Search Results (58)

Long-term monoculture of poplar plantations for industrial material production has been widely reported to cause severe soil degradation, while the presence of understory vegetation might enhance soil nitrogen (N) transformation and supply. This study employed a field experiment using a randomized block design with three blocks and four understory treatments, including understory removal, N-fixing species planting, single-species retention, and diverse vegetation retention, in poplar plantations on a mid-latitude alluvial plain in China over 6 years to assess the effects of different species and richness of understory on soil N transformation and related microbial traits via ¹⁵N assays and shotgun metagenomics. The results showed that understory removal significantly reduced soil N transformation rates, bacterial abundance, and gene abundance associated with N transformation. Compared to a single-species understory, retaining a diverse understory with high species richness significantly increased soil gross N transformation rate of mineralization by 149%, nitrification by 221%, and immobilization by 85%; comprehensively enriched dominant bacterial phyla; and elevated gene abundances of gdh_K15371, ureB, hao, and amoA_B associated with N transformation. No significant difference in N transformation rates existed between N-fixing species planting treatment and single-species retention treatment, while N-fixing species planting treatment specifically promoted the soil bacterial phyla Nitrospirae and Chloroflexi, and increased the gene abundances of gdh_K15371 and hao. These findings demonstrate that both introducing N-fixing species and an increase in species richness of the understory effectively promoted soil N transformation but that different underlying mechanisms existed. Planting N-fixing species selectively increased the soil bacterial phyla of Nitrospirae and Chloroflexi, whereas the increase in species richness broadly enriched soil bacterial diversity, thereby inducing the enrichment of the functional genes and enhancing soil N transformation. In conclusion, both planting N-fixing species and retaining diverse understory vegetation were effective strategies for maintaining sustainable management of poplar plantations by increasing soil N availability. Full article

Acid rain and understory vegetation removal are critical drivers altering soil ecosystem alterations. However, the mechanisms by which these factors influence soil moisture dynamics, nutrient availability, and microbially mediated enzyme activities remain insufficiently elucidated. This study investigated the impacts of simulated acid rain and understory vegetation removal on soil properties, enzyme activities, and microbial community in a subtropical Cinnamomum camphor (Linn) Presl plantation. The results indicated that acid rain and understory vegetation removal significantly decreased the soil organic carbon (SOC) while concurrently elevating the C-acquiring enzyme activities and microbial C limitation. Understory vegetation removal markedly reduced the soil moisture, nutrient availability, and N- and P-acquiring enzyme activities. Additionally, acid rain increased the bacterial diversity, but the understory vegetation removal increased the fungal diversity. Moreover, both acid rain and understory vegetation removal enhanced the bacterial community deterministic processes and destabilized the community by shifting generalists toward specialists, but had no significant effect on the fungal community structure. Partial least squares path modeling revealed that the bacterial stability loss intensified the C limitation, while the fungal stability regulated the P limitation. Collectively, the findings highlighted the critical role of understory vegetation in buffering the soil microclimate and nutrient cycling, and demonstrated that bacterial communities are more responsive to acid rain and understory vegetation removal than fungal communities. This study provides insights into the mechanisms by which anthropogenic disturbances alter soil ecological functions in subtropical plantations, emphasizing the need for integrated forest management strategies to conserve and manage soil ecosystems in subtropical plantations. Full article

The effect of timber cutting and related management on species composition and diversity in tropical forests has been reported in earlier studies, but the potentially different effects on understory and canopy tree species remains unclear. Our study aim was to assess the variation in species composition and diversity of understory and canopy species along a timber removal (“logging”) gradient. We assessed the species composition, alpha and beta diversity, and compared species composition of canopy trees in plots with different management histories in Budongo. Our findings revealed logging contributed 18.1% to the beta diversity of species composition as measured by distance-based redundancy analysis (dbRDA) and species composition decreased with logging intensity (R² = −0.415). Unlogged forest had higher species diversity for both understory and canopy tree species compared with logged forests. Species composition of logged/unlogged forests were significantly different from those of the forest succession types. Our study adds new information on the effect of logging on the species composition of understory and canopy trees in lowland tropical forests. We found logged forests do not recover species composition within seven decades, diversity within, and what previously distinct successional types were, have become, and remain, mixed in nature. Full article

