共查询到20条相似文献，搜索用时 15 毫秒
1.
Abstract. In ecosystems where environments are extreme, such as deserts, adult plant species may facilitate the establishment and growth of seedlings and juveniles. Because high temperatures and evaporative demand characterize tall‐grass prairies of the central United States (relative to forests), we predicted that the grassland‐forest ecotone, by minimizing temperature extremes and moderating water stress, may function to facilitate the expansion of Quercus species into undisturbed tall‐grass prairie. We assessed the carbon and water relations of juvenile Quercus macrocarpa and Q. muhlenbergii, the dominant tree species in gallery forests of northeast Kansas, in ecotone and prairie sites. To evaluate the potentially competitive effects of neighboring herbaceous biomass on these oaks, juveniles (< 0.5 m tall) of both species also were subjected to either: (1) removal of surrounding above‐ground herbaceous biomass, or (2) control (prairie community intact) treatments. Herbaceous biomass removal had no significant effect on gas exchange or water relations in these oak species in either the prairie or the ecotone environment. Although the ecotone did alleviate some environmental extremes, photosynthetic rates and stomatal conductance were ca. 20 % higher (p < 0.05) in both oaks in prairie sites vs. the ecotone. Moreover, although leaf temperatures on average were higher in oaks in the prairie, high leaf temperatures in the ecotone had a greater negative effect on photosynthesis. These data suggest that the grassland‐forest ecotone did not facilitate the growth of Quercus juveniles expanding into this grassland. Moreover, the carbon and water relations of juvenile oaks in the prairie appeared to be unaffected by the presence of the dominant C4 grasses. 相似文献
2.
Abstract. A potentially important organizing principle in arid and semi-arid systems is the inverse-texture hypothesis which predicts that plant communities on coarse-textured soils should have higher above-ground net primary productivity (ANPP) than communities on fine-textured soils; the reverse is predicted to occur in humid regions. Our objectives were: (1) to test predictions from the inverse-texture hypothesis across a regional precipitation gradient, and (2) to evaluate changes in community composition and basal cover on coarse- and fine-textured soils across this gradient to determine how these structural parameters may affect ANPP. Sites were located along a precipitation gradient through the Central Grassland region of the United States: mean annual precipitation ranges from 311 mm/y to 711 mm/y, whereas mean annual temperature ranges from 9 °C to 11 °C. For both coarse- and fine-textured sites in 1993 and 1994, August - July precipitation in the year of the study explained greater than 92% of the variability in ANPP. Soil texture did not explain a significant proportion of the variability in ANPP. However, soil texture did affect the proportion of ANPP contributed by different functional types. Forbs and shrubs made up a larger proportion of total ANPP on coarse- compared to fine-textured sites. Shrubs contributed more to ANPP at the drier end of the gradient. Basal cover of live vegetation was not significantly related to precipitation and was similar for both soil textures. Our results revealed that across a regional precipitation gradient, soil texture may play a larger role in determining community composition than in determining total ANPP. 相似文献
3.
Lori A. Biederman Sydney M. Weldon Derek S. Anderson Mark J. Leoschke 《Ecology and evolution》2020,10(17):9532-9537
The western fringed prairie orchid (WFPO) is a rare plant found in mesic to wet tallgrass prairies in the Great Plains and Midwest regions of the United States. The size of WFPO populations varies considerably from year to year, and studies have suggested that population size is dependent on precipitation during critical periods in the plant's annual development. We hypothesized that plant height and reproductive effort would also be controlled by precipitation, either during these periods or over a broader period. We acquired available images of WFPO from 21 herbaria, and of these 141 individual plants had information adequate for analysis, although some population/year combinations were represented multiple times. For each specimen, we measured plant height (cm) and reproductive effort (as measured by total flower and bud count). We used bootstrapped linear regression, randomly selecting one individual from each population/year combination, to compare precipitation models, both during critical periods and the various summaries. We found that precipitation during the phenologically critical periods was a poor predictor of plant height and reproductive effort. Of the broader precipitation variables, accumulated precipitation from January 1 to collection date best described plant height. We also used correlations to detect a relationship among the variables WFPO height, reproductive effort, precipitation, latitude, and year of collection. Year of specimen collection was negatively correlated with WFPO plant height and accumulated precipitation, suggesting that both have declined in more recent years. Negative correlations with latitude also suggest height and precipitation decrease in the northern part of WFPO's range. Reproductive effort was not related to tested precipitation variables; however, it was weakly correlated with plant height. Although the results are limited, this study leverages available data and makes inferences on WFPO biology over broad ranges of time (1894–2012) and latitude (37.5°–49.9°). 相似文献
4.
