Soil Erosion and Vegetation Succession in Alpine Kobresia Steppe Meadow Caused by Plateau Pika——A Case Study of Nagqu County, Tibet

This paper evaluated the impacts of mounds created by the plateau pika （Ochotona curzoniae） on the vegetation composition, structure, and species diversity of an alpine Kobresia steppe meadow in Nagqu County, Tibet Autonomous Region, China. Based on mound height or the depth of erosion pit, we defined five stages of erosion and compared the floristic features of communities at these stages with those in undisturbed sites. In the study area, the mounds and pits covered up to 7% of the total area. Lancea tibetica, Lamiophlomis rotata, and Potentilla biflarca were the dominant species in erosion pits, and Kobresia pygmaea, the dominant species in undisturbed sites, became a companion species in eroded areas. In the process of erosion, the original vegetation was covered by soil ejected by the pika, then the mounds were gradually eroded by wind and rain, and finally erosion pits formed. The vegetation coverage increased with increasing erosion stages but remained significantly lower than that in undisturbed sites. Improved coverage eventually reduced soil erosion, and pit depth eventually stabilized at around 20cm. Aboveground biomass increased with increasing erosion stage, but the proportion of low-quality forage reached more than 94%. The richness index and Shannon-Wiener index increased significantly with increasing erosion stage, but the richness index in mound and pit areas was significantly lower than that in undisturbed sites.

Responses of soil nitrogen, phosphorous and organic matter to vegetation succession on the Loess Plateau of China

Revegetation is a traditional practice widely used for soil protection. We evaluated the effect of natural revegetation succession on soil chemical properties and carbon fractions （particulate organic carbon （POC）, humus carbon （HS-C）, humic acid carbon （HA-C） and fulvic acid carbon （FA-C）） on the Loess Plateau of China. The vegetation types, in order from the shortest to the longest enclosure duration, were： （a） abandoned overgrazed grassland （AbG3; 3 years）; （b） Hierochloe odorata Beauv. （HiO7; 7 years）; （c） Thymus mongoficus Ronnm （ThM15; 15 years）; （d） Artemisia sacrorum Ledeb （AtS25; 25 years）; （e） Stipa bungeana Trin Ledeb （StB36; 36 years） and （f） Stipa grandis P. Smirn （StG56; 56 years）. The results showed that the concentrations of soil organic carbon, total nitrogen and available phosphorus increased with the increase of restoration time except for ThM15. The concen- tration of NH4-N increased in the medium stage （for ThM15 and AtS25） and decreased in the later stage （for StB36 and StG56） of vegetation restoration. However, NO3-N concentration significantly increased in the later stage （for StB36 and StG56）. Carbon fractions had a similar increasing trend during natural vegetation restoration. The con- centrations of POC, HS-C, FA-C and HA-C accounted for 24.5%-49.1%, 10.6%-15.2%, 5.8%-9.1% and 4.6%-6.1% of total carbon, respectively. For AbG3, the relative changes of POC, HS-C and FA-C were significantly higher than that of total carbon during the process of revegetation restoration. The higher relative increases in POC, HS-C and FA-C confirmed that soil carbon induced by vegetation restoration was sequestrated by higher physical and chemical protection. The increases of soil C fractions could also result in higher ecological function in semiarid grassland ecosystems.

Effects of Vegetation Succession on Soil Fertility Within Farming-Plantation Ecotone in Ziwuling Mountains of the Loess Plateau in China

