Species Composition Of Seedlings Research Articles

Effects of subtle variation in forest canopy openness on cache pilferage and its implications for forest regeneration.

Scatter-hoarding rodents play important roles in plant regeneration and species coexistence in many forest ecosystems. Cache pilferage, the behavior of rodents seeking or relocating seeds cached by other individuals, is ubiquitous during the scatter-hoarding process. The effects of canopy openness on cache pilferage have received considerable attention, most of which have focused on the comparison between full canopy cover and completely open areas, such as forest gaps. However, little attention has been given to whether the subtle variation in forest canopy openness affects cache pilferage, although subtle variation in light environments exists in many forests, especially tropical and subtropical forests, where the overall canopy is large and the forest window is relatively small. Here, we directly tested these questions by simulating 400 artificial caches, each containing one seed from four selected tree species, in a subtropical forest in southwestern China. The overall canopy openness of the forest was relatively small (with a mean value of 11.1%), but subtle spatial variation still existed (ranging from 5.7% to 19.5%). Overall, caches with lower canopy openness were more likely to be pilfered and removed faster, although not all species showed the same pattern. Our study highlights that subtle variation in forest canopy openness, even in a closed primary forest, has significant effects on cache pilferage by rodents, which may influence the following seed germination and forest regeneration processes. Additionally, seedling species composition may further be altered because the canopy effects on cache pilferage are species-specific.

The potential of hay for graminoid introduction in the restoration of subtropical grasslands: Results from a greenhouse experiment

IntroductionSubtropical grasslands have been severely impacted. Due to their low resilience after degradation, active restoration is necessary; however, knowledge still is incipient. Hay transfer is a successfully employed technique to restore other grassland ecosystems and its use is promising in subtropical grasslands. We evaluated the potential of hay transfer for the restoration of the subtropical grasslands in Southern Brazil by assessing the effects of (1) the date of hay harvest and (2) the amount of dry hay used. MethodsIn two protected areas in South Brazilian grasslands, we harvested hay on three dates (mid-Spring, early-Summer, and mid-Summer) and placed it into a greenhouse for seeds in the hay to germinate. Two different amounts of dry hay (375 g/m² and 750 g/m²) were used for each date. We assessed the number of emerging seedlings, species richness, and seedling species composition in each treatment, separately for each site. Emerging forbs were identified as soil seed bank contamination, and only data for graminoids (grasses and sedges) are presented. ResultsThe number of seedlings varied among harvest dates, with mid-Spring and early-Summer resulting in more emergencies in both sites. No common pattern to both sites regarding the effect of the amount of dry hay on seedling emergence was found for the two sites, but interaction with the harvest date is important. Species composition and richness also varied across harvest dates, and, independent of the donor site, more hay resulted in more species. Nevertheless, few species were transferred overall. ConclusionsHay transfer has the potential to introduce seeds of graminoids and appears to be a promising tool for the restoration of South Brazilian grasslands. There is not a single optimal time for hay harvest nor a pattern regarding hay amount. Few species are established from hay and more than one harvest should be done to increase species richness.

Woody seedling community responses to deer herbivory, introduced shrubs, and ash mortality depend on canopy competition and site wetness

Emerald ash borer (EAB) (Agrilus planipennis), non-native shrubs, and white-tailed deer (Odocoileus virginianus) have been independently shown to affect woody seedling communities. Our objective was to determine the relative importance as well as additive and interactive-effects of these stressors in the context of two environmental factors, canopy tree competition and site wetness. We sampled 24 sites, representing three natural non-congruent gradients in ash mortality, deer browse, and introduced shrub invasion. We explored the responses of seedling species abundance, diversity and richness to an array of deer herbivory, ash mortality, and introduced shrubs and varying levels of canopy tree competition, site wetness. The effects of each stressor on the differences in the relative abundance of seedling species was also evaluated. Our results indicate a persistent negative effect of non-native shrubs in drier forest plots on native seedling abundance, richness, and diversity. In wetter forests, non-native shrubs had no effect on native seedling richness or abundance and were positively related to diversity. Deer browse had a negative effect on seedling diversity in wetter forests and no effect in drier forests. Canopy tree competition had a positive effect on seedling diversity in drier forest plots, but negatively affected diversity in wetter forest plots. Ordination analysis revealed that site wetness, non-native shrubs and the total basal area of trees in the stand had the largest impacts on the species composition of seedlings found at each site. Our results suggest that site wetness and chronic stressors like deer and introduced shrubs are interacting to shift seedling communities towards fewer native species as well as to reduce seedling species richness and diversity.

