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1.
Miconia prasina (Melastomataceae) is an important colonizing species during early stages of secondary succession in Puerto Rico but its abundance declines with increasing stand age. We studied its demography for 2 yr (1995–1997) in three populations across a pasture to forest chronosequence (1‐, 12‐, and 25‐yr old) and in one population in a hurricane‐disturbed older forest (>60‐yr old). Vegetative growth was positive in the two young sites, but negative in the two older sites. The highest percentage of plants that flowered occurred in the two younger sites but highest seed production occurred in the 25‐yr‐old site. Although seed germination occurred in the two older sites, no seedlings established. Vegetative reproduction (root sprouts) was found in all sites, with most sprouts occurring in young sites. The 2 yr of census data were used to construct stage‐based transition matrices. In the two young sites, the average population growth rate was positive (λ > 1), while average population growth was negative in the two older sites (λ < 1). Elasticity, a measure of the effects of proportional changes in life‐history transitions to the long‐term population growth rate, varied across both stages and sites. Elasticity shifted from large plants in young sites to small plants in older sites. Across all sites, elasticities related to survival were more important than those of growth or vegetative reproduction. The demographic analysis supported the previous observations of changes in the density of M. prasina based on the chronosequence and also suggests that establishment via seeds must occur prior to abandonment in active pastures.  相似文献   

2.
Summary Seed availability is a major factor limiting the recruitment of rain forest to cleared land, but little is known about the composition of the soil seed bank under different reforestation pathways. We quantified changes in the viable soil seed bank following rain forest clearing and pasture establishment and subsequent reforestation in subtropical eastern Australia. Major reforestation pathways in the region include planting of a diverse suite of native trees for ecological restoration purposes, autogenic regrowth dominated by the non‐native tree Camphor Laurel (Cinnamomum camphora) and management of this regrowth to accelerate the development of a native tree community. These pathways differ considerably in cost: restoration plantings are expensive, autogenic regrowth is free, whilst managing regrowth generally costs much less than restoration plantings. We surveyed five sites within each of three reforestation pathways as well as reference sites in remnant rain forest and pasture. The composition of the seed bank was determined by germinating plants from soil samples collected from each site. Germinants were classified into several functional groups according to life form, origin, dispersal mode and successional stage. The majority of functional groups varied significantly in abundance or richness between rain forest and pasture sites. Most of the functional groups that varied between rain forest and pasture were restored to values similar to rain forest by at least one of the three reforestation pathways examined. The species richness of native woody plants in the soil seed bank was slightly higher in restoration plantings than in autogenic or managed regrowth; nevertheless, the species richness and abundance of native woody plants and vines were higher in the seed bank of autogenic regrowth than pasture, and both attributes were enhanced by the management of regrowth sites. The results of this study show that autogenic regrowth can make an important contribution to rain forest restoration at a landscape scale. The optimal reforestation approach or mix of approaches will depend on the desired rate of recovery and the resources available for restoration.  相似文献   

3.
Recent reviews of rare plant reintroduction success indicate that far fewer studies have been conducted with seeds than whole plants, and of these, less than 10% have established or had long‐term population persistence reported. Because seed reintroductions are relatively less expensive than plant reintroductions, determining ways to increase efficacy of using seeds to establish rare populations has conservation benefits. In laboratory trials, we examined seed germination of an endangered legume, Dalea carthagenensis var. floridana, endemic in South Florida, U.S.A. Laboratory treatments confirmed that seeds are hard seeded, remaining viable for 1,452 days even when moist; nicking, heat, and freezing triggered higher and more rapid germination than controls. Field trials begun in 2009, using pretreated (frozen) and untreated seeds within two habitats (natural and novel) revealed that freezing pretreatment increased germination in both habitats. However, plants matured, reproduced, and established seedlings only in natural habitat, not in novel habitat. By 2012, seed treatment plots in natural pine rockland had significantly greater numbers of reproductive plants and seedlings than controls. In a restoration context, using seed pretreatments to stimulate germination can improve establishment success in suitable habitats. When paired with essential vegetation management and a controlled burn, seed augmentation helped rescue the population from the brink of extinction.  相似文献   

