Implication of community-level ecophysiological parameterization to modelling ecosystem productivity:a case study across nine contrasting forest sites in eastern China

Parameterization is a critical step in modelling ecosystem dynamics.However,assigning parameter values can be a technical challenge for structurally complex natural plant communities;uncertainties in model simulations often arise from inappropriate model parameterization.Here we compared five methods for defining community-level specific leaf area(SLA)and leaf C:N across nine contrasting forest sites along the North-South Transect of Eastern China,including biomass-weighted average for the entire plant community(AP_BW)and four simplified selective sampling(biomass-weighted average over five dominant tree species[5DT_BW],basal area weighted average over five dominant tree species[5DT_AW],biomass-weighted average over all tree species[AT_BW]and basal area weighted average over all tree species[AT_AW]).We found that the default values for SLA and leaf C:N embedded in the Biome-BGC v4.2 were higher than the five computational methods produced across the nine sites,with deviations ranging from 28.0 to 73.3%.In addition,there were only slight deviations(<10%)between the whole plant community sampling(AP_BW)predicted NPP and the four simplified selective sampling methods,and no significant difference between the predictions of AT_BW and AP_BW except the Shennongjia site.The findings in this study highlights the critical importance of computational strategies for community-level parameterization in ecosystem process modelling,and will support the choice of parameterization methods.

Changes in soil organic carbon contents and fractionations of forests along a climatic gradient in China

Background: Soil organic carbon(SOC) is a large reservoir of terrestrial carbon(C); it consists of different fractions of varying complexity and stability. Partitioning SOC into different pools of decomposability help better predict the trend of changes in SOC dynamics under climate change. Information on how physical fractions and chemical structures of SOC are related to climate and vegetation types is essential for spatial model ing of SOC processes and responses to global change factors.Method: Soil samples were col ected from multiple representative forest sites of three contrasting climatic zones(i.e. cool temperate, warm temperate, and subtropical) in eastern China. Measurements were made on SOC contents and physical fractions of the 0–20 cm soil layer, and the chemical composition of SOC of the 0–5 cm soil layer, along with measurements and compilation of the basic site and forest stand variables. The long-term effects of temperature, litter inputs, soil characteristics and vegetation type on the SOC contents and factions were examined by means of "space for time substitution" approach and statistical analysis.Result: Mean annual temperature(MAT) varied from 2.1 °C at the cool temperate sites to 20.8 °C at the subtropical sites. Total SOC of the 0–20 cm soil layer decreased with increasing MAT, ranging from 89.2 g·kg^(-1) in cool temperate forests to 57.7 g·kg^(-1) in subtropical forests, at an average rate of 1.87% reduction in SOC with a 1 °C increase in MAT.With increasing MAT, the proportions of aromatic C and phenolic C displayed a tendency of decreases, whereas the proportion of alkyl C and A/O-A value(the ratio of alkyl C to the sum of O-alkyl C and acetal C) displayed a tendency of increases. Overall, there were no significant changes with MAT and forest type in either the physical fractions or the chemical composition. Based on the relationship between the SOC content and MAT, we estimate that SOC in the top 20 soil layer of forests potentially contribute 6.58–26.3 Pg C globally to the atmosphere if global MAT increases by 1 °C–4 °C by the end of the twenty-first century, with nearly half of which(cf. 2.87–11.5 Pg C) occurring in the 0–5 cm mineral soils.Conclusion: Forest topsoil SOC content decreased and became chemical y more recalcitrant with increasing MAT,without apparent changes in the physical fractions of SOC.

