Understory Plant Diversity Research Articles

Long-term N addition reduced the diversity of arbuscular mycorrhizal fungi and understory herbs of a Korean pine plantation in northern China

With the development of agriculture and industry, the increase in nitrogen (N) deposition has caused widespread concern among scientists. Although emission reduction policies have slowed N releases in Europe and North America, the threat to biodiversity cannot be ignored. Arbuscular mycorrhizal (AM) fungi play an important role in the establishment and maintenance of plant communities in forest ecosystems, and both their distribution and diversity have vital ecological functions. Therefore, we analyzed the effects of long-term N addition on AM fungi and understory herbaceous plants in a Korean pine plantation in northern China. The soil properties, community structure, and diversity of AM fungi and understory herbaceous plants were detected at different concentrations of NH4NO3 (0, 20, 40, 80 kg N ha−1 year−1) after 7 years. The results showed that long-term N deposition decreased soil pH, increased soil ammonium content, and caused significant fluctuations in P elements. N deposition improved the stability of soil aggregates by increasing the content of glomalin-related soil protein (GRSP) and changed the AM fungal community composition. The Glomus genus was more adaptable to the acidic soil treated with the highest N concentration. The species of AM fungi, understory herbaceous plants, and the biomass of fine roots were decreased under long-term N deposition. The fine root biomass was reduced by 78.6% in the highest N concentration treatment. In summary, we concluded that long-term N deposition could alter soil pH, the distribution of N, P elements, and the soil aggregate fractions, and reduce AM fungal and understory herb diversity. The importance of AM fungi in maintaining forest ecosystem diversity was verified under long-term N deposition.

Climate Strengthens the Positive Effects of Stand Structure on Understory Plant Diversity in Chinese Temperate Forests

Stand structure, which links function and management, plays a crucial role in regulating forest ecosystems and influencing biodiversity. Nevertheless, knowledge of the effect of climate change on stand structure and plant diversity is still poorly understood on a large scale. To explore the effects of various climate conditions on stand structure–plant diversity, we conducted a comprehensive analysis of data from 1272 plots across China’s temperate and subtropical forests. Leveraging the structural equation model (SEM), we explored the direct and indirect effects of climate, topography, and tree diversity on understory woody and herbaceous plants with respect to stand structure. Furthermore, we evaluated the effect size of stand structure on understory vegetation diversity under different climatic zones. Our results showed that tree size variation (CV DBH) and stem density (SD) were the key drivers for understory woody plants, while the stand structure complexity index (SSCI) was more important for understory herbaceous diversity. Furthermore, the positive effects of stand structure differed across various climate zones and were enhanced with an increase in the climatic gradient. For instance, the impact of SD on understory woody plants, as well as the influence of the SSCI on the diversity of understory herbaceous vegetation, were both strengthened. These findings raise our awareness of the pressing need to manage stand structure heterogeneity differently across different climate zones, and different management also needs to be implemented among different understory plant types. It becomes evident that distinct forest management measures must be applied under future climate change and forest management practices in order to preserve biodiversity.

Effects of Stand Structure of Artificial Shelter Forest on Understory Herb Diversity in Desert-Oasis Ecotone

