Understory Research Articles

The effect of forest structure on drought stress in beech forests (Fagus sylvatica L.)

The unprecedented drought between 2018 and 2020 had a significant impact on European beech (Fagus sylvatica L.) forests in Central Europe. The role of different forest structures in mitigating drought stress remains controversial. This contentious debate prompted our study, in which we aimed to quantify the effect of forest structure on drought stress in beech forests in two ecoregions of northern Bavaria, Germany. Using a mobile laser scanner, we surveyed 240 plots in drought-stressed forests. We analyzed the responses of beech trees to the drought period through radial growth, wood-derived δ13C signal, and crown defoliation. Results revealed significant responses of beech forests in both regions to the drought event, including increased crown defoliation, reduced tree growth, and altered δ13C signatures compared to pre-drought conditions. Our results show a relationship between crown closure and crown defoliation in beech, suggesting an increased vulnerability of beech to drought in more open canopies. However, the potential for silvicultural intervention to mitigate drought stress, as measured by BAI and δ13C signal, appears limited. Neighboring trees and forest structure had little influence on average drought resistance. The δ13C signal showed minimal responsiveness to variations in canopy openness, as well as to distinctions between single and multi-layered forests. However, increased structural complexity within stands tended to increase resistance due to the compensatory effects of understory trees. Future forest management strategies could focus on promoting structural diversity, selecting resilient individuals but also actively enrich the forests with more drought-adapted species to increase the adaptive capacity of beech-dominated forests in the face of changing climate conditions.

Understory changes in mixed elm stands in response to canopy dieback in Latvia

In the eastern Baltic region, warming is favouring the advance of thermophilic tree species and the formation of mixed stands with a higher share of broadleaves, thus contributing to productivity and other ecosystem services of forests. However, the accelerating environmental changes often trigger the spread and intensification of biotic disturbances such as disease outbreaks at unprecedented rates, which might alter the course of stand development. Within the region, elms (Ulmus sp.), which are of low importance as a source of timber, yet highly important in terms of other ecosystem services, are suffering varying degree of dieback due to the Dutch elm disease, which can threaten the existence of species. Still, there are explicit local differences in the susceptibility of trees, which add uncertainties regarding the sustainability of elms. A permanent sampling plot network was established to monitor changes in mixed elms stands in response to the dieback caused by the disease; canopy and understory trees were accounted. Two surveys in 2016 and 2021 have been made. Canopy elms have suffered moderate dieback during the first wave already before the surveys, as ca. 17% of canopy elms were already dead. However, the susceptibility differed among the species (Ulmus glabra exceeded U. laevis), likely due to the preference of the vectors of the disease. In response to canopy openings, self-regeneration occurred, though the balance between the advance regeneration and undergrowth species was affected by the intensity of canopy dieback. The advanced growth of the former canopy species including elms was sufficient under moderate changes in the canopy, while low and high changes favoured undergrowth, suggesting the formation of shrubland. Accordingly, the additional mortality of elms due to Dutch elm disease tended to diverge the development course of the mixed broadleaved stands; hence further monitoring is advised. Keywords: Ulmus sp.; Ophiostoma sp.; advance growth; undergrowth; Dutch elm disease; succession

Supporting Operational Tree Marking Activities through Airborne LiDAR Data in the Frame of Sustainable Forest Management

Implementing adaptation and mitigation strategies in forest management constitutes a primary tool for climate change mitigation. To the best of our knowledge, very little research so far has examined light detection and ranging (LiDAR) technology as a decision tool for operational cut-tree marking. This study focused on investigating the potential of airborne LiDAR data in enhancing operational tree marking in a dense, multi-layered forest over complex terrain for actively supporting long-term sustainable forest management. A detailed tree registry and density maps were produced and evaluated for their accuracy using field data. The derived information was subsequently employed to estimate additional tree parameters (e.g., biomass and tree-sequestrated carbon). An integrated methodology was finally proposed using the developed products for supporting the time- and effort-efficient operational cut-tree marking. The results showcased the low detection ability (R2 = 0.15–0.20) of the trees with low DBH (i.e., regeneration and understory trees), while the dominant trees were accurately detected (R2 = 0.61). The stem biomass was accurately estimated, presenting an R2 of 0.67. Overall, despite some products’ low accuracy, their full and efficient exploitability within the aforementioned proposed methodology has been endeavored with the aim of actively contributing to long-term sustainable forest management.

