Seedling Abundance Research Articles

Regenerative capacity of old‐fields on semi‐arid floodplains in the northern Murray–Darling basin

Revegetating abandoned agricultural lands is vital to restoring critical ecological functions and services. Natural regeneration, whereby vegetation regrows via the seeds already present within the landscape, has shown to be an effective approach to restoring large agricultural areas, although more research is required to understand the regenerative capacity of the various seed sources. Here, we investigate the regenerative capacity of old‐fields of semi‐arid floodplains of eastern Australia in a year‐long seedling emergence experiment. We examined the germinable seed banks from three potential propagule sources (soil, leaf litter, and animal scats) collected across 24 field sites, comprising 12 old‐fields and 12 adjacent remnant vegetation patches, distributed across four regions. Soil seed banks stored the most germinable species of the three seed bank types, although these were dominated largely by annual herbaceous species. High abundances of seedlings emerged from scat samples, indicating that native animals, such as kangaroos and emus, play a role in transporting seeds in these landscapes. Finally, leaf litter stored the most germinable propagules of woody species, therefore, representing a vital mechanism for woody vegetation regeneration. There were few differences in emerging seedling assemblages in terms of species richness, abundance or composition between seed banks of old‐fields and adjacent remnant vegetation, suggesting that old‐field seed banks have a high level of resilience. Our findings suggest that these seed banks can make an important contribution to natural regeneration of these old‐fields, but mainly with respect to understory and midstory species, with overstory tree species mostly absent from these seed sources.

Grazing Effects on Seedling Emergence in Contrasting Wet and Dry Year in a Semiarid Grassland

Seedlings are a crucial part of the plant community and the basis of vegetation restoration and regeneration. Grazing and climate change are two main factors contributing to vegetation changes in semiarid grasslands. However, the effects of grazing on seedling emergence with rainfall variation are not clearly understood. This study aimed to address how seedling abundance and the emergence dynamics of annuals respond to grazing with rainfall changes in different years. We conducted a seedling investigation experiment in a grassland along a grazing intensity gradient (light grazing—LG; moderate grazing—MG; heavy grazing—HG) in contrasting wet and dry years. The results showed that MG increased the seedling richness of grasses and forbs in the wet year, but increasing grazing resulted in a decline in forb richness in the dry year. Seedling abundance of grasses was enhanced under MG, while seedling abundance of forbs was higher under HG. The monthly emergence dynamics were generally in a single peak pattern, but the peak time of seedling emergence for forbs advanced under HG. Seedling abundance of whole annuals increased with grazing in the wet year but was much higher under MG in the dry year. Our results suggest that more judicious grazing management based on rainfall variation and functional composition of the plant community should be undertaken to facilitate grassland restoration.

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.

Does above‐average rainfall stimulate a recruitment pulse in semi‐arid woodlands of southeastern Australia?

AbstractQuestionsRegeneration success of semi‐arid and arid regions worldwide is episodic and often linked to large rainfall events in consecutive years. It is also influenced by past and current land use, seed availability and herbivore grazing. This is particularly true for four dominant canopy trees — Allocasuarina luehmannii (Buloke), Casuarina pauper (Belah), Callitris gracilis (Slender Cypress Pine) and Myoporum platycarpum (Sugarwood) — within southeastern Australia semi‐arid woodlands. These species also apply hedge‐betting when responding to resource pulses with mass germination while low‐level background recruitment continues. We asked if drought‐breaking rainfall stimulated a germination pulse of these species and if it did, how did other external factors (grazing pressure from rabbits/hares, seed source, suitable seedbed) influence seedling abundance. We also asked if evidence of continuous recruitment had occurred during 14 years of drought by exploring trends in juvenile abundance.LocationVictorian Mallee semi‐arid woodlands, southeastern Australia.MethodsWe recorded seedling and juvenile abundance of the four dominant canopy species at 310 1‐ha sites within semi‐arid woodlands. Seedling presence was explored in relation to rainfall, tree density, ground cover and herbivory. Juvenile presence was explored in relation to rainfall, seedling and tree density, total plant cover and herbivory.ResultsSeedling and juvenile abundance were positively correlated with more mature trees, higher rainfall and no herbivory. Juvenile abundance was also positively correlated with more seedlings. There were more seedlings and juveniles at sites where rabbits/hares were present.ConclusionsAbove‐average rainfall was positively correlated with initiation of recruitment; however, there was limited net recruitment of the four dominant canopy species indicating other factors are influencing germination (e.g. seed viability) or that seedlings are not surviving. The long‐term survival of these semi‐arid woodlands is in jeopardy without a concerted effort to maintain and improve their condition through revegetation works, weed removal and herbivore management.

