Gypsy moth-induced growth decline of Larix sibirica in a forest-steppe ecotone

Effects of a gypsy moth attack on the productivity of Larix sibirica on tree-ring width were analyzed in a case study of a mountain site in the western Khentey in the northern Mongolian forest-steppe ecotone. A major aim of the study was to assess whether reduced productivity by gypsy moth herbivory could contribute to fluctuations of the forest edge to the steppe in larch-dominated woodlands. In the year of the infestation, larch trees at the forest edge lost 90% of their needles and latewood formation was strongly reduced. However, earlywood formation was widely completed before the gypsy moth attack and, therefore, total tree-ring width was not below the average of the five years prior to infestation. In the two years following the gypsy moth invasion, annual stem increment was strongly reduced. Trees growing 30–100 m inside the forest showed a much weaker response of tree-ring widths to the gypsy moth infestation consistent with significantly higher defoliation at forest edge than in the forest interior. Old trees exhibited a stronger growth decline than middle-aged trees, indicating higher infestation of dominant, exposed trees, which are thought to be better accessible to the wind-dispersed gypsy moth larvae hatching in the early growing season on the steppe. Under the current climate, occasional growth reductions are thought to be of little effect on the performance of L. sibirica, as fast-growing competitors of other tree species, which are not or hardly affected by gypsy moth, are absent.     

Individual sensitivity of Larix sibirica L. in open woodland of the Shira forest-steppe

Some indices of individual variability in annual growth of Siberian larch in open woodlands of Khakassia are compared. In the Shira forest-steppe the Siberian larch exhibits high sensitivity of annual growth and diverse responses to changes in vegetative conditions. Stabilizing selection maintains dominance of trees with moderately sensitive annual growth. Such trees are the most vital. It has been shown that the adaptive norm of population’s response and the individual variability of annual growth positively correlate with the total annual precipitation. The sensitivity index of annual growth is a better indicator of the genetic structure of the population than the coefficient of variability of annual growth indices.     

呼伦贝尔森林-草原交错区景观格局时空动态

基于遥感（RS）与地理信息系统（GIS）相结合的方法,解译并提取了1988年、1995年、2000年和2004年四期呼伦贝尔森林．草原交错区的景观格局空间分布信息,并在Fragstats3．3软件中,分别从景观级别和类型级别出发,分析了该区景观格局的时空动态变化。结果表明：（1）16年来,呼伦贝尔森林-草原交错区各景观类型转换频繁。其中,林地面积减少量最多,达7858．15km^2,主要转换为草地;未利用土地面积增加量最多,净增4087．25km^2,增加的面积主要来源于草地和林地。（2）景观格局整体波动较大,景观破碎度、景观多样性指数逐年增大,优势度指数降低。（3）受人为干扰的影响,研究区内各主要景观类型均表现出景观斑块由大到小,由少到多,斑块形状复杂化程度增加的特点。（4）主要景观类型质心向东偏移,其中,林地景观的质心向东南方向偏移了50．22°大约4．48km;草地景观整体向东北方向偏移了79．96°大约29．93km。     

森林-草原交错带夏季鸟类群落多样性特征

2004～2006年夏季利用样线法研究了内蒙古高原东南缘森林-草原交错带鸟类群落多样性特征及变化规律.共记录鸟类73种,隶属于13目28科56属,鸟类区系具有明显的古北界特征.鸟类群落物种数和密度年间差异不显著,α多样性随森林-草原交错带环境梯度变化而发生显著变化:在不同植被地带之间,物种数、密度、Shannon-Wiener指数和Pielou指数差异极显著、但科-属多样性差异不显著,鸟类群落α多样性各项指数表现为森林带＜交错带森林草甸区＞交错带草甸草原区＞草原带的特征与变化趋势(DG-F为交错带草甸草原区＞森林带);其中,森林草甸区是鸟类物种多样性的显著增长区,具有最高的物种数和密度,明显体现了交错区的边缘效应,草甸草原区是鸟类向草原过渡的显著变化区域、物种多样性开始显著减少.β多样性随不同植被地带逐级发生显著变化,环境差异最大的森林带-森林草甸区和草甸草原区-草原带具有最高的β多样性,物种替代速率最大;鸟类物种替代速率与环境梯度"陡度"有密切关系.鸟类优势种在各植被地带之间存在较大变化.鸟类群落的物种数、密度和物种多样性(H')与森林斑块数呈显著的正相关性,在大尺度空间上森林斑块数是影响鸟类群落多样性的最主要因素.     

