Seed Dispersal and Seedling Emergence in a Created and a Natural Salt Marsh on the Gulf of Mexico Coast in Southwest Louisiana, U.S.A.

Early regeneration dynamics related to seed dispersal and seedling emergence can contribute to differences in species composition among a created and a natural salt marsh. The objectives of this study were to determine (1) whether aquatic and aerial seed dispersal differed in low and high elevations within a created marsh and a natural marsh and (2) whether seedling emergence was influenced by marsh, the presence of openings in the vegetation, and seed availability along the northern Gulf of Mexico coast. Aerial seed traps captured a greater quantity of seeds than aquatic traps. Several factors influenced aquatic and aerial seed dispersal in a created and a natural salt marsh, including distance from the marsh edge, cover of existing vegetation, and water depth. The natural marsh had a high seed density of Spartina alterniflora and Distichlis spicata , the low-elevation created marsh had a high seed density of S. alterniflora , and the high-elevation created marsh had a high seed density of Aster subulatus and Iva frutescens . The presence of adult plants and water depth above the marsh surface influenced seed density. In the natural marsh, openings in vegetation increased seedling emergence for all species, whereas in the low-elevation created marsh, S. alterniflora had higher seedling density under a canopy of vegetation. According to the early regeneration dynamics, the future vegetation in areas of the low-elevation created marsh may become similar to that in the natural marsh. In the high-elevation created marsh, vegetation may be upland fringe habitat dominated by high-elevation marsh shrubs and annual herbaceous species.     

Influences of Habitat Isolation on Invertebrate Colonization of Sporadanthus ferrugineus in a Mined Peat Bog

This study experimentally tested the impact of peat bog habitat loss and isolation on the invertebrate community associated with Sporadanthus ferrugineus (Restionaceae), a dominant indigenous plant species in peat bogs. Potted S. ferrugineus plants were exposed to invertebrates at various distances up to 800 m from an intact habitat (the source population) over 18 weeks. Invertebrates rapidly colonized the experimental plants, with all major orders and trophic groups present on S. ferrugineus within 6 weeks. However, with increasing distance away from the undisturbed habitat, there was a significant decrease in total species richness and abundance of invertebrates associated with the potted plants. Of the total taxa captured, only 38% were found on potted S. ferrugineus plants at 800 m compared with 62% found on potted plants 30 m from the intact peat bog. Predator species richness and the predator–prey ratio changed significantly with time available for colonization of potted plants but, more importantly, prey (herbivores and detritivores) and predator (including parasitoids) species richness, as well as the predator–prey ratio, declined significantly with increasing isolation from the peat bog. Thus, the degree of isolation of restoration areas from undisturbed habitat has a major impact on the rate and patterns of recovery in invertebrate community structure. The current recommended practice of restoring the mined area by establishing raised "habitat islands" 30 m apart should result in colonization by most invertebrates associated with S. ferrugineus , but only if the restoration islands are placed as stepping stones outward from existing areas of intact habitat.     

Effects of Habitat Quality and Isolation on the Colonization of Restored Heathlands by Butterflies

In areas with intensive land use, such as the Netherlands, habitat fragmentation and loss of habitat quality due to eutrophication and drainage are major threats to the preservation of species‐rich communities of heathland and acid grassland. Restoration of such nutrient‐poor habitats may be carried out by removing the topsoil from ex‐arable land, in order to lower the nutrient levels. However, the establishment of target plant communities is known to be fragmentary. The current study shows that this also applies to butterflies. Ten years after topsoil removal in eight study areas, on average, only 3.5 of 10 characteristic heathland species were recorded on the sites. Species that did colonize had a significantly lower density than in the source populations. Our study indicates that although isolation effects were limiting colonization, poor habitat quality was the main limiting factor, mainly due to lack of host plants, hydrological conditions, and, to a lesser extent, lack of nectar plants and excessive residual nutrient levels. An experiment with the introduction of cut heather in one study area showed a significantly higher abundance of both target and nontarget butterflies in manipulated sites than in control sites. It can be concluded that habitat restoration by topsoil removal can be successful for butterflies of especially wet heathland habitats, provided that source populations are at close range and care is taken that complete plant communities are restored.     