Effects of landscape structure on restoration success in tropical premontane forest

Reversing large-scale habitat degradation and deforestation goes beyond what can be achieved by site-level ecological restoration and a landscape ecology perspective is fundamental. Here we assess the relative importance of tree cover and its configuration on forest-dependent birds and late-successional tree seedlings in restoration sites in southern Costa Rica. The abundance and species richness of birds increased in landscapes with more corridors, higher tree cover, and lower levels of fragmentation, highlighting the importance of riparian corridors for connectivity, and continuous tree cover as suitable habitat. Landscape variables affected abundance and species richness of seedlings similarly, but effects were weaker, possibly because seedlings face establishment limitation in addition to dispersal limitation. Moreover, the scale of landscape effects on seedlings was small, likely because proximal individual trees can significantly influence recruitment in restoration plots. Results underscore the importance of incorporating landscape-level metrics to restoration projects, as knowing the extent, and how the landscape may affect restoration outcomes can help to infer what kind of species will arrive to restoration plots.

Value of human‐modified forests for the conservation of canopy epiphytes

AbstractHuman‐modified forests—HMFs—now cover more area worldwide than primary forests and could help buffering the ongoing species loss. However, their role in protecting canopy epiphytes remains unclear, partially because these communities require large trees, high humidity, and shade, conditions which are rare in HMFs. Here, we assessed how canopy epiphytes, in different ontogenetic stages, are structured in HMFs. Specifically, we evaluated how species richness, total abundance, and community composition, and how abundance of seedlings and juveniles, are affected by the local and landscape context in the Atlantic Forest of Brazil. Across all sites, we found 82.9% of species and 75.5% of individuals exclusively in old‐growth forest, while HMFs hosted only 15.5% of all species, sharing 75% of their species with old‐growth forests communities, and pastures hosted 1% of species richness and 2.8% of individuals sharing 60% of their species with old‐growth forest communities. We also found that seedling and juveniles were twice as abundant than adults in old‐growth forest, similarly abundant to adults in HMFs and absent from pastures. Low numbers of individuals in early ontogenetic stages in HMFs and pastures are likely to impact future generations of epiphytes in these areas. Although HMFs provide important refuge for many species, our results show that they do not provide suitable conditions for the maintenance of current or future canopy epiphyte communities. Our findings suggest that conserving large continuous old‐growth forests is the only viable conservation option for protecting most vascular epiphytes.Abstract in Portuguese is available with online material.

Modeling Advance Oak Reproduction at Landscape Scale: The Relative Importance of Abiotic and Biotic Factors

Abstract Establishing advance oak reproduction in the understory of mature oak forests before an overstory removal is critical to regenerate mixed-oak forests (Quercus spp.). Many studies have been conducted at the stand scale; however, studies at landscape scale can be particularly useful to guide silvicultural management investments. We developed a model of advance reproduction abundance at landscape scale using inventory, climate, topography, and soils data from ninety-seven mixed-oak forests located in Pennsylvania, USA. A negative binomial model was used to predict the abundance of oak seedlings between 15.2 and 91.4 cm in height and with a root collar diameter of 0.64 to 1.9 cm (established oak seedlings). This model had a Nagelkerke’s pseudo R2 of 58%. Deviance partitioning methods indicate that climate and overstory influence explain similar proportions of total deviance, but climate contributes a higher proportion of nonoverlapping information (22% versus 18%). Overstory basal area of two common oak species were positively associated with seedling abundance, whereas biotic stressors were negatively correlated. Biotic stressors showed considerable overlap with information provided by climate and overstory influences. The results of this study provide a reference to guide silvicultural management at a landscape scale.