Roman N. Zajac 《Journal of experimental marine biology and ecology》2004,313(2):297-315
Biogenic structures created via feeding activities have varying effects on soft sediment communities, altering population dynamics, creating a temporal mosaic of successional patches, and ultimately increasing variation at different spatial scales. This study focused on assessing population responses to pits (P) and mounds (M) in an intertidal mudflat (River Plym, England) in order to determine (a) how these structures (max size 1400 cm2), and their formation, affected infauna and (b) to what extent local variations in ambient communities may have affected infaunal responses. Densities in 0- and 1-week-old pits were significantly lower than in ambient and mound areas for most of the dominant infauna over the study period. Abundances were higher in mounds for some species and responses to both structures differed among juveniles and adults. Recovery to ambient levels in P-M systems took about 3 weeks, although their physical characteristics only lasted about 2 weeks. Correlations among ambient densities and adjacent P-M systems were mixed, but suggested decoupling between local ambient and P-M dynamics for some taxa either in relation to age of the patch and/or size of the individuals. At the community level, local differences appeared to be a significant source of variation in new pits, but differences were swamped out when recruitment was high. Differences were more evident in older P-M systems. These results show that sources of local variation in infaunal dynamics can be attributed to a combination of small-scale disturbance/recovery processes and spatially and temporally changing ambient conditions. Identifying extant spatial and temporal small-scale variation can be a critical component of understanding and interpreting larger-scale dynamics of soft-sediment systems. 相似文献
5.
Abstract. Few empirical data exist to examine the influence of regional scale environmental gradients on productivity patterns of plant species. In this paper we analyzed the productivity of several dominant grass species along two climatic gradients, mean annual precipitation (MAP) and mean annual temperature (MAT), in the Great Plains of the United States. We used climatic data from 296 weather stations, species production data from Natural Resource Conservation Service rangeland surveys and a geographic information system to spatially integrate the data. Both MAP and MAT were significantly related to annual above-ground net primary production (ANPP). MAP explained 54% to 89% of the variation in ANPP of two C4 short-grasses, Bouteloua gracilis and Buchloë dactyloides, and two C4 tall-grasses, Andropogon gerardii and Schizachyrium scoparium (= Andropogon scoparius). MAT explained 19% to 41% of the variation in ANPP of two C4 grasses, B. gracilis and B. dactyloides, and 41% to 66% of the variation in ANPP of two C3 grasses, Agropyron smithii and Stipa comata. ANPP patterns for species along both gradients were described by either linear, negative exponential, logistic, normal or skewed curves. Patterns of absolute ANPP (g/m2) for species differed from those of relative ANPP (%) along the MAP gradient. Responses were similar for species with common functional characteristics (e.g. short-grasses, tall-grasses, C3, C4). Our empirical results support asymmetric responses of species to environmental gradients. Results demonstrate the importance of species attributes, type of environmental gradient and measure of species importance (relative or absolute productivity) in evaluating ecological response patterns. 相似文献
6.
Land conversion and modification threatens many wildlife and plant species in the northern Great Plains, including bats. Our objective was to assess the association of bat species with landscape features in the northern Great Plains of North Dakota, USA, taking the first step towards understanding the habitat needs of bats in this region. We examined patterns of bat activity across different landscapes, identified those landscape features associated with high levels of bat activity, and determined which specific land features (i.e., vegetation and water types) were most commonly associated with each bat species. We used passive acoustic monitoring to measure bat activity at sites across North Dakota, and assessed detailed land characteristics at each site. We used nonmetric multidimensional scaling and multivariate regression tree analysis to examine relationships between bat activity and landscape variables. Bat foraging activity was influenced by structural landscape characteristics and the availability of specific water resources. High levels of bat activity were associated with riparian forested areas of varying structural complexity, ponds, and, to a lesser extent, open riparian lands. Individual bat species were influenced by land type and water resources differently. We identified big brown bats (Eptesicus fuscus) and little brown bats (Myotis lucifugus) as indicators of open riparian and pond landscapes, respectively. These results highlight the importance of prairie riparian landscapes and maintaining heterogeneity across the landscape for conservation and management of bat communities. Further, we identified ponds as an important landscape feature for little brown bats, a species of conservation concern, indicating that this specific feature should be a focus of conservation efforts on prairie wetlands. © 2019 The Wildlife Society. 相似文献
7.