Reconciliation of research on forest carbon sequestration and water conservation

Carbon sequestration and water conservation are two of the key ecosystem services that forests provide for societal need to address environmental issues.Optimization of the dual services is the ultimate goal in forest management for mitigating global climate change and safeguarding terrestrial water balance.However,there are some tradeoff s between gain in forest productivity and ecosystem water balance.We conducted literature review based on published articles for learned knowledge on forest carbon fi xation and hydrological regulations.Some knowledge gaps and research needs are identifi ed by examining the inter-connections between forest carbon sequestration and water conservation.Past researches have helped gain basic understanding of the mechanisms and controls of forest carbon fi xation and hydrological regulations as two separate issues.Tools and approaches are well established for quantifying and monitoring forest carbon and hydrological issues,operating at diff erent spatial and temporal scales.There are knowledge gaps on how to design aff orestation schemes facilitating enhanced ecosystem services in forest carbon sequestration and water conservation.For the top-down planning of aff orestation in regions where water availability is anticipated to be problematic,the questions of how much and where to plant for given land availability,known environmental implications,and sustained regional development and livelihood need to be addressed.For local management considerations,the questions of what and how to plant prevail.Eff orts are needed in joint studies of forest carbon sequestration and water conservation functionalities,specifi cally in relation to establishment and management of planted forests aiming for delivering regulatory ecosystem services in carbon sequestration,water conservation and other social values.We propose an integrated framework with dual consideration of carbon sequestration and water conservation in forest management for future research pursue.

Assessing the vulnerability of ecosystems to climate change based on climate exposure, vegetation stability and productivity

Background: Global warming has brought many negative impacts on terrestrial ecosystems, which makes the vulnerability of ecosystems one of the hot issues in current ecological research. Here, we proposed an assessment method based on the IPCC definition of vulnerability. The exposure to future climate was characterized using a moisture index(MI) that integrates the effects of temperature and precipitation. Vegetation stability, defined as the proportion of intact natural vegetation that remains unchanged under changing climate, was used together with vegetation productivity trend to represent the sensitivity and adaptability of ecosystems. Using this method, we evaluated the vulnerability of ecosystems in Southwestern China under two future representative concentration pathways(RCP 4.5 and RCP 8.5) with MC2 dynamic global vegetation model.Results:(1) Future(2017–2100) climate change will leave 7.4%(under RCP 4.5) and 57.4% of(under RCP 8.5) of areas under high or very high vulnerable climate exposure;(2) in terms of vegetation stability, nearly 45% of the study area will show high or very high vulnerability under both RCPs. Beside the impacts of human disturbance on natural vegetation coverage(vegetation intactness), climate change will cause obvious latitudinal movements in vegetation distribution, but the direction of movements under two RCPs were opposite due to the difference in water availability;(3) vegetation productivity in most areas will generally increase and remain a low vulnerability in the future;(4) an assessment based on the above three aspects together indicated that future climate change will generally have an adverse impact on all ecosystems in Southwestern China, with non-vulnerable areas account for only about 3% of the study area under both RCPs. However, compared with RCP 4.5, the areas with mid-and highvulnerability under RCP 8.5 scenario increased by 13% and 16%, respectively.Conclusion: Analyses of future climate exposure and projected vegetation distribution indicate widespread vulnerability of ecosystems in Southwestern China, while vegetation productivity in most areas will show an increasing trend to the end of twenty-first century. Based on new climate indicators and improved vulnerability assessment rules, our method provides an extra option for a more comprehensive evaluation of ecosystem vulnerability, and should be further tested at larger spatial scales in order to provide references for regional, or even global, ecosystem conservation works.

A comparison of decomposition dynamics among green tree leaves,partially decomposed tree leaf litter and their mixture in a warm temperate forest ecosystem

Decomposition dynamics were compared among green tree leaves, partially decomposed tree leaf litter （i.e., decayed tree leaf litter on forest floor） and a mixture of the two in a warm temperate forest ecosystem in central China to test the influence of litter chemical quality on the degree of decomposition. The study was conducted in situ at two contrasting forest sites, an oak forest dominated by Quercus aliena var. acuteserrata Maxim., and a mixed pine and oak forest dominated by Pinus armandii Franch. and Q. aliena var. acuteserrata. We found marked differences in the rate of decomposition among litter types at both forest sites; the litter decom- position constant, k, was about 39 % greater at the oak forest site and more than 70 % greater at the pine-oak forest site, for green leaves than for partially decomposed leaf litter. The decomposition dynamics and temporal changes in litter chemistry of the three litter types also greatly differed between the two forest sites. At both forest sites, the higher rate of decomposition for the green leaves was associated with a and lower carbon to N ratio higher nitrogen （N） content （C/N） and acid-unhydrolyz- able residue to N ratio （AUR/N）. We did not find any non- additive effects when mixing green leaves and partially decomposed leaf litter. Our findings support the con- tention that litter chemical quality is one of the most important determinants of litter decomposition in forest ecosystems at the local or regional scale, but the effect of litter chemical quality on decomposition differs between the contrasting forest types and may vary with the stage of decomposition.

