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1.
The coastline of southern Brazil is characterized by vast sand dunes. From March 1982 to April 1984 the dune vegetation was sampled along a transect between the Atlantic shore and an inland freshwater marsh, and phenological cycles of plant species were observed at monthly intervals.The occurrence of 23 annual species in the local dunes and peak germination, growth and flowering of 21 perennial species during spring, summer and fall, suggest that unfavourable temperatures and inundation of slacks during winter are seasonally limiting factors for this flora.Differences in the floristic composition between this region and its southern and northern extremes in the southwestern Atlantic together with a marked seasonality of the total species number and of germination and flowering periods, suggest that this area corresponds to a warm temperate biogeographic transition zone between northern tropical and southern cold temperate regions.  相似文献   

2.
Functional diversity indicators are increasingly used to monitor forest function recovery because they connect biodiversity to ecosystem functions. However, identifying which functions deviate from a reference forest has not received much attention, despite its potential to inform restoration interventions. In this study, we used functional groups to assess the recovery of ecosystem functions in regenerating coastal dune forests. We surveyed birds and trees in forest of different ages and a reference old‐growth forest in KwaZulu‐Natal, South Africa. We classified species into functional groups for each taxa based on functional traits or a priori defined categories (i.e. guilds) and quantified the number of species within functional groups as a proxy of function stability. Bird species density followed an asymptotic trajectory, reaching old‐growth forest values after 25 years. Insectivores and granivores showed saturating trajectories, whereas small frugivores and generalists increased linearly. With the exception of large frugivores, relative abundances of bird functional groups progressed towards old‐growth forest values as the forest aged. Tree species density increased linearly with forest age. In contrast to old‐growth forests, large‐canopy trees and understory shrubs were under‐represented, while mid‐canopy trees dominated regenerating forests. Our result suggests that most bird, but not tree, functions may have been restored. The trend in large frugivore numbers may warrant further investigation, as their low numbers may have hampered the recovery of tree functions. We conclude that functional group trajectories can track functions that deviate from a benchmark, and may therefore direct adaptive actions to recover the stability of regenerating forest.  相似文献   

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It has often been assumed that the introduced species Chrysanthemoides monilifera is displacing native species in invaded coastal communities in Australia but no direct evidence has been presented that this displacement is occurring and, if so, to what extent. At an invaded site near Moruya, New South Wales, we found strong negative correlations between the presence (measured as cover, frequency or volume of shrub) of C. monilifera and Acacia longifolia, the hitherto dominant native species, and of C. monilifera and Lomandra longifolia. The negative correlations are partly accounted for by differences in the amounts of each species on different zones on the dune, but the negative correlations remain even within these zones. Also a comparison with uninvaded sites indicates that C. monilifera is displacing A. longifolia from the fore-dune and mid-dune but is having less effect in the swale. In addition, there is a trend towards reduced seed production of A. longifolia when growing in proximity to C. monilifera. There is no significant difference in the presence of L. longifolia in the uninvaded and invaded sites. In invaded sites, significantly fewer C. monilifera seedlings occur in the presence of L. longifolia. Thus it appears that the observed negative associations arise from different causes. Chrysanthemoides monilifera is displacing the structurally similar, and previously dominant A. longifolia, while the tussock-forming L. longifolia is locally hindering the invasion.  相似文献   

5.
The basidiomycete mushroom Hebeloma cylindrosporum is a frequently found pioneer ectomycorrhizal species naturally associated with Pinus pinaster trees growing in coastal sand dune ecosystems along the Atlantic south-west coast of France. The genotypic diversity and spatial structure of three populations of this fungal species have been studied. At each site the basidiocarps were mapped, sampled and propagated as pure mycelial cultures. For each of the isolates, we have studied polymorphisms in the mitochondrial genome, polymorphisms at two different nuclear loci and also fingerprints produced with a multicopy DNA probe. The comparison of the different polymorphisms obtained, with each of the four molecular methods used, allowed the identification of several of the different genets present in each site. In two of the studied sites most of the basidiocarps, which often occurred as dense patches of 10–30 in 1 m2 or less, were of a unique genotype, suggesting the below-ground mycelia to be of a small size (from 50 cm2 to approx. 7 m2 for the larger mycelia) and that the root system of a single Pinus tree can host several genets of the same symbiotic fungus. In the two sites, which were studied again after a 3-year interval, none of the genotypes identified in the first year of sampling was re-identified 3 years later. These results contrast with those reported for other species of soilborne homobasidiomycete species, either ectomycorrhizal, parasitic or saprophytic, showing mostly large clones resulting from the vegetative growth and from persistence of below-ground mycelia. Sexual reproduction through meiospore dispersal seems to play a key role in the structuring of the populations of H. cylindrosporum. Mycelia associated with the root systems seem to be replaced after 1 or a few years, during which basidiocarp differentiation takes place. As opposed to the few other studied ectomycorrhizal species, H. cylindrosporum has the characteristics of ruderal species, with a short life-span adapted to pioneer situations, e.g. to nutrient-poor and unstable sandy soils of coastal sand dunes.  相似文献   

