Effects of road ditches on the vegetation composition in a saline environment

Landscape and Ecological Engineering - The construction of transportation corridors (such as roads) frequently disturbs and alters the natural disturbance regimes of ecosystems in many areas...     

环境因子对太白山高山植被物种组成和丰富度的影响

高山植被是一类具有重要生态和经济价值的植被类型,了解其物种组成和丰富度与环境因子的关系对于该类型植被保护、管理以及植物资源合理开发利用策略的制订具有重要指导意义。基于太白山高山植被和环境因子野外调查及室内实验数据,采用CCA排序法探索了环境因子对物种组成的影响,偏CCA计算了各环境因子对物种组成的总效应和净效应,GLM回归模型拟合了物种丰富度对环境因子的响应。结果表明,13个环境因子共解释了物种组成变异的31.7%,其中海拔、坡度、土壤碱解氮含量、全磷含量、坡向、岩石盖度、p H值、土壤厚度、有机质含量、有效磷含量和全氮含量对物种组成的净效应达显著水平(P0.05),但其作用强度依次减小。GLM拟合结果显示,物种丰富度与环境因子存在4种显著(P0.05)关系,即物种丰富度沿海拔和土壤厚度梯度单调递增,沿坡度和土壤全氮含量梯度单调递减,沿坡向、土壤p H值、碱解氮含量和全磷含量梯度呈单峰分布,与土壤有机质含量和全钾含量呈倒单峰关系。在这些显著的环境因子中,海拔、土壤碱解氮含量,p H值、有机质含量和坡向解释的物种丰富度变异量最大。     

Spatial and temporal changes in species composition of submersed aquatic vegetation reveal effects of river restoration

We examined temporal changes in spatial patterns of submersed aquatic vegetation (SAV) in response to the restoration of geomorphic habitat in Navigation Pool 8 of the Upper Mississippi River from 1998 to 2016. The frequency of occurrence and species composition of SAV at sampling sites were spatially interpolated for each year to create annual maps. Linear models were fitted to temporal changes in SAV within each map pixel. The frequency of occurrence of SAV (across all species) increased over time in much of the impounded region of the pool, including areas near restored islands. However, impounded areas maintained a relatively consistent species composition over time, with species known to be tolerant of higher flow velocities (>0.10 m/second) and wind fetch distances (>1,000 m) (e.g. Vallisneria americana) being most abundant. In contrast, areas protected by newly constructed islands transitioned from V. americana to species found in other protected backwater habitats and known to be intolerant of high flow velocities and wind fetch distances (e.g. Ceratophyllum demersum). The results suggest that previously reported improvements in water clarity may have improved growing conditions for all SAV species, especially in the lower impounded portion of the pool, while island restoration created more backwater‐like habitats and facilitated changes in species composition. Assessing changes in SAV occurrence alone offers only a partial view of local‐scale river restoration (e.g. island building), while analyses of species composition are likely to be more indicative of the types of changes (i.e. reduced flow velocity and wind fetch) associated with restoring geomorphic habitat.     

Combined effects of environment and grazing on vegetation structure in Argentine granite grasslands

Abstract. Effects of grazing and environment on vegetation structure have been widely acknowledged, but few studies have related both factors. We made 57 floristic samples in a highly variable landscape of mountain grasslands in central Argentina; 26 sample were in fence‐lines with contrasting vegetation. For each sample, we recorded topographic and edaphic parameters, as well as grazing intensity indicators. Floristic gradients were analysed with DCA and relations with abiotic and grazing‐related variables were detected with DCCA. Floristic axis 1 was explained by edaphic parameters associated to topography, ranging from communities in well drained soils on upper topographic positions to hydromorphic vegetation in poorly drained soils on lower topographic positions. Species richness decreased as soil moisture increased. Floristic axis 2 was associated with present and long‐term grazing indicators, and reflected shifts in vegetation physiognomy and species evenness. Tall tussock grasslands, with low species evenness and evidences of low or null grazing intensity were located at one extreme. Tussocks were gradually replaced by short graminoids and forbs towards the centre of the gradient, as grazing increased, and evenness reached a maximum. In degraded sites with heavy long‐term grazing intensities, short perennial species were replaced by an annual species, and evenness decreased. The magnitude of changes in floristic composition produced by grazing decreased with increasing soil moisture, and vegetation‐environment relationships were stronger in moderate to highly grazed situations than in lightly or non grazed situations.     