Differential effects of fire regime and site conditions on bark beetles (Coleoptera: Curculionidae) in a longleaf pine (Pinus palustris Mill.) ecosystem

Longleaf pine (Pinus palustris Mill.) ecosystems in the southeastern U.S. are fire-driven. Frequent prescribed fire or lack thereof through shifts in fire regimes may have consequences for tree health and associated herbivorous subcortical beetles (Coleoptera: Curculionidae). Yet, interactions between these ecologically and economically important beetles and prescribed fire in the southeastern U.S. are not well documented. We assessed the effects of various fire regimes, specifically of frequent fire, fire exclusion, and fire reintroduction, on bark and root-feeding beetles in mature longleaf pine stands in two edaphic types (mesic and xeric) in southwestern Georgia. We employed an information theoretic statistical approach to determine the effects of site conditions, as defined by both soil properties and stand structure, and prescribed burning on trap catches of subcortical beetles by species. We trapped a total of 141,611 beetles, indicating that subcortical beetles are abundant in this ecosystem. While the highest trap catches for three Ips beetle species were in the xeric fire-exclusion treatment, catches of I. grandicollis (Eichhoff) were similar at both sites for the fire-exclusion treatment. For the fire-exclusion treatment, I. avulsus (Eichhoff) and I. calligraphus (Germar) catches were 2–10 times higher at the xeric than mesic sites. Orthotomicus caelatus (Eichhoff) and Dendroctonus terebrans (Olivier) catches were 1.1–2.4 times higher in frequent-fire than fire-exclusion treatments. Root-feeding weevils, Pachylobius picivorus (Germar) and Hylobius pales (Herbst), exhibited opposite trends with catches higher and lower in burned treatments, respectively. Ips calligraphus were positively associated with percent basal area of understory trees, indicating this species may benefit from fire exclusion. Ips avulsus catches were negatively correlated with total basal area, suggesting this species may benefit from more open habitats like those facilitated by frequent fire. We conclude that both soil properties and stand conditions interact with the fire regime to differentially affect the catches of southeastern bark and root-feeding beetle species in a longleaf pine ecosystem.

Light more than warming impacts understory tree seedling growth in a temperate deciduous forest

Understanding the distinct impacts of temperature and light on seedling growth is crucial for predicting forest regeneration trajectories under future climate change and forest disturbance. This is because temperature and light can change independently or together, influencing the competitive status of tree seedlings and forest herbs. However, most prior studies tend to explore temperature and light effects either separately or in combination, lacking comprehensive full-factorial designs. Here, we utilized two large-scale full-factorial experiments to explore warming and light effects on tree seedlings growing in mesocosms with herbaceous plants. We found that light increased seedling height, diameter, and biomass, while warming alone had no significant effects. Moreover, we observed that there was an interaction effect between light and warming, where warming increased seedling height, diameter, and biomass under illumination. Understory herbaceous plant cover alone did not affect seedling height, diameter, and biomass, but it decreased seedling biomass when mesocosms were warmed or illuminated. This highlights the importance of considering the indirect negative effects induced by the interaction between forest opening and understory herbaceous plants. By disentangling the effects of increased temperature and light availability on understory seedling height, diameter, and biomass, our results contribute valuable knowledge for future forest management. It is imperative to carefully control the size of the gaps artificially created to facilitate the understory regeneration. Small gaps are recommended considering that the herbaceous plants may interact with both warming and light to negatively affect seedlings.