Abstract. Previous research has indicated that patch structure at small spatial scales (<100m2) in tallgrass prairies was defined by a diverse array of infrequent species because dominant species occurred in all samples at this scale. Also, patch structure was not significantly different from that derived from random species associations. Based on these results, we hypothesized that remo val of a dominant species would have no effect on patch structure in these prairies. We tested this hypothesis by removing a dominant grass, Schizachyrium scoparium (Poaceae), from half of each of four 10 m × 10 m study blocks, and comparing differences in patch structure between control and removal halves before and after removal. The minimum resolution in our study was 1 m2. Patches of similar species composition were defined by cluster analysis of presence/absence data and cover data. Patch sizes ranged from 1 to 34 m2. Following the removal of S. scoparium there was an overall increase in the number of species in the removal half of each block compared to pre-treatment levels. However, the number of patch types and number of spatially mapped groups, based on presence/absence or cover data, did not change between control and removal plots after the removal of S. scoparium. This supports the hypothesis that removal of a large, dominant species would have no effect on patch structure at this scale of resolution in these prairies. Thus, patch structure, as defined here, is an emergent property in these grasslands that is not predictable from changes in species composition. This property of stochastic patch structure results from interactions of processes operating at scales both larger and smaller than our scale of resolution. Stochastic models may provide a reasonable approach to modelling small-scale patch dynamics in tallgrass prairie communities. 相似文献
8.
M. R. Wuellner R. G. Bramblett C. S. Guy A. V. Zale D. R. Roberts J. Johnson 《Journal of fish biology》2013,82(5):1497-1513
The objectives of this study were (1) to determine whether the presence or absence of prairie fishes can be modelled using habitat and biotic characteristics measured at the reach and catchment scales and (2) to identify which scale (i.e. reach, catchment or a combination of variables measured at both scales) best explains the presence or absence of fishes. Reach and catchment information from 120 sites sampled from 1999 to 2004 were incorporated into tree classifiers for 20 prairie fish species, and multiple criteria were used to evaluate models. Fewer than six models were considered significant when modelling individual fish occurrences at the reach, catchment or combined scale, and only one species was successfully modelled at all three scales. The scarcity of significant models is probably related to the rigorous criteria by which these models were evaluated as well as the prevalence of tolerant, generalist fishes in these stochastic and intermittent streams. No significant differences in the amount of reduced deviance, mean misclassification error rates (MER), and mean improvement in MER metrics was detected among the three scales. Results from this study underscore the importance of continued habitat assessment at smaller scales to further understand prairie‐fish occurrences as well as further evaluations of modelling methods to examine habitat relationships for tolerant, ubiquitous species. Incorporation of such suggestions in the future may help provide more accurate models that will allow for better management and conservation of prairie‐fish species. 相似文献
9.
Nicholas A. McMillan Kyran E. Kunkel Donald L. Hagan David S. Jachowski 《Restoration Ecology》2019,27(2):379-388
Keystone species restoration, or the restoration of species whose effect on an ecosystem is much greater than their abundance would suggest, is a central justification for many wildlife reintroduction projects globally. Following restoration, plains bison (Bison bison L.) have been identified as a keystone species in the tallgrass prairie ecoregion, but we know of no research to document similar effects in the mixed‐grass prairie where restoration efforts are ongoing. This study addresses whether Northern Great Plains (NGP) mixed‐grass prairie plant communities exhibit traits consistent with four central keystone effects documented for bison in the tallgrass prairie. We collected species composition, diversity, abundance, bare ground cover, and plant height data in three treatments: where livestock (Bos taurus L.) continuously grazed, livestock were removed for 10 years, and bison have been introduced and resident for 10 years. We observed mixed support for bison acting as keystone species in this system. Supporting the keystone role of bison, we observed higher species richness and compositional heterogeneity (β‐diversity) in the bison treatment than either the livestock retention or livestock removal treatments. However, we observed comparable forb, bare ground, and plant height heterogeneity between bison‐restored sites and sites where livestock were retained, contradicting reported keystone effects in other systems. Our results suggest that after 10 years of being restored, bison partially fulfill their role as a keystone species in the mixed‐grass prairie, and we encourage continued long‐term data collection to evaluate their influence in the NGP. 相似文献
10.
