Is patience a virtue? Succession, light, and the death of invasive glossy buckthorn (Frangula alnus)

Non-native, invasive glossy buckthorn (Frangula alnus P. Mill.) threatens North American forests by inhibiting tree regeneration. While glossy buckthorn commonly invades younger, developing forests, we hypothesized that this species is competitively excluded as secondary succession proceeds. Specifically, we tested the hypothesis that glossy buckthorn mortality in New Hampshire forests is associated with low levels of photosynthetically active radiation (PAR), low levels of nutrients in the soil, and greater abundance of shade tolerant tree species. Twenty-six living and 26 dead glossy buckthorn individuals were randomly selected on three, mid-successional study sites in southeastern New Hampshire, USA. Shrub ages, indicated by wood ring counts, showed that both living and dead shrubs were members of the same cohort, roughly 16–18 years of age. Living and dead shrubs were compared as to (1) tree basal area in the surrounding forest (estimated by plot sampling), (2) light intensity in the vicinity of the buckthorn crowns (measured by Sunfleck Ceptometer), (3) canopy openness and % total transmitted PAR (estimated by hemispheric photography), and (4) concentrations of available Ca, P, Mg, and K in the B horizon. Relative to live buckthorn shrubs, dead individuals were associated with greater basal area of shade tolerant species, decreased PAR in the vicinity of shrub crown, and decreased soil concentrations of Ca, P, and Mg. The results are consistent with the hypothesis that competition for light and perhaps nutrients limits the ability of glossy buckthorn to persist in late successional stands. If these relationships are causal, active removal of glossy buckthorn might not be required to reduce its abundance in late successional stands.     

Passive restoration in Araucaria Forest: useful ecological indicators in monitoring successional advancement in exotic tree plantation landscapes

Monitoring successional advancement is a complex field involving a constant search for applied ecological indicators which facilitate monitoring of secondary forests for both active and passive restoration. In this study, the authors investigate the successional advancement of floristics and tree structure within Araucaria Forest (AF) fragments under passive restoration in a context where exotic tree plantations (mainly Pinus L. genus) dominate the landscape. The ecological indicators used were floristic dissimilarity (β‐diversity inferences), indicator species, ecological groups of species, basal area, and species abundance distribution (SAD) models (α‐diversity inferences). A total of 182 tree species belonging to 91 genera and 43 botanical families were identified. A high β diversity was verified for which each site has indicator species (for the locations CD—Dicksonia sellowiana; CO—Cryptocarya aschersoniana; and PG—Pinus taeda), where pioneer species contributed to much of the abundance. Different SAD models are useful for describing passive restoration sites in exotic tree plantation landscapes, namely Lognormal, Mandelbrot, and Zipf. SAD models together with basal area, taxonomic group (e.g. Myrtaceae assemblage), and tree abundance in ecological groups are strategic ecological indicators for monitoring successional advancement in AF.     

Ecosystem controls on nitrogen fixation in boreal feather moss communities

N fixation in feather moss carpets is maximized in late secondary successional boreal forests; however, there is limited understanding of the ecosystem factors that drive cyanobacterial N fixation in feather mosses with successional stage. We conducted a reciprocal transplant experiment to assess factors in both early and late succession that control N fixation in feather moss carpets dominated by Pleurozium schreberi. In 2003, intact microplots of moss carpets (30 cm × 30 cm × 10–20 cm deep) were excavated from three early secondary successional (41–101 years since last fire) forest sites and either replanted within the same stand or transplanted into one of three late successional (241–356 years since last fire) forest sites and the transverse was done for late successional layers of moss. Moss plots were monitored for changes in N-fixation rates by acetylene reduction (June 2003–September 2005) and changes in the presence of cyanobacteria on moss shoots by microscopy (2004). Forest nutrient status was measured using ionic resin capsules buried in the humus layer. Late successional forests exhibit high rates of N fixation and consistently high numbers of cyanobacteria on moss shoots, but low levels of available N. Conversely, early successional forests have higher N availability and have low rates of N fixation and limited presence of cyanobacteria on moss shoots. Transplantation of moss carpets resulted in a significant shift in presence and activity of cyanobacteria 1 year after initiation of the experiment responding to N fertility differences in early versus late successional forests.     