Assessing current stocks and future sequestration potential of forest biomass carbon in Daqing Mountain Nature Reserve of Inner Mongolia, China

Assessment of regional forest carbon stocks and underlying controls is critical for guiding forest management in the context of carbon sequestration. We investigated the variations in tree biomass carbon stocks relating to forest types, and estimated the total tree biomass carbon stocks and projected gains through natural stand development by 2020 and 2050 in the Daqing Mountain Nature Reserve based on Category II data of the Forest Inventory of Inner Mongolia for the period ending 2008. Over a total area of 388,577 ha,this nature reserve currently stores an estimated 2221 Gg C in tree aboveground biomass alone, with potential to grow by more than 30 % to reach 2938 Gg C by 2020 and nearly double to 4092 Gg C by 2050 through natural development of the existing forest stands. The tree biomass carbon density and potential gain in tree biomass carbon stocks vary markedly among forest types and with stand development.The variations in the potential change of tree biomass carbon density for the periods 2008–2020 and 2008–2050 among forest types partly reflect the varying relationships of tree biomass carbon density with stand age for different tree species, and partly are attributable to variations in the stand age structure among different forest types. Of the major forest types, the ranking of projected changes in tree biomass carbon density are not consistent with variations in the relationship between tree biomass carbon density and stand age, neither are they explainable by variations in stand age structures, implying the interactive effect between forest type and stand dynamics on temporal changes in tree biomass carbon density. Birch rank highest for future biomass carbon sequestration because of its dominance in cover area and better age structure for potential gain in tree biomass carbon stocks. Poplar and larch were out-performers compared to other forest types given their greater contribution to total tree biomass carbon stocks relative to their distributional areas. Findings in this study illustrate that protection and proper management of under-aged forests can deliver marked gains in biomass carbon sequestration. This is of great importance to policy-makers as well as to scientific communities in seeking effective solutions for adaptive forest management and mitigation of anthropogenic greenhouse gases emissions using forest ecosystems.

Spatially diff erentiated changes in regional climate and underlying drivers in southwestern China

The climate in Southwest China are predominantly under the influences of three contrasting climate systems, namely the East Asian monsoon, the South Asian monsoon, and the westerlies. However, it is unclear if the diversified climate systems, in combination with the complex terrain and varying vegetation types, would result in contrasting patterns of changes in climate across the region. Based on the CRU TS data for the period 1901−2017, we examined the spatiotemporal characteristics of the regional climate, and identified types of climate change patterns and drivers. Overall, the region experienced significant increases in annual mean temperature during 1901−2017, with occurrence of a significant turning point in 1954 for a more pronounced warming (0.16 ℃/10 a). The annual precipitation fluctuated greatly over the study period without apparent trend, albeit the occurrence of a significant turning point in 1928 for a slight increase in the later period (1.19 mm/10 a). Spatially the multi-year averages of selective climate variables during 1901–2017 displayed a trend of decreases from southeast to northwest, but with increasing variability. We identified five major climate change types across the study region, including warmer (T^(+)), drier (P^(−)), warmer-drier (T^(+)P^(−)), warmer-wetter (T^(+)P^(+)), and no significant changes (NSC). The type T^(+)P^(+) mainly occurred in the western parts over the plateau sub-frigid semiarid ecozone (77.0%) and the plateau sub-frigid semihumid ecozone (19.9%). The central parts of the region are characterized by the type T^(+), corresponding to six ecozones, including the mid-subtropical humid ecozone (33.1%), the plateau temperate humid-semihumid ecozone (28.8%), the plateau sub-rigid semihumid ecozone (9.5%), the southern subtropical humid ecozone (8.1%), the plateau sub-frigid arid ecozone (7.3%), and the plateau temperate semiarid ecozone (6.6%). No significant change in climate was detected for the eastern parts over the mid-subtropical humid ecozone (67.3%), the plateau temperate humid and semihumid ecozone (19.5%) and the plateau sub-frigid semihumid ecozone (8.8%). The types P^(−) and T^(+)P^(−) together accounted for less than 5% of the entire study region, which predominantly occurred in central Yunnan-Guizhou Plateau and south of the southeastern Xizang, corresponding predominantly to the mid-subtropical humid ecozone. Across the region and within the zonal climate change types, vegetation and topography both played a significant role in determining the climate variability and magnitude of changes. Our results suggest that the southwestern China experienced intensified influences of the southeasterly monsoon and the southerly monsoon in the regional climate, while the westerly alpine influences subsided;topography and vegetation affected the magnitudes of the directional changes in climate at a local scale.

