Understory Vegetation Removal Research Articles

Effects of Canopy Nitrogen Addition and Understory Vegetation Removal on Nitrogen Transformations in a Subtropical Forest

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.

Understory vegetation removal significantly affected soil biogeochemical properties in forest ecosystems

Understory vegetation plays a crucial role in mediating the natural development of forest ecosystems. The removal of understory vegetation, as a common forest management practice, may have a significant impact on soil properties. However, a global perspective on how understory removal might affect soil biogeochemical properties is still lacking. To fill this knowledge gap, we performed a meta-analysis with 2059 observations collected from 71 peer reviewed publications to evaluate the effects of understory vegetation removal on soil carbon (C), nitrogen (N), phosphorus (P), potassium (K), and microbial biomass. We found that (1) removal of the understory significantly increased soil nitrates (NO3−) concentration by 6.5 %, but decreased the stocks of C and N, the concentrations of N, available K (AK) and microbial biomass C (MBC), and fine root biomass by 19.4, 15.1, 7.9, 19.9, 13.5 and 32.2%, respectively; (2) mycorrhizal association significantly mediated understory removal effects on soil organic C (SOC) and dissolved organic C (DOC) concentrations, and soil pH, while canopy type had a significant impact on the effects of understory removal on soil K, AK, NO3−, MBC concentrations, C:N ratio, and soil pH; (3) soil depth had a negative impact on the effects of understory removal on SOC, AK, ammonium nitrogen (NH4+) concentrations, and soil moisture; and (4) mycorrhizal association, soil depth, slope, forest stand age, elevation, and MAT were the most important moderator variables. Our results suggest that the removal of understory vegetation generally have negative effects on soil biogeochemical properties, and that managing understory vegetation is important for promoting the healthy development of forest ecosystems.

Changes in seedlings’ composition and abundance following soil scarification and amendments in a northern hardwood forest

A combination of global changes (e.g., soil acidification, invasive species, forest management, climate) impacts the regeneration dynamics of sugar maple-dominated stands in northeastern North America. More specifically, there are concerns about the regeneration of sugar maple and other high-value species due to the expansion of American beech and its bark disease, killing mature trees, compromising fiber supply and other ecosystem services. Here, we set up a field trial to study the effect of soil scarification, amendments (nitrogen fertilization, liming, and wood ash), and their interactions, on tree species establishment following understory vegetation removal in a beech-invaded sugar maple stand to promote the establishment of high-value species (i.e. sugar maple and yellow birch), to control beech regeneration, and help reduce the impacts of beech bark disease on stand development. After four years of monitoring, we found that maple-beech stands with well-drained soils were promising sites for the success of sugar maple and yellow birch establishment. Soil scarification had a limited effect on sugar maple and beech establishment while it enhanced that of yellow birch, pin cherry and red maple. The combination of soil scarification and amendments was more effective in promoting the recovery of yellow birch and pin cherry and controlling the recovery of beech and red maple than their separated effects. Lime amendment promoted sugar maple establishment without favouring competitors such as yellow birch, pin cherry and red maple, and limited beech establishment. Overall, our results suggest that combining soil scarification and amendments on targeted site types could help fine-tune tree establishment conditions in northern hardwood forests.

Altered energy dynamics of multitrophic groups modify the patterns of soil CO2 emissions in planted forest

Soil microbes and fauna as key components of belowground food webs play important roles in energy flux and carbon cycling in terrestrial ecosystems. However, it remains unclear whether forestry management regimes alter the energetic structure of soil food webs and thereby reshape the patterns of soil CO2 emissions in planted forest. Here, we tested the effects of legume (Cassia alata) addition, understory removal, understory removal with legume addition and all plants removal on energy fluxes through soil food webs and soil CO2 flux in the wet and dry seasons. We show that soil heterotrophic respiration contributed 36.9–57.8% of total CO2 flux in the soil. In the dry season, C. alata addition increased soil heterotrophic respiration by 24.6% and 57.3%, respectively, when compared with the control and understory removal treatment. Compared with the understory removal treatment, the total energy flux across the whole food web increased with legume addition (i.e., C. alata addition and understory removal with C. alata addition). Legume addition supported a high proportion of energy flux through herbivorous nematodes, whereas understory vegetation removal supported a high proportion of energy flux through microbivorous nematodes. Less energy fluxes were transferred from basal resources to fungivorous mites and collembolans compared with microbivorous and herbivorous nematodes. The total soil CO2 flux was positively correlated with metabolic rates of herbivorous and omnivorous-predatory nematodes, and energy fluxes through multitrophic groups. Taken together, legume addition and understory vegetation removal modify the patterns of soil CO2 emissions via changing nematode metabolic rates and re-shaping the energetic structure of soil food webs.