4.
Abstract Analysis was performed of the richness and abundance of woody species, forbs, and annual grasses in the easily germinating soil seed bank (henceforth seed bank) in a mediterranean shrubland of central Chile. The effects of successional development after fire and by microsite type (underneath or outside shrubs) on the density of seeds in the soil, and the relationship of species abundance in the seed bank with its abundance in the above‐ground vegetation was examined. A total of 64 plant species were recorded in the seed bank, of which 44 were annual or biannual. Eight species were woody and another eight were perennial herbs. Four could not be identified to species level. The highest richness of established herbaceous species was recorded in late spring, with 31 species. The regeneration of the herbaceous vegetation was driven by the annual production of seeds and by a reserve of short‐lived propagules in the soil. Density of all germinating seeds was significantly higher during late spring and late summer. Density of grass seeds was greater during late spring, while that of all other species was greater during late summer. Annual grass seeds accumulated in higher proportion at exposed microsites rather than under woody canopy, and in young (< 5 years old) and intermediate‐age patches (10–20 years old) rather than in mature vegetation (30–50 years old). The abundance of established woody and herb species was uncorrelated with that of the seed bank.  相似文献   

5.
四种短命植物若干生物学生态学特性的研究   总被引:24,自引:2,他引:24       下载免费PDF全文
 卷果涩芥(Malcolmia scorpioides)、四齿芥(Tetracme quadricornis)、长齿四齿芥(T.recurvata)和狭果鹤虱(Lappula semiglabra)为新疆北部常见的四种短命植物。本文从种子生物学、发育节律、株形和植株寿命等方面研究它们与生存环境的协调与适应。  相似文献   

6.
I examined the effect of riparian forest restoration on plant abundance and diversity, including weed species, on agricultural lands along the Sacramento River in California (United States). Riparian forest restoration on the Sacramento River is occurring on a large‐scale, with a goal of restoring approximately 80,000 ha over 160 km of the river. In multiuse habitats, such as the Sacramento River, effects of adjoining habitat types and movement of species across these habitats can have important management implications in terms of landscape‐scale patterns of species distributions. Increased numbers of pest animals and weeds on agricultural lands associated with restored habitats could have negative economic impacts, and in turn affect support for restoration of natural areas. In order to determine the distribution and abundance of weeds associated with large‐scale restoration, I collected seed bank soil samples on orchards between 0 and 5.6 km from adjacent restored riparian, remnant riparian, and agricultural habitats. I determined the abundance, species richness, and dispersal mode of plant species in the seed bank and analyzed these variables in terms of adjacent habitat type and age of restored habitat. I found that agricultural weed species had higher densities at the edge of restored riparian habitat and that native plants had higher densities adjacent to remnant riparian habitat. Weed seed abundance increased significantly on walnut farms adjacent to restored habitat with time since restored. I supply strong empirical evidence that large areas of natural and restored habitats do not lead to a greater penetration of weed species into agricultural areas, but rather that weed penetration is both temporally and spatially limited.  相似文献   

7.
Ecological systems are severely damaged by the anthropogenic disturbance of mining. Phosphate open-pit mining fields cover over 200 km2 of the Negev desert, Israel. However, the effects of the ongoing mine site restoration efforts on the plant community have not been studied. Plants and their seed banks have a major role in ecosystem processes and restoration. In this study, we focused on three mining sites, restored in different years, along Zin River valley. We compared the plant community of restored mining plots within these areas to adjacent natural plots. We asked whether plant community germination potential from the soil seed bank differs between the restored plots and the adjacent natural plots within a mining site. We hypothesized that: (1) there is a lack of seed bank in the restored plots; (2) the altered soil composition at the restored plots inhibits germination. We used soil samples collected from the different mining sites and set up greenhouse experiments. One experiment compared natural and restored areas with different soil treatments. In another experiment, we added native seeds to test their germination potential on restored soil. Our results indicate that lack of seed bank is the major limiting factor hindering germination and not the composition of the soil after restoration. Our findings shed light on the constraints of seed bank establishment in post-mining areas of hyper-arid regions. We suggest considering active restoration practices to facilitate natural dispersal and improve seed bank establishment.  相似文献   