Trophic interactions and feedbacks maintain intact and degraded states of Hawaiian tropical forests

AbstractFeedbacks within ecosystems can lead to internal reinforcement of the current state providing ecosystem resilience. Often, multiple biotic interactions across trophic levels play a role in such feedbacks, yet these are generally studied independently, obscuring the relative importance of interactions among different factors. We look at various potential feedbacks in intact and degraded mesic forests on Hawaiʻi Island where managers have planted native Acacia koa (koa) trees in an attempt to jumpstart succession in former cattle pastures. These restoration forests, however, have not undergone secondary succession, instead maintaining a koa overstory with an exotic pasture grass understory. We contrasted different trophic level processes that influence the capacity for natural understory regeneration: feedbacks between bird‐mediated seed rain and fruiting understory (“top‐down”), as well as links between understory composition and microhabitats for native seed germination (“bottom‐up”). We quantified bird‐mediated seed rain under canopy trees along transects spanning intact, fragmented, and restoration forests. Along these transects, we established plots around focal overstory trees to measure abundance of fruiting understory species, ground cover (e.g., exotic grass, bryophyte), and obtained estimates of bird density to evaluate the contribution of each of these factors to seedling abundance. We also used a factorial seed addition/grass removal experiment to directly compare the influence of seed rain and germination substrate. We found evidence of both top‐down and bottom‐up feedbacks that reinforced the current state of each forest type. In the intact and fragmented forests, the combination of comparatively high seed rain and ample germination substrate is likely critical for maintaining a diverse forest system. In contrast, exotic grasses exhibit priority effects in restoration forests, inhibiting seed germination and effectively negating any benefits that could be derived from bird‐mediated seed rain. Such internal reinforcement suggests that active, rather than passive, restoration would be beneficial to increase forest diversity in restoration areas.

Species-level tree crown maps improve predictions of tree recruit abundance in a tropical landscape.

Predicting forest recovery at landscape scales will aid forest restoration efforts. The first step in successful forest recovery is tree recruitment. Forecasts of tree recruit abundance, derived from the landscape-scale distribution of seed sources (i.e., adult trees), could assist efforts to identify sites with high potential for natural regeneration. However, previous work revealed wide variation in the effect of seed sources on seedling abundance, from positive to no effect. We quantified the relationship between adult tree seed sources and tree recruits and predicted where natural recruitment would occur in a fragmented, tropical, agricultural landscape. We integrated species-specific tree crown maps generated from hyperspectral imagery and property ownership data with field data on the spatial distribution of tree recruits from five species. We then developed hierarchical Bayesian models to predict landscape-scale recruit abundance. Our models revealed that species-specific maps of tree crowns improved recruit abundance predictions. Conspecific crown area had a much stronger impact on recruitment abundance (8.00% increase in recruit abundance when conspecific tree density increases from zero to one tree; 95% credible interval (CI): 0.80% to 11.57%) than heterospecific crown area (0.03% increase with the addition of a single heterospecific tree, 95% CI: -0.60% to 0.68%). Individual property ownership was also an important predictor of recruit abundance: The best performing model had varying effects of conspecific and heterospecific crown area on recruit abundance, depending on individual property ownership. We demonstrate how novel remote sensing approaches and cadastral data can be used to generate high-resolution and landscape-level maps of tree recruit abundance. Spatial models parameterized with field, cadastral, and remote sensing data are poised to assist decision support for forest landscape restoration.

