Effects of landscape fragmentation of plantation forests on carbon storage in the Loess Plateau,China

Tree plantation and forest restoration are the major strategies for enhancing terrestrial carbon sequestration and mitigating climate change.The Grain for Green Project in China has positively impacted global carbon sequestration and the trend towards fragmentation of plantation forests.Limited studies have been conducted on changes in plantation biomass and stand structure caused by fragmentation,and the effect of fragmentation on the carbon storage of plantation forests remains unclear.This study evaluated the differences between carbon storage and stand structure in black locust forests in fragmented and continuous landscape in the Ansai District,China and discussed the effects of ecological significance of four landscape indices on carbon storage and tree density.We used structural equation modelling to explore the direct and indirect effects of fragmentation,edge,abiotic factors,and stand structure on above-ground carbon storage.Diameter at breast height(DBH)in fragmented forests was 53.3%thicker,tree density was 40.9%lower,and carbon storage was 49.8%higher than those in continuous forests;for all given DBH>10 cm,the trees in fragmented forests were shorter than those in continuous forests.The patch area had a negative impact on carbon storage,i.e.,the higher the degree of fragmentation,the lower the density of the tree;and fragmentation and distance to edge(DTE)directly increased canopy coverage.However,canopy coverage directly decreased carbon storage,and fragmentation directly increased carbon storage and tree density.In non-commercial forests,fragmentation reduces the carbon storage potential of plantation,and the influence of patch area,edge,and patchy connection on plantation should be considered when follow-up trees are planted and for the plantation management.Thus,expanding the area of plantation patches,repairing the edges of complex-shaped patches,enhancing the connectivity of similar patches,and applying nutrients to plantation forests at regular intervals are recommended in fragmented areas of the Loess Plateau.

Aging Mongolian pine plantations face high risks of drought-induced growth decline:evidence from both individual tree and forest stand measurements

Discerning vulnerability differences among different aged trees to drought-driven growth decline or to mortality is critical to implement age-specific countermeasures for forest management in water-limited areas.An important species for afforestation in dry environments of northern China,Mongolian pine(Pinus sylvestris var.mongolica Litv.)has recently exhibited growth decline and dieback on many sites,particularly pronounced in old-growth plantations.However,changes in response to drought stress by this species with age as well as the underlying mechanisms are poorly understood.In this study,tree-ring data and remotely sensed vegetation data were combined to investigate variations in growth at individual tree and stand scales for young(9-13 years)and aging(35-52 years)plantations of Mongolian pine in a water-limited area of northern China.A recent decline in tree-ring width in the older plantation also had lower values in satellited-derived normalized difference vegetation indices and normalized difference water indices relative to the younger plantations.In addition,all measured growth-related metrics were strongly correlated with the self-calibrating Palmer drought severity index during the growing season in the older plantation.Sensitivity of growth to drought of the older plantation might be attributed to more severe hydraulic limitations,as reflected by their lower sapwood-and leaf-specific hydraulic conductivities.Our study presents a comprehensive view on changes of growth with age by integrating multiple methods and provides an explanation from the perspective of plant hydraulics for growth decline with age.The results indicate that old-growth Mongolian pine plantations in water-limited environments may face increased growth declines under the context of climate warming and drying.

Ecological effect of the plantation of Sabina vulgaris in the Mu Us Sandy Land,China

