Forest Understorey Research Articles

Contrasting strategies in morphological and physiological response to drought stress among temperate forest understory forbs and graminoids.

Drought stress can profoundly affect plant growth and physiological vitality, yet there is a notable scarcity of controlled drought experiments focused on herbaceous species of the forest understorey. In this study, we collected seeds from five forb and four graminoid species common in European temperate forests. Seeds were germinated under controlled glasshouse conditions and subjected to moderate drought stress for 5 weeks. We assessed biomass partitioning, stomatal and leaf morphology, leaf gas exchange, minimum leaf conductance (gmin), and chlorophyll fluorescence parameters. Comparison of the two ecological guilds revealed that graminoids had a higher R/S, improved WUE, greater carboxylation efficiency, and enhanced non-photochemical quenching under drought conditions compared to forbs. In contrast, forbs had significantly lower gmin, with higher total biomass and total leaf area. Despite these differences in morpho-physiological functional traits, both groups experienced a similar relative reduction in biomass after drought stress. Key predictors of biomass accumulation under drought included photochemical quenching, stomatal traits, total leaf area and gmin. A negative correlation between biomass and gmin suggests that plants with lower residual water loss after stomatal closure can accumulate more biomass under drought stress. Additionally, gmin was positively correlated with guard cell length, suggesting that larger stomata contribute to higher residual water loss. Contrasting strategies in morpho-physiological responses to drought define the differences between the two groups. In graminoids, drought resistance suggests greater emphasis on stress tolerance as a survival strategy. In contrast, forbs were able to maintain higher biomass and total leaf area, indicating a competitive strategy for maximizing resource acquisition.

Linking individualistic growth stability of trees to the complexity of understorey layers

Abstract Tree‐growth stability is crucial in upholding forest ecosystem services. Despite extensive research on the correlation between tree growth and climate, the influence of forest understorey on tree‐growth stability remains understudied. We surveyed forest plots and collected tree‐ring samples along two elevational gradients, ranging from 3600 to 4400 m a.s.l., in the southeastern Tibetan Plateau. An index was developed to quantify individualistic growth stability of trees, and its linkage with the complexity of forest understorey structure was examined. We found that tree‐growth stability is more pronounced in complex forest communities. In forests with higher understorey complexity, the proportion of trees experiencing growth release increased during wet years, while those with growth suppression augmented during dry years. Interestingly, a subset of trees exhibits abnormal growth increases even during the driest years, whereas another subset shows abnormal growth reductions during the wettest years. Furthermore, forests with more complex understorey structures exhibited a higher proportion of trees showcasing these two types of ‘anti‐phase’ growth statuses. Synthesis. Our study underscores the linkage between individualistic growth stability of trees and the complexity of understorey structures. The growth stability of the overstorey layer is conveyed at the expense of individual‐level growth stability and synchrony in forests with complex understorey structures. These findings emphasize the necessity for attention to the interplay between tree growth and understorey community structures when assessing the impacts of future climate change on forest dynamics.

Effects of humic acid fertilizer on the growth and microbial network stability of Panax notoginseng from the forest understorey

Humic acid (HA) can substantially enhance plant growth and improve soil health. Currently, the impacts of HA concentrations variation on the development and soil quality of Panax notoginseng (Sanqi) from the forest understorey are still unclear. In this study, exogenous HA was administered to the roots of Sanqi at varying concentrations (2, 4, and 6 ml/L). Subsequently, the diversity and community structure of bacteria and fungi were assessed through high-throughput sequencing technology. The investigation further involved analyzing the interplay among the growth of sanqi, soil edaphic factors, and the microbial network stability. Our finding revealed that moderate concentrations (4 ml/L) of HA improved the fresh/dry weight of Sanqi and NO3-−N levels. Compared with control, the moderate concentrations of HA had a notable impact on the bacterial and fungal communities compositions. However, there was no significant difference in the α and β diversity of bacteria and fungi. Moreover, the abundance of beneficial bacteria (Bradyrhizobium) and harmful bacteria (Xanthobacteraceae) increased and decreased at 4 ml/L HA, respectively, while the bacterial and fungal network stability were enhanced. Structural equation model (SEM) revealed that the fresh weight of Sanqi and bacterial and fungal communities were the factors that directly affected the microbial network stability at moderate concentrations of HA. In conclusion, 4 ml/L of HA is beneficial for promoting Sanqi growth and soil quality. Our study provides a reference for increasing the yield of Sanqi and sustainable development of the Sanqi-pine agroforestry system.