Substrate texture and natural removal processes mediate vascular epiphyte establishment: Experimental evidence from a Panamanian cloud forest1, 2

Epiphytes are a unique group of plants that live nonparasitically on other plants (“hosts”) and constitute approximately one-fifth of Neotropical vascular plant diversity. However, the processes governing early epiphyte community assembly are poorly understood and have scarcely been experimentally tested. Here, we use an in situ experiment in the cloud forest of Santa Fé, Panama, to evaluate the extent to which host substrate texture regulates early epiphyte establishment. We experimentally varied the surface roughness of native wood substrates, applied bromeliad and orchid seeds to the substrates, and monitored emergence of epiphyte seedlings and their persistence for a year. Rougher substrates facilitated higher initial abundance of epiphyte seedlings; after two months, 81% of the 1,934 total germinated epiphytes occurred on the substrates with experimentally added roughness. Via photo analysis, we also show that epiphytes disproportionately established early on in the experimental grooves, wherein 71% more epiphytes per unit area occurred within 1.5 mm of the grooves than on nearby smooth surfaces. While epiphyte cohort survival rates differed between rough and smooth substrates in the first six months, more than 99% of all seedlings died after one year, regardless of experimental roughness treatment. Only 10 seedlings survived through the end of the experiment. Our results suggest that while substrate texture explains some variation in early epiphyte emergence, roughness alone is not sufficient to explain epiphyte persistence to adulthood. Moreover, our results highlight the importance of removal processes (e.g., wind, rain, animals) in structuring early epiphyte community assembly. Variation in substrate texture may contribute to differences in epiphyte diversity and community composition within- and among-host tree species, but more experiments are needed to disentangle removal processes from substrate-mediated host affinity.

Responses of stand growth, regeneration, and understory species diversity in Quercus mongolica secondary forest to stand density.

Six Quercus mongolica plots with an area of 0.1 hm2 were thinned in 2018. A field survey was carried out in 2020 to examine the effects of different stand densities (high: 900 trees·hm-2; medium: 720 trees·hm-2; low: 600 trees·hm-2) on growth and regeneration of stands and understory species diversity of secondary Q. mongolica forests in Qingyuan, Liaoning Province. Due to the short interval after thinning, there was no significant difference in tree height and diameter at breast height under different densities. However, the crown symmetry index under low stand density was significantly higher than that of high stand density, indicating that crown growth was more sensitive to stand density than trunk growth. The abundance of seedlings was the highest in the medium density, and the basal diameter of the seedlings with the same height was significantly higher, and the seedling regeneration and growth at the medium density were much better than the other two densities. A total of 70 species were recorded, belonging to 41 families and 67 genera. Quercus mongolica, Lespedeza bicolor, Melampyrum roseum, and Potentilla freyniana were the dominant species of trees and herbs, respectively. Simpson index, Pielou index and Shannon index of shrub layer and herb layer were the highest at the medium density. It indicated that the stand density of 720 trees·hm-2 could help maintain the sustainable development of Q. mongolica secondary forest in the mountainous area of eastern Liaoning.

Keragaman Permudaan Pohon di Area Sumber Air Blok Seda, Taman Nasional Gunung Ciremai

Water availability in Mount Ciremai National Parks (MCNP) is influenced by sustainability of the vegetation. Therefore, tree regeneration around the water springs area needs to be investigated to maintain the sustainability of water springs ecosystem in the future. The purpose of this study was to analyzed and identify natural seedlings of tree regeneration around the water springs area Seda Block MCNP. The collections of vegetation and abiotic data was carried out on 9 sample plots measuring 3 m × 3 m which is purposively placed around water springs. Result show that vegetation in water springs dominate by seedlings Ficus sp., Ficus hemsleyana, and Trevesia sundaica. Shannon-Weiner diversity index in this location was moderate, but evenness and dominance index classified as high and low, respectively. Overall, seedling of trees dominated by orthodox seed-type and shade tolerant plant. The vegetation in this study dominated by plants categorized least concern (LC) based on IUCN red list. Microclimatic of study site affects 58.89% on abundance and distribution of tree seedlings. Therefore, the springs are in the Seda Block MCNP needs to be conserved and maintain its natural vegetation.
 Keywords: Mount Ciremai National Park, eco-hydrology, canonical correspondent analysis, conservation

Population structure and dynamics of Pinus koraiensis seedlings regenerated from seeds in a montane region of eastern Liaoning Province, China.

