Showing papers on "Growing season published in 1993"

Red edge spectral measurements from sugar maple leaves

Abstract: Many sugar maple stands in the northeastern United States experienced extensive insect damage during the 1988 growing season. Chlorophyll data and high spectral resolution spectrometer laboratory reflectance data were acquired for multiple collections of single detached sugar maple leaves variously affected by the insect over the 1988 growing season. Reflectance data indicated consistent and diagnostic differences in the red edge portion (680-750 nm) of the spectrum among the various samples and populations of leaves. These included differences in the red edge inflection point (REIP), a ratio of reflectance at 740-720 nm (RE3/RE2), and a ratio of first derivative values at 715-705 nm (D715/D705). All three red edge parameters were highly correlated with variation in total chlorophyll content. Other spectral measures, including the Normalized Difference Vegetation Index (NDVI) and the Simple Vegetation Index Ratio (VI), also varied among populations and over the growing season, but did not correlate well with total chlorophyll content. Leaf stacking studies on light and dark backgrounds indicated REIP, RE3/RE2 and D715/D705 to be much less influenced by differences in green leaf biomass and background condition than either NDVI or VI.

Elevated atmospheric CO2 and feedback between carbon and nitrogen cycles

Abstract: We tested a conceptual model describing the influence of elevated atmospheric CO2 on plant production, soil microorganisms, and the cycling of C and N in the plant-soil system. Our model is based on the observation that in nutrient-poor soils, plants (C3) grown in an elevated CO2 atmosphere often increase production and allocation to belowground structures. We predicted that greater belowground C inputs at elevated CO2 should elicit an increase in soil microbial biomass and increased rates of organic matter turnover and nitrogen availability. We measured photosynthesis, biomass production, and C allocation of Populus grandidentata Michx. grown in nutrient-poor soil for one field season at ambient and twice-ambient (i.e., elevated) atmospheric CO2 concentrations. Plants were grown in a sandy subsurface soil i) at ambient CO2 with no open top chamber, ii) at ambient CO2 in an open top chamber, and iii) at twice-ambient CO2 in an open top chamber. Plants were fertilized with 4.5 g N m−2 over a 47 d period midway through the growing season. Following 152 d of growth, we quantified microbial biomass and the availabilities of C and N in rhizosphere and bulk soil. We tested for a significant CO2 effect on plant growth and soil C and N dynamics by comparing the means of the chambered ambient and chambered elevated CO2 treatments.

Comparative effects of isolated trees on their undercanopy environments in high- and low-rainfall savannas.

Abstract: To determine whether agroforestry and silvopastoralism might be introduced more successfully into xeric or into mesic environments, the effects of isolated, mature trees of Acacia tortilis (acacia) and Adansonia digitata (baobab) on herbaceous-layer composition and productivity, soil properties, and microclimate in a moderately mesic savanna (c. 750 mm annual rainfall) were investigated and compared with an earlier study of the effects of the same two species in a more xeric savanna (c. 450 mm annual rainfall) in Tsavo National Park (West), Kenya. Similar to the more xeric site, solar radiation was reduced by 45-65% and soil temperatures were reduced by 5-12 C° under both tree species. Except for early in the growing season, soil-moisture values were similar under tree canopies and in open grasslands (...)

Biomass Production in a Tallgrass Prairie Ecosystem Exposed to Ambient and Elevated CO"2