On the dynamics,floristic subdivision and geographical distribution of várzea forests in Central Amazonia

Abstract. Within different stands of the white-water inundation forest (várzea forest) in the Central Amazon region, composition, abundance, frequency and basal area of tree species were recorded. Determinations of age and radial growth rates were conducted using dendrochronological methods. Results show significant differences in age, history and species composition between stands as well as different growth strategies among dominant species. Assignment of tree species to growth strategies by means of anatomical and morphological features together with quantitative aspects of vegetational analysis permit the further differentiation of successional stages of várzea forests. General features of successional stages were quantitatively described and compared with forest types from outside the várzea. Many tree species of the várzea forests are widespread in South America, and not limited to floodplains. Their occurrence on sites with distinct dry seasons suggests that they are not specifically adapted to flooding but are tolerant to seasonality in general.     

岷江冷杉林皆伐后次生群落结构和物种多样性的演替动态

为阐明岷江冷杉林皆伐后次生群落的演替过程,采用空间代替时间的方法,在川西米亚罗林区海拔3100—3600 m的阴坡选择岷江冷杉林皆伐后次生演替10、20、30、40和50a阶段的次生群落作为研究对象,对其群落结构和物种多样性的动态进行了研究。不同演替阶段的树木均呈显著聚集分布。按群落中优势种的重要值将该演替序列划分为3个类型:悬钩子-蔷薇灌丛、白桦阔叶林和桦木-岷江冷杉针阔混交林。随次生演替,乔木和灌木种的物种丰富度趋于增加,而草本种的物种丰富度趋于减少;乔木和灌木种的Shannon-Wiener多样性指数趋于增大,而草本的Shannon-Wiener多样性指数趋于减小;乔木、灌木和草本层的Pielou均匀度指数均趋于增大;乔木层的Simpson优势度指数趋于减小,灌木和草本层的Simpson优势度指数在演替0—40年阶段趋于增大,而在演替50a阶段趋于减小。在该演替序列中,乔木、灌木和草本层的物种组成均呈耐荫种替代非耐荫种的趋势。     

Ecosystem development in short‐term postglacial chronosequences: N and P limitation in glacier forelands from Santa Inés Island,Magellan Strait

Glacier foreland moraines provide an ideal model to examine the patterns of ecosystem development and the evolution of nitrogen and phosphorous limitation over successional time. In this paper, we focus on a 400‐year soil chronosequence in the glacier forelands of Santa Inés Island in the Magellan Strait, southern Chile by examining forest development on phosphorus (P)‐poor substrates in a uniquely unpolluted region of the world. Results show a steady increase in tree basal area and a humped trend in tree species richness over four centuries of stand development. The increase in basal area suggests that the late successional tree species were more efficient nutrient users than earlier successional ones. Total contents of carbon (C) and nitrogen (N) in soils increased during the chronosequence, reaching an asymptote in late succession. The net increases in soil C : N, C : P and N : P ratios observed over successional time suggest that nutrient limitation is maximal in 400‐year‐old substrates. Foliar C : N and C : P ratios also increased over time to reach an asymptote in old‐growth stages, following soil stoichiometric relationships; however the foliar N‐to‐P ratio remained constant throughout the chronosequence. Biological N fixation was greater in early postglacial succession, associated with the presence of the symbiotic N‐fixer Gunnera magellanica. Declining trends of δ¹⁵N in surface soils through the 400‐year chronosequence are evidence of decreasing N losses in old‐growth forests. In synthesis, glacier foreland chronosequences at this high South American latitude provide evidence for increasing efficiency of N and P use in the ecosystem, with the replacement of shade‐intolerant pioneers by more efficient, shade‐tolerant tree species. This pattern of ecosystem development produces a constant foliar N : P ratio, regardless of variation in soil N‐to‐P ratio over four centuries.     