森林-草原交错带土壤节肢动物群落多样性

在河北北部的塞罕坝森林草原交错区进行了土壤节肢动物群落组成与多样性调查,共获得土壤节肢动物25类,10420头,分属于6纲24目.交错区地带土壤节肢动物群落优势类群为弹尾目和蜱螨目,常见类群有8类,稀有类群15类.群落的多样性分析表明,森林带的多样性指数(H′)、密度-类群指数(DG)和均匀度指数较大,而草甸草原带各种指数较小.pH值与土壤节肢动物的类群数关联度较大,而温度和含水量与土壤节肢动物的个体数关联度较大.     

昆虫植食对植物有性生殖的影响

植物在个体发育的各个阶段都与不同的群落成员相互作用,如竞争的植物、有益的传粉者和敌对的植食动物。昆虫植食在各类生态系统中普遍存在,并可能对植物有性生殖产生各种影响。植食昆虫可通过对植物有性生殖结构的消耗直接对植物生殖产生影响,也可通过影响植物资源分配和花性状等改变传粉者服务,从而间接对植物有性生殖带来正面、负面或中性的影响。同一植物的植食昆虫和传粉者往往对植物的吸引性状 （如花大小、气味、颜色等）有相同的偏好,因此植食者与传粉者均能对植物有性生殖性状施加选择压力。本文从昆虫植食对植物有性生殖的直接影响、间接影响以及植食昆虫对植物有性生殖性状选择的影响三个方面进行综述,以期为昆虫植食和生物资源多样性保护相关研究提供参考。     

Identifying habitat types in a disturbed area of the forest-steppe ecotone of Patagonia

We surveyed an old ranch (22,000 ha) in the eastern catchment of lake Nahuel Huapi (Argentina), representing both landscape and historical use patterns of the forest-steppe ecotone in the Andes foothills. The objective was to describe plant-environment relations and to develop a procedure to classify habitat types for conservation aims. Floristic and landscape variables were recorded in 72 upland sites. Vegetation types were classified with Two-way indicator Species Analysis and environmental gradients detected with Detrended Canonical Correspondence Analysis. Vegetation types were tested for environmental homogeneity with Discriminant Analysis. A key to classify habitat types was built out from the classification functions obtained by DA analysis. Floristic classification resulted in 7 steppe types and 4 shrubland/woodland types. Vegetation samples were placed along two main gradients, one related to topography and the other to the type of substrate. Steppe types occur in all positions of the topographic gradient forming a temperature-soil moisture continuum, but only (except one of them) on accumulated substrates. Islands of woody types are confined to relatively warm positions of the topographic gradient and to deflated, rocky substrates. This distribution pattern would be caused by frost sensibility of forest species, and by the different strategies of water capture of woody and herbaceous plants. Three pairs of plant assemblages were not discriminated, allowing classification of 8 habitat types out of the 11 communities. Undiscriminated communities (3 pairs) and misclassified samples (29%) were discussed as the result of disturbances.     

