首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 540 毫秒
1.
Habitat fragmentation can leave formerly widespread habitat types represented by only small habitat ‘islands’, and the conservation of these remnants is frequently compromised by ongoing disturbance. In northern Victoria, grazing of woodland remnants by sheep and cattle has profound effects on the vegetation structure of the woodland by removing understorey and ground vegetation. To investigate the effects of grazing pressure on remnant grey box Eucalyptus microcarpa woodland in northern Victoria, we surveyed the ground invertebrate fauna in ungrazed woodland remnants, grazed woodland remnants, and grazed pasture. The number of invertebrates caught increased from ungrazed woodland to grazed woodland to pasture, but this increase was due primarily to the most abundant orders (Hymenoptera, Coleoptera and Aranaea), and two abundant taxa characteristic of pasture (Orthoptera and Dermaptera). In contrast, most of the less abundant orders followed the opposite pattern, and were caught in higher numbers (and as a higher proportion of the total catch) in ungrazed woodland. Ungrazed woodland had a more diverse ground invertebrate fauna, most likely due to the greater diversity of food and habitat resources provided by the less disturbed vegetation. The differences in invertebrate communities corresponded to differences in vegetation and litter layers. The reduction in biodiversity of remnants due to grazing has implications for conservation management of remnant woodland in agricultural landscapes.  相似文献   

2.
Island biogeography theory, and the 50/500 rule of genetics, have effectively devalued small habitat fragments for species conservation. Metapopulation theory has given new value to small remnants but data on species persistence are scarce. This study examined the capacity of very small and sheep-grazed remnants of eucalypt woodland in agricultural Western Australia to support remnant-dependent terrestrial arthropods. We surveyed 53 sheep-grazed remnants of wheatbelt wandoo Eucalyptus capillosa for the presence of four species of arthropod with different dispersal strategies (terrestrial versus aerial) and diet (predaceous vs. herbivorous): the harvester and mound-building termite Drepanotermes tamminensis, the wood-eating and mound-building termite Amitermes obeuntis, the predaceous and burrowing scorpion Urodacus armatus and the predaceous 'bull' ant Myrmecia nigriceps. All species with the exception of the scorpion disperse aerially, and all construct above-ground structures that are easily recognized. Remnants ranged in size from 50 m2 to 21 000 m2 (mean 1791 m2), in spatial isolation (distance to the nearest vegetation remnant) from 10 m to 500 m (mean 123 m) and in a length-to-width ratio (shape) from circular (mean ratio 1.0) to linear (mean ratio 4.0). Observations in small and grazed remnants were compared with observations made in six wandoo woodland sites within a large (1040 ha) and ungrazed remnant. The total number of target species was highly correlated with remnant area (r = 0.68). Remnant isolation and remnant shape had no apparent influence on the total number of target species. The minimum area of grazed remnants in which individual species were recorded followed the large predator Urodacus armatus (4515 m2) > smaller predator Myrmecia nigriceps (300 m2) > harvester termites Drepanotermes tamminensis (102 m2) > wood-eating termites Amitermes obeuntis (50 m2). With the exception of U. armatus which occurred only in three of the four largest grazed remnants, the occurrence of all other species increased from small to large grazed remnants, suggesting a remnant-size effect for all species. Remnant isolation or remnant shape had no apparent influence on the occurrence of any one species. The terrestrially dispersing scorpion persisted in remnants despite their isolation from other remnants from 200 m to 500 m. For both termite species, mound heights were significantly greater in large, ungrazed woodlands than in small and grazed woodlands. The incidence of mound abandonment in smaller and grazed remnants was considerably higher for harvester than for wood-eating termite colonies. This suggests differences in spatial requirements and possibly diet-related susceptibilities to fluctuations in food availability. The diameter of Myrmecia nigriceps nests showed no relationship with remnant size or isolation. This study demonstrated that even very small remnant woodlands on farms may play an important role in sustaining small native animals, either as stepping-stones for dispersing individuals (termites, ants) or in providing adequate habitat to sustain populations for longer periods (all four species).  相似文献   

