基于MODIS的中国野火时空分布格局

野火是自然生态系统中重要的干扰因子,在维持生态系统多样性的同时,也对自然生态系统和人民的生命和财产构成重大威胁,野火时空分布格局研究有助于理解野火的发生规律,从而为野火的科学管理提供依据。本文基于MODIS火产品数据(2006—2012年),借助地理信息系统、遥感技术和SPSS统计软件,分析了中国野火的时空分布格局。结果表明:2006—2012年中国野火年过火面积呈下降趋势,年际变化波动较大,对年过火面积变化贡献率较大的省份主要分布在华南地区、西南地区和西北地区;中国野火过火面积月变化明显,其中3月过火面积最大,对月过火面积变化贡献率较大的是南方地区、西南地区、西北地区和东北地区;野火的发生和环境因子有密切关系为在丘陵地区、年降水量在400~800 mm的区域、年平均气温在0~10℃地区和针叶林中最易发生野火。本研究可为中国野火的火险区划和管理提供科学依据。     

气候、植被和地形对大兴安岭林火烈度空间格局的影响

在北方森林中火干扰是森林景观变化的主导因素。林火烈度作为衡量林火动态的重要指标,较为直观地反映了火干扰对森林生态系统的破坏程度,其空间格局深刻地影响着森林景观中的多种生态过程(如树种组成、种子扩散以及植被的恢复)。解释林火烈度空间格局有助于揭示林火干扰后森林景观格局的形成机制,对预测未来林火烈度空间格局以及制定科学合理林火管理策略均有重要意义。基于LandsatTM/ETM遥感影像,将2000—2016年大兴安岭呼中林区的36场火的林火烈度划分为未过火、轻度、中度、重度4个等级。采用FRAGSTAT景观格局分析软件从类型水平上计算了斑块所占景观面积比、面积加权平均斑块面积、面积加权平均斑块分维数、面积加权边缘面积比、斑块密度5个景观指数,以对林火烈度空间格局进行了定量化描述。并且采用随机森林模型,分析了气候、地形、植被对林火烈度空间格局的影响及其边际效应。通过研究得出以下结果:(1)相对于未过火、轻度、以及中度火烧斑块,重度火烧斑块的面积更大、形状更简单;(2)海拔对重度火烧斑块的空间格局起着至关重要的作用,其次是坡向、坡度、植被覆盖度、相对湿度、温度等;(3)随着海拔的升高,面积加权...     

火控制政策对大兴安岭森林景观、可燃物动态及火险的长期影响

大兴安岭50年来严格的火控制政策已经极大地改变了自然火格局,同时也改变了森林的物种组成和年龄结构。理解大兴安岭森林对长期火控制的响应是制定森林可持续发展的依据之一。本文应用LANDIS模型模拟了大兴安岭森林景观对自然火(1950年以前)和灭火(1950年以后)的长期响应(300年)。结果表明：灭火显著增加了落叶松面积,增加其过熟林面积,减少其幼龄林面积;同时也显著减少白桦面积,减少其幼龄林面积;灭火延长火烧轮回期,火烧次数减少,灾难性火灾发生的机率增加,火险在模拟的50年内迅速上升到高火险等级。在自然火格局下,火险在整个模拟过程中保持较低的等级。所以如果现行的高强度灭火政策继续实施的话,必须要制定大范围的可燃物管理措施(计划火烧、粗可燃物处理等),以降低灾难性火灾发生的机率。计划火烧加粗可燃物去除将成为可燃物管理和森林可持续经营的首选措施。如何评价大兴安岭地区可燃物处理措施的效果,在保持木材生产和生态作用稳定的条件下,最大程度地降低火险也是亟待解决的问题。     

ENSO事件对中国森林火险天气的影响

ENSO事件影响中国的气候和森林火险天气,研究ENSO事件对中国各植被区火险天气的影响对于提高森林火险预报准确性有科学和实践意义。利用1951—2016年中国地面国际交换站气候资料的日值数据集(V3.0)数据计算每日的森林火险天气指数(FWI),根据MODIS过火区产品计算各植被区2001—2016年的森林过火面积,分别按事件情景(弱、中、强和超强厄尔尼诺事件以及弱、中和强拉尼娜事件)统计各植被区对应的火险期气温、降水、FWI和过火面积。结果表明: 1950—2016年,共发生19次厄尔尼诺事件和14次拉尼娜事件。受强或超强厄尔尼诺事件影响,西北地区春季火险期的日均最高气温明显升高,而中温带半干旱草原区春季火险期的日均最高气温在中厄尔尼诺年显著降低。厄尔尼诺年,南方和西南林区火险期的降水量一般会增加,中、低强度的拉尼娜事件会减少大部分区域的火险期降水量,但强拉尼娜事件导致大部分林区火险期的降水量增加。弱厄尔尼诺事件导致南方林区FWI降低;强或超强厄尔尼诺事件导致南方和西南林区的FWI有所降低,而北方林区的FWI有所升高。ENSO事件对各植被区FWI的影响存在显著的空间差异性。2001—2016年,当火险期的季节火险严重程度(SSR)显著变化时,暖温带湿润/半湿润地区落叶阔叶林区、中北亚热带湿润地区阔叶林区和热带南亚热带湿润地区阔叶林区的过火面积与SSR的变化一致,其他区域的过火面积受ENSO事件的影响不明显。     