The removal of understory vegetation can rapidly alter the soil microbial community structure without altering the community assembly in a primary tropical forest

There is little known about how understory vegetation affects the soil microbial community assembly, although it exerts strong controls on the soil microbial community composition. We attempted to clarify this question by establishing an experiment in which the understory vegetation was either removed or maintained as controls in a primary tropical forest in south China. The results showed that removing the understory markedly altered the structure of fungal rather than bacterial communities. The bacterial assembly in control sites was dominated by drift (stochasticity), whereas the fungal assembly was governed more by heterogeneous selection (determinism). Removal of the understory had minor effects on the community assembly of bacteria and fungi. These results indicate that the absence ofunderstoryvegetation in tropical forests can quickly alter the fungal community structure without influencing the community assembly.

Aboveground litter input alters the effects of understory vegetation removal on soil microbial communities and enzyme activities along a 60-cm profile in a subtropical plantation forest

Changes in litter input and understory vegetation due to climate change and human activities affect belowground processes in plantation forests. However, it is unclear whether and how aboveground litter interacts with understory vegetation for their effects on soil microbial communities and functions, especially in deep soils. A field manipulation experiment was conducted, including four treatments of understory vegetation removal plus aboveground litter removal (UVR + ALR), understory vegetation preservation plus aboveground litter addition (UVP + ALA), UVR + ALA, and UVP + ALR in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. After seven years of continuous treatment, the soil samples along a 60-cm profile were used to evaluate microbial community compositions, major microbial enzyme activities, and several physicochemical properties in the four treatments. UVR resulted in significant negative effects on microbial biomass and enzyme activities at different soil layers with or without litter input, but it did not change the soil microbial communities such as F/B, G+/G−. Compared with ALR, ALA amplified the negative understory vegetation removal effects (UVREs) on β-D-cellobioside (CB), β-N-acetylglucosaminidase (NAG), and leucine aminopeptidase (LAP) activities, but did not affect UVREs on total soil PLFAs. Lesser negative UVREs on β-1,4-glucosidase (BG), LAP, and acid phosphatase (AP) activities were observed in top soils compared to deep soils in the ALR treatment. UVREs on soil microbial biomass were not significantly different among soil depths. These results indicate that aboveground litter and soil depth altered UVREs on soil physicochemical properties, primarily through soil microbial biomass and enzyme activities. UVREs were generally more sensitive to major enzyme activities than microbial biomass and were interactively influenced by aboveground litter and soil depth due to synergistic effects within soil ecosystems. This study highlights the integrated feedbacks of microbial structures and functions along soil profiles in response to litter and vegetation interactions in subtropical forests.

The Effects of Shrub Removal on Soil Microbial Communities in Primary Forest, Secondary Forest and Plantation Forest on Changbai Mountain.

Shrub removal is a common management method in forest ecosystems, but comparatively little is known regarding the effects of shrub removal on soil microbial communities among primary forest, secondary forest, and plantation forests in temperate forests, which limits our accurate assessment of sustainable management of understory vegetation removal. Given this, we used a long-term operation experiment across a contrasting mixed broadleaved-Pinus koraiensis forest, Betula platyphylla forest, and Larix gmelinii plantation forest to explore the variations of soil properties and microbial community after 5years of shrub removal on Changbai Mountain, as well as the contribution of the soil properties and understory plant diversity to the soil microbial community. The results demonstrated that shrub removal could significantly alter soil SWC and TN, TP, and AP contents of the L. gmelinii, as well as N/P of B. platyphylla. Moreover, shrub removal also clearly improved soil bacterial Pielou_e index and Simpson index of mixed broadleaved-P. koraiensis and soil bacterial Simpson index of L. gmelinii, and decreased soil fungal Pielou_eindex and Shannon index of L. gmelinii and soil bacterial Pielou_e index and soil fungal Shannon index of B. platyphylla. Identically, shrub removal notably altered the soil bacterial community composition. Soil characteristics and understory plant diversity accounted for 48.02% and 26.88%, and 45.88% and 27.57% of the variance in the bacterial and fungal community composition, respectively. This study aimed to provide an important scientific basis for the restoration and sustainable management of temperate forests in the Changbai Mountain region.