The relationship between the spatial structure of shelter forests and the diversity of understory herbaceous plants in desert–oasis ecotones is important for maintaining biodiversity indices and protecting the oasis ecosystem. In this paper, we explore the coupling relationship between tree layer structure (competition index, angle scale, neighborhood comparison, DBH, etc.) and understory herb diversity in the transition zone of shelter forest plots near oases and near deserts; in addition, we also aim to elucidate the dominant stand structure factors affecting herb biodiversity. The results indicated the following: A total of 13 herbaceous plant species were discovered in the transitional zone, with 11 species found near the oasis area and 4 species near the desert region. The Shannon, Simpson, and Pielou indices of understory herbaceous plants were significantly higher near the oasis area compared to the desert region. The Margalef index mean was higher in the oasis area compared to the desert region. Pearson and canonical correlation analyses revealed significant associations between specific stand structure indicators and diversity in the herbaceous layer. The results of the multiple linear regression analysis revealed that the competition index had a significant impact on the Shannon, Simpson, and Pielou diversity indices of the herbaceous layer in the understory of the shelterbelt forest near the oasis, with corresponding impact coefficients of 0.911, 0.936, and 0.831, respectively. The mingling degree was found to be the primary influencing factor for the Margalef index, with an impact coefficient of 0.825. However, in the understory of the shelterbelt forest near the desert, the neighborhood comparison ratio negatively affected the Shannon and Margalef indices, with impact coefficients of −0.634 and −0.736, respectively. Additionally, tree height negatively impacted the Simpson and Pielou indices, with impact coefficients of −0.645 and −0.677, respectively. In order to enhance the diversity of understory herbaceous species in the transitional zone and preserve the ecological system of the oasis, specific modifications to the forest structure and arrangement are essential. Pruning and thinning are necessary for shelterbelt forests located near desert regions, while shelterbelt forests near oases should use a suitable mix of tree species. These measures can help preserve or enhance the diversity of understory herbaceous plants.

Disparities in soil and water conservation functions among different forest types and implications for afforestation on the Loess Plateau

Afforestation is widely acknowledged as an effective approach for enhancing ecological conditions. Considering the challenging ecological environment on the Loess Plateau, prioritizing soil and water conservation functions in stands is crucial. The study aimed to ascertain the future development direction of forestry on the Loess Plateau by examining two representative forest types: planted forest (Robinia pseudoacacia pure forest and Pinus tabulaeformis pure forest), and natural secondary forest (a mixed forest of Quercus liaotungensis and Populus davidiana). The assessment centered on the soil and water conservation functions of the two forest types, encompassing the water conservation function (rainfall distribution and changes in multi-year soil moisture storage (0–200 cm)), soil conservation function (soil physicochemical properties), and understory plant diversity and stability. The results indicated that natural secondary forests outperformed planted forests in terms of water conservation function by effectively converting more precipitation into soil moisture, reducing runoff, and maintaining higher soil moisture storage. Additionally, natural secondary forests exhibited superior soil conservation functions compared to planted forests, characterized by higher soil porosity and nutrient properties. The variation in community structure between the shrub and herbaceous layers was more significant among different forests than within each forest (P < 0.05). Natural secondary forests exhibited higher understory shrub and herb biodiversity and interspecific repeatability compared to planted forests. Therefore, natural secondary forests are a more suitable forest type considering the natural conditions and silvicultural objectives of the Loess Plateau. To enhance the quality of afforestation, it is recommended to adopt near-natural planting patterns that replicate the environmental conditions of natural forests. For instance, actively creating mixed forests that emulate the tree species composition of natural forests and gradually reducing dependence on a single dominant tree species. Furthermore, the arborous and litter layers had a more direct and substantial influence on soil and water conservation functions compared to the shrub and herb layers. Foresters should prioritize regulating stand structure, such as increasing canopy variability, to enhance the water conservation function of stands. Additionally, they should actively protect the understory litter to fulfill its role in enhancing soil quality. This study provides a theoretical foundation and practical guidance for the implementation of vegetation restoration in ecologically vulnerable areas, such as the Loess Plateau.

Effects of nitrogen addition on species composition and diversity of early spring herbs in a Korean pine plantation.