3.
Abstract Within a 50 × 50 m area of wandoo Eucalyptus capillosa woodland in the Western Australian wheatbelt, the diversity and frequency of occurrence of wood-eating termite species was assessed at two food types. Over a 12 month period, monthly termite activity was determined: (i) at sound/undecayed artificial baits (seasoned wooden stakes of Jarrah, Karri, Pine, Batu, Oregon; Jarrah sawdust; paper rolls); and (li) at naturally occurring timber, fallen logs and branches of wandoo, in varying stages of decay. Termite diversity was 11 species at baits, 18 species at wandoo out of an overall site richness of 21 species. Karri attracted the most species (9); sawdust attracted none. At wandoo, Nasutitermes exitiosus, Coptotermes acinaciformis and Occasitermes occasus accounted for 59% of samples where termites were recorded. At baits, Heterotermes occiduus accounted for a mean of 80% of samples across bait types, but was rarely sampled at wandoo (5% of samples). Only H. occiduus, C. acinaciformis and Amitermes neogermanus ate bait. Pine, Oregon and paper rolls were most effective in attracting foraging termites in terms of highest per cent of replicates showing bait consumption and highest consumption rates. Jarrah and Batu were least attractive to foraging termites. Samples from wandoo underestimated the relative frequency of occurrence of H. occiduus within the study site. Coptotermes acinaciformis, which attack large food items, and certain species of Amitermes, which forage on subterranean food, may have been underestimated by both sampling methods. These findings indicate that a proper understanding of the structure of wood-eating termite assemblages within a given area requires a composite sampling strategy which addresses termites that eat sound or decayed wood, as well as surface and subsurface foragers.  相似文献   

4.
Summary Few field studies have attempted to relate effects of actual livestock grazing on soil and plant water status. The present study was initiated to determine the effects of periodic defoliations by cattle during spring on soil moisture and plant water status in a crested wheatgrass (Agropyron cristatum (L.) Gaertn. and A. desertorum (Fisch. ex Link) Schult.) pasture in central Utah. Soil moisture in the top 130 cm of the soil profile was depleted more rapidly in ungrazed plots than in grazed plots during spring and early summer. Soil moisture depletion was more rapid in grazed plots in one paddock after 1 July due to differential regrowth, but there was no difference in soil water depletion between plots in another paddock during the same period. This difference in soil water depletion between paddocks was related to a difference in date of grazing. Although more water had been extracted from the 60 cm to 130 cm depths in ungrazed plots by late September, cumulative soil moisture depletion over the entire 193 cm profile was similar in grazed and ungrazed plots. Prior to 1 July, grazing had no effect on predawn leaf water potentials as estimated by a pressure chamber technique; however, after 1 July, predawn leaf water potentials were lower for ungrazed plants. Midday leaf water potentials were lower for grazed plants before 1 July, but did not differ between grazed and ungrazed plants after 1 July. A 4- to 8-day difference in date of defoliation did not affect either predawn or midday leaf water potentials. The observed differences in water use patterns during spring and early-summer may be important in influencing growth and competitive interactions in crested wheatgrass communities that are subject to grazing by domestic livestock.  相似文献   

5.
Abstract. Spatial heterogeneity, an important characteristic in semi‐arid grassland vegetation, may be altered through grazing by large herbivores. We used Moran's I, a measure of autocorrelation, to test the effect of livestock grazing on the fine scale spatial heterogeneity of dominant plant species in the shortgrass steppe of northeastern Colorado. Autocorrelation in ungrazed plots was significantly higher than in grazed plots for the cover of the dominant species Bouteloua gracilis, litter cover and density of other bunchgrasses. No species had higher autocorrelation in grazed compared to ungrazed sites. B. gracilis cover was significantly auto‐correlated in seven of eight 60‐yr ungrazed exclosures, four of six 8‐yr exclosures, and only three of eight grazed sites. Autocorrelograms showed that B. gracilis cover in ungrazed sites was frequently and positively spatially correlated at lag distances less than 5 m. B. gracilis cover was rarely autocorrelated at any sampled lag distance in grazed sites. The greater spatial heterogeneity in ungrazed sites appeared linked to patches characterized by uniformly low cover of B. gracilis and high cover of C3 grasses. This interpretation was supported by simple simulations that modified data from grazed sites by reducing the cover of B. gracilis in patches of ca. 8 m diameter and produced patterns quite similar to those observed in ungrazed sites. In the one exclosure where we intensively sampled soil texture, autocorrelation coefficients for sand content and B. gracilis cover were similar at lag distances up to 12 m. We suggest that the negative effect of sand content on B. gracilis generates spatial heterogeneity, but only in the absence of grazing. An additional source of heterogeneity in ungrazed sites may be the negative interaction between livestock exclusion and B. gracilis recovery following patchy disturbance.  相似文献   