Impacts of Restored Patch Density and Distance from Natural Forests on Colonization Success

Abstract The reduction and fragmentation of forest habitats is expected to have profound effects on plant species diversity as a consequence of the decreased area and increased isolation of the remnant patches. To stop the ongoing process of forest fragmentation, much attention has been given recently to the restoration of forest habitat. The present study investigates restoration possibilities of recently established patches with respect to their geographical isolation. Because seed dispersal events over 100 m are considered to be of long distance, a threshold value of 100 m between recent and old woodland was chosen to define isolation. Total species richness, individual patch species richness, frequency distributions in species occurrences, and patch occupancy patterns of individual species were significantly different among isolated and nonisolated stands. In the short term no high species richness is to be expected in isolated stands. Establishing new forests adjacent to existing woodland ensures higher survival probabilities of existing populations. In the long term, however, the importance of long‐distance seed dispersal should not be underestimated because most species showed occasional long‐distance seed dispersal. A clear distinction should be made between populations colonizing adjacent patches and patches isolated from old woodland. The colonization of isolated stands may have important effects on the dynamics and diversity of forest networks, and more attention should be directed toward the genetic traits and viability of founding populations in isolated stands.     

Effectiveness of a Newly Created Oxbow Lake to Mitigate Habitat Loss and Increase Biodiversity in a Regulated Floodplain

In 2005, an oxbow lake was constructed in a degraded floodplain area of the Ebro River (NE Spain) to mitigate habitat loss. In this study, we address the effectiveness of this restoration project through the analysis of the macroinvertebrate community that colonized the newly constructed lake, in comparison with a nearby natural oxbow lake and the adjacent river channel. To that end, water and macroinvertebrate samples were taken every 2 months in 2006. Ground movements during construction, wind‐driven bottom resuspension, shore scouring, and lack of vegetation resulted in distinctive water chemistry in the constructed and natural lakes. Regarding biodiversity, only 8 months after the digging of the constructed lake the abundance, richness, Shannon, and trait diversity of macroinvertebrates exceeded that of the natural lake. It is suggested that the constructed lake provided habitat for new mobile species that rapidly dispersed to other wetlands, thus enhancing the biological diversity of the floodplain at a local scale. Furthermore, biodiversity is predicted to continue increasing in the following years, although isolation can lead to early clogging of the system. By showing a dramatic increase in aquatic biodiversity in constructed wetlands, our study suggests that wetland construction can be very effective in mitigating habitat loss and increasing biodiversity in highly degraded floodplain areas. Further monitoring is nevertheless needed to evaluate the sustainability of the newly created habitat in the long term.     

The potential of small Eucalyptus plantations in farmscapes to foster native woody plant diversity: local and landscape constraints

The major focus of ecological restorations has been on understanding local factors. However, landscape factors such as dispersal limitation of individuals or propagules across the surrounding matrix can also constrain the restoration progress. We investigated to what extent native woody species colonize and thrive in plantations, focusing on both the role of local factors such as grazing and canopy cover as well as on landscape factors. We recorded all native tree and shrub species in 60 small Eucalyptus plantations embedded in an open agricultural landscape at 0.1–12 km from a remnant continuous forest in central Ethiopia. We found a total of 1,571 individuals of native woody plants belonging to 55 species. Number of such species in a plantation increased significantly with the height of the grass sword indicating their sensitivity to grazing. Moreover, the number of woody species in the patches decreased significantly with distance to the forest. Our results illustrate the need for regulating the grazing pressure for a successful regeneration of native species in Eucalyptus plantations. In addition, sowing or planting native trees will be necessary in most plantations, as only few remnant natural forests that could act as seed sources occur across the Ethiopian highlands. Another main obstacle might be the prohibition of selling timber of native trees, which indirectly discourage farmers from letting native trees regenerate. Thus, the increasing cover of Eucalyptus seen across the country will not automatically foster a recovery of native woody plant biodiversity, even if managed to optimize local environmental conditions.     