Under the background of global nitrogen deposition, temperate forest ecosystems are suffering increasing threats, and species diversity is gradually decreasing. In this study, nitrogen addition experiments were conducted on Korean pine (Pinus koraiensis) plantations in Northeast China to explore the effect of long-term nitrogen addition on herb species diversity to test the following hypothesis: long-term nitrogen addition further reduced plant species diversity by affecting plant growth, which may be due to soil acidification caused by excessive nitrogen addition. Experimental nitrogen addition was conducted from 2014 to 2021, and the nitrogen treatment levels were as follows: N0 (control treatment, 0/(kg N ha-1 year-1)), N20 (low nitrogen treatment, 20/(kg N ha-1 year-1)), N40 (medium nitrogen treatment, 40/(kg N ha-1 year-1)) and N80 (high nitrogen treatment, 80/(kg N ha-1 year-1)). A herb community survey was conducted in the region from 2015 to 2021. The results showed that long-term nitrogen addition decreased soil pH, changed the species and composition of herbaceous plants, and decreased the species diversity of understory herbaceous plants. With the increase in nitrogen application years, middle- and high-nitrogen treatments significantly reduced the diversity of early-spring flowering herbs and early-spring foliating herbs, and their diversity decreased with the decrease in soil pH, indicating that soil acidification caused by long-term nitrogen addition may lead to the decrease of plant diversity. However, for early-spring growing herbs, adequate nitrogen addition may promote their growth. Our results show that plants have evolved different life-history strategies based on their adaptation mechanisms to the environment, and different life-history strategies have different responses to long-term nitrogen addition. However, for most plants, long-term nitrogen application will have a negative impact on the growth and diversity of herbs in temperate forests.

The Early Effect of Plant Density on Soil Physicochemical Attributes and Bacterial and Understory Plant Diversity in Phoebe zhennan Plantations

The effect of stand density on the soil bacterial community and diversity remains unclear. Spectrophotometry and full-length 16S rRNA sequences were used to determine the effects of planting density on soil physicochemical attributes and the diversity of soil bacterial and understory vegetation in a young Phoebe zhennan plantation at five densities. The findings showed that stand density had significant effects on the total nitrogen, ammonium nitrogen (NH4+-N), nitrate-nitrogen (NO3−-N), organic carbon, and the dominance and evenness of shrubs. Candidatus Udaeobacter and Candidatus Soilbacter were the two most common genera across the five stand densities. The density D5 (850 stems/hm2) demarcated from the others with a lower diversity of soil bacteria. Overall, the relatively low- and middle-density plantations were more conducive to complex and stable understory vegetation, bacterial communities, and soil nutrient cycles. The functional categories of the bacterial communities revealed a high proportion associated with chemoheterotrophy, aerobic chemoheterotrophy, and nitrogen fixation. Bacterial diversity and function were significantly influenced by soil pH, NH4+-N, NO3−-N, total phosphorus, and available phosphorus. However, there were no significant correlations between soil physicochemical attributes, understory vegetation, and bacterial diversity. Therefore, we speculated that the key drivers of the soil bacterial community were the soil physicochemical attributes and that stand density affected the soil bacterial community diversity by changing the soil physicochemical attributes. Overall, P. zhennan plantations with densities below 600 stems/hm2 were conducive to complex and stable soil bacterial communities and nutrient cycles.

Beyond shrub dieback: Understory plant diversity, soil water and soil carbon storage were improved in a semi-arid region

Shrub plantation is an effective approach for controlling soil erosion and land degradation. However, the extensive dieback on shrubs as a result of climatic changes or soil drought may impair shrub plantations’ ecosystem functions in arid and semi-arid regions. In this study, we sampled brown C. korshinskill plantations (shrub dieback > 90%), green plantations (shrub dieback was rarely < 10%) and an over-100 years’ natural grassland as the reference. The changes in plant biomass and diversity of understory vegetation, soil water storage (SWS) and carbon storage (SOCs) across of 0–10 m soil profile were analyzed. The results showed that, (i) the understory herbaceous biomass in brown plantations was 134.1 g m−2 and significantly higher by 49.5% than green plantations. The biomass and diversity of perennial forbs and annual/biennial grasses in brown plantations was also increased significantly; (ii) shrub dieback replenished soil water within 1–5 m depth. The SWS under brown plantations was significantly increased by 44.6% compared with green plantations, and reached 84.7% of that in natural grassland; (iii) the SOCs was notably higher in shrub plantations in the 0–10 m soil profile, increasing by 6.68% and 10.3% compared with natural grassland, respectively. SOC accumulation was mostly occurred at depths below 5 m under brown plantations. Overall, beyond shrub dieback, ecosystem functions of plantations were enhanced unexpectedly. The findings suggest that it was a blessing in shrub dieback disguise, understory herbaceous vegetation may maintain ecosystem functions of plantations in the semi-arid region alternatively.

