Understory Vegetation Research Articles

Copper accumulation in five weed species commonly found in the understory vegetation of Mediterranean vineyards

Copper (Cu) concentration in agricultural soils often exceeds toxicological limits due to application of Cu-based fungicides. The potential of weeds for their use as functional cover plants in vineyard management and phytoremediation practices is little explored. We identified five weed species widely present in vineyards and assessed their Cu accumulation from eleven Mediterranean vineyards (soil Cu: 60–327 μg g−1) and two adjacent control sites (soil Cu: 15–30 μg g−1). Soils and plants were characterized by their physico-chemical properties and nutrient content. We applied multivariate techniques to analyze relationships between soil properties and leaf nutrient composition. Copper tolerance and accumulation traits were further tested in hydroponics using a series of CuSO4 concentrations (0.1–16 μM).Under field conditions, the highest Cu concentration in both roots and leaves were found in Lolium perenne (221 and 461 μg g−1, respectively), followed by Plantago lanceolata, Rumex obtusifolius and Taraxacum officinale (>100 μg g−1 Cu in leaves). Only one species, Trifolium repens, did not accumulate remarkable Cu concentrations. Overall, and as revealed by the multivariate analyses, leaf Cu concentration was driven by soil Cu content, soil texture, organic matter, nitrogen, and Cu uptake into roots. However, functional regression analysis and controlled experiments suggested that Cu might be additionally absorbed from the deposits on the leaf surface related to the Cu-fungicide treatments and soil dust. Our study highlights the importance of intra-specific variability in Cu accumulation among weed species in Cu-contaminated agricultural soils. Further validation of these findings under controlled conditions could provide essential insights for optimizing management and remediation strategies.

Free-ranging livestock cause forest understory degradation in giant panda (Ailuropoda melanoleuca) habitat

Free-ranging livestock are common in reserves established for giant pandas (Ailuropoda melanoleuca), which rely almost exclusively on bamboo in the montane forests of southwestern China. Previous studies have showed that overgrazing by livestock had led to a reduction in bamboo abundance. However, there is limited knowledge of how livestock impact the structure of the understory vegetation. Conducted in the Wanglang National Nature Reserve with a livestock exclosure experiment, our study aimed to fill this gap by examining the impact of livestock grazing on two important elements of forest understory bamboo and moss in giant panda habitat, and quantifying their recovery after excluding livestock. Measurements of bamboo and moss showed that both elements were severely degraded. With a closer examination, we found moss growth was worse in areas with dense bamboo or no bamboo at all, but better when there were many dead stems in bamboo clump, suggesting bamboo exerted both negative competition and positive shelter effects from livestock trampling on moss. Livestock exclusion with fence indeed exempted bamboo and moss from continuous damage which were exemplified by more bamboo shoots inside the fence and significantly decreased moss height outside the fence. However, we observed no recovery of damaged bamboo and moss inside fenced quadrats in two years. Neither the sprouted bamboo shoots matured into stems after the growing season, nor the height of moss increased. Collectively, our results suggested that long-term livestock grazing drastically altered understory layer of bamboo and moss and interactions in between, and there was hardly recovery of the understory bamboo and moss in a short term. Therefore, we recommend artificial intervention with bamboo and moss planting in severely degraded areas and long-term monitoring of understory vegetation to restore the habitat of giant panda.

Forage quantity and protein concentration changes across a forest-savanna gradient with management implications for white-tailed deer