Characteristics of the Psidium cattleianum invasion of secondary rainforests

Strawberry guava (Psidium cattleianum) is a shade‐tolerant shrub or small tree invader in tropical and subtropical regions and is considered among the world's top 100 worst invasive species. Studies from affected regions report deleterious effects of strawberry guava invasion on native vegetation. Here we examine the life history demographics and environmental determinants of strawberry guava invasions to inform effective weed management in affected rainforest regions. We surveyed the vegetation of 8 mature rainforest and 33 successional sites at various stages of regeneration in the Australian Wet Tropics and found that strawberry guava invasion was largely restricted to successional forests. Strawberry guava exhibited high stem and seedling densities, represented approximately 8% of all individual stems recorded and 20% of all seedlings recorded. The species also had the highest basal area among all the non‐native woody species measured. We compared environmental and community level effects between strawberry guava‐invaded and non‐invaded sites, and modelled how the species basal area and recruitment patterns respond to these effects. Invaded sites differed from non‐invaded sites in several environmental features such as aspect, distance from intact forest blocks, as well as supported higher grass and herb stem densities. Our analysis showed that invasion is currently ongoing in secondary forests, and also that strawberry guava is able to establish and persist under closed canopies. If left unchecked, strawberry guava invasion will have deleterious consequences for native regenerating forest in the Australian Wet Tropics.     

Forest decline after a 15-year “perfect storm” of invasion by hemlock woolly adelgid,drought, and hurricanes

Invasions by introduced pests can interact with other disturbances to alter forests and their functions, particularly when a dominant tree species declines. To identify changes after invasion by the insect hemlock woolly adelgid (Adelges tsugae; HWA), coinciding with severe droughts and hurricanes, this study compared tree species composition of eastern hemlock (Tsuga canadensis) forests on 11 plots before (2001) and 15 years after (2016) invasion in the southern Appalachian Mountains, USA. Losses of hemlock trees after HWA invasion were among the highest reported, with a 90% decline in density, 86% decline in basal area, and 100% mortality for individuals ≥ 60 cm in diameter. In contrast to predictions of theoretical models, deciduous tree density declined after HWA invasion, while basal area changed little, at least during the initial 15 years after invasion. Overall, forest density declined by 58%, basal area by 25%, and tree species richness by 8%. Factors additional to HWA likely exacerbating forest decline included: droughts before (1999–2001) and after HWA invasion (2006–2008); tree uprooting from hurricane-stimulated winds in 2004; pest-related declines of deciduous tree species otherwise likely benefitting from hemlock’s demise; death of deciduous trees when large hemlocks fell; and competition from aggressive understory plants including doghobble (Leucothoe fontanesiana), rosebay rhododendron (Rhododendron maximum), and Rubus spp. Models of forest change and ecosystem function should not assume that deciduous trees always increase during the first decades after HWA invasion.     

Feedbacks between canopy composition and seedling regeneration in mixed conifer broad‐leaved forests

To address the role of canopy‐seedling feedbacks in the structure and dynamics of mixed conifer broad‐leaved forests in the eastern US, we monitored seedling regeneration patterns and environmental conditions in the understorey of stands dominated by either hemlock (Tsuga canadensis) or red oak (Quercus rubra) for three years. Hemlock seedlings were favoured over other species’ seedlings in hemlock stands (a true positive feedback), due to a combination of high seed inputs, high seedling emergence and relatively high seedling survival during the growing season, which allowed hemlock to remain dominant under its own canopy. Red oak stands favoured a suite of mid‐successional broad‐leaved species over hemlock. A more even age structure of broad‐leaved species in red oak stands revealed that high seedling survival in such stands were driving this feedback. Canopy‐mediated variations in both understorey light availability (1.5% for hemlock vs 3.5% for red oak) and soil pH (3.9 for hemlock vs 4.4 for red oak) were found to be the primary correlates of stand‐level differences in seedling regeneration dynamics. In mixed temperate forests in the eastern US, canopy‐seedling feedbacks could act to slow successional trajectories and contribute to the maintenance of a stable landscape structure over many generations.     

Converging forest community composition along an edaphic gradient threatens landscape‐level diversity

Aim Plant communities across the temperate zone are changing in response to successional processes and human‐induced disturbances. Here, we assess how upland forest under‐ and overstorey community composition has changed along an edaphic gradient. Location Northern Wisconsin, USA. Methods Forest sites initially sampled in the 1950s were resampled for overstorey composition and diversity, basal area, and understorey composition and diversity. We used clustering methods to identify groups of stands based on overstorey composition, and we used similarity indices, ordination and diversity indices to evaluate changes in species abundance and overall community structure. Results Sites clustered into four overstorey groups along the edaphic gradient: ‘hemlock’ sites dominated by hemlock in 1950, ‘mesic’ sites dominated by northern hardwoods, ‘dry’ sites with a significant pine inclusion in the canopy and diverse ‘dry‐mesic’ sites in the middle. Collectively, forests gained maple, ash and cherry while losing pines, birches and red oaks. The hemlock forest sites gained hardwoods, while the dry‐mesic sites shifted towards a more mesic hardwood composition. Only the driest sites have remained relatively stable in species composition. Main conclusions These trends reflect both ‘mesification’ and homogenization among northern forests. Highly diverse mid‐gradient and mesic hemlock‐dominated stands are transitioning to maple dominance. Fire suppression may be favouring invasions of more mesic plants into historically drier sites, while high deer abundance likely limits hemlock regeneration. If current trends continue, maples will dominate the majority of northern forests, with significant losses of local native species richness and substantial shifts in understorey composition.     