Carbon sequestration of Chinese forests from 2010 to 2060:spatiotemporal dynamics and its regulatory strategies

Forestation is important for sequestering atmospheric carbon,and it is a cost-effective and nature-based solution(NBS)for mitigating global climate change.Here,under the assumption of forestation in the potential plantable lands,we used the forest carbon sequestration(FCS)model and field survey involving 3365 forest plots to assess the carbon sequestration rate(CSR)of Chinese existing and new forestation forests from 2010 to 2060 under three forestation and three climate scenarios.Without considering the influence of extreme events and human disturbance,the estimated average CSR in Chinese forests was 0.358±0.016 Pg C a^(-1),with partitioning to biomass(0.211±0.016 Pg C a^(-1))and soil(0.147±0.005 Pg C a^(-1)),respectively.The existing forests account for approximately 93.5%of the CSR,which will peak near 2035,and decreasing trend was present overall after 2035.After 2035,effective tending management is required to maintain the high CSR level,such as selective cutting,thinning,and approximate disturbance.However,new forestation from 2015 in the potential plantable lands would play a minimal role in additional CSR increases.In China,the CSR is generally higher in the Northeast,Southwest,and Central-South,and lower in the Northwest.Considering the potential losses through deforestation and logging,it is realistically estimated that CSR in Chinese forests would remain in the range of 0.161–0.358 Pg C a^(-1) from 2010 to 2060.Overall,forests have the potential to offset 14.1%of the national anthropogenic carbon emissions in China over the period of 2010–2060,significantly contributing to the carbon neutrality target of 2060 with the implementation of effective management strategies for existing forests and expansion of forestation.

Soil microbial biomass carbon and nitrogen in forest ecosystems of Northeast China:a comparison between natural secondary forest and larch plantation

Aims Natural secondary forest(NSF)and larch plantation are two of the predominant forest types in Northeast China.However,how the two types of forests compare in sustaining soil quality is not well understood.This study was conducted to determine how natural secondary forest and larch plantation would differ in soil microbial biomass and soil organic matter quality.Methods Microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),soil organic carbon(SOC)and total nitrogen(TN)in the 0-to 15-cm and 15-to 30-cm soil layers were investigated by making chemical and biological measurements in the montane region of eastern Liaoning Province,Northeast China,during the growing season of 2008 in stands of NSF and Larix olgensis plantation(LOP).Important Findings We found that soil MBC and MBN were significantly lower in the LOP than in the NSF.Both MBC and MBN declined significantly with increasing soil depth in the two types of stands.The ratios of MBC to SOC(MBC/SOC)and MBN to TN(MBN/TN)were also significantly lower in the LOP than in the NSF.Moreover,the values of MBC,MBC/SOC,and MBN/TN significantly varied with time and followed a similar pattern during the growing season,all with an apparent peak in summer.Our results indicate that NSF is better in sustaining soil microbial biomass and nutrients than larch plantation in the temperate Northeast China.This calls for cautions in large-scale conversions of the native forests to coniferous plantations as a forest management practice on concerns of sustaining soil productivity.