Abstract. We surveyed tornado damage 14 months after disturbance in three adjacent forest sites in southeastern Missouri, USA: upland, an occasionally-flooded lowland and a frequently flooded swamp. We analysed three 0.09-ha plots in the swamp, and three 0.04-ha plots in the other sites and recorded the herbaceous-layer in five 1-m2 quadrats per plot. Overall, 30 % of the individuals and 64 % of the basal area of these sites was blown down. However, mortality was less than structural damage: 20 % of the trees were dead 14 months post-disturbance, an intermediate level of mortality relative to other wind disturbances. Damage varied widely among species, sites and tree sizes, but large trees of all species were most likely to be damaged and least likely to resprout. While damage was greatest in the wettest site, we attribute the increase to larger tree sizes and lower density there, rather than to inherent rooting instability. This study suggests that different forest composition and structure may be sufficient to cause differential damage, without topographic effects. Herbaceous-layer response was more rapid than in a previously reported tornado windthrow in Pennsylvania, and was dominated by fast-growing, shade-intolerant forbs. 相似文献
11.
Abstract. In the mesic grasslands of the central United States, the shrub Cornus drummondii has undergone widespread expansion in the absence of recurrent fire. We quantified alterations in light, water and N caused by C. drummondii expansion in tall‐grass prairie and assessed the hypothesis that these alterations are consistent with models of resource enrichment by woody plants. Responses in graminoid species, particularly the dominant C4 grass Andropogon gerardii, were concurrently evaluated. We also removed established shrub islands to quantify their legacy effect on resource availability and assess the capability of this grassland to recover in sites formerly dominated by woody plants. The primary effect of shrub expansion on resource availability was an 87% reduction in light available to the herbaceous understorey. This reduced C uptake and N use efficiency in A. gerardii and lowered graminoid cover and ANPP at the grass‐shrub ecotone relative to undisturbed grassland. Shrub removal created a pulse in light and N availability, eliciting high C gain in A. gerardii in the first year after removal. By year two, light and N availability within shrub removal areas returned to levels typical of grassland, as had graminoid cover and ANPP were similar to those in open grassland. Recovery within central areas of shrub removal sites lagged behind that at the former grass‐shrub ecotone. These results indicate that the apparent alternative stable state of C. drummondii dominance in tall‐grass prairie is biotically maintained and driven by reductions in light, rather than resource enrichment. Within areas of shrub removal, the legacy effect of C. drummondii dominance is manifest primarily through the loss of rhizomes of the dominant grasses, rather than any long‐term changes in resource availability. C. drummondii removal facilitates grassland recovery, but the effort required to initiate this transition is a significant cost of woody plant expansion in mesic grasslands. Prevention of woody plant expansion in remnant tall‐grass prairies is, therefore, a preferred management option. 相似文献
12.
