Forest responses to simulated elevated CO2 under alternate hypotheses of size‐ and age‐dependent mortality

Elevated atmospheric carbon dioxide (eCO₂) is predicted to increase growth rates of forest trees. The extent to which increased growth translates to changes in biomass is dependent on the turnover time of the carbon, and thus tree mortality rates. Size‐ or age‐dependent mortality combined with increased growth rates could result in either decreased carbon turnover from a speeding up of tree life cycles, or increased biomass from trees reaching larger sizes, respectively. However, most vegetation models currently lack any representation of size‐ or age‐dependent mortality and the effect of eCO₂ on changes in biomass and carbon turnover times is thus a major source of uncertainty in predictions of future vegetation dynamics. Using a reduced‐complexity form of the vegetation demographic model the Functionally Assembled Terrestrial Ecosystem Simulator to simulate an idealised tropical forest, we find increases in biomass despite reductions in carbon turnover time in both size‐ and age‐dependent mortality scenarios in response to a hypothetical eCO₂‐driven 25% increase in woody net primary productivity (wNPP). Carbon turnover times decreased by 9.6% in size‐dependent mortality scenarios due to a speeding up of tree life cycles, but also by 2.0% when mortality was age‐dependent, as larger crowns led to increased light competition. Increases in aboveground biomass (AGB) were much larger when mortality was age‐dependent (24.3%) compared with size‐dependent (13.4%) as trees reached larger sizes before death. In simulations with a constant background mortality rate, carbon turnover time decreased by 2.1% and AGB increased by 24.0%, however, absolute values of AGB and carbon turnover were higher than in either size‐ or age‐dependent mortality scenario. The extent to which AGB increases and carbon turnover decreases will thus depend on the mechanisms of large tree mortality: if increased size itself results in elevated mortality rates, then this could reduce by about half the increase in AGB relative to the increase in wNPP.     

Climate change fingerprints in recent European plant phenology

A paper published in Global Change Biology in 2006 revealed that phenological responses in 1971–2000 matched the warming pattern in Europe, but a lack of chilling and adaptation in farming may have reversed these findings. Therefore, for 1951–2018 in a corresponding data set, we determined changes as linear trends and analysed their variation by plant traits/groups, across season and time as well as their attribution to warming following IPCC methodology. Although spring and summer phases in wild plants advanced less (maximum advances in 1978–2007), more (~90%) and more significant (~60%) negative trends were present, being stronger in early spring, at higher elevations, but smaller for nonwoody insect‐pollinated species. These trends were strongly attributable to winter and spring warming. Findings for crop spring phases were similar, but were less pronounced. There were clearer and attributable signs for a delayed senescence in response to winter and spring warming. These changes resulted in a longer growing season, but a constant generative period in wild plants and a shortened one in agricultural crops. Phenology determined by farmers’ decisions differed noticeably from the purely climatic driven phases with smaller percentages of advancing (~75%) trends, but farmers’ spring activities were the only group with reinforced advancement, suggesting adaptation. Trends in farmers’ spring and summer activities were very likely/likely associated with the warming pattern. In contrast, the advance in autumn farming phases was significantly associated with below average summer warming. Thus, under ongoing climate change with decreased chilling the advancing phenology in spring and summer is still attributable to warming; even the farmers’ activities in these seasons mirror, to a lesser extent, the warming. Our findings point to adaptation to climate change in agriculture and reveal diverse implications for terrestrial ecosystems; the strong attribution supports the necessary mediation of warming impacts to the general public.     

Species richness,abundance and diversity of ichneumonid wasps in Japanese beech forests impacted by sika deer and sawfly herbivory

We investigated the community structure of ichneumonid wasps inhabiting beech forests at six sites in the Tanzawa Mountains of Japan under different magnitudes of impact by sika deer Cervus nippon and beech sawfly Fagineura crenativora on vegetation. Using yellow flight-interception traps, we captured 2,528 ichneumonid wasps representing 367 species in 23 subfamilies. The number of species at each site ranged from 77 to 136 and approximately 80% of these were low-density species (i.e. only one to two individuals captured per site). The number of individuals at each site ranged from 248 to 897, and the percentage of the beech sawfly parasitoids varied widely from 1% to 57%. The numbers of species in parasitoid groups categorized according to their hosts, that is, sawfly (not including the beech sawfly), Lepidoptera, woodborer, fungivore or the others, did not greatly differ among the study sites. Parasitoids attacking herbivorous insects exceeded others in species richness and abundance at all sites. Six sites were classified into four groups in terms of abundance of the host groups when excluding the parasitoids of the beech sawfly, but into only two groups when including these parasitoids. Species diversity and evenness were the highest at the least impacted site even if the beech sawfly parasitoids were excluded from calculation. We suggested some environmental factors, such as groundcover vegetation, abundance of the beech sawfly and structure and age of forest stands, that could have affected the community structure of ichneumonid wasps in the beech forests.     

