Understory Vegetation Composition Research Articles

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.

Abundance, diversity and composition of understory plants along the altitudinal gradient and dominant overstory composition types in the temperate Himalayan region

IntroductionThe Indian Himalayan forests are remarkable landforms experiencing tremendous climatic variation, constituting complex and diversified ecosystems with prominent vegetation zones. Despite their global significance and substantial research efforts focused on plant diversity in the temperate Himalayan region, only a few studies have explicitly assessed the distribution patterns of understory vegetation in relation to forest compositional types along altitudinal gradients.MethodsTo cover a wide range of altitudes and diverse overstory compositions, stands were sampled across four altitudinal ranges from 1500 to 3500 meters above mean sea level with increments of 500 meters in elevation steps. The overstory compositions were classified on the basis of dominant tree species in each stand on the similar sites. Vegetation in the shrub and ground layers was surveyed by visually estimating the percentage coverage within circular plots.ResultsA total of 99 understory species including 37 species each in the shrub layer, 62 species in the herb layer vegetation were recorded. The abundance, species diversity and composition of understory vegetation differed significantly along the altitudinal gradient and dominant overstory composition types. Moreover, distinct understory vegetation communities were observed at lower elevations compared to higher elevations, with middle elevations exhibiting intermediate vegetation characteristics. The study also highlighted the importance of dominant overstory composition types in shaping the pattern of understory vegetation abundance, species diversity and composition in the temperate Himalayan region. The higher resource conditions associated with broadleaved stands supported higher understory species abundance at lower elevations, while the heterogeneous conditions induced by the mixedwood stands promoted higher understory species diversity.ConclusionThe hump shaped pattern along the altitudinal gradient appeared to be the most dominant pattern of plant abundance and species diversity and call for more conservation concern towards the middle elevation zones in the temperate Himalayan region. Furthermore, the management interventions should aim at maintaining diverse range of overstory composition types for conserving biodiversity and their ecological functions in the temperate Himalayan region.

Land use changes effect by slash and burn cultivation to understory diversity composition and soil degradation

This study contributes to understanding ecological changes in land use following slash-and-burn land clearing. This study aimed to compare the richness and density of plant species and soil fertility in farmland cultivated for one year (1 Y), three years (3 Y), and five years (5 Y) after slash-and-burn, with the conditions in the secondary forest (SF) in Berau Regency of East Kalimantan. Understory plant taxon types, numbers, and soil organic matter were measured in each region using a series of nested plots. The size of each observation plot was 20 x 100 m. Data on understory vegetation composition was collected using 1 x 1 m mini plots at 20 sampling points and divided into five blocks, with a 10 m spacing between sampling points on each property. Understory vegetation species and cover percentage, litter cover percentage, open soil percentage, and soil fertility were measured for each observation plot. The results showed that the land cover percentage increased each year during the 5 years transition from secondary forest to farmland. Furthermore, within the 5 years, there was a change in understory species, particularly the presence of grasses and sedges at 3 and 5 years after the land use change. However, the transition from secondary forest to farmland within 5 years did not alter soil organic matter and total nitrogen.

Monitoring Changes in Composition and Diversity of Forest Vegetation Layers after the Cessation of Management for Renaturalization

Overstory and understory vegetation play a vital role in forest ecosystem functionality. However, it is necessary to enhance the knowledge of their diversity and compositional dynamics following cessation of disturbance, which is required to inform restoration approaches and the mechanisms required for maintaining disturbance cessation. We conducted a chronosequence spanning 0–1, 5–6, 11–12, 20–24, and 28–34 years since disturbance cessation, and old-growth forests to investigate the dynamic changes in overstory and understory vegetation diversity and composition, as well as maintenance mechanisms following the cessation of anthropogenic disturbances in subtropical regions of Eastern China. The current study results indicated a decrease in understory cover and periodic fluctuations in the diversity of overstorey and understory vegetation following disturbance cessation efforts. Specifically, the shrub layer exhibited the highest richness in 28–34 years, while the herb layer showed the lowest evenness. Multivariate analysis using multiple-response permutation procedures indicated that the species composition and interspecific quantity ratio of understory plants in the forest at 28–34 years significantly differ from those in the early closure stage. An indicator species analysis revealed that more support was given to sun-loving plants after 0–1 years of the enclosure, while species with shade tolerance and low nutrient requirements were supported after 28–34 years. The structural equation model results show that 38.8% of the impact on herb evenness was related to light and substrate diversity. The ecological restoration time mainly indirectly affects understory vegetation by influencing the upper vegetation, light availability, and substrate heterogeneity. Overall, this study revealed that cessation of anthropogenic disturbance can maintain and care for understorey plant diversity and contribute to the sustainable management of forests.