A Novel Method Based on Kernel Density for Estimating Crown Base Height Using UAV-Borne LiDAR Data

As an essential parameter in forestry, crown base height (CBH) faces many tasks. The methods are still developing for estimating it. Unmanned aerial vehicles (UAVs) light detection and ranging (LiDAR) supplies new, massive, and high-density data for estimating CBH. Many methods had been generated to compute CBH indirectly using regression-based ways or directly using geometric/statistical LiDAR-based ways. However, there were few methods to deal with the problem of understory, trunk, and noise points caused by high-density UAV data. A robust method was first proposed in this study to directly estimate CBH from LiDAR data, which contained two significant skills: 1) understory vegetation removal for each tree using a polynomial curve and 2) computing CBH by kernel densification of the elevation frequency histogram of LiDAR data. It could tolerate the understory and trunk points better through kernel convolution. The method proposed in this study and a previous simple model were applied in a crabapple plot in the Huailai Remote Sensing Comprehensive Experimental Station, Hebei, China, and verified by field-measured data. It was inspiring that our method is slightly better, and the mean CBH of LiDAR-derived trees was only 1.60 cm higher than that of field-measured trees. The mean absolute error (MAE) of CBH was 4.91 cm, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{2}$ </tex-math></inline-formula> was 0.73, the root-mean-squared error (RMSE) was 8.29 cm, and the bias was 2.68% for these trees. Generally, this method showed strong usability for high-density UAV LiDAR data and high precision for measuring CBH of low trees.

Forest disturbance and arthropods: small‐scale canopy and understory disturbances alter movement of mobile arthropods

AbstractDispersal of ground‐dwelling arthropods is understudied in forest ecosystems, which hinders understanding of effects of disturbances on population dynamics. The objective of the study was to quantify movement of ground‐dwelling arthropods in response to a factorial combination of canopy gap formation via girdling and understory vegetation removal, which was shown in a companion study to alter arthropod abundance and species richness. Arthropod movement was quantified using a self‐mark–capture technique where arthropods were marked as they crossed three concentric bands of different colored fluorescent powders located 3, 8, and 15 m from the center of 30 × 30 m experimental quadrats. The number of colors found on an individual was considered representative of dispersal such that the more colors detected, the more an individual moved. The likelihood that arthropods were marked with fluorescent powder and the number of colors detected differed among taxonomic groups. Most taxa were marked with one color and a high proportion of those individuals were collected adjacent to the band in which they were marked, suggesting limited dispersal. Canopy gaps and understory vegetation removal influenced movement of three taxa of highly mobile arthropods: Parajulidae and Paradoxosomatidae (detritivores), and Opiliones (scavengers). Opiliones were less likely to be marked with fluorescent powder in canopy gaps than under closed canopy in July, but more likely to be marked in August. Paradoxosomatidae were less likely to be marked in canopy gaps than under closed canopy in August, but their movement was unaffected in July. Parajulidae were more likely to be marked with fluorescent powders when understory vegetation was removed in July and August. Limited dispersal of most other ground‐dwelling arthropods suggests that these more sessile taxa may experience decreased survival and reproduction if they are unable to cope with environmental change in response to natural and anthropogenic disturbances. Understanding how disturbances mediate arthropod movement can inform biodiversity conservation strategies and sustainable forest management.