Seed supply often limits the size and scope of restoration projects that require active revegetation. To meet demand from more and larger tallgrass prairie restoration projects in the Great Plains, U.S.A., seed is wild‐harvested—collected from remnant habitats—using agricultural combine harvesters. We investigated the potential impacts of wild‐harvest by comparing prairie remnants of northwestern Minnesota that varied in their histories of harvest frequency but were otherwise similar. We asked: (1) Do wild‐harvested prairies differ in species composition from unharvested prairies? (2) If so, can life history traits be used to predict the response of prairie communities to wild‐harvest? We conducted a retrospective study of 17 prairies harvested for seed frequently (annually/biennially), infrequently (2–3 times), or not at all. We sampled vegetation at 45 points within each site, recording all species present within 0.25 m2 quadrats. To address the first question, we used non‐metric multidimensional scaling and Mantel tests, followed by analysis of variance contrasts to identify any species less likely to occur on frequently harvested sites (“harvest‐negative”). For the second question, we used logistic regression to test whether lifespan, clonality, and seed production predicted harvest‐negative species. Plant community composition in frequently harvested prairies differed from that of infrequently or unharvested prairies. Fourteen species, generally short‐lived and non‐clonal, were classified as harvest‐negative. Our results suggest that frequent wild‐harvest disrupts reproduction of species relying on seed, and that life history traits may provide a basis for predicting a species' response to wild‐harvest. 相似文献
13.
Jesse D. Devoe Blake Lowrey Kelly M. Proffitt Robert A. Garrott 《The Journal of wildlife management》2020,84(7):1256-1267
Efforts to recover Rocky Mountain bighorn sheep (Ovis canadensis canadensis) throughout western North America have had limited success with the majority of current populations remaining in small and isolated areas on a fraction of their historical range. Prairie environments with rugged topography throughout the Northern Great Plains ecoregion were historically occupied by relatively robust bighorn sheep populations. We predicted there is likely unrealized potential habitat for restoring bighorn sheep to these areas; however, relatively little attention has been devoted to identifying habitat in unoccupied prairie regions. We used global positioning system (GPS)-collar data collected from 43 female bighorn sheep in 2 populations located in the eastern Montana, USA, portion of the Northern Great Plains during 2014–2018 to estimate a population-level annual resource selection model and identify the important factors affecting bighorn sheep resource selection. We extrapolated model predictions across eastern Montana's prairie region and identified potential habitat to understand restoration potential and assist with future translocations of bighorn sheep. Resource selection of bighorn sheep was most strongly associated with terrain slope and ruggedness, tree canopy cover, and a normalized difference vegetation index metric. Within currently unoccupied areas of the historical range, the model extrapolation predicted 7,211 km2 of habitat, with most owned and managed by private landowners (44%), Bureau of Land Management (33%), and the United States Fish and Wildlife Service (15%). Our results provide an empirical evaluation of landscape covariates influencing resource selection of bighorn sheep occupying prairie environments and provide a habitat model that may be generalizable to other areas in the Northern Great Plains ecoregion. We demonstrate substantial potential for restoration opportunities of bighorn sheep in the Northern Great Plains ecoregion. Broad restoration of bighorn sheep across the ecoregion would likely require strong collaboration among and between public resource managers, private landowners, and livestock producers given the heterogeneous land ownership patterns, management strategies, and domestic sheep distributions. © 2020 The Wildlife Society. 相似文献
14.
Abstract. Grass and herb cover, and woody plant densities were measured on 25 native and 25 exotic grassland plots in southeastern Arizona between 1984 and 1990. At least 40 yr previously, the exotic plots had been seeded with two species of lovegrasses (Eragrostis spp.) native to southern Africa. A 1987 wildfire burned 11 native and 11 exotic plots. The fire reduced cover of both native and African grasses for two post-fire growing seasons. Herb cover as a whole increased after the fire for 2 yr, although there were important differences among species. One of two dominant shrubs (Haplopappus tenuisectus) was killed by the fire, while the other (Baccharis pteronioides) was little affected. Mesquite trees (Prosopis juliflora) were killed to the ground by the fire, but 62 of 66 trees had re-sprouted to an average 48% of pre-burn height by 1990. Native and exotic grasses appeared equally tolerant of fire, probably because both evolved in fire-type ecosystems. There was no evidence that fire can be used to permanently restore the diverse native flora to species-poor plantations of the South African exotics. 相似文献
15.
