摘要:

Changes in the distribution and cycling of N, P, K, Mg, and Ca were investigated in plantations of splash pine (Pinus elliottii var. elliottii) using an age sequence of replicated stands 2, 5, 8, 14, 18, 26 and 34 yr old. All stands had a similar history of management and occurred within 20 km on somewhat poorly drained Ultic Haplaquod soils in northern Florida. Because of the rapid colonization of these sites by grasses, plant nutrient uptake was already high at age 2 yr. Thereafter, uptake of N, P, K, and Mg increased<50% to a maximum at 8 yr, around the time that maximum leaf area for these stands is reached. Ca uptake increased 130% over this time. Uptake declined after age 8 yr for all elements. Nutrient return in litterfall remained relatively constant after 5 yr. Canopy leaching, estimated as the difference between bulk precipitation and throughfall, was negligible for N and P, but highly significant for all three cations. K leaching from the canopy was greatest and amounted to °60% of litterfall in mature stands. Internal redistribution of mobile elements (N, P, K) in the vegetation was negligible until the pine canopy closed, but then increased greatly. From 2 through 26 yr, vegetation nutrient contents increased much more than nutrient uptake rates. The surface soil of the youngest stands appeared to be enriched by material added during site preparation. The nutrient content of the Bh horizon increased through the 8th yr, indicating a downward movement of the added material. Soil contents (to 100 cm depth) of total N and double—acid extractable P and cations then decreased over time, with the greatest decline during the first 18 yr. Forest floor contents increased at a constant rate, with no plateau indicated through 34 yr. Annual precipitation inputs of nutrients varied from 0.3 kg/ha for P to 13.5 kg/ha for N, with cation values of 2.6—5.0 kg/ha. Annual ecosystem balances of N, P, K, and Ca appeared slightly positive, while the content of Mg appeared to decline. Nutrient use efficiencies (net primary production ° uptake) increased greatly with time and were very high in older stands, especially for P. However, it appears that mineralization processes in these very nutrient—poor systems and the small atmospheric inputs cannot supply the annual nutrient requirements of mature stands, especially for P; this leads to a cessation of vegetative biomass increment around age 26 yr.

ISSN:0012-9658    

DOI:10.2307/1940526

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Despite their ability to tolerate long and severe drought and extreme temperature, desiccation—tolerant plants are typically excluded from the most xeric microhabitats. It was hypothesized that this is due to an inability of the plants to maintain a positive cumulative carbon balance during repeated cycles of wetting and drying under highly xeric conditions. To test this hypothesis, the response of net CO2flux to light, temperature, plant water content, and previous desiccation were measured in the desiccation—tolerant moss Grimmia laevigata, the dominant green plant on exposed granitic boulders in the inland chaparral of San Diego County California. Patterns of net CO2flux and results from a simple model of carbon balance were consistent with the hypothesis.

ISSN:0012-9658    

DOI:10.2307/1940527

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Persistent distribution patterns of woody vegetation within the bottomland forest of Passage Creek, Virginia, were related to fluvial landforms, channel geometry, streamflow characteristics, and sediment—size characteristics. Vegetation patterns were determined from species presence as observed in transects and traverses on landforms developed along the stream. Distinct species distributional patterns were found on four common fluvial geomorphic landforms: depositional bar, active—channel shelf, floodplain, and terrace. Independent hydrologic characteristics (flow duration and flood frequency) were determined for each of the landforms. Vegetation data were analyzed by binary discriminant analysis, principal components analysis, and detrended correspondence analysis. Results and related field observations suggest that certain species are significantly associated with specific fluvial landforms. Vegetation patterns appear to develop more as a result of hydrologic processes associated with each fluvial landform rather than from sediment—size characteristics. Flood disturbance may be an important factor in maintaining the vegetation patterns, which may therefore be used as indicators for particular hydrogeomorphic site conditions.

ISSN:0012-9658    

DOI:10.2307/1940528

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Gap—phase regeneration of trees was described for the first 5—6 yr of regrowth in 30 treefall gaps (20—705 m2) in tropical moist forest on Barro Colorado Island, Panama. Trees were classified as pioneers (saplings found only in gaps) or primary species (saplings found in gaps and in the understory of mature forest). In most of the gaps studied, stem densities rose rapidly after gap formation, then levelled off or declined by years 3—6. This pattern was particularly marked in some large gaps (>150 m2), where pioneers attained high densities, then experienced heavy mortality. Stem density of primary species did not vary with gap size. In large gaps the mean rate of growth in height was greater for pioneers than for primary species, size—class distribution broadened more for pioneers than for primary species, and early recruits of both regeneration types grew faster than later ones. Gap formation fosters regeneration of pioneer and primary species and, in this forest, produces patches that differ markedly in tree population dynamics, species composition, and growth rate.