8.
Abstract Many populations of herbaceous perennial plants contain seeds stored in a soil seed bank. The contribution of seeds to population persistence is an important parameter in population models but germination rates of known‐age seeds are difficult to obtain because individual seeds cannot easily be followed. Although Trachymene incisa Rudge plants produce copious seeds that are dispersed into the soil, the existence of a seed bank has not been confirmed. To quantify the potential for a seed bank fresh seeds of T. incisa were sown into experimental seed banks in the eucalypt‐dominated Agnes Banks Woodland in western Sydney, NSW. A recent fire provided the opportunity to compare germination in the burnt and unburnt vegetation. Density of seed sowing and time of maturation/dispersal of seeds were manipulated in 75 seed cages. Emergence of seeds after 5 months was significantly higher for the earliest planting date but after 1 year, germination of seeds planted in the later weeks increased, and the final germination for all weeks was 28%. Density of sowing and the recent fire did not affect emergence. A second experiment planted over a broader time span (9 weeks instead of 3 weeks) confirmed the effect of planting date but also found significant spatial variation on a scale of tens of metres. Laboratory germination rates of over 70% confirmed that the seeds were viable and non‐dormant when sown in the field cages. The carry‐over of non‐germinated seed in the soil seed bank is estimated to be about 70% after 2 years, implying that a cohort of seeds would not be depleted through germination alone for up to 40 years. The potential for a long‐lived seed bank in this species is interesting because the plants are also capable of resprouting from their rootstock after fire, giving them characteristics of both resprouters and seeders.  相似文献   

9.
We are clarifying how the functional embryo growth occurs in germinating seeds of Solanum lycocarpum A. St.‐Hil., a nurse plant with a central role in forest dynamics in the Cerrado (a biodiversity hotspot). For that, we used classical seed germination measurements (germinability, mean germination time, mean germination rate, coefficient of variation of the germination time, synchronisation index and germination time range) and gene expression of mRNA codifying key proteins/enzymes for the success in the seed–seedling transition (Cyclin, Actin, Small Heat Shock Protein, Glutathione S‐transferase, Malate Dehydrogenase, Alcohol Dehydrogenase). Our findings demonstrate: (a) Although germination kinetics in S. lycocarpum seeds is slower than that in tomato seeds, the fold change of genes codifying key enzymes for the embryo development is similar in germinating seeds of both species. (b) The genes used here are useful, from a technical point of view, for classifying commercial seed samples of the species in relation to physiological quality. More notably, cyclin and malate dehydrogenase genes have a greater expression, both in germination sensu stricto and in immediate post‐germination. (c) A molecular framework for the embryo growth in germinating seeds of S. lycocarpum can be a functional explication for the species to be a nurse plant. Thus, the overlapping of classical and contemporary measurements is especially interesting to those species playing a central role in the environment, such as nurse plants, and may represent a new conservationist paradigm.  相似文献   

10.
Plant communities dominated by narrow‐leaved mallee (Eucalyptus cneorifolia) are almost entirely confined to north‐eastern Kangaroo Island, South Australia, an area which has been extensively cleared for agriculture. Consequently, surviving examples consist mostly of small remnants which are thought to be senescent due to the exclusion of fire. This senescence is associated with the loss of many native understory species. Prescribed burns have been suggested as a management tool to stimulate the restoration of native plants from the soil seed bank; however, no seed bank studies have previously been conducted on Kangaroo Island and the seed bank literature usually focuses on particular species rather than on plant communities. We conducted an experiment to investigate the effects of the fire‐related cues heat and smoke on the germination of plants from the seed bank in soil sampled from 10 long‐ungrazed narrow‐leaved mallee sites on Kangaroo Island. Eighty trays of soil were monitored in a controlled glasshouse for five months after being subjected to heat and/or smoke treatments. The overall number of native, but not exotic, plant species germinating from the soil seed bank was significantly increased by all three fire‐related treatments (heat, smoke and heat plus smoke) compared with the control (no fire‐related treatment). Different plant life forms exhibited varying responses to heat and smoke treatments. The results of this study illustrate that the application of fire‐related treatments to soil seed banks in controlled glasshouse conditions can stimulate the recruitment of native species, including several species of conservation concern. These findings also indicate the potential of using these treatments for the ex situ germination of fire dependent species for revegetation purposes and indicate aspects of prescribed burns that may be important for restoring different components of native vegetation.  相似文献   

11.
1. The ability of seeds to survive periods of drying and wetting that do not lead to seed production will determine the potential species pool for future plant communities of temporary wetlands. I investigated characteristics of the seed banks in sediment from Australian temporary wetlands that might contribute to the ability of aquatic plants to re‐establish after extended drought. 2. Experimental investigation into germination from sediment from six sites in five Australian temporary wetlands, with various water regimes, examined two sources of seed bank depletion: (i) length of time dry (longevity up to 12 years) and (ii) successive annual wetting and germination events (up to seven) with intervening periods dry (leaving a residual seed bank), both without any opportunity for replenishment of the seed bank. 3. These wetlands had species‐rich, long‐lived seed banks that were not exhausted by successive germination events. After three years of dry storage, 90% of the original seed bank species germinated, after six years 75% and after 12 years 20%. After seven successive wetting and drying events without seed bank replenishment, 48% of the original species still germinated. The mean survival time dry for seed bank species, 7.4 years, was longer than the duration of recent droughts. 4. Seed bank composition varied among wetlands and over time; most species did not occur in all wetlands and many occurred in one wetland only. The germination patterns of different species, although differing in detail, tended to be consistent in that all species could survive long dry periods and several wetting and drying events. However, experimental drought significantly diminished species richness and abundance, indicating limits to seed bank persistence. 5. Data from such long‐term studies of seed bank persistence should allow prediction of the species richness and composition of the germinating communities in a wetland whose water regime is intentionally or unintentionally altered. This ability to forecast may become particularly important under climate change and the need to predict future wetland conditions.  相似文献   

12.
Summary Assessment of the conservation significance of a species at a particular site involves estimating the population size. Generally this is based on a single survey. However, where plant species vary greatly in abundance in response to disturbance regimes, there will be uncertainty associated with the use of single estimates of abundance. The interpretation of such estimates is dependent on an understanding of the ecology of the species and the disturbance regimes that impact on it. We examined the usefulness of abundance estimates in the endangered shrub Grevillea caleyi (a fire‐sensitive shrub with a persistent soil seed bank) from south‐eastern Australia, where fire is a major landscape disturbance. Comparisons of estimates of abundance before and after fire showed very large changes in the number of plants of G. caleyi above ground. Changes in abundance of over two orders of magnitude were observed. The longer the site was left unburnt, the greater the magnitude of change in abundance after the next fire. Above‐ground plants may be rare or absent at sites unburnt for over 15–20 years, but were abundant after fire, due to re‐establishment from the soil seed bank. Sites burnt by two fires in quick succession showed declines in population abundance, most likely due to the soil seed bank not being replenished between such short interval fires. Assessments of the conservation significance of remnant sites of G. caleyi and similar species based on a single sample of above‐ground plant abundance at one time are considered inappropriate. The amount of available habitat for G. caleyi, either as area of occupancy or preferably extent of available habitat, was a moderate predictor of the likely magnitude of abundance in the species after fire. However, the usefulness of these measures for species whose biology is comparable to Grevillea caleyi, will be limited due to factors relating to the degree of species‐specific habitat requirements, local site fire history and the impact of any one fire on resultant post‐fire germination levels. Any assessment of conservation significance will require the interpretation of available information in relation to the ecology of a species.  相似文献   

