Understory Vegetation Research Articles

Effects of grazing on the relationship between dominant shrubs and understory vegetation along sand dune stability gradient.

During the process of dune vegetation restoration, understanding how grazing disturbance affects the relationship between plant species is a critical issue in ecological studies. However, there is insufficient evidence on the changes in the interaction between dominant shrubs and understory vegetation under grazing behavior. We aimed to study how grazing and dune stabilization affects the relationship between Caragana microphylla and understory vegetation. We established fencing at various stages of dune stabilization and proceeded to compared the performance indicators (e.g., richness and biomass) and the relative interaction index of understory vegetation and different functional groups along the dune stability under grazing and fencing conditions. Results showed that C. microphylla had facilitation on understory plants, and increased with dune stability, while the facilitation of Caragana microphylla on understory vegetation was stronger under grazing conditions. As sand dune stabilization increases, the facilitation of C. microphylla on understory vegetation diversity decreases significantly. However, there was no significant difference in the facilitation of C. microphylla on understory vegetation biomass at different stages of sand dune stabilization. This is related to the survival strategy of perennials being less tolerant to environmental stress than annuals, because grazing increased the richness of both annuals and perennials while reducing the overall biomass, and in the later stages of sand dune stabilization, and the facilitation of C. microphylla on perennials was higher than on annuals. Our study highlights the importance of the responses of different life-form groups to environmental factors and grazing disturbance during the process of sand dune vegetation restoration, as they play a crucial role in shaping the development of the relationship between understory vegetation and dominant shrubs.

Understory vegetation diversity and composition in intensively managed plantations compared to extensively managed forests

The benefits of plantations for wood production are well known, but it is unclear whether they have a clear negative effect on biodiversity, compared to natural forests. It is also unclear how overstory species identity (i.e., exotic, compared to native) would interact with the simple plantation effects on understory vegetation biodiversity. Here, we assessed bryophyte, lichen, and vascular plant diversity and composition in mono-specific and mixed plantations of exotic and native hybrid poplars (Populus spp.) and exotic and native spruces (Picea spp.). We compared these plantations to reference forests with similar overstory types (coniferous, deciduous, mixed) to those of the plantations in the southern boreal forest of Quebec. We also assessed whether the overstory species identity in plantations influenced understory vegetation biodiversity compared to reference forests. Our results show that plantations were not biological deserts, since mixed plantations contained similar bryophyte and vascular plant diversity as reference mixed native forests. The presence of native spruces and exotic poplars in mixed plantations increased bryophyte and vascular plant diversity respectively. This suggests that the influence of plantations on understory species diversity, compared to reference forests, was linked to the overstory species identity. Plantations were associated with ruderal plant species, while reference forests were composed of forest species. Bryophyte composition was similar in plantations and reference forests, while lichen species were only present in plantations. Our findings highlight that plantations, especially mixtures of white spruce and exotic poplar, are a promising option for planting strategies to enhance biodiversity.

Protection of understory vegetation by deer exclosure fences prevent the reduction of beech growth due to soil erosion

Overbrowsing by ungulates has degraded understory vegetation in worldwide forests. Understory degradation causes soil erosion and environmental degradation, causing mature tree decline. Although ungulate exclosure fences are installed to protect vegetation, their effectiveness in preventing tree decline associated with soil degradation remains unclear. We aimed to fill this gap on slopes of Mt. Shiraga, Japan, where sika deer have overbrowsed for >20 years. Tree-ring records in 1960–2022 for eight beeches per each of inside and outside fences were analyzed to compare stem basal area increment (BAI, cm−2 yr−1) and trend change timings for BAI (i.e., break-point). Soil properties, exposed root height (ERH) as cumulative soil erosion index, and intrinsic water use efficiency (iWUE) as water limitation proxy were also compared. Compared with areas inside fences, areas outside fences had no understory vegetation, higher ERH, and higher soil hardness and moisture. BAI outside fences turned their growth trend from positive to negative since 2004, but not inside fences. Break-point of BAI outside fences matched the understory degradation period in the field. The long-term BAI trend (i.e., regression slope of BAI) after the break-point was negatively related to ERH but not to soil properties (e.g., soil hardness and moisture). Furthermore, BAI outside fences was negatively related to iWUE after the break-point, whereas BAI inside fences was not. These results indicate that the maintenance of understory by fencing prevents overbrowsing-associated mature tree decline through mitigating root exposure and related water limitation, despite the potential of water competition with understory.