Colonization processes and the maintenance of genetic diversity: insights from a pioneer rainforest tree, Aucoumea klaineana

Despite recurrent episodes of range expansion and contraction, forest trees often harbour high genetic diversity. Studies of temperate forest trees suggest that prolonged juvenile phase and high pollen flow are the main factors limiting founder effects. Here, we studied the local colonization process of a pioneer rainforest tree in central Africa, Aucoumea klaineana. We identified 87% of parents among trees up to 20-25 years old and could thus compare direct parentage structure data with classical population genetics estimators. In this species, genetic diversity was maintained during colonization. The absence of founder effects was explained by (i) local random mating and (ii) local recruitment, as we showed that 75% of the trees in the close neighbourhood participated in the recruitment of new saplings. Long-distance pollen flow contributed little to genetic diversity: pollen and seed dispersal was mainly within stand (128 and 118 m, respectively). Spatial genetic structure was explained by aggregated seed dispersal rather than by mother-offspring proximity as assumed in classical isolation-by-distance models. Hence, A. klaineana presents a genetic diversity pattern typical of forest trees but does not follow the classical rules by which this diversity is generally achieved. We suggest that while high local genetic variability is of general importance to forest tree survival, the proximate mechanisms by which it is achieved may follow very different scenarios.     

Dispersal of aquatic organisms by waterbirds: a review of past research and priorities for future studies

1. Inland wetlands constitute ecological islands of aquatic habitat often isolated by huge areas of non-suitable terrestrial habitats. Although most aquatic organisms lack the capacity to disperse by themselves to neighbouring catchments, many species present widespread distributions consistent with frequent dispersal by migratory waterbirds.
2. A literature review indicates that bird-mediated passive transport of propagules of aquatic invertebrates and plants is a frequent process in the field, at least at a local scale. Both endozoochory (internal transport) and ectozoochory (external transport) are important processes.
3. The characteristics of the dispersed and the disperser species that facilitate such transport remain largely uninvestigated, but a small propagule size tends to favour dispersal by both internal and external transport.
4. We review the information currently available on the processes of waterbird-mediated dispersal, establishing the limits of current knowledge and highlighting problems with research methods used in previous studies. We also identify studies required in the future to further our understanding of the role of such dispersal in aquatic ecology.     

Natural Regeneration in Plantations of Native Trees in Lowland Brazilian Atlantic Forest: Community Structure,Diversity, and Dispersal Syndromes

Plantations of native‐tree species are often recommended for ecological restoration, but the understanding of how these techniques catalyze natural ecological processes is limited. We investigated natural regeneration in five plantations of native trees in the Poço das Antas Biological Reserve (PABR) in the state of Rio de Janeiro, Brazil. The plantations were 9–11 years old, and contained 8–14 native‐tree species with different compositions and relative density of species. We analyzed floristic composition, structure (density and basal area) of overstory and understory strata, as well as other ecological attributes (dispersal syndromes, fruit or seed size, and the availability of fruit for frugivores). Zoochorous species comprised 77% of the community, with a prevalence of the two smallest size classes of propagules (< 0.6 and 0.6–1.6 cm) in natural regeneration. The density of zoochorous plants in the understory was positively correlated with their density in the overstory, indicating their influence on natural regeneration (r² = 0.36; p < 0.0002). Fruit availability for frugivores (density and richness of plants fruiting during the year) was also positively correlated with the density of stems in the understory. Therefore, attributes such as dispersal syndrome and fruiting season should be considered in selecting species to be planted. The differences in natural regeneration observed in each of the native‐tree plantations indicated that the performance of plantations as a restoration strategy may differ, depending on initial species composition, planting density, and site conditions.     