呼中林区火烧点格局分析及影响因素

林火是森林生态系统景观格局、动态和生态过程的重要自然驱动力,理解林火发生空间格局与影响因素对于林火安全管理具有重要的作用。采用点格局分析方法,以黑龙江大兴安岭呼中林区1990-2005年火烧数据为研究案例,分析了火烧点空间格局及其影响因素。结果表明,火烧点在空间上的分布是不均匀的,呈现聚集分布,存在一些火烧高发区和低发区。呼中林区火烧概率是0.004-0.012次/(km² · a),平均火烧概率为0.0077次/(km² · a)。人类活动因子、地形因子和植被因子对林火的发生均具有重要作用。应用空间点格局分析方法表明,距离居民点和道路的距离、高程、坡度和林型是影响林火发生的显著因子。因此在进行森林防火管理时,仅仅通过控制人类活动对于降低林火火险的效果是有限的,地形和林型也是林火防控时重点要考虑的因素。     

黑龙江大兴安岭呼中林区火烧点格局分析及影响因素

林火是森林生态系统景观格局、动态和生态过程的重要自然驱动力,理解林火发生空问格局与影响因素对于林火安全管理具有重要的作用.采用点格局分析方法,以黑龙江大兴安岭呼中林区1990-2005年火烧数据为研究案例,分析了火烧点空间格局及其影响因素.结果表明,火烧点在空间上的分布是不均匀的,呈现聚集分布,存在一些火烧高发区和低发区.呼中林区火烧概率是0.004--0.012次/(km2.a),平均火烧概率为0.0077次/(km2.a).人类活动因子、地形因子和植被凶子对林火的发生均具有重要作用.应用空间点格局分析方法表明,距离居民点和道路的距离、高程、坡度和林型是影响林火发生的显著因子.因此在进行森林防火管理时,仅仅通过控制人类活动对于降低林火火险的效果是有限的,地形和林型也是林火防控时重点要考虑的因素.     

西藏高原冬虫夏草资源适宜性区划分析

冬虫夏草是分布在西藏高原高寒草甸中稀缺的可再生生物资源,具有很高的药用价值和经济价值,然而资源的数量、空间分布格局及分布适宜度尚不清晰。根据西藏高原冬虫夏草产区生态环境条件,以海拔高度、植被类型、土壤类型、年平均降水量、年平均气温为区划主要指标,利用GIS空间分析方法对西藏高原冬虫夏草生长区进行适宜性综合区划。结果表明:那曲地区的比如县、索县,昌都市的边坝县、丁青县、类乌齐县、江达县、洛隆县、察雅县、贡觉县部分产区处在适宜区;那曲地区的那曲县、嘉黎县、巴青县、聂荣县,拉萨市的当雄县及其他产区处在次适宜区;日喀则市的大部分地区、林芝市和山南市的低海拔地区为不适宜区。在出产冬虫夏草的地区(市)中,那曲地区、昌都市分布面积占当地产冬虫夏草县域国土面积的52.1%—59.3%,山南市、日喀则市、拉萨市和林芝市分布面积占当地产冬虫夏草县域国土面积的13.7%—26.1%,整个西藏高原产区的冬虫夏草分布面积平均占当地产冬虫夏草县域国土面积的34.5%。综合区划图能比较真实的反映西藏高原冬虫夏草空间分布格局,区划结果与采挖地乡镇调查结果符合程度高,与冬虫夏草单位草原面积统计产量分布较为一致。这一研究方法可为以后冬虫夏草资源调查提供参考,为冬虫夏草资源评估及区划等相关研究提供方法支持。     

基于NBR指数分析大兴安岭呼中森林过火区的林火烈度

基于TM影像和3S技术手段,利用NBR指数对1986—2010年大兴安岭呼中林区森林过火区林火烈度进行了定量评价,分析了林火烈度与植被类型、海拔、坡度和坡向等环境因子的关系.结果表明:呼中林区的林火发生次数和面积年际变化明显,每年6—8月是林火的高发期,重度火烧区占总过火面积的84.2%.过火区中,兴安落叶松林占89.9%;海拔1000～1500m区域占68.8%;东、南、西、北4个坡向的过火面积占62.5%,阴、阳坡过火面积差异不明显;坡度15～25°的斜坡区域过火面积占38.4%.不同程度林火烈度的过火面积由大到小依次为重度火>中度火>轻度火>未过火,其中,重度火过火面积>70%,中度火过火面积在10%左右,轻度火和未过火的过火面积<5%.呼中林区林火烈度以重度火为主,对森林资源的破坏程度极大.在大兴安岭林区的林火管理中,应尽早开展森林可燃物处理工作,以降低林火烈度,保障森林生态系统的安全.     

