井冈山中亚热带森林植被碳储量及固碳潜力估算

国内外关于森林碳汇功能的研究集中于热带和温带森林,就中国东部亚热带森林,尤其是中亚热带常绿阔叶林的碳汇功能的研究较为薄弱。该研究选取井冈山国家级自然保护区作为中国中亚热带森林生态系统的典型代表,针对不同森林类型分别设置样地,采用材积源生物量法估算该地区森林生态系统植被碳储量,并以老龄林生态系统碳储量为参考标准,通过计算参考碳储量与基准碳储量之差,估算研究区森林植被的固碳潜力,旨在明确中国中亚热带森林生态系统在全球碳循环中的作用及贡献。研究发现,(1)井冈山自然保护区森林植被总碳储量为1 589 531 t,平均碳密度为7.29 kg·m-2,高于中国及全球中高纬度森林植被平均碳密度。常绿阔叶林植被碳密度最高,为9.25 kg·m-2,其次是针阔叶混交林和常绿落叶阔叶混交林,其植被碳密度分别为8.12和7.83 kg·m-2。(2)各林型老龄林的植被碳密度均高于平均植被碳密度,常绿阔叶林的老龄林植被碳密度最大,达10.53 kg·m-2。(3)研究区森林植被的固碳潜力为182 868 t,常绿阔叶林的植被固碳潜力最大,达74 086 t,其次为常绿落叶阔叶林混交林、暖性针叶林和针阔叶混交林。研究结果表明中国中亚热带森林生态系统具有较高的固碳能力。     

四川省老君山常绿阔叶林乔木碳储量及其分布特征

森林生物碳储量作为森林生态系统碳库的重要组成部分,在全球碳循环中发挥着重要作用。以四川省老君山典型亚热带常绿阔叶林为研究对象,通过外业样地调查与室内实验分析相结合的方法,利用2012年和2015年的植被调查数据,对其乔木层生物量和碳储量进行了计量,分析了乔木层碳储量的空间分配格局,并对不同样地年固碳能力与碳汇潜力进行了探讨。结果表明:老君山亚热带常绿阔叶林在1 500 m处普查样地和1 700 m复查样地的森林乔木层碳储量(以C计)分别为142.95和139.67 t·hm~(-2),乔木年平均固碳增量分别为7.45和7.11 t·hm~(-2),年平均增长率分别为5.83%和5.68%。其中,普查样地的乔木层碳储量、年平均固碳增量、平均年增长率均大于复查样地,显示了老君山亚热带常绿阔叶林具有较强的固碳能力,而且海拔1 500 m处的乔木层在碳蓄积方面占主导优势。另外,海拔1 500 m处常绿阔叶林乔木层碳储量主要存储在树高h≥10m(比例50.54%)和径级10 cm≤d20 cm(比例40.08%)的乔木中,1 700 m处的常绿阔叶林乔木碳储量主要存储在树高5m≤h10 m(比例56.88%)和径级10 cm≤d20 cm(比例48.82%)的乔木中。尤其是老君山常绿阔叶林目前中龄林所占的比重较大,具有较大的碳汇潜力。研究结果可为该地区森林经营管理及碳汇功能评价提供参考。     

井冈山两种典型森林土壤有机碳密度及其影响因素的比较

森林土壤有机碳是土壤有机碳库的重要组成部分,研究森林土壤有机碳及其影响因素对于应对气候变化具有非常重要意义。以井冈山自然保护区两种典型森林类型（常绿阔叶林和人工杉木林）为研究对象,各选取12个样地,对比分析了两种森林土壤有机碳密度的垂直分布特征以及与年均温、年降雨量之间的相关性。结果表明：①常绿阔叶林0-100cm层平均土壤有机碳密度为（25．65±3,27）kg-^2,大于人工杉木林0-100cm层平均土壤有机碳密度为（20．37±3．37）kg·m^2;②常绿阔叶林和人工杉木林土壤有机碳密度均随土壤深度的增加显著减少;③常绿阔叶林与人工杉木林土壤有机碳密度随年均温的变化趋势差异较明显,常绿阔叶林0-100cm层土壤有机碳密度随年均温的上升呈显著增加趋势（P〈0．05）,而人工杉木林随年均温的上升先减小后增加再减小,且变化趋势显著（P〈0．05）;④常绿阔叶林与人工杉木林土壤有机碳密度随年降雨量的变化趋势差异亦明显,常绿阔叶林0-100cm层土壤有机碳密度随年降雨量的增加呈显著减小趋势（P〈O．05）,而人工杉木林随年降雨量的增加先增加后减少再增加,且变化趋势极显著（P〈0．005）;⑤森林土壤有机碳质量分数与土壤容重呈极显著负相关（P〈0．0001）。     