The Impact of Juniper Removal on Shrubs and Understory Vegetation and its Implications for Sagebrush Dependent Vertebrate Herbivores

The expansion of trees into previously grass- and shrub- dominated ecosystems is a global phenomenon threatening ecosystem integrity and function in encroached systems, including the North American sagebrush biome. This ecosystem is currently in peril, threatened in part by juniper (Juniperus sp.) encroachment. Sagebrush (Artemisia sp.) ecosystems contain a diversity of forage, including grasses, forbs, and shrubs, that serve as a key food source for vertebrate herbivores. Removal of encroached juniper has been used by land managers as a widespread restoration technique in sagebrush ecosystems, however, the long-term impact of this restoration action on shrubs and understory vegetation has not been thoroughly examined in the context of sagebrush dependent vertebrate herbivores. In 2020 and 2021, we studied shrub and understory vegetation response to juniper treatment in the sagebrush of northern Nevada and northeastern California. Juniper treatments completed between 2008 and 2020 were surveyed and sampled to assess the impact of this restoration action on grasses, forbs, and shrubs over time. Forage biomass was higher in old treatments than untreated reference sites, which was a trend that persisted across all vegetation functional groups. Differences in plant cover were slight or had inconsistent nonlinear trends between reference sites and treatments. Forage from treated sites had higher crude protein levels than forage from untreated sites, although the nutritional difference was slight. Our results suggest that juniper treatments that increase forage quantity and improve forage quality may benefit sagebrush dependent wildlife or domestic livestock in conifer-encroached ecosystems.

Analyzing the impact of phosphorous and nitrogen on Castanopsis sclerophylla early growth stages

Plant growth elements, particularly nitrogen (N) and phosphorus (P) are vital for their growth and development, particularly for understory vegetation and their excess limits the net productivity of terrestrial ecosystems. This study focuses on the understory vegetation responds and adaptation to key essential nutrients under changing climate scenarios in subtropical evergreen broad-leaved forests, still needs research attention. this, we set up an experiment taking four treatments in a 50-year-old Castanopsis sclerophylla secondary forest under (a) control (CK), (b) N, (c) P, and (d) combined N and P addition, applied to natural forest regeneration seedlings of C. sclerophylla attained similar growth parameters of diameter of 3 cm and 10 cm height. In addition, carbon, N, P, and non-structural carbohydrates (NSC) were determined through the anthrone colorimetric approach in different parts of seedlings. Results show that the combined N + P application enhanced the N and P by 14.48 %−140.55 % in the seedlings in both dry and wet seasons, respectively. However, during wet season, the content of NSC in the plant leaves significantly exceeded under P addition. Remarkably, CK showed increased P in the growing season but lower during the dry season. Furthermore, the root starch content of seedlings showed a significant increase under the application of N and P compared to combined N + P, ranging between 45.60 % and 58.70 %. Overall, the plant growth is attributed to N and P intake. The nutrient addition and seasonal variations have a coupled effect on seedling growth as proved in the in the natural open forest experiment. The study outcomes emphasize that the alterations in NSC allocation in the roots and leaves of C. sclerophylla seedlings under N + P addition could enhance their adaptation to future global climate changes, drought conditions, and high N concentrations.

Optimizing key parameters (biological-control factor) of soil erosion simulation models at a regional scale– The case of Jiangxi Province, China

Unveiling the spatial information of actual soil erosion is a prerequisite for subsequent soil erosion research and is critical for soil and water conservation as well as ecological resource protection. However, the existing regional-scale soil erosion simulation models often ignore the vertical structure of vegetation, particularly near-surface vegetation information, which leads to discrepancies with the real-world conditions. This study aims to optimize the biological-control factor (B factor) of the Chinese Soil Loss Equation (CSLE) model to improve simulation accuracy. The Global Ecosystem Dynamics Investigation (GEDI) can provide accurate layered vegetation data. Thus, this study focuses on the forest of Jiangxi Province, simulating the understory vegetation structure by vegetation type using a combination of GEDI data and sampled data. By considering the soil and water conservation benefits of different vegetation layers, we developed a B factor optimization method to simulate soil erosion in forests at a regional scale. Compared to previous methods, the optimized B factor mean value for Jiangxi Province’s forested areas increased from 0.0034 to 0.0096. The estimated soil erosion changed from 38 t·km-2a-1 (with 86.6 % of forests exhibiting no soil erosion) to 166.7t·km-2a-1 (with 28.2 % of forests exhibiting no soil erosion). Our findings indicate that the optimized assessment results are more consistent with the actual situation. The optimization method is a good attempt at regional-scale B factor simulation and can provide a more accurate depiction of the spatial information of soil erosion in forest at the regional scale. This study can lay a solid foundation for future regional-scale soil erosion assessments and offer valuable data support and methodological references for the regional-scale dynamic monitoring of soil and water loss, as well as research in soil and water conservation.