Abstract: Responses to elevated CO"2 have not been measured for natural grassland ecosystems. Global carbon budgets will likely be affected by changes in biomass production and allocation in the major terrestrial ecosystems. Whether ecosystems sequester or release excess carbon to the atmosphere will partly determine the extent and rate that atmospheric CO"2 concentration rises. Elevated CO"2 also may change plant community species composition and water status. We determined above- and belowground biomass production, plant community species composition, and measured and modeled water status of a tallgrass prairie ecosystem in Kansas exposed to ambient and twice-ambient CO"2 concentrations in open-top chambers during the entire growing season from 1989 through 1991. Dominant species were Andropogon gerardii, A. scoparius, and Sorghastrum nutans (C"4 metabolism) and Poa pratensis (C"3). Aboveground biomass and leaf area were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 1991, peak biomass and leaf area were estimated by an early August harvest. Relative root production among treatments was estimated using root ingrowth bags which remained in place throughout the growing season. Latent heat flux was simulated with and without water stress. Botanical composition was estimated annually. Compared to ambient CO"2 levels, elevated CO"2 increased production of C"4 grass species, but not of C"3 grass species. composition of C"4 grasses did not change, but Poa pratensis (C"3) declined, and C"3 forbs increased in the stand with elevated CO"2 compared to ambient. Open-top chambers appeared to reduce latent heat flux and increase water-use efficiency similar to the elevated CO"2 treatment when water stress was not severe, but under severe water stress, the chamber effect on water-use efficiency was limited. In natural ecosystems with periodic moisture stress, increased water-use efficiency under elevated CO"2 apparently would have a greater impact on productivity irrespective of photosynthetic pathway.

Comparative responses of phenology and reproductive development to simulated environmental-change in sub-arctic and high arctic plants

Abstract: The effects of temperature, precipitation and nutrient perturbations, and their interactions, are being assessed on two contrasting arctic ecosystems to simulate impacts of climate change. One, a high arctic polar semi-desert community, is characterised by a sparse, low and aggregated vegetation cover where plant proliferation is by seedlings, whereas the other, a sub-arctic dwarf shrub heath, is characterised by a complete vegetation cover of erect, clonal dwarf shrubs which spread vegetatively. The developmental processes of seed production were shown to be highly sensitive, even within one growing season, to specific environmental perturbations which differed between sites

Patterns of Leaf Development and Herbivory in a Tropical Understory Community

Abstract: Most plant-herbivore studies have demonstrated that young leaves are pre- ferred over mature leaves, and that the majority of lifetime damage occurs during the 1 st mo In spite of this, we know little about how young leaves are defended Young leaves are an ephemeral resource, and herbivore damage may be reduced by (1) producing leaves at times of low herbivore abundance, (2) synchronous leaf production, or (3) rapid leaf expansion To address these hypotheses I examined patterns of leaf phonology, leaf ex- pansion, and herbivory in saplings of 32 species in a Panamanian lowland moist forest Leaf phonology ranged from continuous to highly synchronous, and mean monthly damage rates varied from 6 to 60% Within species, leaves produced during the dry season, a period of relatively low insect abundance, received less damage than leaves produced during the wet season Leaves produced during synchronous flushes received less damage than leaves produced out of synchrony Species with continuous or synchronous leaf pro- duction had lower damage rates than intermediate species, but growth rates and survi- vorship were not correlated with leaf production It appears that higher damage rates in intermediate species may be compensated by reduced investment in chemical defenses compared with continuous species, and a less restricted growing season and reduced storage costs compared with synchronous species Previous studies have identified leaf expansion rate as an important young leaf defense, but in this study there was no correlation between expansion rate and herbivory

Influences of neighbouring plants on seedling establishment in limestone grassland

Abstract: . Influences of neighbouring plants on seedling establishment of six dicotyledonous species was investigated in a nutrient-poor limestone grassland (Mesobrometum) in northern Switzerland. Microsites with different vegetational structure were created and seeds sown in them. The fate of emerging seedlings was followed for one or two years. A plant surviving its first growing season was regarded as established. Shelter by neighbouring plants appeared to be necessary for the establishment of Arabis hirsuta and Primula veris. Because of drought and frost heave, hardly any seedlings of these species established in gaps (4 - 21 %). In microsites with vegetation, their survival was significantly higher (40–57 %). Neighbouring plants slightly reduced the survival of Plantago lanceolata and Sanguisorba minor, but these species established well both in gaps (74 - 81 %) and in vegetated microsites (54 - 67 %). Medicago lupulina established well in all microsites in one year (71 - 79 %), but poorly in the next year (18–32 %). Linum catharticum emerged poorly in one year and was completely extinguished by a fungal pathogen the following year. The overall conclusion is, that gaps are of minor importance for recruitment of these species in this grassland. Physical hazards and pathogens control seedling establishment to a greater extent than competition by neighbouring plants. Some species are hardly able to establish without shelter of vegetation. Seed size is an important factor for success of establishment, especially in gaps. It is suggested, that the relatively low productivity and the absence of litter accumulation (due to mowing and biomass removal) are important conditions for the observed behaviour of the seedlings and juvenile plants in this community.

