摘要:

The showy Indian paint—brush, Castilleja coccinea (L.) Spreng., is photosynthetic, but its roots produce haustoria that penetrate the roots of plants growing near it. It interacts with those plants as a parasite; unless it penetrates them, it does not mature beyond the seedling stage, and once it does it significantly lowers their dry weight. Phosphate, sulfate, and fructose are known to move across the haustoria rapidly, but what the plant actually uses from its hosts is not known. Artificial feeding of common vitamins, phytohormones, and respiratory substrates does not take the place of a host. C. coccinea will attack plants of many vascular species, including several that do not occur in its range.

ISSN:0012-9658    

DOI:10.2307/1933763

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Seventeen grass species and two forbs, planted on a minimal Chestnut soil in northern Nevada, were grown under various degrees of competition in the native shrub, Artemisia tridentata, for 18 years. Grass species included seven native bunchgrasses, six exotic bunchgrasses, one native sodformer, and three exotic sodformers. Forbs gave no persistent stands. Performance of native bunchgrasses was poor. The surviving exotic bunchgrass, Agrophyron desertorum, A. elongatum, and Elymus junceus, rated fair, poor, and good, respectively, after 18 years. These three species produced well for 11 years, after which yields declined sharply. As a group the sodforming agropyrons, Agropyron intermedium, A. trichophorum, and A. smithii, performed better than did the bunchgrasses. The greatest production of Bromus tectorum was on plots that had failed after 5 years or where species were not well adapted to the site. Only scanty B. tectorum grew on plots of A. intermedium and A. trichophorum. When re—invasion by Artemisia tridentata occurred, greatest brush numbers were found on plots of species that failed early in the study and on plots where seeded species failed after 5 years. The sodforming agropyrons were most effective in preventing shrub re—invasion. The ability of Agrophyron intermedium, A. Smithii, and A. trichophorum, especially the latter, to establish readily, to suppress brush and annual grass invasion to produce superior yields, and to spred vegetatively under considerable precipitation fluctuation and brush competition indicates the adaptability, aggressiveness, and competitive strength of these sodformers.

ISSN:0012-9658    

DOI:10.2307/1933764

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Bacterial and fungal counts, mycelial growth, microbial evolution of Co2,and substrate moisture and temperature in bags with litter of either mulberry, redbud, white oak, loblolly pine, or beech were measured biweekly over the period November 1960—November 1961 in oak, pine, and maple stands at Oak Ridge, Tennessee. Serial dilution plate method and closed—box technique were effective for measuring microbial densities and microbial respiration respectively. Microbial densities, microbial respiration, and annual weight losses of species declined in the order mulberry, redbud, white oak, pine, beech, ad were significantly positively correlated. Stand effects were not significant possibly due to partial exclusion of stand effects in the bags. Microbial densities and moisture conditions of the various leaf species converged with time and their short—term fluctuations decreased indicating homogenation of substrate and stabilization of microbial populations. Microbial respiration was controlled in decreasing order by temperature (T), bacterial density (B), moisture (M/D), and the number of weeks (W) since leaf drop. An effective model for prediction of microbial respiration (C) is C = 46.5 + 3.2T + 26.9 M/D + 11.4 log B — 0.6W. Mean CO2production was 0.17 liters/g substrate decomposed. Production was higher for rapidly decomposing leaf species dominated by relatively inefficient bacterial flora than for slowly decaying litter with predominantly more efficient fungi. Loss of weight and respiration were highly correlated with a microbial population estimate, combining bacterial and fungal counts.

ISSN:0012-9658    

DOI:10.2307/1933765

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Between two lrge dunes near the northern edge of the grass—covered Nebraska Sandhills on the Rosebud Indian Reservation is an alluviated lowland containing more than 6 m of organic sand and silt. Pollen and seed analyses of the lowest 120 cm of sediment imply that a boreal forest with spruce grew around the site 12,600 c14years ago and was succeeded abruptly by grassland, with perhaps more pine than exists today (as Pinus ponderosa) in the nearby Niobrara River Valley and the Pine Ridge escarpment of northwestern Nebraska. Pollen analyses of surface samples were used to determine the modern pollen rain at different distances from the modern pine forests of the western plains. The presence of spruce fossils at the Rosebud site, along with similar finds in northeastern South Dakota and southern Minnesota, implies a late—Wisconsin boreal forest over much of the present prairie region. The major disjunction of Picea glauca in the Black Hills, 200 km northwest of the site and 700 km from from the spruce forest of Manitoba, may thus be explained as a relic of a semi—continuous distribution during late—Wisconsin time.

ISSN:0012-9658    

DOI:10.2307/1933766

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Whole plant lethal points of foliage moisture content (FMC) for ponderosa pine, sugar pine, Douglas—fir, grand fir, and incense—cedar were established from foliage tissue of various ages. Exact lethal level depended upon the age of the tissue, but there was a general plateau between the ages 6 and 13 months for sugar pine and Douglas—fir and 3 and 13 months for incense—cedar. Whole plant relative turgidity (RT) lethal points were set for the pines and firs using 13—month—old needles. Dry—weight loss upon soaking the needles was found to increase with the severity of the drought, especially for the firs. Soil moisture content (SMC) lethal points were established for all five species on builders' sand (death began at an SMC probably equivalent to tension above 24 atm) and on pumice soil (death points equivalent to tensions from 15 to 19 atm). Foliage moisture content declined with decreasing soil moisture stress in a straight—line relationship; FMC may be used as an index of soil moisture stress within a rather narrow range of SMC and may also be calibrated with leaf tissue diffusion pressure deficits developing under soil moisture stress to give an index of the water balance of the plant. Based on the SMC at the death point and also upon some species' ability to outlive other under competitive conditions, ponderosa pine, incense—cedar, and Douglas—fir were the most drought resistant, sugar pine the least, and grand fir intermediate. Ways are suggested in which the mixed—conifer forests could become established and retain their mixed composition through maturity. The findings suggest that if planting is used to regenerate clearcuts, ponderosa pine and incense—cedar would be first choice, but that sugar pine would also be a preferred species if seeding is used.