滇中亚高山典型森林生态系统碳储量及其分配特征

同一区域不同植被类型的生长习性、土壤类型、林分立地状况等的差异,可能导致生态系统碳储量的变化。采用标准地调查和生物量实测相结合的方法,对云南省新平县磨盘山国家森林公园5种典型森林类型——华山松(Pinusarmandii)林、云南松(Pinus yunnanensis)林、滇油杉(Keteleeria evelyniana)林、高山栎(Quercus aquifolioides)林和常绿阔叶林各器官(叶、枝、干、皮和根)碳含量、生物量、碳储量及分配特征进行了比较研究,探讨该区域典型森林生态系统碳储量及其分配格局,揭示滇中亚地区各林分植被层的碳源-汇变化和土壤各层碳动态规律。结果表明,(1)5种林分类型各器官碳含量在45.60%～57.60%之间波动,乔木层、灌木层、草本层和凋落物生物量分别占植被层的56.46%～92.28%、1.12%～13.15%、0.003%～2.19%和6.21%～30.26%。各林分类型植被层碳储量大小表现为:华山松常绿阔叶林云南松滇油杉高山栎。(2)5种林分的土壤碳储量随着土层深度的增加而显著降低,主要集中在0～30 cm表土层,占总碳储量的52.6%～79.8%;0～60 cm土壤碳储量大小顺序表现为:滇油杉常绿阔叶林华山松高山栎云南松。(3)5种林分的生态系统碳储量表现为:常绿阔叶林华山松滇油杉云南松高山栎,其中乔木层和土壤层之和占总碳储量的95.1%～99.2%,林下植被层占比较低。华山松、滇油杉和常绿阔叶林生态系统具有较高的碳储量,云南松林和高山栎林植被碳储潜力较大,应通过制定出切实可行的森林管理措施,提高林分质量、增加林分碳密度,发挥其更大碳汇功能。     

几种不同更新的森林群落碳储量结构特征分析

森林更新是维持和扩大森林资源的主要途径,也是森林结构调整、森林可持续经营和构建多功能高效的森林生态系统的过程。在安徽南部的岭南林场,选择了马尾松（Pinus massoniana Lamb）人工林（MP）、杉木（Cunninghamia lanceolata）人工林（CF）、阔叶混交天然次生林（MB）和针阔混交人工次生林（MN）等4种具有典型代表性的森林群落类型,研究了不同更新方式形成的森林群落的碳储量结构特征。结果表明：（1）针阔混交次生林树干生物量密度最大,为（67.32±56.57）mg.hm-2,杉木人工林生物量密度最小,为（43.79±9.13）mg.hm-2,而马尾松树干生物量所占比例最大,为（64.04±1.49）%。阔叶混交次生林碳储量最高,为（126.47±90.75）mg.hm-2;（2）4种群落类型中,阔叶混交林与马尾松群落碳密度最大,分别为95.67和98.21mg.hm-2,杉木群落碳密度最小,为55.41 mg.hm-2。阔叶混交林中的灌木层生物量碳密度最大,为（17.438±24.627）mg hm-2,马尾松林的草本层和枯落层生物量碳密度最高,分别为（1.326±0.431）、（5.517±2.846）mg.hm-2;（3）阔叶混交林群落的地下碳储量最高,为（10.5±9.8）mg.hm-2,群落地下碳储量从大到小的顺序是阔叶混交林〉针阔混交林〉杉木林〉马尾松林。相应的群落地上碳储量从大到小的顺序是阔叶混交林〉针阔混交林〉马尾松林〉杉木林。杉木林根茎比（R/S）最大,为0.21±0.01,杉木林群落中的灌木层根茎比（R/S）最大,为1.61±0.11;（4）在阔叶混交林中,株数密度与乔木层、草本层的碳比例正相关。在杉木林群落中,平均胸径、株数密度与乔木层碳所占比例成负相关。除杉木林群落外,灌木层碳含量之比与胸径及密度等调查因子都呈负相关。     

