Clumped planting arrangements improve seed production in a revegetated eucalypt woodland

The arrangement of plants within revegetated sites is rarely considered an important characteristic of these communities. However, in natural systems, plant spatial arrangements can influence a range of ecological processes, including pollination and seed set. Pollinators tend to preferentially visit larger and/or more closely spaced populations, with plants in these populations generally receiving more outcrossed pollen, resulting in increased seed set and better quality seed. Similar trends may occur in revegetated populations, but little is known about the influence of planting arrangement on seed production in restored systems. Here, we quantified the effect of plant abundance (number of conspecifics within 100 m) and distance to nearest reproductive conspecific on the level of seed set for six eucalypt species (n = 422 trees in total) in 1 year and for one of these species (Eucalyptus leucoxylon), across three additional years. Seed number per fruit was highly variable both between individuals and within individuals across years. Despite this variability, there was a consistent trend of higher seed production (seed number per fruit) when another reproductive conspecific was within 20 m. In contrast, plant abundance had little influence on seed production. Further investigation of nearest neighbor arrangements found the distance to either the first, second, third, or fourth reproductive neighbors were the key predictors of seed production. Therefore, revegetation designs that consider plant spacing and aggregation, rather than only planting to overall density criteria (i.e. trees/ha), at least for the eucalypts studied here, has the potential to improve seed production in revegetated populations.     

Variation of pollination and resource limitation in a low seed-set tree, Liriodendron chinense (Magnoliaceae)

Pollen limitation and resource limitation have been documented as the major factors responsible for plants commonly producing more ovules than seeds, but few studies have examined pollen deposition directly in natural populations at different sites and times. We investigated the causes of low seed set in four populations of Liriodendron chinense (Magnoliaceae), an insect‐pollinated endangered tree endemic to southern China, over 2–3 years. One pistil potentially produces two ovules. The number of pistils per flower varies among populations, but in three of the four populations the variation in a given population was not significantly different among years. Overall, populations with higher pistil numbers tend to set more seeds per flower, but a positive correlation between pistil numbers and seed production per flower was observed in only one of the four populations. The numbers of pollen grains deposited per stigma varied from 0 to 60. The proportion of pollinated stigmas per flower ranged from 44% to 88% among populations and years. The numbers of pollen grains deposited per stigma and the percentages of pollinated stigmas were significantly different between populations, and two populations showed significant differences between years. A positive correlation between stigmatic pollen load and seed set was sought in ten population‐by‐year combinations but, in a given population, high stigmatic pollen loads did not always result in high seed set. Examination of pollen deposition, pistil and seed production over several sites and years showed that in addition to pollination, other factors such as resource or genetic loads were likely to limit the (lower than 10%) seed set in L. chinense. It appears that small, isolated populations experience severe pollination limitation; one population studied had seed/ovule ratios of 0.84% and 1.88% in 1995 and 1996. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140 , 31–38.     

Effect of the specialist herbivore Luehdorfia puziloi on the performance of a woodland herbaceous plant, Asarum heterotropoides

Plants show many responses to herbivore damage caused by insects. We investigated the effect of the specialist leaf herbivore Luehdorfia puziloi on the performance of a deciduous forest understory perennial herb Asarum heterotropoides . We conducted artificial defoliation experiments with different levels of damage (0, 50 or 100% clipping) in the early growing period (flowering time: early May) and in the late growing period (when natural herbivory by L. puziloi larvae occurs: early June) in a natural population. Effects of the defoliation treatments on reproduction (seed-set ratio) of A. heterotropoides in the treated year and on survival and development of the plant in the subsequent year were investigated. Severe defoliation conducted in the early period resulted in less current-year seed production and increased regression to a dormant or non-reproductive stage in the following year, which would reduce the probability of future flowering. In contrast, defoliation conducted in the late period had no effect on the reproduction, survival and development of A. heterotropoides . Similarly, we found no obvious correlation between the damaged leaf area during the later period and seed set. Our results show that the specialist herbivore L. puziloi did not influence the performance of A. heterotropoides by damaging the plant later in the season when it was tolerant of damage.     