森林草原过渡带持久土壤种子库沿降水梯度的格局

为了解全球气候变化背景下森林草原过渡带持久土壤种子库对未来降水减少的响应,本研究以呼伦贝尔森林草原过渡带为研究区域,沿降水梯度采集0～10 cm土层的持久土壤种子库样本,研究种子库密度、物种组成、多样性及其与地上植被的关系,并利用结构方程模型研究年降水量对持久土壤种子库的直接影响及其通过地上植被和土壤有效氮、有效磷、土壤pH值产生的间接影响。结果表明: 随着降水量的降低,种子库密度和物种丰富度有增加趋势,森林草原过渡带草地土壤种子库物种多样性高于森林。土壤种子库与地上植被相似性整体较低。结构方程模型结果显示,年降水量对种子库的密度和物种丰富度的总效应为负效应,标准路径系数为-0.051和-0.122。年降水量对种子库的密度和物种丰富度的直接效应为正效应,降水量通过土壤全氮对种子库密度和物种丰富度产生显著的间接正效应,通过土壤pH和土壤有效磷对种子库物种丰富度产生显著的间接负效应,通过土壤pH对种子库密度产生显著的间接负效应。气候变化下降水减少会改变植物应对风险的策略,森林草原过渡带的持久土壤种子库对应对未来可能发生的降水减少具有一定的缓冲作用。     

Seedling emergence and establishment of Pinus sylvestris in the Mongolian forest-steppe ecotone

The potential of Scots pine (Pinus sylvestris) for regeneration and encroachment onto dry grasslands in the forest-steppe ecotone was experimentally studied at the south-eastern distribution limit of the species in Mongolia. The experiment consisted of a sowing and planting (2-year old seedlings) assay at two different distances from the forest line and manipulation of the water supply by irrigation in one half of the replicate plots. Seedling emergence was strongly inhibited by post-dispersal seed predation (between 50 and >90 % of the seeds were apparently consumed) and by drought. Seedling survival was limited by drought and phytopathogenic fungi that infected the needles. Herbivory by insects or rodents, a key factor for seedling mortality in Larix sibirica, the most frequent tree species in Mongolia’s forest-steppe ecotone, was of little importance in Scots pine, probably due to the production of efficient allelochemicals. The potential of Scots pine to regenerate in Mongolia’s forest-steppe ecotone and to encroach onto the steppe is very limited and mostly restricted to the immediate vicinity of the forest; it might even decrease in future in the face of climate warming. The observed dependence of seedling emergence and survival on soil moisture suggests that regeneration outside the forest may only be successful in exceptionally moist years. Livestock grazing is certainly an additional limiting factor for Scots pine regeneration in Mongolia, but was not relevant in the present study area.     

Effects of environmental factors on wood formation in larch (Larix sibirica Ldb.) stems

 Effects of temperature and precipitation on xylem cell production by the cambium, radial cell expansion and secondary wall thickening in larch stems have been studied. The observations were carried out over two seasons on ten 50- to 60-year-old trees, growing in central Siberia and chosen according to growth rate (the number of cells in radial rows of each of two of the preceding seasons was equal). The data on the number of cells in differentiation zones and mature xylem along radial rows of tracheids, radial and tangential sizes of tracheids and their lumina were used for calculating cambial activity, the rates and durations of cell development in the zones, and both the thickness and cross-sectional areas of tracheid walls. The mean day air temperature, mean maximum diurnal and mean minimum nocturnal temperatures as well as precipitation have been shown by correlation and regression analyses to affect differentially separate stages of tracheid differentiation. Throughout all the seasons it was temperature that had the main influence on the initial divisions in the xylem, radial cell expansion and biomass accumulation. However, the levels of such an effect on separate stages of cytogenesis were different, especially the influence of nocturnal temperature on xylem cell production by cambium and primary wall growth. The optimum values of temperature and precipitation for cell production by cambium, for radial cell expansion and secondary wall thickening have been calculated. These optimum values of the first and second processes proved to be practically equal, while the last differs considerably in response to temperature. The data are discussed in connection with formation of early and late tracheids. Received: 3 July 1996 / Accepted: 7 February 1997     

Studies on species diversity of Larix chinensis community ecotone

The communities of Larix chinensis and their ecotone in Qinling Mountains were investigated by sampling belt method.Species richness,Simpson diversity,Shannon-Weiner diversity,PIE and Pielou evenness indices of vascular plants in their communities and ecotone were calculated.Structure and composition of the communities in 6 sampling belts within the sites were analyzed.The results showed that the edge effect was obvious in the ecotone with a less changing environment(such as soil and terrain)and acute variation of composition and structure,while inconspicuous or even none in the ecotone with worse environmental condition(such as great space fluctuation).It is apparent that the edge effect of community was affected by soil and terrain,but not by microclimate.     