To further understand the relationship between vegetation succession and soil fertility within farming-plantation ecotone in Ziwuling Mountains of the Loess Plateau, nine kinds of widely distributed communities at different succession stages were selected, and the effects of vegetation succession on soil fertility were studied through the methods of comparing two hierarchical clustering （similarity index： B） and other multivariate analysis. The results showed that： （i） the similarity in clustering pattern of nine communities which classified by plant species and soil nutrients respectively showed a trend of B ^-overall plant-soil0-10cn〉B^-overall plant-soil 10-20 cm 〉B^- overall plant-soil 20-40 cm, and for the top soil, it showed a trend of B^- grass-soil 0-10 cm 〉 B^-shrub-soil 0-10 cm 〉 Btree-soil0-10 cm; （ii） soil fertility increased during the succession process from abandoned land to forest community, and the soil fertility of forest community showed an increased order of coniferous forest →mixed forest →broadleaf forest; （iii） during the process of vegetation succession, the variation of topsoil fertility was higher than that of the subsurface soil （coefficient of variation： CV0-10 cm 〉CV 10-20 cm 〉 CV20-40 cm）, and when the succession developed into the stages of shrub and forest communities, the top soil fertility had been improved significantly; and （iv） for the subsurface soil of the communities at the advanced succession stages, the soil fertility also increased to some extent. Our results suggested that the method of comparing two hierarchical clustering reflected the similarity level of different cluster patterns, therefore, it was helpful to study the relationship between vegetation succession and soil fertility. There was a corresponding relationship between the change process of soil fertility from the top soil to subsurface soil and the process of vegetation succession from the early stages to the advanced stage. The differentiations of soil fertility in vertical space and horizontal space were both caused by vegetation succession, which was significant for both the shrub and forest communities. The improved level of forest soil fertility was related to forest vegetation types and the improved fertility level of broad-leaved forest-soil community was higher than that of the coniferous forest soil. In the practice on soil fertility ecological restoration of the loess plateau, it is important to carry out reasonably artificial forestation so as to enhance the restoration and improvement of soil fertility.

Effects of soil organic matter components and iron aluminum oxides on aggregate stability during vegetation succession in granite red soil eroded areas

Soil aggregates determine the basic structure of soil,and their composition and stability are influenced by the various types of cementitious substances occurring in soil.To explore the main limiting factors of soil aggregation in the process of vegetation succession with granite as the parent material,five stages of vegetation succession in an eroded area were selected:bare land(BL),grassland(GL),grassland shrub transition land(GS),shrubland(SL)and secondary forest(SF).Soil samples were collected to determine the composition and stability of aggregates.The contents of organic and inorganic cementitious substances,including organic matter components and iron aluminum oxides,were determined at five soil aggregate grain levels.The results indicated that the stability of soil aggregates and the>0.25 mm water-stable aggregate content(WR_(0.25))increased with vegetation succession.Based on the Le Bissonnais(LB)method,the mean weight diameter(MWD)of soil aggregates increased,and the relative dissipation index(RSI)and relative mechanical crushing index(RMI)decreased.The humic acid(HA)and fulvic acid(FA)contents in soil aggregates increased with vegetation succession,and the soil humus content at the SF stage increased by more than 13.54%over the BL level.Upon different vegetation succession stage,the iron and aluminum oxides for the SL and the SF were at a high level,and the contents of free-form iron oxide(Fe_(d))and amorphous iron oxide(Fe_(o))for BL were high.Correlation analysis indicated that the soil humic degree(PQ)and the contents of amorphous alumina(Al_(o))were positively correlated with aggregate stability to varying degrees.Redundancy analysis(RDA)revealed that PQ values of 1-2 mm(PQ_(2))and 0.25-0.5 mm(PQ_(4))aggregates,the contents of Fe_(o) of bulk soil(Fe_(oB)),>2 mm(Fe_(o1)),1-2 mm(Fe_(o2)),and<0.25 mm(Fe_(o5))aggregates,and the contents of Al_(o) of>2 mm(Al_(o1))aggregates could explain 99.4%of the changes in soil aggregate stability at different vegetation succession stages.Al_(o1) had a contribution rate of 71.2%and is the key factor for improving the stability of soil aggregates.

Interaction between salinity intrusion and vegetation succession:A modeling approach

Predicting potential changes in groundwater salinity in low-lying coastal regions due to climate change is important, where coastal vegetation is abundant, succession competition between halophytes and glycophytes plays a significant role in the salinity budget. Sea level rise enhances salinity intrusion, contributing an additional dimension to vegetation competition. A new simulation model known as mangrove-hardwood hammock model coupled with saturated-unsaturated transport （MANTRA） has recently been developed by the authors to simulate groundwater salinity regimes in the presence of vegetation competition, subject to climate change. MANTRA is based upon linking two existing Unites States geological survey （USGS） simulation models known as mangrove-hardwood hammock model （MANHAM） and saturated-unsaturated transport （SUTRA）. MANHAM simulates the evolution of vegetation succession subject to changing groundwater salinity. SUTRA simulates saturated and unsaturated transport of solutes and salinity in groundwater given sea salinity. MANTRA improves the simulation robustness to simultaneously simulate groundwater hydrology, salinity and coastal vegetation succession subject to sea level rise. Some simulation results will be presented to demonstrate the impact of sea level rise on coastal vegetation succession and groundwater salinity.