White-tailed deer (Odocoileus virginianus) hunting is an important economic activity associated with the management of forests and rangelands in the USA, with over $12.9 billion dollars of related annual expenditures. Reducing tree cover through thinning and prescribed fire both have the potential to increase the quantity and quality of deer forage. We evaluated the long-term impacts of eight different combinations of fire return intervals and tree harvest on forage productivity and protein content of the forage. Based on management regime, study units ranged from savanna to closed-canopy forest. Aboveground net primary production (ANPP) of six functional groups (grass, panicum, forb, legume, woody, sedge) of understory vegetation was measured in October 2019 and 2020 using destructive sampling. Samples for foliar crude protein (CP) concentration were collected in spring, summer, and fall of 2020. Total understory ANPP ranged from 2.9 to 466.3 g m−2 and was up to 566% greater in savanna systems maintained by frequent fire (return interval of three years or less) than in non-burned forest treatments. Annual burning resulted in ANPP dominated by herbaceous plants composed mostly of fire-tolerant grasses (e.g., Andropogon gerardii, Schizachyrium scoparium). Longer fire return intervals or no fire resulted in roughly equal ANPP from understory woody and herbaceous species. Crude protein concentrations were up to 45.7% greater in the woodland and forest units than in the savanna units for seven of the eleven species sampled. The greater CP in the forests was most noticeable in the summer when deer needs for quality forage are substantial. Increased protein concentrations of understory species in the forests, but greater ANPP in the savannas indicate that managing for a mix of savanna and woodland could be ideal for balancing forage quantity with increased forage protein.

The Effect of Surrounding Vegetation on Basal Stem Measurements Acquired Using Low-Cost Depth Sensors in Urban and Native Forest Environments.

Three colour and depth (RGB-D) devices were compared, to assess the effect of depth image misalignment, resulting from simultaneous localisation and mapping (SLAM) error, due to forest structure complexity. Urban parkland (S1) was used to assess stem density, and understory vegetation (≤1.3 m) was assessed in native woodland (S2). Individual stem and continuous capture approaches were used, with stem diameter at breast height (DBH) estimated. Misalignment was present within point clouds; however, no significant differences in DBH were observed for stems captured at S1 with either approach (Kinect p = 0.16; iPad p = 0.27; Zed p = 0.79). Using continuous capture, the iPad was the only RGB-D device to maintain SLAM in all S2 plots. There was significant correlation between DBH error and surrounding understory vegetation with the Kinect device (p = 0.04). Conversely, there was no significant relationship between DBH error and understory vegetation for the iPad (p = 0.55) and Zed (p = 0.86). The iPad had the lowest DBH root-mean-square error (RMSE) across both individual stem (RMSE = 2.16cm) and continuous (RMSE = 3.23cm) capture approaches. The results suggest that the assessed RGB-D devices are more capable of operation within complex forest environments than previous generations.

Terrestrial Laser Scan Metrics Predict Surface Vegetation Biomass and Consumption in a Frequently Burned Southeastern U.S. Ecosystem

Fire-prone landscapes found throughout the world are increasingly managed with prescribed fire for a variety of objectives. These frequent low-intensity fires directly impact lower forest strata, and thus estimating surface fuels or understory vegetation is essential for planning, evaluating, and monitoring management strategies and studying fire behavior and effects. Traditional fuel estimation methods can be applied to stand-level and canopy fuel loading; however, local-scale understory biomass remains challenging because of complex within-stand heterogeneity and fast recovery post-fire. Previous studies have demonstrated how single location terrestrial laser scanning (TLS) can be used to estimate plot-level vegetation characteristics and the impacts of prescribed fire. To build upon this methodology, co-located single TLS scans and physical biomass measurements were used to generate linear models for predicting understory vegetation and fuel biomass, as well as consumption by fire in a southeastern U.S. pineland. A variable selection method was used to select the six most important TLS-derived structural metrics for each linear model, where the model fit ranged in R2 from 0.61 to 0.74. This study highlights prospects for efficiently estimating vegetation and fuel characteristics that are relevant to prescribed burning via the integration of a single-scan TLS method that is adaptable by managers and relevant for coupled fire–atmosphere models.

Homogenization of understory vegetation by an overabundance of deer (Cervus nippon) in a temperate forest in central Japan

ABSTRACT Deer browsing is a form of selective disturbance that homogenizes plant community composition and structure. In mountainous regions, disturbance intensity, together with topographical factors, affect plant communities. However, studies on the multiple effects of deer browsing and topographical factors on plant communities are limited. Here, we investigated the effects of deer exclusion on understory vegetation across the upper and lower slopes of a temperate deciduous forest in a mountainous area of Japan. We established six pairs of exclosure and control quadrats, with three pairs at each topographical position. We assessed changes in vegetation and plant structure (coverage and height), species composition, numbers of flowering/fruiting species, and damage to the plant species caused by deer browsing between 2009–2016. Vegetation coverage and the number of flowering/fruiting plant species increased in the exclosure quadrats during the study period, indicating that browsing prevents herb-layer species from reaching the flowering and fruiting stages in this site. Moreover, dissimilarity in species composition between the exclosure and control quadrats increased on the upper slope. However, the dissimilarity between upper and lower slopes in the control quadrats tended to decrease. Large herbs, which mainly include forbs and perennial species, were characteristically abundant on the lower slopes and decreased in the control quadrats on the lower slope. Our results indicate that the exclusion of deer had different effects on the understory vegetation of upper and lower slopes, suggesting that deer overbrowsing weakens the correlation between plant functional traits and topographic factors, resulting in homogenized plant communities.