Thinning promotes litter decomposition and nutrient release in poplar plantations via altering the microclimate and understory plant diversity

Thinning is widely employed in forest management to improve productivity, protect forest biodiversity and maintain ecosystem functions. Here a thinning experiment with four treatments (unthinned, CK; 30% tree removal from below, MB; 50% tree removal by interlaced thinning, HI; and 50% tree removal from below, HB ) was set up in the poplar plantation, while a followed decomposition experiment with four litter types was conducted under the poplar plantations of undergoing four thinning treatments using the litterbag technique. Thinning affected the microclimate, but only the heavy thinning (HI and HB) significantly enhanced photosynthetic photon flux density (PPFD) and soil moisture in the plantations during the growing season. Thinning promoted understory vegetation biomass and vegetation diversity via modifying the microclimate parameters. Pearson correlation analysis showed that PPFD and understory herbaceous biomass were significantly correlated to Shannon-Weiner diversity index. Both thinning intensity and litter type significantly affected the litter remaining mass over times. Overall, increasing thinning intensity and litter complexity enhanced decay rate, while reduced half live (t0.5) and t0.95 values. Correlation analysis showed that air relative humidity, soil temperature, air temperature and soil moisture significantly influenced the litter mass loss rates. Non-additive (synergistic) effects were observed when different litters were mixed, but the non-additive effect was most pronounced when more herbaceous species litter were mixed with poplar leaves and 50% thinning intensity was applied. Dynamics of nutrient release from different litter types were similar to those on the litter mass lose, depending on the litter quality and microclimatic conditions. Our results suggest that a thinning operation with 50% tree removal from below (HB) would maintain the structural and functional features of the poplar plantations at the similar sites.

Priority conservation area of Larix gmelinii under climate change: application of an ensemble modeling.

Larix gmelinii (Rupr.) Kuzen is a major tree species with high economic and ecological value in the Greater Khingan Mountains coniferous forest of Northeast China. Reconstructing the priority Conservation Area of Larix gmelinii under Climate could provide a scientific basis for its germplasm conservation and management. The present study used ensemble and Marxan model simulations to predict species distribution areas and delineate priority conservation areas for Larix gmelinii in relation to productivity characteristics, understory plant diversity characteristics, and climate change impacts. The study revealed that the Greater Khingan Mountains and the Xiaoxing'an Mountains, with an area of approximately 300 974.2 km2, were the most suitable for L. gmelinii. The stand productivity of L. gmelinii in the most suitable area was significantly higher than that in the less suitable and marginally suitable areas, but understory plant diversity was not dominant. The increase in temperature under future climate change scenarios will reduce the potential distribution and area under L. gmelinii; the species will migrate to higher latitudes of the Greater Khingan Mountains, while the degree of niche migration will gradually increase. Under the 2090s-SSP585 climate scenario, the most suitable area for L. gmelinii will completely disappear, and the climate model niche will be completely separated. Therefore, the protected area of L. gmelinii was demarcated with a target of the productivity characteristics, understory plant diversity characteristics and climate change sensitive area, and the current key protected area was 8.38 × 104 km2. Overall, the study's findings will lay a foundation for the protection and rational development and utilization of cold temperate coniferous forests dominated by L. gmelinii in the northern forested region of the Greater Khingan Mountains.