Forest soils play a key role in the global carbon (C) pool and in mitigating climate change. The mechanisms by which understory and litter management affect soil organic C (SOC) concentrations are unclear in subtropical forests. We collected soils along a 60 cm profile in a Chinese fir (Cunninghamia lanceolata) plantation treated by only aboveground litter removal and understory vegetation preservation (Only-ALR), both aboveground litter and understory vegetation removal (ALR+UVR), and both aboveground litter and understory vegetation preservation (control) for 7 consecutive years. Five SOC fractions, physico-chemical properties, the biomass of microbial communities and the activities of C-acquiring enzymes were measured, and their correlations were analyzed for each of four soil layers (0–10, 10–20, 20–40 and 40–60 cm). Compared with control, Only-ALR decreased labile C pool I (LP-C I), labile C pool II (LP-C II) and dissolved organic C (DOC) in topsoil (0–20 cm) but had no effect on soil C fractions in subsoil (20–60 cm). A higher fungi and bacteria biomass in LP-C II and microbial biomass C (MBC) stock was observed in Only-ALR compared to ALR+UVR treatment. Soil pH and Gram-positive bacteria generally had impact on the variation of soil C fractions in topsoil and subsoil, respectively. Understory vegetation preservation offsets the declines of SOC and recalcitrant C but not the decreases in labile C caused by aboveground litter removal. Understory vegetation helps sustain SOC stock mainly via decreased C input and elevated soil pH which would change microbial biomass and activities when litter is removed. Our findings highlight the potential influence of long-term understory manipulation practices on C pool within a soil profile in subtropical plantation forests. Full article

Managing forest understory has a significant impact on soil greenhouse gas (GHG) emissions and the ecosystem’s capacity for carbon sequestration. However, its specific impacts and mechanisms within hickory (Carya cathayensis Sarg) forests remain unclear. The objective of this study was to examine the effects of different understory vegetation treatments on hickory stands with similar growth history, site conditions, and slopes: Cinnamomum chekiangense (Cinnamomum chekiangense Nakai) and strip-sown ryegrass (Lolium perenne L.) (CR1), Cinnamomum chekiangense and scattered ryegrass (CR2), Torreya grandis (Torreya grandis’ ‘Merrillii’ Hu) and strip-sown wild rapeseed (Brassica napus L.) (TW1), Torreya grandis and scattered wild rapeseed (TW2), and removal of understory vegetation (CK). Twenty experimental plots were established at the Lin’an Forestry Carbon Sink Pioneer Base, and after 12 months of monitoring, the responses of GHG emissions, vegetation, and soil organic carbon (SOC) sequestration were analyzed, revealing the differences in ecosystem carbon sequestration capacity. Compared to CK, CR1, CR2, TW1, and TW2 increased the global warming potential (GWP) by approximately 26%, 55%, 26%, and 16%, respectively. The SOC increased by approximately 76%, 102%, 51%, and 32%, respectively, while the vegetation carbon sink increased by approximately 30%, 27%, 53%, and 62%, respectively. In summary, ecosystem carbon sequestration increased by approximately 109%, 98%, 95%, and 92%, respectively. The findings indicate that managing understory vegetation in pecan forests significantly enhances ecosystem carbon sequestration but also increases soil GHG emissions. To enhance future research priorities, it is essential to focus on increasing carbon sequestration in hickory forests and managing soil GHG emissions through effective and rational understory vegetation management. Full article

Masson pine (Pinus massoniana Lamb.) is a tree species that is widely distributed throughout southern China and holds significant economic and ecological value. The main objective of our study was to assess the effects of thinning on aboveground biomass increments and tree diversity in both the overstory and understory. Additionally, the underlying factors and mechanisms responsible for driving changes in biomass increment were analyzed. Four different thinning treatments (control, light thinning, moderate thinning, and heavy thinning) were implemented in 214 plots (~1800 tree ha⁻¹) in three Masson pine forests in Hunan Province, China. A robustly designed experiment was used with over six years of repeated measurements. The differences in biomass increment and tree diversity among the different treatments were compared using repeated measures ANOVAs. The Mantel test was used to determine environmental metrics correlated with biomass increments across tree strata. Structural equation modeling was utilized to explore the multivariate relationships among site environment, tree diversity, and post-treatment biomass increment. The results indicated that thinning overall increased biomass increment, the Shannon index, and the Gini index, while decreasing the Dominance index over time. Moderate thinning (25%–35% of trees removed) was found to promote overstory biomass increment to 9.72 Mg·ha⁻¹·a⁻¹ and understory biomass increment to 1.43 Mg·ha⁻¹·a⁻¹ six years post-thinning, which is significantly higher than that of other treatments. Environmental metrics such as light intensity, soil organic matter, and other soil physiochemical properties were positively correlated with biomass increments, and their effects on the overstory and understory differed. Structural equation modeling revealed that thinning treatments, environmental metrics, tree diversity, and their interactions could be the main drivers for biomass increments across tree strata. Specifically, thinning treatments, light intensity, and tree size diversity (Gini index) had significant effects on overstory biomass increment, while understory species richness (Shannon index) and soil organic matter affected understory biomass increment. In conclusion, moderate thinning is an effective silvicultural treatment for stimulating biomass increments of both the overstory and understory in Masson pine forests in southern China if a middle period (e.g., six years) is considered. Some factors, such as species richness, tree size diversity, and environmental metrics (e.g., light and soil), are suggested for consideration to improve the efficiency of thinning. Full article