Planting density and mechanical site preparation effects on understory composition, functional diversity and planted black spruce growth in boreal forests

Mechanical site preparation (MSP) is used prior to planting to control competing vegetation and enhance soil conditions, particularly in areas prone to paludification. Tree planting density can be adapted to the management context and objectives, as it influences yield and wood quality. However, the combined effects of MSP and planting density on understory vegetation composition, functional traits, and diversity remain uncertain. We thus conducted a study in the Clay Belt region of northwestern Quebec, Canada. After careful logging, the study area was divided into nine sites, each receiving one of three treatments: plowing, disc trenching, or no preparation. Sites were further divided into two, with black spruce (Picea mariana [Mill.] Britton, Sterns & Poggenb.) seedlings planted at either a low planting density of 1100 seedlings ha-1 or a high planting density of 2500 seedlings ha-1. After nine years, we assessed understory composition, diversity, key functional traits, sapling density and growth of planted trees. Careful logging alone led to a higher density of naturally established conifers compared to plowing or disc trenching. The interaction between planting density and MSP significantly influenced understory diversity and composition in plowed plots. Understory composition was affected by the soil C/N ratio, coniferous species, and deciduous species density. The growth of black spruce was notably enhanced with higher planting density in the plow treatment only. Neither planting density nor MSP alone affected tree height and diameter. Our results suggest that combining plowing with high-density planting can enhance stand growth and improve forest productivity. These findings guide future research on paludified forests.

Developmental Dynamics and Driving Factors of Understory Vegetation: A Case Study of Three Typical Plantations in the Loess Plateau of China

Understory vegetation is one of the most important links for improving forest biodiversity, and its restoration is conducive to sustainable forest development, energy flow, and nutrient cycling. However, little is known about the developmental dynamics and main driving factors of the long-time series coverage, biomass, diversity, and species composition of plantation understory vegetation. In a case study of three typical plantations, with a natural secondary forest as reference in the Loess Plateau of China, we collected understory vegetation from a Robinia pseudoacacia Linn. deciduous broad-leaved plantation, Pinus tabulaeformis Carr. evergreen coniferous plantation, and mixed plantation with an age span of 10 to 50 years. (1) The understory plantation coverage and biomass results of stands with different ages showed the R. pseudoacacia plantation to be significantly higher than the P. tabulaeformis plantation, and the species diversity of the P. tabulaeformis plantation changed the most with the stand age. However, the growth resource imbalance, and drastic changes in the stands’ environment caused by excessive intraspecific competition in the early stage of the P. tabulaeformis plantation vegetation restoration, are the main reasons that make the species diversity of undergrowth vegetation of P. tabulaeformis plantation lower than that of other stand types. (2) The understory species composition of the plantations revealed their degree of community stability. Compared to the R. pseudoacacia plantation and P. tabulaeformis plantation, the mixed plantation had higher stability, and its species composition closely resembled a natural secondary forest. The community stability of the P. tabulaeformis plantation was the lowest because it had the lowest coverage, biomass, and species diversity of understory vegetation. However, the understory species composition of the three plantation types converged, which was due to atypical species contribution. (3) The dynamic changes of canopy and soil nutrients were the main driving factors affecting the R. pseudoacacia plantation understory vegetation species composition. Stand density and elevation limited the understory vegetation communities of P. tabulaeformis plantation restoration. Soil bulk density is the key factor affecting understory vegetation in mixed plantations, and this effect weakens with the stand age. In future studies, the focus should be on the converged action and further development trend of atypical species, choosing an appropriate recovery strategy (active or passive), and providing more possibilities for the intensive management of vegetation under different plantations.