Diverse Understory Vegetation Alleviates Nitrogen Competition with Crop Trees in Poplar Plantations

Understory vegetation plays a crucial role in nutrient turnover and cycling in plantations, but it also competes for nutrients with crop trees when only a single species is present due to its specific nutrient requirements. However, it remains unclear whether this competition can be alleviated when the species richness of understory vegetation increases. In this study, we tested different gradients of understory vegetation species richness, including understory vegetation removal (UR), the retention of a single main understory vegetation species (RS), and the retention of natural diverse understory vegetation (RD) as part of a poplar (Populus deltoides ‘Nanlin-3804′) plantation, to study their effects on poplar growth, and to evaluate nitrogen (N) usage and how this was affected by the interactions between the poplar and understory vegetation. The results showed a generally lower periodic growth, and a significant decline in the foliar chlorophyll content and glutamine synthetase activity of poplar under treatment with RS and RD compared to those under UR treatment conducted in July 2019, which clearly indicated N competition between the understory vegetation and poplar trees. However, no significant difference was detected in the foliar chlorophyll content and glutamine synthetase activity of poplar under RD and RS treatment; only the nitrate reductase activity in poplar leaves under RD treatment declined significantly, by 22.25%, in June 2019. On the contrary, the diameter at breast height (DBH) of the poplar under RD treatment showed an increase of 34.69% from July to August 2019, compared with that under RS treatment. Furthermore, the increase in the species richness of understory vegetation resulted in an increase in the δ15N values in the poplar leaves, which was strongly regulated by the NH4+-N pool in the 10–20 cm soil layer, indicating the effective coordination of N utilization between poplar and understory vegetation when diversified understory plant species were present. These findings demonstrate the essential role of understory vegetation species diversity in alleviating N competition with crop trees, and provide guidance for understory vegetation management in poplar plantations.

林下植被和凋落物对寒温带森林生长季土壤CH4通量的影响

为进一步探究林下植被和凋落物管理对我国寒温带森林生长季土壤CH₄通量的影响，采用静态箱-气相色谱法对大兴安岭北部4种林型（白桦林、山杨林、樟子松林和兴安落叶松林）4种处理（自然状态、去除凋落物、去除林下植被以及去除林下植被和凋落物）的土壤CH₄通量排放特征进行观测研究。结果表明：该地区森林生长季土壤均表现为CH₄的汇，4种林型不同处理后土壤CH₄通量表现为单峰变化趋势，吸收峰值出现在7月或8月。自然状态4种林型土壤CH₄平均吸收通量表现为白桦林（-79.23±14.92）μg m^-2 h^-1>山杨林（-64.27±9.60）μg m^-2 h^-1>樟子松林（-62.54±15.48）μg m^-2 h^-1>兴安落叶松林（-48.73±12.26）μg m^-2 h^-1，兴安落叶松土壤CH₄平均吸收通量显著小于其他三种林型（P<0.05）。相比于自然状态，4种林型在去除凋落物后土壤CH₄吸收通量提高了2.12%-12.15%，但变化幅度均没有达到显著水平（P>0.05）。去除林下植被后4种林型CH₄吸收通量提高了0.84%-20.55%，且只有山杨林吸收增加达到显著水平（P<0.05）。同时去除林下植被和凋落物后，对白桦林和樟子松土壤CH₄通量影响不显著（P>0.05），但对山杨林和兴安落叶松林影响显著（P<0.05）。总之，去除凋落物或林下植被均会提高土壤对CH₄吸收，去除林下植被对土壤CH₄通量的影响要大于去除凋落物的影响，但不同林型不同处理之间还存在差异。;In order to explore the impacts of understory vegetation and litter management on soil CH₄ flux of cold temperate zone forest during the growth season, the characteristics of soil CH₄ flux emission under different treatments were analyzed and studied, which provides a scientific basis and theoretical reference for the management of the forest ecosystem in the Greater Xing'an Mountains in China. The static chamber-gas chromatography was used to analyze the characteristics of soil CH₄ flux emission in four forest types (Betula platyphylla forest, Populus davidiana forest, Pinus sylvestris var. mongolica forest, and Larix gmelini forest) with 4 kinds of treatments (natural state, removal of litter, removal of understory vegetation, and removal of understory vegetation and litter). The results showed that the soil of the four forest types all appeared as CH₄ sinks in this area during growth season. The soil methane showed a single-peak change trend in the four forest types with different treatments, and the absorption peak appeared in July and August. In the natural state, the average soil CH₄ absorption flux of the four forest types showed the trend of Betula platyphylla forest (-79.23±14.92) μg m^-2 h^-1> Populus davidiana forest (-64.27±9.60) μg m^-2 h^-1> Pinus sylvestris var. mongolica forest (-62.54±15.48) μg m^-2 h^-1> Larix gmelini forest (-48.73±12.26) μg m^-2 h^-1. The average absorption flux of soil CH₄ in Larix gmelini forest was significantly smaller than the other three forest types (P<0.05). Compared with the natural state, the soil CH₄ absorption flux increased by 2.12%-12.15% after the removal of litter in the four forest types, but the change range did not reach a significant level (P>0.05). After removing the understory vegetation, the CH₄ absorption flux of the four forest types increased by 0.84%-20.55%, of which only the Populus davidiana forest showed a significant (P<0.05) increase in the soil CH₄ absorption flux. The removal of understory vegetation and litter had no significant effects on the soil CH₄ flux of Betula platyphylla forest and Pinus sylvestris var. mongolica forest (P>0.05), but had significant effects on Populus davidiana forest and Larix gmelini forest (P<0.05). In short, the removal of litter and understory vegetation both increased the soil's absorption of CH₄. The removal of understory vegetation had a greater impact on soil CH₄ flux than the removal of litter, but there were still differences between different forest types and different treatments. Therefore, a scientific and reasonable forest management method is the prerequisite for regulating the absorption of CH₄ by forest soil in this area and the ecological environment protection.

