & Bliss 1973; Liddle 1975; Liddle & Greig-Smith 1975; Rogova 1976) but there has been no experimental comparison of the effects of different modes of trail travel. The experiments reported below compare the effects of hiker, motorcycle, and horse trampling on level and sloping sites in both a meadow and a forest with a dwarf shrub understorey.
Biomass of fifty conifer forests and nutrient exports associated with their harvest
(1977) Weaver, T.; Forcella, F.
Biomasses of climax Rocky Mountain forests studied ranged from less than 50 to more than 300 tons/ha. Total biomass was approximately 1.5 times the biomass of normally merchantable boles. When compared with conventional bole harvest, the nutrient exports associated with harvest of all aboveground parts in these stands would apparently be at least three times higher for nitrogen, six times higher for phosphorus, four times higher for potassium, and three times higher for calcium.
Root distribution and soil water regimes in nine habitat types of the northern Rocky Mountains
(Colorado State University, 1977) Weaver, T.
Root distribution and the annual cycle of' soil water availability were measured in nine habitat types of the northern Rocky Mountains. Water stress periods became progressively longer under Abies lasiooarpa forests, Populus trerrruloides groves, Pseudotsuga menziesii forests, Festuoa idahoensis grasslands, Artemisia tridentata shrublands, and Agropyron spioatum grasslands. Water stress periods were longer under Pseudotsuga forests than under adjacent logged areas. Live feeder root biomass (1) was similar under grassland, shrubland, and forest types, (2) increased within a vegetation type with altitude, and (3) decreased at a site with depth. Seral grasslands had less live feeder root biomass than forests in the same habitat type, but climax grasslands and forests were similar in root biomass.
Biomass and productivity of the subalpine Pinus albicaulis — Vaccinium scoparium association in Montana, USA
(1977-10) Forcella, F.; Weaver, T.
Changes in soils along a vegetational (altitudinal) gradient of the northern Rocky Mountains
(Soil Science Society of America, 1979) Weaver, T.
As one moves from the warm dry plains of eastern Montana to the cool moist peaks of the northern Rocky Mountains he might pass through a series of native vegetation types: Bouteloua gracilis, Agropyron spicatum, Featuca idahoensis, and Festuca scabrella grasslands; Pinua ponderosa, Pseudotsuga menziesii, and Abies lasiocarpa forests; and alpine tundra (Kuchler 1964, Muggler and Handl 1974, Pfister et al. 1977). It is commonly observed that when one moves up a vegetational gradient he moves up a soils gradient (e.g. Eyre 1963, Whittaker et al. 1968, Hanawalt and Whittaker 1976 and 1977). In the northern Rocky Mountains, Thorp (1931, N Wyoming) observed that organic matter increased, that pH decreased, that the depth to free lime increased and that the thickness of A- and B-horizons increased as he moved up a vegetational gradient similar to that described above. The same trends, as well as a tendency for nutrients to become most available at the grassland-forest boundary, were observed along a similar vegetation gradient in British Columbia (Spilsbury and Tisdale 1944). Such trends correlate well with broad groups in the 1938 Soil Taxonomy (Agricultural Experiment Station 1964 and Nimlos 1963) as well as in the 1977 Soil Taxonomy (Weaver 1978). The objects of this paper are I) to describe the change in soils observed along this gradient in more detail, 2) to consider their genesis briefly, and 3) to consider their importance to plants.