The management of understory vegetation and anthropogenic nitrogen (N) deposition has significantly resulted in a nutrient imbalance in forest ecosystems. However, the effects of canopy nitrogen addition and understory vegetation removal on N transformation processes (mineralization, nitrification, ammonification, and leaching) along with seasonal variations (spring, summer, autumn, and winter) remain unclear in subtropical forests. To fill this research gap, a field manipulation experiment was conducted with four treatments, including: (i) CK, control; (ii) CN, canopy nitrogen addition (25 kg N ha⁻¹ year⁻¹); (iii) UR, understory vegetation removal; and (iv) CN+UR, canopy nitrogen addition plus understory vegetation removal. The results revealed that CN increased net mineralization and nitrification by 294 mg N m⁻² month⁻¹ in the spring and 126 mg N m⁻² month⁻¹ in the winter, respectively. UR increased N mineralization and nitrification rates by 618 mg N m⁻² month⁻¹ in the summer. In addition, CN effectively reduced N leaching in the spring, winter, and autumn, while UR increased it in the spring and winter. UR increased annual nitrification rates by 93.4%, 90.3%, and 38.9% in the winter, spring, and summer, respectively. Additionally, both net N ammonification and annual nitrification rates responded positively to phosphorus availability during the autumn. Overall, UR potentially boosted nitrification rates in the summer and ammonification in the spring and winter, while CN reduced N leaching in the spring, winter, and autumn. Future research should integrate canopy nitrogen addition, understory vegetation removal, and phosphorus availability to address the global N deposition challenges in forest ecosystems. Full article

Forest management, especially understory vegetation conversion, significantly affects soil greenhouse gas (GHG) emissions and soil C and N pools. However, it remains unclear what effect renovating understory vegetation has on GHG emissions and soil C and N pools in plantations. This study investigates the impact of renovating understory vegetation on these factors in Chinese hickory (Carya cathayensis Sarg) plantation forests. Different understory renovation modes were used in a 12-month field experiment: a safflower camellia (SC) (Camellia chekiangoleosa Hu) planting density of 600 plants ha⁻¹ and wild rape (WR) (Brassica napus L.) strip sowing (UM1); SC 600 plants ha⁻¹ and WR scatter sowing (UM2); SC 1200 plants ha⁻¹ and WR strip sowing (UM3); SC 1200 plants ha⁻¹ and WR scatter sowing (UM4); and removal of the understory vegetation layer (CK). The results showed that understory vegetation modification significantly increased soil CO₂ and emission fluxes and decreased soil CH₄ uptake fluxes (p < 0.01). The understory vegetation transformation significantly improved soil labile carbon and labile nitrogen pools (p < 0.01). This study proposes that understory vegetation conversion can bolster soil carbon sinks, preserve soil fertility, and advance sustainable development of Chinese hickory plantation forests. Full article

(1) Background: Heterotrophs can affect plant biomass and alter species diversity–productivity relationships. However, these studies were conducted in systems with a low nitrogen (N) availability, and it is unclear how heterotroph removal affects the relationship between plant species diversity and productivity in different N habitats. (2) Methods: Three typical understory herbaceous plants were selected to assemble the plant species diversity (three plant species richness levels (1, 2, and 3) and seven plant species compositions), and the control, insecticide, fungicide, and all removal treatments were performed at each plant species diversity level in systems with or without N addition treatments. (3) Results: In systems without N addition, the insecticide treatment increased the plant aboveground biomass, total biomass, and leaf area, while the fungicide treatment reduced the plant belowground biomass, root length, and root tip number; the presence of Bidens pilosa increased the plant aboveground biomass. Similarly, the presence of Bletilla striata increased the plant belowground biomass and root diameter under each heterotroph removal treatment. In systems with N addition, all removal treatments reduced the plant belowground biomass and increased the plant leaf area; the presence of B. pilosa significantly increased the plant aboveground biomass, total biomass, and root length under each heterotroph removal treatment. The presence of B. striata significantly increased the plant belowground biomass and leaf area under insecticide and fungicide treatments. (4) Conclusions: Heterotroph removal alters the plant species diversity–biomass relationship by affecting the plant functional traits in systems with different N availabilities. The impact of biodiversity at different trophic levels on ecosystem functioning should be considered under the background of global change. Full article