Based on the static life table and survival curve, we explored the population structure and dynamics of Korean pine (Pinus koraiensis) seedlings regenerated from seeds in three different forest belts of Korean pine plantation in a montane region of eastern Liaoning Province. The results showed that the age structure of Korean pine seedlings in three different forest belts (i.e., larch forest belt, mixed coniferous forest belt, and mixed broadleaved forest belt) showed a "∩" type of left skewed distribution. The abundance of seedlings was rich but the mortality rate was high in the early phase, and the abundance of seedlings decreased in the later phase, which indicated that the population was depressing. The survival curve of the population conformed to the Deevey-Ⅱ type. The life expectancy of Korean pine seedlings at each age class in larch forest belt was higher than that in mixed coniferous forest belt and mixed broadleaved forest belt. The survival analysis showed that the survival rate of Korean pine seedlings in three different forest belts decreased but the cumulative mortality rate increased with increasing age. The death density function tended to be flat after the age class of Ⅱ-Ⅲ, while the risk function value showed a decreasing trend with the increases of age. The time series predictive analysis showed that the population showed a certain growth trend with increasing age class, indicating that the population could achieve natural regeneration and have a certain growth potential, but with regeneration obstacles.

Mangrove seedling abundance in mangrove ecosystem outgrowth in Ajkwa Island, Mimika Regency, Papua

Mangrove is one of the essential ecosystems for coastal areas. Mangrove is an individual or community which survives in tidal areas. Ajkwa Island is an island created by sedimentation activities from Ajkwa river. Ajkwa Island has a tidal supply well and it makes this island be an essential area for mangrove growth. This research was conducted in Ajkwa Island, Mimika Regency, Papua Province. The research is in permanent monitoring plots in 2011, 2014, and 2018. Based on the research, 2 categories were found in the monitoring plot, there are seedling and herbs. Species for seedling category are Avicennia marina, Bruguiera gymnorrhiza, Bruguiera cylindrica, Diospyros sp., Nypa fruticans, Sonneratia alba, and Xylocarpus sp. Species for herbs category are Allamanda cathartica and Hoya sp. Mangrove ecosystem type in Ajkwa Island is over-wash mangrove. The result, Sonneratia alba and Bruguiera gymnorrhiza had density and important value index higher than the other species in every monitoring year. Mangrove spreading in Ajkwa Island increases in each monitoring year. Mangrove seedling spread significantly from 2014 to 2018. On the monitoring plots, mangrove density in 2014 is 41.700 ind/ha and for 2018 is 74.000 ind/ha. Beside vegetation analysis, this research does spatial analysis to support the result from field monitoring data. Spatial analysis also proved the spreading of the seedling increased significantly from 2014 to 2018.

Restoration Trajectories and Ecological Thresholds during Planted Urban Forest Successional Development