Patch-size effects on plant phenolics in successional openings of the southern appalachians'

Abstract: We examined the seasonal changes in plant chemical defenses of key tree species (Robinia pseudoacacia, Liriodendron tulipifera, Acer rubrum, and Cornus florida) regenerating during early succession in different patch sizes within Southern Appalachian forests. Trees of each species were sampled from five sizes of forest openings (0.016, 0.08, 0.4, 2.0, and 10 ha; two replicates each) and from the understory of surrounding forests. Leaves of rapidly growing, pioneer species (Robinia and Liriodendron) were slightly less tough and contained lower levels of hydrolyzable tannins and total phenolics, but higher condensed tannin concentrations than the slower growing, more shade-tolerant species (Acer and Cornus). These results generally support earlier findings indicating the evolu- tionary development of greater levels of constitutive phenolics in slow-growing than fast- growing species. The differential use of condensed and hydrolyzable tannins by slow- and fast-growing species may reflect adaptive trade-offs in the allocation of different types of phenolics. Regenerating trees often had tougher leaves and contained higher levels of phenolics in large than small openings by midsummer. The differences in phenolics were more pronounced for condensed tannins and when comparing the smallest canopy openings with larger patch sizes. Plant phenolics were also generally lower in understory trees than in nonspecific sprouts in openings. These findings may reflect phenotypic carbon/nutrient adjustments as light availability changes across the patch-size gradient. The greater sunlight in large than small openings apparently promotes excess carbon production and a metabolic buildup of phenolic compounds. Independent measures of phenolic compounds peaked at different times during the growing season. Hydrolyzable tannins reached peak levels quite early whereas condensed tannins increased later in the growing season. Total phenolics peaked in midsummer. Herbivore damage was consistently high (5-9%) on Robinia sprouts in all openings. Insect herbivory on the remaining three species (1-5%) was significantly lower in large than small patch sizes. Tree species regenerating in the high sunlight of larger openings in Southern Appalachian forests thus tend to have tougher leaves, contain greater phenolics, and experience less herbivore damage than conspecifics in small openings.

Short-Term Responses of Alpine Buttercups to Experimental Manipulations of Growing Season Length

Abstract: We examined the role of growing season length in regulating percentage cover and seed mass of the alpine snow buttercup, Ranunculus adoneus, in a snowbed habitat. Season length varies from °50 d in early—melting portions of the snowbed to 35 d in late—melting locations. Percentage cover and seed mass of snow buttercups decrease from early— to late—melting locations. Time available for growth was manipulated experimentally by altering the snowmelt schedule. Advancing snowmelt by 14 d in typically late—melting portions of the snowbed led to a threefold increase in percentage cover of snow buttercups (P < .025). However, delaying snowmelt to the same extent in typically early melting locations had little influence on snow buttercups. These results indicate that time available for growth limits cover of snow buttercups in late—emerging vegetation, whereas other factors regulate cover of snow buttercups in early—emerging vegetation . Perturbation of snowmelt scheduled also had significant effects on seed mass (P < .0055). These effects are probably mediated through changes in time available for seed maturation. Snow manipulation treatment accounted for 71% of the variation in seed maturation interval. Maturation interval, in turn, was correlated with seed mass (P < .01). Reducing or increasing the seed maturation interval by 12 d caused a 33% change in seed mass. These findings show strong direct effects of growing season length on plant performance at diverse life history stages.

Site preparation burning to improve southern Appalachian pine-hardwood stands: fire characteristics and soil erosion, moisture, and temperature

Abstract: Three southern Appalachian stands with sparse and unproductive pine–hardwood overstories and dense Kalmialatifolia L. understories were treated to restore productivity and diversity on steep slopes. An adaptation of the fell and burn practice was applied in summer and fall 1990. About one-half of the woody fuels were consumed at each site. A range of fire intensities was observed. Flame temperatures approached 800 °C, but the heat pulse into the forest floor only reached 60 °C at 5 cm. Humus and charred leaf litter remained on most of the surface after burning. Evidence of soil erosion was spotty and related to points of local soil disturbance. No soil left the sites. At the end of the first growing season, 23% of the burned surfaces were covered by growing plants and 62% by residual forest floor and woody debris. Felling and burning reduced evapotranspiration so that soil in the treated areas remained moister than under adjacent uncut stands. Opening the sites increased soil temperatures 2 to 5 °C at 10 ...