Vegetation restoration through artificial plantation is an effective method to combat desertification,especially in arid and semi-arid areas.This study aimed to explore the ecological effect of the plantation of Sabina vulgaris on soil physical and chemical properties on the southeastern fringe of the Mu Us Sandy Land,China.We collected soil samples from five depth layers(0-20,20-40,40-60,60-80,and 80-100 cm)in the S.vulgaris plantation plots across four plantation ages(4,7,10,and 16 years)in November 2019,and assessed soil physical(soil bulk density,soil porosity,and soil particle size)and chemical(soil organic carbon(SOC),total nitrogen(TN),available nitrogen(AN),available phosphorus(AP),available potassium(AK),cation-exchange capacity(CEC),salinity,p H,and C/N ratio)properties.The results indicated that the soil predominantly consisted of sand particles(94.27%-99.67%),with the remainder being silt and clay.As plantation age increased,silt and very fine sand contents progressively rose.After 16 years of planting,there was a marked reduction in the mean soil particle size.The initial soil fertility was low and declined from 4 to 10 years of planting before witnessing an improvement.Significant positive correlations were observed for the clay,silt,and very fine sand(mean diameter of 0.000-0.100 mm)with SOC,AK,and p H.In contrast,fine sand and medium sand(mean diameter of 0.100-0.500 mm)showed significant negative correlations with these indicators.Our findings ascertain that the plantation of S.vulgaris requires 10 years to effectively act as a windbreak and contribute to sand fixation,and needs 16 years to improve soil physical and chemical properties.Importantly,these improvements were found to be highly beneficial for vegetation restoration in arid and semi-arid areas.This research can offer valuable insights for the protection and restoration of the vegetation ecosystem in the sandy lands in China.

Long-term thinning decreases the contribution of heterotrophic respiration to soil respiration in subalpine plantations

Interest in the dynamics of soil respiration(R_(S))in subalpine forest ecosystems is increasing due to their high soil carbon density and potential sensitivity to environmental changes.However,as a principal silvicultural practice,the long-term impacts of thinning on R_(S) and its heterotrophic and autotrophic respiration components(R_(h) and Ra,respectively)in subalpine plantations are poorly understood,espe-cially in winter.A 3-year field observation was carried out with consideration of winter CO_(2) efflux in middle-aged sub-alpine spruce plantations in northwestern China.A trench-ing method was used to explore the long-term impacts of thinning on Rs,Rn and R_(a).Seventeen years after thinning,mean annual Rs,Rn and R_(a) increased,while the contribu-tion of R_(h) to R_(s) decreased with thinning intensity.Thinning significantly decreased winter R,because of the reduction in R_(n) but had no significant effect on Ra.The temperature sensitivity(Q_(10))of R_(h) and R_(a) also increased with thinning intensity,with lower Q_(10) values for R_(h)(2.1-2.6)than for Ra(2.4-2.8).The results revealed the explanatory variables and pathways related to R_(n) and R_(a) dynamics.Thinning increased soil moisture and nitrate nitrogen(NO_(3)^(-)-N),and the enhanced nitrogen and water availability promoted R_(h) and R_(a) by improving fine root biomass and microbial activity.Our results highlight the positive roles of NO_(3)^(-)-N in stimulating R_(s) components following long-term thinning.Therefore,applications of nitrogen fertilizer are not recommended while thinning subalpine spruce plantations from the perspective of reducing soil CO_(2) emissions.The increased Q_(10) values of R_(s) components indicate that a large increase in soil CO_(2) emissions would be expected following thinning because of more pronounced climate warming in alpineregions.

Effects of three coniferous plantation species on plant-soil feedbacks and soil physical and chemical properties in semiarid mountain ecosystems

Background:Large-scale afforestation can significantly change the ground cover and soil physicochemical properties,especially the soil fertility maintenance and water conservation functions of artificial forests,which are very important in semi-arid mountain ecosystems.However,how different tree species affect soil nutrients and soil physicochemical properties after afforestation,and which is the best plantation species for improving soil fertility and water conservation functions remain largely unknown.Methods:This study investigated the soil nutrient contents of three different plantations(Larix principis-rupprechtii,Picea crassifolia,Pinus tabuliformis),soils and plant-soil feedbacks,as well as the interactions between soil physicochemical properties.Results:The results revealed that the leaves and litter layers strongly influenced soil nutrient availability through biogeochemical processes:P.tabuliformis had higher organic carbon,ratio of organic carbon to total nitrogen(C:N)and organic carbon to total phosphorus(C:P)in the leaves and litter layers than L.principis-rupprechtii or P.crassifolia,suggesting that higher C:N and C:P hindered litter decomposition.As a result,the L.principis-rupprechtii and P.crassifolia plantation forests significantly improved soil nutrients and clay components,compared with the P.tabuliformis plantation forest.Furthermore,the L.principis-rupprechtii and P.crassifolia plantation forests significantly improved the soil capacity,soil total porosity,and capillary porosity,decreased soil bulk density,and enhanced water storage capacity,compared with the P.tabuliformis plantation forest.The results of this study showed that,the strong link between plants and soil was tightly coupled to C:N and C:P,and there was a close correlation between soil particle size distribution and soil physicochemical properties.Conclusions:Therefore,our results recommend planting the L.principis-rupprechtii and P.crassifolia as the preferred tree species to enhance the soil fertility and water conservation functions,especially in semi-arid regions mountain forest ecosystems.