Changes in soil microbial biomass and community structure with addition of contrasting types of plant litter in a semiarid grassland ecosystem

Aims Elevated atmospheric CO_(2)has the potential to enhance the net primary productivity of terrestrial ecosystems.However,the role of soil microorganisms on soil C cycling following this increased available C remains ambiguous.This study was conducted to determine how quality and quantity of plant litter inputs would affect soil microorganisms and consequently C turnover.Methods Soil microbial biomass and community structure,bacterial community-level physiological profile,and CO_(2)emission caused by different substrate C decomposition were investigated using techniques of biological measurements,chemical and stable C isotope analysis,and BIOLOG-ECO microplates in a semiarid grassland ecosystem of northern China in 2006 and 2007 by mixing three contrasting types of plant materials,C_(3)shoot litter(SC_(3)),C_(3)root litter(RC_(3)),and C4 shoot litter(SC4),into the 10-to 20-cm soil layer at rates equivalent to 0(C0),60(C60),120(C120)and 240 g C m
2(C240).Important Findings Litter addition significantly enriched soil microbial biomass C and N and resulted in changes in microbial structure.Principal component analysis of microbial structure clearly differentiated among zero addition,C_(3)-plant-derived litter,and C4-plant-derived litter and among shoot-and root-derived litter of C_(3)plants;soilmicroorganismsmainly utilized carbohydrates without litter addition,carboxylic acids with C_(3)-plant-derived litter addition and amino acidswith C4-plant-derived litter addition.We also detected stimulated decomposition of older substratewith C4-plant-derived litter inputs.Our results showthat both quality and quantity of belowground litter are involved in affecting soil microbial community structure in semiarid grassland ecosystem.

Contrasting responses of net primary productivity to inter-annual variability and changes of climate among three forest types in northern China

Aims A lack of explicit information on differential controls on net primary productivity(NPP)across regions and ecosystem types is largely responsible for uncertainties in global trajectories of terrestrial carbon balance with changing environment.The objectives of this study were to determine how NPP of different forest types would respond to inter-annual variability of climate and to examine the responses of NPP to future climate change scenarios across contrasting forest types in northern China.Methods We investigated inter-annual variations of NPP in relation to climate variability across three forest types in northern China,including a boreal forest dominated by Larix gmelinii Rupr.,and two temperate forests dominated by Pinus tabulaeformis Carr.and Quercus wutaishanica Mayr.,respectively,and studied the responses of NPP in these forests to predicted changes in climate for the periods 2011–40,2041–70 and 2070–100 under carbon emission scenarios A2 and B2 of Intergovernmental Panel on Climate Change.We simulated the responses of NPP to predicted changes in future climate as well as inter-annual variability of the present climate with the Biome-BGC version 4.2 based on site-and species-specific parameters.The modeled forest NPP data were validated against values in literature for similar types of forests and compared with inter-annual growth variations reflected by tree-ring width index(RWI)at the study sites.Important Findings Inter-annual variations in modeled NPP during the period 1960–06 were mostly consistent with the temporal patterns in RWI.There were contrasting responses of modeled NPP among the three forest types to inter-annual variability of the present climate as well as to predicted changes in future climate.The modeled NPP was positively related to annual mean air temperature in the L.gmelinii forest(P<0.001),but negatively in the P.tabulaeformis forest(P=0.05)and the Q.wutaishanica forest(P=0.03),while the relationships of modeled NPP with annual precipitation for the three forest types were all positive.Multiple stepwise regression analyses showed that temperature was a more important constraint of NPP than precipitation in the L.gmelinii forest,whereas precipitation appeared to be a prominent factor limiting the growth in P.tabulaeformis and Q.wutaishanica.Model simulations suggest marked,but differential increases in NPP across the three forest types with predicted changes in future climate.

Variations in leaf litter decomposition across contrasting forest stands and controlling factors at local scale