Cone production in Pinus albicaulis Forests
(Inland Mountain West Symposium, 1985-08) Weaver, T.; Forcella, F
Whitebark pine cone production was estimated for a 6 to 8 year period in each of 29 stands widespread in.the northern.Rocky Mountains. 1) One-time sampling was possible since the estimate was m2de by multiplying the number of branches perm by an estimate of annual cone production made from counts' of cone lets, mature cones, or cone scars on successively older annual increments of those branches. 2) Average cone production ranged from 0.3 to 3.6 cones·m^-2 ·yr^1 and from 22-270 seeds·m^-2·year^-1 . 3) Regression analysis was used to relate the variance observed to time and place. a) Year-to-year variation in the cone yield of branches, trees, and stands in a region appears to be both internally and externally controlled. Internal control is suggested by the fact that good cone years were usually preceded by poor cone years. While external control is indicated by significant correlations between growth and weather conditions, control is not dominated by the effect of any one factor or any particular developmental stage. b) Although cone production of the average branch varied significantly within 30 percent of the trees and within 48 percent of the stands observed, it did not vary significantly among stands. c) Regressions relating stand cone production to easily measured stand characteristics such as canopy cover, fallen cones, and/or stand size explain no more than 50 percent of the variance among stands.
Bibliography of Montana vegetation description
(1988) Burgeron, P.; Kratz, A.; Weaver, T.; Weidman, N.
Listed in alphabetical order by author are 549 references to literature that describes the native vegetation of Montana. This updates the 1965 list of Habeck and Hartley. A keyword subject index is included.
Distribution of Exotic Plants in the N. Rocky Mountains by Environmental Type and Disturbance Condition
(Montana State Univeristy, 1989-06) Weaver, T.; Gustafson, D.; Lichthardt, J.; Woods, B.
This report lists seventy-three exotic species found in a systematic sampling of major environmental zones of the Rocky Mountains between the Canadian border and central Wyoming. For each exotic it states the regional distribution, the environmental types (HTs) it occupies (% constancy), the disturbance conditions (DCs) it occupies (% constancy), and its dominance (in terms of% frequency and% cover) in each cell of the HT x DC matrix. Park managers need to develop policy with respect to legally noxious weeds, forage grasses (eg Phleum pratense, Poa pratensis, Bromus inermis, and Dactylis glomerata), and forage legumes (eg Melilotus and Trifolium spp).
Climates of subalpine pine woodlands
(1990) Weaver, T.
The climate of whitebark pine (Pinus albicaulis) woodlands is generally cold (average daily maxima and minima in January are -2 and -11 °C, respectively) and snowy 1 to 3 m maximum pack) in winter and warm (July average temperatures are 21 and 4 °C, respectively) and dry (July to September precipitation averages 102 mm and individual months can be rain free) in summer. The tree's lower altitudinal limit probabily is set by the competition of trees better able to compete for necessary resources such as light, water, and nutrients. In contrast its upward extension may be limited zonally by summer frosts and locally by desiccation. While the presence of one stone pine species is apparently a good indicator of an equivalent climate for other stone pine species, its presence does not indicate an identical climate and may therefore not indicate an equivalent climate for nonpine species with different climatic requirements.
Biotic and microsite factors affecting whitebark pine establishment
(1990) McCaughey, Ward W.; Weaver, T.
To enhance establishment of future whitebark pine (Pinus albicaulis) forests, information is needed on the physical and biological factors affecting whitebark seed germination and seedling establishment. This paper summarizes the first-year results of field examinations designed to evaluate predator and seedbed factors affecting whitebark pine establishment. Predator effects were estimated by recording seedling emergence under four levels of predator exclusion (free predator access, rodents excluded, birds excluded, and both rodents and birds excluded). Rodents ate or removed 100 percent of available surface-sown seeds. Emergence was higher on plots excluding rodents only and significantly higher on plots excluding rodents and birds. Seedling emergence did not differ significantly between mineral (although numerically higher) and litter seedbeds. The effects of three seedbed factors were also examined by comparing seedling emergence under three light levels (open, 25, and 50 percent shade cover), two seedbed conditions (mineral and litter), and two sowing depths (on surface and 0.8 to 1.6 inches beneath surface). Buried seeds had significantly higher emergence rates than did surface-sown seeds. Even though the first season was hot and dry, 78 percent of seedlings survived.
Occurrence of Multiple Stems in Whitepark Pine
(1990) Weaver, T.; Jacobs, J.