Responses of understory vascular plant communities up to 6 years after retention harvesting in planted Abies sachalinensis forests

Planted forests managed to supply timber are usually harvested by clearcutting but are also expected to contribute to biodiversity conservation. The retention forestry approach that retains important forest structures, such as trees and decayed logs at harvest, can be applied in planted forests to mitigate the negative impacts of clearcutting. Planted forests are disturbed by harvesting and postharvest silvicultural management activities, such as site preparation, planting, and weeding. The responses of understory vascular plant communities to various retention harvesting and postharvest silvicultural management were studied by comparing the composition of understory plant species before and after harvesting at the Retention Experiment for plantation FoREstry in Sorachi, Hokkaido, Japan (REFRESH). Dispersed and aggregated retention sites were established in planted Abies sachalinensis forests. In the dispersed retention sites, broad-leaved trees established in conifer plantations were retained. Clearcut and unharvested stands were used as controls and patch-cutting sites (one third of the area was clearcut by patches of 1-ha) were also established. Harvesting took place the year after the preharvest survey, and postharvest surveys were conducted in the first, third, and sixth years thereafter. The effects on species richness, the persistence of species occurrence in the preharvest survey, and the species composition of understory plants were then examined. Colonization by early seral species resulted in changes to the understory plant communities after harvesting and site preparation, irrespective of overstory tree retention. The species composition within aggregated retention patches was not altered, even though most overstory trees were blown down and are expected to provide a refuge for forest species. The presence of retained trees and steep slopes enhanced preharvest species persistence, which was presumed to be due to hampered soil disturbance. Harvesting and site preparation methods that avoid soil disturbance may help to maintain habitats for more understory plants in planted forests. The effects of weeding on the persistence of understory species differed from that of harvesting and site preparation. The trajectories for each site in the Non-metric multidimensional scaling ordination space were almost parallel from the preharvest to postharvest surveys, suggesting that the preharvest vegetation left a legacy. The direction of movement was reversed in the survey six years after harvesting. It is necessary to determine the resistance and resilience of understory plants within the management cycle (planting through harvesting) to establish management practices that maintain the diversity of understory plants in planted forests.

Understory plant diversity and phenolic allelochemicals across a range of Eucalyptus grandis plantation ages

Understory plant diversity and phenolic allelochemicals across a range of Eucalyptus grandis plantation ages

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.

Effects of canopy density on understory plant diversity in Robinia pseudoacacia plantations on the Loess Plateau of China

To solve the problems of understory plant shortage and biodiversity reduction caused by high tree density of Robinia pseudoacacia plantations on the Loess Plateau in northwest China, we analyzed the data collected by field survey and from literatures. We used the upper boundary line method to examine the impacts of canopy density on understory plant diversity. Based on field survey at the Guanshan Forest Farm of Jingchuan County of Gansu Pro-vince, the species number of understory plants in R. pseudoacacia plantations was higher than that in natural grassland (91 vs. 78). The dominant species varied with canopy density, which was completely different from that of natural grassland. A comprehensive analysis of both literature data and field survey data showed that, when mean annual precipitation (MAP) <550 mm or >550 mm, the increases in canopy density first led to a stable understory plant coverage and then a sharp or slight decrease, and understory plant biomass showed a sharp and continuous decrease or a slight increase and then decrease. Understory plant species richness and other diversity indices (Shannon, Simpson, and Pielou indices) first increase and then decrease, with bigger variation range under lower MAP. In all, the characteristics (coverage, biomass and species diversity, etc.) of understory plant community in R. pseudoacacia plantations were strongly affected by canopy density, with higher sensitivity under lower MAP. There was a general threshold range of canopy density of 0.45-0.6. When canopy density was above or below this thre-shold range, it would lead to a rapid decrease of the most characteristics of understory plant community. Therefore, keeping canopy density within the rational range of 0.45-0.6 in the management of R. pseudoacacia plantations is the key to make all the above-mentioned understory plant characteristics at relatively high level.

Dynamics and recovery of forest understory biodiversity over 17 years following varying levels of retention harvesting