Insectivorous birds and bats outperform ants in the top-down regulation of arthropods across strata of a Japanese temperate forest.

Birds, bats and ants are recognised as significant arthropod predators. However, empirical studies reveal inconsistent trends in their relative roles in top-down control across strata. Here, we describe the differences between forest strata in the separate effects of birds, bats and ants on arthropod densities and their cascading effects on plant damage. We implemented a factorial design to exclude vertebrates and ants in both the canopy and understorey. Additionally, we separately excluded birds and bats from the understorey using diurnal and nocturnal exclosures. At the end of the experiments, we collected all arthropods and assessed herbivory damage. Arthropods responded similarly to predator exclusion across forest strata, with a density increase of 81% on trees without vertebrates and 53% without both vertebrates and ants. Additionally, bird exclusion alone led to an 89% increase in arthropod density, while bat exclusion resulted in a 63% increase. Herbivory increased by 42% when vertebrates were excluded and by 35% when both vertebrates and ants were excluded. Bird exclusion alone increased herbivory damage by 28%, while the exclusion of bats showed a detectable but non-significant increase (by 22%). In contrast, ant exclusion had no significant effect on arthropod density or herbivory damage across strata. Our results reveal that the effects of birds and bats on arthropod density and herbivory damage are similar between the forest canopy and understorey in this temperate forest. In addition, ants were not found to be significant predators in our system. Furthermore, birds, bats and ants appeared to exhibit antagonistic relationships in influencing arthropod density. These findings highlight, unprecedentedly, the equal importance of birds and bats in maintaining ecological balance across different strata of a temperate forest.

Forest floor environment overrules global change treatment effects on understorey communities in a mesocosm experiment.

Light availability profoundly influences plant communities, especially below dense tree canopies in forests. Canopy disturbances, altering forest floor light conditions, together with other environmental changes such as climate change, nitrogen deposition and legacy effects from previous land-use will simultaneously impact forest understorey communities. Yet, knowledge on the individual effects of these drivers and their potential interactions remains scarce. Here we performed a forest mesocosm experiment to assess the influence of warming, illumination (simulating canopy opening), nitrogen deposition and soil land-use history (comparing ancient and post-agricultural forest soil) on understorey community composition trajectories over a 7-year period. Strikingly, understorey communities primarily evolved in response to the deeply shaded ambient forest conditions, with experimental treatments exerting only secondary influences. The overruling trajectory steered all mesocosms towards slow-colonizing forest specialist communities dominated by spring geophytes with lower nutrient-demand. The illumination treatment and, to a lesser extent, warming and agricultural land-use legacy slowed down this trend by advancing fast-growing resource-acquisitive generalist species. Warm ambient temperatures induced thermophilization of plant communities in all treatments, including control plots, towards higher dominance of warm-adapted species. Nitrogen addition accelerated this thermophilization process and increased the community light-demand signature. Land-use legacy effects were limited in our study. Our findings underscore the essential role of limited light availability in preserving forest specialists in understorey communities and highlight the importance of maintaining a dense canopy cover to attenuate global change impacts. It is crucial to integrate this knowledge in forest management adaptation to global change, particularly in the face of increasing demands for wood and wood products and intensified natural canopy disturbances.