ISSN:0012-9658    

DOI:10.2307/1933767

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Nine plant species believed to be important to mule deer (Odocoileus hemionus) on the Cache la Poudre range of Colorado were collected at four seasons during 1961, from five study areas which varied in altitude from 6,400 to 10,300 ft. Eleven chemical components were analyzed for each of the 77 plant samples. In a deciduous species (Purshia tridentata) the percentage dry matter and crude fat, and the caloric content varied from high autumn—winter levels to low spring—summer values; and beta carotene and percentage protein, ash, phosphorus, potassium, calcium, sodium, and magnesium levels varied from low autumn—winter values to high spring—summer values. In an evergreen species (Juniperus scopulorum) the seasonal changes in plant chemistry were not so pronounced. Major variations in the measured components were attributable to two causes in the following order: (1) differences in nutrient levels between species; (2) differences in nutrient levels measured for one plant species at the four seasons. Minor variations were evident within single species when sampled in a specific season at different areas throughout its range. The normal and predictable variation in plant chemistry caused by seasonal changes in plant phenology and physiology and physiology has important implications to the nutrition and physiology of deer.

ISSN:0012-9658    

DOI:10.2307/1933768

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Structure and species composition were sampled in 49 stands of foothill woodland in the vincinity of Hastings Reservation. Most of the stands were nearly pure blue oak (Quercus Douglasii). There was an average of 207 trees per acre, but an average of only 75 saplings per acre. The majority of saplings were blue oaks so that blue oak is not being replaced by other species. Fire and livestock grazing have probably not limited blue oak reproduction recently, but deer browsing limits the growth of many oak seedlings. Annual right counts on stumps showed that the majority of blue oak trees originated over a relatively short period from approximately 1870 to 1890, a dynamic period of land use in the study area, but the factor or factors that accounted for this flush of oak reproduction cannot be determined.

ISSN:0012-9658    

DOI:10.2307/1933769

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Species distribution of the ground cover of a Scots pine stand along the slope of a fixed inland dune closely reflected micro—relief and profile of the soil. Depth of a fine sand deck on coarse sand varied from 0 cm at the bottom to 150 cm at the top of the dune. Corresponding water—holding capacity (WHC) to a depth of 150 cm varied from 459 to 284 liters/m2. Tree height was significantly correlated with WHC. Dependance of litter and humus formation on primary production, and of mycelium growth on litter and humus resulted in significant correlation of these factors and moisture. Mycelium length was significantly correlated with fungal plate counts in January. The annual cycle of mycelium length did not show a peak in autumn as was found in broad leaft forest, presumably a result of differences in nutrient release from the litter. Of the organic mass to a depth of 1 m trees contributed 13%—34%, ground cover + litter + humus 49%—66%, soil organic matter 16%—22%, and fungal mycelium in soil 0.6%—0.9%. Reasons for the low fungal mass may be its ephemeral character, low influx of organic matter into the soil, and presence of much mycelium which was not measured on top of the soil.

ISSN:0012-9658    

DOI:10.2307/1933770

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Perognathus californicus is a nocturnal, burrowing rodent and in the mountains of southern California is locally distributed in association with the edge of grasslands. The thermal environment of P. Californicus is moderate. Temperatures on the surface of the ground at night range from 0 to 25°C in summer. P. Californicus undergoes a daily period of torpor if its food supply is reduced below its ad libitum consumption. At an ambient temperature of 15°C, 17 g of bird seed per 100 g body weight is required each day to maintain weight in the absence of torpor. If this food ration is reduced, mice on a 12—hr photoperiod with lights on from 0600 to 1800 hr enter torpor between 2000 and 0500 hr and allow their body temperatures to drop to about 16°C. The earlier times of entry into torpor are associated with smaller food rations. Since the mean time of arousal is between 1100 and 1330 hr on all food rations, the duration of the torpor period increases as the food ration decreases. The torpor period in the laboratory may encroach on the nightly activity period and decrease the total activity of mice on rationed food. A linear relation exists between daily food ration, time in torpor, and weight loss. This relation can be explained theoretically and measures the food requirement for weight maintenance in the absence of torpor, the food savings associated with torpor, and the influence of food ration on the rate of weight loss. This information, together with data on population dynamics, could be used to estimate the population energetics of P. californicus.

ISSN:0012-9658    

DOI:10.2307/1933771

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Introductions of American smelts, Osmerus mordax, from six established populations into eight new environments were made in Maine in 1957—62 to determine which characteristics of the parent populations would be altered by transfer to the new environments and which would remain unaltered. Four of the host lakes had not contained smelts previously, three had contained smelts which were removed by rotenone, and one is thought to have contained a smelt population which disappeared 4 or 5 years before the experimental transfer. In several cases the growth rates, lengths, and longevities attained by smelts changed greatly with change in their environment. The time of the spawning season for one stock of smelts remained unaltered following transfer to an environment where the previous smelt population routinely had spawned much later. In one case smelts hatched from eggs of a stream—spawning population adapted immediately to the shore—spawning habit in a host lake where tributaries are absent. The success of smelts in the various new environments appeared to depend mostly upon the intensity of interspecific competition and other biotic factors, as with most fishes.

ISSN:0012-9658    

DOI:10.2307/1933772

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY