Fruit removal efficiency and success: influence of crop size in a neotropical treelet

The reproductive success of animal-dispersed plants is closely linked to the number of seeds that they are able to disperse. The fruit crop size hypothesis states that a plant with large fruit crop size will attract more dispersers than a plant with a smaller fruit crop, which may result in more seeds being dispersed from the foremost. In this study, we experimentally examined the effect of crop size and other factors on primary seed dispersal in a neotropical shrub/tree, Casearia corymbosa (Flacourtiaceae). We used two predictive variables of reproductive success, which produce an accurate picture of seed dispersal ratio: fruit removal efficiency (proportion of a fruit crop removed by frugivores) and fruit removal success (relative contribution of each individual tree to the number of fruits removed in the population). We established two levels of fruit crop size at the C. corymbosa individuals, using plants with large (150 fruits) and small crops (50 fruits). We found that individual plants with larger crops had significantly higher values of fruit removal efficiency (92.6%) and success (5%) than plants with smaller crops (69.3% and 1.3%, respectively). Fruit removal efficiency was related to vegetation type, plant height and fruit width, but the variance explained by these variables was low ( < 8%). Fruit removal success was significantly related to crop size ( > 90% of the variance explained). These results suggest that fruit removal efficiency and success are strongly related to fruit crop size of C. corymbosa plants.     

Assessing the potential for recovery of lakeshore vegetation: species richness of sediment propagule banks

To assess the potential and develop appropriate techniques for the recolonization of lakeshore vegetation at sites where it had been completely lost, a pilot project was launched at Lake Kasumigaura, Japan. We investigated the species composition and density of the soil seed banks (propagule banks) of lake sediments at nine sites (total area, 65,200 m²) where lake sediments were spread thinly (∼10 cm) on the surfaces of artificial littoral zones. These zones were constructed in front of concrete levees and had microtopographic variations. In total, 180 species, including six endangered or vulnerable species and 12 native submerged plants that had disappeared from the aboveground vegetation of the lake, were recorded during the first year of restoration. The distribution of each restored species at the sites suggested the importance of microtopographic variation for recolonizing species-rich lakeshore vegetation. Furthermore, the origin of the source sediment affected the species composition of the established vegetation.     

洪湖湿地退耕初期种子库的季节动态

 为了研究水田退耕初期种子库的特征,在两个不同水位条件下通过幼苗萌发法对洪湖的濒湖退耕田种子库的结构和季节动态进行了研究。结果表明,种子库季节变化明显,种子库的密度于12月达到最大值2.61×105 ind.·m-2,6月时最小,为2.90×104ind.·m-2。而萌发的物种数则相反,6月时最大,12月时最小。Simpson 和Shannon-Wiener多样性指数及Shannon均匀度指数表现出较为一致的季节变化规律,在6月最高,12月和3月最低。该种子库类型属于持续性种子库。种子库与地表植被群落种相似性系数变化较大。0～5 cm和 5～10 cm土层中的种子库萌发的物种数差异不显著,但在数量上有明显分层现象,上层种子库占总数的78%。One-way ANOVA分析表明,萌发时的水位条件可显著影响种子库萌发的种类和数量。结合种子库研究的结果,讨论了种子库在退田还湖后湿地植被恢复过程中的重要性。     

Establishment and persistence of target species in newly created calcareous grasslands on former arable fields

The effects of different restoration measures and management variants on the vegetation development of newly created calcareous grasslands were studied in southern Germany from 1993 to 2002. In 1993, fresh seed-containing hay from a nature reserve with ancient calcareous grasslands was transferred onto ex-arable fields with and without topsoil removal. Nine years after start of the restoration, the standing crop was lower and the cover of bare soil was higher on topsoil-removal sites than on sites without soil removal. Topsoil removal had a positive effect on the proportion of target species (class Festuco-Brometea), because the number and cover of productive meadow species (class Molinio-Arrhenatheretea) were reduced. Persistence of hay-transfer species and the number of newly colonizing target species were highest on topsoil-removal sites. On plots with and without soil removal, species richness and the number of target species increased quickly after hay transfer and were always higher on hay-transfer plots than on plots that had not received hay in 1993. In 2002, differences induced by hay transfer were still much more pronounced than differences between management regimes. Management by mowing, however, led to higher species richness, a greater number of target species and a lower number of ruderals in comparison to no management on restoration fields without soil removal. A detrended correspondence analysis (DCA) indicated that vegetation composition of the hay-transfer plots of the restoration fields still differed from the vegetation of ancient grasslands in the nature reserve. Vegetation of an ex-arable field in the nature reserve (last ploughed in 1959) showed an intermediate successional stage. In general our results indicate that the transfer of autochthonous hay is an efficient method for the restoration of species-rich vegetation, which allows not only quick establishment but also long-term persistence of target species.     

Do plant-community-based grazing regimes lead to epizoochorous dispersal of high proportions of target species?

The contribution of large-herbivore epizoochory to the transfer of seeds within and between areas is thought to be significant. But often seeds of ubiquitous species are dispersed, which may enhance ruderalization processes. In order to study the dispersal of target species by sheep, we employed a community-based grazing approach followed by intra- and inter-area sheep transfers (maximum transfer distance 3 km). In case of inter-area transfers, well-developed target communities of an open inland sand ecosystem are used as “source”, linked to less-developed sand habitats (“sink”) via sheep. Also other factors determining which species become dispersed under field conditions were tested: seed surface structure, seed mass, plant seed-releasing height and animal behaviour. Finally the influence of animal movement on seed detachment and the actual arrival of seeds within a “sink” were studied.

Sheep transfers resulted in the dispersal of 56 seed species, dominated by Red List (seven species) and other target species. Quantitatively, most transported seeds belonged to target species, whereas graminoid competitors were highly under-represented. Morphological traits enhance the attachment probability regardless of seed mass. But for seeds without these epizoochory-facilitating traits, mass seems to affect attachment negatively. Plant height affected the number of species present in sheep coats but not the seed quantities. Probably certain species in the vegetation produced large numbers of seeds, e.g. low-growing Medicago minima with seed surface structures and high-growing species Verbascum phlomoides without seed surface structures. Also, although transfer half-times were three times lower than grazing half-times, naturally attached Stipa capillata and Agrimonia procera seeds showed no significant detachment rates during transfer, whereas considerable losses were found during grazing. Other 3-km sheep transfers did not result in significant losses of either epizoochorously transported seed or species quantities. Our study shows that community-based grazing can lead to the dispersal of especially target species. Besides that, different habitat fragments can be connected to each other via sheep without significant seed losses along the way.     

Linking seed dispersal,germination and seedling recruitment in the invasive species <Emphasis Type=\"Italic\">Berberis darwinii</Emphasis> (Darwin’s barberry)

Seedling recruitment is a multi-phased process involving seed production, dispersal, germination, seedling establishment and subsequent survival. Understanding the factors that determine success at each stage of this process is of particular interest to scientists and managers seeking to understand how invasive species spread and persist, and identify critical stages for management. To understand the factors and processes influencing recruitment of the invasive species Berberis darwinii Hook. (Darwin’s barberry), temporal and spatial patterns of seed dispersal, germination and seedling establishment were examined. Seed dispersal from a large source population was measured over two fruiting seasons, and subsequent patterns of seedling emergence and survival within each cohort were measured. Seed longevity was tested under both natural and artificial conditions. Seeds were widely dispersed by birds, up to 450 m from the source population. Dispersal was essential to seedling establishment, as few seedlings survived beneath the parent canopy. Seeds were relatively short-lived in the soil under both field and glasshouse conditions, with few surviving for more than 1 year. Patterns of newly emerged seedlings largely reflected patterns of seed rain, but seedling survival was significantly affected by distance from source population, seedling density and light environment. These results suggest that recruitment of B. darwinii is dependent on dispersal of seeds to favourable microsites. Management priorities should include the removal of fruiting plants, and seedling control in highlight areas.     

Soil diaspore reserves above the timberline in the Austrian Alps

Soil diaspore reserves are considered to support self-healing processes after vegetation disturbances. Therefore, the stratified reserves of viable diaspores in superimposed soil layers of four sites above the timberline in the Austrian Alps were assessed. At each site, a semi-natural (“undisturbed”) extensive alpine pasture and the disturbed vegetation on hiking trails were investigated. Eighty soil cores in total (corresponding to 400 slices, each representing a 1-cm layer between 0 and 5 cm depth) were taken in autumn and subjected to germination tests after vernalization. The total diaspore numbers in disturbed and undisturbed plots did not differ significantly, but all undisturbed soils contained higher species numbers than disturbed ones. Seed shape and size clearly influenced the vertical distribution. Intact soils showed a significant decrease in big/long diaspores with increasing soil depth. Disturbances influenced the aboveground species composition and therefore the distribution of seeds of different size. In case of disturbances, the restriction of most big seeds to superficial layers means a threat for small populations of rare and protected species such as Viola lutea subsp. sudetica with relatively big seeds near the soil surface. When the disturbances stop, the diaspore communities might initiate a first, but with respect of landscape protection and preservation of species diversity insufficient step of vegetation restoration.     

Aerial seed bank dynamics and seedling emergence patterns in two annual Mediterranean Asteraceae

Question: We explored the functional significance of seasonal aerial seed banks in two coexisting, heterocarpic annual Asteraceae with dormant (Chrysanthemum coronarium) and non‐dormant (Anacyclus radiatus) achenes. We hypothesised that the plant achene pool is a significant component of total seed reserves, and that within‐season seedling emergence timing is shaped by achene release patterns. Location: SW Spain. Methods: In an observational study, we established temporal achene release patterns. We also quantified the aerial and soil achene pools throughout the release season, and assessed seedling emergence timing. Sowing experiments were used to explore the influence of achene release dynamics on emergence timing, and to establish achene morph‐specific patterns of between‐year distribution of germination. Results: Achene release extended from late spring to late autumn (Chrysanthemum), or from early autumn to early winter (Anacyclus). Within species, achene morphs differed in release timing. Only in Chrysanthemum, a small achene fraction seemed to persist in the soil, and between‐year germination distribution differed among morphs. In coexisting populations, the Anacyclus plant achene pool was an order of magnitude higher than the soil pool throughout the release season, whereas in Chrysanthemum both pools were of the same magnitude during autumn. Within‐year seedling emergence was significantly staggered beneath parent plants compared with the pattern resulting solely from the germination response in soil, with the exception of Chrysanthemum in one of the two study years. Conclusions: Results suggest that seasonal aerial seed banks are effective within‐season, risk‐reducing traits in ruderal Mediterranean habitats characteristic of the study species.     

金沙江干热河谷山地植被恢复区土壤种子库和地上植被研究

土壤种子库在植物种群动态中起着重要作用。土壤种子库可缓解种群的灭绝过程,保存群落中植物种的表现特征,是植被天然更新的物质基础。通过对金沙江干热河谷山地植被恢复区（包括水平阶、自然坡面、沟底）和未恢复区（包括放牧地）的土壤种子库和地上植被的组成、大小及多样性进行比较研究表明,植被恢复区土壤种子库和地上植被的密度、丰富度、多样性及均匀度均大于未恢复区。恢复区地上生物量要远大于未恢复区。水平阶和各类型间的土壤种子库密度与地上植被密度差异显著。土壤种子库中草本植物占很大比例。孔颖草和扭黄茅是土壤种子库和地上植被的两大优势种,两者的个体数量、重要值及生物量最大。土壤种子库和地上植被有较高的相似性,且随着恢复程度的加深,相似性有增高的趋势;土壤种子库密度和地上植被密度之间关系可以用二次和三次曲线拟合。