Aims litter decomposition is a critical pathway linking the above-and belowground processes.However,factors underlying the local spatial variations in forest litter decomposition are still not fully addressed.We investigated leaf litter decomposition across con-trasting forest stands in central China,with objective to determine the spatial variations and controlling factors in forest floor leaf lit-ter decomposition in relation to changes in forest stands in a tem-perate forest ecosystem.Methods leaf litter decomposition was studied by using litterbag method across several typical forest stand types in baotianman Nature reserve,central China,including pure stands of Quercus aliena var.acuteserrata,Q.glandulifera var.brevipetiolata and Q.vari-abilis,respectively,and mixed pine/oak stands dominated by Pinus armandii and Q.aliena var.acuteserrata,as well as stands of pure Q.aliena var.acuteserrata trees ranging in stand age from~40 to>160 years.measurements were made on litter mass remaining and changes in litter chemistry during decomposition over a 2-year period,along with data collections on selective biotic and environmental factors.a reciprocal transplant experiment involv-ing Q.aliena var.acuteserrata and Q.variabilis was concurrently carried out to test the occurrence of‘home-field advantage(HFa)’in local forests when only considering contrasting oak tree spe-cies.Correlation analyses and path analyses were performed to identify the dominant drivers and their relative contributions to variations in leaf litter decomposition.Important findingssignificant variations were found in the rate of leaf litter decomposi-tion among stands of different tree species but not among stand age classes.The values of decay constant,k,varied from 0.62 in Q.aliena var.acuteserrata stands to 0.56 in Q.variabilis stands.The reciprocal litter transplant experiment showed that the rate of leaf litter decom-position was on average 5%slower in home-fields than on recipro-cal sites.Path analysis identified litter acid-unhydrolyzable residue(AUR)to N ratio,soil microbial biomass carbon(MBC),soil pH and soil organic carbon(SOC)as most prominent factors controlling the rate of leaf litter decomposition,collectively accounting for 57.8%of the variations;AUR/N had the greatest negative effect on k value,followed by weaker positive effects of SOC and MBC.our findings suggest that tree species plays a primary role in affecting forest floor leaf litter decomposition by determining the litter quality,with site environment being a secondary factor contributing to the local vari-ations in leaf litter decomposition in this temperate forest ecosystem.

Application of two remote sensing GPP algorithms at a semiarid grassland site of North China

Estimation of gross primary production(GPP)from remote sensing data is an important approach to study regional or global carbon cycle.However,for a given algorithm,it usually has its limitation on applications to a wide range of vegetation types and/or under diverse environmental conditions.This study was conducted to compare the performance of two remote sensing GPP algorithms,the MODIS GPP and the vegetation photosynthesis model(VPM),in a semiarid temperate grassland ecosystem.Methods The study was conducted at a typical grassland site in Ujimuqin of Inner Mongolia,North China,over 2 years in 2006 and 2007.Environmental controls on GPP measured by the eddy covariance(EC)technique at the study site were first investigated with path analysis of meteorological and soil moisture data at a daily and 8-day time steps.The estimates of GPP derived from the MODIS GPP and the VPM with site-specific inputs were then compared with the values of EC measurements as ground truthing at the site.Site-specific emax(a)was estimated by using rectangular hyperbola function based on the 7-day flux data at 30-min intervals over the peak period of the growing season(May to September).Important Findings Between the two remote sensing GPP algorithms and various estimates of the fraction of absorbed photosynthetic active radiation(FPAR),the VPM based on FPAR derived from the enhanced vegetation index(EVI)works the best in predicting GPP against the ground truthing of EC GPP.A path analysis indicates that the EC GPP in this semiarid temperate grassland ecosystem is controlled predominantly by both soil water and temperature.The site water condition is slightly better simulated by the moisture multiplier in the VPM than in the MODIS GPP algorithm,which is a most probable explanation for a better performance of the VPM than MODIS GPP algorithm in this semiarid grassland ecosystem.

A test of BIOME-BGC with dendrochronology for forests along the altitudinal gradient of Mt. Changbai in northeast China

Aims Process-based models are basic tools for predicting the response of forest carbon to future climate change.The models have commonly been tested for their predictions of spatial variation in forest produc-tivity,but much less for their ability to predict temporal variation.Here,we explored methods to test the models with tree rings,using BIOME-BGC as an example.Methods We used net primary productivity(NPP)data and tree rings col-lected from five major forest types along the altitudinal gradient of Mt.Changbai,northeast China,to test local-parameterized BIOME-BGC model.We first test the model’s predictions of both spatial(Test 1)and temporal changes(Test 2)in productivity.Then we test if the model can detect the climatic factors limiting forest productiv-ity during historical climate change,as revealed by dendroclimatic analyses(Test 3).Important Findings Our results showed that BIOME-BGC could well simulate NPP of five forest types on Mt.Changbai,with an r^(2) of 0.69 between mod-eled and observed NPP for 17 plots along the altitudinal gradient(Test 1).Meanwhile,modeled NPP and ring-width indices were cor-related and showed similar temporal trends for each forest type(Test 2).While these tests suggest that the model’s predictions on spatial and temporal variation of NPP were acceptable,a further test that relate the correlations of modeled NPP with climate variables to the correlations of ring widths with climate(Test 3)showed that the model did not well identify the climatic factors limiting historical productivity dynamics for some forest types,and thus cannot reli-ably predict their future.Both dendrochronology and BIOME-BGC showed that forest types differed markedly in the climate factors limiting productivity because of differences in tree species and cli-mate condition,and thus differed in responses to climate change.Our results showed that a successful prediction of spatial NPP pat-terns cannot assure that BIOME-BGC can well simulate histori-cal NPP dynamics.Further,a correlation between modeled NPP and tree-ring series cannot assure that the limiting climatic factors for productivity have been correctly identified by the model.Our results suggest the necessity to test the temporal predictions of pro-cess-based models in a more robust way,and further integration of dendrochronology and biogeochemistry modeling may be helpful for this purpose.