Decades of atmospheric deposition have not resulted in widespread phosphorus limitation or saturation of tree demand for nitrogen in southern New England

It is commonly assumed that nitrogen (N) is the primary mineral resource limiting the productivity of temperate forests. Sustained inputs of N via atmospheric deposition are altering the N status of temperate forests raising the possibility that nutrients such as phosphorus (P) are increasingly limiting productivity. The objective of this study was to determine whether P availability limits tree growth alone or in combination with N. This study was conducted in two forest types common throughout the New England landscape of the northeastern United States; in sugar maple and white ash dominated stands growing on base rich parent material characterized by rapid rates of N cycling and high N availability, and in red oak–beech–hemlock dominated stands growing on base-poor parent material characterized by slow rates of N cycling and low N availability. Starting in 2004, N and P were added to replicate plots in each forest type in factorial combination at a rate of 150 and 50 kg ha⁻¹ year⁻¹, respectively. Diameter growth rates of all trees >10 cm DBH were measured in 2005 and 2006 using dendrometer bands and converted into units of basal area increment (BAI) and wood production. Following 2 years of fertilization, basal area increment in the sugar maple–white ash forests remained strongly N limited. Fertilization with P did not significantly increase BAI alone, although both N and P fertilization tended (P < 0.10) to increase diameter growth in white ash. Wood production in the N-fertilized plots increased by 100 g C m⁻² year⁻¹, roughly doubling production in the non-fertilized plots. In the red oak–beech–hemlock stands, there was no overall effect of N or P fertilization on BAI or wood production because BAI in some species was stimulated by fertilization with N alone (e.g., black cherry, red oak), while in other species BAI was unaffected (e.g., red maple, beech) or negatively affected by fertilization with N or P (e.g., eastern hemlock). Given that BAI in several tree species responded to fertilization with N alone and that only one species responded to P fertilization once N was added, this study suggests that decades of atmospheric N deposition have not (yet) resulted in widespread P limitation or saturation of tree demand for N.     

Earthworms, stand age, and species composition interact to influence particulate organic matter chemistry during forest succession

The landscapes colonized by invasive earthworms in the eastern U.S. are often patchworks of forest stands in various stages of successional development. We established six field sites in tulip poplar dominated forests in the Smithsonian Environmental Research Center in Edgewater, MD, that span mid (50–70 years-three plots) and late (120–150 years-three plots) successional stages where younger sites had greater earthworm density and biomass than older sites and were dominated by non-native lumbricid species. In particular Lumbricus rubellus, a litter-feeding species, was abundant in mid successional forests. Here, we separated particulate organic matter (POM) from the bulk soil by a combination of size and density fractionation and found that patterns in soil POM chemistry were similar to those found previously during litter decay: in younger forests with high abundance of earthworms, organic carbon normalized cutin- and suberin-derived substituted fatty acid (SFA) concentration was lower and lignin-derived phenols greater than in older forests where earthworms were less abundant. The chemistry of the dominant litter from mid versus late successional tree species did not fully explain the differences in POM chemistry between age classes. Instead, the differences in leaf body versus petiole and leaf versus root chemistry were the dominant drivers of POM chemistry in mid versus late successional stands, although aspects of stand age and tree species also impacted POM chemistry. Our results indicate that preferential ingestion of leaf body tissue by earthworms and the subsequent shifts in sources of plant biopolymers in soil influenced POM chemistry in mid successional forests. These results indicate that invasive earthworm activity in North American forests contributes to a shift in the aromatic and aliphatic composition of POM and thus potentially influences carbon stabilization in soil.     