Hydrologic effects on riparian vegetation in a boreal river: an experiment testing climate change predictions

Climate change is expected to alter the magnitude and variation of flow in streams and rivers, hence providing new conditions for riverine communities. We evaluated plant ecological responses to climate change by transplanting turfs of riparian vegetation to new elevations in the riparian zone, thus simulating expected changes in water‐level variation, and monitored the results over 6 years. Turfs moved to higher elevations decreased in biomass and increased in species richness, whereas turfs transplanted to lower elevations gained biomass but lost species. Transplanted plant communities responded slowly to the new hydrologic conditions. After 6 years, biomass of transplanted turfs was statistically indistinguishable from target level controls, but species richness and species composition of transplants were intermediate between original and target levels. By using projections of future stream flow according to IPCC climate change scenarios, we predict likely changes to riparian vegetation in boreal rivers. Climate‐driven hydrologic changes are predicted to result in narrower riparian zones along the studied Vindel River in northern Sweden towards the end of the 21st century. Present riparian plant communities are projected to be replaced by terrestrial communities at high elevations as a result of lower‐magnitude spring floods, and by amphibious or aquatic communities at low elevations as a result of higher autumn and winter flows. Changes to riparian vegetation may be larger in other boreal climate regions: snow melt fed spring floods are predicted to disappear in southern parts of the boreal zone, which would result in considerable loss of riparian habitat. Our study emphasizes the importance of long‐term ecological field experiments given that plant communities often respond slowly and in a nonlinear fashion to external pressures.     

森林群落物种组成对凋落物组成的影响

在海南铜鼓岭山麓灌木林和季雨矮林固定大样地的基础上,通过收集凋落物,比较两林型的凋落物数量及其器官组成、凋落叶物种组成,探讨森林群落物种组成与凋落物组成的关系。结果表明:(1)两林型的凋落物总量及其器官组成不同,山麓灌木林(6.227 t/hm~2)比季雨矮林的年凋落量大(5.636 t/hm~2);凋落叶是凋落物的主要组成部分,能反映凋落物的凋落情况。(2)山麓灌木林凋落物优势种和主要物种为贡甲、林仔竹、橄树等15个物种,凋落叶总量占77.72%;季雨矮林的凋落物优势种和主要物种为方枝蒲桃、肖蒲桃、贡甲等17个物种,凋落叶总量占71.84%;山麓灌木林中凋落物优势种和主要物种的叶凋落量与其组成物种的株数、总断面积、树冠面积极显著正相关而季雨矮林的凋落物优势种和主要物种的叶凋落量与其组成物种的株数极显著正相关。山麓灌木林中两者的Jaccard相似性系数为20%,季雨矮林为25.93%,两林型的群落物种组成与凋落叶物种组成不一致,热带森林群落优势种不一定是凋落物优势种。     

桂西北喀斯特地区不同退化程度植被群落物种组成及多样性特征

世界范围内,很多自然生态系统均在不同程度上受到了损害,喀斯特脆弱生态系统的退化是一个复合过程,喀斯特地区不同退化程度植被群落特征有何差异有待研究。该文采用样方法进行全面的调查,研究了桂西北喀斯特地区5个退化程度植被群落的物种组成、群落结构特征和物种多样性。结果表明:(1)不同退化程度群落物种组成和生活型组成有较大差异,潜在退化群落科属种丰富度最高,沿着退化程度递增的梯度,群落乔木树种逐渐减少至消失,灌木比例呈先增后减的趋势,草本比例逐渐增加。(2)调查到维管束植物218种,隶属于86科168属;以大戟科、楝科、蔷薇科、马鞭草科、禾本科和肾蕨科植物为主;退化过程中,优势种的重要值逐渐降低,其在群落内的支配地位逐渐减弱,伴生种重要值逐渐升高。(3)退化过程中,群落结构趋于简单化,群落木本植物密度、高度和盖度逐渐减少。(4)不同退化程度植被群落乔灌草层物种多样性存在显著性差异,随着退化程度的增加,群落总植被物种丰富度指数、Shannon-Wiener多样性指数、Simpson优势度指数整体呈下降趋势。     