6.
We studied avian frugivory and seed dispersal in a dioecious shrub, Rhamnus alaternus, focusing on the quantitative and qualitative components of effectiveness. The study took place at three locations in the northeast of the Iberian Peninsula, and examined bird behaviour, intensity of feeding, and the consequences for seedling emergence. The coincidence between the bird breeding season and fruit ripening of R. alaternus in the absence of other ripe fruit, generates a monospecific interaction. The extant frugivorous species were mainly legitimate seed dispersers and their abundance was low. Sylvia melanocephala and S. undata were the most important at one site whereas S. atricapilla, Erithacus rubecula and Turdus merula predominated at the other two sites. Fruit handling took place directly on the branches. Bird species used microhabitats differently as first post-feeding perch, which usually was a short distance away. The low density of frugivorous birds in all localities, among others factors, resulted in satiation of the disperser community and many mature fruits unconsumed. Both adults and juveniles feed upon the plants and their foraging patterns are similar. Adults of S. melanocephala were observed to feed fruit to nestlings and consequently a second phase of dispersal potentially arises from the transport of fecal sacs. Pulp removal and passage through the digestive tract increased the probability of seedling emergence. This plant-dispersal interaction has important consequences, both positive and negative for the plant. Positively, the fruiting of R. alaternus at a time when other ripe fruits are not available avoids interspecific competition for seed dispersers. In addition, a low density of seed rain may reduce intraspecific competition. Negatively, the low density and small size of the breeding frugivorous bird community limit fruit handling and removal away from the parent plants, while the territorial behaviour of birds at that time of the year reduces the potential distances of seed dispersal.  相似文献   

7.
A. B. Ali 《Hydrobiologia》1990,190(3):215-222
Fish yields from the captural method of rice-fish farming system were monitored from 1985 to 1987. Seven species were obtained, with Trichogaster pectoralis, Clarias macrocephalus, and Channa striatus dominant and economically important. Low number of species is due to double cropping of rice resulting in increased human activities. The maximum yield obtained, 174.6 kg ha–1, is probably near the maximum for this type of rice-fish farming and the harvests have also stabilised when compared to those obtained in the early 1970s. Fish populations included more than one year-class in each harvest. A decline in individual weight, especially of herbivores, was recorded and correlated to the abundance of the species, and hence, to food supply.  相似文献   

8.
Restoration of coastal dune slacks in the Netherlands   总被引:6,自引:1,他引:5  
Grootjans  A.P.  Geelen  H.W.T.  Jansen  A.J.M.  Lammerts  E.J. 《Hydrobiologia》2002,478(1-3):181-203
In order to stop the continuous decline of typical dune slack communities along the Dutch coast, restoration projects have been carried out since 1952. Restoration measures consisted of re-introducing traditional management techniques in dune slacks, such as mowing, grazing and sod removal, or constructing artificial dune slacks to compensate for lost biodiversity elsewhere. An analysis of successful and unsuccessful projects showed that constructing new dune slacks was not very successful for maintaining new populations of endangered dune slack species, since such projects were often carried out in areas where seed banks were depleted, while hydrological conditions and seed dispersal mechanisms were sub-optimal. The construction of sand dikes to prevent sea intrusion in large beach plains was, unintentionally, a temporary success for the establishment of many Red List species, although such measures often disrupted natural dune slack formation. Successful sites were all characterised by a regular discharge of calcareous groundwater provided by local or regional hydrological systems, where not very long ago populations of typical dune slack plants were present. Under such conditions, sod removal was a successful measure to create pioneer stages which were relatively stable, due to a very slow accumulation of organic matter in the topsoil. It is argued that new and more flexible coastal defence strategies can provide new opportunities for natural and relatively stable pioneer stages of dune slack formation, suitable for the long term preservation of endangered dune slack species.  相似文献   