13.
14.
Spatial and temporal variation in critical life history traits differ markedly between two co-occurring, rare and endangered annual plants, Gilia tenuiflora arenaria and Chorizanthe pungens pungens, that have restricted, but overlapping geographic distributions in coastal habitats of central California, USA. Environmental variation was extreme during the 6-year study (1997–2002), with the greatest differences between an intense wet, warm El Niño year (1998), followed by a very dry, cool La Niña (1999). Both species have similar increases in adult survival and seed set with wetter, warmer weather in spring, but they differed in other traits: more Gilia germinated in years with high rainfall and temperature, while more Chorizanthe germinated in dry, cooler years; Gilia abundance increased with the number of years since the previous large El Niño event, while Chorizanthe abundance declined; and Gilia abundance was independent of the previous year’s seed set, while Chorizanthe density was directly related to the previous year’s seed set. The strong negative associations of Chorizanthe abundance with warm, wet weather and with time since the previous El Niño probably reflect the particular sequence of annual weather patterns from 1997 through 2002, especially the extremes in 1998 and 1999. Since it germinates readily in most years under a wide range of winter conditions and does not develop a long-lived seed bank, Chorizanthe seedling abundance reflects recent additions and depletions of its seed bank, rather than prevailing weather, per se. In contrast, Gilia seeds may remain in the seed bank for many years, until relatively rare winter conditions trigger significant germination. These species-specific demographies enhance persistence and coexistence of these species, but the mechanisms differ from each other and from those described for annuals in other highly variable environments.  相似文献   

15.
The restoration of disturbed ecosystems is challenging and often unsuccessful, particularly when non‐native plants are abundant. Ecosystem restoration may be hindered by the effects of non‐native plants on soil biogeochemical characteristics and microbial communities that persist even after plants are removed. To examine the importance of soil legacy effects, we used experimental restorations of Florida shrubland habitat that had been degraded by the introduction of non‐native grasses coupled with either mechanical disturbance or pasture conversion. We removed non‐native grasses and inoculated soils with native microbial communities at each degraded site, then examined how habitat structure, soil nitrogen, soil microbial abundances, and native seed germination responded over two years compared to undisturbed native sites. Grass removal treatments effectively restored some aspects of native habitat structure, including decreased exotic grass cover, increased bare ground, and reduced litter cover. Soil fungal abundance was also somewhat restored by grass removals, but soil algal abundance was unaffected. In addition, grass removal and microbial inoculation improved seed germination rates in degraded sites, but these remained quite low compared to native sites. High soil nitrogen persisted throughout the experiment regardless of treatment. Many treatment effects were site‐specific, however, with legacies in the more degraded vegetation type tending to be more difficult to overcome. These results support the need for context‐dependent restoration approaches and suggest that the degree of soil legacy effects may be a good indicator of restoration potential.  相似文献   

16.
The timing of germination is a key life‐history trait that may strongly influence plant fitness and that sets the stage for selection on traits expressed later in the life cycle. In seasonal environments, the period favourable for germination and the total length of the growing season are limited. The optimal timing of germination may therefore be governed by conflicting selection through survival and fecundity. We conducted a field experiment to examine the effects of timing of germination on survival, fecundity and overall fitness in a natural population of the annual herb Arabidopsis thaliana in north‐central Sweden. Seedlings were transplanted at three different times in late summer and in autumn covering the period of seed germination in the study population. Early germination was associated with low seedling survival, but also with high survival and fecundity among established plants. The advantages of germinating early more than balanced the disadvantage and selection favoured early germination. The results suggest that low survival among early germinating seeds is the main force opposing the evolution of earlier germination and that the optimal timing of germination should vary in space and time as a function of the direction and strength of selection acting during different life‐history stages.  相似文献   

17.
Traits are important for understanding how plant communities assemble and function, providing a common currency for studying ecological processes across species, locations, and habitat types. However, the majority of studies relating species traits to community assembly rely upon vegetative traits of mature plants. Seed traits, which are understudied relative to whole‐plant traits, are key to understanding assembly of plant communities. This is particularly true for restored communities, which are typically started de novo from seed, making seed germination a critical first step in community assembly and an early filter for plant establishment. We experimentally tested the effects of seed traits (mass, shape, and embryo to seed size ratio) and phylogeny on germination response in 32 species commonly used in prairie grassland restoration in the Midwestern USA, analyzing data using time‐to‐event (survival) analysis. As germination is also influenced by seed dormancy, and dormancy break treatments are commonly employed in restoration, we also tested the effects of two pretreatments (cold stratification and gibberellic acid application) on time to germination. Seed traits, phylogeny, and seed pretreatments all affected time to germination. Of all traits tested, variables related to seed shape (height and shape variance) best predicted germination response, with high‐variance (i.e., pointier and narrower) seeds germinating faster. Phylogenetic position (the location of species on the phylogenetic tree relative to other tested species) was also an important predictor of germination response, that is, closely related species showed similar patterns in time to germination. This was true despite the fact that all measured seed traits showed phylogenetic signal, therefore phylogeny provided residual information that was not already captured by measured seed traits. Seed traits, phylogenetic position, and germination pretreatments were important predictors of germination response for a suite of species commonly used in grassland restoration. Shape traits were especially important, while mass, often the only seed trait used in studies of community assembly, was not a strong predictor of germination timing. These findings illustrate the ecological importance of seed traits that are rarely incorporated into functional studies of plant communities. This information can also be used to advance restoration practice by guiding restoration planning and seed mix design.  相似文献   