Characterization and development of 14 microsatellite markers for mountain stewartia (Stewartia ovata): an uncommon, Appalachian-endemic member of the tea family

ABSTRACT Mountain stewartia [Stewartia ovata (Cav.) Weatherby] is a rare, endemic understory tree native to the southeastern U.S.A. While found only in microsites across southeastern Appalachia, the species distribution spans from northern Alabama and Georgia to southern Kentucky and Virginia. However, most occurrences have been recorded in Tennessee. While recent distribution surveys and habitat suitability modeling conducted for this species have improved our understanding of the environmental parameters that constitute its fundamental niche, the ecological profile of S. ovata remains poorly understood. Consequently, its rarity has raised concerns as to the long-term resilience of this species in the wild. Faced with these challenges, the assessment of existing genetic diversity in S. ovata through genetically informative molecular resources is critical to understanding the adaptive potential and ecological resilience of the species. Microsatellites are cost-efficient molecular tools capable of addressing these concerns by elucidating trends in population structure, population demography, and inbreeding. To increase the available genetic resources for S. ovata, we screened 105 microsatellite loci for their suitability to assess these population features using capillary gel electrophoresis. The utility of these markers was evaluated by assessing polymorphism information content (PIC) and population statistics, which yielded 14 highly polymorphic microsatellite markers. These markers displayed an average PIC of 0.695 (PIC range of 0.538–0.851), which supports their ability to capture fine-scale genetic diversity within the species. We also report a low average observed heterozygosity of 0.375 (versus an expected heterozygosity of 0.645) among screened loci, which reinforces the need for broader genetic diversity assessments within this species.

Developing a Structural Complexity Index for Oriental Beech Forests in Northern Iran

Abstract The structural complexity index (SCI) has become an important metric for forest managers to monitor ecosystem services and conservation value in a wide variety of forest types. In this study, we developed an SCI for an unmanaged mixed Fagus orientalis Lipsky forest in northern Iran, which incorporated structural information specific to mature and old-growth forests. Our results showed that we were able to develop an SCI for this forest that would assist managers to make conservation decisions in a forest where large overstory trees and small understory trees are equally important. The SCI was significantly positively correlated with the density of five minor tree species (Acer velutinum Boiss., Acer cappadocicum Gled., Tilia begoniifolia Chun & H.D. Wong, Quercus castaneifolia C.A. Mey., and Prunus avium L.) and the density of large ([50 cm < diameter at breast height {DBH} < 75 cm]) and very large (DBH > 75 cm) overstory trees. The SCI remains a highly flexible tool for forest conservation and decision making and may assist with decisions about forest management in response to climate change and shifting disturbance regimes. Study Implications: Forest managers have begun to use the structural complexity index (SCI) to assess the successful achievement of conservation management objectives. In many mature, mixed-species forests, large trees, minor species, and understory tree species are important structural components. In this study, we demonstrate that reduction of the minimum diameter used for sampling trees and careful selection of the variables used to calculate SCI results in a valuable metric for making conservation decisions. The advantage of SCI as a forest decision tool is that forest managers are able to adjust the inputs used to calculate SCI to reflect specific management objectives or monitoring goals.

Functional traits and adaptive capacity of cloud forest Ternstroemia species in response to climatic variation

Tropical Mountain Cloud Forests (TMCFs) produce distinct climatic gradients that can both constrain and facilitate the presence of tree species and/or specific combinations of functional traits. Local climatic adaptation allows for maximum fitness under hydric stress, resulting in specific morphological adaptations to the TMCF tree species. In this study, we assessed the hypothesis that the functional traits of two uncommon TMCF species (Ternstroemia huasteca and T. sylvatica) would show similar morpho-anatomical adjustments to climate variation. Our research questions were: how do the Ternstroemia functional traits vary interspecifically between TMCFs? Which of these two species is the most climatically vulnerable? To answer these questions, we examined differences in wood anatomical traits and leaf vascular tissues between both species. For this, we assessed the effects of temperature, precipitation, and evapotranspiration on the functional traits of Ternstroemia in different TMCFs. Our analyses suggested that, not all climatic factors considered affected the functional traits of Ternstroemia at the same magnitude. These findings provide insights into the ecophysiological functional trait adaptation mechanisms in response to hydraulic deficit in TMCF understory tree species.

Symbiotic control of canopy dominance in subtropical and tropical forests.

Subtropical and tropical forests in Asia often comprise canopy dominant trees that form symbioses with ectomycorrhizal fungi, and species-rich understorey trees that form symbioses with arbuscular mycorrhizal fungi. We propose a virtuous phosphorus acquisition hypothesis to explain this distinct structure. The hypothesis is based on (i) seedlings being rapidly colonised by ectomycorrhizal fungi from established mycelial networks that generates positive feedback and resistance to pathogens, (ii) ectomycorrhizal fungi having evolved a suite of morphological, physiological, and molecular traits to enable them to capture phosphorus from a diversity of chemical forms, including organic forms, and (iii) allocation of photosynthate carbon from adult host plants to provide the energy needed to undertake these processes.