Life cycle of an endangered riffle beetle,Leptelmis gracilis Sharp (Coleoptera: Elmidae), in the Hiikawa River system,Shimane prefecture,Japan

We studied the life cycle of the riffle beetle Leptelmis gracilis Sharp, 1888 from a population located in a river stream with lotic environments. Samples were collected monthly, between September 2018 and August 2019, from a tributary of the Hiikawa River in Izumo city, Shimane Prefecture, Honshu, Japan. Larvae were separated into five distinct groups based on size. The first and last instar larval sizes were identified through rearing methods. From these results, we determined that the larval stage of this species consists of five instars. From the monthly evaluations, the number of individuals corresponding to each instar period suggested that last-instar larvae were dominant in May and that new adults emerged from July to August. Landing and pupation were estimated to occur from May to June. Monthly observations revealed that mature eggs were present in the female abdomen from April to June, as well as from August to September. It is, therefore, predicted that overwintering adults mainly oviposit from spring to early summer, while new adults oviposit from late summer to early autumn.     

上海城市近自然森林的重建动态

近自然森林作为城市植被恢复的重要模式,已在我国多地开展了实践,并衍生了新的造林模式。为评估不同近自然森林建设模式的群落恢复进程,本研究以上海城市裸地上重建的近自然森林为对象,通过长期监测两处分别应用原"宫胁法"与新"异龄复层落叶—常绿混交林"种植模式的近自然森林重建过程,从物种组成、垂直结构、生活型组成和目标恢复物种4个方面解析恢复动态。结果表明:两种造林模式恢复的近自然森林,随恢复进程其物种组成逐渐趋同,在十多年内已形成了落叶—常绿垂直混交结构;"异龄复层落叶—常绿混交林"造林模式可更好地促进常绿阔叶树种的恢复,尤其是常绿建群种红楠与小叶青冈。本研究证实了近自然森林恢复技术可以缩短亚热森林群落向演替后期发展的时间,以及新造林模式的有效性,为近自然森林技术的应用与实施提供了科学依据。     

林火干扰对广东省桉树林生态系统碳密度的影响

林火作为森林非连续的生态因子,引起森林生态系统碳库碳储量与碳分配的变化,影响森林演替进程及固碳能力。以桉树林不同林火干扰强度的火烧迹地为对象,采用相邻样地比较法,以野外调查采样与室内试验分析相结合为主要手段,研究不同林火干扰强度对森林生态系统各碳库及生态系统碳密度变化和空间分布格局的影响,探讨林火干扰对生态系统碳密度与碳分布格局的影响机制。结果表明:林火干扰降低了植被碳密度(P<0.05),轻度、中度和重度林火干扰样地植被碳密度依次为67.88、35.68和15.50 t·hm^-2,相比对照分别下降了15.86%、55.78%和80.79%;在轻度、中度和重度林火干扰样地中,凋落物碳密度分别为1.43、0.94和0.81 t·hm^-2,相比对照分别降低了28.14%、52.76%和59.30%;不同林火干扰强度样地土壤有机碳密度均低于对照,且减少幅度随土壤剖面深度增加而逐渐变小,轻度、中度和重度林火干扰样地土壤有机碳密度分别为103.30、84.33和70.04 t·hm^-2,相比对照分别下降了11.67%、27.89%和40.11%;轻度、中度和重度林火干扰后桉树林生态系统碳密度分别为172.61、120.95和86.35 t·hm^-2,相比对照依次下降了13.53%、39.41%和56.74%;林火干扰降低了桉树林的碳密度,表现为随林火干扰强度增加,碳密度呈递减的规律;与对照相比,轻度林火干扰强度对桉树林碳密度的影响不显著(P>0.05),而中度和重度林火干扰强度对桉树林碳密度的影响差异显著(P<0.05)。     