The role of landuse and natural determinants for grassland vegetation composition in the Swiss Alps

The Alps provide a high habitat diversity for plant species, structured by broad- and fine-scale abiotic site conditions. In man-made grasslands, vegetation composition is additionally affected by the type of landuse. We recorded vegetation composition in 216 parcels of grassland in 12 municipalities representing an area of 170×70 km in the south-eastern part of the Swiss Alps. Each parcel was characterized by a combination of altitudinal level (valley, intermediate, alp), traditional landuse (mown, grazed), current management (mown, grazed, abandoned), and fertilization (unfertilized, fertilized). For each parcel we also assessed the abiotic factors aspect, slope, pH value, and geographic coordinates, and for each municipality annual precipitation and its cultural tradition. We analysed vegetation composition using (i) variation partitioning in RDA, (ii) cover of graminoids, non-legume forbs, and legumes, and (iii) dominance and frequency of species. Species composition was determined by, in decreasing order of variation explained, landuse, broad-scale abiotic factors, fine-scale abiotic factors, and cultural tradition. Current socio-economically motivated landuse changes, such as grazing of unfertilized former meadows or their abandonment, strongly affect vegetation composition. In our study, the frequency of characteristic meadow species was significantly smaller in grazed and even smaller in abandoned parcels than in still mown ones, suggesting less severe consequences of grazing for vegetation composition than of abandonment. Therefore, low-intensity grazing and mowing every few years should be considered valuable conservation alternatives to abandonment. Furthermore, because each landuse type was characterized by different species, a high variety of landuse types should be promoted to preserve plant species diversity in Alpine grasslands.     

贵州省普定县不同植被演替阶段的物种组成与群落结构特征

通过对贵州省普定县喀斯特地区不同植被演替阶段群落的调查, 研究了植被演替过程中群落物种组成和群落结构的变化。结果表明, 该地区的植被主要处于5个演替阶段, 即次生乔木林、乔灌过渡林、藤刺灌丛、稀灌草丛以及火烧干扰后的蕨类植物群落。本次调查共记录到植物365种, 隶属89科218属。其中, 蕨类植物31种, 隶属14科23属; 种子植物334种, 隶属75科195属。物种分布较多的科主要有蔷薇科、菊科、禾本科、百合科、忍冬科、唇形科、莎草科、樟科、葡萄科和水龙骨科。随着正向演替的推进, 物种丰富度增加, 群落结构趋于复杂化。藤刺灌丛与乔灌过渡林群落层次不明显, 次生乔木林分层明显。从藤刺灌丛向次生乔木林演替的过程中, 小径级个体所占比例明显降低, 高于1.3 m植物的总密度、乔木密度和藤本密度都先升高后降低, 而灌木密度呈逐渐降低的趋势。对喀斯特地区植被的恢复提出了参考措施。     

川西周公山柳杉人工林群落的边缘效应

为研究人工林群落的边缘效应特征, 本文以川西周公山森林公园的柳杉(Cryptomeria fortunei)人工林破碎化大斑块为对象, 以植株平均胸径、平均高度、平均密度、丰富度指数(D)和Shannon-Wiener指数(H)来综合衡量边缘效应深度。在实地踏查的基础上, 从林缘向林内(梯度1至梯度5)设置5条样带(宽度为10 m), 在每条样带中设置4个10 m × 10 m的小样方进行调查。结果表明: (1)从物种组成上看, 在总面积为2,000 m²的20个小样方中共记录到111个物种, 隶属于54科96属, 物种数从林缘至林内递减。(2)从群落结构上看, 乔木层的平均胸径从林缘至林内呈减小趋势, 平均密度则相反, 平均高度无显著变化; 灌木层的平均密度从林缘向林内减小, 平均高度无显著变化; 草本层的平均密度和平均高度均呈减小趋势。(3)从物种多样性上看, 总体上各层次的丰富度指数和Shannon-Wiener指数均从林缘向林内呈减小趋势, 其中灌木层和草本层的变化趋势最明显; 同时, 林内各梯度与梯度1 (林缘)的共有种和相似性系数从林缘向林内递减。(4)分析各项群落特征发现, 平均高度、平均密度和相似性系数的数值在梯度2向梯度3过渡时的起伏变化最明显, 推断本研究中柳杉人工林斑块的边缘深度可达林内20 m。     