大兴安岭南部温带山杨天然次生林不同生长阶段生物量及碳储量

基于内蒙古赛罕乌拉森林生态系统定位研究站山杨（Populus davidiana Dode）天然次生林幼龄林、中龄林、近熟林、成熟林及过熟林生物量调查,探讨了不同龄组山杨天然次生林单株木、林分、林下植被和枯落物的生物量及群落碳储量的时空变化规律。结果表明：随林龄的增大,山杨天然次生林木和各器官生物量总体呈增加趋势,树干所占比例增加,中龄林增加尤为明显;林下植被层、枯落物层生物量随林龄增大呈增加趋势。群落总碳储量的空间分布序列是：乔木层〉枯落物层〉林下植被层。幼龄林、中龄林、近熟林、成熟林和过熟林群落的碳储量分别为27.146 6、53.545 1、60.889 8、77.915 8、79.135 3t.hm-2,乔木层碳储量分别为22.206 5、47.215 7、52.056 3、68.445 3、68.773 1 t.hm-2,枯落物层和林下植被层碳储量平均值分别为5.814 4、2.172 7 t.hm-2。乔木层、枯落物层和林下植被层碳储量占总量的平均率分别为86.05%、10.39%和3.57%。研究认为山杨天然次生林群落碳储量随林龄增加的变化规律明显,碳汇潜力巨大;中龄林为碳储量增长迅速期,且持续较长一段时间,是林分管理的关键阶段;自然稀疏有利于促进林木生长,林分碳储量并未随林分密度下降而减小。     

帽峰山森林土壤碳氮随雨季月及土壤深度的时空变化特征

采用森林生态系统定位观测及对比试验方法,对广州帽峰山常绿阔叶林和杉木人工林（16年）土壤（0~90 cm）有机碳、无机碳、总氮及有机氮的雨季月（5—10月）含量动态、垂直梯度变化特征及土壤湿度影响进行了对比观测研究。结果表明：常绿阔叶林及杉木林土壤有机碳、无机碳雨季月的剖面权均含量变化趋势均为倒S型,常绿阔叶林土壤有机碳剖面权均质量分数较相应杉木林大0.14%、土壤无机碳则小0.12%。常绿阔叶林土壤表层0~10、10~30 cm有机碳雨季月含量变差较杉木林分别高出1.83%、0.61%,土壤30~90 cm雨季月含量变差相对较小;常绿阔叶林土壤70~90 cm无机碳含量在5—8月份较高、杉木林则以土壤30~50 cm在5、6及10月含量较高;常绿阔叶林群落土壤0~20 cm的总氮雨季月含量均大于相应杉木林,植被吸收作用影响使土壤20 cm以下层的雨季各月总氮相对较低;常绿阔叶林土壤剖面雨季月无机氮含量随土层深度递减变化显著,即表层0~30 cm受矿化作用影响较大、深层30~90 cm则受植被吸收作用影响较大;而杉木林土壤剖面层无机氮含量则随雨季的月变化显著,5—7月份含量相对较小、8—10月份含量相对较大。常绿阔叶林土壤有机碳、总氮含量随土壤深度的增加均呈幂函数规律的递减,而杉木人工林土壤有机碳随土壤深度的增加呈对数函数规律的递减、土壤总氮含量则随土壤深度的增加呈二次函数规律的递减。在0~10 cm处,土壤有机碳和有机氮含量与土壤湿度呈负相关。     

广东省森林植被碳储量空间分布格局

基于广东省2007年森林资源清查档案数据,采用材积源生物量法,量化广东省森林植被碳储量,研究广东省森林植被碳储量空间分布格局。结果表明,广东省森林植被碳储量为246.35Tg,碳密度为22.96mg·hm-2。受人为干扰和环境因素的影响,广东省森林植被碳储量在不同经济区和流域空间分布格局严重不均。就不同经济区而言,粤北及周边经济区森林植被碳储量最大,达180.22Tg;珠三角经济区次之,为34.60Tg;接着是粤西沿海经济区,为21.49Tg;粤东沿海经济区最小;仅为10.04Tg。在不同流域方面,森林植被碳储量依次为：北江流域〉东江流域〉西江流域〉韩江流域〉其他流域。广东省乔木林碳储量为202.85Tg,以中幼龄林为主,占77.1%;乔木林龄组结构与碳密度近乎成正比关系,存在较大的相关性。     