Colonization of vineyards by phytoseiid mites: their dispersal patterns in the plot and their fate

The effect of wind and woody margins on the dispersal and population dynamics of phytoseiid mites was studied in a vine plot for a period of two years. Mites were sampled in the plot and in the surrounding vegetation (crops and natural vegetation) in order to determine phytoseiid mite abundance. The surrounding vegetation was considered to be a reservoir of phytoseiids from where the vine plot could be invaded. Directional and non-directional soil and aerial traps were placed in the plot to determine predatory mite exchange between the two areas. Colonization of the plot occurred in two stages: first, mite migration into the plot, followed by their establishment. The two-year study partially clarified the first of these two stages. Kampimodromus aberrans was the main species caught in the aerial traps. Phytoseiid mite dispersal within the vine plot seemed to be affected by both wind (direction, intensity and regularity) and phytoseiid mite density in the woody margin. However, the woody margin had a large effect only over a short distance. Some observations pointed towards an effect of other reservoir areas but it was not possible to characterize these. The population density of the phytoseiid mites in the plot increased from 1996 to 1998, but these increases are much smaller than one would expect on the basis of the number of mites migrating by air in the plot. Moreover, blocks where most mites were trapped were not the blocks where densities of phytoseiid mites on vine leaves were the largest. It therefore seems likely that not all migrants were able to develop. Their settlement pattern was not determined and this could constitute a potential research focus for the future.     

Restoring Lepidopteran Communities to Oak Savannas: Contrasting Influences of Habitat Quantity and Quality

Ecological restoration is deemed important for the long‐term conservation of biodiversity, but ecologists still lack an understanding of how habitat availability and habitat quality in a restored system interact to determine species diversity. This problem seems particularly apparent in Tallgrass Prairie and savanna ecoregions, where restored management units represent the majority of extant habitat. In this study, we tested three principal hypotheses, each stating that the diversity of Lepidoptera would be greater in (1) patches of savanna habitat that were larger; (2) patches that were of higher habitat quality; and (3) patches that had greater connectivity to management units of similar physiognomy. Lepidoptera were sampled in 2003 from 13 unmanaged woodland remnants within Neal Smith National Wildlife Refuge, a 2,292‐ha prairie and savanna reconstruction project. We also measured 11 environmental variables within each site to assess variation in habitat quantity and quality. Principal components analysis (PCA) was used to identify major gradients of environmental variation among the 13 sites. Our PCA differentiated among woodlands along three environmental gradients, defined by (1) stand size, shape, topography, and oak dominance; (2) degree of disturbance; and (3) isolation. Total lepidopteran species richness, however, was only predicted by variation in the first principal component. Species richness of Lepidoptera known to be oak specialists was significantly affected by variation along all three PCA gradients. Surprisingly, more isolated woodland remnants contained a greater richness of oak feeders. Our results suggest that approaches to restoring oak savannas should emphasize aspects of both habitat quantity and quality. Beyond making individual management units larger, priority sites for restoration should possess a low importance of trees that are indicative of past habitat disturbance (e.g., Honey locust, White mulberry) even if canopy closure is substantial. Connectivity among restored habitats may benefit savanna moth communities only when habitat linkages contain a flora similar in composition to focal patches.     

Succession of a Southern Appalachian Mountain Wetland Six Years following Hydrologic and Microtopographic Restoration

Microtopography, which is known to play a key role in the structure and function of wetland communities, is receiving increasing attention in wetland restoration projects. One goal of the Tulula Wetlands Mitigation Bank, which was the first large-scale wetland restoration project in the Blue Ridge Province, was to restore the microtopography in a degraded swamp forest–bog complex. This wetland type has become increasingly rare in the southern Appalachians and is characterized by a distinct microtopography of depressions and low ridges. We examined vegetation and soils in depression and ridge plots over a 6-year period, during which the hydrology and microtopography of the floodplain were restored. Our results showed that the flora of the depression and ridge plots differed, with greater coverage by obligate wetland species in the depression plots but greater overall taxonomic richness in the ridge plots. The edaphic characteristics that we measured varied very little during the study period. Creating microtopographic relief during the restoration of this wetland seems to have provided a variety of niches and may have increased the likelihood that the site will succeed back to a swamp forest–bog complex, rather than as a forested terrace of Tulula Creek.     