太白红杉群落交错带物种多样性的研究

应用样带法对太白红杉群落及其交错带进行调查,采用各群落维管植物的物种丰富度指数(S)、 Simpson物种多样性指数(D)、Shannon Weiner物种多样性指数(H′)、种间相遇机率(PIE)及Pielou均匀度 指数(Jsw和Jsi),分析了6条样带的群落结构和物种组成。结果显示在环境条件(土壤和地形)变化较小、层 次结构剧变的群落交错带中,边缘效应明显。而在环境条件较差(即空间波动大)的群落交错带中,边缘效应 不明显,甚至无边缘效应出现。可见,群落的边缘效应不仅受小气候影响,也受地形和土壤等因子的影响。     

Effects of leaf and root herbivory by potential insect biological control agents on the performance of invasive Vincetoxicum spp.

The European leaf-feeding moth Abrostola asclepiadis and root-feeding beetle Eumolpus asclepiadeus are promising biological control agents for two European swallow-worts (Vincetoxicum rossicum and Vincetoxicum nigrum) in North America, however, their impact on plant performance is uncertain. Densities of each herbivore were manipulated in a common garden to determine whether leaf and root herbivory affect the performance of these plants. During the second year of the experiment, V. rossicum and V. nigrum unexpectedly became infected with the fungal pathogens Ascochyta sp. and Cercospora sp. (Ascomycota), respectively. Although pathogen infection mainly reduced shoot height and delayed reproduction, herbivore effects on plant growth were still evident. Leaf herbivory by A. asclepiadis had no effect on plant growth 1 year after defoliation. Root herbivory by E. asclepiadeus reduced shoot height and plant biomass and decreased the ability of plants to compensate for pathogen attack. Pathogen infection prevented detection of herbivore effect on reproduction. Due to its substantial impact on plant biomass, E. asclepiadeus should be further evaluated as a biological control agent against Vincetoxicum spp. populations invading open habitats in North America. Further research is needed to evaluate the impact of A. asclepiadis in combination with E. asclepiadeus and plant competition under high and low light conditions.     

模拟昆虫取食对牛膝菊防御特征的影响

为了解入侵植物牛膝菊的入侵机理,研究其应对昆虫取食的响应,在开花前喷洒不同浓度(5、10、20 mmol·L-1)的茉莉酸甲酯(MeJA)来模拟不同程度的昆虫取食,试验结束时测定其株高、叶片数、花序数、生物量、比叶面积、叶上表皮毛密度,以及叶和花序中的缩合单宁、总酚、黄酮含量.结果表明:5 mmol·L-1 MeJA处...     

Effects of seedling conspecific density and heterospecific frequency on insect herbivory in a tropical dry forest

1. Conspecific plant density and heterospecific frequency are key drivers of herbivore damage. However, most studies have investigated their effects separately and for single (rather than multiple) focal plant species.
2. We conducted an experiment involving three tree species, namely: Cordia dodecandra (Boraginaceae), Manilkara zapota (Zapotaceae), and Piscidia piscipula (Fabaceae). We manipulated understory densities of M. zapota and C. dodecandra (focal species) and their frequency relative to P. piscipula. Three months after planting, we surveyed insect leaf chewer and sucking damage on the former two. Because these species are attacked by different herbivores, we predicted a negative effect of heterospecific frequency on herbivory.
3. Density and frequency varied in the direction and function of their effects on herbivory depending on the plant species and attacking herbivore. As expected, Piscidia piscipula frequency had a negative linear effect on M. zapota leaf-chewer damage, whereas conspecific density did not affect chewer damage on this species. In contrast, density and frequency had non-linear effects on C. dodecandra chewer damage, namely positive (hump-shaped) and negative (U-shaped) relationships, respectively. In addition, density and frequency had positive linear effects on C. dondecandra damage by leafhoppers.
4. These findings call for more work jointly assessing plant inter-specific variation in density- and frequency-dependent variation in herbivory and its underlying drivers.