喜马拉雅山脉种子植物多样性特征及分布格局

喜马拉雅山脉是全球著名的生物多样性热点地区之一。该研究对以往收集的喜马拉雅山脉南、北坡植物物种名录及其分布数据进行整合,借助在线数据库对分布数据进行补充与修订,最后整理并汇总了喜马拉雅山脉位于中国、印度、尼泊尔、不丹4国境内的种子植物分布情况,并在此基础上对科属特征、物种组成相似性、区系成分以及海拔梯度上物种分布格局进行分析,为该区域的生物多样性研究以及保护提供数据支撑。结果表明：(1)喜马拉雅山脉共分布有种子植物11 875种,隶属223科2 086属,其中包含7 906种草本植物(66.6%),2 583种灌木(21.8%)和1 386种乔木(11.7%)。(2)研究区涵盖物种数量位于前20的科有菊科(Asteraceae)、兰科(Orchidaceae)、禾本科(Poaceae)、豆科(Fabaceae)、杜鹃花科(Ericaceae)等科,共包含物种7 456种,约占喜马拉雅山脉植物种的62.8%;涵盖物种数量位于前20的属有杜鹃花属(Rhododendron)、报春花属(Primula)、马先蒿属(Pedicularis)、虎耳草属(Saxifraga)、薹草属(Carex)...     

Testing a facilitation model for ecosystem restoration: Does tree planting restore ground layer species in a grassy woodland?

Planning for the restoration of degraded ecosystems has a strong basis in facilitation successional theory, which, as applied in restoration practice, states that planting of structurally dominant tree species will assist the entry of other native species into a restored community. In Australia, tree planting has been widely applied in restoration of grassy woodland ecosystems. Trees have been postulated to reduce the cover and diversity of weed species, thus facilitating recolonization of native woodland species (indirect facilitation). The expected outcomes of this process include reduced species richness and abundance of exotic plant species and increased species richness and abundance/dominance of natives in areas beneath tree canopies, with these trends strengthening with time. To assess whether this was occurring, we carried out a comparative analysis of species assemblages found underneath and outside of planted tree canopies in sites replanted with juvenile canopy tree species 3–5 or 8–10 years previously. We sampled revegetated stands of Cumberland Plain Woodland, an endangered ecological community in Western Sydney, Australia. We found that neither the number nor abundance of native ground layer species beneath canopies increased as a result of trees being planted at sites of both ages. Where seed is limited, we predicted an increase in abundance of existing native species under planted tree canopies. On this point, the results were mixed and showed some natives with an increased abundance while others decreased. Exotic species richness showed the reverse of the expected pattern, being greater under tree canopies. These findings lend no support to the theory of indirect facilitation. We conclude that simple facilitation models may be inadequate to support planning of grassy woodland restoration and that those models incorporating successional time lags and restoration barriers are likely to be more informative about the development of communities initiated by tree planting.     

Restoring grassy woodland diversity through direct seeding: Insights from six ‘best‐practice’ case studies in southern Australia

Ecological restoration of grassy woodland ecosystems is now a significant landscape‐scale conservation objective throughout southern Australia. Technological improvements in direct seeding are now sufficiently well‐advanced to examine whether cost‐effective restoration of grassy woodlands is feasible. Consideration of six ‘best practice case studies shows substantial evidence of success. Further refinement of direct seeding techniques, in combination with native seed production systems, however, will be required into the future to meet the scale of woodland conservation targets and restore ecological function.     

New insights into plants co‐existence in species‐rich communities: The pollination interaction perspective

Questions

In animal‐mediated pollination, pollinators can be regarded as a limiting resource for which entomophilous plant species might interact to assure pollination, an event pivotal for their reproduction and population maintenance. At community level, spatially aggregated co‐flowering species can thus be expected to exhibit suitable suites of traits to avoid competition and ensure pollination. We explored the problem by answering the following questions: (1) are co‐flowering species specialized on different guilds of pollinators; (2) do co‐flowering pollinator‐sharing species segregate spatially; and (3) do co‐flowering pollinator‐sharing species that diverge in anther position spatially aggregate more than those that converge in anther position?

Study Site

Euganean Hills, NE Italy.