Dynamics of litterfall production in a forest damaged by oak wilt disease: a case study in a warm-temperate secondary forest

ABSTRACT Quantification of litterfall production is crucial for evaluating net primary productivity and nutrient cycling in forest ecosystems. High mortality among trees in the family Fagaceae due to Japanese oak wilt disease (JOW) might affect litterfall production in secondary forests; however, few studies have quantified these effects. We investigated litterfall production and forest structure in warm-temperate secondary forests in the Kaisho Forest over 6 and 12 years, respectively, and compared the dynamics among different phases of a JOW outbreak to assess the impacts of JOW on litterfall production. We found that total annual litterfall and leaf fall showed little change in peak to post-JOW periods and that changes in basal area were unrelated to total litterfall and leaf fall. The observed fluctuation in BA in the Kaisho Forest may not have been large enough to clearly reveal the effect of JOW during these periods. Canopy gaps formed by JOW may enhance the recruitment and growth rates of sub-canopy and understory trees. Our results may only be applicable to warm secondary forests where evergreen trees are replacing deciduous trees. Additional information on litterfall production in JOW-disturbed secondary forests is needed.

Differences of oribatid mite community and trophic structure between karst caves and surface different moss habitats.

In order to reveal the community characteristics and trophic structure of oribatid mites in different moss habitats in karst caves, the oribatid mites in the moss habitats of ground (GD), understory (US), cave wall (CW), surface shrub (SB) and farmland (FL) outside the cave were collected in October 2021. Through the identification and data analysis of oribatid mites, 2352 oribatid mites were found, belonging to 45 families and 72 genera, most of which were Gymnonota. The family number, genus number, individual number, individual density, dominant genus composition, community diversity, community similarity, MGP (Analysis methods for ecological groups of oribatid mites) ecological group of oribatid mites and trophic structure of oribatid mites in different moss were analyzed. The results showed that: (1) The number of families, genera, individuals, and individual density of SB and FL are higher than those of the other three habitats; (2) Platyliodes, Oppiella, Tectocepheus, Scutovertex, Scheloribates and Trichogalumna are the dominant genera of the oribatid mites in the cave moss habitat, among them, Tectocepheus and Trichogaluna have the most obvious advantages; (3) The diversity index of shrub (SB) was higher than that of other four habitats; Similarity between ground and cave wall, shrub and farmland is high; (4) The MGP ecological group of oribatid mites in different habitats is dominated by O type (Overall type belongs to MGP analysis results, 20%≤M,G,P≤50%), and a total of 42 genera of oribatid mites preliminarily constitute the trophic structure of oribatid mites in the cave moss habitat. Based on the above results, it can be concluded that there are differences in the community structure of oribatid mites in different moss habitats in the study area, and the use of dominant genera of mites can preliminarily indicate the environmental conditions of different moss habitats. This study enriches the study of mites in karst cave mosses, and can provide theoretical significance for the protection of cave biodiversity in karst areas.

The Grove of Giants: Tasmania's most carbon‐dense forest

AbstractThe Grove of Giants in the Huon Valley of Tasmania, Australia is renowned for its large trees. A team of tree climbers and citizen scientists undertook a carbon assessment of a 2 hectare plot within the Grove of Giants. The largest 16 trees in the plot (>2.5 m DBH) were measured by tree climbers allowing for accurate estimation of tree volume. Understory trees, coarse woody debris, root biomass and soil carbon were also estimated, making this study the most comprehensive assessment of forest carbon in Tasmania. Total forest carbon was estimated to be 1312 tonnes per hectare. Large trees had the highest carbon stocks, accounting for 44% of the total store. Coarse woody debris represented 19% of the forest's carbon, root biomass was 14%, while the understory trees accounted for 12% and soil carbon for 11%. This is the highest carbon stock recorded in Tasmania and is above the average estimates for temperate forest ecosystems in other parts of the world. Protecting Tasmania's forests, especially mature wet Eucalypt forests, is important to avoid potential greenhouse gas emissions and ensure safe storage of the carbon in the land sector.

Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest

Windthrow (i.e., trees broken and uprooted by wind) is a major natural disturbance in Amazon forests. Images from medium-resolution optical satellites combined with extensive field data have allowed researchers to assess patterns of windthrow tree-mortality and to monitor forest recovery over decades of succession in different regions. Although satellites with high spatial-resolution have become available in the last decade, they have not yet been employed for the quantification of windthrow tree-mortality. Here, we address how increasing the spatial resolution of satellites affects plot-to-landscape estimates of windthrow tree-mortality. We combined forest inventory data with Landsat 8 (30 m pixel), Sentinel 2 (10 m), and WorldView 2 (2 m) imagery over an old-growth forest in the Central Amazon that was disturbed by a single windthrow event in November 2015. Remote sensing estimates of windthrow tree-mortality were produced from Spectral Mixture Analysis and evaluated with forest inventory data (i.e., ground true) by using Generalized Linear Models. Field measured windthrow tree-mortality (3 transects and 30 subplots) crossing the entire disturbance gradient was 26.9 ± 11.1% (mean ± 95% CI). Although the three satellites produced reliable and statistically similar estimates (from 26.5% to 30.3%, p < 0.001), Landsat 8 had the most accurate results and efficiently captured field-observed variations in windthrow tree-mortality across the entire gradient of disturbance (Sentinel 2 and WorldView 2 produced the second and third best results, respectively). As expected, mean-associated uncertainties decreased systematically with increasing spatial resolution (i.e., from Landsat 8 to Sentinel 2 and WorldView 2). However, the overall quality of model fits showed the opposite pattern. We suggest that this reflects the influence of a relatively minor disturbance, such as defoliation and crown damage, and the fast growth of natural regeneration, which were not measured in the field nor can be captured by coarser resolution imagery. Our results validate the reliability of Landsat imagery for assessing plot-to-landscape patterns of windthrow tree-mortality in dense and heterogeneous tropical forests. Satellites with high spatial resolution can improve estimates of windthrow severity by allowing the quantification of crown damage and mortality of lower canopy and understory trees. However, this requires the validation of remote sensing metrics using field data at compatible scales.

Tree species growth response to climate warming varies by forest canopy position in boreal and temperate forests.

Reports of forest sensitivity to climate change are based largely on the study of overstory trees, which contribute significantly to forest growth and wood supply. However, juveniles in the understory are also critical to predict future forest dynamics and demographics, but their sensitivity to climate remains less known. In this study, we applied boosted regression tree analysis to compare the sensitivity of understory and overstory trees for the 10 most common tree species in eastern North America using growth information from an unprecedented network of nearly 1.5 million tree records from 20,174 widely distributed, permanent sample plots across Canada and the United States. Fitted models were then used to project the near-term (2041-2070) growth for each canopy and tree species. We observed an overall positive effect of warming on tree growth for both canopies and most species, leading to an average of 7.8%-12.2% projected growth gains with climate change under RCP 4.5 and 8.5. The magnitude of these gains peaked in colder, northern areas for both canopies, while growth declines are projected for overstory trees in warmer, southern regions. Relative to overstory trees, understory tree growth was less positively affected by warming in northern regions, while displaying more positive responses in southern areas, likely driven by the buffering effect of the canopy from warming and climate extremes. Observed differences in climatic sensitivity between canopy positions underscore the importance of accounting for differential growth responses to climate between forest strata in future studies to improve ecological forecasts. Furthermore, latitudinal variation in the differential sensitivity of forest strata to climate reported here may help refine our comprehension of species range shift and changes in suitable habitat under climate change.