Soil macrofauna under laying hens’ grazed fields in two different agroecosystems in Portugal

Abstract Although chickens can improve the chemical properties of soil through the deposition of excreta, their effects on soil macrofauna are poorly known. This work assessed the effects of grazing indigenous laying hens on soil macrofauna of two agroecosystems in Portugal: an organic horticultural field and a conventional orchard. At the horticultural field, laying hens were used to control weeds and the results were compared with those of two other weed control treatments: mechanical (rototiller) and thermal (flame weeding). At the orchard, the effects of hens were compared to that of the orchard understory vegetation, as a control. Soil epigeic macrofauna was collected in both locations, and earthworms were only collected in the horticultural field. Relative to the other treatments, grazing in the horticultural field increased the density of earthworms in the medium term (ranging from 150 to 625 earthworms/m2), without harming the density and diversity of epigeic macrofauna. However, at the orchard, the grazed soils presented lower soil epigeic macrofauna diversity, as well as significantly lower density of spiders than the control (4.67 vs 8.67 individuals/sample, respectively). These results suggest that the grazing effects can be affected by several factors, including the type of agroecosystem and farm management. Further research is required to optimize grazing management in different farming systems, considering animal density and grazing duration, thus ensuring the best contributions of chickens to soil fertility.

Response of Understory Plant Diversity to Soil Physical and Chemical Properties in Urban Forests in Beijing, China

Understory vegetation affects the richness and stability of urban forest ecosystems. To investigate the influence of soil physicochemical properties on the diversity of understory plants in urban forests, this study used 30 urban forest communities in the Beijing Plain area as the research object and analyzed the correlation between understory plant diversity and soil factors by correlation analysis. Furthermore, pH, soil bulk density (SBD), total soil porosity (TSP), soil water content (SWC), soil organic carbon (SOC), soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), effective phosphorous (AP), and effective potassium (AK) were determined in this study. The Shannon diversity index (H’), Pielou evenness index (E), Simpson dominance index (C), and Margalef richness index (DMG) of understory plants were calculated. The soil nutrient contents and the understory plant diversity indices of the different community types showed significant differences. There was a strong correlation between soil properties and the diversity index of understory vegetation. SOM and SOC were the main factors affecting the Shannon-Wiener index, Pielou index, Simpson index, and Margalef richness index of the understory plants. We conclude that soil properties were one of the primary drivers of the formation of understory vegetation diversity. The results of the study can provide scientific guidance for the management of urban forests.

Recognition of Area without Understory Vegetation Based on the RGB-UAV Ultra-High Resolution Images in Red Soil Erosion Area

Understory vegetation plays an important ecological role in maintaining the diversity of the ecosystem, the stability of ecosystem services, and the accumulation of nutrient elements, as an important part of a forest ecosystem. In this study, a new method of recognizing areas without understory vegetation is proposed. The method makes full use of the advantages of spectral characteristics, spatial structure information and temporal resolution of UAV images, and can quickly and simply distinguish understory, without vegetation cover. Combined with fractional vegetation coverage (FVC) and vegetation dispersion, understory, with no vegetation area, can be successfully recognized, and the Pr, Re and F1 are all above 85%. The proportion of bare soil under forest in our study area is 20.40%, 19.98% and even 41.69%. The study area is located in Changting County, Fujian Province, which is a typical red soil area in China where serious soil erosion is taking place in the forest. The method provides a promising, quick and economic way of estimating understory vegetation coverage with high spatial accuracy.