Methods

Plant composition, flowering phenology and interactions between each entomophilous plant species and pollinating insects were monitored every 15 days in 40 permanent plots placed in an area of 16 ha. We quantified the degree of flowering synchrony, pollinator‐sharing and spatial aggregation between each pair of entomophilous species. We then tested the relationship between the degree of co‐flowering, pollinator‐sharing and spatial aggregation, and between spatial aggregation and anther position.

Results

Entomophilous species converged, at least partially in flowering time, and the phenological synchronization of flowering was significantly associated with the sharing of pollinator guilds. Co‐flowering pollinator‐sharing species segregated spatially. Furthermore, co‐flowering pollinator‐sharing species that diverged in anther position aggregated more than those that converged in anther position.

Conclusions

Reproductive traits that facilitate the co‐existence of co‐flowering species include specialization on different pollinator guilds and a phenological displacement of the flowering time. Furthermore, in circumstances of increased competition due to phenological synchronization, pollinator‐sharing and spatial aggregation, the chance of effective pollination might depend on differences in anther position, resulting in a divergent pollen placement on pollinator bodies. One of the most interesting results we obtained is that the presence of one mechanism does not preclude the operation of others, and each plant species can simultaneously exhibit different strategies. Although more studies are needed, our results can provide additional information about plant–plant interactions and provide new insights into mechanisms allowing the co‐existence of a high number of plant species in local communities.

     

Mating system and early viability resistance to habitat fragmentation in a bird-pollinated eucalypt

Habitat fragmentation has been shown to disrupt ecosystem processes such as plant-pollinator mutualisms. Consequently, mating patterns in remnant tree populations are expected to shift towards increased inbreeding and reduced pollen diversity, with fitness consequences for future generations. However, mating patterns and phenotypic assessments of open-pollinated progeny have rarely been combined in a single study. Here, we collected seeds from 37 Eucalyptus incrassata trees from contrasting stand densities following recent clearance in a single South Australian population (intact woodland=12.6 trees ha⁻¹; isolated pasture=1.7 trees ha⁻¹; population area=10 km²). 649 progeny from these trees were genotyped at eight microsatellite loci. We estimated genetic diversity, spatial genetic structure, indirect contemporary pollen flow and mating patterns for adults older than the clearance events and open-pollinated progeny sired post-clearance. A proxy of early stage progeny viability was assessed in a common garden experiment. Density had no impact on mating patterns, adult and progeny genetic diversity or progeny growth, but was associated with increased mean pollen dispersal. Weak spatial genetic structure among adults suggests high historical gene flow. We observed preliminary evidence for inbreeding depression related to stress caused by fungal infection, but which was not associated with density. Higher observed heterozygosities in adults compared with progeny may relate to weak selection on progeny and lifetime-accumulated mortality of inbred adults. E. incrassata appears to be resistant to the negative mating pattern and fitness changes expected within fragmented landscapes. This pattern is likely explained by strong outcrossing and regular long-distance pollen flow.     

Flora and fauna assemblages vary with local topography in a subtropical eucalypt forest

Local‐scale spatial patterning (over hundreds of metres) in terrestrial assemblages was investigated by sampling a variety of organisms within a 400 ha eucalypt forest area in the lowlands of south‐east Queensland. Organisms were trees, shrubs, birds, insects extracted from the litter layer, and insects caught in pitfall traps. Each group was sampled using a standardized methodology, and the component taxa were counted and identified to a level commonly used in ecological studies of that organism – varying from species to order levels. Sites adjacent to drainage lines or ephemeral streams were biotically more similar to one another than they were to paired upslope sites 100–200 m distant and 15–35 m higher in altitude. This phenomenon occurred irrespective of the level of taxonomic resolution or type of organism. Within each taxonomic group, some components were mainly riparian, while others were more characteristic of upslope sites. Characteristically riparian taxa included trees in the genus Glochidion, the shrub genus Leptospermum, birds in the Pachycephalidae and Meliphagidae families, and litter invertebrates in the order Acarina. Upslope taxa included shrubs in the Rutaceae, birds in the Artamidae, and ants. Within the groups of trees, birds and litter invertebrates, more taxa were characteristic of riparian than upslope sites. Local scale biotic patterns were more strongly correlated with altitude than with measured soil characteristics; however, microtopographical differences would also be highly correlated with a large suite of covarying environmental features. The patterns of diversity and the implications for survey design and conservation are discussed.     