Colonization in metapopulations: a review of theory and observations

In metapopulation dynamics turnover of populations in isolated patches may be frequent. Regional survival of a species in such a system with frequent extinctions hinges on its colonization ability. Colonization is more than just dispersal; when a propagule reaches a new patch it faces higher extinction probabilities than does an established population. Extinction models as well as empirical data suggest that a large propagule with a potential for rapid increase in a varying environment, or with a low mortality rate in an environment perceived as constant, has a higher probability of successful colonization. Large variation in population size when it is still small increases the risk of failure. Factors introducing such variation are demographic stochasticity and environmental variation. It is hard to single out demographic traits that ensure good colonizing ability, since colonization can be achieved in many different ways, but generalists and species with self-fertilization seem to be superior.     

The Influence of the Chemical Composition of Typha Domingensis and Nymphaea Ampla Detritus on Invertebrate Colonization During Decomposition in a Brazilian Coastal Lagoon

The aims of this study were to investigate the structure and composition of the invertebrate community during the detritus decomposition (colonization features) of the two most abundant aquatic macrophytes Typha domingensis Pers. and Nymphaea ampla in Jurubatiba Lagoon and verify if the chemical composition of the substratum has any influence on invertebrate colonization and which are the functional groups possibly affected by these compounds. The substratum T. domingensis had higher percentages of cell wall fraction (F= 108.33; p < 0.0001) and organic matter (F= 225.77; p < 0.0001), while nitrogen (F= 408.61; p < 0.0001) and phosphorus (F= 224.59; p < 0.0001) contents were higher in N. ampla. These differences in the chemical composition of the substrata influenced the decomposition rate, and the detritus of N. ampla(4.37% DW day^–1) decomposed approximately 26 times faster than the T. domingensis(0.17% DW day^–1) detritus. The main groups of invertebrates that colonized both substrate were Chironomidae, with more than 50% of the total, followed by Oligochaeta, Nematoda, Copepoda and Cladocera. The results showed that the slow breakdown rate of T. domingensis detritus provided a higher probability for colonization and that the main driving force structuring the invertebrates' community was degradative ecological succession (DES).     

黑河中游湿地不同恢复方式对土壤和植被的影响——以张掖国家湿地公园为例

湿地是自然界最富生物多样性的生态景观和人类社会赖以生存和发展的环境之一,对维护生态系统功能和区域生态安全有着重要意义。为阐明不同湿地恢复方式对土壤和植被的影响,以黑河中游地区张掖国家湿地公园为研究对象,比较了自然恢复方式、恢复利用方式和恢复保护方式下植物多样性、植物生长状态、土壤pH、盐分、容重、水分含量、有机碳、全氮、全磷、速效氮、速效磷的变化特征,研究结果表明:在自然恢复方式下,湿地各层土壤全磷、土壤速效磷、土壤速效氮、物种多样性值最高,反映出自然恢复方式可能成为干旱区土壤磷固存的有效手段,适当干扰可能成为干旱区提高物种多样性的有效方法;恢复保护方式下,湿地植物多度最高165.67±25,表明恢复保护方式有助于植被的生长繁殖;恢复利用方式下,湿地各层土壤含水量、土壤有机碳、土壤全氮、植被盖度值最高,土壤盐分含量、土壤pH值最低,湿地物种多样性较高。表明恢复利用方式可以有效降低湿地土壤盐分,提高土壤碳、氮含量的潜力,适当人为管理可能成为干旱区湿地恢复过程中提高湿地物种多样性的有效管理方法。该研究结果对于干旱区湿地恢复、保护与重建的效应评估和恢复方式的选择提供一定的理论支持和决策参考。     