6.
This paper documents changes in the floristic composition of Eucalyptus marginata Donn (jarrah) woodlands over 7 years of recovery from continual, intensive livestock grazing. In remnants of native woodland left after agricultural clearing, which have been subjected to livestock grazing, comparisons were made between the floristics of fenced exclosure plots and open plots that continued to be grazed. The vegetation in nearby remnants, which had not been subjected to livestock grazing, was also surveyed. An initial increase in annual exotic pasture species after grazing relief was only temporary and highly influenced by fluctuations in annual climatic patterns, particularly rainfall distribution and abundance. Subsequent years saw a decrease in exotic annuals in exclosure plots and an increase in native perennials, in a trend towards becoming more floristically similar to the ungrazed sites. Germination of overstorey species was observed in the exclosure plots, however, development of seedlings and saplings was sparse. Results indicate that for jarrah woodland in southwestern Australia, natural regeneration is possible after the removal of livestock, with the return (within 6 years) of native species richness to levels similar to those found in ungrazed vegetation. Re‐establishment of cover, however, appears to take longer. The floristic dynamics are described in terms of a nonequilibrium model. Two vegetation states exist, degraded remnants with an understorey dominated by annual species, and ungrazed vegetation with an understorey dominated by perennial shrubs and herbs. The former state is maintained by continual heavy grazing by livestock. Upon relief from grazing, the vegetation undergoes a transition towards floristic similarity to ungrazed vegetation. After 6 years, vegetation change in the exclosure plots appears to be continuing and therefore it is still in transition.  相似文献   

7.
放牧是影响草地生态系统中土壤动物组成和凋落物分解的重要因素.2010—2012年,选择内蒙古锡林郭勒盟白音锡勒牧场境内的禁牧草地、放牧草地和沙地为研究样地,以凋落物袋法研究了大针茅凋落物分解过程中主要理化特性以及其中土壤动物群落的变化特征.共采集到土壤动物67056头52类,隶属于5门8纲,其中螨类23科,昆虫19科.大针茅凋落物的初始有机质含量为92.5%,分解780 d后分别降至40.0%(禁牧草地)和41.3%(放牧草地),差异不显著;凋落物残留率分别降低至50.0%(禁牧草地)和23.0%(放牧草地),差异显著.放牧影响下,大针茅残留凋落物中土壤动物多度显著降低.将大针茅凋落物置入沙地环境,有机质分解速率无显著变化,但凋落物残留率显著降低,螨类群落组成发生显著变化.在内蒙古典型草原环境下,放牧显著改变了植物凋落物中的土壤动物群落组成和多度,但凋落物中有机质分解速率未发生显著变化;半干旱地区土壤动物的凋落物分解功能较为微弱.  相似文献   