Tradeoffs between timber and wildlife habitat quality increase with density in longleaf pine (Pinus palustris) plantations

Longleaf pine (Pinus palustris), a historically abundant tree species in the southeastern United States, is often planted to restore the ecologically and culturally important longleaf pine ecosystem that once covered vast acreages in the southeastern United States. Government cost-share programs that support establishment of these plantations place restrictions on planting rates to promote wildlife habitat, as greater tree planting density may reduce canopy openness and herbaceous plant cover that are critical components of habitat for priority species, including gopher tortoise (Gopherus polyphemus) and Bachman’s sparrow (Peucaea aestivalis). However, there is expressed concern among some forest managers that more open grown trees in the plantations will be of inferior timber quality with more and larger horizontal branches and associated knots. We examined how density affects dynamics and tradeoffs among understory vegetation structure and composition, longleaf pine stem form (branch density and straightness), and longleaf pine survival by sampling 73 plantations of various ages (5–25 years) and planting rates (653–2445 trees per hectare (TPH)/264–990 trees per acre (TPA)) throughout the southeastern United States. We documented a relationship between planting rate and longleaf pine stand density at time of sampling (r = 0.69, p = 0.0001) and relationships between stand density and habitat and timber quality metrics. Greater stand density resulted in lower tree diameters but greater stand basal area than lower stand density. Higher planting rates led to lower branch density and lower straightness grades than lower planting rates. Canopy openness decreased with greater stand density, and bare ground cover and herbaceous cover decreased as density and stand age at time of sampling increased. Based on our results, we suggest that lower maximum planting rates are appropriate when wildlife habitat is a program objective because lower rates result in fewer tradeoffs, as reducing planting rates slows degradation of wildlife habitat when compared with higher maximum planting rates that have only mixed benefits on timber quality.

Effects of species mixture on understory vegetation, soil properties and bacterial diversity of Acacia cincinnata, Eucalyptus robusta and Acacia mangium plantations in Southeastern China

The establishment of mixed forests is gaining increasing attention as a way to optimize forest production, improve ecological benefits, and serve as a safety net for impacts of future climate uncertainties. However, practical knowledge about which species and what proportion of them should be mixed is still lacking. Thus, this study was conducted to identify suitable species for a mixture with Acacia cincinnata. The mixtures tested in this study were A. cincinnata and Eucalyptus robusta (6:4), A. cincinnata and Acacia mangium (3:1), and monoculture plantation of A. cincinnata established in 2014. After seven years of growth, we analyzed the effects of species mixing on tree species growth, understory vegetation, and soil physicochemical properties as well as bacterial community structure and diversity. The results showed that species mixing had no significant effect on the diameter and individual volume of A. cincinnata. However, mixed planting increased the total stocking volume compared to monoculture plantation of A. cincinnata. The species diversity, biomass and nutrient stocks in the understory vegetation were significantly increased by stand mixing. The soil of mixed stand of A. cincinnata and A. mangium had the highest C and N contents, whereas the soil of monoculture A. cincinnata stands had the highest P content. The diversity of soil bacterial community was highest in the mixing stand of A. cincinnata and E. robusta, followed by monoculture A. cincinnata stand and mixed stand of A. cincinnata and A. mangium. The relative abundance of Proteobacteria and Actinobacteria was highest in mixed stand soil of A. cincinnata and E. robusta. Furthermore, the relative abundance of Firmicutes was high in the mixed stand soils of A. cincinnata and A. mangium while the relative abundance of Verrucomicrobia was high in the mixed stand of A. cincinnata and E. robusta stand. In general, the study revealed that the establishment of mixed-species forest enhances the diversity and composition of understory vegetation, soil physicochemical and soils bacterial community; thereby increasing biodiversity, nutrient cycling and carbon sequestration in the biomass and soil. From the viewpoints of forest productivity and ecological benefits, it is advisable to establish a mixed forest of A. cincinnata and A. mangium in southern China. Overall, our work revealed that the sustainability of mixed-species plantations relies on the interactions between soil attributes, vegetation, and bacterial community.

How does understory vegetation diversity and composition differ between monocultures and mixed plantations of hybrid poplar and spruce?