杨树人工林幼林阶段林下植被管理对土壤微生物生物量碳、氮酶活性的影响

为了探讨林下植物物种多样性对杨树（Populus spp.）人工幼林阶段土壤微生物区系的影响，在林下设计了林下植被物种数量递增的3种处理，即清除林下植被（无林下植物）、保留单一林下植物（一种林下植物）和保留物种多样的自然林下植被（多种林下植物），于处理1年后采样分析土壤微生物生物量碳（MBC）和氮（MBN）含量、基于Biolog-ECO微平板的土壤微生物群落代谢特征以及与土壤碳、氮转化相关的胞外酶活性的差异，以期从土壤养分转化和供应的角度为科学管理人工林林下植被提供依据。结果表明，林下植被处理对8月份0-5 cm土层的土壤MBC、MBN含量以及酶活性有较大影响。与清除林下植被处理相比，保留单一林下植物处理8月份0-5 cm土层的土壤MBC、MBN含量以及β-葡萄糖苷酶、多酚氧化酶和芳基酰胺酶活性显著增加，增幅分别为27.91%、54.48%、14.74%、32.53%和6.20%，而保留物种丰富度高的自然林下植被处理林地土壤的上述指标进一步分别增加了4.88%、14.93%、9.22%、13.63%和12.86%。此外，林下植被处理还改变了土壤微生物群落代谢特征，8月份0-5 cm土层的土壤微生物Shannon指数随着林下植被物种数量的增加而显著增大。清除林下植被处理的土壤微生物主要利用的碳源包括部分糖类、氨基酸类和酯类，与清除林下植被处理相比，保留单一林下植物处理的土壤微生物提高了对上述几种碳源的利用能力，同时对糖类、氨基酸类、酯类和有机酸类碳源的利用种类范围明显扩大，而保留物种多样的自然林下植被的土壤微生物对31种碳源基本上可以全面有效利用。因此，保留林下植被，特别是提高林下植被的物种丰富度，有利于增加土壤微生物生物量，提高土壤微生物的代谢功能和分解活性，可以在一定程度上加快土壤的物质转化和养分循环功能。;Understory vegetation plays crucial roles on nutrient turnover and cycling in plantation soil by regulating soil microbial biomass and extracellular enzyme activity. Under normal condition, the understory vegetation generally contains diverse plant species in plantations. Whether increasing the species abundance of understory vegetation can change the effect of understory vegetation is still inconclusive. In this study, a diversity gradient of understory vegetation species was setup to study its effects on soil microbial biomass carbon (MBC) and nitrogen (MBN), soil microbial communities' metabolic profiles, and enzyme activities that related to soil C and N turnover in a popular plantation. Three understory treatments were designed including the understory vegetation removal, the retention of single main understory vegetation species, and the retention of natural diverse understory vegetation. The soils were sampled in June, August and October after one year treatment for the analysis of corresponding soil microbial properties. The results showed that the understory vegetation treatments had strong effects on 0-5 cm soil layer in August. Compared with understory vegetation removal, the retention of single main understory species resulted in significant increases in soil MBC and MBN contents and the activities of soil β-glucosidase, polyphenol oxidase and arylamidase by 27.91%, 54.48%, 14.74%, 32.53%, and 6.20%, respectively, in the 0-5 cm soil layer in August; moreover, the retention of natural understory vegetation showed further increases by 4.88%, 14.93%, 9.22%, 13.63%, and 12.86%, respectively, when compared with the retention of single main understory species. Understory vegetation treatments also changed soil microbial communities' metabolic profiles, soil microbial Shannon index of the 0-5 cm soil layer in August increased significantly with the increase in understory vegetation species. The main carbon sources utilized by soil microorganism with understory removal treatment were a few kinds of carbohydrates, amino acids and esters. By contrast, soil microorganisms under the retention of single main understory species treatment improved the utilization capacity of the above-mentioned carbon sources, and expanded the available carbon sources to some organic acids. At the same time, the retention of natural diverse understory vegetation enabled soil microorganisms to effectively utilize all of the 31 carbon source types. Therefore, the retention of understory vegetation, especially with high diversity, was beneficial to increase soil microbial biomass, improve soil microbial metabolism and activities, and to a certain extent accelerate the decomposition of soil organic matter and nutrient cycling.