18.
Seed development, dormancy and germination of the American invasive tree species, Prunus serotina, are described for plants growing in a large forest in Belgium. Seeds of P. serotina were collected following anthesis in the first week of July and thereafter at fortnightly intervals. Seed dormancy, temperature requirements for germination and the soil seed bank were investigated. At maturation (about 105 days after anthesis), seed moisture content had decreased to around 13.7%, and 44% of the seeds had attained the capacity to germinate. Mature seeds of P. serotina exhibited physiological dormancy, germinating only after a long cold, moist stratification period. Highest germination percentage occurred in seeds treated with gibberellic acid (GA3), at 10°C. We found no evidence that P. serotina forms a persistent seed bank but noticed a persistent seedling bank in the field.  相似文献   

19.
Restoration is used to conserve biodiversity; however, it is unclear to what extent restoration impacts ecosystem functions. Pollination is an ecosystem function that is critical to plant reproduction and thus restoration success. Few studies have assessed whether pollination is restored within restoration areas themselves. Plant–animal interactions may be affected by factors beyond the scale of the restoration. For example, surrounding landscape context may influence pollinator abundance and consequently the amount of pollen deposited. Decreased pollen receipt might then limit seed set. We hypothesized that in restorations surrounded by more agriculture, pollinator‐dependent forbs would experience greater pollen limitation. This would likely be due to declines in pollinator abundance within the restorations with an increase in surrounding agriculture. We deployed potted Chamaecrista fasciculata (Fabaceae), an obligatorily bee‐pollinated forb, and sampled bee communities in restored prairies in Minnesota, U.S.A. We measured pollen limitation by comparing seed set among open and supplementally pollinated plants. We also sampled native bees in seven of the eight sites. We tested for a relationship between proportion row crop agriculture (corn and soy) surrounding a restoration and pollen limitation, as well as an effect of agriculture on bee abundance. We did not find evidence that increasing proportion of surrounding agriculture negatively affected pollen limitation or bee abundance. Our results indicate that greater surrounding agriculture may not influence pollination of C. fasciculata through declines in pollinator availability, and suggest for some plants that landscape context might not limit pollination in restorations.  相似文献   

20.
The main objective of this study was to analyze whether plant material transfer is a suitable approach for establishing plant populations with spatial patterns and population structures resembling those of remnant populations. We studied pattern formation and population characteristics in three remnant and two restored populations of the biennial plant species Arabis nemorensis in the upper Rhine valley in southwestern Germany over a period of 2 years. We investigated spatial patterns of seedlings, juveniles, and adults as well as the small‐scale horizontal and vertical distribution of seeds in the soil, followed the fate of individual plants and recorded structural habitat parameters such as vegetation and litter cover. Population dynamics differed between the study sites, but there was no pronounced difference between restored and remnant sites. Seedlings, juveniles, and adults as well as seeds in the seed bank showed aggregated spatial patterns on all study sites, with positive autocorrelation on a scale of 20–60 cm. Within sites, patterns remained approximately stable through time. Restored sites experienced rapid seed bank formation as a result of the restoration measures. Our results suggest that the restoration measures were not only successful in transferring the target species but also triggered rapid formation of spatially structured populations that, years after restoration, closely resembled those of remnant sites.  相似文献   

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