Although monocultures are important for timber production, they are often associated with lower biological diversity than mixtures. Thus, mixed plantations have been suggested as a way to enhance biodiversity because of their inherent compositional diversity. However, the effects of monocultures versus mixtures on understory diversity and composition can vary in different ecosystems. The objective of this study was to assess how monocultures and mixed plantations influence understory vegetation diversity and composition in the boreal forest region of southern Quebec. We sampled plantations established with deciduous Populus trichocarpa Torrey & A. Gray × balsamifera L. and P. maximowiczii Henry × balsamifera L. and coniferous Picea abies (L.) Karst. and Picea glauca (Moench) species planted in monocultures and in mixed plantations on abandoned farmlands and a forest site. We assessed understory vegetation diversity and composition in each canopy type (coniferous, deciduous, mixed) and in each plantation type. We evaluated bryophyte and lichen diversity and composition specifically in tree microhabitats: soil, tree bases, and tree trunks. We found that vascular plant and lichen species richness was similar in all plantation types, while bryophyte species richness was higher in spruce monocultures and in mixed plantations compared to poplar monocultures. Our results also highlight how land-use history influenced vascular plant composition as abandoned farmland sites were composed of more ruderal vascular plants, while the previously forested site was composed of species found in natural forests. In the context of reforestation and plantations, our study suggests mixing spruce with poplars to maximize understory vegetation diversity as the addition of spruce in mixed plantations promoted the establishment of terrestrial bryophytes, while poplars favored the establishment of epiphytic lichens.

Impact of different storm severity levels and post-storm management on understory vegetation richness, diversity and composition 19–20 years after wind disturbance

The herbaceous understory is a key component of forest biodiversity. Moreover, it holds the capability to alter the dynamics and composition of the overstory. Severe wind disturbance changes the conditions in a forest ecosystem radically, causing alteration of understory characteristics as well. In this paper we analyze impacts of different storm damage levels and post-storm management on understory vegetation richness, diversity and composition in mixed spruce–hardwood forest stands located in hemiboreal Estonia. We examined understory vegetation in moderately damaged (n = 4), heavily damaged (n = 4) and post-storm salvage-logged stands (n = 4) 19–20 years after storm disturbance. Mature mixed spruce–hardwood forests were included as a reference group (n = 4). Study plots were also assessed regarding canopy openness, richness of microhabitats and coverage of woody species. A total of 98 herbaceous and 2 dwarf shrub taxa were found on 208 vegetation quadrats (1 m2 square each). Total coverage of the herb layer and species richness were greatest at salvage-logged plots when compared to other treatments. However, we found no significant effect of treatment on diversity (Shannon’s H’) nor evenness (Pielou’s index) of herbaceous species. Our results indicate that approximately-two decades after wind disturbance, the understory communities differ from each other as a response to different storm damage levels and post-storm management. Compared to control plots, salvage-logged plots demonstrated greatest contrast regarding species composition. Salvage-logged plots had greatest light levels, but lowest estimates for microsite richness and woody species coverage. Moderately damaged plots demonstrated greatest within-group variation regarding light conditions and species composition. Our findings suggest that salvage logging after severe wind disturbance might induce delayed succession toward a closed canopy due to intense understory competition and lack of opportunity-providing microhabitats for tree regeneration.

Rotational cattle grazing improves understory vegetation biodiversity and structural complexity in oil palm plantations

AbstractHerbicide overuse decimates understory vegetation, including those beneficial plants which may lead to a reduction of some production‐related ecosystem services such as nutrient cycling, water regulation, natural pest control, and pollination. Such conventional weed management practices need to be replaced with environmentally friendly methods such as ecological grazing to make palm oil supply chain environmentally sustainable. Contrary to chemical weeding, livestock integration is believed to be a useful tool to control weeds without negative impact to human health and the environment. However, little is known about the influence of different livestock grazing practices on oil palm understory vegetation. Thus, the present study investigates the effects of weed management practices (i.e., rotational grazing, free‐ranged grazing, and conventional weeding) on understory vegetation species richness, composition assemblages, and structural complexity. Based on plant surveys that were conducted on 360 sampling points, 120 understory vegetation species consisting of grasses, sedges, ferns, and legume covers were recorded. We found understory vegetation composition assemblages were different between treatments. Results revealed that the number of understory vegetation species, coverage, and height were significantly higher in rotational grazing compared with other practices. Given the major contribution of vegetation composition assemblages and structure on palm oil productions and biodiversity, oil palm growers should adopt rotational livestock grazing as a part of an integrated pest management strategy to control understory vegetation.