Functional diversity dominates positive species mixture effects on ecosystem multifunctionality in subtropical plantations

Mixed-species plantations generally exhibit higher ecosystem multifunctionality than monospecific plantations.However,it is unclear how tree species functional composition influences species mixture effects on ecosystem multifunctionality.We selected 171 monospecific and mixed-species plantations from nine regions across subtropical China,and quantified 13 key ecosystem functional properties to investigate how species mixture effects on ecosystem multifunctionality are modulated by functional diversity and identity.We found that ecosystem multifunctionality was significantly higher(p<0.05)in mixed tree plantations than in monospecific plantations except the mixed-conifer species plantations.Across all regions,ecosystem multifunctionality was significantly higher(p<0.05)in mixed conifer-broadleaf plantations than in monospecific plantations of the corresponding species,but not different between mixed and monospecific coniferous plantations.The magnitude of species mixture effects on ecosystem multifunctionality varied greatly with tree species compositions.Taking Cunninghamia lanceolata Lamb.as an example,the effects varied from a range of 2.0%–9.6%when mixed with a conifer species to 36%–87%when mixed with a broadleaf species.The functional diversity was the dominate driver shaping ecosystem multifunctionality,while functional identity,as expressed by community-weighted mean of specific leaf area,also had a positive effect on ecosystem multifunctionality through the increased below-ground nitrogen and phosphorus stocks regulated by specific leaf area of the mixing tree species.Our study highlights the important role of functional diversity in shaping ecosystem multifunctionality across region-wide environmental conditions.Mixed conifer-broadleaf tree plantations with distinct functional traits benefit the enhancement of ecosystem multifunctionality,and the magnitude of species mixture effects is modulated by the functional identity of tree species composition;those relationships deserve a special consideration in multifunctional management context of subtropical plantations.

Silvicultural Systems for Restoration of Mahogany in Degraded Landscapes in Africa: Influence of Mixed Rainforest Plantation on Growth and Pest Damage

African mahogany, one of the world’s most valuable timber species is threatened by over-exploitation in natural forests and failure of plantations due to attacks by the shoot borer Hypsipyla robusta. Mixed-species plantations has been reported to be an effective component of integrated pest management of major pest in other crops;but there is very limited empirical data on its use for managing Hypsipyla in mahogany mixed stands in West Africa. The aim of this study was to assess the effect of mixed-species stands as management intervention, on the growth of Khaya grandifoliola and Khaya ivorensis in relation to Hypsipyla robusta attack in a 10 ha experimental plantation in the wet evergreen forest type in Ghana. Khaya grandifoliola recorded faster growth than Khaya ivorensis in this forest type though the later naturally grow in this forest type while the former is introduced from the dry forest. Two years after planting, diameter and height growth were greater in the mixed-species stand than the pure stands for K. grandifoliola and K. ivorensis. Hypsipyla damage was less in the mixed stands of both K. grandifoliola and K. ivorensis compared to the pure stands, with the 20% and 10% Khaya mixed stand recording the lowest attack in both species. It can be recommended that mixed stands of the two Khaya species at 20% or lower Khaya density might be ideal for reducing the levels of Hypsipyla attack in this type of forest.