Effect of Caragana microphylla Lam. on Desertified Grassland Restoration

Background: The restoration of the degraded sandy grasslands in Hulun Buir is crucial for maintaining the local ecological balance and sustainable development. Caragana microphylla Lam., a shrub species widely employed in the restoration of sandy vegetation. It is essential to understand its impact on the understory vegetation and soil properties during this process. Methods: This study employed ANOVA, Pearson correlation, and redundancy analysis to systematically analyze the impact of C. microphylla on the three critical stages of desertified grassland vegetation recovery: semi-fixed dunes, fixed dunes, and sandy grasslands. It provided strategies for the restoration of desertified grassland vegetation and offered additional theoretical evidence for the role of vegetation in promoting the recovery of sandy lands. Results: (1) As the degree of vegetation recovery in desertified grasslands increases, the species richness of understory vegetation, Shannon–Wiener index, community height, and biomass also increase. Both the community height and biomass within shrublands are higher than outside, with species richness within the shrublands being higher than outside during the semi-fixed and fixed-sand land stages. (2) In both the 0~10 cm and 10~20 cm soil layers, soil water content showed an increasing trend, peaking in the sandy grassland stage (1.2%), and was higher within the shrublands than outside. The soil water content at 10~20 cm was higher than in the 0~10 cm layer. In both layers, clay and silt content gradually increased with the degree of vegetation recovery in the sandy land, and higher within the shrublands than outside, while the opposite was true for sand content. (3) In both soil layers, soil organic carbon gradually increased with the degree of vegetation recovery, peaking in the sandy grassland stage (4.12 g·kg−1), and was higher within the shrublands than outside. Total nitrogen increased from the semi-fixed-sand land stage to the fixed-sand land stage, with higher levels within the shrublands than outside at all stages. Soil pH within the shrublands decreased as the degree of vegetation recovery increased. There was no significant change in the total phosphorus content. (4) In both soil layers, soil physicochemical characteristics accounted for 59.6% and 46.9% of the vegetation changes within and outside the shrublands, respectively, with the main influencing factors being the soil particle size, total nitrogen, soil water content, and soil organic carbon. Conclusions: In the process of sandy grassland restoration, C. microphylla facilitates the growth and development of vegetation by enhancing the underlying soil physicochemical properties, specifically regarding the soil particle size distribution, soil water content, soil organic carbon, and total nitrogen.

Tradeoffs between Stand Volume and Understory Vegetation Diversity in Quercus wutaishanica Forests under Climate Change

Natural forests play a crucial role in providing various ecosystem services, including timber production and biodiversity conservation. However, climate change and anthropogenic factors pose a severe threat to competing forest ecosystem services functions. Therefore, to optimize and sustainably utilize competing forest services, tradeoffs are often necessary. This study was conducted in Northwest China to explore tradeoffs aimed at improving the quality of Quercus wutaishanica Mayr natural forests under climate change conditions, focusing on stand volume, timber production, and understory vegetation diversity conservation. Data from 77 field surveys were used to construct a coupled model for stand growth, stand structure, and site conditions. Changes in understory vegetation species number (UVSN) with crown cover were quantified. These models and relationships can be used as tools to estimate tradeoffs. As stand density increased, single-tree volume decreased, whereas timber volume increased. UVSN increased and then decreased with increasing crown cover and was able to maintain a relative maximum at 0.5–0.65. Under the current climatic conditions, the optimum stand densities corresponding to 30, 40, 50, and 60 years were 1390, 1153, 1042, and 871 trees/ha, respectively, to maintain a high UVSN and adequate stand volume. When mean annual temperature rose, stand densities could be reduced to maintain high-quality timber. Although only two major services were considered, the tradeoffs presented in this study can inform future research to improve the quality of natural forests.