Successfully reconstructing functioning forest ecosystems from early-successional tree plantings is a long-term process that often lacks monitoring. Many projects lack observations of critical successional information, such as the restoration trajectory of key ecosystem attributes and ecological thresholds, which signal that management actions are needed. Here, we present results from a 65 ha urban temperate rainforest restoration project in Aotearoa New Zealand, where trees have been planted annually on public retired pasture land, forming a 14 years chronosequence. In 25 plots (100 m2 each), we measured key ecosystem attributes that typically change during forest succession: native tree basal area, canopy openness, non-native herbaceous ground cover, leaf litter cover, ground fern cover, dead trees, and native tree seedling abundance and richness. We also monitored for the appearance of physiologically-sensitive plant guilds (moss, ferns, and epiphytes) that may be considered ecological indicators of succession. Linear regression models identified relationships between all but one of the key ecosystem attributes and forest age (years since planting). Further, using breakpoint analysis, we found that ecological thresholds occurred in many ecosystem attributes during their restoration trajectories: reduced canopy openness (99.8% to 3.4%; 9.6 years threshold), non-native herbaceous ground cover (100% to 0; 10.9 years threshold), leaf litter cover (0 to 95%; 10.8 years threshold), and increased tree deaths (0 to 4; 11 years threshold). Further, juvenile native plant recruitment increased (tree seedling abundance 0 to ~150 per 4 m2), tree seedling species richness (0 to 13 per 100 m2) and epiphytes colonized (0 to 3 individuals per 100 m2). These and other physiologically-sensitive plant guilds appeared around the 11 years mark, confirming their utility as ecological indicators during monitoring. Our results indicate that measurable, ecological thresholds occur during the restoration trajectories of ecosystem attributes, and they are predictable. If detected, these thresholds can inform project timelines and, along with use of ecological indicators, inform management interventions.

IMPACTS OF BAMBUSA BAMBOS SPREAD ON SEEDLING RECRUITMENT, MORTALITY AND REGENERATION POTENTIAL OF NATIVE SPECIES IN TROPICAL MOIST EVERGREEN FORESTS OF SRI LANKA

Some native plants expand their populations rapidly in their home ranges, altering their structure and composition. Bambusa bambos, a native bamboo species, shows a rapid population expansion in tropical moist evergreen forests in the intermediate climatic zone, Sri Lanka. The present study was conducted to evaluate its impacts on the regeneration potential of other native forest species. The seedling emergence, survival and mortality were observed for a period of one year using quadrats laid along 18 transects marked from the forest edge towards the forest interior in forest patches with and without bamboo (+Bb and –Bb, respectively). The results revealed a higher abundance, richness and diversity of seedlings in +Bb than in -Bb, with lianas and herbs contributing more to these differences. However, tree seedlings showed higher turnover rates (recruitment and mortality) in -Bb, indicating their preference for undisturbed habitats. Tree and shrub seedlings survived better in -Bb forests while liana and herbaceous seedlings displaying the opposite. The results indicate that B. bambos spread showed an ability to alter the regeneration potential of native forests probably resulting bamboo-driven changes to micro-environmental conditions in the forest floor.

Regeneration Status and Role of Traditional Ecological Knowledge for Cloud Forest Ecosystem Restoration in Ecuador

The importance of forests for biodiversity conservation has been well recognized by the global community; as a result, conservation efforts have increased over the past two decades. In Ecuador, the lack of integrated information for defining and assessing the status of local ecosystems is a major challenge for designing conservation and restoration plans. Thus, the objectives of this study were (1) to examine the regeneration status of cloud forest remnants, some of which had experienced past human disturbance events, (2) to explore a local rural community’s traditional ecological knowledge (TEK) relevant for restoration and (3) to investigate the integration between TEK and ecological science-based approaches. A survey of regeneration status was conducted in four remnants of cloud forests (n = 16) in Cosanga, Napo Province, in the Andes of northeastern Ecuador. The species of young trees (0.5–5 m height) were identified over 0.16 ha. In-depth interviews of individuals from local communities (n = 48) were conducted to identify socio-ecologically important native species. The results showed significant differences (p < 0.001) in species richness and the stem density of seedlings and saplings in gaps. The stem density of Chusquea sp., a bamboo species, explained 63% of the variation in species richness and 48% of the variation in the abundance of seedlings and saplings between plots. Informants cited 32 socio-ecologically important species, of which 26 species were cited as sources of food and habitats for wildlife. The ranking of species based on a relative importance index and a cultural value index—taking into account both the spread of knowledge among local informants and the multiplicity of uses—revealed that Hyeromina duquei, Citharexylum montanum, Eugenia crassimarginata and Sapium contortum were traditionally the most valuable species for both humans and wildlife. Informants also recommended 27 species for future planting, of which 19 species were amongst the rarest species in the regeneration survey. In conclusion, the results demonstrate a synergy between TEK and ecological science-based approaches (regeneration survey) to natural ecosystem research. Thus, traditional ecological knowledge can provide insights into ecosystem–plant–animal interaction, and to identify native species useful for both humans and wildlife for forest restoration projects to reconnect isolated cloud forest fragments.