兴安落叶松林火烧迹地土壤有效磷与土壤微生物生物量磷时空演变特征

野火是大兴安岭活跃的生态干扰因子,显著影响火烧迹地土壤有效磷(AP, Available Phosphorus)和土壤微生物生物量磷(MBP, Microbial Biomass Phosphorus),本文旨在了解兴安落叶松林火烧迹地AP、MBP的时空演变特征,并在此基础上探究两者间的偶联机制。采用“以空间换时间”的研究方法,于大兴安岭塔河地区兴安落叶松林火烧迹地选取实验样地,于未过火兴安落叶松林选取对照样地,踏查每个样地的海拔、坡度、坡向、坡位信息,测定火烧迹地土壤AP、MBP含量,分析兴安落叶松林火烧迹地AP与MBP的时空演变特征。火干扰后,火烧迹地土壤AP、MBP含量均随恢复时间表现出先减少后增加的趋势,恢复初期火烧迹地MBP含量显著低于未过火样地,AP含量显著高于未过火样地(P<0.05);不同海拔火烧迹地AP、MBP含量差异显著(P<0.05),不同海拔未过火样地AP、MBP含量均无显著差异(P>0.05)。火烧迹地土壤MBP、AP的随机森林回归模型的模型总解释度约为84%,而未过火样地的模型总解释度约为60%,两个模型均达到了极显著水平(P<0.0...     

黄土残塬沟壑区流域次生植被物种分布的地形响应

研究流域次生植被物种对地形因子的响应规律,识别影响次生植被物种分布的主要地形因子,是流域近自然植被生态恢复和重建的基础。采用ArcGIS空间分析模块和地形分析模块TauDEM,并与统计软件SPLUS2000中的GRASP工具相结合,建立了位于黄土高原残垣沟壑区山西省吉县蔡家川流域次生植被各个物种分布基于地形因子的广义相加模型(GAM)。模型中的地形因子包括:海拔、坡向、坡度、平面曲率、坡位指数(SPI)、地形湿度指数(TWI)、单宽汇水面积(SCA)等。受试者操作特征曲线(ROC)测试中AUC值表明:大部分测试物种(约62%)拟合模型效果较好,且模型较为稳定。总体来看,研究流域次生植被物种分布体现了水分限制的空间分异特征:阴坡各物种分布概率较大,且随海拔升高而减小。影响研究流域次生植被物种空间分布的潜在重要因子为海拔和坡向,而单宽汇水面积(SCA)和地形湿度指数(TWI)虽然是多个物种响应模型的预测因子,但受高一级尺度海拔的影响,SCA与TWI对物种分布的影响作用较小;坡度影响作用最小。据此,在流域植被恢复和防护林建设目标区选择及立地条件划分时应首先以海拔和坡向为依据,单宽汇水面积(SCA)和地形湿度指数(TWI)则可以作为次一级立地分类依据,而坡度则仅能作为最后一级的分类依据。     

On the origin of the Hirudinea and the demise of the Oligochaeta

The phylogenetic relationships of the Clitellata were investigated with a data set of published and new complete 18S rRNA gene sequences of 51 species representing 41 families. Sequences were aligned on the basis of a secondary structure model and analysed with maximum parsimony and maximum likelihood. In contrast to the latter method, parsimony did not recover the monophyly of Clitellata. However, a close scrutiny of the data suggested a spurious attraction between some polychaetes and clitellates. As a rule, molecular trees are closely aligned with morphology-based phylogenies. Acanthobdellida and Euhirudinea were reconciled in their traditional Hirudinea clade and were included in the Oligochaeta with the Branchiobdellida via the Lumbriculidae as a possible link between the two assemblages. While the 18S gene yielded a meaningful historical signal for determining relationships within clitellates, the exact position of Hirudinea and Branchiobdellida within oligochaetes remained unresolved. The lack of phylogenetic signal is interpreted as evidence for a rapid radiation of these taxa. The placement of Clitellata within the Polychaeta remained unresolved. The biological reality of polytomies within annelids is suggested and supports the hypothesis of an extremely ancient radiation of polychaetes and emergence of clitellates.     