Effects of natural forest conversion and plantation tree species composition on soil macrofauna communities in Northeast China mountains

As primary and secondary forests are being replaced by plantations across the globe,the soil macrofauna community structure is also affected,but little is known about the impact of mixed culture plantations compared with monocultures on the soil macrofauna.To determine the impact of forest conversion on soil macrofauna,we surveyed the soil macrofauna in two broad-leaved and three coniferous monoculture stands and four coniferous-broadleaved mixed stands,and in adjacent reserved secondary stands as a reference.Soil macro fauna community composition was significant affected by forest type,season and their interaction(P<0.05).The abundance,taxa richness and diversity of soil macro fauna changed to different degrees depending on the plantation type.Broadleaved monoculture stands and secondary stands had similar macrofauna abundance and taxa richness,but values were lower in coniferous stands than in secondary stands.The Shannon index for macrofauna in coniferous stands was also the lowest,but the Pielou index did not differ between forest types.The negative effects of the conifer monoculture on soil macro fauna were not present in the mixed stands with broad-leaved trees.Forest conversion impacted soil properties;soil moisture,NO_(3)^(-),and pH were significant drivers of soil macrofauna community structure.The impact of forest conversion on soil macrofauna was closely dependent on tree species composition and diversity.The macro fauna community structure in the broadleaved and the mixed stands were relatively similar to that in the natural forest,and thus recommended for forest conversion in the study area.

Effects of tropical forest conversion into oil palm plantations on nitrous oxide emissions:A meta-analysis

Oil palm plantations have dramatically expanded in tropical Asia over the past decades.Although their establishment has been projected to increase nitrous oxide(N_(2)O)emissions,earlier reports have shown inconsistent results.This study analyzed these previously published data to compare N_(2)O emissions in oil palm plantations to reference forests.A linear mixed-eff ects model was used to examine the signifi cance of the eff ect of establishing oil palm plantations on N_(2)O emissions,rather than to calculate mean eff ect sizes because of limitations in the data structure.The results indicated that N_(2)O emissions were signifi cantly greater from oil palm plantations than from reference forests,as expected.This is the fi rst study to report the eff ect of oil palm plantations on N_(2)O emissions by synthesizing previously published data.To quantify the size of this eff ect,additional studies with frequent and long-term monitoring data are needed.

NUTRIENT CYCLING IN THE DAHURIAN LARCH PLANTATION ECOSYSTEM

Based on the determinations of the nutrient elements including N,P,K,Ca, and Mg of Dahurian larch plantation ecosystem in the eastern part of northern China,the analysis of contents.distribution,accumulation of plant and soil nutrient elements,and the properties of the nutrient cycling throuth the larch plantation ecosystem were conducted,The results were as follows:the nutrient content of various ecosystem varied with plant organs,ages and distributive layer.The totan amount of nutrinet elements accumulated in the larch ecosystem was 27098kg/hm2,in which soil accumulation and plant accumulation were 268946 kg/hm2 and 2040.602kg/hm2,respectively;the annual absorption of nutrient elements was 197.394kg/hm2,in which the annual relention and annual return of nutrientelements were 76.183 and 121.211kg/hm2,respectively,Compare to other forest communities,the cycling rates of various nutrient elements through larch plantation ecosystem was relatively higher.

Structure and functions of Pinus sylvestris var. Sylvestriformis plantation ecosystem

Changbai pine (Pinus sylvestris var.Sylvestriformis) is an endemic and important tree species in Changbai Mountain. There were only 63 plant species in Changbai pine plantation, where hemicryptophyte was dominant(39.68%). Simpson diversity index was 0.87, Shannon-Wiener diversity index was 2.96, and evenness index was 0.82. Community structure were divided into three layers: tree layer, shrub layer and herb layer. The total biomass and net production were 111.982 t/hm2 and 8942.80 kg/(hm2 a) respectively. The total biomass for tree, shrub and herb layers were 106.150, 2.230, 2.264 t/hm2, accounting for 94.79%, 1.99%, and 2.02%, respectively, and net production for those were 7465, 223, and 1182 kg/(hm2 a), accounting for 83.47%, 2.49%, and 13.22% of the total respectively. The nutrient content in various organs is in the order of needle> branch> root> bark> trunk, For the assimilated organ, the nutrient content is in the order of N> K> Ca> P> Mg, and that in absorption organ is in the order of Ca> N> K> P> Mg. For the whole plantation ecosystem, nutrient content is in the order of soil> litter> herb layer> shrub layer> tree layer. Nutrient storage and its accumulation rate in tree layer take up 88.79% and 76.43% of the total, respectively.