中国植被分类系统修订方案

为了推动《中国植被志》研编工作, 该文回顾了中国植被分类系统的发展过程和主要阶段性成果, 提出了作为《中国植被志》研编技术框架组成部分的中国植被分类系统修订方案, 对各植被型组及各植被型进行了简单定义和描述, 并针对中国植被分类系统若干问题, 特别就中国植被分类系统总体框架、混交林的界定以及土壤在植被分类中的重要性等问题进行了讨论。1960年侯学煜在《中国的植被》中首次提出了中国植被分类的原则和系统, 1980年出版的《中国植被》制定了分类等级和划分依据等更加完善的系统, 之后《中国植被及其地理格局——中华人民共和国1:1 000 000植被图说明书》和《中国植物区系与植被地理》以及很多省区的植被专著对该系统进行过修订。2017年宋永昌在《植被生态学》中提出了一个分类等级单位调整的方案。本次提出的中国植被分类系统修订方案基本沿用《中国植被》的植被分类原则、分类单位及系统, 采用“植物群落学-生态学”分类原则, 主要以植物群落特征及其与环境的关系作为分类依据, 包含三级主要分类单位, 即植被型(高级单位)、群系(中级单位)和群丛(低级单位); 在三个主要分类单位之上分别增加辅助单位植被型组、群系组和群丛组, 在植被型和群系之下主要根据群落的生态差异和实际需要可再增加植被亚型或亚群系。修订方案包含了森林、灌丛、草本植被(草地)、荒漠、高山冻原与稀疏植被、沼泽与水生植被(湿地)、农业植被、城市植被和无植被地段9个植被型组, 划分为48个植被型(含30个自然植被型、12个农业植被型、5个城市植被型和无植被地段)。自然植被中有23个植被型进一步划分出了81个植被亚型。     

地被植物对广东常绿阔叶林土壤养分的指示作用

为了解地被植物群落对土壤养分的响应和指示作用,利用指示种分析(ISA)法研究了广东常绿阔叶林地被植物与土壤养分的关系。结果表明,速效氮(AN)、速效磷(AP)、速效钾(AK)和有机质(OM)的综合作用对地被植物分布有显著影响(P0.05),且以速效磷有机质速效钾速效氮。地被植物的组成与分布在不同AP和OM梯度中均有显著差异(P 0.05),但在不同AK和AN梯度中差异不显著。土壤AN≤270 mg/kg的指示种是广东蛇葡萄(Ampelopsis cantoniensis)和油点草(Tricyrtis macropoda),270～360 mg/kg的指示种是狗骨柴(Tricalysia dubia);AP≤2 mg/kg的指示种是华山姜(Alpinia chinensis);AK≤100mg/kg的指示种是赤楠蒲桃(Syzygiumbuxifolium),AK为100～150mg/kg的指示种是十字苔草(Carexcruciate),AK150 mg/kg的指示种是金钗凤尾蕨(Pterisfauriei);OM 0.8%的指示种是箬竹(Indocalamustessellatus),OM≤0.6%的指示种是华山姜(Alpinia chinensis)和蔓胡颓子(Elaeagnus glabra),OM为0.6%～0.8%的指示种是豆腐柴(Premna microphlla)。利用有效的地被植物调查方式来监测森林的土壤状况为森林经营管理及土壤健康评价带来方便。地被植物指示种对土壤养分的响应不但能为研究地的立地条件提供理论支撑,还能为该物种的人工栽培提供理论依据,这对于生物多样性保育、生境恢复的引种栽培有重要意义。     

基于中国生态系统研究网络的典型森林生态系统土壤保持功能分析

森林生态系统土壤保持功能在控制土壤侵蚀以及维持生态安全方面具有不可替代的作用。根据不同气候带降雨特征进行降雨侵蚀力参数校正,基于中国生态系统研究网络(CERN)的森林生态系统长期定位观测样地2005—2015年监测数据利用修正的通用土壤流失方程(RUSLE)定量分析了典型森林生态系统土壤保持功能的时空变化特征,并探讨了土壤保持功能的影响因素。研究结果表明:①日雨量侵蚀力模型在降雨丰富的热带模拟效果优于降雨相对较少的亚热带和温带,参数校正后模拟效果明显提升;②研究期内10个典型森林生态系统土壤保持量变化范围为4.44—891.67 t hm~(-2) a~(-1),呈现北低南高的空间格局(R~2=0.65~(***));土壤保持率均达到97%以上;③降雨、归一化植被指数、土壤质地和植被林龄是影响森林生态系统土壤保持功能的主要影响因素;降雨量与土壤保持量显著相关(R~2=0.52~*),NDVI和土壤质地与实际土壤侵蚀量显著相关(R~2=0.64~(**),R~2=0.41~*),植被林龄主要影响土壤保持率的变化速率。