Shifts in light availability driven by dieback across a marsh‐forest gradient

AbstractEcological zonation in coastal forests is driven by sea level rise and storm‐surge events. Mature trees that can survive moderately saline conditions show signs of stress when soil salinity increases above its tolerance levels. As leaf burn, foliar damage, and defoliation reduce tree canopy cover, light gaps form within the crown. At the forest‐marsh edge, canopy cover loss is most severe; trunks of dead trees without canopies form “ghost forests.” Canopy thinning and light from the edge alter conditions for understory vegetation, promoting the growth of shrubs and facilitating establishment and spread of invasive species that were previously limited by light competition. In this research, we present an analysis of illuminance and temperature in a coastal forest transitioning to a salt marsh. Light sensors above the ground surface were used to measure light attenuation of trees and understory vegetation and to observe the effect of reduced canopies at the forest‐marsh edge. Farther from the marsh, where salinity is lower and trees are healthy, dense canopies attenuate light. We estimate that during the growing season, tree canopies intercept 50% of illuminance on average. Closer to the marsh, canopy thinning, and tree death allow greater light penetration from above, as well as from the adjacent marsh. These illuminance values are further increased by light penetration from the forest‐marsh edge (edge effect). Here, higher illuminance may permit Phragmites australis expansion. At intermediate locations, trees intercept between 32% and 49% of light and the understory shrub Morella cerifera intercepts a further 45% of penetrating light based on comparisons of illuminance above and below shrub canopies. Light penetration from the edge can also be felt. The presence of M. cerifera reduces the air temperature close to the soil surface, creating a cooler summer microclimate. The tree health state is reflected in the canopy size. The canopy patterns and the edge effect are responsible for light availability distribution along forest‐marsh gradients, consequently affecting the understory vegetation biomass. We conclude that during forest retreat driven by sea level rise, tree dieback increases light availability favoring the temporary encroachment of Ph. australis and M. cerifera in the understory.

Characteristics of forest understory herbaceous vegetation and its influencing factors in biodiversity hotspots in China

Forest ecosystems, especially within biodiversity hotspots, heavily rely on the often-overlooked understory herbaceous communities (USHC) for their structural integrity and ecological functions. Because of their modest stature, these communities have garnered insufficient attention from researchers. Therefore, in this study attention is focused on USHC, which attempts to fill this research gap. To achieve this, we established 105 sample plots in 2022 within forest ecosystems situated in the biodiversity hotspot of southwest China. Our investigation unveiled a rich biodiversity tapestry, identifying 424 plant species from 108 families and 284 genera. Notable were the 217 herbaceous species identified in the understory layer, representing 67 families and 163 genera. These understory herbaceous species accounted for 51.2 % of the overall species count. Through a detailed analysis, the sample plots were categorized into eight distinct communities using a two-way indicator species analysis. These communities exhibited diverse variations in species composition, diversity, biomass, and nutrient characteristics. Notably, community I (Eucalyptus robusta Smith + Rubus corchorifolius L. f. + Alternanthera philoxeroides (Mart.) Griseb.), V (Camptotheca acuminata Decne + Rubus parkeri Hance + Iris tectorum Maxim), VIII (Platycladus orientalis (L.) Franco + Viburnum dilatatum Thunb. + Cyclosorus interruptus (Willd.) H. Ito) stood out for their exceptional species diversity and productivity. Moreover, correlation analyses highlighted the substantial impact of topographic and soil factors on USHC. Altitude, soil water content, and total carbon content emerged as the primary determinants of species diversity. Biomass demonstrated close associations with total soil carbon and nitrogen. Furthermore, the nutrient characteristics displayed significant correlations with soil nutrient contents. These findings underscore the critical importance of prioritizing USHC attention in forest conservation and management strategies within biodiversity hotspots. The implications strongly advocate for the inclusion of these communities in planning and decision-making processes, emphasizing their pivotal role in maintaining structural and functional diversity in ecosystems.

Divergent seed dispersal outcomes: Interactions between seed, disperser, and forest traits.

Animals disperse seeds in various ways that affect seed deposition sites and seed survival, ultimately shaping plant species distribution, community composition, and ecosystem structure. Some animal species can disperse seeds through multiple pathways (e.g., defecation, regurgitation, epizoochory), each likely producing distinct seed dispersal outcomes. We studied how seed traits (size and toughness) interact with disperser species to influence seed dispersal pathway and how this ultimately shapes the proportion of seeds deposited in various habitat types. We focused on three frugivorous species of duikers (African forest antelopes) in the Dja Faunal Reserve, a tropical rainforest in southern Cameroon. Duikers can both defecate and regurgitate seeds, the latter predominantly occurring during rumination at their bedding sites (or "nests"). We located duiker nests and dungs along 18 linear 1-km-transects to assess: (1) how seed traits affect the likelihood of dispersal via defecation versus regurgitation, (2) if defecated versus regurgitated seeds are deposited at different rates in different forest types (assessed by indigenous Baka), microhabitats, and forest structural attributes (measured by drone lidar), and (3) if these differ between three duiker species that vary in size and diel activity patterns. We found that duikers predominantly defecated small seeds (<3 mm length) and regurgitated larger and tougher seeds (>10 mm length), the latter including 25 different plant species. The three duiker species varied in their nesting habits, with nocturnal bay duikers (Cephalophus dorsalis) nesting in dense understory vegetation at proportions 3-4 times higher than Peter's and yellow-backed duikers (Cephalophus callipygus and Cephalophus silvicultor). As a result, bay duikers deposited larger regurgitated seeds at a higher rate in habitats with denser understory where lianas and palms predominate and near fallen trees. This directed regurgitation seed deposition likely plays an important and unique role in forest succession and structure. This study highlights the importance of ungulate seed dispersal by regurgitation, a vastly understudied process that could impact many ecosystems given the prevalence of ruminating ungulates worldwide.