DYNAMIC THINNING SYSTEM FOR LARCH PLANTATION

Systematic researches were carried out in dahurian larch (Larixgmelini) plantation in the spring of 1958 at Maoershan Forest Farm attached to Northeast Forestry University. First of all, a new tree classificdtion method. relat11'e classification in small group, was presented. Each small group was composed of one tree in the center and six adjacent trees, which formed a hexagon in space. All these seven trees. then, can be divided into five classes such as class A class B,class C. class D and class E respectiveiy. For the conxenience of comparison. the stand used for the trial was duvided into five experimental plots in which the thinning intensity for each plot was controllca as follows: 10% for the first plot; 20% for the second plot- 30% for the third plot; 40% for the fourth plot and the fifth plot without thinning for comparison. Thinning operation was carried out according to the principle of reserving A-class trees, cutting B- class trees in the intensity as required, releasing C-class trees and removing D and E class trees.Through 14 years study- the result shows that if the stand volume of contrast plot is considered as 100% after the first thinning' the volume of other plots are 114. 9% for the first plot, 128. 4% for the second plot, 133. 1% fOr the third plot and 118. 5% for The fourth plot respectively. Meanwhile, biomass and increment of diameter can also be increased significantly after thinning by this method.

Ecological environment analysis of Abies holophylla plantations under different cutting systems

Different types of plantations were observed in Baishilazi National Nature Reserve, Liaoning Province, for 34 a. The environmental quality ofAbies holophylla plantations was analyzed under different cutting systems. Analysis factors included soil erosion rate, humification degree of litters, and water hold capacity. The surface soil loss of clear cutting area was 19000t·km?2·a?1 more than that of selective cutting area. The content of soil organic matter in board-leaved—Abies holophylla forest was 4.62% more than that in pure stand, and the water hold capacity of the mixed forest was 1.43 time of that of pure stand. The mixed forest of board-leaved—Abies holophylla by selective cutting can upgrade the ecological environment quality.

Biomass Production of Poplar Plantation Ecosystem in Yangtze River Beach Land

Currently, China is home to more than four million hectares of oil plants nationwide, and 154 kinds of energy trees could produce seeds containing more than 40 percent of oil, with total production of the seeds totaling five million tons. Another 57 million hectares of waste land are available and suitable for planting trees for the production of forest-based bioenergy, of which there is 630,000 hm2 beach land in the middle and lower reaches of Yangtze River where is suited for poplar growing. In order to approach the potential of poplar biomass production, the test was conducted in the paper. The result indicated that in the poplar forest ecosystem the herbaceous biomass production was 15.554 t/hm2. While biomass production for trees was 43.164 t/hm2, totally in the poplar plantation ecosystem biomass production reached 58.718 t/hm2. As well, poplars growing added incomes for local farmers.

