Diss. no. 12271 nat. sc. SFIT Zurich. / Literaturverz.

The response of grass, forb, and shrub seeds to the subalpine environment during the fall and under winter snow and under laboratory conditions at 20/28 C was observed for 3 consecutive years at an elevation of about 3000m on the Wasatch Plateau in central Utah. Seeds in nylon sleeves were planted under 2 cm of soil before snowfall. Under snow plantings were made directly on the soil surface and under 2 cm of soil. The seeds planted before snowfall were removed each year on four occasions: when under snow plantings were made, after snow depth exceeded 130 cm (deep snow), just before spring snowmelt, and 10 or more days following snowmelt when soils had warmed. Seeds planted under snow or under snow and soil were removed on two occasions: after snow depth exceeded 130 cm and just before the snow melted in the spring. Environmental conditions which produced seed germination varied with species, origin of species, age of seed, and temperature. Fifty-four of the 60 species planted in September under 2 cm of soil before snowfall had some seed germinated when examined just before the snow melted in the spring. Fifty of the same species planted after winter snow covered the ground in November also had some seed germination just before the snow melted in the spring. Seed germination at the near 0 C temperatures on the soil surface under snow was usually similar to the comparable seed lots also placed under 2 cm of soil. Germinability of the grasses, forbs, and shrubs studied was placed in three broad classifications: (1) Little or no seed dormancy with germination at low and warm temperatures. Seeds germinated soon after harvest at temperatures near 0 C and also in the laboratory at 20/28 C. Examples are Agropyron desertorum, A. intermedium, Chrysothamnus viscidiflorus, and Lupinus alpestris. (2) Little or no seed dormancy with germination only at warm temperatures. Seeds did not germinate at the low temperatures present in the subalpine zone during the fall and winter but germinated readily in the laboratory at 20/28 C. Examples are Aquilegia caerulea , Potentilla gracilis var. pulcherrima, Rudbeckia occidentalis, and Valeriana edulis. (3) Dormancy at seed harvest. Germination was usually increased by near 0 C temperatures, by aging, and by other environmental conditions present under deep snow. Examples are Agropyron trachycaulum, Delphinium barbeyi, Madia glomerata, and Ribes cereum var. inebrians.

Zugl.: Diss. Bern, 1971.

The relationship between temperature and soil respiration has been well explored although uncertainties remain. This thesis examined the relationship between temperature and rates of heterotrophic respiration in soils from three adjacent sub-alpine Australian vegetation types; woodland, shrubland and grassland. Temperature sensitivity of soil (Q10) has recently been a hotly debate topic, one side concluding that decomposition of recalcitrant, less labile components of soil organic matter are insensitive to temperature. Whilst others argue that there is no difference in the temperature sensitivities of labile and recalcitrant carbon pools. Robust modeling of rates of soil respiration requires characterization of the temperature response of both labile and recalcitrant pools. Laboratory incubation provides a means of characterizing the temperature response of rates of respiration whilst reducing the confounding effects encountered in the field, such as seasonal fluctuations in temperature, moisture and substrate supply. I used a novel system that allowed laboratory measurement of gas exchange in soils over a range of temperatures under controlled conditions. Measurements included CO2 efflux and O2 uptake over a range of temperatures from 5 to 40oC, characterization of temperature response and sensitivity, and respiratory quotients. Rates of heterotrophic respiration fitted both exponential and Arrhenius functions and temperature sensitivity varied and depended on the model used, vegetation type and depth in the soil profile. Long-term incubation indicated both labile and resistant pools of carbon had similar temperature sensitivities. Respiratory quotients provided a strongly predictive measure of the potential rate of decomposition of soil C, independent of the temperature response of respiration, providing a tool that may be used alongside derived parameters to help understand shifts in microbial use of C substrates. Vegetation type influenced soil chemical properties and rates of heterotrophic respiration. Rates of respiration correlated well with concentrations of carbon and nitrogen as has been previously observed, unlike previous studies however a positive correlation was observed between indices of plant available phosphorus and respiration. The soils examined were from three adjacent vegetation types formed on common geology, I concluded that vegetation type had a significant influence on soil, in contrast to the commonly held view by ecologists that soil type drives patterns in vegetation. Climatic effects such as longer, dryer hotter summer, reduced snow cover and increased incidence of extreme weather events such as frosts and bushfire are likely to drive patterns in vegetation in this region and therefore have a significant impact on carbon cycling in Sub-alpine Australian soils.