Deer exclusion is necessary to promote post‐fire herbaceous regeneration in the understorey of a Mediterranean forest

The frequency of severe wildfires is on the rise in the Mediterranean Basin as a result of climate change and land abandonment. Recurrent wildfires may retard or impede ecosystem recovery, frequently requiring the implementation of restoration practices. In that context, a post‐fire deer exclusion experiment was conducted in a Mediterranean mixed forest ecosystem with high population densities of deer species (Fallow deer and Red deer). A deer exclusion area was established as a form of restoration intervention to promote post‐fire vegetation recovery. We surveyed plant species during the second and third springs after fire in both deer‐excluded and deer‐allowed areas in order to detect changes in the community. We analyzed the plant species composition, species diversity, and structure of herbaceous and woody plant communities. We also compared the frequency of annual and perennial herb species, functional groups, and post‐fire plant regeneration strategies. The main differences were due to differences between springs rather than of deer‐excluded and deer‐allowed plots. Deer consumed both woody and herbaceous species, favoring the assemblage of herbaceous over woody species. Deer favored the establishment of annual forbs, including unpalatable and/or exotic species, while limiting the abundance of graminoids. Observed deer impacts could have been magnified during the second spring by a drought. Our study demonstrates that deer exclusion can be an effective restoration practice for promoting post‐fire herbaceous regeneration in forests with significant densities of wild ungulates, although seasonal effects may override restoration practice effects.

Contrasting light capture strategies between shade-tolerant and -intolerant tree seedlings responding to solar canopy spectral composition

Forest regeneration is a crucial ecological process for promote self-reproduction and restoration, which is essential for maintaining complex community structure and preserving biological resources. Although sunlight have been considered as the main driver of forest regeneration, how light quality shapes functional traits of seedlings is poorly understood in the forest understorey, where spectral compositions of solar radiation change dramatically. We investigated the responses of 15 typical functional traits of Pinus koraiensis and Quercus mongolica to five filter treatments that differed in the spectral transmittance: (a) 95 % of solar radiation was transmitted (280–700 nm); (b) ultraviolet (UV)-B radiation was attenuated (>315 nm); (c) all UV radiation was attenuated (>400 nm); (d) all UV radiation and blue light was attenuated (>500 nm); (e) all UV radiation, blue-green light was attenuated (>580 nm). Our results showed that functional traits responded to UV-B radiation (contrasting treatment [a] vs. [b]) with species-dependence, but consistently showed a positive response to blue light (contrasting treatment [c] vs. [d]). UV-B radiation decreased the relative growth rate (RGR) and leaf area ratio (LAR) of P. koraiensis seedlings by 48 % and 42 %, respectively; however, it increased seedling height, total leaf area (TLA), and above-ground biomass of Q. mongolica. Blue light consistently increased LAR and RGR of two species. Furthermore, Q. mongolica was more plastic in morphological traits (including plant height and TLA) and root/shoot ratio than P. koraiensis to the single spectral region (UV-B, UV-A, blue, and green light), but opposite in physiological and biochemical traits (such as chlorophyll and anthocyanidin). These suggest that two studied species have evolved different light capture strategies in the understorey: Q. mongolica seedlings tended to adjust morphology and biomass allocation to enhance light interception capacity, while P. koraiensis seedlings preferred to adjust physiological and biochemical traits to enhance light utilization efficiency. A better understanding how canopy spectral compositions affect seedling regeneration may provide a new insight for future forest management (i.e. the appropriate gap creation or tree species combination).

Enhanced mangrove index: A spectral index for discrimination understorey, nypa, and mangrove trees

Unsupervised classification using vegetation indices has been extensively employed to map mangrove forests using medium-resolution satellite images. However, its capability is restricted to determining the extent of mangroves only. This study introduces a new spectral index called the enhanced mangrove index (EMI) for accurately mapping different components of mangrove vegetation, including mangrove trees, nypa, and understorey. An immediate effort is required to monitor the invasion of nypa and understorey in the mangrove forest of Segara Anakan Lagoon, located in Central Java, Indonesia. This issue may also be prevalent in other mangrove areas worldwide. The development of EMI involved: 1). the analysis of the reflectance exhibited by different types of mangrove vegetation, and 2). The performance of EMI was evaluated by comparing it with spectral indices such as automated mangrove map and index (AMMI), as well as supervised classification models like random forest (RF). The accuracy assessment indicates that the overall accuracy and Kappa coefficient achieved values of 0.87 and 0.84, respectively, surpassing other spectral indices and supervised classification models. AMMI and RF exhibited high overall accuracy, with values of 0.82 and 0.73, respectively. Additionally, they demonstrated a Kappa coefficient of 0.77 and 0.66, respectively.