Abandoned Wood Ant Nests as Sites for Seedling Germination

We compared the species composition of seedlings germinated on ten recently abandoned Formica polyctena nests with the plant species on active nests and the plant species composition of the forest floor around the nests. Compared to no plants at all, when the nests were inhabited, seedlings of 12 different vascular plant species germinated on the nests after their abandonment. Four of them were myrmecochorous, of which two occurred only on the nests. After abandonment, ant activity ceases, the water content of the nests increases, and decomposition of the organic nest material is accelerated, resulting in faster nutrient mineralization. Consequently, more nutrients are available for plants. Our results suggest that abandoned nests can serve as “regeneration niches”, ensuring genetic diversity, especially in plant populations which rely mainly on vegetative propagation. However, more research on a larger scale is needed to assess the role of wood ants and their abandoned nests in forest vegetation development.

Little trace of floristic homogenization in peri‐urban Andean secondary forests despite high anthropogenic transformation

Abstract Pervasive human impact in heavily transformed landscapes may lead disturbance‐adapted species to thrive, resulting in floristic homogenization across forest stands. However, environmental heterogeneity and dispersal limitation may be antagonistic forces to homogenization, maintaining inherent floristic differentiation across sites. We evaluated the extent to which peri‐urban Andean forests are undergoing floristic homogenization in both late‐ and early‐successional stands. We considered seedling assemblages as well, as they provide key insights into forests’ future. We then quantified the relative importance of dispersal limitation and environmental filtering in determining the observed patterns of floristic similarity across the landscape. We used tree, seedling, soil and climatic data from six sites located in the high plain where Bogotá lies (Colombia). Within each site, we established six 20 × 20 m plots, three in early‐successional stands and three in late‐successional stands, for a total of 36 plots. To evaluate the extent of floristic homogenization, we defined tree floristic similarity among late‐successional stands as a baseline, reflecting our best‐guess of the original species composition that would have once occurred previous to intense anthropogenic intervention. Tree floristic turnover across the landscape was alike in late‐ and in early‐secondary stands, a finding that does not support the homogenization scenario. Seedling species composition, in contrast, was more homogeneous among early‐ than among late‐secondary stands, an outcome suggestive of homogenization. The relative importance of spatial and environmental drivers shifted between life stages. Distance between plots was the best predictor of tree species dissimilarity (29% of variance explained), whereas seedling compositional variation was more sensitive to changes in environmental conditions (41% of the variance explained). Relative humidity and several variables related to soil fertility showed a significant effect on floristic dissimilarity across the landscape, although significant factors were often different between life stages. Synthesis. Despite high anthropogenic transformation, we found little trace of floristic homogenization in these peri‐urban landscapes. Inherent floristic differentiation, promoted both by dispersal limitation and environmental heterogeneity, suggests that all patches are important to the conservation in these Andean forests, critical centres of endemism.

A model evaluation framework applied to the Forest Vegetation Simulator (FVS) in Colorado and Wyoming lodgepole pine forests