Nitrate and Ammonium Deposition in the Midwestern Fragmented Forest

Whereas the impacts of N deposition on forest ecosystems have been well studied in remote areas in predominantly forested landscapes, we know relatively less about the impacts of N deposition on forests in heavily human-modified landscapes. We studied the influence of adjacent land use, local point sources, and woodlot stand structure on subcanopy N transport and enrichment via throughfall in three woodlot fragments in southern Lower Michigan, USA. We found that one site had markedly higher TF N concentrations compared to the other two; however, our data indicate that elevated TF concentrations resulted from differences in tree species composition, rather than differences in surrounding land use. Specifically, we observed that the local abundance of basswood (Tilia americana) was positively associated and the local abundance of northern red oak (Quercus rubra) was negatively associated with TF N concentrations. One site had markedly greater TF N fluxes compared to the other two, which was driven by a lack of understory vegetation, possibly due to higher deer browsing at this site. Together, the results of this study demonstrated that TF N concentrations and fluxes were more strongly influenced by the internal characteristics of fragmented woodlots, such as forest structure and species composition, than by the surrounding land use.

Substantial niche overlap in carrion beetle habitat and vegetation use

Abstract The habitat affinities of carrion beetles (Coleoptera: Silphidae), a speciose group with wide cooccurrence, are only coarsely described for well‐studied species, particularly in the western United States. We aim to identify if the 15 species of montane carrion beetle in Colorado differ substantially in their use of habitats and across more uniquely defined, fine‐scale vegetation characteristics. Habitat and vegetation data as well as carrion beetle abundance were collected along four elevational transects in the Front Range and San Juan Mountains from 2010 to 2012 across 32 sites. Multiple habitat types were sampled, including forest, meadow, riparian, rocky outcrops and tundra. The fine‐scale vegetation characteristics included percent coverage of ground vegetation (grass, forb, shrub, cacti, bare ground), understory vegetation biomass and height, canopy cover and tree species, number and size. Canonical correspondence analysis models examined whether vegetation characteristics strongly segregated species using abundances and presence‐absences. Habitat and vegetation models explained a maximum of 18.93% of the variation in species' abundances and 2.48% in species' presence–absences. Only one likely habitat specialist was identified by the models (Heterosilpha ramosa) and the remaining species had substantial overlap in habitat and vegetation use. The arid, low productivity and generally open understory habitats in Colorado mountains likely play a large role in the substantial vegetation overlap. Other mechanisms of partitioning likely exist in this system to reduce niche overlap, which could include differences in activity time and seasonality, physiological traits, other life history strategies and body size.

Effects of Pruning on Vegetation Growth and Soil Properties in Poplar Plantations

Artificial pruning is an important silvicultural practice that can produce clear wood in poplar plantations. This study focused on the growth of poplar, understory vegetation diversity and soil properties in response to different pruning intensities in poplar plantations. We implemented three different pruning treatments based on the height-to-crown base (HCB) to tree height (H) ratio in Populus deltoides ‘Nanlin 3804′ plantations: CK (no pruning), a 1/3 pruning treatment and a 1/2 pruning treatment. The poplar growth conditions, understory vegetation biodiversity and soil properties were investigated for one year after pruning. Compared with CK, the 1/2 pruning treatment significantly decreased the increment of diameter at breast height (DBHi) and stem volume increment (Vi) by 16.4% and 12.8%, respectively. Meanwhile, pruning significantly promoted understory vegetation biomass and increased the Shannon–Weiner diversity index of understory vegetation, and these variables were positively correlated with pruning intensity. The 1/2 pruning treatment significantly reduced the contents of soil nitrate nitrogen (NO3-N), total inorganic nitrogen (IN) and microbial biomass nitrogen (MBN) by 21.9%, 13.9% and 22.4%, respectively. However, the 1/3 pruning treatment had no significant influence. Pruning mainlyaffectedthe soil enzyme activity in the surface (0–10 cm) layer. The 1/3 and 1/2 pruning treatments significantly decreased soil urease activity by 20.1% and 15.0%, respectively. Furthermore, nonmetric multidimensional scaling analysis showed that the seasonal variation in soil properties was significant, and significant differences among pruning treatments were mainly observed in July and October. Redundancy analysis showed that the growth of aboveground vegetation was significantly correlated with soil properties, particularly soil IN content and urease activity. Therefore, the results highlighted that pruning could promote the growth of understory vegetation and accelerate the transformation of soil nutrients. The 1/2 pruning treatment significantly inhibited the growth of poplar in terms of DBH and V, while the 1/3 pruning treatment promoted the growth of poplar in the short term. Overall, we think that the 1/3 pruning intensity is more suitable for pruning practice.