8.
Question: What are the changes in vegetation structure, soil attributes and mesofauna associated with grazing in mesic grasslands? Location: Southern Campos of the Río de la Plata grasslands, in south‐central Uruguay. Methods: We surveyed seven continuously grazed and ungrazed paired plots. Plant and litter cover were recorded on three 5‐m interception lines placed parallel to the fence in each plot. We extracted soil fauna from a 10 cm deep composite sample and analysed the oribatids. Soil attributes included bulk density, water content, organic carbon (in particulate and mineral associated organic matter) and nitrogen content and root biomass at different depths. Changes in floristic, Plant Functional Types and mesofauna composition were analysed by Non‐metric Multidimensional Scaling. Results: Species number was lower in ungrazed than in grazed plots. Of 105 species in grazed plots only three were exotics. Shrub and litter cover were significantly higher inside the exclosures, while the cover of Cyperaceae‐Juncaceae was lower. Grazing treatments differed significantly in plant and oribatid species composition. Grazing exclusion significantly reduced soil bulk density and increased soil water content. Carbon content in particulate organic matter was lower in the upper soil of ungrazed sites, but deeper in the profile, grazing exclosures had 8% more carbon in the mineral associated organic matter. Conclusions Our results generally agree with previous studies but deviate from the results of previous analyses in (1) the increase of shrub cover in ungrazed sites; (2) the redistribution of the soil organic carbon in the profile and (3) the low invasibility of the prairies regardless of grazing regime.  相似文献   

9.
Selective sheep grazing in the Patagonian Monte induces the reduction of total and perennial grass cover, species replacement within life forms, and the increase in dominance of long-lived evergreen woody plants with slow growth rates and high concentration of secondary compounds in leaves. We hypothesized that these changes in the canopy structure induced by sheep grazing will affect the mass, chemistry and decomposability of leaf litter and fine roots. We selected two sites in the Patagonian Monte, representative of ungrazed and grazed vegetation states. At each site, we assessed canopy structure (total cover and absolute and relative grass and shrub cover), monthly leaf litterfall, and fine-root biomass and production in the upper soil (15 cm). We also estimated the rates of mass, C, soluble phenolics, lignin and N decay in litterbags containing both leaf litter and fine roots of each site under field conditions during two consecutive years. The ungrazed site exhibited higher total plant cover, absolute and relative grass- and shrub-cover than the grazed one. Leaf litterfall was lower at the grazed site than at the ungrazed site. Fine-root production did not vary between sites. Leaf litter and fine root tissues had higher concentration of secondary compounds at the grazed than at the ungrazed site. However, fine roots showed lower mass and C decay than leaf litter, attributable to the predominant secondary compound (lignin and soluble phenolics, respectively). Leaf litter decomposed slower but released more N during decay at the ungrazed than at the grazed site, probably due to its low concentration of secondary compounds. We concluded that changes in canopy structure induced by grazing disturbance such as those explored in our study could reduce leaf litterfall mass and increase the concentration of secondary compounds of both leaf litter and fine roots leading to slow N release to soil during decay.  相似文献   

10.
Summary Data are presented which illustrate the range of ion values obtained from soil solutions eluted fromin situ ion exchange resin bags in grazed and ungrazed grassland soils sampled in the summer and early autumn. Overall, higher levels of cations were being supplied in both the grazed and ungrazed plots in the autumn compared with during the summer. Variation in ion levels reflected spatial heterogeneity in ion supply in these soils. This variation was correlated with the distribution and abundance of the dominant plants and soil surface microtopography. The use ofin situ ion exchange resin bags allow an understanding of short-term temporal and spatial heterogeneity in ion supply.  相似文献   

11.
Reindeer Rangifer tarandus L. grazing shapes forest vegetation, microclimate, and soil respiration in Lapland, especially due to grazing on lichens (Cladina). We studied how these changes and their magnitude affect ground‐dwelling species of beetle families Carabidae (predators) and Curculionidae (herbivores), by using pitfall traps to collect invertebrates from pairs of grazed and ungrazed study plots over a wide range of site types. Changes in abundance, composition, richness and diversity of beetle assemblage were tested in relation to magnitude of the impacts on vegetation. The species compositions of Carabidae and Curculionidae differed between grazed and ungrazed plots in all sites. The relative difference between grazed and ungrazed plots in the number of individuals increased linearly with the impact of reindeer on vegetation cover. Carabid beetles, as a family, were more common in grazed plots in all sites. Curculionid beetles were more common in ungrazed plots in the birch dominated sites. This difference was mainly due to the species that feeds on deciduous leaves. In the pine dominated sites with high Cladina cover and more changes in ground vegetation, the number of curculionids feeding on conifers was higher in grazed plots. Species richness and diversity (H’) of both families were higher in grazed plots. Of the total 27 species, 11 were found only in grazed plots, while not a single species was found only in ungrazed plots. The relative difference between plots in diversity and evennes (H’/H'max) had humped response to the difference in Cladina cover. The diversity values were greater in grazed plots at the intermediate levels of grazing impact, and only in sites with very low or extremely high Cladina cover difference was the diversity higher in ungrazed plots. The response of beetle diversity resembled the hypotheses suggested for the relationship between grazing and vegetation diversity: greatest positive effect at intermediate grazing intensity and negative effects at unproductive sites.  相似文献   