Post‐drought community turnover and functional redundancy in a tropical forest understorey

AbstractQuestionsDrought events are increasingly frequent, threatening the biodiversity of tropical forests. The understorey comprises a large fraction of the total plant species richness of these systems with the presence of highly diverse angiosperm families. Here, we quantified the effects of a drought on abundance and functional structures and on the ecosystem functioning of Rubiaceae assemblages along a topographic gradient.LocationMata das Flores State Park, an Atlantic Forest fragment in southeast Brazil.MethodsTwo vegetation surveys were performed: one during an El Niño‐induced drought, and the other three years after this drought. Abundance and functional structures were assessed using the 16 most‐abundant species of Rubiaceae, which comprised 92% of the total abundance. A litter decomposition experiment was carried out to estimate the percentage of mass loss by the Rubiaceae species. We carried out Procrustes analyses on abundance and functional structures and used Generalized Linear Mixed Models to test the effects of drought and topographic habitats on taxonomic and functional compositions, and mass loss.ResultsWe found that the functional structure and mass loss remained constant despite significant changes in the abundance structure after the drought.ConclusionThe evidence points to the maintenance of ecosystem functioning through functional redundancy, because functionally similar less‐abundant species replaced each other after the drought. We show that swarms of species can maintain biological diversity and stability in ecosystem functioning under drought in the understorey of a tropical forest.

Elevation differentially shapes functional diversity patterns in understorey forest communities when considering intraspecific and interspecific trait variability

AbstractQuestionsWhat is the relative importance of interspecific and intraspecific trait variation and their covariation in the herb layer of European temperate beech forests, and how do they vary with elevation? Is there evidence of interspecific trait convergence at higher elevations, as postulated by the habitat‐filtering hypothesis, and is this convergence enhanced or counteracted by intraspecific variation?LocationNational Park “Foreste Casentinesi, Monte Falterona and Campigna”, Italy.MethodsWe measured four functional traits – plant height, specific leaf area (SLA), leaf dry matter content (LDMC) and leaf area – across 775 individuals from 60 herb‐layer species in 28 forest plots (10 m × 10 m) spanning an 800 m elevation gradient. For each trait in each plot, we computed community‐weighted means (CWMs) and the standardized effect size of functional diversity (SES‐FD). We decomposed total trait variation into its interspecific and intraspecific components, and their covariation. We run linear regression models to assess the impact of elevation on these three components of functional variation. Lastly, we investigated whether higher elevation communities exhibited lower SES‐FD, indicating functional convergence that could hint to a stronger habitat filtering.ResultsInterspecific trait variation was more important than the intraspecific counterpart both for CWMs and SES‐FD. Only CWMs calculated for plant height and LDMC showed a significant relationship with elevation. Low‐elevation communities featured taller, more‐conservative species, whereas shorter, faster‐growing species were more common at higher elevations. SES‐FD remained consistently negative for species turnover and total variation, suggesting stable functional convergence across the gradient.ConclusionsOur findings suggest that interspecific and intraspecific trait variability can be decoupled along an elevation gradient, stressing the importance of individually considering each component of trait variation when studying community composition. Elevation significantly influenced various components of plant community trait variation, with habitat filtering playing a substantial role in selecting plants with specific traits across elevations.