Soil Carbon Dioxide Characteristics under Different Forest Types and after Harvest

Abstract: To characterize soil CO2 under different forest types and several years after a clear-cut harvest, soil CO2 evolution and soil air CO2 concentrations were measured at three sites in Maine: the Howland Integrated Forest Study (HIFS) site, the Bear Brook Watershed in Maine (BBWM) site, and the Letter E township (Letter E) site. Soil CO2 evolution means ranged from 0.19 to 0.32 g m 2 h 1 among sites, whereas soil air CO2 concentration means ranged from 1023 L 1 for the O horizon to 3296 L 1 for the C horizon for the 1990 growing season. Soil CO2 evolution and soil air CO2 concentrations were similar under deciduous and coniferous forests and 4 to 6 yr after harvest. Limited multiple-year data suggest that significant annual variations in temporal patterns of these properties exist as a function of short-term climatic factors. These data suggest that soil CO2 evolution and soil air CO2 concentrations may be somewhat similar across a diversity of soil types, forest types, and forest conditions at any point in time for northern New England. View complete article To view this complete article, insert Disc 5 then click button8

Seasonal variations of soil microbial biomass carbon within the plough layer

Abstract: Over 31 months microbial biomass-C was estimated using the substrate induced respiration technique in fields with conventional soil management, where sugar beet-winter wheat-winter barley were grown in a crop rotation. Analysing the plough layer at different depths (0–10, 10–20 and 20–30 cm) seasonal variations were observed in the amount of microbial biomass-C due to soil and crop management. Although after ploughing microbial biomass-C distribution was homogeneous, a gradient, with decreasing amounts of biomass-C with depth, developed within the plough layer during the early growing season. This was due to a rapid increase of microbial biomass-C in the surface layer (0–10 cm). Throughout autumn and winter there was no change in microbial biomass-C distribution with depth. Within the crop rotation microbial biomass-C content increased in the order sugar beet, winter wheat and winter barley.

Rowcovers and High Tunnels Enhance Crop Production in the Northeastern United States

Abstract: Crop growth is enhanced with the use of relatively inexpensive rowcovers and high tunnels. Even though these structures do not provide the same degree of environmental control as greenhouses, they modify the climate sufficiently to lengthen the growing season from 1 to 4 weeks in the spring and 2 to 8 weeks in the fall. Rowcovers generally remain over a crop for 2 to 4 weeks, whereas a high tunnel may function for an entire growing season. Both systems require a relatively low capital investment, provide a good return on investment, and improve the ability of new growers to succeed in the crop production business. The selection of either rowcovers or high tunnels will depend on the management program of a grower; however, both growing systems potentially are economically viable means of season extension.

Adaptation of Lentil to the Mediterranean Environment. I. Factors Affecting Yield Under Drought Conditions

Abstract: Lentil frequently suffers from drought stress towards the end of the growing season in rainfed Mediterranean farming systems. This study aimed to quantify the contribution of yield potential under irrigated conditions and of drought escape to the adaptation of lentils to drought, and to identify traits of value in selection for adaptation to a rain-fed Mediterranean environment. Twenty-five diverse lentil lines were sown under both irrigated and rainfed conditions in the 1987/88 and 1988/89 seasons in northern Syria. In 1987/88 the total seasonal rainfall was 403 mm and average rainfed biomass and seed yields were 5.0 and 1.8 t ha" 1 , respectively. In contrast, in 1988/89 the total season rainfall was 180 mm and average biomass and seed yields were only 0.67 and 0.12 t ha~', respectively. Early vigour (estimated as a visual score) and percentage ground cover were strongly associated with final biomass, and were of value in predicting economic yield (seed + straw). Early maturity was correlated with seed yield. In the dry season 1988/89, 49% of the variation in seed yield among lines was accounted for by variation in flowering time. Drought escape was clearly the key response to drought. For severely drought-prone areas, selection for early flowering is therefore required. Variation in flowering time and seed yield under irrigated conditions accounted for 62% of seed yield variation under drought stress. Adaptation de la lenteja a la sequia