重庆喀斯特生境中桢楠种群结构与动态特征

PDF HTML阅读 XML下载 导出引用 引用提醒 重庆喀斯特生境中桢楠种群结构与动态特征 DOI: 10.5846/stxb202106171607 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 重庆市自然科学基金项目（cstc2020jcyj-msxmX0244）；中央高校基本科研业务费专项（XDJK2020B037）；国家自然科学基金项目（31500399） Population structure and dynamic characteristics of Phoebe zhennan S. Lee in karst areas of Chongqing Author: Affiliation: 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:桢楠是我国珍稀渐危树种，国家二级保护植物，野生多散生于海拔1500 m以下的亚热带常绿阔叶林中。而喀斯特生境岩石裸露、土壤浅薄贫瘠、岩溶干旱频发，理论上并不适合喜湿耐荫且喜酸性土壤的桢楠生长及幼苗更新。因此重庆市大足区和永川区喀斯特生境中的天然桢楠种群可能存在一定的更新困难。为明确这两个桢楠种群的生存现状及动态特征，采用野外调查法，从径级结构、静态生命表、存活曲线、结构动态及分布格局等方面分析桢楠种群结构及其数量动态规律，以期预测种群未来发展趋势，为喀斯特地区桢楠种群的保护、群落更新及植被恢复提供理论基础。结果表明：（1）大足区桢楠种群的年龄结构趋于稳定型，而永川区桢楠种群的年龄结构为增长型。两地区幼苗充足但死亡率高。（2）静态生命表及相关曲线分析显示，两个桢楠种群存活数量总体上随径级增大而减少；两个桢楠种群的生存期望值在不同径级间存在波动，大足区桢楠种群在第Ⅱ径级而永川区则是第Ⅳ径级期望值最高。（3）两个种群的存活曲线均为Deevey-Ⅲ型，即幼树死亡率较高，并且种群的增长速度较为缓慢。（4）大足区种群为随机分布，永川区种群为集群分布；种群各生长发育阶段均为集群分布，但聚集强度随着龄级的增加而减弱。桢楠种群在喀斯特地区生长周期长，天然更新能力较强但对外部干扰敏感。建议加强对幼苗的抚育工作，提高幼苗存活率，促进桢楠种群的自然更新和恢复。 Abstract:Phoebe zhennan S. Lee is a rare and endangered tree species in China, a nationally protected secondary plant. It is mostly scattered in the wild in subtropical evergreen broad-leaved forests below 1500 m above sea level. As the primary populations are almost destroyed, the existing resources are limited and scattered. Karst habitat has exposed rocks, shallow and barren soil and frequent drought. In theory, it is not suitable for the growth and seedling regeneration of P. zhennan, which likes humidity, shade and acid soil. Therefore, it may be difficult to renew the natural P. zhennan population in karst habitats in Dazu District and Yongchuan District of Chongqing. To explore the survival status and distribution model of the two P. zhennan populations, the field survey method is used to analyze the structure and the dynamic law of the populations and their quantity, by assessing the diameter structure, static life table, survival curve, structural dynamics and distribution pattern. It is hoped that the future development trend of the population can be predicted, and the theoretical basis for the protection, community renewal and vegetation restoration of the karst area will be provided. The results showed that:(1) the age structure of P. zhennan population in Dazu District tended to be a stable type, while it was an increase type in Yongchuan District. Both areas had abundant seedlings but with high mortality rates. (2) The individual numbers of both populations of P. zhennan generally decreased with the diameter class increased. The life expectation of the two P. zhennan populations fluctuated between different diameter classes. It was the highest in the diameter class Ⅱ in the population of P. zhennan in Dazu District, while it highest in the diameter class Ⅳ in Yongchuan District.(3) Both populations had Deevey-Ⅲ type survival curves, that was, the mortality of young trees was relatively high, and a relatively low population growth rate. (4) The population in Dazu District was randomly distributed, while that of the Yongchuan District was consolidated. P. zhennan were clustered populations at the growth and development stage, but their strength weakened with the growth of the age group. The population of P. zhennan in the karst region had a long growing time, a strong capacity for natural regeneration but sensitive to external disturbances. It is suggested to enhance seedling selection and improve seedling survival to promote natural renewal and restoration of P. zhennan population. 参考文献 相似文献 引证文献