12.
Large herbivores may alter carbon and nutrient cycling in soil by changing above- and below-ground litter decomposition dynamics. Grazing effects may reflect changes in plant allocation patterns, and thus litter quality, or the site conditions for decomposition, but the relative roles of these broad mechanisms have rarely been tested. We examined plant and soil mediated effects of grazing history on litter mass loss and nutrient release in two grazing-tolerant grasses, Lolium multiflorum and Paspalum dilatatum, in a humid pampa grassland, Argentina. Shoot and root litters produced in a common garden by conspecific plants collected from grazed and ungrazed sites were incubated under both grazing conditions. We found that grazing history effects on litter decomposition were stronger for shoot than for root material. Root mass loss was neither affected by litter origin nor incubation site, although roots from the grazed origin immobilised more nutrients. Plants from the grazed site produced shoots with higher cell soluble contents and lower lignin:N ratios. Grazing effects mediated by shoot litter origin depended on the species, and were less apparent than incubation site effects. Lolium shoots from the grazed site decomposed and released nutrients faster, whereas Paspalum shoots from the grazed site retained more nutrient than their respective counterparts from the ungrazed site. Such divergent, species-specific dynamics did not translate into consistent differences in soil mineral N beneath decomposing litters. Indeed, shoot mass loss and nutrient release were generally faster in the grazed grassland, where soil N availability was higher. Our results show that grazing influenced nutrient cycling by modifying litter breakdown within species as well as the soil environment for decomposition. They also indicate that grazing effects on decomposition are likely to involve aerial litter pools rather than the more recalcitrant root compartment.  相似文献   

13.
The distribution and abundance, and habitat differences in biomass of subterranean termites, were assessed through soil trenching for woodland, mallee and heath habitats in the central wheatbelt of Western Australia. Over an 11 month sampling period, there were no significant habitat differences in biomass. Mean dry biomass in the surficial layer of soil (per 5000 cm3) averaged 46 mg in woodland, 28 mg in mallee, and 23 mg in heath. Termite biomass peaked in September, with 141 mg for woodland, 83 mg for mallee and 47 mg for heath (per 5000 cm3). Soil moisture and termite activity near the surface were positively correlated. A total of 36 species of termites, comprising 11 genera, were identified, and species abundance within and across habitats differed significantly.  相似文献   

14.
Subterranean termite assemblages in woodland, mallee and heath habitats of the Western Australian wheatbelt were sampled for seasonal changes in species richness and species abundance. The study was carried out in Durokoppin and Kodj Kodjin Nature Reserves between January and November 1988, and a trench method was used to sample termites. Species richness changed over time, with monthy means of: woodland 10 species (range: 5–15), mallee 8 species (range: 4–15), heath 8 species (range: 5–15). Species richness was highest in autumn and spring when termite activity in the soil was also highest due to favourable soil moisture. Amitermes neogermanus and Tumulitermes petilus were the most abundant species in woodland and mallee in all seasons. During summer, the pooled observations of these two species accounted for 50% (woodland) and 82% (mallee) of all observations. Their predominance may be due to greater tolerance of low soil moisture and a more diverse diet than obligate wood-feeders (e.g. Rhinotermitidae). The latter were generally absent near the soil surface in summer, possibly because food sources deeper within the soil were utilized. Four species were abundant in heath: Tumulitermes dalbiensis (monthly mean 20% of all species observations), T. comatus (13%), Amitermes. sp.‘R’ (18%)and Drepanotermes rubriceps (12%). These four species showed no seasonal change in their relative abundance, possibly because their diet restricted them to surface-foraging.  相似文献   