Environmental, social and economic sustainability in Lao coffee

Laos has experienced an emergence of coffee cultivation as Loa farmers, many of them women, have been cultivating coffee in the understorey of natural forests. This form of agroforestry produces high-quality specialty coffee, earning farmers a significant income while preserving biodiversity. Farmers’ adoption of agroforestry, in place of traditional shifting agriculture has been supported by initiatives like the Swiss Agency for Development and Cooperation (SDC) project, which establishes agroforestry learning centres and mini-processing centres, in collaboration with companies such as the MX Coffee Company and the Comma Coffee Company. Developments in coffee cultivation have been on the rise in the last three decades in Keoset, a community in Khoun District, where failed development projects were later revived by SDC and improved upon with market-oriented initiatives. The project has assisted in establishing coffee nurseries, providing training, and establishing partnerships with private companies for processing and marketing and as a result, farmers have advanced from selling unprocessed cherries to selling parchment (semi-processed beans), earning them a higher income. Farmers selling green beans are also collecting a premium price from roasting companies and exporters. The ability to generate an income from coffee cultivation is significant, because 90% of the farmers engaged in coffee cultivation are women, who are now able to depend on an independently earned income, granting them a greater voice in household decision-making. Climate change poses potential risk to the future of coffee production, but the protection offered by forests largely shields coffee crops from storms and changes in temperature. The forests' maintenance of biodiversity also protects the predators of pests and disease, ensuring no chemical methods are needed for pest control, including against the coffee cherry borer (Hypothenemus hampei). A variety of challenges remain for which there are recommended responses. Challenges of institutional and legal context require capacity building within the government; world price fluctuations necessitate that farmers practice a mixed farming system to not rely solely on coffee; geographical limitations promote a focus on specialty-grade coffee; and competition from other cash crops requires awareness of the environmental risks associated with other crops and stricter zoning and regulation over different production systems. It is worth heeding these recommendations, as agroforestry coffee systems enhance livelihoods, empower women, promote environmental sustainability and demonstrate resilience to climate change, making it a potential model for countries facing similar challenges in similar agroecological zones.

Extinction drives recent thermophilization but does not trigger homogenization in forest understorey.

The ongoing climate change is triggering plant community thermophilization. This selection process ought to shift community composition towards species adapted to warmer climates but may also lead to biotic homogenization. The link between thermophilization and homogenization and the community dynamics that drive them (colonization and extinction) remain unknown but is critical for understanding community responses under rapid environmental change. We used 14,167 pairs of plots to study shifts in plant community during 10 years of rising temperature in 80 forest ecoregions of France. We computed community mean thermal optimum (thermophilization) and Δβ-diversity (homogenization) for each ecoregion and partitioned these changes into extinction and colonization dynamics of cold- and warm-adapted species. Forest understorey communities thermophilized on average by 0.12 °C per decade and up to 0.20 °C per decade in warm ecoregions. This rate was entirely driven by extinction dynamics. Extinction of cold-adapted species was a driver of homogenization but it was compensated for by the colonization of rare species and the extinction of common species, resulting in the absence of an apparent homogenization trend. Here we show a dieback of present cold-adapted species rather than an adaptation of communities via the arrival of warm-adapted species, with a mutually cancelling effect on β-diversity. These results suggest that a future loss of biodiversity and delayed biotic homogenization should be considered.

Effects of leaf silicon on drought performance of tropical tree seedlings.

Elevated leaf silicon (Si) concentrations improve drought resistance in cultivated plants, suggesting Si might also improve drought performance of wild species. Tropical tree species, for instance, take up substantial amounts of Si, and leaf Si varies markedly at local and regional scales, suggesting consequences for seedling drought resistance. Yet, whether elevated leaf Si improves seedling drought performance in tropical forests is unknown. To manipulate leaf Si concentrations, seedlings of seven tropical tree species were grown in Si-rich and -poor soil, before exposing them to drought in the forest understorey. Survival, growth and wilting were monitored. Elevated leaf Si did not improve drought survival and growth in any of the species. In one species, drought survival was reduced in seedlings previously grown in Si-rich soil, contrary to our expectation. Our results suggest that elevated leaf Si does not improve drought resistance of wild tropical tree species. Elevated leaf Si may even reduce drought performance, suggesting differences in soil conditions influencing leaf Si may contribute to soil-related variation of tropical seedling performance. Furthermore, our results are at odds with most studies on cultivated species and show that alleviative effects of Si in crops cannot be generalized to wild plants in natural systems.