辽宁省森林植被碳储量及其动态变化

森林是陆地生态系统的主要组成部分,在全球碳循环中起着十分重要的作用。利用1990─2010年间5期的森林资源清查资料,采用森林植被生物量换算因子连续法,估算了辽宁省森林植被碳储量和碳密度,并分析其动态变化。结果表明:在1990─2010年间,辽宁省森林面积增加了17.05×105 hm2,年均增长率为1.70%。辽宁省5次(1989─1993、1994─1998、1999─2003、2004─2008、2009─2013年)森林资源清查期的植被碳储量分别是87.10、100.78、108.04、122.06、141.80 Tg,年均增长率为2.47%,这说明辽宁省森林起着碳汇作用。乔木林、疏林和灌木林、经济林碳储量分别增加50.90、2.97、0.83Tg,碳储量平均年增加量分别为2.55、0.15、0.04 Tg·a-1。在不同植被类型中,阔叶林的碳储量和碳密度均大于针叶林,其中,栎类、杨树及阔叶混交林是阔叶林碳储量的主要贡献者,而在针叶林中,落叶松、油松占主导地位。在不同龄级的乔木林中,幼、中龄林碳储量所占比重大。在现阶段(2010年),辽宁省乔木林碳储量分别为121.49 Tg,碳密度为31.12 Mg·hm-2。幼龄林和中龄林的面积占总面积的73.38%,碳储量占总碳储量的60.12%,其碳密度仅为19.52和36.18 Mg·hm-2,远低于成熟林的碳密度(54.32 Mg·hm-2)。可知现阶段辽宁省森林具有幼龄林和中龄林面积大、林龄小和平均碳密度低的特点,因此随着幼龄林和中龄林的碳密度和碳储量的不断增长,未来辽宁省森林植被的碳汇功能将进一步增强。     

长江流域森林植被碳储量分布特征及动态变化

准确评估区域尺度下森林生态系统固碳能力和趋势,对实现森林可持续经营和固碳增汇具有重要意义。基于全国第四次(1989—1993年)、第五次(1994—1998年)、第六次(1999—2003年)和第七次(2004—2008年) 4次全国森林资源清查数据,结合生物量估算模型和植被含碳系数,研究长江流域森林植被碳储量、碳密度分布特征及动态变化。结果表明,1989—2008年长江流域森林植被碳储量由1 345. 30 Tg增加到1 924. 98 Tg,年均增长率为2. 15%,比全国年均增长率高0. 29百分点,表明该流域森林植被碳汇功能不断增强。长江流域森林植被平均碳密度分别为42. 25、40. 34、41. 00和41. 42 Mg·hm-2。从森林龄组来看,长江流域森林植被碳储量主要集中于幼、中龄林和近熟林,这3者对林分碳汇的贡献超过85%,且幼、中龄林和近熟林碳密度远低于成熟林和过熟林,表明流域森林植被碳汇潜力巨大。从森林起源来看,流域内森林植被碳储量主要分布于天然林,占同期森林植被碳储量的78%以上,但人工林碳储能力不断提高,人工林碳储量占同期森林植被碳储量的比例也呈增加趋势,且碳密度明显低于天然林,表明人工林将在该流域森林植被碳汇功能中扮演重要角色。长江中上游是流域内森林植被碳储量主要贡献区,占全流域森林植被碳储量的96%以上。     

Influences of canopy structure and physiological traits on flux partitioning between understory and overstory in an eastern Siberian boreal larch forest

Boreal forests play an important role in the global balance of energy and CO₂. Our previous study of elaborate eddy covariance observations in a Siberian boreal larch forest, conducted both above the forest canopy and at the forest floor, revealed a significant contribution of latent heat flux (LE) from the cowberry understory to the whole ecosystem LE. Thus, in the present study, we examined what factors control the partitioning of whole ecosystem LE and CO₂ flux into the understory and overstory vegetation, using detailed leaf-level physiology (for both understory and overstory vegetation) and soil respiration property measurements as well as a multilayer soil-vegetation-atmosphere transfer (SVAT) model. The modeling results showed that the larch overstory's leaf area index (LAI) and vertical profile of leaf photosynthetic capacity were major factors determining the flux partitioning in this boreal forest ecosystem. This is unlike other forest ecosystems that tend to have dense LAI. We concluded that control of the larch overstory's LAI had a relationship with both the coexistence of the larch with the cowberry understory and with the water resources available to the total forest ecosystem.     