9.
Dispersal or recruitment limitation may arrest succession after disturbance. In north-eastern South Africa the Acacia karroo successional pathway is used to facilitate coastal forest recovery after strip-mining. However, although A. karroo establishes naturally, it forms monospecific stands, arresting forest succession for decades. This casts doubt on the efficacy of this restoration pathway. We investigated the causes of arrested succession. The seed and seedling banks of A. karroo stands and of forest at Cape Vidal, and three A. karroo stands (7–27 years old) on rehabilitated strip-mined dunes at nearby Richards Bay were examined. The establishment and growth of seedlings at Cape Vidal were also considered. The seed bank was larger and more diverse in forest, but the seedling bank was larger in Acacia stands. At Richards Bay, the size of the seed bank increased and the seedling bank decreased with Acacia stand age. Excluding mammalian herbivores in Acacia stands at Cape Vidal resulted in greater species richness and survival of naturally established seedlings, as well as two experimentally planted species. Neither seed dispersal nor seedling establishment limited recruitment of tree species in Acacia stands. Herbivory arrested forest succession by causing the differential mortality of seedlings. In contrast, at Richards Bay where there were few mammalian herbivores, the advanced regeneration in A. karroo stands converged on the diversity of nearby forests 29 years after restoration. Controlling herbivore access and seeding Acacia stands with forest species are site-specific options for preventing arrested succession when using the A. karroo successional pathway.  相似文献   

10.
Within global biodiversity hotspots such as the California Floristic Province, local patterns of diversity must be better understood to prioritize conservation for the greatest number of species. This study investigates patterns of vascular plant diversity in relation to coast–inland environmental gradients in the shrublands of Central California known as northern coastal scrub. We sampled coastal shrublands of the San Francisco Bay Area at coastal and inland locations, modeled fine‐scale climatic variables, and developed an index for local exposure to maritime salts. We compared diversity, composition, and structure of the coastal and inland plots using indirect gradient analysis and estimated species accumulation using rarefaction curves. Coastal plots were significantly higher in alpha, beta, and gamma diversity than inland plots. Plant diversity (effective species number) in coastal plots was 2.1 times greater than inland plots, and beta diversity was 1.9 times greater. Estimated richness by rarefaction was 2.05 times greater in coastal sites than inland sites. Salt deposition and water availability were the abiotic process most strongly correlated with increased maritime plant diversity and compositional differences. Stands of northern coastal scrub on the immediate coast with higher maritime influence exhibit markedly higher plant diversity than most interior stands, paralleling previous work in other vegetation types in this region. These studies suggest that the California coastline deserves special consideration for botanical conservation. Fine‐scale climatic models of cloud frequency, water availability, and the salt deposition index presented here can be used to define priority areas for plant conservation in California and other coastal regions worldwide.  相似文献   

11.
Summary An experiment was conducted to examine the relationship between reproduction and longevity in an annual iteroparous species of grasshopper, Melanoplus sanguinipes. Two hypotheses derived from life history theory were tested. These included: 1) virgin females produce fewer eggs and live longer than mated females, and 2) the rate of egg production and longevity are negatively related. The results of this study indicated that there is no trade-off between reproduction and longevity in this species of grasshopper. It is suggested that other factors, such as male-female interactions, may be more important in affecting female survival than reproduction.  相似文献   

12.
Question: How do two shrubs with contrasting life‐history characteristics influence abundance of dominant plant taxa, species richness and aboveground biomass of grasses and forbs, litter accumulation, nitrogen pools and mineralization rates? How are these shrubs – and thus their effects on populations, communities and ecosystems – distributed spatially across the landscape? Location: Coastal hind‐dune system, Bodega Head, northern California. Methods: In each of 4 years, we compared vegetation, leaf litter and soil nitrogen under canopies of two native shrubs –Ericameria ericoides and the nitrogen‐fixing Lupinus chamissonis– with those in adjacent open dunes. Results: At the population level, density and cover of the native forb Claytonia perfoliata and the exotic grass Bromus diandrus were higher under shrubs than in shrub‐free areas, whereas they were lower under shrubs for the exotic grass Vulpia bromoides. In contrast, cover of three native moss species was highest under Ericameria and equally low under Lupinus and shrub‐free areas. At community level, species richness and aboveground biomass of herbaceous dicots was lower beneath shrubs, whereas no pattern emerged for grasses. At ecosystem level, areas beneath shrubs accumulated more leaf litter and had larger pools of soil ammonium and nitrate. Rates of nitrate mineralization were higher under Lupinus, followed by Ericameria and then open dune. At landscape level, the two shrubs – and their distinctive vegetation and soils – frequently had uniform spatial distributions, and the distance separating neighbouring shrubs increased as their combined sizes increased. Conclusions: Collectively, these data suggest that both shrubs serve as ecosystem engineers in this coastal dune, having influences at multiple levels of biological organization. Our data also suggest that intraspecific competition influenced the spatial distributions of these shrubs and thus altered the distribution of their effects throughout the landscape.  相似文献   