The Forest Vegetation Simulator (FVS) growth and yield model is widely used throughout the United States, but recent studies have reported unexpectedly large bias for some regional model variants. Here we propose a general framework for model evaluation, designed to highlight model strengths and weaknesses and inform calibration efforts. We apply the framework to evaluate the Lodgepole Pine (LP) model of the FVS Central Rockies Variant (FVS-CR), which has rarely been evaluated in the literature despite its widespread use in the western US. We started with a qualitative verification of the structure and logic of the FVS-CR LP model against a modified Bakuzis matrix, determining that it adequately reproduces known patterns of stand dynamics. We then compared stand-level growth simulations to a chronosequence developed from 554 Forest Inventory and Analysis (FIA) plots measured in Colorado and Wyoming lodgepole pine forests. This quantitative validation exercise revealed that the default model settings substantially over-predict basal area and total stand carbon after 50 years for both pure lodgepole pine stands and mixed lodgepole pine stands containing a minor proportion of Engelmann spruce, subalpine fir, and quaking aspen. Using equivalence testing to validate the large-tree diameter increment model against a separate dataset of 3,790 remeasured trees on 124 lodgepole pine FIA plots, we found that the default FVS–CR LP model adequately predicts lodgepole diameter growth, though we observed large variation in model errors. Equivalence tests also revealed systematic under-estimation of spruce–fir and over-estimation of aspen productivity. Finally, we conducted a sensitivity analysis to identify the most important model parameters and data inputs driving simulated stand structure and carbon accumulation in both the short- (50 years) and long-term (200 years). The model shows the greatest sensitivity to initial species composition; a small proportion of aspen, spruce, or fir seedlings led to long-term stand re-structuring and greatly increased carbon accumulation. Other sensitive parameters included site index, the fixed large-tree diameter increment adjustment factor, and the parameter controlling the point at which density-dependent self-thinning begins (maximum stand density index). This evaluation leads us to conclude that the FVS-CR LP model tends to under-estimate tree mortality (particularly in young stands) and the default site index represents relatively high productivity stands, such that re-calibration may often be necessary to capture realistic long-term stand behaviors. Our sensitivity analysis provides guidance for future efforts to re-calibrate the FVS-CR LP model and highlights the importance of collecting site index and seedling species composition data wherever possible to produce the most realistic simulations.

Endozoochorous seed dispersal by free-ranging herbivores in an abandoned landscape

Seed dispersal is a crucial process for the dynamics and maintenance of plant populations. Free-ranging animals are effective dispersal vectors because they can move between similar habitats and transport seeds into favourable environments. Dung samples from two species of common free-ranging mammals—deer and wild boar—were used to study endozoochorous dispersal of seeds in a military training area in western Bohemia. The area was abandoned after WWII, and the military training area was established in 1953. The vegetation consists of shrublands and dry grasslands. Data on the local species pool of grassland herbs and forbs were collected to compare the characteristics of dispersed versus non-dispersed plants. Deer and wild boar dispersed 84 plant species; however, species composition of seedlings emerging from dung samples showed significant differences between dispersal vectors and notable change across the growing season. 80% of all seedlings extracted from the dung samples belonged to stinging nettle, Urtica dioica. From trait analyses, seeds of endozoochorous plants had a higher longevity index in the soil seed bank than non-endozoochorous plants and more often possessed a mucilaginous surface. Our results show that deer and boar are successful, though not substitutable dispersers.

Variant responses of tree seedling to seasonal drought stress along an elevational transect in tropical montane forests

Seasonal drought is a common phenomenon in many forests predominated by monsoon climate. The impact of seasonal drought, however, may vary with elevations, and tree species of forests hence may differ in their response to elevations. In this study, we monitored the seasonal variation of seedling species composition, and their relative growth rate (RGR) along an elevational transect in tropical forests of southwest China for two years. We found tree seedling species richness declined with rising elevation. Seedling abundance and species richness increased significantly from dry season to rainy season. In dry season, RGR declined progressively from low to high elevational bands, while positive RGR occurred in each elevation in rainy season. We grouped seedling species into low and high elevation specialists based on their elevational distributions. Seasonal variance in soil moisture may lead to seasonal dynamics of seedling community in this area. Our results suggest that the observed change in local climate over the last 40 years tends to allow the tree species from high elevation to expand their distribution to the lower elevation, while the ranges of those at low elevations could be compressed or at the risk of extinction.

Changes in biotic and abiotic drivers of seedling species composition during forest recovery following shifting cultivation on Hainan Island, China