北方滨海人工湿地水生生物群落快速重建目标及适宜物种清单确定——以天津临港二期湿地为例

由于滨海湿地的萎缩和退化对全球鸟类迁徙构成了严重威胁,开展自然湿地或人工构建湿地生态恢复已经成为滨海湿地保护与研究的重要内容。以天津临港二期湿地为例,研究北方滨海人工湿地生物群落快速重建目标及适宜物种清单的确定方法。临港二期湿地2019年共检出浮游植物110种、浮游动物28种,而大型底栖动物仅1种,鱼类未检出,水体生物种类结构单一,难以为迁徙侯鸟提供充足食源。选择与临港二期湿地相同（近）区域、同盐度水平的北大港湿地自然保护区以及临港一期湿地作为备选参照湿地（参考湿地）进行同步生物多样性调查分析,结果表明,北大港水库东区、北大港水库西区、临港一期湿地具有较好的浮游动植物、底栖动物多样性及鱼类资源,可以作为临港二期湿地修复的参照湿地。与参照湿地相比,临港二期湿地具有较好的浮游植物生物多样性,应重点恢复底栖动物与鱼类群落,考虑到后期鱼类恢复后的食物需求,可同步进行浮游动物的增殖放流。以参照湿地生物多样性调查结果与文献资料数据为依据,确定临港二期湿地底栖动物生态恢复目标为：Shannon-Wiener生物多样性指数远期（10年）达到3.00,近期（5年）达到1.58;生物密度远期（10年）恢复至600个/m²,近期（5年）恢复至300个/m²;同时确定了临港湿地生物群落快速重建的底栖动物清单（15种）与鱼类清单（14种）,并提出了临港二期湿地生态系统恢复的食物网构建路线图。研究结果表明,选择同区域、类似的天然湿地作为参考湿地,通过生物调查与生物多样性比选,确定具体参照湿地,并依据参照湿地生态特征确定待修复湿地的生物群落快速重建目标与适宜物种清单,是合理可行的。     

湿地公园鸟类栖息地营建研究——以北京琉璃河湿地公园为例

北京地区处于全球候鸟东亚-澳大利西亚的迁徙路线上,是候鸟重要的迁徙路线,近些年,随着人为活动的影响,该区生境破碎化问题愈发突出,直接威胁着本地鸟种和过境迁徙鸟类的生存。为达到保护鸟类多样性的目的,需开展相应的栖息地恢复工作。不同生态类群的鸟类对栖息地有着不同的要求,相同鸟种在不同空间、季节和生活期对栖息地的选择也有着不同的特点。因而,鸟类栖息地恢复应针对目标鸟种根据其繁殖特点、巢位空间分布、食性特点、活动空间特点等进行规划营造。以北京房山琉璃河湿地公园为例,针对项目所在区域的鸟类分布特征,确定目标恢复鸟种,结合项目区现场条件,围绕目标鸟种对于栖息地水系、植被等方面的需求,从岸线重塑、水深设计、植物配置、生态鸟岛等方面规划设计鸟类栖息地修复措施。     

城市生态系统中AM真菌侵染与群落结构特征

丛枝菌根(AM)真菌作为土壤微生物的重要成员之一,对城市生态系统可持续发展具有重要意义.本文系统总结了城市生态系统中AM真菌着生状况和群落结构特点,探讨了城市生态因子,如人类行为、植被重建与维护、城市土壤状况等对AM真菌着生状况和群落结构的影响,认为今后应加强城市生态系统中AM真菌群落结构与功能的研究,如关键城市生态因子(如水资源匮乏、热岛效应等)改变AM真菌群落结构的效应与机制.