A simplified approach to implement forest eco-hydrological properties in regional hydrological modelling

The topic of this paper is a simplified model for simulating the hydrological properties of forest stands based on a robust computation of the temporal LAI (leaf area index) dynamics. The approach allows the simulation of all hydrologically relevant processes. It includes interception of precipitation and transpiration of forest stands with and without groundwater in the rooting zone. The model also considers phenology, mortality and simple management practice. It was implemented as a module in the eco-hydrological model SWIM (Soil and Water Integrated Model). The approach was tested on Scots pine (Pinus sylvestris) and common oak (Quercus robur and Q. petraea).The results demonstrate a good simulation of annual biomass increase and LAI and satisfactory simulation of litter production (annual mean value). A comparison of the date of May sprout for Scots pine and leaf unfolding for Oak (1980–1990) with observed data of the DWD (German Weather Service) shows a good reproduction of the temporal dynamic. The daily simulation of transpiration shows an excellent correlation of r = 0.81 for the year 1998 but only r = 0.65 for 1999. The interception losses were also simulated and compared with weekly observed data showing satisfactory results in the vegetation periods and annual sums, but worse agreement in autumn and spring time. A regional assessment study was done in the federal state of Brandenburg (Germany) to test the applicability and multi-criteria evaluation capabilities of the approach on the landscape and catchments scale using forest data, daily river discharge and regional water balance.     

Modeling the effect of photosynthetic vegetation properties on the NDVI--LAI relationship

Developing a relationship between the normalized difference vegetation index (NDVI) and the leaf area index (LAI) is essential to describe the pattern of spatial or temporal variation in LAI that controls carbon, water, and energy exchange in many ecosystem process models. Photosynthetic vegetation (PV) properties can affect the estimation of LAI, but no models integrate the effects of multiple species. We developed four alternative NDVI-LAI models, three of which integrate PV effects: no PV effects, leaf-level effects, canopy-level effects, and effects at both levels. The models were fit to data across the natural range of variation in NDVI for a widespread High Arctic ecosystem. The weight of evidence supported the canopy-level model (Akaike weight, wr = 0.98), which includes species-specific canopy coefficients that primarily scale fractional PV cover to LAI by accounting for the area of unexposed PV. Modeling the canopy-level effects improved prediction of LAI (R2 = 0.82) over the model with no PV effect (R2 = 0.71) across the natural range of variation in NDVI but did not affect the site-level estimate of LAI. Satellite-based methods to estimate species composition, a variable in the model, will need to be developed. We expect that including the effects of PV properties in NDVI-LAI models will improve prediction of LAI where species composition varies across space or changes over time.     

Leaf-area index and light attenuation in rapidly expanding shrub thickets

There is increasing interest in the changes in ecosystem services that accompany the conversion of grasslands to shrub-dominated communities. Shrub structure and associated effects on the light environment may be especially important in affecting productivity and diversity. Leaf-area index (LAI) and understory light levels of Morella cerifera shrub thickets were assessed on Hog Island, Virginia, USA, at four sites along a soil chronosequence. LAI was estimated from annual leaf litter, with allometric models relating stem diameter to leaf area, with a portable integrating radiometer (LI-COR LAI-2000), and from photosynthetically active radiation (PAR) using the Beer-Lambert law. For the two youngest thickets, LAI estimates from leaf litter (approximately 10.0) approached levels often associated with tropical rain forest. Allometric models estimated LAI values at 9.8 and 12.5 for the same thickets. High LAI in thickets also results in high light attenuation. Light levels within thickets were as low as 0.7% of above-canopy PAR in the youngest thicket. These data suggest that M. cerifera shrub thickets have a very high potential for annual net primary production. Furthermore, extreme modification of the light environment, coupled with heavy shrub litter fall, may exclude potential competitors during thicket establishment and rapidly alter community structure and ecosystem function.     

An architectural model of spring wheat: Evaluation of the effects of population density and shading on model parameterization and performance

ADELwheat is an architectural model that describes development of wheat in 3D. This paper analyzes the robustness of the parameterization of ADELwheat for spring wheat cultivars in relation to plant population density and shading. The model was evaluated using data from two spring wheat experiments with three plant population densities and two light regimes. Model validation was done at two levels of aggregation: (a) by comparing parameterization functions used as well as parameter values to the data (leaf and tiller appearance, leaf number, blade dimensions, sheath length, internode length) and (b) by comparing ground cover (GC) and leaf area index (LAI) of simulated virtual wheat plots with GC and LAI calculated from data. A sensitivity analysis was performed by modulating parameters defining leaf blade dimensions and leaf or tiller appearance rate.In contrast to population density, shading generally increased phyllochron and delayed tiller appearance. Both at the level of the organ and at the level of the canopy the model performed satisfactorily. Parameterization functions in the model that had been established previously applied to independent data for different conditions; GC and LAI were simulated adequately at three population densities. Sensitivity analysis revealed that calibration of phyllochron and blade area needs to be accurate to prevent disproportional deviations in output.The robustness of the model parameterization and the simulation performance confirmed that the model is a complete architectural model for aboveground development of spring wheat. It can be used in studies that require simulation of spring wheat structure, such as studies on plant–insect interaction, remote sensing, and light interception.     

Simulation of interannual responses of trembling aspen stands to climatic variation and insect defoliation in western Canada

A carbon-based model has been developed to simulate responses of trembling aspen (Populus tremuloides Michx.) stands to interannual climatic variation and insect defoliation. The model is designed for medium time scale (10–100 years) simulations and requires only daily maximum and minimum temperature and precipitation as meteorological inputs. The modelling approach is similar to FOREST-BGC but includes additional processes known to be important in deciduous forests. These include removal of leaf area during outbreaks of forest tent caterpillar (Malacosoma disstria Hbn.), phenological changes in leaf area index, storage and allocation of non-structural carbohydrate and the contribution of understorey vegetation to evapotranspiration. The model was used for simulations of growth and mortality of biomass carbon in two mature aspen forests located in the climatically dry transition zone between the boreal forest and prairie grassland regions of Saskatchewan, Canada. Model inputs of annual defoliation intensity were based on historic records of insect defoliation and the incidence of light-coloured tree rings in disks or cores collected from aspen at each of the two sites. At both sites, moderately good correlations (r²=0.47–0.54) were obtained between modelled interannual changes in stem carbon growth and observed interannual changes in stem basal area increment obtained from tree-ring analysis. Model outputs of stem biomass carbon were found to be highly sensitive to parameters describing seasonal leaf area duration, insect defoliation intensity, photosynthesis and root respiration and carbohydrate allocation to growth versus storage.     

Modeling cotton (Gossypium spp.) leaves and canopy using computer aided geometric design (CAGD)

The research presented here develops a geometrically accurate model of cotton crop canopies that can be used to explore changes in canopy microenvironment and physiological function with leaf structure. We develop an accurate representation of the leaves, including changes in three-dimensional folding and orientation with age and cultivar. Photogrammetrical analysis of leaf surfaces is used to generate measured points at known positions. Interpolation of points located on the surface of the cotton leaves is then performed with a tensor product interpolants model that generates a generic leaf shape. Dynamic changes in leaf shape and canopy position over the growing season are based on measurements of cotton canopies in the field, and are used to modulate the generic leaf shape. The simulated leaves populate a canopy element based on statistical distributions from measured crop canopies. The simulation is found to give a good representation of cotton canopy leaves, adequately capturing the three-dimensional structure of the leaves and changes in leaf shape and size over the growing season. The simulated canopy accurately estimates leaf area index, except for the earliest measurement period prior to canopy closure. The application of the CAGD algorithm for representing cotton leaf and canopy geometry, and the technique for changing the leaves’ spatial position, size and shape through time of four representative cotton canopies is found to be a useful tool for developing a realistic crop canopy. We use leaf area index (LAI) as a measure of the accuracy of model-predicted LAI values in comparison to LAI in crop canopies in situ, obtaining r² values ranging from 0.82 to 0.92. The level of detail captured in the model could contribute greatly to future studies of physiological function and biophysical dynamics within a crop canopy.     