ISSN:0012-9658    

DOI:10.2307/1940529

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Five Costa Rican species of Piper (Piperaceae) co—occur in evergreen forest sites at Santa Rosa National Park, Costa Rica. The species were found to have distinctive spatial distribution patterns with two species (Piper marginatum and P. pseudofuligineum) occurring in early successional sites and the others, P. amalago, P. jacquemontianum, and P. tuberculatum, occurring in less disturbed sites in dry forest, evergreen forest, and riparian forest, respectively. These habitat differences are associated with differences in seed and seedling biology and seasonal changes in the foraging behavior of the chiropteran seed dispersers of these plants. Excluding the uncommon P. tuberculatum, overall pairwise spatial overlap, measured by Pianka's (1974) symmetrical index, averaged 0.61. Relatively low phenological overlap allows the species to share animal visitors. Average pairwise flowering overlap (0.13) was about one—half the value of pairwise fruiting overlap (0.22). Responses to different rainfall cues and/or different inflorescence growth rates produce temporally separated phenological cycles. However, results of computer simulations suggest that observed phenological overlap was neither significantly lower nor significantly higher than expected by chance, for most pairs of species. Insect visitation is necessary for high seed—set, and species differ in their attractiveness to pollinators. Pairwise insect overlap (0.59) was greater than expected by chance, however. The plants also utilize the same six species of frugivorous bats as seed dispersers, and pairwise bat overlap was extremely high (0.96). Because they are important fruit sources for three common bat species, Piper species are keystone mutualists in dry tropical forests.

ISSN:0012-9658    

DOI:10.2307/1940530

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

In 10 stands of deciduous forest, evidence was sought for competitive inhibition between groundlayer species photosynthetically active in different seasons. In each stand, the forest floor had probably not been disturbed catastrophically for>50 yr, thus favoring detection of cumulative competitive effects. The underlying hypothesis was that long—lived species occupying the same microsites but not competing directly for light may, nevertheless, interfere with each other's growth by seasonal depletion of labile soil nutrients. For a plot size that holds, on average, two species, coefficients of rank correlation were computed, stand by stand, between the cover values of (1) species that are in leaf only through early spring, and (2) species that leaf out later in the growing season. Fewer than 5% of the correlations were significantly negative at the 5% level, indicating that competition between phenologically distinct plants may be too weak or sporadic to affect local species patterns. The magnitude of negative correlations, or the percentage of significant negative correlations, was, however, greater than average between certain abundant species thought to be liberal in uptake of labile nutrients. This was most pronounced for correlations between Erythronium americanum, a spring—ephemeral herb, and Parthenocissus quinquefolia, a summer—active shrub with relatively indeterminate shoot growth. Another result suggesting nutrient—based competitive inhibition was a 50% lower mean cover for two nutrient—demanding summer—active species (Acer saccharum and Ulmus rubra, both abundant as groundlayer plants) in plots with an exceptionally high density of shoots in early spring. In contrast, the pooled cover sums for all summer—active species were unaffected by locally high densities of shoots in early spring.

ISSN:0012-9658    

DOI:10.2307/1940531

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

We assessed competition among five wind—dispersed perennial fugitive plant species. The species constitute a guild on small open sites formed by foraging badgers on the Cayler Prairie Preserve in northwestern Iowa, USA. The outcome of interactions among individuals at a site depended on the intervals between immigrations. When immigrations were separated by more than one growing season, preemptive competition occurred: initial colonists were not affected, but most later arrivals died during the first growing season, and none survived to maturity. When multiple immigrations occurred within a single year, exploitative competition depressed growth and propagule production of co—occurring species in inverse proportion to their propagule size. By manipulating the density of colonization sites and the production of propagules, we demonstrated a direct nonlinear relationship between immigration and intra— and interspecific competition. With infrequent immigration, neither preemptive nor exploitative competition was likely among offspring; reproductive success of parents was proportional to the likelihood of immigration. As immigration increased, preemptive and exploitative competition among offspring was accelerated, and per—propagule gains in parental reproductive success declined. Losses of reproductive success were inversely related to species—specific exploitative capabilities. For individuals of each species, the competition threshold was that immigration rate above which reproductive success was lowered due to the combined effects of preemptive and exploitative competition are directly related (as with competition for sites or resources within sites), competition increases with the density of the limiting resource and will have greatest effect on plants at high densities of the limiting resource. Our results further indicate that intra— and interspecific competition are likely to influence reproductive success within local populations of these fugitive species. Mean fecundities among adjacent populations of fugitive plants were more similar than expected for noninteracting populations distributed along a gradient of site densities, suggesting that interspecific competition has influenced life history attributes in this guild. Differences in life history attributes influencing immigration and exploitative capabilities may result in there being regions along the gradient within which each species is competitively superior. Persistence in the guild may be maintained by: (1) an inverse relationship between immigration and exploitative ability, (2) variation in the density of sites, and (3) the occurrence of both preemptive and exploitative competition on sites.