Successional trends in herbaceous plant production and diversity were studied in an age sequence of sites, i.e. chronosequence, inferred to represent a meadow to aspen to fir to spruce-fir sere. Primary production was observed to decrease in a linear fashion with successional development. Three components of diversity; richness, heterogeneity, and equitability or evenness, each had low early successional values, reaching maximum diversity in mid-succession, and declining to intermediate levels with maturity. The magnitude of these trends varied greatly, depending on the methods used to determine plant dominance. Characteristics of various dominance indices and their applicability to this study were examined. Mean daily photosynthetic biomass was found to be an especially appropriate index of dominance for studying these seasonally dynamic communities. A checklist of 141 vascular plant taxa encountered in the study is included. The flora was determined to be exceedingly species rich, with values of the calculated diversity indices among the highest reported in the literature reviewed. The limitations of diversity indices to sampled data is discussed.

The effect of particle size distribution of suspended sediment vii upon a turbidity reading at a known concentration has been relatively quantified for stream bank materials on the Moccasin Basin - North Fork Fish Creek (MB-NFFC) Watershed, located in northwestern Wyoming. As expected, an increase in the median particle size in suspension results in a decrease of turbidity at a given concentration. The relationship derived correlates the particle size distribution of a chemically dispersed stream-bank material sample, with the Coefficient of Fineness for a mechanically dispersed portion of the sample.

The spider communities of four stages of a successional sere leading to and including spruce forests were studied in northern Utah. Four seral stages were recognized. These include: meadows, aspen (Populus tremuloides) stands, subalpine fir (Abies lasiocarpa) forest, and the climax Engelmann spruce (Pica engelmanii) forests. During the snow-free periods of 1976, 1977 and 1978, 15,987 spiders were collected by three methods including: pitfall traps, by beating vegetation, and with sweep-net samples. Additionally, 1600 15-second intervals of behavioral observations, and measurements of 182 web locations were made. Of 99 species collected, 44 were considered residents of the sere: criteria for assigning the spiders to foraging strategies (3) and guilds (9) are presented. Five spider communities were ostensively defined--one in the ground stratum of each of the stages and one in the tree stratum of the conifer stages. The data were used to compare the guild strategies of the spiders of the seral stages and to address various hypotheses about successional change in animal community characteristics. Increases with maturity as predicted were observed for 6 spider community parameters including: total biomass, species diversity--richness component, species diversity--equitability component, stratification and spatial heterogeneity, mean organism size, and temporal stratification. A life cycle hypothesis (i.e., short and simple life cycles in early stages, long and complex ones in mature stages) could not be tested because, depending on the life cycle type considered, I found diametrically opposed trends (semi-annual and biennial life cycle types both increased with maturity). The spider species of the ground-stratum meadow community were primarily dispersed in a time dimension (seasonal); the spiders of the tree-stratum community were primarily distributed in a spatial dimension (microhabitat). Spiders of the forest ground-strata communities were dispersed in spatial and temporal dimensions. No dimension was ascertained to be of fundamental importance. Distributions of ground-dwelling species with different foraging strategies, and the resident species of the ground-stratum communities were correlated canonically to 8 environmental variables. Spider species of the meadow community were correlated with a bare dirt variable. Spiders of the aspen community were correlated with 2 environmental variables including: grasses and forbs and a low foliage index. Hunting spiders were correlated with the meadow and aspen variables. Ambushing spiders, web-building spiders, and the spider species of the ground stratum spruce community were correlated with 5 environmental variables including: litter depth, canopy cover, tree basal area, dead leaves and needles, and logs.