AbstractSeedlings play an important role in the processes of plant community succession. We compared seedling (dbh < 1 cm) species composition and diversity over a chronosequence (18‐, 30‐, 60‐year‐old second growth and old growth forest) after shifting cultivation in a tropical lowland rain forest area on Hainan Island, China. Seedling diversity reached a maximum in the 60‐year‐old second growth forest, which is consistent with the intermediate disturbance hypothesis. With the progression of secondary succession, canopy openness (CO), soil organic matter, soil phosphorus content, and tree abundance showed a general decreasing trend; soil water content and tree basal area showed a general trend of increase, while soil pH and other nutrients reached maximum values and tree richness reached a minimum value at intermediate stages of succession. Seedling composition and diversity were significantly affected by soil water, pH, soil nutrient content, and biotic factors in the 18‐year‐old second growth forests; by soil pH, soil nutrient content, and biotic factors in the 30‐year‐old second growth forests; by CO, soil nutrient content and tree abundance in the 60‐year‐old second growth forests; and by CO, soil pH, and soil nutrient content in the old growth forests. At earlier stages of succession, the effect of the proportion of old growth forest in the surrounding landscape on seedling diversity was greater than that of land‐use history, but the importance of these drivers was reversed at later stages of succession.

Experimental simulation of pollinator decline causes community-wide reductions in seedling diversity and abundance.

Pollinator decline can disrupt the mutualistic interactions between plants and pollinators and potentially affect the maintenance of plant populations. However, there is still little knowledge on how changes in pollinator abundance can affect seedling recruitment, which is essential for population persistence. We experimentally simulated a community-wide reduction in pollinator availability during four years to examine its effects on seedling recruitment in 10 perennial herbs in a Norwegian hay meadow. Our experimental reduction in pollinator availability significantly reduced community-wide seedling diversity. Overall seedling abundance was also consistently lower under reduced pollinator availability, although this effect was only significant when the most abundant plant species in the community was excluded from the analysis. Despite an overall negative effect on seedling abundance, the experimental reduction in pollinator availability had contrasting effects on individual plant species. This tended to cause a larger change in seedling species composition in the experimental than in the control plots after the four study years. Our study demonstrates for the first time a direct causal link between reduced pollinator availability and reduced plant diversity and abundance.

Plant diversity and regeneration in a disturbed isolated dry Afromontane forest in northern Ethiopia

We studied the diversity, community composition and natural regeneration of woody species in an isolated but relatively large (> 1,000 ha) dry Afromontane forest in northern Ethiopia to assess its importance for regional forest biodiversity conservation. The principal human-induced disturbance regimes affecting this forest include logging and livestock grazing. Vegetation data were collected in 65 plots (50 m × 50 m); seedling species composition and density were determined in 10 m × 10 m nested plots. We used a cluster analysis to identify plant communities and non-metric multidimensional scaling (NMDS) ordination to investigate environmental factors that influenced the distribution of the emergent plant communities. Three plant communities were identified: a Juniperus procera-Maytenus senegalensis community, which represented a phase of the potential natural dry Afromontane forest vegetation on steep slopes with shallow soils, a Pterolobium stellatum-Celtis africana community, found on more mesic sites, and a Cadia purpurea-Opuntia ficus-indica community, typically representing severely disturbed habitats. Altitude, slope, soil depth and distance to the nearest stream, which we collectively interpreted as a moisture gradient, and forest disturbance separated the plant communities. With only 39 of the 79 recorded woody species present in the seedling layer, the forest currently faces an extinction debt of 50 per cent of the total woody species pool. Human disturbance has clearly affected plant species diversity in this forest as degraded plant communities typically lacked the commercially interesting or otherwise valuable tree species, were encroached by shrubs and in areas severely invaded by alien species. Further disturbance will most likely result in additional declines in biodiversity through local extinction of indigenous tree species. Despite the problems associated with conserving plant species diversity in small and isolated populations, this relic forest is of particular importance for regional conservation of forest biodiversity, as species with high conservation value, such as Afrocarpus falcatus, Allophylus abyssinicus and Bersama abyssinica, are still present as mature trees, and as other forest fragments in the region are two orders of magnitude smaller, and therefore more heavily impacted by small population sizes and unfavourable edge effects. Forest management should focus on avoiding further degradation, increasing natural regeneration and improving stakeholder participation.