On the ontogeny of the haptor and the evolution of the Monogenea

Data on the ontogeny of the posterior haptor of monogeneans were obtained from more than 150 publications and summarised. These data were plotted into diagrams showing evolutionary capacity levels based on the theory of a progressive evolution of marginal hooks, anchors and other attachment components of the posterior haptor in the Monogenea (Malmberg, 1986). 5 + 5 unhinged marginal hooks are assumed to be the most primitive monogenean haptoral condition. Thus the diagrams were founded on a 5 + 5 unhinged marginal hook evolutionary capacity level, and the evolutionary capacity levels of anchors and other haptoral attachement components were arranged according to haptoral ontogenetical sequences. In the final plotting diagram data on hosts, type of spermatozoa, oncomiracidial ciliation, sensilla pattern and protonephridial systems were also included. In this way a number of correlations were revealed. Thus, for example, the number of 5 + 5 marginal hooks correlates with the most primitive monogenean type of spermatozoon and with few sensillae, many ciliated cells and a simple protonephridial system in the oncomiracidium. On the basis of the reviewed data it is concluded that the ancient monogeneans with 5 + 5 unhinged marginal hooks were divided into two main lines, one retaining unhinged marginal hooks and the other evolving hinged marginal hooks. Both main lines have recent representatives at different marginal hook evolutionary capacity levels, i.e. monogeneans retaining a haptor with only marginal hooks. For the main line with hinged marginal hooks the name Articulon-choinea n. subclass is proposed. Members with 8 + 8 hinged marginal hooks only are here called Proanchorea n. superord. Monogeneans with unhinged marginal hooks only are here called Ananchorea n. superord. and three new families are erected for its recent members: Anonchohapteridae n. fam., Acolpentronidae n. fam. and Anacanthoridae n. fam. (with 7 + 7, 8 + 8 and 9 + 9 unhinged marginal hooks, respectively). Except for the families of Articulonchoinea (e.g. Acanthocotylidae, Gyrodactylidae, Tetraonchoididae) Bychowsky's (1957) division of the Monogenea into the Oligonchoinea and Polyonchoinea fits the proposed scheme, i.e. monogeneans with unhinged marginal hooks form one old group, the Oligonchoinea, which have 5 + 5 unhinged marginal hooks, and the other group form the Polyonchoinea, which (with the exception of the Hexabothriidae) has a greater number (7 + 7, 8 + 8 or 9 + 9) of unhinged marginal hooks. It is proposed that both these names, Oligonchoinea (sensu mihi) and Polyonchoinea (sensu mihi), will be retained on one side and Articulonchoinea placed on the other side, which reflects the early monogenean evolution. Except for the members of Ananchorea [Polyonchoinea], all members of the Oligonchoinea and Polyonchoinea have anchors, which imply that they are further evolved, i.e. have passed the 5 + 5 marginal hook evolutionary capacity level (Malmberg, 1986). There are two main types of anchors in the Monogenea: haptoral anchors, with anlages appearing in the haptor, and peduncular anchors, with anlages in the peduncle. There are two types of haptoral anchors: peripheral haptoral anchors, ontogenetically the oldest, and central haptoral anchors. Peduncular anchors, in turn, are ontogenetically younger than peripheral haptoral anchors. There may be two pairs of peduncular anchors: medial peduncular anchors, ontogentically the oldest, and lateral peduncular anchors. Only peduncular (not haptoral) anchors have anchor bars. Monogeneans with haptoral anchors are here called Mediohaptanchorea n. superord. and Laterohaptanchorea n. superord. or haptanchoreans. All oligonchoineans and the oldest polyonchoineans are haptanchoreans. Certain members of Calceostomatidae [Polyonchoinea] are the only monogeneans with both (peripheral) haptoral and peduncular anchors (one pair). These monogeneans are here called Mixanchorea n. superord. Polyonchoineans with peduncular anchors and unhinged marginal hooks are here called the Pedunculanchorea n. superord. The most primitive pedunculanchoreans have only one pair of peduncular anchors with an anchor bar, while the most advanced have both medial and lateral peduncular anchors; each pair having an anchor bar. Certain families of the Articulonchoinea, the Anchorea n. superord., also have peduncular anchors (parallel evolution): only one family, the Sundanonchidae n. fam., has both medial and lateral peduncular anchors, each anchor pair with an anchor bar. Evolutionary lines from different monogenean evolutionary capacity levels are discussed and a new system of classification for the Monogenea is proposed.In agreeing to publish this article, I recognise that its contents are controversial and contrary to generally accepted views on monogenean systematics and evolution. I have anticipated a reaction to the article by inviting senior workers in the field to comment upon it: their views will be reported in a future issue of this journal. EditorIn agreeing to publish this article, I recognise that its contents are controversial and contrary to generally accepted views on monogenean systematics and evolution. I have anticipated a reaction to the article by inviting senior workers in the field to comment upon it: their views will be reported in a future issue of this journal. Editor