Depending on the stand, Montana-Wyoming whitebark pines (Pinus albicaulis) may have multiple stems in 8 to 79 percent of the trees. The clumps had one to 11 stems with stand medians between two and three. Multiple stems may arise from several seeds germinating together. from basal branching, or both. Median. stem number and mm• mum stem number per clump decrease with stand age, probably due to both within-clump and between-clump competition. While declines are slight in open woodlands, clumps almost disappear in closed forests. The presence of clumps is correlated with stand density in other conifers as well.
Berry production in three whitebark pine forest types
(1990) Weaver, T.; Kendall, K.; Forcella, F.
In the whitebark pine lwhortleberry (Pinus albicaulis/Vaccinium scoparium) habitat type of southwestern Montana, whortleberry plants produced seven to 69 berries I m• X yr in 1974. In subalpine fir (Abies lasiocarpa) habitat types of northwestern Montana, huckleberry plants (Vaccinium globulare) may produce from 13 to 228 berries I m2 X yr. While removal of competing trees increases production, thinning the understory apparently reduces berry production in direct proportion to the shrubs removed; there is no compensatory production indicative of shrub-shrub competition in fully vegetated plots. Fifty- to 100-fold variation in production among years in Vaccinium globulare berry production is attributed to variation in weather conditions.
Whitebark pine community types and their patterns on the landscape
(1990) Arno, Stephen F.; Weaver, T.
Within whitebark pine's (Pinus albicaulis) relatively narrow zone of occurrence-the highest elevations of tree growth from California and Wyoming north to British Columbia and Alberta-this species is a member of diverse plant communities. This paper summarizes studies from throughout its distribution that have described community types containing whitebark pine and the habitat types (environmental types based on potential vegetation) it occupies. Whitebark pine is most abundant and widespread in the semiarid inland mountain ranges of the northwestern United States and southwestern Canada, where it occurs in a continuum of environmental situations. It can be (1) a fire-dependent, early seral component of spruce-fir forests on moist sites; (2) a persistent seral or minor climax associate in drier forest habitats; (3) a major climax species or the only tree under still drier or more wind-exposed conditions; or (4) a major component or sole dominant of krummholz communities above tree line. The timberline landscape is a mosaic of cover types including windswept fellfields and grassy balds, wet meadows, snowdrift communities, and krummholz (shrub-like conifers) and forest communities with various proportions of whitebark pine. Four factors explain much of the variation in cover types: (1) rugged topography, through its influence on microclimate; (2) differences in surface rockiness, ranging from boulder piles to moderately well-developed soils; (3) differences in substrate composition, with especially noteworthy changes occurring between calcareous and noncalcareous geologic parent materials; and (4) a patchwork of different disturbance histories in the aftermath of fires, bark beetle epidemics, blowdowns, or snow avalanches. Whitebark pine communities also vary regionally, with changes in both climate and competing species. For example, in maritime mountain regions whitebark pine is unable to compete in the closed upper subalpine forest; it is, therefore, restricted to tree islands in the open heath parklands at timberline.
Stand development in whitebark pine woodlands
(1990) Weaver, T.; Forcella, F.; Dale, D.
Analysis of density data from stands in the Northern Rocky Mountains shows that, while seedlings establish at the rate of over 1,000 I ha x year in whitebark pine-grouse whortleberry (Pinus albicaulis-Vaccinium scoparium) forests of all ages, stem numbers in the canopy thin to 400 at 30 years, 150 at 200 years, and 100 at 300 to 600 years. Indices of productive potential, cover, and total circumference rise to an asymptote at about 100 years. Total basal area rises from 0 to 60 m21 ha at about 200 years, the aggregate basal area of trees with diameters over 20 em rises from 0 to 40 m21 ha at about 250 years, and tree height maximizes (12 m) at 200 years. It is hypothesized that further growth in productive potential (that is leaf and I or root area) is prevented by limited supplies of water or a nutrient, further growth in basal area is prevented by lack of a nutrient (probably not carbon, hydrogen, oxygen, or nitrogen) and further growth in height is prevented by scarcity of water.
Seeing whitebark pine in a northern Rocky Mountain (USA) landscape: notes for a field trip
(1990) Weaver, T.