Interactive effects of chronic anthropogenic disturbances on Prosopis woodland structure in the Central Monte, Argentina

In drylands all over the world, chronic anthropic disturbances are relevant factors for woodland degradation. Different disturbances can potentially interact to change vegetation structure. Knowing woodland structure is crucial for better predicting forest dynamic because trees of different sizes significantly affect the regeneration processes, number of saplings and young trees, crown traits and competition attributes. Throughout the Monte biogeographic region, grazing and wood extraction are the main anthropogenic disturbances on Prosopis dry woodlands that can generate modifications in key ecosystem processes. First, we aimed to assess woodland structure at sites under chronic anthropic disturbances. Subsequently, we explored how the combination of grazing and wood extraction affected the population structure of P. flexuosa considered by classes: seedlings, saplings and adults. We found that sites under disturbances presented a high density of trees of smaller sizes. Besides, the interaction effect between grazing and wood extraction depended on the intensities of each of the disturbances. The combination of high intensities of both grazing and wood extraction negatively affected the abundance of all classes, but low or moderate grazing intensities combined with high wood extraction had a positive effect on the abundance of saplings and adults. High intensities of co-occurring disturbances decreased seedling abundance affecting forest recruitment which also was negatively reflected in sapling and adult abundance. However, the combination of low or moderate grazing and high wood extraction generated a woodland structure characterized by few seedlings, and many saplings and adult trees of small size. Application of management options (e.g., spatial or temporal separation of human use, programmed management of grazing and wood extraction intensities or planned practices as wood removal for local use) should contribute to enhance the provision of ecosystem services in Prosopis sp. woodlands without risking regeneration persistence and improving the woodland structure.

Relationships between tree-community composition and regeneration potential of Shorea trees in logged-over tropical rain forests

ABSTRACT Logged-over forests are widespread in SE Asia, and these forests vary greatly in tree-community composition ranging from a near pristine to a greatly modified forest due to repeated high-impact logging. It is a critical concern in terms of forest management and conservation whether modified forests can recover to their original states. However, greatly modified forests may lose the resilience due to the lack of next-generation seedlings. We examined the regeneration potential of Shorea, a dominant genus in pristine forests, in various forests ranging from pristine to degraded forests, and investigated the relationship between the tree-community composition in canopy layer and the regeneration potential in north Borneo. In non-metric multidimensional scaling (nMDS) analysis based on the tree-community composition at genus level, 31 study plots were sorted in the order from pristine to degraded forests along the axis-1 with decreasing the axis-1 scores, and this score was used as a metric of forest intactness. Size distribution of Shorea trees combining all congeneric species showed an inverse-J shape in most plots excluding some degraded forests. The skewness of size distribution was high in pristine forests but remarkably decreased in degraded forests. The skewness reflected the abundance of seedlings in the population of Shorea trees, and it was an important metric indicating regeneration potential. The number of seedlings also decreased abruptly with decreasing forest intactness along the nMDS axis-1. The reduction in these two metrics suggests that regeneration potential is abruptly lost when the forest intactness in terms of tree-community composition is decreasing.