     

Edge and land-use effects on epiphytic lichen diversity in the forest-steppe ecotone of the Mongolian Altai

Epiphytic lichen diversity was studied in forests of Siberian larch (Larix sibirica) in the forest-steppe ecotone of the Mongolian Altai. These forests are utilized for livestock grazing, fuelwood collection and occasional logging by pastoral nomads. The density of nomad households in the proximity of the forests influences epiphytic lichen diversity more strongly than the position of sample trees in the forest interior or at the forest line to the steppe. This suggests that land use exerts a stronger effect on lichen diversity than the distinct gradient in microclimate between the forest interior and the forest edge. The co-occurrence of nitrophytes with anitrophytic acidophytes on a small spatial scale as well as higher N and Ca concentrations and pH values in the bark of larch trees at the forest edge than in the forest interior indicate that moderate livestock grazing increases the epiphytic lichen diversity due to an increase of the diversity of chemically different microhabitats. Preference of many lichen species (and of rare species in particular) for overmature and decaying trees suggests that logging and fuelwood collection has adverse effects on epiphytic lichen diversity. This adverse effect is likely to be more crucial for lichen diversity than the putatively positive effect of livestock grazing, since more lichens with a preference for old and decaying trees than for nitrogen-enriched bark were found. The present study is the first one investigating the impact of pastoral nomadism in Central Asia on epiphyte diversity.     

Reindeer herbivory reduces willow growth and grouse forage in a forest-tundra ecotone

Browsing mammals strongly modify the structure of vegetation of forest-tundra ecotones. We investigated the impact of reindeer browsing on growth and morphology of an arctic willow, Salix glauca, by studying plants inside and outside fenced areas in a tundra habitat at the tree line. We also studied if reindeer feeding has an effect on the forage availability for willow grouse, a herbivore sharing the same food plant. Analyses of 6-year data show that reindeer strongly reduces the growth of tundra willow and changes plant morphology to a stunted growth form. Intense reindeer browsing on willow limited the forage availability for willow grouse and grouse fed less on reindeer-browsed willow than willows protected from reindeer browsing. The results of this study imply that herbivores can counteract the increase of shrubs in forest-tundra ecotones, as has been predicted in some studies discussing the effects of climatic warming on vegetation. Furthermore, trophic interactions should be incorporated in modelling vegetation changes as a response to increased temperatures.     

Synergistic effect of insect herbivory and plant parasitism on the performance of the invasive tree Schinus terebinthifolius

Schinus terebinthifolius Raddi (Anacardiaceae) is an introduced tree from South America that has invaded many ecosystems throughout central and south Florida, USA. Exploratory surveys in the plant's native range identified several potential biocontrol agents, including the leaflet rolling moth, Episimus unguiculus Clarke (Lepidoptera: Tortricidae). The larval stages of E. unguiculus tie together the plant leaflets while feeding and can completely defoliate small plants. The native love vine, Cassytha filiformis L. (Lauraceae), has been found parasitizing S. terebinthifolius in Florida. Natural processes such as plant parasitism may be one of the components of an integrated approach for S. terebinthifolius management in Florida. Thus, the objective of this study was to evaluate the combined effects of insect herbivory and plant parasitism on the performance of S. terebinthifolius . A factorial design experiment was conducted in the greenhouse to determine the effect of C. filiformis parasitism and E. unguiculus feeding damage on the growth and biomass of S. terebinthifolius . Results showed that plant parameters, including leaflet biomass, growth rate, and flower production, were negatively affected by plant parasitism and insect herbivory. Moreover, the decrease in S. terebinthifolius performance was greater when these two factors were combined, indicative of a synergistic relationship. In addition, the combined effect of C. filiformis and E. unguiculus suppressed plant performance for at least 2 months after the moths were removed. Therefore, increased control of S. terebinthifolius stands may be achieved in those areas where C. filiformis is present in Florida (e.g., pinelands, hammock forests) if the biocontrol agent E. unguiculus is approved for release.