The changing role of whitebark pine (Pinus albicaulis) along an altitudinal gradient typical of the Northern Rocky Mountains (USA) can be seen from the gondolas at the "Big Sky" resort near Bozeman, MT. Whitebark pine appears mostly as seedlings in the lowest zone (7,500 to 8,500 ft), becomes increasingly important in the canopy between 8,400 and 8,900 ft, assumes climax dominance in the woodland zone (8,900 to 9,300 ft), and maintains that dominance to treeline. On this gradient the mature tree's growth form changes from tall-lyrate, to shorter-spherical, to krummholz. The tree is seral in the lowest zones; frequent fires exclude it from canopies in the lowest zone, while low fire frequency gives it subclimax status higher (8,400 to 8,900 ft) in the zone dominated by subalpine fir (Abies lasiocarpa) at climax. Above 8,900 ft, whitebark dominates woodlands (formed, probably, when subalpine fir is excluded by cold) and krummholz (due, probably, to winter desiccation). Mountain pine beetles (Dendroctonus ponderosae) have killed much of the lodgepole (P. contorta) and whitebark pine in the area, and whitebark groves tend to be ringed with dead trees because the especially vigorous trees at grove edges are most susceptible. Cirque bowls on Lone Mountain demonstrate an inverted timberline at which conifers disappear downward, probably due to spring frosts.
Exotic invasion of timberline vegetation, northern Rocky Mountains, USA
(1990) Weaver, T.; Lichthardt, J.; Gustafson, D.
Thirty-five exotic species were found in vegetation characteristic of Northern Rocky Mountain timberlines. At least 20 percent were intentionally introduced along road-sides. The diversity of invading exotics declined from subalpine to alpine vegetation. While exotic diversity generally increased with increasing disturbance, severe trampling excluded some species from road-shoulder sites. The exotics of greatest concern to wildland managers are Phleum pratense (timothy) and Poa pratensis (Kentucky bluegraass) because they establish widely, spread vigorously, and usually escape early detection. Control of any exotic should involve its eradication and simultaneous introduction of desirable competitors to minimize reinvasion.
Effects of temperature and temperature preconditioning on seedling performance of whitebark pine
(1990) Jacobs, J.; Weaver, T.
Four experiments explored the effects of temperature on the germination and seedling performance of whitebark pine (Pinus albicaulis). While 1 month of stratification increased germination from 5 percent to about 40 percent, longer stratification periods (to 8 months) did not improve germination. Germination occurred throughout the 10 to 40 °C range with a broad optimum near 30 °C. Root growth occurred throughout the 10 to 45 °C range with an optimum near 30 °C. Long exposure (5 months) to low temperature (1.5 °C) lowered the temperature threshold for both germination and root growth. The apparent temperature range (perhaps 0 to 35 °C) and optimum (20 °C) for net photosynthesis at light saturation were lower than for germination and growth. While no preconditioning effect of light level (200 to 800 uE I M2*S) on the photosynthetic capacities of mature leaves was seen, photosynthesis increased progressively from needles preconditioned with winter, spring (5 °C day to 5 °C night), summer (15 °C day to 5 °C night), and abnormally warm (25 °C day to 15 °C night) temperatures.
Reference Guide to Whitebark Pine
(1990) McCaughey, Ward W.; Weaver, T.
The purpose of this guide is to provide an easy access to literature about whitebark pine (Pinus albicaulis) for those managers and researchers who are concerned with this species. Because of the uniqueness of the species and the lack of concentrated research programs in the past, documents about whitebark pine are found in a wide variety of places, including some rather obscure sources. We assembled this guide to help those needing access to whitebark pine information. This document references all the literature we could find specific to whitebark pine. Biological Abstracts from 1927 to 1988 was our primary source of references; therefore, bioabstract index numbers are provided to give the user easy access to the author's own annotation. Other papers-listed in Forestry Abstracts and Agricola were added. The papers included in this symposium proceedings are not listed here.

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