Browsing by non-native invasive sambar deer dramatically impacts forest structure

Large herbivores introduced to novel habitats can cause major ecosystem impacts. While impacts of overabundant deer have been documented around the world, there are few examples from Australia, where deer are non-native and natural predators are absent.Here, we outline the impacts of sambar deer in wet eucalypt forest understoreys of the Yarra Ranges National Park, south-eastern Australia. Using data obtained from a full and partial (permitting native herbivores) exclusion experiment over four years, we (i) demonstrate differences between native herbivore and introduced deer browsing, (ii) identify plant species commonly browsed by deer, and (iii) provide evidence that vegetation condition can recover in the absence of deer.While species richness and composition were unaffected, the exclusion of deer led to substantial recovery of several attributes of forest understorey vegetation. Treatments excluding deer (partial and full exclosures) saw increases in the cover of understorey trees, shrubs, ferns and climbers. Within the 1–2 m height class (the primary deer browse zone), vegetation cover-abundance increased 3–4 fold over time in full and partial exclusion plots compared to non-exclusion controls.Tree ferns (Dicksonia antarctica and Cyathea australis) were particularly impacted by deer, and browsing impacts to tree ferns were dramatically reduced from ∼50% of fronds browsed to negligible levels with deer exclusion. Deer exclusion also saw substantial reductions in browsing to individual trees, shrubs and ground ferns. The growth of commonly browsed trees, e.g. Pomaderris aspera, were demonstrably higher in partial and full exclosures than unfenced control plots. The low levels of browsing on trees and shrubs that persisted in partial exclosures probably indicates the background levels of browsing pressure attributable to native herbivores in these forests.In the absence of effective deer control, commonly browsed understorey trees, shrubs and tree ferns are likely to decrease substantially in cover over coming decades, potentially leading to increased light availability, drying of the understorey, and increased susceptibility to wildfire. The potential cascading ecological effects of unabated and increasing deer impacts may be substantial and pose major challenges to forest management.Despite management culls and recreational hunting in recent years, deer populations are increasing across Australia. As sambar populations increase, ecological impacts are likely to exacerbate. It is therefore critically important to reduce sambar numbers, before negative and potentially irreversible changes occur to forest structure, composition and function.

Elevated mortality rates of large trees allow for increased frequency of intermediate trees: A hypothesis supported by demographic model comparison with plot and LiDAR data

Tree diameter distributions are important indicators of forest structure, are a principal element of forest carbon stock estimates, and are theoutcome of forest demography. Hump-shaped tree diameter distributions, also known as rotated-sigmoid diameter distributions, are characterized by an increased frequency of intermediately-sized trees over what would be extrapolated from the small tree size distribution and are common in temperate forests. One hypothesis to explain hump-shaped tree size distributions is the U-shaped mortality curve, where the mortality rates of the largest canopy trees are higher than those of intermediately-sized canopy trees. However, studies that have directly tested this hypothesis by comparing tree diameter distributions predicted from forest demographic models with empirical diameter distributions are lacking, and how the U-shaped mortality curve influences other aspects of forest structure such as canopy height is not well understood. We used model-data comparisons to test the hypothesis that the U-shaped mortality curve generates the hump-shaped tree diameter distribution. We used two versions of a forest demographic model (the PPA model) to predict tree diameter distributions, one that assumed that tree demographic rates varied only between understory and canopy trees, and a second that assumed tree demographic rates varied among understory trees, small canopy trees, and large canopy trees, consistent with the U-shaped mortality curve. We compared predictions from each form of the model with empirical tree diameter distributions from the Wind River Forest Dynamics plot, a 27.2 ha forest dynamics plot with a hump-shaped diameter distribution. We found that the model that accounted for the higher mortality rates of larger canopy trees generated a hump-shaped distribution, whereas the model that did not account for the higher mortality rates of larger trees was not able to generate a hump-shaped diameter distribution. To understand how the assumptions of forest demographic patterns affected other aspects of forest structure that could be derived from remote sensing, we compared predictions of forest canopy height from each form of the model with measurements of forest canopy height derived from airborne LiDAR. We found that accounting for the higher mortality rates of larger trees became even more critical to accurate prediction of forest canopy height because intermediate-sized trees occupy large areas in the canopy. Our results demonstrate the link between the U-shaped mortality curve and hump-shaped diameter distributions, and suggest that accurate characterization of the demography of large trees may be particularly important for predicting forestcanopy structure and carbon stocks.