Abstract Retention harvesting is advocated as an alternative to intensive timber harvesting, such as clear‐cutting, to better maintain or facilitate recovery of biodiversity and other ecological values in managed forests. However, it is not clear how long the benefits of retention harvests persist. We investigated responses of understory vascular plant cover, richness, diversity (inverse Simpson index) and composition to a gradient in dispersed retention (2% [clear‐ cut], 10%, 20%, 50% and 75% retention; unharvested reference [100% retention]) at 3, 6, 11, and 17 years after harvest, in four boreal mixedwood forest types (deciduous (broadleaf)‐dominated, deciduous‐dominated with conifer understory, mixed, and conifer‐dominated) in western Canada. Understory cover and richness tended to increase in the short‐term (3 years), peaked at 6–11 years with differences following the gradient of harvesting intensity, then plateaued or declined in the second decade (17 years), by which time there were minimal or no differences among harvesting levels, including the reference. Responses for diversity were minimal. In contrast, composition varied along the gradient of harvesting intensity and showed little recovery towards the unharvested condition over the 17‐year period. Generally, for plant community composition, clear‐cut and lower retention treatments (10%, 20%) were similar to one another but differed from the higher retention and unharvested reference treatments. Synthesis and applications: Retention harvests can moderate the negative impacts of harvesting and facilitate the recovery of biodiversity. Our results suggest that for the cover, richness and diversity of understory vascular plants, this moderating influence is weak and short‐lived. However, higher levels of retention can temper changes in understory composition relative to the unharvested forest, but full recovery is likely to be slow and will be complicated by post‐harvest regeneration dynamics.

Twenty Years of Urban Reforestation: Overstory Development Structures Understory Plant Communities in Lexington, KY, USA

Urban forests provide critical ecosystem services in an increasingly urbanized global landscape. The reforestation of undeveloped parcels and serially mowed grasslands can increase urban forest cover, but plant community development in planted urban forests is poorly understood. We conducted a study to elucidate the roles of time since tree planting, invasive species abundance, and other abiotic and biotic site-level factors in structuring understory plant communities within a 20-year chronosequence of planted urban forests in Lexington, KY, USA. We assessed the percent of groundcover of all understory species in fixed-radius plots on the site. Understory herbaceous plant communities demonstrated shifts from graminoid dominance to forb dominance over time, and plant communities in successively younger sites were increasingly dissimilar from that of the 20-year-old site. Invasive plant species were abundant, representing 21% of total groundcover across all surveyed plots, and became increasingly prevalent over time. Understory plant diversity was negatively associated with invasive species abundance. Overall, site factors, including time since planting, forest canopy closure, density of tree and shrub reproduction, and soil pH, accounted for much of the variability among understory communities. Understory plant communities across the chronosequence of planted sites demonstrated apparent structural shifts with overstory canopy development, but the increasing prevalence of invasive species and their negative impacts to plant diversity warrant future management to ensure the continuation of the desired successional trajectories.

Response of understory plant species richness and tree regeneration to thinning in Pinus tabuliformis plantations in northern China

BackgroundChinese pine (Pinus tabuliformis Carr.) is one of the major afforestation species in northern China and plays a key role in restoring forest ecosystems and preserving soil and water. However, most Chinese pine plantations are experiencing ecological problems such as the low diversity of understory plants and difficulty in natural regeneration. Thinning has been widely used to maintain and improve a variety of forest ecosystem services from plantations. To date, however, few studies have been conducted to systematically determine the effects of thinning on understory plant diversity and the regeneration of Chinese pine in plantations. MethodsWe conducted a literature search, and selected 22 publications covering a total of 83 treatments related to thinning effects on the species richness of understory plants and 15 publications covering a total of 43 treatments related to thinning effects on the regeneration of Chinese pine, in tree plantations of northern China. The data from the literature were synthesized and evaluated with meta-analysis approach to determine the treatment effects. ResultsCompared with the control stands, thinning increased the species richness of shrubs and herbs by an average of 25.3% and 26.5%, respectively. While the varying thinning intensities all had significantly positive effects on the species richness of understory plants, only moderate thinning (30%–50%) had a positive effect on the density of regenerating seedlings and saplings of Chinese pine (60.2%). The species richness of understory plants was greatest after 14 years of thinning with an increase of 36.3%, whereas the density of regenerating Chinese pine seedlings and saplings reached a maximum after ≥11 years of thinning with an increase of 76.5%, compared to that of the unthinned stands. Thinning in the half-mature plantations had the greatest effects on the understory shrub richness (44.1%) and the density of regenerating Chinese pine seedlings and saplings (86.5%). Both single and multiple thinning were found to significantly promote the species richness of understory plants and the density of regenerating Chinese pine seedlings and saplings, and the positive effects of thinning were greater in areas with a humidity index (HI) ​< ​30 than in areas with an HI ​≥ ​30. In general, age group, planting density and recovery time were prominent factors affecting the species richness of understory plants, whereas the slope, HI and recovery time were the dominant controls of the density of regenerating Chinese pine seedlings and saplings, indicating differential effects of thinning on the species richness of understory plants and the regeneration capacity of Chinese pine in plantations. ConclusionThinning appears to be a feasible management measure to improve the understory plant diversity and regeneration capacity of Chinese pine in plantations. We postulate that moderate thinning in half-mature forest stands with an HI ​< ​30 can help effectively promote the species diversity of understory plants and the natural regeneration of Chinese pine, thereby maintaining a more resilient stand structure and the development of Chinese pine plantations.