Soil degradation and feedback processes affect long‐term recovery of tropical secondary forests

AbstractQuestionsWhat processes govern the long‐term recovery of tropical secondary forests? Specifically, how are seedling species density, stem density and functional groups in older regenerating forests affected by existing trees, the regeneration environment and distance to seed sources?LocationCentral Catchment Nature Reserve, Singapore.MethodsWe investigated three primary forest plots and nine 60‐yr‐old secondary forest plots varying in their degree of recovery. We analysed seedling parameters as a function of the abiotic and biotic regeneration environment as well as distance to primary and mature secondary forests.ResultsThe secondary forest plots had functional composition distinct from, and Chao‐estimated species richness and stem density lower than the primary forest plots. Seedling communities were most strongly associated with the mature tree communities within each plot; associations with other intra‐plot variables and distance to potential seed sources were lower but still highly significant. Overall, aside from the mature tree community, the most significant predictors of seedling species composition were fern cover, VPD, soil Al, available P and C:N ratio. Primary forest species were associated with low light environments, low macronutrients and low Al saturation. Secondary forest species were associated with high P, low soil pH and low total exchangeable bases. Long‐lived pioneers differed from short‐lived pioneers in their association with high soil C:N ratio, low Al saturation, low P and tolerance of a wider light range. Overall, improved seedling recruitment was associated with decreasing fern cover, thinner layer of leaf litter and higher light. At the landscape level, species density was inversely related to distance to potential seed sources.ConclusionsOur findings suggest that historical soil degradation and subsequent feedback processes among the adult trees, seedling communities and the regeneration environment strongly affect forest succession. Nutrient‐efficient and Al‐tolerant pioneers, such as the fern Dicranopteris linearis, were probably initial colonizers. Chance dispersal and recovery of the regeneration environment subsequently affected the establishment of long‐lived or short‐lived pioneers. Persistence of D. linearis and long‐lived pioneers slowed forest recovery, while short‐lived pioneers improved nutrient recovery and ameliorated the above‐ground conditions to facilitate subsequent succession, provided that seeds of primary forest species were present.

Composition and temporal dynamics of tree seedlings at different successional stages of conifer and broad-leaved mixed forests in Jiaohe, Jilin Province, China

Aims Our objective was to explore the composition and temporal dynamics of woody plant seedlings and the ecological processes that affect the amount of seedlings in Jiaohe, Jilin Province, China. Methods We established a total of 415 seed-seedling census stations in three large permanent field plots belong- ing to three successional stages in the conifer and broad-leaved mixed forests. Based on three seedling censuses from 2012 to 2014, we analyzed species composition, quantitative character, height-classes structure and their inter-annual dynamics. Multiple linear regression was used to test the relationship between the abundance of seed- lings for five major species and the forest types, the sum of the basal area of conspecific adult within 20 m away from a seed trap, as well as canopy openness. Important findings Our results show that: (1) The species composition of seedlings slightly varied among dif- ferent successional stages, and was similar with that of trees in the plots. The rank of important values for seedling species among different years and successional stages varied slightly. (2) The number of seedlings and seedling species distributed mainly between 5-20 cm height classes, and decreased with the increasing height class. The number of seedlings decreased faster than that of seedling species, indicating that compared with interspecific competition, intraspecific competition was the main driver that led to seedling death. It confirmed the role of the negative density dependence in affecting seedling regeneration. (3) The amount of seedlings for all of the five major species was significantly positively related to the sum of the basal area of conspecific adults, which indicated that the quantity and distribution of seedlings were affected by dispersal limitation as well as niche

Tree community reassembly after selective and clear-cut logging in an Afro-tropical rainforest

Understanding the process of community reassembly is crucial for the conservation of biodiversity and rehabilitation of ecosystems. This study tested whether tree communities in logged forests follow an equilibrium (deterministic) or non-equilibrium (stochastic) model of succession. We assessed reassembly of tree communities in different size classes along a successional gradient consisting of nine differently aged successional forests, namely, four regenerating former clear-cuts (9–19 years), three selectively logged (42–43 years) and two primary forests (PFs) in Kibale National Park, Uganda. The results show that the forests are converging and undergoing reassembly towards PFs. The species composition of seedlings, saplings and poles declined in similarity to the PF with age but that of mature trees in the different successional stages increased towards the PFs. These differences in tree species composition among the different size classes might be due to dominance of some particular species. Recovery of tree species density, diversity and dominance in all the size classes showed directional patterns as predicted by the deterministic model of succession. Compared to other variables, tree species density and diversity in selectively logged forests recovered relatively faster and was equivalent to or higher than that of PFs at 43 years. The results of the present study indicate that community reassembly in smaller sized trees followed a stochastic model of succession. However, as trees matured, they conform to the deterministic model of succession.