Leaf litter lignin degradation in response to understory vegetation removal in a Masson pine plantation

AbstractUnderstory vegetation changes, caused by forestry management, can alter the litter species composition and microclimate in situ, which while profoundly influence litter lignin degradation processes, is seldom investigated. To reveal the effects of these changes, understory vegetation in plots was treated as follows: no understory vegetation removal; only shrub removal; only herb removal; and, both shrub and herb removal. Single‐ and mixed‐species litterbags (1.0 mm mesh with uncut leaf litter) matching the treated vegetation characteristics (complied with a 7:2:1 air‐dried mass ratio for the litter form trees, shrubs, and herbs) were placed on the floor. After 2 years, 5.9% (single‐tree litter in the plots with shrub removal) to 41.4% (mixture in the plots with no understory vegetation removal) of the initial lignin content was degraded among litterbag types and plot treatments. Incidence of nonadditive effects was reduced, and the nonadditive lignin degradation rate varied but remained low among plot treatments when understory vegetation was removed. In all plot treatments, lignin degradation rate was higher in single‐shrub or single‐herb litter than in single‐tree litter (at least 9.7% ± 1.2% for the deviation). Mixtures in the plots, with no understory vegetation removal, exhibited a greater lignin degradation rate than that of the litter mixtures in the other plots. Path analysis indicated that microbial biomass nitrogen, average temperature, and lignin concentration were positively correlated with lignin degradation rate. Therefore, in addition to the litter species composition, alterations in microclimate as a result of understory vegetation changes can be a key factor that influence lignin degradation rate.

Understory vegetation removal reduces the incidence of non-additive mass loss during leaf litter decomposition in a subtropical Pinus massoniana plantation

Improvement cutting or harvesting can change the coverage of understory vegetation, which can significantly influence the litter decomposition process in plantations. However, difference in potential non-additive mass loss in response to understory vegetation changes is poorly studied. A field litterbag experiment involving various litter types and treatments with no understory vegetation removal, shrub removal, herb removal and whole-understory vegetation removal was conducted to examine non-additive mass loss. During approximately 2 years of decomposition, the decomposition rate of shrub and herb components was accelerated in the mixed litter with full understory vegetation. There was significant non-additive mass loss during decomposition in the plots with trees, shrubs and herbs, while the incidence of non-additive mass loss was lower in the plots with understory vegetation removal. Statistical analysis revealed a significant difference between the expected mass loss calculated with the data from the corresponding decomposition plots and that calculated with the data from the plots with whole-understory vegetation removal. Our results show that understory vegetation removal can inhibit litter decomposition in Masson pine plantation ecosystems in subtropical China. We highlight that non-additive litter decomposition should be assessed on the basis of litter species composition and decomposition microenvironments in situ.