Ectomycorrhizal fungi and the nitrogen economy of Nothofagus in southern Patagonia.

Subantarctic Nothofagus forests are the southernmost forests in the world, with negligible atmospheric nitrogen (N) deposition. Most paradigms about the role of ectomycorrhizal (ECM) fungi in N cycling and plant N uptake at high latitudes have been tested in boreal coniferous forests, while in the southern hemisphere, ECM hosts are primarily angiosperms. Using ITS1 meta-barcoding, we characterized ECM and saprotrophic fungal communities in evergreen and deciduous Nothofagus forests forming monodominant and mixed stands in the archipelago of Tierra del Fuego (Chile and Argentina). We assessed the N economy of Nothofagus by correlating host species with fungal relative abundances, edaphic variables, net N mineralization, microbial biomass N and the activity of eight extracellular soil enzymes activities. The N economy of deciduous N. pumilio forests was strikingly similar to boreal coniferous forests, with the lowest inorganic N availability and net N mineralization, in correlation to higher relative abundances of ECM fungi with enzymatic capacity for organic N mobilization (genus Cortinarius). In contrast, the N economy of evergreen N. betuloides forests was predominantly inorganic and correlated with ECM lineages from the family Clavulinaceae, in acidic soils with poor drainage. Grassy understory vegetation in deciduous N. antarctica forests likely promoted saprotrophic fungi (i.e., genus Mortierella) in correlation with higher activities of carbon-degrading enzymes. Differences between Nothofagus hosts did not persist in mixed forests, illustrating the range of soil fertility of these ECM angiosperms and the underlying effects of soil and climate on Nothofagus distribution and N cycling in southern Patagonia.

Response of understory vegetation to long-term occupancy by introduced Pinus species in temperate deciduous hardwood forests

In many temperate regions of the world, conifer species have been planted to stabilize soils and promote site recovery on former hardwood sites that were cleared for agriculture. In many areas of eastern North America, these conifer plantings consisted of introduced (non-native) Pinus species planted on abandoned agricultural land once dominated by mesophytic hardwood species. These plantings constitute a shift in overstory composition away from native hardwood species with nutrient-rich litter that decomposes more quickly towards Pinus species with recalcitrant litter that may alter soil chemistry and nutrient availability. To examine how edaphic conditions associated with long-term introduced Pinus species occupancy are related to forest regeneration and herbaceous-layer diversity and composition, we sampled a total of 97 plots in planted Pinus echinata and Pinus strobus stands and naturally regenerated hardwood stands growing on two ecological landtype phases (ELTPs) of southern Indiana, USA forests, Fagus-Acer saccharum/Arisaema Mesic Ridges, and Acer saccharinum/Boehmeria Bottomlands. We collected vegetation data and analyzed soil samples to examine herbaceous-layer species distribution across gradients using non-metric multidimensional scaling (NMS) ordination. Two-way ANOVA was used to examine differences in individual species and species functional groups across stand types (P. echinata, P. strobus, and native hardwoods) and ELTPs. Our results show that differences in soil chemistry resulting from Pinus spp. occupancy were associated with differences in the composition and distribution of herbaceous-layer species in ordination space. Species across stand types and ELTPs were distributed across dominant gradients related to litter depth, cation exchange capacity, cation content, and soil aluminum concentration. Hardwood sites had significantly greater herbaceous-layer cover (139.6 ± 8.0 %) than P. echinata (48.5 ± 6.2 %) or P. strobus sites (81.7 ± 7.7 %), as well as greater herbaceous-layer species richness and diversity (mean species richness was 46.9 ± 2.1 on hardwood stands vs. 33.3 ± 1.6 and 36.4 ± 2.0 on P. echinata and P. strobus stands, respectively). Pinus echinata stands contained a greater density of woody regeneration, including Quercus spp. (201 ± 48 saplings ha−1) and Fagus grandifolia stems (415 ± 82 saplings ha−1), both of which occurred in greater density than Acer saccharum (163 ± 93 saplings ha−1) and A. rubrum (70 ± 64 saplings ha−1). Our results suggest that pine occupancy has created divergent successional trajectories in comparison to hardwood stands. These differing trajectories may offer both challenges and opportunities for restoration efforts. For example, the greater abundance of Quercus reproduction under P. echinata on ridges, combined with less productive soils, may allow Quercus stems to be promoted into the canopy with less competition from mesophytic competitors.