Community associations and ecological drivers of understory vegetation across temperate forests of Kashmir Himalayas, India

We assessed the understory vegetation types in temperate Kashmir Himalayan coniferous forests, their species composition and what function ecological drivers execute in shaping compositional trends using a multivariate statistical approach. The agglomerative clustering analysis depicted eight discrete plant associations in terms of herb species composition with simple underlying indicator species and ecological drivers. At one extreme, we found alpine and subalpine areas (Tanacetum multicaule Sch.Bip. – Aconitum heterophyllum Wall. ex Royle – Lomatogonium caeruleum (Royle) Harry Sm. ex B.L. Burtt community (TAL)) occupying high elevations (2961.88±205.56 m) with notable species richness (6.04), while lower (2459.36±94.07 m) areas are inhabited by Thalictrum minus L. – Galium aparine L. – Achillea millefolium L. (TGA) community. The Poa pratensis L.– Senecio chrysanthemoides DC. – Clinopodium umbrosum (M.Bieb.) Kuntze (PSC) community was most diverse, supported higher species diversity (Shannon=2.22±0.07; Simpson=0.84±0.01; Fisher's α=4.51±0.30) and also exhibited a maximum number of trails crossing the plot. Canonical Correspondence analysis (CCA) examined the species-ecological interactions and displayed a significant role of most studied environmental variables in the species distribution patterns. The latter in the decreasing significance order comprised precipitation (F = 2.3; p = 0.001), latitude (F = 2.15; p = 0.001), grazing (F = 1.56; p = 0.01), longitude (F = 1.63; p = 0.013), slope (F = 1.33; p = 0.07), elevation (F = 1.32; p = 0.07), aspect (F = 0.1; p = 0.47), trails (F = 0.78; p = 0.85) and mean monthly minimum temperature (F = 1.23; p = 0.172). The variance partitioning used to evaluate the comparative significance of topographic, climatic and disturbance factors on understory vegetation composition depicted that topography (14.26%) strongly partitioned the vegetation distribution subsequently followed by climatic (11.52%) and disturbance (4.49%) factors.

Strip Clearcutting Drives Vegetation Diversity and Composition in the Moso Bamboo Forests

Abstract Strip clearcutting of Moso bamboo forests in southern China has seen increasing interest as a way of reducing harvesting costs. Previous research has shown that cutting influences the overstory structure and drives changes in the microclimate and soil properties. However, the effects of strip cutting on understory vegetation diversity and composition remain unclear. To better understand the influence of cutting on the understory vegetation, this study compares sites under natural restoration after cut and uncut sites in the Moso bamboo forest. We selected plots that were cut in 2019 (C19) and 2017 (C17), as well as unharvested plots as controls (CK). The results showed that strip clearcutting increased the understory vegetation richness and diversity, and a significant difference (A = 0.23, P = 0.001) existed in the composition of the vegetation between the three treatments. Furthermore, the decrease of soil total phosphorus and total potassium content resulted in the difference in undergrowth vegetation distribution and composition between the uncut plots and the cut plots. Our results suggest that strip clearcutting may not be harmful to biodiversity on a local scale in the Moso bamboo forest.

Impacts of pre-fire conifer density and wildfire severity on ecosystem structure and function at the forest-tundra ecotone.

Wildfire frequency and extent is increasing throughout the boreal forest-tundra ecotone as climate warms. Understanding the impacts of wildfire throughout this ecotone is required to make predictions of the rate and magnitude of changes in boreal-tundra landcover, its future flammability, and associated feedbacks to the global carbon (C) cycle and climate. We studied 48 sites spanning a gradient from tundra to low-density spruce stands that were burned in an extensive 2013 wildfire on the north slope of the Alaska Range in Denali National Park and Preserve, central Alaska. We assessed wildfire severity and C emissions, and determined the impacts of severity on understory vegetation composition, conifer tree recruitment, and active layer thickness (ALT). We also assessed conifer seed rain and used a seeding experiment to determine factors controlling post-fire tree regeneration. We found that an average of 2.18 ± 1.13 Kg C m-2 was emitted from this fire, almost 95% of which came from burning of the organic soil. On average, burn depth of the organic soil was 10.6 ± 4.5 cm and both burn depth and total C combusted increased with pre-fire conifer density. Sites with higher pre-fire conifer density were also located at warmer and drier landscape positions and associated with increased ALT post-fire, greater changes in pre- and post-fire understory vegetation communities, and higher post-fire boreal tree recruitment. Our seed rain observations and seeding experiment indicate that the recruitment potential of conifer trees is limited by seed availability in this forest-tundra ecotone. We conclude that the expected climate-induced forest infilling (i.e. increased density) at the forest-tundra ecotone could increase fire severity, but this infilling is unlikely to occur without increases in the availability of viable seed.