Effects of Fire on Seedling Diversity and Plant Reproduction (Sexual vs. Vegetative) in Neotropical Savannas Differing in Tree Density

AbstractLittle is known about the effects of fire on the structure and species composition of Neotropical savanna seedling communities. Such effects are critical for predicting long‐term changes in plant distribution patterns in these ecosystems. We quantified richness and density of seedlings within 144 plots of 1 m2 located along a topographic gradient in long‐unburned (fire protected since 1983) and recently burned (September 2005) savannas in Brazil. These savannas differ in tree density and canopy cover. Sites along the gradient, however, did not differ in species composition prior to the fire. In recently burned savannas we also evaluated the contribution of vegetative reproduction relative to sexual reproduction by quantifying richness and density of root suckers. Finally, we tested seed tolerance to pulses of high temperatures—similar to those occurring during fires on the soil surface and below—of five dominant savanna tree species. Seedlings were more abundant and diverse in unburned than in burned savannas. Seedling species composition differed among unburned and burned savannas probably reflecting early differences in root: shoot biomass allocation patterns. In recently burned savannas, root suckers were more abundant and diverse than seedlings. Relatively long exposures (>10 min) of temperatures of 90 °C reduced seed germination in all studied species suggesting a negative effect of fire on germination of seeds located at or aboveground level. Because vegetative reproduction contributes more than sexual reproduction in burned environments, frequent fires are likely to cause major shifts in species composition of Neotropical savanna plant communities, favoring clonally produced recruits along tree density/topographic gradients.

Pathogens and insect herbivores drive rainforest plant diversity and composition

Tropical forests are important reservoirs of biodiversity, but the processes that maintain this diversity remain poorly understood. The Janzen-Connell hypothesis suggests that specialized natural enemies such as insect herbivores and fungal pathogens maintain high diversity by elevating mortality when plant species occur at high density (negative density dependence; NDD). NDD has been detected widely in tropical forests, but the prediction that NDD caused by insects and pathogens has a community-wide role in maintaining tropical plant diversity remains untested. We show experimentally that changes in plant diversity and species composition are caused by fungal pathogens and insect herbivores. Effective plant species richness increased across the seed-to-seedling transition, corresponding to large changes in species composition. Treating seeds and young seedlings with fungicides significantly reduced the diversity of the seedling assemblage, consistent with the Janzen-Connell hypothesis. Although suppressing insect herbivores using insecticides did not alter species diversity, it greatly increased seedling recruitment and caused a marked shift in seedling species composition. Overall, seedling recruitment was significantly reduced at high conspecific seed densities and this NDD was greatest for the species that were most abundant as seeds. Suppressing fungi reduced the negative effects of density on recruitment, confirming that the diversity-enhancing effect of fungi is mediated by NDD. Our study provides an overall test of the Janzen-Connell hypothesis and demonstrates the crucial role that insects and pathogens have both in structuring tropical plant communities and in maintaining their remarkable diversity.

Recruitment and functionality traits as bioindicators of ecological restoration success in the Lurg Hills district, Victoria, Australia

Abstract Introduction The Regent Honeyeater Project commenced ecological restoration in the Lurg district in 1994, with an aim to restore habitats for the critically endangered Regent Honeyeater Anthochaera phrygia and a range of other threatened and declining species. Within this context, our study aimed to explore whether plant reproduction can be an effective measure of ecological restoration success. Methods Evaluation involved comparing attributes at unrestored, restored and remnant sites to establish whether sites displayed evidence of a clear restoration trajectory. Five age classes (unrestored, 4–6 years old, 8–10 years old, 12–14 years old and remnant areas) and two landforms (upper hills and lower hills) were considered. The diversity of woody plant species—which have easily recognisable reproductive material and which all recruit seedlings—provides easily measured parameters that have the potential to allow the determination of early establishment success and long-term ecological development of restored ecosystems. Results Restoration plantings developed in a hybrid state towards a benchmark in the lower hills; seedling species composition differed significantly among age classes, increasing in similarity with time since restoration, with some divergence from the target pathway. Composition of functional groups with reproductive outputs was also significantly different among age classes; however, a restoration trajectory was only evident in the upper hills where sites converged towards the target goal. Conclusions Divergence or deviation from the restoration trajectory was not deemed to be a restoration failure, as the variety of functional groups with fruits and diversity of seedlings recruiting indicated a potential increase in resilience in the future due to greater variability across the landscape. Plant recruitment was effective in detecting development trends towards a restoration target in this study and therefore may be a useful measure that contributes to determining ecological restoration success.