Changes in salinity and vegetation growth under different land use types during the reclamation in coastal saline soil

The ecological construction in coastal saline-alkali areas urgently needs to be explored in terms of water-salt regulation management and functional irrigation. In this paper, the extremely severe saline soil in the eastern coastal area of the North China Plain was selected for vegetation rehabilitation by drip irrigation. Through two-year field experiments, the spatial and temporal soil salinity-water dynamics of three land use types (LUTS) under two irrigation strategies (IIS) were systematically studied. The results revealed: (1) The soils in the understory grassland and shrub land root zones remained stable for desalination, with the average ECe decreasing to 0.69 dS/m and 0.71 dS/m under autumn irrigation at surface, and 0.66 dS/m and 0.85 dS/m under winter irrigation. And a slight salt accumulation occurred in the bare land in stage IV. (2)The soil surface moisture increased, and the bulk density decreased significantly with drip irrigation. The final moisture of understory grassland and shrub land was 3.85 and 2.97 times that of the bare land layer at 0–10 cm, 2.55 and 1.97 times at 10–20 cm, and 1.61 times and 1.47 times at 20–40 cm, respectively. (3)Due to quick salt rinsing, Salix matsudana and Hibiscus maintained a high survival rate, and the germination of understory vegetation further increased the vegetation coverage. Meanwhile perennial understory herbs gradually became the dominant species, which positively effects on the maintenance of soil low-salt environment. (4)There were significant differences in SWC and ECe between autumn and winter irrigation treatment during stage I and stage II, indicating that irrigation strategies only impact on soil water-salt movement in the early stage. While there was no significant difference between understory grassland and shrub land, indicating that the research about the effects of vegetation cover type on water-salt transport should take a longer time scale.

Response of Fuel Characteristics, Potential Fire Behavior, and Understory Vegetation Diversity to Thinning in Platycladus orientalis Forest in Beijing, China

Objective: Active fuel management operations, such as thinning, can minimize extreme wildfire conditions while preserving ecosystem services, including maintaining understory vegetation diversity. However, the appropriate thinning intensity for balancing the above two objectives has not been sufficiently studied. Methods: This study was conducted to assess the impact of various thinning intensities (light thinning, LT, 15%; moderate thinning, MT, 35%; heavy thinning, HT, 50%; and control treatment, CK) on fuel characteristics, potential fire behavior, and understory vegetation biodiversity in Platycladus orientalis forest in Beijing using a combination of field measurements and fire behavior simulations (BehavePlus 6.0.0). Results: A significant reduction in surface and canopy fuel loads with increasing thinning intensity, notably reducing CBD to below 0.1 kg/m3 under moderate thinning, effectively prevented the occurrence of active crown fires, even under extreme weather conditions. Additionally, moderate thinning enhanced understory species diversity, yielding the highest species diversity index compared to other treatments. Conclusions: These findings suggest that moderate thinning (35%) offers an optimal balance, substantially reducing the occurrence of active crown fires while promoting biodiversity. Therefore, it is recommended to carry out moderate thinning in the study area. Forest managers can leverage this information to devise technical strategies that simultaneously meet fire prevention objectives and enhance understory vegetation species diversity in areas suitable for thinning-only treatments.

Smoke Emissions and Buoyant Plumes above Prescribed Burns in the Pinelands National Reserve, New Jersey