Influence of volcanic activity on vegetation succession and growth environment on the hillslope of Sakurajima Volcano in southern Kyushu,Japan

This study was conducted in order to examine the influence of long-term volcanic activity on vegetative succession and growth on the slope of Sakurajima in southern Kyushu, Japan. We investigated the vegetation,depth of the volcanic ash layer, and dry density and p H of the surface soil at six places on the north-northwestern slope, 2.3–3.4 km from the Minami-dake crater, where a layer of pumice stone was deposited by the Taisho eruption in 1914. The height and diameter at breast height（DBH） of the trees increased with increasing distance from the Minami-dake crater, as did the number of individuals and species, and basal area. The Shannon–Wiener diversity index（H＇） demonstrates that vegetative succession is significantly affected by distance from the Minami-dake crater, as areas farther from the crater exhibited later seral stages. Comparison of the diversity index and species number of the crater region with that of the climax forest in Kagoshima indicates that vegetative growth alone cannot advance succession in the study area, as the local vegetative community is heavily influenced by the harsh environmental conditions associated with continual exposure to long-term volcanic activity. Seral stage, ash layer depth,dry density, and p H of the soil surface layer are governed by distance from the Minami-dake crater. The results of this study indicate that conditions for vegetative growth and succession improve with increasing distance from the source of constant volcanic activity. Thus, soil development is promoted by the acidification of the soil, which decreases the dry density and p H of the soil surface layer.The introduction of plant species resistant to volcanic ash and gas is recommended to promote soil development and improve the infiltration capacity of the soil.

Shrub interactions drive vegetation succession of subalpine grasslands under two climatic conditions

Aims The abandonment of agronomic practices in subalpine systems has led to shrub encroachment,which has transformed grasslands into woodlands.The competitive and facilitative interactions among incoming shrub species might influence vegetation succession and might be affected by climate change.This study aimed to identify the nature of shrub species interactions between an early colonizer and a secondary succession shrub in the successional encroach-ment process and whether it differs between two contrasting cli-matic conditions.Methods The interactions between the two main encroaching shrub spe-cies in the Central Pyrenees(Spain),Buxus sempervirens and Echinospartum horridum,were studied at the current upper limit of the altitudinal range of B.sempervirens,where it coexists with E.horridum(high site),and in a milder location at lower eleva-tion(low site).in the studied areas,E.horridum is the first shrub species that encroaches upon the abandoned grasslands and B.sempervirens enters the system after E.horridum has become established.A neighbor-removal experiment was used to assess the bidirectional interactions between both species,and whether those interactions differed among the life stages of B.sempervirens(seed-lings,juveniles and adults),at the two study sites.Survival,annual crown growth and developmental instability(error in development caused by stress)were the performance indices used to quantify plant responses.Differences in air temperatures and soil nutrient amelioration were evaluated as possible mechanisms of facilitation of E.horridum on B.sempervirens.Important Findings E.horridum enhanced the survival of B.sempervirens seedlings under its crown,whereas,B.sempervirens adults outcompeted E.horridum.Therefore,the invasion of the grasslands by E.horridum facilitated the settlement and expansion of B.sempervirens,pro-moting vegetation succession at the Pyrenees.in addition,climatic differences associated with elevation affected shrub interactions.Under low temperatures at the upper limit of B.sempervirens alti-tudinal range,the presence of E.horridum enhanced the growth of B.sempervirens juveniles.At low elevation,under a milder climate,B.sempervirens exerted a high degree of competition toward E.hor-ridum.An increase in temperatures associated with climate change would benefit B.sempervirens juveniles growth which might affect the successional process because it would increase their competi-tive ability when B.sempervirens juveniles become adults.