15.
Plant traits are known to control litter decomposition rates through afterlife effects on litter quality. Land-use practices that modify plant traits, e.g. livestock grazing and soil fertilization, also have cascading effects on litter decomposition. However, almost all studies of these afterlife effects ignored the role of soil detritivores in the decomposition processes. We explored how the feeding activities of a macroarthropod modify microbial activity in leaf litter. Dead leaves from two grassland species, Bromopsis erecta and Potentilla verna, were collected in fertilized or unfertilized grazed plots and fertilized or unfertilized ungrazed plots. We determined how intraspecific variation in litter quality in response to sheep grazing and soil fertilization (i) influences the consumption and assimilation of leaf litter by the millipede Glomeris marginata, and (ii) affects the activity of microbial decomposers, assessed by substrate-induced respiration (SIR), in leaf litter before consumption and in faecal pellets and litter remains processed by Glomeris under all treatments. In the absence of millipedes, microbial activity was significantly higher in leaf litter from fertilized plots. Glomeris consumed larger amounts of leaf litter from fertilized grazed plots, owing to increased consumption of the otherwise poorly palatable Bromopsis, and produced larger amounts of faecal pellets when fed on this food. However, irrespective of the food consumed, SIR in faecal pellets was found to be similar in all treatments. Moreover, SIR in litter remains unconsumed at the end of the experiment was reduced to low and similar levels in all treatments. Overall, homogenization of microbial activity by Glomeris suppressed differences in SIR between leaf litter from fertilized and unfertilized plots, in both Bromopsis and Potentilla. Our results suggest that studies that assess afterlife effects of plant traits on decomposition using methods that exclude soil macrofauna may prove inadequate in ecosystems with abundant populations of detritivores.  相似文献   

16.
The effects of stock grazing on native grassy ecosystems in temperate southern Australia are well documented. However, less is known about the potential of ecosystems to recover after a long history of stock grazing and, in particular, whether the removal of stock will have positive, negative or neutral impacts on biodiversity. We examined the response of understorey vegetation to the removal of sheep grazing in a herb‐rich Eucalyptus camaldulensis (red gum) woodland in western Victoria. Using a space‐for‐time chronosequence, woodlands were stratified into groups based on their time‐since‐grazing removal; these were long‐ungrazed (>20 years), intermediate‐time‐since‐grazing (9–14 years), recently ungrazed (5 years) and continuously grazed. We found significantly higher species density in long‐ungrazed sites relative to sites with a more recent grazing history. No differences were found in species density between continuously grazed sites and those ungrazed in the previous 14 years. Species composition differed with time‐since‐grazing removal and indicator species analysis detected several native species (including tall native geophytes and herbs) associated with long‐ungrazed sites that were absent or in low abundance in the more recently grazed sites. Seven of the eight species significantly associated with continuously grazed sites were exotic. Removal of sheep grazing in red gum woodlands can have positive benefits for understorey diversity but it is likely that recovery of key indicators such as native species will be slow.  相似文献   