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Summary Coastal sage scrub is a community found extensively throughout cismontane California south of San Francisco, but has been surprisingly little studied. In the study area, which extends from Santa Barbara to the San Gorgonio Pass, two major floristic groupings can be found. In the basin bounded coastwards by a line drawn along the axis of the Santa Ana Mountains a large number of native and introduced annual herbs and a few shrubs (e.g.Encelia farinosa), rare or absent in the remainder of the study area, characterize one floristic group. In the coastal region the variety of shrub species increases, and the herbs are predominantly native and more restricted in number. Eleven groups defined by physiognomy, structure and species dominance, and arbitrarily called associations, are recognized. These associations can be grouped into four physiognomic-structural types which transgress the boundaries of the floristic groups. The results of this study and the limited previous literature suggest that Californian coastal sage scrub could be divided, mainly on floristic criteria, into Venturan, San Diegan and Riversidian sage.Plant nomenclature follows Munz & Keek (1968).We gratefully acknowledge the financial help provided by the Department of Earth Sciences, University of California, Riverside, and the aid in plant identification provided by Mr. Oscar Clarke, Museum Scientist, Department of Biology, University of California, Riverside.  相似文献   

15.
Alien plants from psammophilous ecosystems have been studied in southern Spain. Sixteen sites, which are included in the Andalusian Network of Protected Spaces, have been chosen along 1100 km of Andalusian coasts in order to verify the degree of abundance and influence of these species on different communities. Out of the 26 localized species, the increase of some invasive plants, such as Arctotheca calendula, Agave americana, A. sisalana, Cortaderia selloana, Lantana camara and Opuntia dillenii, affects the conservation of some natural coastal ecosystems.  相似文献   

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A test for hydrotropic behavior by roots of two coastal dune shrubs   总被引:1,自引:0,他引:1  
Root hydrotropism could be a means by which plants forage for limited and patchy distributions of soil water. While root hydrotropism has been induced in distinctly artificial conditions, it is unclear if it operates in natural settings. Here, we tested for this possibility in seedlings of two species of dune shrubs. Growth of individual roots in sand-filled observation chambers was monitored in response to moisture-rich patches and resultant soil water gradients. Chambers were designed so that roots could intercept the moisture gradients but not the moisture-rich patches simply through gravitropism. While up to 12% of the Eriogonum parvifolium roots grew into the moisture-rich patches, comparable root growth was observed in the control. None of the Artemisia californica roots grew into the patches. Thus, in a reasonable simulation of field conditions, we found no compelling evidence for hydrotropic root behavior in seedlings of these two dune shrubs. Our results leave the ecological significance of root hydrotropism in question.  相似文献   

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Abstract. Coastal sage scrub exhibits floristically dissimilar subassociations on opposing aspects in the Santa Monica Mountains of southern California. Southward-facing (Venturan I) and northward-facing (Ventaran II) subassociations were sampled at two scales (1 m2 and 625 m2) each spring for five years following a fire. Mature (10- and 28 yr-old) sites of these subassociation types were also sampled in the study area. The subshrub and herbaceous components that were most prevalent on northerly slopes following the first post-burn year contributed the most cover for all ages examined. Aspect-related differences in species richness were most apparent at the smaller sampling scale where they were equal the first post-burn year and varied inversely thereafter. At this scale, richness values were two times higher on older north-facing sites, largely due to the herbaceous component. South-facing sites displayed progressive decreases in equitability through time. This pattern reflects gradual reduction in overall species richness combined with progressive site domination by fewer species, as manifested by increasing dominance concentration values. By contrast equitability on north-facing sites fluctuated little through time, though dominance concentration tended to decrease. Higher richness, equitability, and overall cover with time after burning on north-facing sites is associated with the relatively mesic habitats upon which this subassociation develops. Post-burn patterns of species richness and stratal differentiation on south-facing slopes are consistent with those reported for other mediterranean-type shrublands, i.e. peak richness was attained the first two years following a fire with subsequent decrease to a constant level.  相似文献   

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