Prescribed burning is a cost-effective method for reducing hazardous fuels in pine- and oak-dominated forests, but smoke emissions contribute to atmospheric pollutant loads, and the potential exists for exceeding federal air quality standards designed to protect human health. Fire behavior during prescribed burns influences above-canopy sensible heat flux and turbulent kinetic energy (TKE) in buoyant plumes, affecting the lofting and dispersion of smoke. A more comprehensive understanding of how enhanced energy fluxes and turbulence are related during the passage of flame fronts could improve efforts to mitigate the impacts of smoke emissions. Pre- and post-fire fuel loading measurements taken during 48 operational prescribed burns were used to estimate the combustion completeness factors (CC) and emissions of fine particulates (PM2.5), carbon dioxide (CO2), and carbon monoxide (CO) in pine- and oak-dominated stands in the Pinelands National Reserve of southern New Jersey. During 11 of the prescribed burns, sensible heat flux and turbulence statistics were measured by tower networks above the forest canopy. Fire behavior when fire fronts passed the towers ranged from low-intensity backing fires to high-intensity head fires with some crown torching. Consumption of forest-floor and understory vegetation was a near-linear function of pre-burn loading, and combustion of fine litter on the forest floor was the predominant source of emissions, even during head fires with some crowning activity. Tower measurements indicated that above-canopy sensible heat flux and TKE calculated at 1 min intervals during the passage of fire fronts were strongly influenced by fire behavior. Low-intensity backing fires, regardless of forest type, had weaker enhancement of above-canopy air temperature, vertical and horizontal wind velocities, sensible heat fluxes, and TKE compared to higher-intensity head and flanking fires. Sensible heat flux and TKE in buoyant plumes were unrelated during low-intensity burns but more tightly coupled during higher-intensity burns. The weak coupling during low-intensity backing fires resulted in reduced rates of smoke transport and dispersion, and likely in more prolonged periods of elevated surface concentrations. This research facilitates more accurate estimates of PM2.5, CO, and CO2 emissions from prescribed burns in the Pinelands, and it provides a better understanding of the relationships among fire behavior, sensible heat fluxes and turbulence, and smoke dispersion in pine- and oak-dominated forests.

Ecological Restoration Increases the Diversity of Understory Vegetation in Secondary Forests: An Evidence from 90 Years of Forest Closures

Ecological restoration and biodiversity are currently hot issues of global environmental concern. However, knowledge about the specific impacts of restoration duration on understory vegetation diversity remains limited. Therefore, this study comprehensive employed a spatial approach to compare the differences in understory plant diversity and species composition among secondary forests with varying ecological restoration ages (0, 10, 30, 60, and 90-year-old stands) in Huangfu Mountain National Forest Park. This methodology allowed us to clarify the key factors affecting the composition of the understory plant community and investigate the regulatory mechanisms influencing changes in understory plant diversity. The results showed that shrub Shannon’s index value, shrub evenness, herb Shannon’s index value, herb richness, and herb evenness were significantly affected by the years of restoration, with 10 years and 90 years being the highest and 60 years being the lowest. Substrate diversity was the main factor influencing plant diversity in the shrub layer. Overstory richness, soil C/N, soil C, soil N, soil bacterial Observed OTUs, soil bacterial Chao1, soil bacterial Pielou_e, and substrate diversity were the drivers of plant diversity in the herb layer. Overstory evenness had a direct effect (0.256) and an indirect effect (0.284) on herb evenness through light availability and fungal Simpson’s index value. Light availability directly negatively affected herb evenness (−0.360). In addition, 52.6% of the factors affecting the herb evenness index were from the arboreal layer evenness, light availability, and fungal Simpson’s index value. To sum up, moderate disturbance of the understory environment of natural secondary forests can be carried out after 10 years of restoration, which is more conducive to the increase of understory plant diversity. This comprehensive study provides a theoretical basis for formulating ecological restoration measures for secondary forests, particularly in understanding the optimal timing and nature of disturbance in the restoration process, reassuring the audience about the validity and reliability of the findings.

Cattle exclusion increases encounters of wild herbivores in Neotropical forests

Abstract Ongoing habitat loss and species extinctions require managers to implement and quantify the effectiveness of conservation actions for protecting biodiversity. Fencing, when done properly, is an important management tool for conservation in landscapes where wildlife and domestic animals co‐occur, potentially enhancing habitat use through selective exclusion of domestic species. For instance, the fencing of forest patches in the Neotropics is expected to reduce the degradation of understory vegetation by cattle, releasing these resources for the native community of browsers and fruit consumers. Here, we implemented an ecological experiment using a before‐after control‐impact design to quantify the effect of cattle exclusion on encounter probability of the native community of browsers and fruit consumers, and percent ground cover in multifunctional landscapes of the Colombian Orinoquía. We built 14 km of wildlife‐permeable fences along forest edges in four forest patches (i.e. blocks) containing control and fenced (treatment) sites. We installed 33 camera traps to obtain information about wildlife and cattle encounter probabilities, before and after the fences were constructed. We used Bayesian generalised linear mixed effects models to quantify the effect of fences via the interaction between the time period (before and after the fences were built) and treatment (control or fenced sites). Fencing was effective at reducing encounter probabilities of cattle in the treated sites, and it had a positive impact on relative encounter probabilities of four of seven studied wildlife species (herbivores including the black agouti [dry season only], lowland tapir [dry season only] and spotted paca [both seasons] and an omnivore, the South American coati [rainy season only]). The effect of fencing was negative for the collared peccary but only during the dry season. No statistically significant effect was detected for the white‐lipped peccary or white‐tailed deer. Synthesis and applications: We provide experimental evidence that fences are effective at selectively excluding cattle and increasing encounter rates of wild browsers and fruit consumers in forest patches where these species co‐occur with cattle. Our results highlight an important application of fencing ecology in Neotropical forests, where the implementation of wildlife‐permeable fences is feasible due to smaller body sizes of wildlife compared to domestic animals such as cattle.