Structure changes and succession dynamic of the natural secondary forest after severe fire interference

The structure and dynamic succession law of natural secondary forest after severe fire interference in recent 20 years were studied by adopting the method of deducing time series from the spatial sequence of vegetation in Heihe region, Heilongjiang, China. Two typical and widely distributed forest types in the study area, namely forest type A and forest type B, were selected as study subjects. Forest type A is pure broadleaf forest or broadleaf mixed forest mainly composing of superior Betula platyphylla and Populus davidiana in the area with gradient 〈25°, while forest type B is pure forest or mixed forest composing of superior Quercus mongolica and Betula davurica in the area with gradient 〉25°. Species richness, vegetation coverage, important value, and similarity index of commtmity in different layers （Herb, shrub, small tree, and arbor layers） were investigated and analyzed for the two typical forests. The results show that after fire interference, the species richness and coverage in each layer in forest type A were higher than that in forest type B. Both for forest type A and B, with elapse of post-fire years, the species richness and coverage of herbs and shrubs showed a decline tendency, while those of arbor layer present a rising tendency. Through comparison of the important values of species in each layer and analysis of community structure changes, the dynamic process of post-fire vegetation succession for forest type A and B was separately determined. Post-fire 80 years＇ succession tendency of forest type A is B. platyphylla and Larix gmelinii mixed forest. Its shrub layer is mainly composed of Corylus heterophylla and Vaccinium uliginosum, and herb layer is dominated by Carex tristachya, Athyrium multidentatum, and Pyrola incarnate; whereas, the post-fire 80 years＇ succession of forest type B is Q. mongolica and B. davurica mixed forest. Its shrub layer is mainly composed of lespedeza bicolar and corylus heterophylla and herb layer is dominated by Carex tristachya, Asparagus densiflorus, and Hemerocallis minor.

Spatial-Temporal Changes of Soil Organic Carbon During Vegetation Recovery at Ziwuling, China

To probe the processes and mechanisms of soil organic carbon (SOC) changes during forest recovery, a 150-yearchronosequence study on SOC was conducted for various vegetation succession stages at the Ziwuling area, in the centralpart of the Loess Plateau, China. Results showed that during the 150 years of local vegetation rehabilitation SOC increasedsignificantly (P < 0.05) over time in the initial period of 55-59 years, but slightly decreased afterwards. Average SOCdensities for the 0-100 cm layer of farmland, grassland, shrubland and forest were 4.46, 5.05, 9.95, and 7.49 kg C m-3,respectively. The decrease in SOC from 60 to 150 years of abandonment implied that the soil carbon pool was a sink forCO2 before the shrubland stage and became a source in the later period. This change resulted from the spatially variedcomposition and structure of the vegetation. Vegetation recovery had a maximum effect on the surface (0-20 cm) SOCpool. It. was concluded that vegetation recovery on the Loess Plateau could result in significantly increased sequestrationof atmospheric CO2 in soil and vegetation, which was ecologically important for mitigating the increase of atmosphericconcentration of CO2 and for ameliorating the local eco-environment.

Soil water repellency and influencing factors of Nitraria tangutorun nebkhas at different succession stages

Abstract： Soil water repellency （WR） is an important physical characteristic of soil surface. It is capable of largely influencing the hydrological and geomorphological processes of soil, as well as affecting the ecological processes of plants, such as growth and seed germination, and has thus been a hot topic in recent research around the world. In this paper, the capillary rise method was used to study the soil WR characteristics of Nitraria tangutorun nebkhas. Soil water repellencies at different succession stages of Nitraria tangutorun were investigated, and the relationships between soil WR and soil organic matter, total N, and total P, soil texture, pH, and concentrations of CO32, HCO3-, CI, SO42-, Na~, K~, Ca2~ and Mg2＋ were discussed. Soil WR may be demonstrated at the following nebkhas dune evolvement stages： extremely degraded〉degraded〉stabilized〉well developed〉newly developed〉quick sand. Apart from some soil at the bottom, the WR of other soils （crest and slope of dune） was found to be largest at the topsoil, and decreased as the soil depth increased. The results showed that multiple factors affected soil WR characteristics e.g. WR increased significantly as the contents of soil organic matter and total N increased, but did not change as the total P content increased. Soil texture was a key factor affecting soil WR; soil WR increased significantly as clay content increased, and decreased significantly as sand content increased. Low pH was shown to be more suitable for the occurrence of soil WR. Four cations （Ca2＋, Mg2＋, K＋ and Na＋） and two anions （CI and SO42） enhanced soil WR, while CO32-decreased it. HCO3- did not show any observable effect. Finally, we established a best-fit general linear model （GLM） between soil-air-water contact angle （CA） and influencing factors （CA=5.606 sand＋6.496 （clay and silt）-2.353 pH＋470.089 CQ2＋11.346 Na＋-407.707 Cl--14.245 SO42-＋0.734 total N-519.521 ）. It was concluded that all soils contain subcritical WR （0°〈CA〈90°）. The development and succession of Nitraria tangutorun nebkhas may improve the formation of soil subcritical WR. There exist significant relationships between soils subcritical WR and soil physical or chemical properties.