Mid-Rotation Impacts of Stand Tending with Glyphosate on Plant Diversity in the Boreal Forest of West-Central Alberta

Stand tending using glyphosate to promote coniferous overstory trees has been a common practice in the boreal forests of Alberta. However, there are concerns about the impact of this practice on biodiversity of understory species. This study examined the impact of broadcast glyphosate application during the active reforestation phase, two to several years post-harvest, on forest plant diversity 25 to 40 years post-harvest. Herbicide treatments had the desired effect of shifting tree layer dominance from deciduous to coniferous species, driven by a 25-fold reduction in the density of trembling aspen (3927 vs. 154 stems·ha−1, untreated and treated, respectively). However, understory plant diversity was not significantly different between treated and untreated sites as examined by the Shannon–Wiener (H) and evenness (E) indices. Shared plant species (beta) across sites was high. Of the seven site-indicator species examined, three had significantly lower cover on treated sites: Wild sarsaparilla, low bush-cranberry and oak fern. Total understory plant cover was significantly greater in the treated portion (98.0%) versus untreated (71.4%); however, this difference was not significant when bryophytes were excluded in the analysis. The establishment, maintenance and monitoring of larger long-term trials is strongly recommended.

The Coupling Relationship between Herb Communities and Soil in a Coal Mine Reclamation Area after Different Years of Restoration

In a complete organic ecosystem restoration in mining areas, soil and vegetation complement and influence each other. It is of great significance to evaluate the ecological restoration effect on and ecosystem stability of the mining area, with the coupling and coordinating relationship between herb community and soil physicochemical properties after land reclamation. Therefore, this study takes Juxinlong Coal Mine in Dongsheng District of Ordos City, Inner Mongolia Autonomous Region as the study area. The understory herbaceous plant community and soil factors with restoration time of 3 to 7 years were selected as the research objects. In addition, artificial grassland and natural restoration grassland were used as controls to investigate the species composition of herbaceous communities and soil physicochemical properties in different sites. The grey relational coupling model was adopted not only to study the relationship between herb community and soil factors but also to explore the coupling mechanism between herb community and soils’ physicochemical properties. The results included: (1) 51 herbaceous plants were investigated in the study area, among which Gramineae, Compositae, Leguminosae, and Chenopodiaceae were the primary ones, accounting for 70% of the total. (2) With the increase of restoration years, the diversity indices of understory herbaceous plants generally showed an increasing trend, but the diversity indices of understory herbaceous plants with different restoration years was smaller than that of artificial grassland. (3) The results of grey correlation analysis showed that the diversity of herbaceous plant community in the study area was closely related to soils’ available nitrogen and water content. (4) The degree of coupling and coordinating between the diversity of herbaceous plants and soils in the study area presented a trend of first increasing then decreasing during the accumulating restoration years. Among them, the degree of coupling between the diversity of understory herbaceous plants and soil system in the 5-year restoration’s sample plot (0.73) was found to be the highest, which was classified as medium coordination. The lowest coupling degree of herb diversity and soils was identified in the artificial grassland (0.51), which was light incoordination. Therefore, it is suggested that the control of water and nitrogen resources should be strengthened, the herbaceous vegetation should be reasonably selected, and the artificial tending should be carried out in the later stage of understory herbaceous vegetation construction in the study area to better promote the vegetation construction in the mining area.