Community assembly during recovery of tropical lowland rain forest from abandoned shift-ing cultivation lands on Hainan Island, China

Aims A major challenge in studies of tropical forest successional dynamics is to reveal the relative importance of deterministic versus stochastic processes affecting species composition, spatial distributions and their rates of change. Here, we tested succession trajectory of tropical secondary forests follow equilibrium or non-equilibrium dynamics by evaluating community reassembly for tropical lowland rainforest recovery on the abandoned shifting cultivation lands on Hainan Island of south China. Methods We explored species composition and dominance of different size classes (seedlings, saplings and adult trees) of communities along a chronosequence of secondary forest plots ranging from 15 to 60 years since abandonment after shifting cultivation. We included two old-growth forest plots for comparison. Important findings Both species diversity for the three size classes and the species similarity index among size classes in old-growth forests were significantly higher than in secondary forests. However, the proportion of dominant species in old-growth community was lower than that of secondary forests. Species similarity between secondary forests and old-growth forests increased with forest recovery, supporting the view of equilibrium succession dynamics. In each recovery stage, the number of individuals, species richness and abundance-based coverage estimator of seedlings were lower than those of both saplings and adult trees. Moreover, the species composition of seedlings in secondary forests differed significantly from that of both saplings and adult trees, suggesting that seedling recruitment might be an unpredictable process. Our results highlighted that the community assembly processes during secondary forest recovery are driven simultaneously by stochastic and deterministic processes.

Canopy gaps and tree regeneration patterns in multi-species unmanaged natural forest Sitno (preliminary results)

The study of canopy gaps structure and tree regeneration patterns was conducted in mixed old-growth forest Sitno. We asked the following questions: What is the spatial scale of disturbance events? How does gap size affect the density of tree seedlings and saplings? Are there any differences in species composition of seedlings and saplings between the closed canopy and expanded gap? The research was conducted on a 2.5-ha (250 × 100 m) research plot. In total, 25 canopy openings were recorded. Canopy gaps and expanded gaps covered 22.8 % and 59.5 % of the research area. The most frequent were canopy gaps with the size up to 300 m2(64 %). Regarding the number of gapmakers, we recorded a quite large variability with the highest frequency of the gaps with 1 and 4 gapmakers. Regeneration structure (density and frequency) was sampled in 3.14 m2circular plot (n = 216) established on the grid intersections (10 × 10 m). A total of 8 tree species were identified in natural regeneration. The difference between overall density of natural regeneration under closed canopy and in expanded gaps was observed. The density of all tree species seedlings (except ofCarpinus betulus) was higher under closed canopy than in expanded gaps. The most frequent were seedlings ofAcer pseudoplatanusandAcer platanoideswhich occurred on 80 % and 73 % of the plots under closed canopy, and 75 % and 68 % of the plots in expanded gaps. Seedlings ofQuercus petraeawere not recorded. Density of saplings was higher in expanded gaps than under canopy (except of saplings ofAcer platanoidesandTilia cordata). The density of saplings ofAcer pseudoplatanusandAcer platanoidesincreased with increasing size of expanded gap, whileFraxinus excelsiorsaplings density decreased. There was no significant relationship between density of other species seedlings and saplings and expanded gap size.