Soil phosphorus fractions and their availability over natural succession from clear-cut of a mixed broadleaved and Korean pine forest in northeast China

To assess phosphorus(P)status of forest soil under naturally restored vegetation,P fractions in the 10-cm soil layer were quantified at different successional stages on the clear-cut site of mixed broadleaved and Korean pine forest.Four communities of shrub,softwood broad-leaved forest,softwood and hardwood broad-leaved forest,and hardwood broad-leaved forest represented different successional stages.A soil sample from a primary broad-leaved and Korean pine stand was the control.A sequential P fractionation scheme extracted empirically defined pools of P and path analysis used to partition the direct and indirect contribution of soil P fractions to available P.The results show that available P increased significantly with long-term succession,while both sodium bicarbonate-extractable P(NaHCO_(3)-P)and sodium hydroxide-extractable P(NaOHP)fractions were reduced in early successional stages and increased in late stages.Compared to the primary forest,concentrations of P fractions in the four stages significantly decreased except for HCl-P,indicating that soil P supplements over the long-term did not return to primary forest levels.The results of related analysis also showed that NaHCO_(3)-P_(i)levels were significantly related to available phosphorus.According to the path analysis coefficient,NaHCO_(3)-P_(i)exhibited the highest effect on available P among eight P fractions;the indirect effects of other P fractions via NaHCO_(3)-P_(i)were larger than those with other P fractions.Overall,this study suggests that soil P bioavailability gradually improved during natural vegetation restoration on clear-cut sites mainly through the increase of NaHCO_(3)-P,where phosphorous is immediately available,and subsequently available phosphorus Na OH-P.

Effects of Lateral Variation in Vegetation and Basin ‘Dome' Shape on Tropical Lowland Peat Stabilisation in the Kota Samarahan-Asajaya Area, West Sarawak, Malaysia

Field surveys indicate lateral variation in peat humification levels （von Post） in dominantly occurring fibric,fibric to hemic,sapric and hemie to sapric peats across a gradient from the margin towards the centre of tropical lowland peat domes.Cement-peat stabilisation can be enhanced by adding mineral soil fillers （silt,clays and fine sands） obtained from Quaternary floodplain deposits and residual soil （weathered schist）.The unconfined compressive strength （UCS） of the stabilised cement-mineral soil fifler-peat mix increases with the increased addition of selected mineral soil filler.Lateral variation in the stabilised peat strength （UCS） in the top 0 to 0.5 m layer was found from the margin towards the centre of the tropical lowland peat dome.The variations in the UCS of stabilised tropical lowland peats along a gradient from the periphery towards the centre of the peat dome are most likely caused by a combination of factors due to variations in the mineral soil or ash content of the peat and horizontal zonation or lateral variation in the dominant species of the plant assemblages （due to successive vegetation zonation of the peat swamp forest from the periphery towards the centre of the tropical lowland peat dome）.

Changes in vegetation and soil properties during recovery of a subtropical forest in South China

Secondary forests account for a large amount of subtropical forest due to persistent anthropogenic disturbance in China.The interaction between vegetation and soil during recovery process is rather complex and dependent on forest conditions.Understanding how vegetation and soil properties changes and how their relationship develops in secondary forests is key to effective forest restoration and management.Here we explored the patterns of vegetation and soil properties as well as their correlations during forest recovery process in a subtropical forest in south China.Plots of three forest types,i.e.,broadleaf-conifermixedforest,broadleaved forest and old growth stand,were established to represent the recovery stages.The results showed that diversity patterns in the tree,shrub and herb layers were different:in the tree layer the species diversity peaked at the intermediate stage,while in the understory layers it decreased chronologically.Most of the soil factors showed an increasing trend,and different effects of soil factors were found for the three layers as well as for the two spatial scales.Together,our results suggested that vegetation and soil might be interdependent during the recovery course.Further studies are needed on exploring how vegetation interplays with soil at different scales and how nutrient limitations affects the vegetation development in a chronosequence.