Intensive Management Increases Phytolith-Occluded Carbon Sequestration in Moso Bamboo Plantations in Subtropical China

Plantation management practices could markedly change the sequestration of phytolith-occluded carbon (PhytOC) in plants and soils. However, for Moso bamboo (Phyllostachys pubescens) plantations, the effect of intensive plantation management (including fertilization, tillage, and removal of understory vegetation) on the accretion rate of PhytOC in the soil-plant system is much less understood than extensive management (without fertilization, tillage, and removal of understory vegetation). The objectives of this study were to investigate the effect of intensive and extensive management practices on the production, accumulation, and runoff of PhytOC and their distribution in physical fractions in Moso bamboo plantations. Our results showed that intensive management (1) increased PhytOC production mainly due to increased forest productivity; (2) increased PhytOC storage in the heavy fraction but decreased its storage in the light fraction of organic matter, resulting in the lack of effect on soil PhytOC storage; (3) increased the rate of dissolution of phytolith and the loss of PhytOC in runoff; and (4) promoted PhytOC sequestration in the soil-plant system, mostly in the plants, due to the greater rate of PhytOC production than the rate of loss. We conclude that intensive bamboo plantation management practices are beneficial to increasing long-term PhytOC sequestration in the soil-plant system.

Understory plant interactions along a successional gradient in Central Amazon

Plant-plant interactions, other than competition for light, may be responsible for arrested succession in secondary forests dominated by species of the genus Vismia. We aimed to investigate seedlings’ responses to the cumulative effect of root competition and the presence of understory vegetation in Vismia stands. We conducted a trenching and understory vegetation removal experiment in Vismia-dominated secondary forests of different ages. We planted three species with contrasting functional traits. For each seedling, we measured biotic damage, functional traits, and final mass. In each experimental block, we measured canopy openness, vegetation cover, and clay content of the soil. The effect of root and understory competition was not related to secondary forest age. However, the net effect had a quadratic relationship with site suitability for all species. Specifically, facilitation occurred only at low levels of suitability, when biotic damage was intense; competition, however, was stronger at intermediate levels of suitability. The net effect of plant-plant interactions in Vismia-dominated forests depends on the site suitability for each species. We conclude that seedlings are negatively affected mainly by other types of plant-plant interactions, but facilitation can occur when biotic damage is high.

Forest disturbance and arthropods: Small‐scale canopy gaps drive invertebrate community structure and composition

AbstractIn forest ecosystems, disturbances that cause tree mortality create canopy gaps, increase growth of understory vegetation, and alter the abiotic environment. These impacts may have interacting effects on populations of ground‐dwelling invertebrates that regulate ecological processes such as decomposition and nutrient cycling. A manipulative experiment was designed to decouple effects of simultaneous disturbances to the forest canopy and ground‐level vegetation to understand their individual and combined impacts on ground‐dwelling invertebrate communities. We quantified invertebrate abundance, richness, diversity, and community composition via pitfall traps in response to a factorial combination of two disturbance treatments: canopy gap formation via girdling and understory vegetation removal. Formation of gaps was the primary driver of changes in invertebrate community structure, increasing activity‐abundance and taxonomic richness, while understory removal had smaller effects. Families of Collembola and Diplopoda, as well as some families of Coleoptera, increased in combined canopy and understory disturbance treatments, whereas Curculionidae and Nitidulidae were more abundant in undisturbed forest. Gaps increased light availability, height and cover of understory vegetation, and soil moisture levels, and decreased depth and cover of leaf litter compared to undisturbed forest. Decoupling of canopy and understory vegetation disturbances revealed gap formation as an important short‐term driver of ground‐dwelling invertebrate community structure and composition. Our findings increase understanding of how ground‐dwelling invertebrate communities respond to disturbance and inform sustainable management of forest ecosystems to foster biodiversity and resilience.