17.
We investigated ground beetle communities (Coleoptera, Carabidae) in ancient woodland remnants in north-western Lower Saxony, Germany. A total of 90 pitfall traps was exposed in a stratified design in 10 stands of mature oak–beech and oak–hornbeam forests in the year 2003. Overall, 47 species (10,676 individuals) were recorded. Among these were the two relict species Carabus glabratus and Abax parallelus, and 14 further eurytopic forest species. Eleven species exhibited a high frequency and were found in all of the ten stands. Multiple linear regressions showed several significant relationships at two scales for species richness of different groups of carabids and for several of the measured environmental factors. Forest area, litter depth, amount of dead wood, distance to forest edge, and soil moisture were found to be key factors determining species richness. Furthermore, recent disturbance by logging reduced the number of forest species. According to direct gradient analyses soil moisture and litter depth have greatest influence on species communities of both, forest species and widespread species. Habitat suitability models for the two recorded relict species, A. paralellus and C. glabratus, were developed using logistic regression. The presence of A. parallelus in the mature ancient woodland remnants depends mainly on higher values of soil moisture, whereas for C. glabratus none of the measured environmental variables appeared to be key factors. Implications for the conservation of carabid assemblages in mature ancient woodlands include the advice to spread out logging over long periods of time and over various woodlands in order to keep the stand disturbance at a long-term low level. Variation in logging practices may help to conserve diverse structures. Afforestation with non-native tree species should be avoided in the managed ancient woodlands. Finally, especially the preservation of a high soil moisture seems to be important to conserve typical carabid communities.  相似文献   

18.
Abstract The heat-pulse method was used to estimate transpiration rates continuously for periods up to 2 years in mature trees of Eucalyptus wandoo and Eucalyptus salmonophloia at two topographic locations in a remnant native woodland in the Western Australian wheatbelt. Annual transpiration per tree ranged from about 11400 to 18000 L per tree. Highest transpiration rates occurred in late spring or early summer, depending on rainfall distribution. The trees were able to rapidly utilize water following heavy rain outside the agricultural growing season. Extrapolating transpiration rates from single trees to an area of woodland showed that annual transpiration at the ridge site was 150 mm and 168 mm at a site alongside a drainage line. Scaling up transpiration from individual trees requires caution and should allow for variability in trees and soils. The role of trees in curtailing salinization is discussed.  相似文献   

19.
Abstract. The biodiversity of species‐rich semi‐natural meadows is declining across Europe due to ceased management. In this study we aimed to find out how successfully the local species richness of an overgrown semi‐natural mesic meadow could be restored by sheep grazing after a long period of abandonment. The cover of vascular plant species in grazed plots and ungrazed exclosures was studied for five years and the responses of different functional plant groups were followed (herbs vs grasses, tall vs short species, species differing in flowering time, species representing different Grime's CSR strategies and species indicative of rich vs poor soil). Grazing increased species number by nearly 30%. On grazed plots the litter cover practically disappeared, favouring small herbs such as Rhinanthus minor, Ranunculus acris, Trifolium pratense and the grass Agrostis capillaris. Grazing decreased the cover of the late flowering tall herb Epilobium angustifolium but had no effect on the abundance of the early flowering tall herbs Anthriscus sylvestris or Geranium sylvaticum. We suggest that to succeed in restoration it is useful to determine the responses of different functional plant groups to grazing. Grassland managers need this information to optimize the methods and timing of management used in restoration. Additional management practices, such as mowing, may be needed in mesic meadows to decrease the dominance of tall species. The availability of propagules seemed to restrict further increase of species richness in our study area.  相似文献   

20.
Abstract Trunk‐associated invertebrates were sampled on marri trees (Eucalyptus (Corymbia) calophylla) along a transect from Karragullen, near Perth, through to Dryandra, 150 km to the south‐east. This represents a drop in annual rainfall from 1078 to 504 mm, which is accompanied by a change from jarrah (Eucalyptus marginata) forest to wandoo (Eucalyptus wandoo) woodland. Invertebrates were sampled by intercept traps, which collect invertebrates that attempt to land on the trunks, and bark traps, which collect invertebrates that move, or live, on the trunk. Trends are reported here at the ordinal level. The variety and abundance of invertebrates sampled was generally greater in the intercept than the bark traps. Invertebrate abundance, activity and biomass on bark were strongly seasonal, with greater numbers being found during the moister periods. Invertebrate abundances tended to be greater at the drier, eastern end of the transect, particularly on the three sites within wandoo woodland. These trends were analysed in terms of rainfall, soil nutrients and plant community composition. The analysis failed to detect an underlying influence of any of these factors, suggesting that the observed trends on marri trunks may be the result of invertebrate responses to the dominant tree species at the western and eastern ends of the transect, namely jarrah and wandoo respectively.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号