Growth and photosynthesis of two deciduous forest species at elevated carbon dioxide

Abstract: Two-year-old sweet chestnut (Castanea sativa) and beech (Fagus sylvatica) seedlings were grown in large pots of forest soil, at ambient (± 350 μll l −1 ) and double (700 μl l −1 ) atmospheric CO 2 concentration in constantly ventilated mini-greenhouses during an entire growing season. CO 2 enrichment caused very different changes in these two temperate deciduous species. A 20% dry weight enhancement was obtained for sweet chestnut, and a 60% enhancement in beech. This greater effect of elevated CO 2 in beech was the result of a significant increase of net photosynthesis of the seedlings occurring during the whole season (...)

Aerodynamic and canopy resistance of short-rotation forest in relation to leaf area index and climate

Abstract: The aerodynamic and canopy resistances of a willow short-rotation stand were estimated during the course of a growing season on the basis of micrometeorological measurements. The normalized roughness length (z0/h) decreased from about 0.10 at a leaf area index of one to 0.05 at a leaf area index of seven. This implies that the aerodynamic resistance at peak leaf area index is more than twice the value at zero leaf area index, all other variables unchanged. The canopy resistance depended strongly on air water concentration deficit and on leaf area index. The Lohammar equation showed good agreement between estimated and “measured” canopy resistances over the whole course of leaf development. The stand was well-coupled to the atmosphere only for very small values of leaf area indices, less than one, and it was practically de-coupled for leaf area indices above two. From the point of view of factors controlling evaporation, this type of stand acts as a traditional forest at the beginning and end of the season and as an agricultural crop in the middle of the season.

Timing of the First Irrigation in Corn and Water Stress Conditioning

Abstract: Delaying the first irrigation is thought to encourage root growth and to condition crop plants for stress later in the growing season. We tested this common practice for corn (Zea mays L.) grown under arid conditions in Tucson, AZ, in 1989 and 1990. In field studies conducted on an Agua sandy clay loam (coarse-loamy over sandy, mixed, thermic Typic Torrifluvent), the first irrigation was applied at the 2-leaf, 4-leaf, or 6- to 8-leaf stages, followed by irrigation or water stress at anthesis. Delaying the first irrigation did not encourage root growth but actually restricted it in 1989. Seasonal water use was decreased from an average of 796 mm to 705 or 652 mm if the first irrigation was delayed from the 2-leaf to the 4-leaf or 6- to 8- leaf stages, respectively [...]

Effect of paclobutrazol on flower-bud production and vegetative growth in two species of Eucalyptus

Abstract: A series of experiments on field-grown seed-derived trees between 2 and 17 years old demonstrated that the growth regulator paclobutrazol could be used to reduce vegetative growth and enhance flower-bud production in Eucalyptusglobulus Labill. and Eucalyptusnitens (Dean & Maid.) ex Maid. Responses to high levels of trunk injection and collar drenching persisted for up to six growing seasons, yielding both increases in frequency of flowering and heaviness of bud crop. Growth responses were expressed in the immediate growing season, but flowering responses were not evident for another year. Foliar spray treatments reduced vegetative growth in young trees of both species for one growing season, but only the E. globulus showed an associated flowering response. Assessment of seed yield per capsule and subsequent germination tests showed no deleterious effects on seed development or quality. Choice of application method will vary with objective and size of tree. Collar drenching shows the most promise for treat...

Factors affecting methane production under rice

Abstract: To understand why atmospheric methane is increasing worldwide, accurate estimates are needed of the global input from rice fields. We report greenhouse and laboratory studies over three growing seasons to isolate and control factors that might affect methane emission from rice paddies, including soil texture, added exogenous organic matter (OM), nitrogen and sulfate ion, and water management. Without added OM, methane production was relatively low, increasing during the growing season, and continuing after harvest, provided the soil remained water-logged. If ground rice straw was added to the soil prior to planting, methane production began shortly after flooding, with an initial burst of the gas after 3 to 5 weeks, and then a gradual increase to a second peak later in the season (and after harvest), with rates considerably higher than in treatments without added OM.