Abstract. Soil resource availability may affect plant regeneration by resprouting in disturbed environments directly, by affecting plant growth rates, or indirectly by determining allocation to storage in the resprouting organs. Allocation to storage may be higher in stressful, low resource‐supply soils, but under such conditions plant growth rates may be lower. These factors could act in opposite directions leading to poorly known effects on resprouting. This paper analyses the role played by soil resources in the production and growth of resprouts after removal of above‐ground plant tissues in the Mediterranean shrub Erica australis. At 13 sites, differing in substrate, we cut the base of the stems of six plants of E. australis and allowed them to resprout and grow for two years. Soils were chemically analysed and plant water potential measured during the summer at all sites to characterize soil resource availability. We used stepwise regression analysis to determine the relationships between the resprouting response [mean site values of the number of resprouts (RN), maximum length (RML) and biomass (RB)] and soil nutrient content and plant water potential at each site. During the first two years of resprouting there were statistically significant differences among sites in the variables characterizing the resprouting response. RML was always different among sites and had little relationship with lignotuber area. RN was less different among sites and was always positively correlated with lignotuber area. RB was different among sites after the two years of growth. During the first months of resprouting, RN and RML were highly and positively related to the water status of the plant during summer. At later dates soil fertility variables came into play, explaining significant amounts of variance of the resprouting variables. Soil extractable cations content was the main variable accounting for RML and RB. Our results indicate that resprout growth of E. australis is positively affected by high water availability at the beginning of the resprouting response and negatively so by high soil extractable cation content at later periods. Some of these factors had previously shown to be related, with an opposite sign, to the development of a relatively larger lignotuber. Indeed, RML and RB measured in the second year of resprouting were significantly and negatively correlated with some indices of biomass allocation to the lignotuber at each site. This indicates that sites favouring allocation to the resprouting organ may not favour resprout growth. 相似文献
16.
Abstract. In temperate grasslands, the relative importance of above‐ground competition for light compared to below‐ground competition for water and nutrients is hypothesized to increase with increasing precipitation. Thus, competition for light is likely to exert an increasing influence on canopy structure and species composition as precipitation increases. We quantified canopy structure, light availability and changes in species composition at seven sites across the central grassland region of the United States to determine how these properties change across a precipitation gradient. Across the region, there was a disproportionate increase in leaf area and canopy height with increasing precipitation, indicating that plants become taller and leafier across the gradient. Leaf area index increased by a factor of 12 across the gradient while above‐ground net primary productivity increased by a factor of only 5.5. As precipitation increased, there was decreased light availability at the soil surface, increased seasonal variability in light transmission, increased biomass and leaf area at higher canopy layers and an increased proportion of tallstatured species. These observed changes in canopy structure support the prediction that competition for light increases in importance with increasing precipitation. 相似文献
17.
Aim To evaluate the utility of island biogeography theory as a model for understanding and conserving native communities of nonvolant terrestrial vertebrates at prairie dog towns. Location Oklahoma Panhandle, USA. Methods We surveyed mammal, reptile and amphibian communities on 36 black‐tailed prairie dog (Cynomys ludovicianus) towns during the summers and falls of 1997 to 1999. We used a Geographic Information System (GIS) to characterize the landscape within 10 km of each town. We used Principal Components Analysis (PCA), Correlation Analysis, and Linear Regression to test for patterns in species richness relative to area and isolation of towns, local habitat characteristics, and characteristics of the adjacent landscape. Results Species richness was not significantly correlated with town size, town isolation, or local habitat characteristics. On the other hand, species richness was significantly correlated with characteristics of the landscape within 10 km of the focal town. In addition, species richness of mammals at prairie dog towns during the summer increased in a northerly direction, while richness of mammals at towns during fall increased to the west. Main conclusions These results, albeit contrary to traditional island biogeography theory, are consistent with an emerging view that communities on relatively small islands are strongly influenced by characteristics of the adjacent landscape (or seascape). We recommend that to the extent possible, networks of reserves for prairie dogs and their associated species should include clusters of large towns (i.e. larger than those studied here), as well as large but isolated towns, and that conservation efforts should include management of the intervening matrix of anthropogenic habitats. 相似文献
18.