The success of plant reproduction is highly dependent on effective seed dispersal. This study aimed to evaluate the potential seed dispersal effectiveness of cattle for Malus sieversii. The impact of cattle on the dispersal quantity and dispersal quality of M. sieversii seeds was explored based on camera trapping, GPS tracking, and germination trials. The results showed that, on average, cattle visited M. sieversii trees 477.33 times during a two-month observation period. Out of these visits, 315 were specifically for fruit removal. The fruit removal rate per cattle visit was as high as 96.67%. Additionally, cattle were able to disperse M. sieversii seeds up to a maximum distance of 533.67 m, with an average dispersal distance of 134.62 m. The average distance of cattle movement was recorded as 176.95 m/h, with peak activity observed during 11:00–13:00 and 19:00–21:00. The germination rate of M. sieversii seeds that passed through the digestive tract of cattle was significantly higher than that of control seeds. Finally, the emergence rate and survival rate of seeds dispersed by cattle to forest edges and gaps were significantly higher than those dispersed to understory. These findings suggest that cattle can serve as effective long-distance dispersers of M. sieversii seeds and may play a crucial role in the regeneration and expansion of M. sieversii populations in the Ili Botanical Garden. Full article

It is crucial to evaluate the effects of thinning on litterfall production, soil chemical properties, and fine root dynamics when implementing thinning as a silvilcultural technique to enhance tree growth and timber yield in Pinus koraiensis plantations. Thus, we determined the 10-year effects (2007–2017) of different thinning intensities on litterfall production, soil chemical properties, and fine root biomass and necromass within a P. koraiensis plantation in South Korea. The soil chemical parameters and fine root biomass and necromass were also compared across three soil depths (0–10, 10–20, and 20–30 cm). Three thinning treatments were employed: no thinning (CON), light thinning (32% removed, LT), and heavy thinning (64% removed, HT). Results revealed that litterfall was consistent across all thinning treatments, but broadleaf species had considerably higher litterfall production at HT stands than at CON/LT stands. Soil chemical properties, except exchangeable K⁺, were generally lower at LT stands, particularly at a depth of 20–30 cm soil. After ten years, there was a decrease in fine root biomass and necromass with increasing soil depth. Over 80% of fine roots were found in the upper layer (0–20 cm), while very fine roots (0–1 mm) consisted mainly of 47% pine and 53% other species and were concentrated in the 0–10 cm soil depth in HT. In conclusion, different thinning intensities had diverse effects on the parameters measured within the plantation. Future studies can explore how the effects of thinning intensities on litterfall production, soil chemistry, and fine root dynamics affect species diversity, carbon storage, and understory vegetation in P. koraiensis plantations. Full article

To understand the contribution of different sub-assemblages (sub-communities) in the shrub and herb layers to the distribution patterns of community species richness and the stability of the Pinus massoniana Lamb. community, this study was carried out by using 160 shrub quadrats (5 m × 5 m) and 200 herb quadrats (1 m × 1 m). These quadrats were selected from 40 plots on six islands. In this study, common and rare species were classified according to the frequency, and “new communities” (sub-communities) were formed by adding or removing species. Then the changes of species richness and community stability in the “new communities” were analyzed. A redundancy analysis was also used to explore the factors affecting the size of the species richness in the understory of the Pinus massoniana community. The results showed the following: (1) The distribution patterns of both shrub and herb layer species frequencies in this area were plainly to the right, indicating a large proportion of non-common species (common species accounting for 37.87% in the shrub layer and 16.67% in the herb layer). (2) The higher the frequency of species, the greater their contribution to the pattern of species richness. Common species had a high frequency and were the most important contributors to the patterns of species richness in plant communities (64 common species and 41 most common species in the shrub layer and 10 common species in the herb layer each accounted for 95.72, 88.9, and 90.52%, respectively, of the species richness distribution pattern). However, rare species also made significant contributions to the species richness in regions with hard conditions (the (most) rare species in the herb layer explained more than 70% of the species richness distribution pattern, and the remaining species after removing the (most) common species explained more than 90%). (3) In relatively stable communities, rare species had relatively little influence on the stability of the community, which was mostly governed by the dominant species (common species (10 species) were more stable than rare species (38 species), Exc.-rare species (22 species) were more stable than except-common species (50 species), and Exc.-rarest species (35 species) were more stable than Exc.-most common species (55 species) in the herb layer). In less stable communities, the stability of the community gradually increased with the increase in species richness, which may be associated with the growth habit of the increased species (the stability of the herb layer was higher than that of the shrub layer, as shown by the Euclidean distance). The community stability was determined by not only the dominant species in the community but also the rare species that were important contributors to the stability of the communities. (4) The species richness of the shrub layer was considerably influenced (p-value < 0.05) by the soil pH, soil organic matter, and wind speed, whereas the species richness of the herb layer was significantly influenced (p-value < 0.05) by the soil pH. The greater the pH and wind speed, the greater the species richness in the island community. On islands, the soil stability was maintained in large part by the soil organic matter. The lack of soil organic matter can affect soil nutrients, destroy island habitats, and reduce species richness, all of which are harmful to the community stabilization. Full article