Spatial Heterogeneity and Key Influencing Factors of Soil Organic Carbon, Soil Total Nitrogen, and Carbon to Nitrogen Ratio in main plantations of Torreya grandis cv. Merrillii

Soil organic carbon （SOC） and soil total nitrogen （STN） serve as important indicators of the elemental balance within forest ecosystems reflecting soil fertility and quality. Accurate knowledge regarding the spatial variability of regional SOC, STN, and C∶N ratio and their influencing factors is of great significance for precise fertilization and soil health. In this study, a total of 117 topsoil samples （0-20 cm in depth） based on a 1 km×1 km grid were collected in the Torreya grandis cv. Merrillii plantation in Zhejiang Province. A combination of multi-dimensional statistical approaches （random forest model, structural equation model, redundancy analysis, and variation partitioning analysis） and diverse spatial analytical techniques （geostatistics, Moran's I index, etc.） were applied to reveal the spatial distributions and influencing factors of SOC, STN, and C∶N ratio in the Torreya. grandis cv. Merrillii region. The results showed that the average ω（SOC）, ω（STN）, and C∶N ratio were 17.63 g·kg-1, 1.48 g·kg-1, and 12.65, respectively, and their coefficients of variation were 68.08%, 67.41%, and 46.03%, respectively, indicating a moderate degree of variability. In general, the SOC, STN, and C∶N ratio of the Torreya grandis cv. Merrillii plantations were at an intermediate level in the national plantation. The semi-variance results showed that the nugget/sill values of SOC, STN, and C∶N ratio were 49.98%, 45.88%, and 49.93%, respectively, demonstrating a moderate level of spatial autocorrelation. The spatial distribution results showed that SOC, STN, and C∶N ratio decreased from northeast to southwest, with the majority of the region exhibiting above-medium fertility levels of SOC. The results of correlation analysis and redundancy analysis indicated that AN, AP, and AK were significantly correlated with both SOC, STN, and C∶N ratio （P&lt;0.05）. The results of random forest, structural equation model, and variation partitioning analysis evidenced that the main influencing factors of SOC and STN were soil-available nutrients （AN, AP, and AK）. Therefore, our results could provide important insights for enhancing soil carbon and nitrogen pools in special plantations in Zhejiang Province, enhancing the capacity of plantations to adapt to regional climate change through ecological measures such as appropriate fertilization practices and strategic understory vegetation cultivation.

Silvicultural regime shapes understory functional structure in European forests

Abstract Managing forests to sustain their diversity and functioning is a major challenge in a changing world. Despite the key role of understory vegetation in driving forest biodiversity, regeneration and functioning, few studies address the functional dimensions of understory vegetation response to silvicultural management. We assessed the influence of the silvicultural regimes on the functional diversity and redundancy of European forest understory. We gathered vascular plant abundance data from more than 2000 plots in European forests, each associated with one out of the five most widespread silvicultural regimes. We used generalized linear mixed models to assess the effect of different silvicultural regimes on understory functional diversity (Rao's quadratic entropy) and functional redundancy, while accounting for climate and soil conditions, and explored the reciprocal relationship between three diversity components (functional diversity, redundancy and dominance) across silvicultural regimes through a ternary diversity diagram. Intensive silvicultural regimes are associated with a decrease in functional diversity and an increase in functional redundancy, compared with unmanaged conditions. This means that although intensive management may buffer communities' functions against species or functional losses, it also limits the range of understory response to environmental changes. Policy implications. Different silvicultural regimes influence different facets of understory functional features. While unmanaged forests can be used as a reference to design silvicultural practices in compliance with biodiversity conservation targets, different silvicultural options should be balanced at landscape scale to sustain the multiple forest functions that human societies are increasingly demanding.