漫溢干扰过程中微地形对幼苗定居的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 漫溢干扰过程中微地形对幼苗定居的影响 DOI: 10.5846/stxb201105170646 作者: 作者单位: 中国科学院 新疆生态与地理研究所,中国科学院 新疆生态与地理研究所,新疆师范大学地理科学与旅游学院,新疆师范大学地理科学与旅游学院,新疆师范大学地理科学与旅游学院,中国科学院 新疆生态与地理研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(30970549,40971284);自治区高校青年教师培育基金项目(XJEDU2008S41) Effects of the microhabitats on the seedling emergence during the flooding disturbance Author: Affiliation: Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences,Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences,Geography Science and Tourism Department of Xinjiang National University,Geography Science and Tourism Department of Xinjiang National University,Geography Science and Tourism Department of Xinjiang National University,Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:通过对比漫溢干扰后边坡、坡中和坡底幼苗的物种组成、密度、幼苗周边的环境条件及土壤种子库的差异来分析漫溢干扰过程中,微地形对幼苗定居的影响。结果表明:(1)微地形对幼苗物种组成和生物多样性指数的影响很大。漫溢干扰后,位于边坡、坡中和坡底幼苗的Simpson多样性指数和Mcintosh均匀度指数在0.01的水平上差异极显著,Margalef丰富度指数在0.05的水平上差异显著。(2)微地形对土壤盐分含量影响很大。方差分析的结果表明,除HCO3-和K+外,边坡、坡中和坡底的pH值、CO32-、SO42-、Ca2+和Mg2+各指标在0.01的水平上差异极显著;全盐、总盐、Cl-和Na+各指标均在0.05的水平上差异显著。(3)微地形通过改变幼苗定居的环境条件,进而影响幼苗库的物种组成、密度和生物多样性指数。微地形中,幼苗库的各种生态指标均小于对应的土壤种子库的生态指标,从坡底到坡中到边坡,除单位面积上的植被密度外,土壤种子库和幼苗库的各项生态指标的变化趋势均不同。 Abstract:The Tarim River is the longest continental river in China and charactered by its fragile ecosystem in the word. The ecological processes of the Tarim River basin have undergone great changes due to the irrational human activities over the past 50 years, especially in the lower reaches of Tarim River. Therefore, the ecological water conveyance project(EWCP) has been implemented since 2000. The EWCP is an emergency plan for conserving the natural vegetation, controlling the desertification and improving the environment in the lower reaches of Tarim River. It transfers water from the Bosten Lake, to Daxihaizi Reservoir, and finally to Taitema Lake along the water channel. There have been 12 times of watering to the lower Tarim River during the period from 2000 to 2011. After the EWCP,the natural vegetation has obvious response to the water condition change. The studies on the soil seed bank in the region are very important to restoring the degraded ecosystem in lower reaches.Soil seed bank is the potential plant population or plant community. It plays an important role in occurrence, succession, and recovery process of vegetation. The germinated species and germinated seed number in soil seed bank determine the species composition and species number of seedlings in a certain degree. Meanwhile, the topography condition in the study areas is also an important factor on influencing germination ability of soil seed bank. Micro-topography impacts the seedling species composition and distribution pattern through the spatial differences in germination ability of soil seed bank, light, water and salt conditions. This paper takes the EWCP as a case study to analyze the effects of micro-topography on the seedling emergence during the flooding disturbance by the method of variance analysis. The species composition, seedling density, environmental condition and soil seed bank in three micro-topography type of the side slope, hillside and base of slope are compared after river flooding disturbance. The study results revealed that: (1) Species composition and diversity indices of the seedling were significantly influenced by different types of the micro-topography. After overflowing disturbance, Simpson index and Mcintosh index of seedling species in three types of micro-topography are aloes highly significant at the level of 0.01, and Margalef index is significantly different at the level of 0.05.(2) There is also a great effect on soil salt in the different micro-topography. The variance analysis showed that: except for the HCO3- and K+, the value of pH, CO32-, SO42-, Ca2+ and Mg2+ in three types of micro-topography are all significantly different at the level of 0.01, and the value to total salt, soluble salt, Cl- and Na+ are significantly different at the level of 0.05. (3) Micro-topography can affect the species composition, density and diversity indices of the seedling by changing the resided seedling's microhabitat. Under the condition of the micro-topography, the values of the ecological indicators in the seedling bank were less than those in the soil seed bank. From the base slope, hillside slope to side slope, the changing trends of the ecological indicators were different between the soil seed bank and seedling bank expect for the indicator of the vegetative density..The results can better reveal the impact mechanism of river flooding on compose and construction of the plant community, which has an important significance on the degraded ecosystem restoration. Furthermore, the results have a practical reference on protecting and recovering of the natural vegetation in the study region after river flooding interference. 参考文献 相似文献 引证文献