Regeneration capacity and carbohydrate reserves in a clonal plant Rumex alpinus : effect of burial

Abstract: The morphological and anatomical responses to different depths of burial were examined in Rumex alpinus (Polygonaceae), a perennial plant with monopodial, horizontally growing rhizome. Its segments, which consist of 12–20 internodes, 1 to 2 mm in length each, are products of single growing seasons. The rhizomes regenerated from 5, 10 and 20 cm, but failed to emerge from 30 cm. Number of internodes produced during a growing season was not affected by burial but the length of internodes increased up to about 30-fold. The rhizomes growing up to the surface were subsidized by older rhizome segments. In the case of deeply buried rhizomes the carbohydrate reserves of the last-year-segment were nearly completely depleted. Evolutionary significance of the regeneration capacity is discussed.

Production and nutrient dynamics of a Syringodium filiforme Kütz. Seagrass bed in Indian River Lagoon, Florida

Abstract: A year-long analysis of the characteristics of the seagrassSyringodium filiforme and the associated dynamics of the nutrient pool in the sediment pore water was done to assess co-variation. Changes in seagrass growth rate and standing stock throughout the year were accompanied by seasonal changes in the nutrient pools. The link between plant production and morphometrics and the sediment nutrient pool was found to be predominantly physiological, with the plant balancing the ability to photosynthesize with the nutrients needed for maintaining production. Measurements of whole plant growth for this seagrass, rather than the more typical leaf growth measurements, show that the production of new shoots and rhizome elongation for these plants represents as substantial amount of growth that usually goes unmeasured. Further, these whole plant growth measures demonstrate the rapid lateral rhizome spread of this species, exceeding one meter per plant per year. The primary cause of seasonal variation in the yearly seagrass cycle was investigated. Correlation analysis supported the hypothesis that the major factor controlling seasonal variation in this seagrass was light. During the peak growing season, however, growth was not regulated by light but by nitrogen. Depletion of the sediment ammonium pool and reduction in pore water ammonium relative to adsorbed ammonium, as well as changes in N content of seagrass leaves, support our hypothesis of peak growing season nitrogen limitation. Our results forSyringodium filiforme in terrigenous sediments are in contrast to our recent findings of phosphorus limitation in this same species occurring in carbonate sediments.

Managing Soil Moisture on Waste Burial Sites in Arid Regions

Abstract: In semiarid regions, where potential evapotranspiration greatly exceeds precipitation, it is theoretically to preclude water form reaching interred wastes by (i) providing a sufficient cap of soil to store precipitation that falls while plants are dormant and (ii) establishing sufficient plant cover to deplete soil moisture during the growing season, thereby emptying the water storage reservoir of the soil. Here we discuss the theory and rationale for such an approach an then present the results of a field study to test its efficacy at the Idaho National Engineering Laboratory (INEL) []

Species richness and canopy productivity of Australian plant communities

Abstract: The species richness (number of vascular plants per hectare) of Australian plant communities (containing a mosaic of gap, regeneration, maturation and senescent phases) is correlated with the annual biomass productivity of the overstorey canopy. The annual production of leaves and stem in the canopy of the plant community is shown to be limited by the requirements of photosynthesis (particularly light and the availability of water) and the length of the growing season. The species richness of Australian plant communities is the product of the blance between the dominance of the overstorey and the response of the understorey to the shading of the overstorey. For all climatic regions and zones the species richness of the overstorey of the plant community is shown to be exponentially related to the annual shoot growth of the overstorey canopy, until the latitudinal or altitudinal tree line is reached. With latitudinal increase outside the tropics, overstorey canopies of forest communities absorb increasingly more of the incident solar radiation. markedly reducing the species richness of the understorey strata. In contrast, in these latitudes the overstorey of plant communities with widely spaced trees or tall shrubs will absorb far less solar radiation, thus enabling the species richness of the understorey to be maintained.