ISSN:0012-9658    

DOI:10.2307/1940532

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Scatter diagrams and regression analysis of paired pollen and tree—inventory data show how pollen percentages represent the percent basal area for the major arboreal genera in Michigan and Wisconsin. We show that the relationship between pollen and tree percentages for each taxon is generally similar for two states of comparable size and similar vegetation (Wisconsin and Michigan), but that the relationship is influenced by the size of the pollen—collecting site and the size of the area surveyed for trees around each site. These results provide information concerning the relative size of the pollen—source area for seven arboreal pollen types: Pinus, Quercus, Betula, Tsuga, Ulmus, Fagus, and Acer, listed in descending order of pollen—source area. Moderate—sized lakes (30—150 ha) accumulate significant quantities of Pinus and Quercus pollen produced farther than 30 km away, but accumulate relatively few Fagus grains from>4.5 km, and even fewer Acer grains from>2.3 km. The source areas for Betula, Tsuga, and Ulmus pollen lie within 30 km of each lake, and significant quantities of these grains travel farther than 4.5 km. Regression analysis of data from basins of different size supports the hypothesis that small basins collect their pollen from a smaller area of the surrounding vegetation than do large basins.

ISSN:0012-9658    

DOI:10.2307/1940533

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Pressure—volume curves were measured in three co—occurring chaparral shrubs, Arctostaphylos glandulosa, Quercus dumosa, and Ceanothus greggii, during a seasonal drought cycle. The pressure—volume approach was used to quantify diurnal and seasonal changes in plant water relations. Field measurements of plant water potentials and microclimate were also made to relate the pressure—volume results to the field setting. The seasonal trend was toward increasingly negative osmotic potentials with little (Q. dumosa) or no (A. glandulosa and C. greggii) recovery following the end of the drought. Shifts in the turgor loss point occurred both seasonally and diurnally. The largest diurnal shifts occurred during periods of maximum air temperature and minimum soil water potential. Concurrent field measurements of water potential indicate that these shifts were necessary for preventing turgor loss during periods of midday water stress in Q. dumosa and C,. greggii. The shrubs differed in their mode of seasonal osmotic adjustment. Ceanothus greggii accomplished changes in osmotic potential by variation in the osmotic water volume; the other two shrubs appeared to accomplish such changes largely by solute variation while maintaining relatively constant osmotic water volumes.

ISSN:0012-9658    

DOI:10.2307/1940534

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The effects of inter— and intraspecific interference on size hierarchies (size inequalities) were investigated in populations of the annual plants Trifolium incarnatum and Lolium multiflorum. Variables experimentally manipulated included plant density, species proportions, soil fertility, and spatial pattern of plantings. Densities were below those for extensive density—dependent mortality. Size inequality always increased with increasing density. Plants grown individually showed very low inequality, while plants grown at the highest density had the most developed hierarchies. Size inequality usually increased with an increase in productivity when interference was occurring. When dominant in mixtures, Lolium showed less size inequality than in monoculture, while the suppressed species, Trifolium, usually displayed an increase in inequality. Spatial pattern appeared to be less important than other factors in causing size inequalities; plants sown in a uniform spatial pattern showed significantly lower size inequality than plants sown in a random pattern in only one out of four cases. Inequality in reproductive output of Trifolium, as estimated by dry mass of flower heads, was always greater than inequality in plant in dry mass. The results support a model of plant interference in which large plants are able to usurp resources and suppress the growth of smaller individuals more than they themselves are suppressed. While interference decreases mean plant mass, it increases both relative variation in plant mass and the concentration of mass within a small fraction of the population.

ISSN:0012-9658    

DOI:10.2307/1940535

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY