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《生态学杂志》2025,44(2)
东北地区作为中国最大的森林分布区;其森林碳储量约占全国的40%。在过去的几十年中;该地区实施了大规模的植树造林及森林恢复工作;但其对碳循环的影响尚不明确。因此;准确预测东北地区未来森林的地上碳储量及固碳潜力对制定东北森林未来管理政策具有重要意义。本研究基于森林清查数据;耦合生态系统过程模型和森林景观模型;模拟未来百年东北地区森林的演替过程及其碳储量动态。同时;本研究通过多源数据（遥感数据、森林清查数据、其他模型结果）对模拟结果进行多尺度验证;提高模型模拟精度;在此基础上估算东北地区森林未来固碳潜力;量化其固碳拐点。结果表明:（1）模型模拟的森林地上碳储量空间分布结果与其他文献基于遥感数据得到的地上碳储量空间分布数据基本一致（Kappa系数=0.81）。此外;模型从林龄角度对模拟结果进行验证;各区域森林及主要树种在各林龄段的比例结果与森林清查数据存在相关性（R2>0.6）。（2）在现行气候条件下;东北地区森林地上碳储量将在2070年达到峰值（6.38 Pg C）;相比2000年森林地上碳储量及碳密度分别增加4.57 Pg C、67.46 Mg·hm-2。（3）在不考虑气候变化和森林经营管理政策的前提下;东北地区森林固碳速率呈现先增后降的趋势;峰值出现在2020—2025年;为0.108 Pg C·a-1;0值出现在2070—2075年;森林将由碳汇转为碳源。 相似文献
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Qualitative validation consists in showing that a model is able to mimic available observed data. In population level biological
models, the available data frequently represent a group status, such as pool testing, rather than the individual statuses.
They are aggregated. Our objective was to explore an approach for qualitative validation of a model with aggregated data and
to apply it to validate a stochastic model simulating the bovine viral-diarrhoea virus (BVDV) spread within a dairy cattle
herd. Repeated measures of the level of BVDV-specific antibodies in the bulk-tank milk (total milk production of a herd) were
used to summarise the BVDV herd status. First, a domain of validation was defined to ensure a comparison restricted to dynamics
of pathogen spread well identified among observed aggregated data (new herd infection with a wide BVDV spread). For simulations,
scenarios were defined and simulation outputs at the individual animal level were aggregated at the herd level using an aggregation
function. Comparison was done only for observed data and simulated aggregated outputs that were in the domain of validation.
The validity of our BVDV model was not rejected. Drawbacks and ways of improvement of the approach are discussed. 相似文献
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树木死亡是多种因素共同作用的结果,然而不同径级的林木,导致其死亡的原因是否相同尚不明确。以坝上地区小叶杨为对象,于2016-2017年调查了100块20m×20m样地。以林木胸径、林木相对断面积、林龄、林分密度、不同土层土壤含水量和土壤容重等11个因子为输入变量,运用随机森林算法分别不同径级建立树木死亡模型,分析各因子对不同径级树木死亡的影响大小,并得到关键影响因子的阈值。结果表明：依据不同径级树木死亡与影响因子的相关性不同,可将林木径级划分为 < 10cm、10-25cm、 > 25cm;胸径 < 10cm时,林木相对断面积对树木死亡的影响最大,当0.23 < 林木相对断面积 < 0.43时,树木死亡率最低;胸径为10-25cm时,密度对树木死亡的影响最大,当密度 > 600株/hm2时,树木死亡率随着密度的增加明显上升;胸径 > 25cm时,20-60cm土壤水分和林分断面积对树木死亡的影响最大且相近,当20-60cm土壤质量含水量 > 5%时,树木死亡率明显下降;基于随机森林算法建立的树木死亡模型可以解释树木死亡70%-90%的变异,具有一定的预测优势和应用价值,可为坝上地区树木死亡预测和防护林的经营管护提供参考。 相似文献
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Accounting for water stress‐induced tree mortality in forest productivity models remains a challenge due to uncertainty in stress tolerance of tree populations. In this study, logistic regression models were developed to assess species‐specific relationships between probability of mortality (Pm) and drought, drawing on 8.1 million observations of change in vital status (m) of individual trees across North America. Drought was defined by standardized (relative) values of soil water content (Ws,z) and reference evapotranspiration (ETr,z) at each field plot. The models additionally tested for interactions between the water‐balance variables, aridity class of the site (AC), and estimated tree height (h). Considering drought improved model performance in 95 (80) per cent of the 64 tested species during calibration (cross‐validation). On average, sensitivity to relative drought increased with site AC (i.e. aridity). Interaction between water‐balance variables and estimated tree height indicated that drought sensitivity commonly decreased during early height development and increased during late height development, which may reflect expansion of the root system and decreasing whole‐plant, leaf‐specific hydraulic conductance, respectively. Across North America, predictions suggested that changes in the water balance caused mortality to increase from 1.1% yr?1 in 1951 to 2.0% yr?1 in 2014 (a net change of 0.9 ± 0.3% yr?1). Interannual variation in mortality also increased, driven by increasingly severe droughts in 1988, 1998, 2006, 2007 and 2012. With strong confidence, this study indicates that water stress is a common cause of tree mortality. With weak‐to‐moderate confidence, this study strengthens previous claims attributing positive trends in mortality to increasing levels of water stress. This ‘learn‐as‐we‐go’ approach – defined by sampling rare drought events as they continue to intensify – will help to constrain the hydraulic limits of dominant tree species and the viability of boreal and temperate forest biomes under continued climate change. 相似文献
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Industrial development in northwesternAustralia is largely concentrated in fiveports involved with resource export. Thispaper examines the distribution ofmangroves in one of these ports and theeffects of harbour development upon them.The hypothesis tested was that developmenthad not had a significant effect on creekerosion rates or mangrove mortality. Avicennia marina (Forsk.) Vierh. dominatedthe mangrove coverage followed by Rhizophora stylosa Griff. Ceriopstagal (Perr.) C.B. Rob., Aegialitisannulata R. Br. and Aegicerascorniculatum (L.) Blanco comprisedslightly more than 2% of the mangroves inthe harbour. Aerial photography was lessuseful than in situ measurements fordiscerning smaller mangrove communities andthe changes associated with creek bankerosion. Erosion rates varied from 0 to2.8 m y-1 and there were fewsignificant differences between creeksadjacent to industrial development andthose far removed from it. It was concludedthat the development within the harbour hasnot significantly impacted on creekerosion. Mangrove mortality was highlyvariable at the landward sites examined andthere was no significant difference betweentree death within and outside the harbour.Recovery of apparently dead trees occurred,possibly due to a reduction in localgroundwater salinity. There was no evidenceto support the hypothesis that harbourdevelopment has adversely affected theaspect of tree health measured in thisstudy. 相似文献
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Gerard J. Kleywegt 《Acta Crystallographica. Section D, Structural Biology》2007,63(9):939-940
Statistical cross‐validation has become an integral part of the model‐refinement process in macromolecular crystallography. However, the test set of reflections, for which the free R value is calculated, is used both to optimize the parameterization of the structure model and to validate the model itself. This practice could introduce bias and diminish the value of Rfree as an independent check of model quality. It is proposed here that by introducing a dormant hold‐out set of reflections, any problems with such bias can be avoided. This procedure requires only a small modification of the standard cross‐validation protocol. 相似文献
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Yitong Yao Philippe Ciais Nicolas Viovy Emilie Joetzjer Jerome Chave 《Global Change Biology》2023,29(3):747-762
During the last two decades, inventory data show that droughts have reduced biomass carbon sink of the Amazon forest by causing mortality to exceed growth. However, process-based models have struggled to include drought-induced responses of growth and mortality and have not been evaluated against plot data. A process-based model, ORCHIDEE-CAN-NHA, including forest demography with tree cohorts, plant hydraulic architecture and drought-induced tree mortality, was applied over Amazonia rainforests forced by gridded climate fields and rising CO2 from 1901 to 2019. The model reproduced the decelerating signal of net carbon sink and drought sensitivity of aboveground biomass (AGB) growth and mortality observed at forest plots across selected Amazon intact forests for 2005 and 2010. We predicted a larger mortality rate and a more negative sensitivity of the net carbon sink during the 2015/16 El Niño compared with the former droughts. 2015/16 was indeed the most severe drought since 1901 regarding both AGB loss and area experiencing a severe carbon loss. We found that even if climate change did increase mortality, elevated CO2 contributed to balance the biomass mortality, since CO2-induced stomatal closure reduces transpiration, thus, offsets increased transpiration from CO2-induced higher foliage area. 相似文献
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We surveyed seven lightning strike sites in the northern Peruvian Amazon. An average of 17.3 trees were damaged per strike; large trees (> 60 cm diameter) were disproportionately affected. The results contribute to a growing body of evidence that lightning is an important agent of disturbance pantropically. Abstract in Spanish is available with online material. 相似文献
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Tree encroachment in fire‐maintained woodlands and grasslands is a major management concern, yet little information exists regarding the mechanisms of small tree mortality following prescribed burns. We sought to clarify the relative importance of tree size and fire‐induced injury in the post‐fire mortality of encroaching Douglas‐fir trees and to compare results with an existing mortality model for larger Douglas‐fir trees. Crown injury to small Douglas‐fir trees was a significant explanatory variable in post‐fire mortality models, with results suggesting a 20% threshold in crown scorch. Crown injury was strongly related to bole injury, and delayed mortality was important as we documented new mortality 20 months post‐burn. Mortality models for large Douglas‐fir tend to over‐predict small tree mortality, underscoring the need to better understand the mechanisms of fire‐caused mortality for small, encroaching trees. 相似文献
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The main objective of this study was to determine the optimal oxytetracycline hydrochloride (OTC) dosage for otolith marking in Dicentrarchus labrax and Diplodus puntazzo. Adult reared individuals of these two species were marked with OTC intraperitoneal injections at three recommended doses (25, 45 and 60 mg kg(-1) fish) and a blank. Fishes were monitored for 36-49 days from when they were marked. The effectiveness of the otolith marking was inversely related to the OTC dosage. The injections were found to have deleterious effects at the highest dosages: (1) mortality was nearly 0% during the first 4 days but then it suddenly rose to 85-100% depending on the fish and treatment, (2) no daily growth increments were formed after marking and (3) no or negative somatic growth was observed. These results suggest that most of the current studies using OTC marking for estimating mortality of wild fishes use an observation period between marking the fishes and releasing that is too short to allow the deleterious effects of OTC to be detected. Species-specific experiments for assessing the long-term mortality should be undertaken when OTC marking is used on wild fishes. 相似文献
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Roderick J. Fensham Michelle E. Freeman Boris Laffineur Harry Macdermott Lynda D. Prior Patricia A. Werner 《Austral ecology》2017,42(7):772-782
Rainfall, fire and competition are emphasized as determinants of the density and basal area of woody vegetation in savanna. The semi‐arid savannas of Australia have substantial multi‐year rainfall deficits and insufficient grass fuel to carry annual fire in contrast to the mesic savannas in more northern regions. This study investigates the influence of rainfall deficit and excess, fire and woody competition on the population dynamics of a dominant tree in a semi‐arid savanna. All individuals of Eucalyptus melanophloia were mapped and monitored in three, 1‐ha plots over an 8.5 year period encompassing wet and dry periods. The plots were unburnt, burnt once and burnt twice. A competition index incorporating the size and distance of neighbours to target individuals was determined. Supplementary studies examined seedling recruitment and the transition of juvenile trees into the sapling layer. Mortality of burnt seedlings was related to lignotuber area but the majority of seedlings are fire resistant within 12 months of germination. Most of the juveniles (≤1 cm dbh) of E. melanophloia either died in the dry period or persisted as juveniles throughout 8.5 years of monitoring. Mortality of juveniles was positively related to woody competition and was higher in the dry period than the wet period. The transition of juveniles to a larger size class occurred at extremely low rates, and a subsidiary study along a clearing boundary suggests release from woody competition allows transition into the sapling layer. From three fires the highest proportion of saplings (1–10 cm dbh) reduced to juveniles was only 5.6% suggesting rates of ‘top‐kill’ of E. melanophloia as a result of fire are relatively low. Girth growth was enhanced in wet years, particularly for larger trees (>10 cm dbh), but all trees regardless of size or woody competition levels are vulnerable to drought‐induced mortality. Overall the results suggest that variations in rainfall, especially drought‐induced mortality, have a much stronger influence on the tree demographics of E. melanophloia in a semi‐arid savanna of north‐eastern Australia than fire. 相似文献
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S. E. Campana 《Journal of fish biology》2001,59(2):197-242
Many calcified structures produce periodic growth increments useful for age determination at the annual or daily scale. However, age determination is invariably accompanied by various sources of error, some of which can have a serious effect on age-structured calculations. This review highlights the best available methods for insuring ageing accuracy and quantifying ageing precision, whether in support of large-scale production ageing or a small-scale research project. Included in this review is a critical overview of methods used to initiate and pursue an accurate and controlled ageing program, including (but not limited to) validation of an ageing method. The distinction between validation of absolute age and increment periodicity is emphasized, as is the importance of determining the age of first increment formation. Based on an analysis of 372 papers reporting age validation since 1983, considerable progress has been made in age validation efforts in recent years. Nevertheless, several of the age validation methods which have been used routinely are of dubious value, particularly marginal increment analysis. The two major measures of precision, average percent error and coefficient of variation, are shown to be functionally equivalent, and a conversion factor relating the two is presented. Through use of quality control monitoring, ageing errors are readily detected and quantified; reference collections are the key to both quality control and reduction of costs. Although some level of random ageing error is unavoidable, such error can often be corrected after the fact using statistical ('digital sharpening)' methods. 相似文献
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Problem: A series of long‐term field experiments is described, with particular reference to monitoring and quality control. This paper addresses problems in data‐management of particular importance for long‐term studies, including data manipulation, archiving, quality assessment, and flexible retrieval for analysis Method: The problems were addressed using a purpose‐built database system, using commercial software and running under Microsoft Windows. Conclusion: The database system brings many advantages compared to available software, including significantly improved quality checking and access. The query system allows for easy access to data sets thus improving the efficiency of analysis. Quality assessments of the initial dataset demonstrated that the database system can also provide general insight into types and magnitudes of error in data‐sets. Finally, the system can be generalised to include data from a number of different projects, thus simplifying data manipulation for meta‐analysis. 相似文献
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Emily K. Roberts;Michael R. Elliott;Jeremy M. G. Taylor; 《Biometrical journal. Biometrische Zeitschrift》2024,66(1):2200324
A common practice in clinical trials is to evaluate a treatment effect on an intermediate outcome when the true outcome of interest would be difficult or costly to measure. We consider how to validate intermediate outcomes in a causally-valid way when the trial outcomes are time-to-event. Using counterfactual outcomes, those that would be observed if the counterfactual treatment had been given, the causal association paradigm assesses the relationship of the treatment effect on the surrogate outcome with the treatment effect on the true, primary outcome. In particular, we propose illness-death models to accommodate the censored and semicompeting risk structure of survival data. The proposed causal version of these models involves estimable and counterfactual frailty terms. Via these multistate models, we characterize what a valid surrogate would look like using a causal effect predictiveness plot. We evaluate the estimation properties of a Bayesian method using Markov chain Monte Carlo and assess the sensitivity of our model assumptions. Our motivating data source is a localized prostate cancer clinical trial where the two survival outcomes are time to distant metastasis and time to death. 相似文献