Effect of lime application on soil respiration is modulated by understory vegetation in subtropical Eucalyptus L’Hér. plantations

ObjectiveLime application and understory plant clearance are two common forest management methods employed to increase forest productivity in subtropical regions. However, the effect of these two management methods, or their combined application, on soil respiration in forest plantation settings is still not fully understood.MethodsHere, a field experiment was conducted to determine how lime application, understory clearance, and their combined application, would impact total soil respiration (Rs), autotrophic respiration (Ra), and heterotrophic respiration (Rh) in a Chinese subtropical Eucalyptus plantation. Changes in soil microclimate and microbial community (PLFAs), as well as Eucalyptus fine root biomass were also assessed.ResultsLime application stimulated Rh, but decreased Ra of understory vegetation (primarily Dicranopteris dichotoma), thus consequently inhibiting Rs. Understory clearance also reduced Rs, primarily due to reductions in soil PLFAs and associated Rh, and Ra of understory vegetation. Since the increase in Rh induced by lime application was greater than the decrease in Rh caused by understory clearance, the combined application of lime application and understory clearance decreased Rs primarily by reducing understory root respiration.ConclusionOur observations suggest that understory plants can modulate the effect of lime application on Rs, highlighting the important role of understory vegetation in regulating soil carbon cycling in subtropical Eucalyptus plantations. We concluded that the potential interactive effects should be considered in developing management practices that optimize the yield and sustainability of subtropical plantations.

Understory vegetation diversity, soil properties and microbial community response to different thinning intensities in Cryptomeria japonica var. sinensis plantations.

Soil microorganisms are the key factors in elucidating the effects of thinning on tree growth performance, but the effects of vegetation and soil on the species composition and function of soil microorganisms after thinning are still not well elaborated. The effects of thinning on understory vegetation diversity, soil physicochemical properties and soil microbial community composition were investigated in a thinning trial plantation of Cryptomeria japonica var. sinensis, including four thinning intensities (control: 0%, LIT: 20%, MIT: 30% and HIT: 40%), and the relationships of the microbial community structure with the understory vegetation diversity and soil properties were assessed. The results showed that thinning had a greater effect on the diversity of the shrub layer than the herb layer. The soil bulk density and the contents of soil organic matter, total potassium and nitrogen increased with increasing thinning intensities. The Shannon and Chao indices of soil bacteria and fungi were significantly lower in the LIT, MIT and HIT treatments than in the control. Thinning can significantly increase the abundance of Proteobacteria and Actinobacteria, and higher thinning intensities led to a higher relative abundance of Ascomycota and a lower relative abundance of Basidiomycota, Rozellomycota, and Mortierellomycota. Redundancy analysis indicated that soil physicochemical properties rather than understory vegetation diversity were the main drivers of microbial communities, and fungi were more sensitive to soil properties than bacteria. Functional prediction showed that thinning significantly reduced the potential risk of human diseases and plant pathogens, and the nitrogen fixation capacity of bacteria was the highest in the HIT treatment. Thinning significantly increased the relative abundance of cellulolysis and soil saprotrophs in bacteria and fungi. The findings provide important insights into the effects of thinning on C. japonica var. sinensis plantation ecosystems, which is essential for developing thinning strategies to promote their ecological and economic benefits.