More asymmetric tree competition brings about more evapotranspiration and less runoff from the forest ecosystems: A simulation study

The present paper reports how stand size-structure dynamics due to competition between different-sized trees affect long-term forested water balance in Japanese cool-temperate planted stands (evergreen coniferous Cryptomeria japonica and deciduous coniferous Larix kaempferi stands) using a fully coupled multi-layered meteorological surface physics—terrestrial ecosystems model. The simulation captured the well-known annual variation in leaf area index (LAI) accurately with stand age in monocultured and even-aged stands; the occurrence of maximum LAI during the early growth stage and then a gradual decline followed by a steady state after the maximum LAI. The simulations also detected a high dependency of annual evapotranspiration (AETr) on LAI with stand age that is well known by prior observational researches. In the C. japonica (shade-tolerant late-successional species) stand, the relationship between annual net primary productivity of an individual tree (NPP_ind) and individual tree mass (w) changed from linear to a convex curve during self-thinning, indicating that the degree of asymmetric tree competition intensified with forest stand development. The higher degree of competitive asymmetry characterized by the convex-shaped NPPind-w relationship produced greater size inequality, i.e., the formation of trees stratified by height. Under such conditions, AETr and annual transpiration (ATr) were mainly regulated by larger trees. On the other hand, the NPPind-w relationships in the L. kaempferi (shade-intolerant early-successional species) stand were linear throughout the simulated period, indicating the lower degree of competitive asymmetry. Under such conditions, the growth of intermediate-sized trees was enhanced and these trees became a dominant source of AETr (and also ATr) during self-thinning. Furthermore, the sensitivity analysis of the effects of ecophysiological parameters such as foliage profile (i.e., vertical distribution of leaf area density) of an individual tree (distribution pattern is described by the parameter η), the maximum carboxylation velocity (V_cmax0) and biomass allocation pattern of individual plant growth (μ₁) on AETr, ATr and annual runoff (AR_off) showed that the temporal trends of AETr, ATr, AR_off and NPPind-w relationships were completely the same as those in the control simulations. However, the NPPind-w relationship during self-thinning indicated higher degrees of competitive asymmetry when η or V_cmax0 were greater than those in the control simulation and generated greater AETr and ATr and thus smaller AR_off. We found that more asymmetric tree competition brings about greater size inequality between different-sized trees and thus more evapotranspiration and less runoff in a forest stand. Overall, our simulation approach revealed that not only LAI dynamics but also plant competition, and thus size-structure dynamics, in a forest ecosystem are essential to long-term future projections of forested water balance.     

垂直面绿化植物遮阳系数与叶面积指数研究

比较、分析了农业研究中提出的叶面积指数LAI与用于建筑节能领域的垂直面绿化植物叶片遮阳系数SCPVW两个概念的异同和各自的应用范围。指出城市绿化采用水平或垂直绿化方式时，由于下垫面差异，植物叶片的遮阳系数应当分别采用LAI和SCPVW进行计算。     

The role of canopy structural complexity in wood net primary production of a maturing northern deciduous forest

The even-aged northern hardwood forests of the Upper Great Lakes Region are undergoing an ecological transition during which structural and biotic complexity is increasing. Early-successional aspen (Populus spp.) and birch (Betula papyrifera) are senescing at an accelerating rate and are being replaced by middle-successional species including northern red oak (Quercus rubra), red maple (Acer rubrum), and white pine (Pinus strobus). Canopy structural complexity may increase due to forest age, canopy disturbances, and changing species diversity. More structurally complex canopies may enhance carbon (C) sequestration in old forests. We hypothesize that these biotic and structural alterations will result in increased structural complexity of the maturing canopy with implications for forest C uptake. At the University of Michigan Biological Station (UMBS), we combined a decade of observations of net primary productivity (NPP), leaf area index (LAI), site index, canopy tree-species diversity, and stand age with canopy structure measurements made with portable canopy lidar (PCL) in 30 forested plots. We then evaluated the relative impact of stand characteristics on productivity through succession using data collected over a nine-year period. We found that effects of canopy structural complexity on wood NPP (NPPw) were similar in magnitude to the effects of total leaf area and site quality. Furthermore, our results suggest that the effect of stand age on NPPw is mediated primarily through its effect on canopy structural complexity. Stand-level diversity of canopy-tree species was not significantly related to either canopy structure or NPPw. We conclude that increasing canopy structural complexity provides a mechanism for the potential maintenance of productivity in aging forests.