Changes of Productivity and Bearing Capacity of Grassland in Arid Zone of Central Ningxia over 20 Years

[Objective] The paper was to explore the vegetation regressive succession law in arid zone of central Ningxia.[Method] Based on the survey data during 1982-2001,the grass type vegetation characteristics,grassland productivity and the quality of grass in 7 survey sites were analyzed.[Result] The grass type in arid zone of central Ningxia had changed or was changing in the last 20 years;the dominant species within communities were also replacing by other species,vegetation coverage and number of plant species within communities were continuously declined,the bearing capacity of grassland had averagely declined by 114%,and the quality of grassland seriously declined.[Conclusion] The study provided basic data for the sustainable use of typical grassland.

Transformation of vegetative cover on the Ustyurt Plateau of Central Asia as a consequence of the Aral Sea shrinkage

The gradual shrinkage of the Aral Sea has led to not only the degradation of the unique environments of the Aral Sea,but also numerous and fast developing succession processes in the neighborhood habitats surrounding the sea.In this study,we investigated the vegetative succession processes related to the Aral Sea shrinkage in the Eastern Cliff of the Ustyurt Plateau in Republic of Uzbekistan,Central Asia.We compared the results of our current investigation(2010–2017)on vegetative communities with the geobotany data collected during the 1970s(1970–1980).The results showed great changes in the mesophytic plant communities and habitat aridization as a result of the drop in the underground water level,which decreased atmospheric humidity and increased the salt content of the soil caused by the shrinkage of the Aral Sea.In the vegetative communities,we observed a decrease in the Margalef index(DMg),which had a positive correlation with the poly-dominance index(I-D).The main indications of the plant communities'transformation were the loss of the weak species,the appearance of new communities with low species diversity,the stabilization of the projective cover of former resistant communities,as well as the appearance of a new competitive species,which occupy new habitats.

Response of soil microorganisms to vegetational succession in Ziwuling Forest

This study investigates the changes in soil microbial populations as vegetational succession progress from abandoned farmland to climax forest in the Ziwuling Forest,which is located in the northern part of the Loess Plateau,China.Different organic C and total extractable N between the fumigated and non-fumigated soils were assumed to be released from soil microorganisms.Soil microbial C was calculated using Kec=0.38 and microbial N was calculated using Ken=0.45.The released P was converted to microbial biomass P using Kep=0.40.Soil bacteria,fungi,and actinomycetes increased as the vegetational succession progressed.Microbial C was of the highest amount in farmland.Microbial C,N,and P generally increased from abandoned land to climax community.The results indicated significant(P<0.05)diversities of soil microbial biomass under different vegetation.There was a significant correlation between microbial biomass and soil nutrients.Knowledge about soil microbial populations is important for forecasting vegetational succession and determining the ecological condition of the environment.

Vegetation and ecosystem carbon recovery following shifting cultivation in MizoramManipur-Kachin rainforest eco-region,Southern Asia

Background:Shifting cultivation(locally known as“jhum”)is a major driver of deforestation and loss of ecosystem services in rainforests.For developing any effective conservation of biodiversity and carbon service program,an indepth understanding to the recovery of vegetation and carbon after abandonment of jhum is essential.We estimated species richness,abundance and composition of trees,shrubs and herbs,carbon distribution in aboveground and belowground components along a chronosequence of jhum fallow in northeast India,and elucidated the factors affecting the recovery processes of jhum fallows.Methods:Species composition and other plant community attributes,carbon storage in different pools were studied in 5 jhum fallows(<5,5-10,11-15,16-20,21-25 years old)and an old-growth forest.The data were subjected to linear mixed effect modeling using R-package“nlme”for identifying the important factors contributing to the recovery of vegetation and carbon.Results:Species composition varied significantly(P<0.05)between jhum fallows and old-growth forest.Tree density varied from 28 stems ha−1 in 5 years old jhum fallow to 163 stems ha−1 in old-growth forest.Both biomass carbon in all components and soil organic carbon were significantly(P=0.01)lower in jhum fallows than in the old-growth forest except living non-woody biomass component.The recovery of aboveground biomass carbon was faster during early successive years than the mid-successive jhum fallows.Total ecosystem carbon and soil organic carbon stock in the oldest jhum fallow was 33%and 62%of those in the old-growth forest,respectively.The fallow age was found to be the most important explanatory factor in the recovery process of vegetation and carbon stock in re-growing fallows.Conclusion:The shifting cultivation fallows gradually recovered both vegetation and carbon and are potential repository sites for biodiversity conservation,which may take much longer time to reach up to old-growth forest in northeast India.