Multifaceted diversity changes reveal community assembly mechanisms during early stages of post-logging forest succession

Plant succession is a fundamental process of vegetation recovery on disturbed sites. Elucidating its mechanisms remains a challenge as succession is influenced by stochastic and deterministic processes related to abiotic and biotic filters. Here, we use a multifaceted diversity approach to reveal mechanisms of successional changes in European oak-hornbeam forests during the first 10 years after selective logging. As the mechanisms controlling succession may depend upon initial abiotic conditions and colonization potential of the surrounding vegetation, we compare changes in taxonomic, functional, and phylogenetic diversity between clearings connected with open habitats and those isolated inside forests. Despite fewer dispersal barriers and higher biomass production in connected clearings, similar mechanisms initially governed succession in post-logging sites. Both clearings had low taxonomic and functional diversity in the first year of succession, as evidenced by significant trait convergence, caused by the legacy of interactions between overstory and understory vegetation in pre-disturbance closed-canopy forests. Colonization by short-lived and light-demanding species in the second and third years after logging has markedly increased the overall taxonomic and functional diversity, as evidenced by significant trait divergence. Connected clearings had higher functional but lower taxonomic and phylogenetic diversity than isolated clearings from the fourth to ten years of succession, probably due to intense competition in more productive habitats. All diversity facets markedly decreased in the last years due to increasing asymmetric competition from regenerating trees. The successional processes were largely deterministic, driven by species’ life-history strategies and biotic interactions (competition) rather than abiotic constraints and stochastic events.

Initial responses of soil chemical properties to simulated warming in Norway spruce (Picea abies (L.) H.Karst.) stands in the Western Carpathians

The present-day decline observed in Norway spruce stands in the Western Carpathians is particularly worrying given the large forest area of this species. Relatively little attention has been paid to the contribution of soil chemistry to the Norway spruce decline in the context of global warming. We conducted a field experiment to simulate warming for almost 500 days in the Western Carpathians, in a mature Norway spruce stand. Soil samples were collected approximately every 3 months from the organic and mineral topsoil horizons. Total carbon, total nitrogen, pH, dissolved organic carbon (DOC), total dissolved nitrogen (TDN), nitrate (NO3-N), and ammonium (NH4-N) nitrogen concentrations were estimated. Warming caused increase in DOC, TDN, NH4-N, and pH in organic horizon, as well as increased pH in mineral topsoil. A trend for increasing total carbon and total nitrogen concentrations in the warmed organic horizon was observed. Increased concentrations of DOC and TDN may be associated with decrease in SOM stability or increase in production of biomass of the understory vegetation or soil microbial activity. Increased pH in warmed soil may be associated with the increased NH4-N and may contribute to the decrease in soil ability to adsorb DOC. We conclude that soil warming negatively stimulates soil organic matter stability, resulting in higher concentrations of easy migrating labile forms, mostly organic acid anions. Observed changes may contribute to the deterioration of Norway spruce stands.

Silva Nova – Restoring soil biology and soil functions to gain multiple benefits in new forests

Afforestation is proposed as one of the most effective climate solutions for carbon sequestration. As a majority of threatened species are linked to forests, afforestation can also contribute to mitigate the biodiversity crisis. There is however a caveat: the agricultural legacy (high nutrient availability, altered soil biota structure and function) of new forests constrains the development of forest-adapted species, affects tree growth and stability, and delays environmental benefits from afforestation. We hypothesize that inoculation of former arable land with soil (including microbiome, fauna and seeds/rhizomes of understory vegetation) from old forests along with targeted tree species mixtures will improve productivity and more rapidly restore forest-adapted communities. This will ultimately result in diverse, stable and resilient multifunctional forests. We will test this hypothesis and develop applied inoculation methods by: i) exploring soil biota and benchmarking biodiversity in existing afforestation research Chronosequence platforms (chronosequences and sites with increasing distance to other forests); ii) conducting inoculation experiments in mesocosms to measure seedling performance and, above- and belowground linkages; iii) establishing field-scale inoculation experiments in new and existing afforestations to test short- and long-term inoculation success on forest productivity, biodiversity and soil functioning at the ecosystem scale; iv) incorporating the landscape context into guidelines and tools for spatially explicit prioritization of areas for assisted dispersal. The aims are to resolve barriers for successful restoration and develop landscape-scale afforestation strategies that optimize productivity and biodiversity for the planning and implementation of green infrastructure; and produce basic knowledge on the tree, understory vegetation, soil fauna and microbiome nexus and its effect on forest productivity, biodiversity and soil functions (N-retention, C-sequestration, methane uptake).