Spatial variation of soil properties and plant colonisation on cut slopes: a case study in the semi-tropical hilly areas of China

Background: Transport infrastructure has severe impacts on ecosystems and results in large numbers of cut slopes, which are difficult to revegetate. To increase successful revegetation, it is crucial to understand the relationships of soil properties and vegetation during spontaneous vegetation recovery on cut slopes.

Aims: To assess the effects of different slope positions on soil properties and vegetation on a cut slope and to determine the key factor(s) affecting vegetation distribution on a cut slope in a semi-tropical environment.

Methods: Soil samples were collected in three slope positions: upper slope (US), middle slope (MS) and foot slope (FS). Soil pH, moisture and bulk density and concentrations of soil organic carbon (C), total nitrogen (N_T), available nitrogen (N_A), total phosphorus (P_T), available phosphorus (P_A), total potassium (K_T) and available potassium (K_A) were determined. Vegetation composition and cover were recorded along the slope. One-way analysis of variance (ANOVA), indicator species analysis (ISA) and detrended canonical correspondence analysis (DCCA) were applied to analyse differences in soil properties among slope positions and vegetation distributions.

Results: N_T, N_A, P_T, P_A, K_A, C and pH tended to increase from the US to the FS. Two indicator species were abundant in their respective slope positions: Achyranthes bidentata in the FS and Dicranopteris dichotoma in the US. DCCA showed that pH and some soil nutrients (N_A, P_T, P_A and C) influenced the vegetation distribution on cut slope.

Conclusions: Soil pH and some soil nutrients including N_A, P_T, P_A and C had large impacts on vegetation distribution along slope positions in a semi-tropical area of China. We suggest increasing soil pH to provide a better soil environment for plant colonisation in further research concerning the restoration of such cut slopes.     

Altitudinal variation in flowering area and position and their ecological significances of an alpine cushion Arenaria polytrichoides,a gynodioecious herb

Aims As foundation species in the alpine ecosystems, the reproduction and recruitment of alpine cushion plants are very important for sustaining the alpine ecosystem functions. However, it still remains unclear that how cushion plants effectively allocate resources to optimize reproductive fitness.Methods Here we selected five populations of a gynodioecious herb Arenaria polytrichoides with different exposures and slopes along an altitudinal gradient on the Baima snow mountain in northwest Yunnan, southwest China, to investigate and compare flowering area and positions, within and among populations and between female and hermaphroditic morphs. By doing so, we further discuss how the environmental stresses affect the cushion’s flowering attributes thus the population-level reproduction.Important findings The results showed that, individual plant size and resources allocated to flowering (flowering area %) both decreased with increasing elevation, indicating that the reproductive allocation strategy was significantly affected by elevation. However, a population at lower elevation showed lower reproductive investment than higher populations, suggesting that elevation was not the only factor affecting the cushion’s reproductive allocation. In addition, absolute flowering area increased with increasing individual size, but the flowering area ratio decreased, indicating that the increases in reproductive allocation are fewer than that in vegetative allocation. Hermaphroditic individuals invested more resources to flowering than females did, but again, such effect was affected by elevation. Moreover, within a single population, the flowering areas were significantly different among the four directions (east, south, west and north) within one single individual canopy, but such differences varied in different populations.     