Vegetation changes in the understory of nitrogen-sensitive temperate forests over the past 70 years

Since the industrial revolution, atmospheric nitrogen deposition has increased strongly and has been shown to alter nitrogen cycles, species composition and diversity in many ecosystems, including forests. At the same time, nitrogen removal from forests through biomass extraction via historical management techniques has decreased considerably. A proven tool to analyze the effects of long-term environmental changes are vegetation resurveys.In this study, we tested whether environmental changes resulting from atmospheric nitrogen deposition and altered forest management are reflected in the vegetation composition of temperate forest understories in six acidophilic and oligo-mesophilic forest types in south-western Germany. We compared historical surveys from 1950 to 1976 with surveys from 2017/18 and examined changes in the vegetation using NMDS ordinations and Ellenberg indicator values.While an increase in the number of nitrophilic species was detected in all forest types, only the acidophytic and oligotrophic Vaccinio-Abietetum and Luzulo-Quercetum forests (dominated by Abies alba (Mill.) and Quercus spec., respectively) exhibited a replacement of oligotrophic species by nitrophilic species, amounting to an overall trend of eutrophication.Despite the uncertainties resulting from different plot locations and the slow dynamics of forests, we demonstrate a significant trend in the understory vegetation composition, which is likely caused by atmospheric N deposition. Differences in the sensitivity of different forest types indicate an influence of geological and climatic site characteristics and historical land use on the effects of environmental changes.

Reduction of Grazing Capacity in High-Elevation Rangelands After Black Locust Invasion in South Africa

The growing invasion of ecosystems by invasive alien plants (IAPs) has substantially affected biodiversity worldwide, compromising provision of ecosystem services. In this study, we present evidence of the impacts of an IAP, Robinia pseudoacacia L., on native plant diversity in montane rangelands of South Africa and its threats to grazing, an ecosystem service. We assessed stand characteristics, understory vegetation composition and rangeland condition similarities in invaded and uninvaded sites. We observed a shift in grass communities after invasion by R. pseudoacacia as invaded communities differed by 96% from uninvaded rangeland. Invaded habitat was dominated by nitrophilous, shade-tolerant alien ruderals that follow the primitive C3 carbon fixation pathway. Nitrogen fixation and light-demanding properties of R. pseudoacacia are likely to be the main factors driving these changes. As a result, range condition was significantly lower in invaded habitats with smaller and dense trees (180 ± 24.3) (mean ± standard error) when compared with adjacent uninvaded habitat (401 ± 24.3). These preliminary findings support an urgent need for sustainable control of R. pseudoacacia as an effective approach to stop further reduction in grazing capacity and losses in livestock production.

Understory Vegetation Composition and Stand Are Mainly Limited by Soil Moisture in Black Locust Plantations of Loess Plateau

Forestry eco-engineering programs in China occupy 721.77 × 104 km2, among which plantations have a pivotal role in protecting the fragile ecological environment. Reforestation understory is often ignored because of the simple vertical structure. The importance of light in understory has been discovered. However, how other ecology factors (e.g., soil properties and geographical factors) influence understory composition and stratification remain unclear. In this study, we investigated the effects of understory composition and stratification on environmental factors in black locust plantations. We used systematic clustering analysis based on plant average height to describe understory stratification. The finding of this study was that black locust plantation understory consisted of three levels: (I) a low herbaceous layer (<80 cm), (II) a high herbaceous layer (80–130 cm), and (III) a shrub layer (>130 cm). Redundancy analysis indicated that soil moisture content and soil total phosphorus content were the largest contributors to the variation in understory vegetation composition. Soil moisture content, altitude, and soil organic carbon content were the largest contributors to the variation in understory stratification. Overall, by analyzing understory stratification and the relationship between soil and geographical factors, we gained a more comprehensive understanding of the interaction between understory and the microenvironment. This is especially important for reforestation management that maintains understory ecology function in the face of global climate change.