Understory plant diversity and soil physicochemical properties of Pinus tabuliformis artificial water conservation forests in the upper reaches of Miyun Reservoir, China

We examined the characteristics of understory plant diversity and physicochemical properties and analyzed the correlation between understory plant diversity and soil factors across four Pinus tabuliformis artificial water conservation forests (P. tabuliformis × Larix gmelinii plantation, P. tabuliformis × Quercus mongolica plantation, P. tabuliformis × Armeniaca sibirica plantation, and P. tabuliformis plantation) in Fengning County, upstream of Miyun reservoir. The results showed that the composition and structure of understory community of the four forests were significantly different. The understory community in the P. tabuliformis × A. sibirica plantation was the richest in species composition, with Spiraea salicifolia, Ostryopsis davidiana, and Carex lanceolata as the main dominant species. In terms of species richness, Simpson index, Shannon diversity index, and Pielou index, plant diversity in the P. tabuliformis × A. sibirica plantation was the highest. Species diversity in the shrub layer and the herb layer was the highest in the P. tabuliformis × Q. mongolica plantation and the P. tabuliformis × Q. mongolica plantation, respectively. All physical and chemical indicators except total phosphorus differed significantly among the four forests. Soil physical and chemical properties of the P. tabuliformis × A. sibirica plantation were the best overall, and that in the P. tabuliformis × Q. mongolica plantation was the worst. Soil capillary porosity, pH, and organic matter were the main factors affecting species diversity in the shrub layer, while soil pH and capillary moisture capacity were the main factors affecting plant species diversity in the herb layer. The construction of P. tabuliformis × A. sibirica plantation was more conducive to increasing the diversity of understory plants and promoting soil improvement. Soil pH, organic matter, capillary porosity, and capillary moisture capacity were the dominant soil factors affecting the diversity of understory plants in the study area.

Forest gaps alter the soil bacterial community of weeping cypress plantations by modulating the understory plant diversity.

Weeping cypress is an endemic tree species that is widely planted in China, and the simple stand structure and fragile ecosystem of its plantation are common issues. Exploring the effect of different gap sizes on the soil bacterial community structure of weeping cypress plantations can provide a theoretical basis for the near-natural management of forest plantations. We, therefore, constructed three kinds of forest gaps with different sizes in weeping cypress plantations, namely, small (50–100 m2), medium (100–200 m2), and large gaps (400–667 m2), for identifying the key factors that affect soil bacterial communities following the construction of forest gaps. The results suggested that the herb layer was more sensitive than the shrub layer, while the Simpson, Shannon, and richness indices of the herb layer in plots with gaps were significantly higher than those of designated sampling plots without any gaps (CK). The presence of large gaps significantly increased the understory plant diversity and the Shannon and Simpson indices of the soil bacterial alpha diversity. There were obvious changes in the community composition of soil bacteria following the construction of forest gaps. The dominant bacterial phyla, orders, and functions were similar across the plots with different gap sizes. Of the indicator bacterial species, the abundance of the nitrogen-fixing bacteria, Lysobacter_ yangpyeongensis, and Ensifer_meliloti, was significantly different across plots with different gap sizes and accounted for a large proportion of the bacterial population of plots with medium and large gaps. The understory plant diversity was mostly related to the soil bacterial community than to other soil factors. The results of structural equation modeling indicated that the understory plant diversity was the most important environmental factor in driving the composition and diversity of bacterial communities. The construction of forest gaps significantly improved the understory plant diversity, physicochemical properties of the soil, and bacterial diversity in weeping cypress plantations, and the results of the comprehensive evaluation were in the order: large gaps > small gaps > medium gaps > CK. Our results suggested that large gaps are beneficial for the diversity of above-ground plant communities and underground soil bacterial communities.