Marijordaania (Celastraceae: Cassinoideae), a new monotypic genus from South Africa

Background and aims – The species name Gymnosporia filiformis, validly published in a 1927 revision of South African Celastraceae, was based on syntypes representing both Maytenus cordata and a new species. Subsequent studies supported the distinction of Gymnosporia and Maytenus as separate genera. From 1984, this new species was provisionally referred to by the designation “Maytenus sp. A”. Maytenus in Africa comprises a diverse group of species not closely related to the New World members of Maytenus. Here, we clarify the taxonomic identity and generic placement of G. filiformis, and compare it with species with which it has historically been confused. Material and methods – Descriptions and observations are based on extensive field work, supported by conventional taxonomic methods, including study of relevant literature and herbarium collections. Key results – The name Gymnosporia filiformis is lectotypified using a syntype representing “Maytenus sp. A”. We describe a new monotypic genus, Marijordaania, to accommodate “Maytenus sp. A”, and propose the new combination, Marijordaania filiformis. An amended description is provided for the species. It is morphologically quite different from Maytenus cordata, but also from Maytenus acuminata and Maytenus abbottii, species with which it has been confused in the past. Marijordaania filiformis grows in the understorey of evergreen Scarp Forest and is relatively rare, known with certainty only from KwaZulu-Natal and the Eastern Cape provinces, South Africa. A preliminary conservation assessment suggests that M. filiformis should be classified as Endangered. Conclusion – Marijordaania filiformis is a taxonomically isolated species with no apparent close relatives among African Celastraceae. While the generic status of other African members of Maytenus still needs to be resolved, it would not impact the taxonomic status of Marijordaania. In a recent key for Celastraceae genera based on morphology and geography, M. filiformis ran to the genus Euonymus, but this association lacks support from available molecular evidence.

Newly found leaf arrangement to reduce self-shading within a crown in Japanese monoaxial tree species.

A newly found leaf arrangement to reduce self-shading was observed in a Japanese warm-temperate forest. For monoaxial trees that deploy leaves directly on a single stem, leaf arrangements involving progressive elongation of the petiole and progressive increase in deflection angle (the angle between stem and petiole) from the uppermost to the lowermost leaves act to reduce self-shading. However, the progressive reduction in petiole length and deflection angle from the uppermost to the lowermost leaves should also result in the reduction of self-shading. Nevertheless, the latter leaf arrangement has not been reported previously for any tree species. Four Araliaceae species, namely, Gamblea innovans, Chengiopanax sciadophylloides, Dendropanax trifidus and Fatsia japonica, which are typical monoaxial tree species in Japan, were studied. We examined the crown structure of saplings growing in the light-limited understorey in a Japanese warm-temperate forest. Two evergreen species, Dendropanax trifidus and F. japonica showed progressive petiole elongation and progressive increase in the deflection angle from the uppermost to the lowermost leaves. In contrast, saplings of deciduous species, G. innovans and C. sciadophylloides had a leaf arrangement involving progressive reduction in petiole length and deflection angle from the uppermost to the lowermost leaves. The leaf arrangement has diversified among members of the same family, but all four studied species develop a crown with little self-shading that is adapted for growth in the light-limited understorey. Although trees are likely to be under the same selective pressure to reduce self-shading, this study revealed that there is flexibility in its morphological realisation, which has been poorly appreciated previously.

Multiple drivers of functional diversity in temperate forest understories: Climate, soil, and forest structure effects