大兴安岭不同演替阶段天然林物种多度格局模拟

为实现大兴安岭地区落叶松天然林的全周期可持续经营,以新林林业局翠岗林场3块100m×100m不同演替阶段(白桦林、落叶松-白桦混交林和落叶松林)的天然林固定调查样地数据为基础,采用统计模型(对数正态模型)、生态位模型(断棍模型、生态位优先占领模型、Zipf模型、Zipf-Mandelbrot模型)和中性模型(群落零和多项式模型、Volkov模型)对不同演替阶段天然林的乔木层、幼苗层和由乔木层划分的不同林层的物种多度格局进行拟合,并用χ² 检验和Kolmogorov-Smirnov检验选择最佳模型。结果表明:(1) 在大兴安岭地区不同演替阶段的落叶松天然林群落中,Zipf-Mandelbrot模型的拟合效果均最好。(2) 对数正态模型对于稳定的演替阶段白桦林和落叶松林的群落相较于过渡阶段群落落叶松-白桦混交林的物种多度分布的拟合效果更好。(3) 在大兴安岭地区落叶松天然林中,生境过滤主导群落构建,随着群落不断演替生境过滤和中性过程减弱。(4) 天然林群落乔木层的群落构建过程与乔木层内不同生长阶段林层的构建过程不同,生境过滤过程在落叶松林乔木层中逐渐减弱,而在落叶松林不同生长阶段的林层和更新层中增强。     

Riverscape-level patterns of riparian plant diversity along a successional gradient, Willamette river, Oregon

Riparian forest communities dominated by Populus balsamifera ssp. trichocarpa L. (Torr. and Gray ex Hook.) Brayshaw are important contributors to biodiversity in terrestrial and aquatic ecosystems of the Western United States. Species composition along a successional gradient from stand initiation to late-succession of P. balsamifera-dominated riparian forests was investigated along 145 km of the Willamette River, Oregon. There were 151 total species encountered across 28 stands and a mean species richness of 33.3 species per stand. Young stands were dominated by P. balsamifera and Salix tree spp. and opportunistic herbaceous species. Understory trees, shrubs, and herbaceous species as well as late-successional tree species established 12–15 years after stand initiation. Fraxinus latifolia Benth. was the dominant late-successional tree species. Vertical structural diversity, P. balsamifera mean diameter at breast height, large tree biomass, and stand age were strongly correlated with understory species presence and abundance based on non-metric multidimensional scaling (NMS) ordination. There were no young stands on mid and high terraces and this was reflected in geomorphic position being strongly correlated with the stand age gradient. Abundance of Phalaris arundinacea L. an invasive grass species, was also significantly correlated with plant species composition and abundance. This study indicates that Willamette River riparian forests are diverse and therefore important to the biodiversity of the Willamette River valley and that their presence as a mosaic of communities of different successional stages may be threatened by human interventions, including influences exerted by introduced plant species.     

Species diversity and community structure in sal (<Emphasis Type="Italic">Shorea robusta</Emphasis>) forests of two different rainfall regimes in West Bengal,India

Knowledge on the structure and composition of the plant communities has enormous significance in conservation and management of forests. The present study aimed to assess the community attributes, viz., structure, composition and diversity in the moist and dry sal (Shorea robusta) forests in the West Bengal province of India and compare them with the other sal forests of India. The phytosociological data from these forests were quantitatively analysed to work out the species richness, diversity, evenness, dominance, importance value, stand density and the basal area. The analysis showed that plant richness and diversity in moist sal forests of northern West Bengal are higher than the dry sal forests of south-west Bengal; a total of 134 tree (cbh ≥30 cm), 113 shrub and 230 herb species were recorded in the moist sal forest compared to 35 tree, 41 shrub and 96 herb species in dry sal forest. Papilionaceae was observed to be the dominant family. Dry sal forests had higher tree dominance (0.81) and stand density (1,006 stems ha⁻¹) but lower basal area (19.62 m²ha⁻¹) while moist sal forest had lower tree dominance (0.18) and stand density (438 stems ha⁻¹) but higher basal area (56.52 m²ha⁻¹). Tree species richness and stem density across girth classes in both the types decreased from the smallest to largest trees, while the occurrence rate of species increased with increase in girth class. A t-test showed significant differences in species richness, basal area and the stand density at 95% confidence level (p = <0.05) in the two forest types. The CCA indicated very low overall match (canonical correlation value = 0.40) between the two sets of variables from moist and dry sal types. The differences in these forests could be attributed to the distinct variations in climatic conditions- mainly the rainfall, disturbance regimes and the management practices.     