Ecological restoration and recovery in the wind-blown sand hazard areas of northern China: relationship between soil water and carrying capacity for vegetation in the Tengger Desert

The main prevention and control area for wind-blown sand hazards in northern China is about 320000 km2 in size and includes sandlands to the east of the Helan Mountain and sandy deserts and desert-steppe transitional regions to the west of the Helan Mountain.Vegetation recovery and restoration is an important and effective approach for constraining wind-blown sand hazards in these areas.After more than 50 years of long-term ecological studies in the Shapotou region of the Tengger Desert,we found that revegetation changed the hydrological processes of the original sand dune system through the utilization and space-time redistribution of soil water.The spatiotemporal dynamics of soil water was significantly related to the dynamics of the replanted vegetation for a given regional precipitation condition.The long-term changes in hydrological processes in desert areas also drive replanted vegetation succession.The soil water carrying capacity of vegetation and the model for sand fixation by revegetation in aeolian desert areas where precipitation levels are less than 200 mm are also discussed.

Early-Middle Permian palynoflora of Shandong Province,eastern North China

The Permian Taiyuan and Shanxi formations exposed in Shandong Province,eastern North China,contain abundant spores and pollen.In this study,a total of 42 genera and 146 species of spores and pollen from these Permian formations,native to northern China,are identified and related to the three epochs of the Permian Period(Cisuralian,Guadalupian,and Lopingian Epochs)as two assemblages:Assemblage I—the Laevigatosporites-Granulatisporites assemblage,inferred as the Cisuralian(~298.9-272.9 Ma);and,Assemblage II—the Gulisporites-Sinulatisporites assemblage,inferred as the Guadalupian(~272.9-259.1 Ma).Assemblage I represents growing ferns,whereas Assemblage II represents gymnosperms.The assemblage division and analysis indicated that the palaeoclimate of the study area during Early-Middle Permian time was dominated by warm and humid conditions,and later in the Middle Permian changed into moderately dry conditions.

Bracken-induced increase in soil P availability, along with its high P acquisition efficiency, enables it to invade P-deficient meadows

Changes in soil chemistry after invasion by bracken(Pteridium aquilinum)have been studied in heathlands,but comparable studies in meadows are lacking.We investigated if bracken invasion into P-deficient meadows alters the soil nutrient-resource pool,as well as the mechanisms behind it linked to soil processes and bracken nutrition.Furthermore,we investigated how community composition responds to differences in soil chemistry before and after the invasion.Soil and plant material sampling,along with vegetation survey,were performed during bracken peak biomass.Data analyses included analysis of variance and canonical correspondence analysis(CCA).Bracken invasion increased soil P availability,soil organic C concentration,as well as C:N,C:S and N:S ratios,while decreasing Fe and Co concentrations.Bracken pinnae were rich in P,and its rhizomes were rich in K,whereas N:P of pinnae and rhizomes was low.CCA showed contrasting abundance patterns of frequent meadow species related to P and K availability.Holcus lanatus exhibited competitive advantage under extremely low P availability.Increase in P availability under bracken may have occurred through promoting the leaching of Fe and Al.By increasing P availability for its growth and increasing N limitation for other species,bracken can gain a competitive advantage from the soil resource-niche perspective.Its ability to increase soil P availability,along with the physiological mechanisms behind its high P acquisition efficiency,seem to differentiate bracken from other species of competitive ecological strategy,which are mainly confined to nutrient-rich environments.This enabled bracken to invade P-deficient meadows.