Browsing by Author "Weaver, T."

Now showing 1 - 20 of 26

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.
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.
Biomass and productivity of the subalpine Pinus albicaulis — Vaccinium scoparium association in Montana, USA
(1977-10) Forcella, F.; Weaver, T.
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.
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.
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.
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.
Climates Where Stone Pines Grow, A Comparison
(International Workshop on Subalpine Stone Pines and Their Environment: the Status of Our Knowledge, 1992) Weaver, T.
------ Abstract-While stone pine climates are similar adapted to relatively moderate climates may be excluded from, species the ranges of congeners by more severe climates, and species with longer warm-moiBt growing seasons are probably more productive than congeners. Absolute low/summer average/absolute high temperatures for stone pines listed in order of increasing absolute low temperature are Pinus sibirica (-65/13/37 °C), P. pumila (-52.19/36 °C), P. koraiensis (-42/1s1/36 °C), P. albicaulis (-3419/29 °C), and P. cembra (-23/8/27 °C). The Walter drought index shows little stress in stone pine forests despite large differences in summer/winter precipitation: in order of increasing summer rainfall, precipitation is P. albicaulis (102.I 829mm), P. pumila (1421.264mm), P. sibirica (1871245=), P. cembra (3231616mm), P. koraieT18is (3941242mm). Estimated thawed-soil growing season increases from P. albicaulis (4.5mo), throughsP. pumila (4.6mo), P. sibirica (5.5mo), and P. cembra (6.3mo) to P. koraiensis (7.8mo); growing seasons of the first three trees could be shortened by drought.
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.
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).
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.
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.
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.
Long-term decline in grassland productivity driven by increasing dryness
(2015) Brookshire, E. N. Jack; Weaver, T.
Increasing aridity and drought severity forecast for many land areas could reduce the land carbon (C) sink. However, with limited long-term direct measures, it is difficult to distinguish direct drying effects from counter effects of CO2 enrichment and nitrogen (N) deposition. Here, we document a >50% decline in production of a native C3 grassland over four decades and assign the forcing and timing to increasing aridity and specifically to declining late-summer rainfall. Analysis of C and N stable isotopes in biomass suggests that enhanced water use efficiency via CO2 enrichment may have slightly ameliorated the productivity decline but that changes in N had no effects. Identical declines in a long-term snow-addition experiment definitively identified increasing late-summer dryness as the cause. Our results demonstrate lasting consequences of recent climate change on grassland production and underscore the importance of understanding past climate–ecosystem coupling to predicting future responses to changing climate.
Long-term snowpack manipulation promotes large loss of bioavailable nitrogen and phosphorus in a subalpine grassland
(2015-05) Yano, Yuriko; Brookshire, E. N. Jack; Holsinger, Jordan P.; Weaver, T.
Nutrient retention in ecosystems requires synchrony between the supply of bioavailable nutrients released via mineralization and nutrient uptake by plants. Though disturbance and chronic nutrient loading are known to alter nitrogen (N) and phosphorus (P) dynamics and induce nutrient export, whether long-term shifts in climate affect source-sink synchrony, and ultimately primary productivity, remains uncertain. This is particularly true for snow-dominated ecosystems, which are naturally subject to lags between nutrient inputs and uptake. To address how climate change may affect nutrient source-sink synchrony we examined the impacts of deepened snowpack on N and P losses in a subalpine grassland in the Northern Rocky Mountains, USA, where we have experimentally increased snowpack depths by two- and four-times ambient snow for 45 years. Long-term snow addition resulted in remarkably high levels of bioavailable-N leaching (up to 16 kg ha^-1 year^-1) that were 11-80 times higher than those under ambient snowpack. Estimated bioavailable-P losses also increased with snow addition, but to a lesser degree (up to 0.3 kg ha^-1 year^-1), indicating greater enhancement of N losses over P losses during snowmelt. Because these losses could not be explained by changes in nutrient inputs in snowpack or by changes in plant-soil turnover, our results suggest that high bioavailable-N leaching under deep snowpack originates not from a lack of N limitation of plant productivity, but rather from enhanced subnivean microbial processes followed by snowmelt leaching prior to the growing season. This is supported by reduced soil N pools in the snow treatments. Snow-dominated regions are projected to experience shifts in seasonal snowpack regime. These shifts may ultimately affect the stoichiometric balance between available N and P and future plant productivity.
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.
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.
PLANTS ESTABLISHING IN ROCKY MOUNTAIN ENVIRONMENTS-- a manual for choosing native species for revegetation
(Montana State University, 1995) Weaver, T.; Gustafson, D; Lichthardt, J
Species which have established naturally on a disturbed site in a given environment-- climate and disturbance level (defined below)-- are good candidates for revegetation plantings in that environment. On this basis we recommend native plants (grasses, forbs, and shrubs) for revegetation plantings, if they occur on at least half of the sites sampled in the environmental type and cover at least 1% of the ground there. We also list exotic plants establishing on once disturbed roadside sites; if these plants do not invade native vegetation they might, under some circumstances, be used for revegetation The environmental types considered include dry grasslands (BOGR/STCO and AGSP/BOGR), moist grasslands (FESC/FEID and FEID/AGCA) sagebrush (ARAR/FEID and ARTRVAS/FEID) , warm dry forests (PSME/ SYAL and PSME/PHMA), warm moist forests (POTR/CARU, THPL/OPHO, TSHE/CLUN, ABLA/CLUN), cool forests (ABLA/XETE, ABLA/ARCO, and ABLA/VACC), mountain meadows (FEID/AGCA, listed above) and alpine (DESC/CARX) . In each environment plant performance is contrasted across five disturbance types: continually disturbed types (roadshoulders and the adjacent ditch slope), once disturbed sites (roadcuts with organic matter removed and cleared right-of-way without organic matter removal), and undisturbed late seral sites.
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.
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.