Microsite variability and safe site description for western larch germination and establishment

Abstract: OSWALD, B. P. (Department of Plant and Soil Science, Alabama AM shading, moss, and large vegetation were not significantly effected by treatment. Seven western larch (Larix occidentalis) seeds were distributed after burning treatment on each sample point, and the number of germinations, germinants and seedlings were tracked over two growing seasons. Germinations (741) and germinants (656) from 17,500 seeds occurred on a wide variety of burned and unburned microsite types. Microsite types with successful germination, germinants, and seedling establishment are the "safe sites" (seedbed with proper conditions) for these stages of seedling development. Safe site requirements became more specific as the seedling developed, with only 47 seedlings surviving to the end of the first growing season. Seedlings survived on safe sites which represented 1.5% of the -total area. The eight physical characteristics used to describe microsite types were evaluated with discriminant analysis for significance at each seedling stage. Significant variables and interactions were identified for regression. Analysis produced high (R2 = 0.75) predictability at the end of the first growing season for initial seedling establishment. Safe sites are described for seedling establishment, with site, seedbed treatment, shading and moss as significant variables. The safe site concept appears useful in evaluating germination and initial establishment of western larch.

Impacts of Burning on Primary Productivity of Festuca and Stipa-Agropyron Grasslands in Central Saskatchewan

Abstract: -Grassland communities dominated by Festuca scabrella or by Stipa curtiseta and Agropyron dasystachyum were burned experimentally in spring or autumn. Forb, shrub and graminoid biomasses were greater in the unburned Festuca community than in the StipaAgropyron type. Spring and autumn burning delayed early season growth of graminoids in both grassland types in the 1st growing season after fire. Peak green biomass was reached later in the season in burned plots relative to reference areas. Plant growth in the spring of the 2nd yr after fire was more rapid in burned plots and peak biomass was reached earlier than in the reference plots. Autumn burning reduced forb biomass significantly early in the growing season during 1 of 3 yr that this parameter was measured. No effect of burning on shrub biomass was detected. Autumn and spring burning of Festuca grassland reduced peak, green, graminoid biomass production in the 1st and 2nd yr after fire; autumn burning had the most negative effect. Reductions in graminoid biomass after burning Stipa-Agropyron stands were smaller than in the Festuca community. Nitrogen concentrations in F. scabrella shoots regrown after fire were higher than those from the reference areas. Soil water content during the growing season, and snow trapping were reduced by burning. Peak green biomass and total graminoid biomass in Festuca grassland recovered to the level of the reference plots 2-3 yr after burning. Recovery was slower in the Stipa-Agropyron community.

Home range and social organization of the singing vole (Microtus miurus)

Abstract: Intensive live-trapping over four summers revealed that neither population density nor season (early or late growing season) affected the home-range size of singing voles. Home-range size increased with body size for both sexes, and males generally had larger home ranges than females (average areas of 1,250 and 450 m2 for adult males and females, respectively). Seasonal patterns of overlap for reproductive animals suggested that singing voles have a promiscuous mating system and that territorial behavior is flexible (males tended to be territorial early in the breeding season and females tended to be territorial late in the breeding season). The construction of haypiles in August provided winter forage with higher protein content and occurred primarily in the home ranges of immature animals, the only cohort found to survive over winter.

Spatial and Temporal Variation in Competitive Effects on Soil Moisture and Pine Response

Abstract: The effects of different plant life—forms, including a bunch grass species, Andropogon virginicus L. (broomsedge), and a sprouting deciduous tree species, Liquidambar styraciflua L. (sweetgum), on soil moisture and competitive responses of a transplanted coniferous tree seedling, Pinus taeda L. (loblolly pine), were investigated. Addition of the bunch grass and/or hardwood sprouts either had no effect or increased soil moisture in the surface soil (0—14 cm) depending on the time, while addition of sweetgum and/or broomsedge (greatest density alone) decreased soil moisture in deeper portions of the solum during the summer months. Soil moisture available to pine seedlings at various points in time was assessed by measuring predawn xylem pressure potential. Temporal variation in predawn xylem pressure potential was accounted for through a water stress integral approach. More than half of the variation in pine size after one growing season could be accounted for by the water stress integral. See full-text art...