Increased demand for sustainable timber products has resulted in large investments in agroforestry in Australia, with plantations growing various Pinus species, selected to suit a plantation’s environment. Juvenile Pinus species have a low fire tolerance. With Australia’s history of wildfires and the likelihood of climate change exacerbating that risk, the potential for a total loss of invested capital is high unless cost-effective targeted risk minimisation is part of forest management plans. Based on the belief that the understory profiles within the juvenile plantations are a major factor determining fuel hazard risks, an accurate assessment of these profiles is required to effectively mitigate those risks. At present, assessment protocols are largely reliant on ground-based observations, which are labour-intensive, time consuming, and expensive. This research project investigates the effectiveness of using geospatial analysis of drone-derived photographic data collected in the commercial pine plantations of south-eastern Queensland as a cost-saving alternative to current fuel hazard risk assessment practices. Understory composition was determined using the supervised classification of orthomosaic images together with derivations of canopy height models (CHMs). The CHMs were subjected to marker-controlled watershed segmentation (MCWS) analysis, isolating and removing the plantation pine trees, enabling the quantification of understory fuel profiles. The method used proved highly applicable to immature forest environments with minimal canopy closure, but became less reliable for close canopied older plantations. Full article

Central European coniferous forests are facing the most significant bark beetle outbreak in history. The consequence is the creation of large clearings, which are associated with changes in environmental parameters. We studied how these changes affected the survival of wood ant nests. Specifically, we monitored the relationship between mound occurrence, tree coverage, and the coverage and height of vegetation on ant mounds. We found that wood ant nests were less likely to survive (39% decline) in bark beetle-affected forests than in unaffected forests. The Formica rufa species was more affected than F. polyctena. The bark beetle attack was significantly positively correlated with increases in understory vegetation cover and height. Several factors may explain the negative effects of bark beetles on wood ants. The removal of trees subsequently increased the amount of light on ground vegetation. The support of understory vegetation growth on ant mounds cast shadows on the nests and disrupted nest thermoregulation. Additionally, the bark beetle attack may have been associated with a loss of food resources for wood ants. Our results showed that early (small-scale) management intervention against the spread of bark beetles is the preferred method for maintaining the ant population in conifer forests prone to bark beetle attacks. Full article

Bryophytes play an important role in biogeochemical cycles and functions in forest ecosystems. Global climate changes have led to the population decline of bryophytes; however, the effects of bryophyte loss on the soil organic carbon stock and microbial dynamic remain poorly understood. Here, bryophytes were artificially removed to simulate the loss of bryophytes in two forests in Southwest China, i.e., evergreen broad-leaved forest and temperate coniferous forest. Soil physicochemical properties, microorganisms, and soil organic carbon stocks were analyzed and factors regulating soil organic carbon stocks were explored. Results showed that bryophyte removal significantly decreased soil organic carbon in the coniferous forest but had a negligible effect on the evergreen broad-leaved forest. Bryophyte removal had an insignificant effect on soil properties and microbial PLFAs except that soil nitrogen significantly increased in the 0–10 cm layer in the evergreen broad-leaved forest, while soil temperature and bulk density increased in the coniferous forest in the 0–10 and 10–20 soil layers, respectively. Soil organic carbon stocks increased by 14.06% in the evergreen forest and decreased by 14.39% in the coniferous forest. In the evergreen forest, most soil properties and microorganisms contributed to the change of soil organic carbon stocks, however, only soil organic carbon and depth had significant effects in the coniferous forest. Our findings suggest that soil physiochemical properties and microorganisms regulated the different responses of soil organic carbon stocks after bryophyte removal in the two forests. More research is needed to better understand the effects of understory plants on soil organic carbon stocks in various forest ecosystems. Full article