Imanuel Noy-Meir 《植被学杂志》1995,6(5):701-710
Abstract. The separate and combined effects of fire and cattle grazing on structure and diversity of productive Mediterranean grasslands in northern Israel were examined within a set of climatically and edaphically similar sites. Cover and height of green and dry plants in winter, and species richness and diversity in spring, were measured in paired transects on both sides of cattle fences, and on both sides of boundaries of both incidental and experimentally lit fires. Early in the first growing season after a fire, plant cover as well as height of green plants were reduced, compared to unburnt grassland. These structural effects of fire were similar to the effects of grazing, but they were greater in ungrazed than in grazed grasslands, indicating a fire-grazing interaction. The effects of fire were considerably attenuated in the second growing season after the fire. Species richness and diversity tended to be higher in grazed than in adjacent ungrazed grasslands. Richness consistently increased after a fire only in grazed grasslands with a strong perennial component. In ungrazed grasslands, and in predominantly annual grasslands, fires reduced species richness and diversity at least as often as they increased it. Fire and grazing should be regarded as two agents with distinct and interactive effects on the community, rather than as two alternative mechanisms of a general disturbance factor. 相似文献
19.
Keith Paustian Edward T. Elliott Gary A. Peterson Kendrick Killian 《Plant and Soil》1995,187(2):351-365
In agroecosystems, there is likely to be a strong interaction between global change and management that will determine whether soil will be a source or sink for atmospheric C. We conducted a simulation study of changes in soil C as a function of climate and CO2 change, for a suite of different management systems, at four locations representing a climate sequence in the central Great Plains of the US.Climate, CO2 and management interactions were analyzed for three agroecosystems: a conventional winter wheat-summer fallow rotation, a wheat-corn-fallow rotation and continuous cropping with wheat. Model analyses included soil C responses to changes in the amount and distribution of precipitation and responses to changes in temperature, precipitation and CO2 as projected by a general circulation model for a 2 × CO2 scenario.Overall, differences between management systems at all the sites were greater than those induced by perturbations of climate and/or CO2. Crop residue production was increased by CO2 enrichment and by a changed climate. Where the frequency of summer fallowing was reduced (wheat-corn-fallow) or eliminated (continuous wheat), soil C increased under all conditions, particularly with increased (640 L L–1) CO2. For wheat-fallow management, the model predicted declines in soil C under both ambient conditions and with climate change alone. Increased CO2 with wheat-fallow management yielded small gains in soil C at three of the sites and reduced losses at the fourth site.Our results illustrate the importance of considering the role of management in determining potential responses of agroecosystems to global change. Changes in climate will determine changes in management as farmers strive to maximize profitability. Therefore, changes in soil C may be a complex function of climate driving management and management driving soil C levels and not be a simple direct effect of either climate or management. 相似文献
20.
Abstract. The characteristics of microhabitats of established Pinus sylvestris and Betula seedlings were studied in a small windthrow gap in a mature P. sylvestris-dominated forest in the Petkeljärvi National Park in eastern Finland. Seedlings were strongly clustered in disturbed microhabitats, particularly uprooting pits and mounds, formed by tree falls. They covered 3% of the 0.3.ha study area consisting of the gap and some of the forest edge. Although Betula occurred only as scattered individuals in the dominant canopy layer of the forest, it accounted for 30% of the seedlings found in the study area. Betula regeneration was almost completely restricted to pits and mounds, where 91% of the seedlings were found. Uprooting spots were also the most important regeneration microhabitats for Pinus, where 60% of the seedlings grew, even though the seedlings were found in other substrates as well, particularly on sufficiently decomposed coarse wood. Undisturbed field- and bottom-layer vegetation had effectively hindered tree seedling establishment, which emphasises the role of soil disturbance for regeneration. While the establishment of seedlings was found to be clearly determined by the availability of favourable regeneration microhabitats, the early growth of seedlings was affected by a complex interaction of environmental variables, including the type of microhabitat, radiation environment and interferences caused by competing seedlings and adjacent trees. In the most important regeneration microhabitats, i.e. in uprooting pits and on mounds, the distributions of the local elevations of Pinus and Betula seedlings were different. Pinus seedlings occurred closer to ground level, i.e. on the fringes of pits and lower on mounds, while Betula seedlings grew deeper in pits and higher on mounds. The position of the Betula seedlings indicate that they may have a competitive advantage over Pinus seedlings in the dense seedling groups occurring in uprooting spots. We suggest that this initial difference in Pinus and Betula establishment may affect the subsequent within-gap tree species succession and can, in part, explain the general occurrence of Betula in conifer-dominated boreal forests. 相似文献