Sampling grain influences trends in vegetation composition and diversity with time since fire in Australian heathland

Scale‐dependency of pattern and process is well‐understood for many ecological communities; however, the influence of spatial scale (sampling grain) in detecting temporal change in communities is less well‐understood. The temperate lowland heathlands of south‐east Australia are one of the most fire‐prone ecosystems on earth. Despite the extensive literature documenting the effect of time since fire on heathlands, we know little about how sampling grain influences trends in vegetation variables over time, and whether these trends are scale‐dependent. Using 3500 ha of heathland in the Gippsland Lakes Coastal Park, south‐east Australia, we investigated how above‐ground species composition and diversity, and trends in these variables with increasing time since fire, were influenced by sampling grain (1 m², 10 m², 100 m², 900 m², 1 ha, 4 ha). Sampling grain influenced patterns detected in vegetation variables and in some instances, significantly affected their relationship with time since fire. Richness decreased with time since fire, with mean richness decreasing at three of the four grains, while total richness decreased at half of the sampled grains. Evenness (J) decreased with increasing time since fire for all grains except 1 m². The decline in diversity (H) with time since fire appeared to be independent of scale, as all grains decreased significantly with increasing time since fire. Community heterogeneity demonstrated a weak response to time since fire across most grains. Changes in composition among young (0–6 years since fire), intermediate (9–19 years) and old (23–27 years) sites were dependent on sampling grain, with all grains exhibiting significant differences in composition, apart from the 1 m² grain and the 100 m² grain (presence/absence data). Overall, species composition, richness, evenness, diversity and community heterogeneity were dependent on the scale at which the vegetation was sampled. In addition, trends in many of these vegetation variables with increasing time since fire were scale‐dependent. This work provides strong evidence that sampling at multiple grains contributes substantially to understanding pattern and process in heathlands.     

中国南部亚热带森林地表植被动态变化

系统研究了南方5个亚热带森林生态系统地表植被的动态变化情况.研究方法是:在每个研究区域内,按照地形梯度分别布设50个1m2 的样方,记录样方内所有物种的频度及相关的环境变量,5个研究区域共设250个样方,每个样方分别调查两次.通过单元及多元统计方法分析表明:维管植物物种频度在一个区域明显下降,另二个区域显著增加;苔藓物种频度在一个区域有明显下降,另一个区域明显增加;苔藓物种数量在3个区域显著增加,另二个区域显著下降;维管植物物种数量显著增加在二个区域;物种组成沿着第一个植被梯度轴DCA 1没有显著变化,沿着第二个植被梯度轴DCA 2在二个区域有显著变化.综合分析表明,苔藓对气候变化及其波动反映敏感,是较好的气候变化及气候波动生物指示因子,而管植物数量及频度的变化没有明显证据显示与土壤酸化和大气污染有紧密关系.     

Warming effects on greenhouse gas fluxes in peatlands are modulated by vegetation composition

Understanding the effects of warming on greenhouse gas feedbacks to climate change represents a major global challenge. Most research has focused on direct effects of warming, without considering how concurrent changes in plant communities may alter such effects. Here, we combined vegetation manipulations with warming to investigate their interactive effects on greenhouse gas emissions from peatland. We found that although warming consistently increased respiration, the effect on net ecosystem CO₂ exchange depended on vegetation composition. The greatest increase in CO₂ sink strength after warming was when shrubs were present, and the greatest decrease when graminoids were present. CH₄ was more strongly controlled by vegetation composition than by warming, with largest emissions from graminoid communities. Our results show that plant community composition is a significant modulator of greenhouse gas emissions and their response to warming, and suggest that vegetation change could alter peatland carbon sink strength under future climate change.