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

Allelopathy is an important mechanism in Eucalyptus plantations that causes detrimental impacts on understory diversity.Phenolic compounds are the main allelochemicals suppressing understory plants.However,the dynamic changes in phenolic allelochemicals and their relationship with understory diversity with increasing age of Eucalyptus plantations remain largely unclear.In this study,the understory plant diversity was assessed and phenolic compounds identified from leaf litter,roots,and rhizosphere soil samples in a Eucalyptus grandis plantation at two-year intervals for ten years using ultra-performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS).The abundance and diversity of under story plant species were lowest in 4-year-old plantations and increased significantly with age.Seven phenolic acids and 10 flavonoids were identified from leaf litter,roots,and rhizosphere soils.Most of the potential phenolic allelochemicals,such as salicylic acid,gallic acid,4-hydroxybenzoic acid,and epicatechin,were more abundant in younger plantations,especially at4 years old.The concentrations of phenolic compounds in the rhizosphere zone were significantly lower than in litter and root samples and did not change significantly with an increase in age.Notably,phenolic compounds contributed more to the variation in the understory plants than soil factors.Hydroxyphenyllactic acid,ellagic acid,quercetin,salicylic acid,and 4-hydroxybenzoic acid were the main phenolic compounds explaining the variation in plant diversity with plantation age.These findings indicate that young E.grandis plantations,especially at four years of age,merit a greater focus because of their lower understory plant diversity and higher allelopathic potential.

Litter removal impacts on soil biodiversity and eucalypt plantation development in the seasonal tropics

The little layer of tree plantations provides primary nutrients for uptake,buff ers changes in soil moisture,and provides habitat and substrate to soil epigeic fauna.However,this layer in eucalypt plantations is often removed to reduce fuel load during the fi re season in the Brazilian savanna(Cerrado).Therefore,it is necessary to quantify the eff ects of changes in litter dynamics on the function of these plantations,on key nutrient cycling processes and on epigeic fauna diversity and abundance.In two adjacent stands(one juvenile and one mature),the consequences of two years of litter removal were quantifi ed as monthly litterfall,leaf and fi ne wood litter decomposition,epigeic fauna abundance and diversity,soil biogeochemical variables,and tree diameter and basal area increments.Monthly litterfall rates in juvenile and mature stands did not change with litter removal over the study period.Annual litterfall ranged from 4.1 to 4.9 Mg ha^(−1)a^(−1)in litter removal plots and from 3.9 to 4.8 Mg ha^(−1)a^(−1)in control plots.Fine wood litter decomposition was slower in litter removal plots compared to controls,while leaf decomposition rates were similar in both.Two years of litter removal in the juvenile stand did not aff ect topsoil biogeochemical parameters but decreased available phosphorus at 20–40 cm depth relative to controls.In the mature stand,total cation exchange capacity(0–20 cm)was higher in controls(6.4 cmol c dm^(−3))relative to litter removal plots(6.3 cmol c dm^(−3)),while soil moisture(0–40 cm depth)was lower in litter removal(25.45 m 3 m^(−3))compared to control plots(26 m^(3)m^(−3))in the dry season.A non-metric multidimensional scaling ordination revealed an increased homogeneity in epigeic fauna where litter was removed.Litterfall,decomposition,diameter increment,four soil physical parameters and fourteen chemical parameters at 0–20 and 20–40 cm depth explained the diff erences in soil epigeic fauna composition between litter removal and control plots.Diameter increment decreased with litter removal only in the juvenile stand,which had reached its growth peak.The results indicate that removing excess litter to decrease fuel volume can alter soil biodiversity and edaphic conditions that negatively aff ect nutrient cycling and tree growth.

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

Background:Chinese 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.Methods:We 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.Results:Compared 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.Conclusion:Thinning 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.

Species composition and influencing factors of understory woody species in Robinia pseudoacacia plantations on the Loess Plateau

Black locust(Robinia pseudoacacia L.)plantations have contributed significantly to soil and water conservation and ecological reconstruction on China’s Loess Plateau.Understanding the impact of stand and environment on species composition of understory woody plants will improve the stability of existing black locust plantations.Ten stands were selected in second-generation black locust plantations in tableland and gully areas of the Loess Plateau.The number of understory tree species in the tablelands was significantly lower than in the gully stands.Regenerated black locust(19.76%)and Rubus corchorifolius L.f.(64.85%)were the most abundant understory tree and shrub species,respectively,in the tableland stands;Broussonetia papyrifera(L.)L’Hér.ex Vent.(6.77%)and Acanthopanax senticosus(Rupr.Maxim.)Harms.(37.22%)were most abundant in the gully stands.Species richness(S),Shannon diversity(H),and evenness index(J)of the understory plants were significantly lower in the tableland stands than in the gully stands.More diverse understory species and community structures occurred in the gully stands.Differences in species diversity among landform positions may be attributed to differences in soil moisture.In addition,77.57%of the variation in understory species composition was explained,among which shrub and herb coverage,stand age,leaf area index,slope and total soil phosphorus in the 10-20 cm layer were the main factors.Soil organic carbon and total potassium significantly impacted S,H and J.Considering the environmental conditions and the biological characteristics of the plants investigated,R.corchorifolius should be given priority in the development of tableland stands,while B.papyrifera and Celtis sinensis Pers.should form mixed forests with black locust in gully stands.This management could promote biodiversity and stability of the existing black locust plantations but also optimize regional landscape patterns.