Forest dynamics following eastern hemlock mortality in the southern Appalachians

Understanding changes in community composition caused by invasive species is critical for predicting effects on ecosystem function, particularly when the invasive threatens a foundation species. Here we focus on dynamics of forest structure, composition and microclimate, and how these interact in southern Appalachian riparian forests following invasion by hemlock woolly adelgid, HWA, Adelges tsugae. We measured and quantified changes in microclimate; canopy mortality; canopy and shrub growth; understory species composition; and the cover and diversity in riparian forests dominated by eastern hemlock Tsuga canadensis over a period of seven years. Treatments manipulated hemlock mortality either through invasion (HWA infested stands) or girdling (GDL) hemlock trees. Mortality was rapid, with 50% hemlock tree mortality occurring after six years of invasion, in contrast to more than 50% mortality in two years following girdling. Although 50% of hemlock trees were still alive five years after infestation, leaf area lost was similar to that of girdled trees. As such, overall responses over time (changes in light transmittance, growth, soil moisture) were identical to girdled stands with 100% mortality. Our results showed different growth responses of the canopy species, shrubs and ground layer, with the latter being substantially influenced by presence of the evergreen shrub, rhododendron Rhododendron maximum. Although ground layer richness in the infested and girdled stands increased by threefold, they did not approach levels recorded in hardwood forests without rhododendron. Increased growth of co‐occurring canopy trees occurred in the first few years following hemlock decline, with similar responses in both treatments. In contrast, growth of rhododendron continued to increase over time. By the end of the study it had a 2.6‐fold higher growth rate than expected, likely taking advantage of increased light available during leaf‐off periods of the deciduous species. Increased growth and dominance of rhododendron may be a major determinant of future responses in southern Appalachian ecosystems; however, our results suggest hemlock will be replaced by a mix of Acer, Betula, Fagus and Quercus canopy genera where establishment is not limited by rhododendron.     

Successional shifts in tree demographic strategies in wet and dry Neotropical forests

Aim

Tropical forest succession and associated changes in community composition are driven by species demographic rates, but how demographic strategies shift during succession remains unclear. Our goal was to identify generalities in demographic trade-offs and successional shifts in demographic strategies across Neotropical forests that cover a large rainfall gradient and to test whether the current conceptual model of tropical forest succession applies to wet and dry forests.

Location

Mexico and Central America.

Time period

1985–2018.

Major taxa studied

Trees.

Methods

We used repeated forest inventory data from two wet and two dry forests to quantify demographic rates of 781 tree species. For each forest, we explored the main demographic trade-offs and assigned tree species to five demographic groups by performing a weighted principal components analysis to account for differences in sample size. We aggregated the basal area and abundance across demographic groups to identify successional shifts in demographic strategies over the entire successional gradient from very young (<5 years) to old-growth forests.

Results

Across all forests, we found two demographic trade-offs, namely the growth–survival trade-off and the stature–recruitment trade-off, enabling the data-driven assignment of species to five demographic strategies. Fast species dominated early in succession and were then replaced by long-lived pioneers in three forests. Intermediate and slow species increased in basal area over succession in all forests, but, in contrast to the current conceptual model, long-lived pioneers continued to dominate until the old-growth stage in all forests. The basal area of short-lived breeders was low across all successional stages.

Main conclusions

The current conceptual model of Neotropical forest succession should be revised to incorporate the dominance of long-lived pioneers in late-successional and old-growth forests. Moreover, the definition of consistent demographic strategies that show clear dominance shifts across succession substantially improves the mechanistic understanding and predictability of Neotropical forest succession.     

Tree species composition and diversity gradients in white-water forests across the Amazon Basin