How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement

How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement

Nectar microbes may indirectly change fruit consumption by seed-dispersing birds

An increasing number of recent studies show that nectar-inhabiting microorganisms influence plant fitness by mediating interactions between plants and pollinators. However, whether the effects of nectar microbes extend beyond pollination to affect subsequent stages of plant reproduction remains largely unknown. This study aims to explore whether nectar microbes can indirectly affect fruit consumption by birds, which can be essential for seed dispersal and germination. Wild flowers of Eurya japonica trees were experimentally inoculated with the nectar-inhabiting yeast Metschnikowia reukaufii and the nectar-inhabiting bacterium Acinetobacter boissieri, both of which had been previously isolated frequently from E. japonica flowers. In this experiment, I examined whether these microbes changed female reproductive success of the understory tree. Experimental inoculation of flowers with yeasts decreased fruit and seed set compared to those inoculated with bacteria, and the control. Furthermore, fruits with higher seed set tended to be larger, and larger fruits were more likely to be consumed by seed-dispersing birds, including the Japanese white-eye Zosterops japonica, the brown-eared bulbul Hypsipetes amaurotis, and the Daurian redstart Phoenicurus auroreus. These results suggest that nectar-inhabiting microorganisms have the potential to affect plant reproduction by influencing not only plant-pollinator interactions, but also by indirectly modifying plant-frugivore interactions via changes in plant-pollinator interactions.

The photosynthetic eco-physiological adaptability of the endangered plant Tetracentron sinense to different habitats and altitudes

Tetracentron sinense Oliv, the only tall deciduous tree in the family Tetracentraceae, is listed as a national second-grade key protected plant in China. To reveal the effect of associated species, irradiance, and altitudes on photosynthetic capacity of T. sinense, photosynthetic physiological characteristics of T. sinense and its associated species Acer pictum and Pterocarya stenoptera were measured by a Li-6400 portable photosynthetic meter. The light saturation point (LSP), the maximum net photosynthetic rate of the PN-PAR (PNmax), carboxylation efficiency (CE), the maximum net photosynthetic rate of the PN-CO2 (P*Nmax), carbon dioxide compensation point (CCP) and light respiration rate (Rp) of T. sinense in forest gap (FG) were higher than those in forest edge (FE) and understory (US). In FE, the net photosynthetic rate (PN), light compensation point (LCP), LSP, P*Nmax of T. sinense were lower than those of Pterocarya stenoptera, while the LSP, PNmax, and saturation point of carbon dioxide (Ciast) of T. sinense in US were lower than those of Acer pictum and Pterocarya stenoptera. The specific leaf area (SLA) of T. sinense decreased with reduction in the irradiance. With increasing altitude, the PNmax, LSP, and SLA of young individuals of T. sinense (YT) increased; the LCP of YT or the LSP of mature individuals of T. sinense (MT) increased first and then decreased. The results showed that 1) the photosynthetic capacity and adaptability of T. sinense were better in FG than that in FE and US; 2) the photosynthetic capacity of T. sinense in FE and US was weaker than that of its associated species, and its ecological range of light adaptation was also narrower than that of its associated species, placing T. sinense at a competitive disadvantage, which may be one of the important reasons for its poor regeneration; and 3) the environmental conditions at higher altitude can contribute to the growth and survival of T. sinense. Therefore, active artificial intervention should be undertaken to expand area of forest gap for T. sinense and transplant its seedlings to higher altitude to promote growth and population regeneration of T. sinense.

Lianas increase lightning-caused disturbance severity in a tropical forest.

Lightning is an important agent of plant mortality and disturbance in forests. Lightning-caused disturbance is highly variable in terms of its area of effect and disturbance severity (i.e. tree damage and death), but we do not know how this variation is influenced by forest structure and plant composition. We used a novel lightning detection system to quantify how lianas influenced the severity and spatial extent (i.e. area) of lightning disturbance using 78 lightning strikes in central Panama. The local density of lianas (measured as liana basal area) was positively associated with the number of trees killed and damaged by lightning, and patterns of plant damage indicated that this occurred because lianas facilitated more electrical connections from large to small trees. Liana presence, however, did not increase the area of the disturbance. Thus, lianas increased the severity of lightning disturbance by facilitating damage to additional trees without influencing the footprint of the disturbance. These findings indicate that lianas spread electricity to damage and kill understory trees that otherwise would survive a strike. As liana abundance increases in tropical forests, their negative effects on tree survival with respect to the severity of lightning-related tree damage and death are likely to increase.