Taxonomic and community composition of epigeal arthropods in monoculture and mixed tree species plantations in a deciduous forest of Ghana

Tropical forests provide several ecosystem services and functions and support approximately two-thirds of the world’s biodiversity but are seriously threatened by deforestation.Approaches to counteract this menace have revolved around aff orestation with several or a single tree species.We thus investigated how plantation forests with either a single or several tree species infl uenced arthropod taxonomic and community composition using pitfall traps to sample selected groups of epigeal arthropods(Araneae,Coleoptera,Orthoptera and Hymenoptera)and with environmental variables assessed simultaneously.Our results revealed 54 taxonomic groups with signifi cantly higher taxonomic richness,activity density,and diversity in the mixed stands than in the monoculture stands.The significant differences in community composition were mainly driven by families including Lycosidae,Formicidae,Staphylinidae,Scotylidae,Hydrophilidae,Gryllidae and Scarabaeidae and were explained by distinct habitat characteristics(canopy openness,litter depth,deadwood volume,and tree height).While the diverse tree communities and heterogeneous vegetation structure off ered food and habitat resources for diverse arthropod groups,the allelopathic nature coupled with homogenous stand characteristics of the Tectona grandis stands in the monoculture suppressed the growth of understorey vegetation that could otherwise serve as food and habitat resources for arthropods,which might have led to limited activities and diversity of arthropods in the monoculture plantation stands.The fi ndings thus highlight the need to promote mixed tree plantations in degraded tropical areas,especially when restoring biodiversity is the prime management focus.

An Edge-assisted, Object-oriented Random Forest Approach for Refined Extraction of Tea Plantations Using Multi-temporal Sentinel-2 and High-resolution Gaofen-2 Imagery

As a consumed and influential natural plant beverage,tea is widely planted in subtropical and tropical areas all over the world.Affected by(sub)tropical climate characteristics,the underlying surface of the tea distribution area is extremely complex,with a variety of vegetation types.In addition,tea distribution is scattered and fragmentized in most of China.Therefore,it is difficult to obtain accurate tea information based on coarse resolution remote sensing data and existing feature extraction methods.This study proposed a boundary-enhanced,object-oriented random forest method on the basis of high-resolution GF-2 and multi-temporal Sentinel-2 data.This method uses multispectral indexes,textures,vegetable indices,and variation characteristics of time-series NDVI from the multi-temporal Sentinel-2 imageries to obtain abundant features related to the growth of tea plantations.To reduce feature redundancy and computation time,the feature elimination algorithm based on Mean Decrease Accuracy(MDA)was used to generate the optimal feature set.Considering the serious boundary inconsistency problem caused by the complex and fragmented land cover types,high resolution GF-2 image was segmented based on the MultiResolution Segmentation(MRS)algorithm to assist the segmentation of Sentinel-2,which contributes to delineating meaningful objects and enhancing the reliability of the boundary for tea plantations.Finally,the object-oriented random forest method was utilized to extract the tea information based on the optimal feature combination in the Jingmai Mountain,Yunnan Province.The resulting tea plantation map had high accuracy,with a 95.38%overall accuracy and 0.91 kappa coefficient.We conclude that the proposed method is effective for mapping tea plantations in high heterogeneity mountainous areas and has the potential for mapping tea plantations in large areas.