A comparison of species composition and stand structure between planted and natural mangrove forests in Shenzhen Bay,South China

Aims For assisting faster restoration of damaged or severely disturbed coastal ecosystems,selected mangrove species have been planted on previously mangrove-inhabited sites of the tropical and subtropical coasts of southern China.The objective of this study was to understand the stand dynamics of the planted mangroves and their functional traits in comparison with natural mangrove forests under similar site conditions.Methods Species composition,stand density,tree size distribution,and aboveground production were investigated along three transects in a 50-year-old planted mangrove stand and three transects in an adjacent natural mangrove stand in Shenzhen Bay,South China.Measurements were made on tree distribution by species,stand structure,and aboveground biomass(AGB)distribution.Analyses were performed on the spatial patterns of tree size distribution and species association.Important Findings We found that the planted and natural mangrove stands did not differ in stand density,average diameter at breast height(DBH),species composition,and AGB.Spatial distribution of AGB and frequency at species level were also similar between the planted and natural stands.However,the traits in stand structure were more variable in the planted stand than in the natural stand,indicating higher spatiotemporal heterogeneity in the development and succession of planted mangroves.Geostatistical analyses show that both DBH and AGB were spatially auto-correlated within a specific range in the direction perpendicular to coastline.More than 60%of the variance in these attributes was due to spatial autocorrelation.The Ripley’s K-function analysis shows that the two dominant species,Kandelia obovata and Avicennia marina,clumped in broader scales in the natural stand than in the planted stand and displayed significant interspecific competition across the whole transect.It is suggested that interspecific competition interacts with spatial autocorrelation as the underlying mechanism shaping the mangrove structure.This study demonstrates that at age 50,mangrove plantations can perform similarly in stand structure,spatial arrangement of selected stand characteristics and species associations to the natural mangrove forests.

Parameter uncertainty and identifiability of a conceptual semi-distributed model to simulate hydrological processes in a small headwater catchment in Northwest China

Introduction:Conceptual hydrological models are useful tools to support catchment water management.However,the identifiability of parameters and structural uncertainties in conceptual rainfall-runoff modeling prove to be a difficult task.Here,we aim to evaluate the performance of a conceptual semi-distributed rainfall-runoff model,HBV-light,with emphasis on parameter identifiability,uncertainty,and model structural validity.Results:The results of a regional sensitivity analysis(RSA)show that most of the model parameters are highly sensitive when runoff signatures or combinations of different objective functions are used.Results based on the generalized likelihood uncertainty estimation(GLUE)method further show that most of the model parameters are well constrained,showing higher parameter identifiability and lower model uncertainty when runoff signatures or combined objective functions are used.Finally,the dynamic identifiability analysis(DYNIA)shows different types of parameter behavior and reveals that model parameters have a higher identifiability in periods where they play a crucial role in representing the predicted runoff.Conclusions:The HBV-light model is generally able to simulate the runoff in the Pailugou catchment with an acceptable accuracy.Model parameter sensitivity is largely dependent upon the objective function used for the model evaluation in the sensitivity analysis.More frequent runoff observations would substantially increase the knowledge on the rainfall-runoff transformation in the catchment and,specifically,improve the distinction of fast surface-near runoff and interflow components in their contribution to the total catchment runoff.Our results highlight the importance of identifying the periods when intensive monitoring is critical for deriving parameter values of reduced uncertainty.