Aim Attention has increasingly been focused on the floristic variation within forests of the Amazon Basin. Variations in species composition and diversity are poorly understood, especially in Amazonian floodplain forests. We investigated tree species composition, richness and α diversity in the Amazonian white‐water (várzea) forest, looking particularly at: (1) the flood‐level gradient, (2) the successional stage (stand age), and (3) the geographical location of the forests. Location Eastern Amazonia, central Amazonia, equatorial western Amazonia and the southern part of western Amazonia. Methods The data originate from 16 permanent várzea forest plots in the central and western Brazilian Amazon and in the northern Bolivian Amazon. In addition, revised species lists of 28 várzea forest inventories from across the Amazon Basin were used. Most important families and species were determined using importance values. Floristic similarity between plots was calculated to detect similarity variations between forest types and over geographical distances. To check for spatial diversity gradients, α diversity (Fisher) of the plots was correlated with stand age, longitudinal and latitudinal plot location, and flood‐level gradient. Results More than 900 flood‐tolerant tree species were recorded, which indicates that Amazonian várzea forests are the most species‐rich floodplain forests worldwide. The most important plant families recorded also dominate most Neotropical upland forests, and c. 31% of the tree species listed also occur in the uplands. Species distribution and diversity varied: (1) on the flood‐level gradient, with a distinct separation between low‐várzea forests and high‐várzea forests, (2) in relation to natural forest succession, with species‐poor forests in early stages of succession and species‐rich forests in later stages, and (3) as a function of geographical distance between sites, indicating an increasing α diversity from eastern to western Amazonia, and simultaneously from the southern part of western Amazonia to equatorial western Amazonia. Main conclusions The east‐to‐west gradient of increasing species diversity in várzea forests reflects the diversity patterns also described for Amazonian terra firme. Despite the fine‐scale geomorphological heterogeneity of the floodplains, and despite high disturbance of the different forest types by sedimentation and erosion, várzea forests are dominated by a high proportion of generalistic, widely distributed tree species. In contrast to high‐várzea forests, where floristic dissimilarity increases significantly with increasing distance between the sites, low‐várzea forests can exhibit high floristic similarity over large geographical distances. The high várzea may be an important transitional zone for lateral immigration of terra firme species to the floodplains, thus contributing to comparatively high species richness. However, long‐distance dispersal of many low‐várzea trees contributes to comparatively low species richness in highly flooded low várzea.     

Experimental Native Tree Seedling Establishment for the Restoration of a Mexican Cloud Forest

The cloud forests of Mexico have been degraded and severely fragmented, and urgently require restoration. However, progress with restoration has been constrained by a lack of information concerning the seedling ecology of native tree species. An experiment was therefore conducted to assess the influence of different environmental factors on the seedling survival and growth of four native tree species (Fagus grandifolia var. mexicana, Carpinus caroliniana, Symplocos coccinea, and Quercus acutifolia). The seedlings were established on three sites, in two contrasting environments: inside forest fragments and on adjacent agricultural land. Highly significant differences were recorded in seedling survival and growth among sites, environments, species, and interactions between these factors. Highest survival was recorded for Quercus, which uniquely among the four species displayed the same survival percentage inside and outside the forest. Survival of the other species was higher inside the forest. In contrast, growth rates of all four species were higher outside the forest. The most important cause of mortality outside the forest was desiccation, although significant seedling predation was also observed on two sites. Results indicate that all four species can be established successfully both within forest fragments and in neighboring agricultural areas, emphasizing the scope for forest restoration. However, the interactions observed between species, sites, and environments highlight the importance of accurate species–site matching if optimum rates of growth and survival are to be obtained. Quercus spp. have great potential for establishment on agricultural sites.     

Differential susceptibility of tree species to oviposition by periodical cicadas

Abstract 1. Periodical cicadas occur widely in deciduous forests of eastern North America and represent the largest insect emergences in the world. Their effects on forest community dynamics, via oviposition damage and root feeding, are potentially great but not well understood. If tree species vary in their susceptibility to cicada oviposition and root colonization, then periodical cicadas may affect ecological interactions among tree species and forest composition. 2. We measured oviposition damage on 63 tree species at 52 sites in southern Indiana, U.S.A. for two broods of periodical cicadas. We compared oviposition damage among different sites, habitats, and tree species. We also measured cicada emergence rates in mature and successional forest habitats and from beneath different tree species. 3. Certain tree species received significantly more oviposition damage than others, and the most and least damaged species were consistent between the two broods. For some species, oviposition damage varied between mature and successional sites. Despite the differences in oviposition rates among species, there was no difference in emergence rates from beneath different tree species, suggesting that initial differences in cicada density among tree species are not maintained through the nymphal life cycle. 4. Cicadas oviposited more at successional sites, but emerged more in mature forest stands, suggesting that successive generations of cicadas represent a shifting mosaic between forests of different ages. As tree species consistently vary in their susceptibility to oviposition damage, periodical cicadas could alter local competitive interactions and therefore affect forest dynamics.