In macroecology, shifting from coarse- to local-scale explanatory factors is crucial for understanding how global change impacts functional diversity (FD). Plants possess diverse traits allowing them to differentially respond across a spectrum of environmental conditions. We aim to assess how macro- to microclimate, stand-scale measured soil properties, forest structure, and management type, influence forest understorey FD at the macroecological scale.Our study covers Italian forests, using thirteen predictors categorized into climate, soil, forest structure, and management. We analyzed five traits (i.e., specific leaf area, plant size, seed mass, belowground bud bank size, and clonal lateral spread) capturing independent functional dimensions to calculate the standardized effect size of functional diversity (SES-FD) for all traits (multi-trait) and for single traits. Multiple regression models were applied to assess the effect of predictors on SES-FD.We revealed that climate, soil, and forest structure significantly drive SES-FD of specific leaf area, plant size, seed mass, and bud bank. Forest management had a limited effect. However, differences emerged between herbaceous and woody growth forms of the understorey layer, with herbaceous species mainly responding to climate and soil features, while woody species were mainly affected by forest structure.Future warmer and more seasonal climate could reduce the diversity of resource economics, plant size, and persistence strategies of the forest understorey. Soil eutrophication and acidification may impact the diversity of regeneration strategies; canopy closure affects the diversity of above- and belowground traits, with a larger effect on woody species. Multifunctional approaches are vital to disentangle the effect of global changes on functional diversity since independent functional specialization axes are modulated by different drivers.

Vapor pressure deficit drives the mortality of understorey woody plants during drought recovery in the Atlantic Forest

AbstractQuestionDrought‐induced tree mortality has been documented in forests worldwide but the mechanisms related to drought recovery are still poorly understood. To better predict forest trajectories under future climate scenarios, it is essential to disentangle physiological mechanisms underlying plant mortality caused by El Niño droughts. Here, we assessed how vegetation structure, vapor pressure deficit (VPD), and functional traits interact to mediate tree mortality after a severe drought in a tropical forest.LocationMata das Flores State Park, an Atlantic Forest fragment in southeast Brazil.MethodsWe established 20 permanent plots with contrasting vegetation structure and topography. In each plot, we measured tree abundance and diameter at breast height (DBH) of every woody plant (1–10 cm diameter) at the end of the drought, and two years after the break of drought, to calculate mortality rates during drought recovery. Hydraulic (e.g., maximum stomatal conductance to water vapor, stomatal density, etc.) and economic traits (specific leaf area, wood density, etc.) were measured on the 10 most abundant species. We also measured local air temperature and air humidity using HOBO dataloggers in each plot to calculate the VPD.ResultsThe studied Atlantic Forest understorey did not recover from the 2014–2016 drought, in terms of tree mortality. Lower VPD, driven by big trees in the valley, protected understorey plants with acquisitive economic attributes and conservative hydraulic attributes against mortality. On the other hand, higher VPD, driven by smaller trees and higher stem density on the ridge and slope, increased the mortality of understorey plants with acquisitive attributes.ConclusionRidges represent the most important fraction of the Atlantic Forest and our results suggest this type of forest is at high climate risk due to global change. Altogether, our results highlight that valleys are microclimate refuges for understorey plants and might help mitigate drought impacts in tropical forest under forecasted climate changes.

Spider Fungi: New species of Marasmius and Pusillomyces in the aerial rhizomorph webmaker guild in Amazonia

Rhizomorphs are hair- or wire-like melanized structures with structural differentiation analogous to plant roots that help fungi spread over an area and find food resources. Some species of multiple groups of the Ascomycota and the Basidiomycota produce different types of rhizomorphs. In the Agaricales, the structures are largely found in Marasmiineae, particularly in the Omphalotaceae, Marasmiaceae, and Physalacriaceae. Many rhizomorph-forming species spread over the forest floor (ground level), while others form aerial litter-trapping rhizomorph systems that hang on living branches of the forest understorey. Here, we describe three new species that form aerial systems, two in Marasmius and one in Pusillomyces, all of which inhabit areas of the Amazon rainforest in Amazonas State, Brazil. Support for these new species is based on evidence derived from morphological and molecular phylogenetic analyses using nuclear ribosomal internal transcribed spacer region (nrITS) and nuclear ribosomal large subunit (nrLSU) markers. Marasmius foliauceps sp. nov., with a pileipellis made up of Rotalis-type broom cells, is different from all other species described to date and branched along with species of the monophyletic Marasmius sect. Marasmius subsect. Marasmius, being conspecific with specimens from Guyana. Also different from all other described Marasmius species, Marasmius arachnotropus sp. nov. has a pileipellis mostly composed of Siccus-type but in transition to Rotalis-type broom cells and branched along with species of the Marasmius crinis-equi species complex. Pusillomyces cuieirasensis is morphologicallyvery similar to Pusillomyces manuripioides to which it is sister, but it has a non-umbonate pileus and smaller basidiospores. They all form aerial litter-trapping rhizomorph systems that mimic spider webs, particularly those hanging on the understorey. Whether made of mycelia or silk, such webs serve to capture food. The aerial rhizomorph-forming ‘spider fungi’ make up a guild with hidden species diversity in tropical systems.