Four general post-fire successional pathways leading to a climax Engelmann spruce (Picea engelmannii Parry)/subalpine fir (Abies lasiocarpa [Hook] Nutt.) forest were identified operating on the T.W. Daniel Experimental Forest in northern Utah. These included initial colonization by seral quaking aspen (Populus tremuloides Michx.), seral lodgepole pine (Pinus contorta Dougl. ex Loud.), colonization by lodgepole pine followed by a low intensity surface fire, and immediate colonization by late successional Engelmann spruce and subalpine fir. Post-fire establishment of the late successional species occurred earliest in the Engelmann spruce/subalpine fir pathway followed by the lodgepole pine and lodgepole pine ground fire pathways, and the quaking aspen pathway . The late successional species 11 grew fastest in the Engelmann spruce/subalpine fir pathway followed by the quaking aspen, lodgepole pine, and lodgepole pine ground-fire pathways. Conceptual models were presented showing how perturbations by fire, insect epidemics, and disease could interact to influence succession and shape the subalpine landscape. The subalpine forest changes through time to facilitate different types of disturbance that have varying effects on succession. In the continued suppression of fire, species and age class diversity will be reduced and disturbances may occur that are larger and more intense than those that have occurred historically.

Site classification of the biogeoclimatic ecosystem classification system is based on climatic regime (expressed by biogeoclimatic subzone), soil moisture regime (SMR), and soil nutrient regime (SNR). A SNR represents a segment of a regional soil nutrient gradient, i.e., a population of soils which provide similar levels of plant-available nutrients over a long period. SNR is identified in the field using a number of easily observable soil morphological properties and indicator plant species. However, we do not know the extent to which soil nutrient properties are supported by these indirect field-estimates. There have been several studies that quantitatively characterized regional soil nutrient gradients in different climatic regions (see Sciencia Silvica Number 21 for subalpine coastal forests), but this has not been done in the subalpine interior forest (Engelmann Spruce - Subalpine Fir (ESSF) zone) where soils are influenced by a continental subalpine boreal climate. In the study summarized here, relationships between soil chemical properties and field-estimated SNRs are examined and soil chemical properties and field-identified SNRs are related to the site index of subalpine fir (Abies lasiocarpa (Dougl. ex Loud.) Forbes) and Engelmann spruce (Picea engelmannii Parry ex Engelmann) - two major timber crop species in the ESSF zone.

Knowledge of ecological characteristics of sites and growth of trees on different sites is fundamental for silvicultural decision-making and planning. With the biogeoclimatic ecosystem classification in place in British Columbia, silvicultural management has been given an ecological foundation; however, relationships between growth and site quality have not yet been fully investigated, particularly for high-elevation tree species and sites. One of the contributing factors for this situation is limited knowledge of forest productivity in the high-elevation Mountain Hemlock (MH) and Engelmann Spruce - Subalpine Fir (ESSF) biogeoclimatic zones. Consequently, the management and planning in the high-elevation forest is fraught with difficulties and uncertainties. Current harvest rates of old-growth forest stands and the method and distribution of cuttings in these zones suggest that there needs to be more recognition of the uppermost elevation limit for harvesting. Subalpine fir (Bl), Engelmann spruce (Se), and lodgepole pine (Pl) are important timber crop species in the interior high-elevation forest which is represented predominantly by the subalpine boreal ESSF zone. This zone extends from 49° to approximately 57° N latitude and from approximately 900 to 1,700 m in the north, from 1,200 to 2,100 m in central BC, and from 1,500 to 2,300 m in the south. In view of this relatively wide climatic and edaphic amplitude, a large variability in productivity is expected. The objective of this study was to quantify relationships between site index (height @ 50 yrs @ bh) of Bl, Se, and Pl, and three ecological determinants of site quality: climate, soil moisture, and soil nutrients. Quantitative relationships between site index and these measures provide predictive models for estimating site index. Additionally, we compared the site indices of the three study species to each other to examine their early height growth performance on the same sites.