高山垫状植物团状福禄草开花面积与方位随海拔的变化及其适应性

作为高山生态系统中的奠基种(foundation species), 垫状植物自身种群的繁殖与扩张, 对高山生态系统功能稳定性起着关键作用。但是, 垫状植物如何在极端环境条件下实现资源的有效利用与分配, 达到繁殖最优化, 至今鲜为人知。该研究在滇西北白马雪山沿海拔梯度选择具有不同坡度及坡向的5个团状福禄草(Arenaria polytrichoides)种群, 调查、比较种群内、种群间以及具有不同性系统的植株个体之间的开花面积比、开花方位, 并分析不同生态因子对其开花特性的影响。结果表明: 随着海拔的升高, 团状福禄草个体变小, 其分配到开花的资源比例总体上随海拔上升呈现下降的趋势, 说明团状福禄草的繁殖分配受到由海拔所引起的生态因子的调控。但是, 部分低海拔种群内植物个体的繁殖分配显著低于部分高海拔种群, 说明海拔并非控制植物繁殖分配的唯一因素。此外, 植株开花总面积随植株个体增大而增加, 但开花面积比却随个体增大而变小, 说明植株分配到开花的资源增长速率可能低于植株个体的增长速率。在性别差异方面, 两性植株对开花的资源分配比例要显著高于雌性植株, 但是, 其差异程度受到海拔因素的影响。最后, 在同一种群内, 团状福禄草在冠层表面不同方位上的开花面积比存在显著差异性, 这种差异性在不同种群之间又具有不同的表现形式。     

Cell wall invertase expression at the apical meristem alters floral, architectural, and reproductive traits in Arabidopsis thaliana

Resource allocation is a major determinant of plant fitness and is influenced by external as well as internal stimuli. We have investigated the effect of cell wall invertase activity on the transition from vegetative to reproductive growth, inflorescence architecture, and reproductive output, i.e. seed production, in the model plant Arabidopsis thaliana by expressing a cell wall invertase under a meristem-specific promoter. Increased cell wall invertase activity causes accelerated flowering and an increase in seed yield by nearly 30%. This increase is caused by an elevation of the number of siliques, which results from enhanced branching of the inflorescence. On the contrary, as cytosolic enzyme, the invertase causes delayed flowering, reduced seed yield, and branching. This demonstrates that invertases not only are important in determining sink strength of storage organs but also play a role in regulating developmental processes.     

Diversity of climbing seed plants and their reproductive habit in a karst seasonal rain forest in Nonggang,Guangxi, China

Aims Diversity of climbing seed plants and their reproductive habits and characteristics are central for the understanding of community structure and dynamics of forests and hence are important for forest protection. However, little is known about the climbing seed plants in northern tropical karst seasonal rain forests. Here, using the data of the species diversity and reproductive habits of climbing seed plants in Nonggang, Guangxi, China, we aim to 1) explore the species diversity and distribution of climbing seed plants in northern tropical karst seasonal rain forests, 2) study the flowering and fruiting phenology and 3) the associations of reproductive characteristics to the environment. Methods Species composition, preferred habitat, flowering time, fruiting time and fruit types of climbing seed plants were surveyed. The seasonality of flowering and fruiting were analyzed by concentration ratio and circular distribution. Climbing seed plants were divided into three groups according to their growth forms and places in spatial forest structure: bush ropes, herbaceous vines and lianas. Monthly flowering ratios, fruiting ratios, fruit types and their ratios in different groups were determined. These relationships of flowering ratio, fruiting ratio, fruit type and its ratio to meteorological factors were investigated using Pearson correlation analysis. Important findings There were a total of 333 species of climbing seed plants in Nonggang karst seasonal rain forest, belonging to 145 genera and 56 families. Bush ropes, herbaceous vines and lianas contained 119, 88 and 126 species, respectively. At species level, herbaceous vines were more abundance in valleys, while bush ropes and lianas were more abundance on slopes. Flowering and fruiting of climbing seed plants occurred seasonally, with flowering peaking in April to September, while fruiting peaking in July to December. The seasonality of flowering and fruiting in bush ropes was weaker than in herbaceous vines and lianas. Flowering ratio was significantly positively correlated with rainfall and air temperature, which suggest that flowering peaks in monsoon season. Peak time for fruiting was about three months later than the peak time of flowering, around the end of monsoon season. The ratio of samara species to all fruiting species in lianas was significantly positively correlated with wind speed, but negatively correlated with rainfall and air temperature. It showed that samara in lianas tended to occur in dry season with high wind speed. In conclusion, species diversity and the seasonal features of reproduction of climbing seed plants in Nonggang karst seasonal rain forest were closely related to the spatial and temporal variations of habitat resources.