Combining multiple investigative approaches to unravel functional responses to global change in the understorey of temperate forests

AbstractPlant communities are being exposed to changing environmental conditions all around the globe, leading to alterations in plant diversity, community composition, and ecosystem functioning. For herbaceous understorey communities in temperate forests, responses to global change are postulated to be complex, due to the presence of a tree layer that modulates understorey responses to external pressures such as climate change and changes in atmospheric nitrogen deposition rates. Multiple investigative approaches have been put forward as tools to detect, quantify and predict understorey responses to these global‐change drivers, including, among others, distributed resurvey studies and manipulative experiments. These investigative approaches are generally designed and reported upon in isolation, while integration across investigative approaches is rarely considered. In this study, we integrate three investigative approaches (two complementary resurvey approaches and one experimental approach) to investigate how climate warming and changes in nitrogen deposition affect the functional composition of the understorey and how functional responses in the understorey are modulated by canopy disturbance, that is, changes in overstorey canopy openness over time. Our resurvey data reveal that most changes in understorey functional characteristics represent responses to changes in canopy openness with shifts in macroclimate temperature and aerial nitrogen deposition playing secondary roles. Contrary to expectations, we found little evidence that these drivers interact. In addition, experimental findings deviated from the observational findings, suggesting that the forces driving understorey change at the regional scale differ from those driving change at the forest floor (i.e., the experimental treatments). Our study demonstrates that different approaches need to be integrated to acquire a full picture of how understorey communities respond to global change.

Short-interval, high-severity wildfires cause declines in soil seed bank diversity in montane forests of south-eastern Australia

Wildfires in forested ecosystems are increasing in severity and extent. The adaptations many plants have acquired in response to their natural fire regime may not be sufficient to allow some species to persist. This could impact the forest understorey and its seed bank, which are vital reservoirs of biodiversity, and forest resilience in the face of global change. We present a case study of the montane forests of south-eastern Australia, an area subjected to an increase in frequency and severity of fires. We utilise field surveys and a soil seed bank germination study to investigate if short-interval, high-severity wildfires affect the understorey diversity in montane forests, and if the extant vegetation and the soil seed bank exhibit contrasting responses. We consider species diversity and plant functional traits to explore plant diversity in long unburned sites, and sites with one, two or three short-interval, high-severity fires in the past 25 years. With increasing fire frequency, we found a decrease in total species richness, Shannon’s diversity, and the richness of resprouters in the soil seed bank, contrasting a lack of response in the extant vegetation. Increased fire frequency shifted the species composition and the frequency of plant functional groups of both extant vegetation and soil seed bank towards a decrease in clonal resprouters and increase in grasses and other upright herbs. The frequency of wind-dispersed perennials and short-lived seeders and exotics increased sharply following single high severity burn, particularly in the soil seed bank, and remained elevated relative to long unburnt with subsequent fire. The combined species (extant vegetation plus soil seed bank) pool mirrored shifts in the frequency of functional groups in extant vegetation and soil seed bank. These findings highlight the importance of considering the soil seed bank when examining the effects of fire on fire-prone forests. Although a lack of response in the extant vegetation may be a buffering effect of the soil seed bank, the shift in the frequency of plant functional groups in the combined species pool suggests this cannot be maintained indefinitely. The increase in frequency and abundance of species characteristic of early successional states has implications for increased flammability and potential positive feedbacks between past fire and future fire, especially in a warming and drying climate. These shifts were independent of the fire response strategy of eucalypt canopy species raising significant questions of whether artificial re-seeding programs should extend beyond the current focus on obligate seeding forests and an obligate seeding tree.