Labile organic carbon pools and enzyme activities of Pinus massoniana plantation soil as affected by understory vegetation removal and thinning

The effects of forest management on carbon (C) sequestration are poorly understood, particularly in the Three Gorges Reservoir area. We aimed to identify the effects of forest management on C sequestration in Pinus massoniana plantations. An intact control forest (CK), a site undergoing regular shrub cutting with the simultaneous removal of residues (SC), a site under low-intensity thinning (LIT), and a site under high-intensity thinning (HIT) were compared for soil labile organic carbon (LOC), related enzyme activities, and soil characteristics. Soil organic carbon (SOC) significantly decreased in the HIT treatment as compared with that in the CK treatment. Soil EOC, DOC, MBC contents in treated plots were higher than those in the CK treatment; particularly, the HIT treatment significantly increased those values in 0–10 cm layer. Thinning resulted in a decrease in cellulase and amylase activities, but an increase in invertase activity. In addition, the SOC content was significantly correlated with four enzymes activities and LOC components, which suggested that the soil LOC components and enzymes activities were sensitive to the changes of SOC. Our results suggest that high-intensity thinning treatment in Pinus massoniana plantation could significantly decrease the SOC content and lead to an increase of LOC components.

Understory Vegetation and Drought Effects on Soil Aggregate Stability and Aggregate‐Associated Carbon on the Loess Plateau in China

Core Ideas Precipitation–throughfall exclusion and the removal of understory had no influence on total SOC. Throughfall exclusion and removal of the understory significantly affected soil aggregate stability. Throughfall exclusion and lack of understory also affected aggregate‐associated organic C pools. Restoration of understory vegetation had some potential to increase total SOC sequestration. Artificial afforestation is a common strategy for ecological recovery on the Loess Plateau, China, which causes the development of understory vegetation and drought stress. However, the influence of the understory vegetation and drought conditions on soil aggregate stability and aggregate‐associated soil organic carbon (SOC) are still not well understood. We evaluated the impacts of understory development and drought stress on soil aggregate stability and associated SOC during 2015 and 2016 in an artificial afforestation area in Shaanxi Province, China. The study had four treatments: control (CK), precipitation and throughfall excluded + understory present (TE), precipitation and throughfall allowed + understory removed (NU), and precipitation and throughfall excluded + understory removed (TE‐NU). Soil moisture was significantly reduced by the exclusion of precipitation and throughfall. Aboveground biomass in the CK was significantly higher than that of TE. Precipitation–throughfall exclusion and the removal of understory vegetation significantly decreased soil aggregate stability and aggregate‐associated organic C pools, while they had no influence on the total SOC pools. This indicated that soil aggregate stability and aggregate‐associated organic C may be more sensitive to changes in the external environment. These suggest that understory vegetation restoration had some potential to increase total SOC sequestration in the artificial afforestation on the Loess Plateau of China.

Altered leaf functional traits by nitrogen addition in a nutrient-poor pine plantation: A consequence of decreased phosphorus availability

This study aimed to determine how specific leaf area (SLA) and leaf dry matter content (LDMC) respond to N addition and understory vegetation removal in a 13-year-old Mongolian pine (Pinus sylvestris var. mongolica) plantation. Traits (SLA, LDMC, individual needle dry weight, N and P concentrations) of different-aged needles and their crown-average values were measured, and their relationships with soil N and P availability were examined. N addition and understory removal reduced soil Olsen-P by 15–91%. At the crown level, N addition significantly reduced foliar P concentration (by 19%) and SLA (by 8%), and elevated N concentration (by 31%), LDMC (by 10%) and individual leaf dry weight (by 14%); understory removal did not have a significant effect on all leaf traits. At the needle age level, traits of the previous year’s needles responded more strongly to N addition and understory removal than the traits of current-year needles, particularly SLA and N concentration. SLA and LDMC correlated more closely with soil Olsen-P than with soil inorganic N, and LDMC correlated more closely with soil Olsen-P than SLA did. These results indicate that aggravated P limitation resulting from N addition and understory removal could constrain Mongolian pine growth through their effects on the leaf traits.