Presence of understory dwarf bamboo determines ecosystem fine root production in a cool-temperate forest in northern Japan

ABSTRACT Fine root biomass (FRB) and production (FRP) are crucial in forest carbon and nutrient cycling, but the factors controlling FRB and FRP are not well understood. Here, we examined FRB, FRP, aboveground environmental and stand factors, and soil environmental factors in four stands in a forest covered with dense understory vegetation of dwarf bamboo, Sasa senanensis (hereafter, Sasa). The four stands had different tree species composition and included a primary forest (PF), secondary forest (SF), conifer plantation (CP), and Sasa area (SA). We quantified the FRB and FRP of trees and Sasa separately using the ingrowth core method. Total FRP was higher in stands with substantial presence of Sasa (99–130 g m−2 yr−1) than in CP with scarce Sasa (69 g m−2 yr−1). Despite being occupied by Sasa alone, SA had high FRP, suggesting that the presence of Sasa regardless of trees is a key determinant of ecosystem FRP. Tree FRB increased with increasing tree aboveground biomass, tree density, or basal area at breast height, but Sasa FRB and total FRB decreased. Total FRP was also lower at higher values of these aboveground stand factors. In Sasa, specific root length was significantly higher, and root tissue density was significantly lower, than in trees, indicating the capacity of Sasa for explosive growth. Positive correlations between Sasa FRB or FRP and soil inorganic N or ammonium contents (i.e. N availability) were detected. We conclude that Sasa is important in determining FRB and FRP in this northern forest with understory vegetation.

Atmospheric ammonia deposition and its role in a cool-temperate fragmented deciduous broad-leaved forest

Forest fragmentation can increase dry deposition of atmospheric ammonia (NH3) volatilized from agricultural areas, and consequently increase spatial variability of Nr deposition within the forest (“elevated reactive nitrogen (Nr) deposition”). However, little is known about this effect and its impact on forest production in a deciduous broad-leaved forest in Asian countries. Here, we performed the field observations of atmospheric concentration and deposition of inorganic Nr gases and particles in a Japanese fragmented forest from May 2018 to April 2019. Leaf traits and growth of Japanese oak tree and understory vegetation were also measured. Atmospheric concentration and deposition of dissolved inorganic Nr (DIN) to tree canopies were measured via filter sampling and throughfall methods, respectively. Canopy retention/exchange was also estimated as a part of dry deposition using the canopy budget model. The results demonstrated that annual dry deposition of NH3 to tree canopies (4.4 kgN ha−1 y−1) was dominant in the annual total DIN deposition (7.1 kgN ha−1 y−1) at the forest edge, including the elevated Nr deposition of approximately 2 kgN ha−1 y−1. Additionally, agricultural activities such as fertilization in the area surrounding the forest likely enhanced the potential of canopy retention of NH4+, readily absorbed by tree canopy. The growth rates of tree and understory vegetation (dwarf bamboo) were higher at the edge than that at the interior, emphasizing a need for further investigation to quantify the effect of low Nr deposition (<3–5 kgN ha−1 y−1) on forest production, along with the conventional experimental studies under a high Nr deposition.

Tree Growth and Vegetation Diversity in Northern Idaho Forest Water Reclamation Facilities

Forest water reclamation can improve tree growth and renovate municipal wastewater. Although there are indications that long-term application may exceed forest assimilation capacity, there is limited information on the long-term effects of reclaimed water application on coniferous ecosystems. The purpose of our study was to assess the impacts of prolonged reclaimed water application on forest growth responses and vegetation diversity. We examined the effects of reclaimed water at five water reuse facilities established between 1978 and 2013 in a four-decade time series. We collected tree cores and stem measurements to determine current and retrospective increments. We assessed plant diversity with vegetation surveys. The greatest diameter response observed for reclaimed water amendment compared to controls was 166.1% for western redcedar, while Douglas-fir increased up to 116.4% and ponderosa pine increased up to 100.6%. The minimum response observed was 30.3%. Current annual increments showed that the basal area and volume were significantly greater at long-established facilities for reclaimed-water-amended plots. The understory vegetation diversity declined with application time, while overstory vegetation diversity increased with application time. We conclude that reclaimed water can be a valuable resource to improve forest productivity, but continued application without stocking control may have detrimental effects on forest growth and vegetation diversity.