Relationship among water penetration, soil structure and understory vegetation according to the land conditions around the greenway in Kohoku New Town

In the slope forest of suburban area, which is affected by the land development, rainwater is getting to be more difficult to be penetrated because of the long-term compaction of surface soil. In the slopes along the greenway in Kohoku New Town, we selected survey plots according to the land conditions and the existence of understory vegetation cover, comparing original slopes of tablelands, slopes of constructed fill and cut mud slopes. We investigated rainwater penetration capacity, soil softness, soil particle size composition, and cover and biomass of understory vegetation, and analyzed their relationships. As a result, soil softness and the hierarchical diversity of understory vegetation had positive correlation with water penetration capacity, and these relationships were found in the cut mud slopes, same as in the original slopes, although no such relation was confirmed in the filled slopes. In the filled slopes, the effect of the underground structure to water penetration is stronger than that of surface soil, but in the cut mud slopes, hierarchical vegetation and softened surface soil are distributed with higher water penetration capacity. It was suggested that it is important to utilize such cut mud slopes to recover rainwater penetration capacity, with conserving the developing vegetation, in the restructuring of the greenway.

Understory vegetation dynamics of Chinese fir plantations and natural secondary forests in subtropical China

Understory vegetation is a vital component of forest ecosystems and contributes to terrestrial plant diversity, nutrient cycling and energy flows. Plantations and natural secondary forests are two dominant types that emerge following stand-replacing disturbances in managed landscapes. However, to date, the long-term dynamics of the cover, diversity, and composition of understory vegetation in plantations and secondary forests remain poorly understood. We sampled understory vegetation of Chinese fir plantations and natural secondary forests with their ages spanning 4 to 40 years and used primary forests as a reference in subtropical China. The cover and species diversity of the shrub layer were significantly higher in the natural secondary forests than in Chinese fir plantations in two younger age classes, but they converged in older stands. In the herb layer, Chinese fir plantations possessed a higher total and vascular species diversity across all age classes, but their covers did not differ significantly between the two forest types, except for a higher cover of vascular plants in the 8–12-year-old Chinese fir plantations. The bryophyte cover did not differ with forest type nor stand age, while bryophyte species diversity was significantly higher in Chinese fir plantations. The cover and species diversity of understory vegetation in the primary forests were similar to those in the 35–40-year-old natural secondary forests. Across all forest types and age classes, the cover and diversity were positively correlated within each plant group, and the shrub cover and diversity were negatively correlated with vascular diversity in the herb layer, but neither the cover nor the diversity of bryophytes was correlated with those of the shrub layer or herb layer. Species composition differed significantly with forest type and stand age. Natural secondary forests had more similar understory species composition to primary forests than Chinese fir plantations did. Our results suggest that forest management may increase the diversity of the herb layer, but at the expense of the abundance and diversity of the shrub layer. The shrub layer may not regenerate, or its regeneration will be slow due to exhausted seed and propagulum banks after multiple management rotations. Moreover, the high cover of the shade-intolerant and nutrient-demanding herbaceous plants in Chinese fir plantations may have adverse effects on ecosystem service functions.

Responses of Temperate Forests to Nitrogen Deposition: Testing the Explanatory Power of Modeled Deposition Datasets for Vegetation Gradients

Eutrophication due to increased nitrogen concentrations is known to alter species composition and threaten sensitive habitat types. The contribution of atmospheric nitrogen deposition to eutrophication is often difficult to determine. Various deposition models have been developed to estimate the amount of nitrogen deposited for both entire regions and different landscape surface types. The question arises whether the resulting deposition maps allow direct conclusions about the risk of eutrophication-related changes in the understory vegetation composition and diversity in nitrogen-sensitive forest ecosystems. We combined vegetation and soil data recorded across eutrophication gradients in ten oligo-mesotrophic forest types in southwest Germany with datasets from two different deposition models specifically fitted for forests in our study region. Altogether, 153 forest stands, with three sampling replicates each, were examined. Linear mixed-effect models and NMDS analyses revealed that other site factors, in particular the soil C/N ratio, soil pH and canopy cover, played a greater role in explaining vegetation gradients than nitrogen deposition. The latter only rarely had effects on species richness (positive), nitrophyte cover (positive or negative) and the cover of sensitive character species (negative). These effects varied depending on the deposition model used and the forest types examined. No effects of nitrogen deposition on average Ellenberg N values were found. The results reflect the complex situation in forests where nitrogen availability is not only influenced by deposition but also by nitrogen mineralization and retention which depend on soil type, pH and (micro)climate. This context dependency must be regarded when evaluating the effects of nitrogen deposition.