Do moss samples,pollen traps and modern lake sediments all collect pollen in the same way? A comparison from the forest limit area of northernmost Europe

Moss polsters, pollen traps and lake surface sediment samples are commonly used as climate calibration data or as modern analogues for reconstructing vegetation from fossil profiles, but the differences in pollen content between these media have received little attention. This study aims to analyse how the three media differ in reflecting individual vegetation types and spatial differences in vegetation. 119 modern samples (64 moss polsters, 37 lake surface sediment samples and 18 pollen traps from which a collection was made annually) were taken from northern Fennoscandia and the Kola Peninsula as a broad transect crossing the northernmost forest limits of Betula pubescens ssp. czerepanovii (mountain birch), Pinus sylvestris (Scots pine) and Picea abies (Norway spruce). The pollen assemblages from these samples were compared with the surrounding vegetation visually and via PCA (principle components analysis) and cluster analysis. Both comparisons allow a correct distinction between pollen assemblages of arctic/alpine heath, mountain birch dominated areas, and boreal coniferous forests. The differences between the vegetation zones are stronger than the differences between the sampling media. Nevertheless, lake sediment samples from the mountain birch woodland zone tend to overestimate pine and underestimate birch. Pollen traps are biased towards lower tree pollen percentages and higher values of shrubs, herbs and Cyperaceae. This bias is especially strong in traps that have missing years in the data. Irrespective of the vegetation zone, pollen traps tend to have lower Pinus pollen percentages than in the adjacent moss polsters.     

佛坪国家级自然保护区植被垂直带谱及其与邻近地区的比较

在首先确定垂直带划分的原则和将佛坪自然保护区植被划分为落叶阔叶林带、中山小叶林带和亚高山针叶林带３个垂直带,各垂直带植被物种组成的区系、生活型组成和物种多样性的差异证实了这种划分的合理性。与邻近地区植被垂直带谱的比较表明,佛坪自然保护区的植被垂直带谱与秦岭北坡有明显差异,表现为典型的暧温带与北亚热带过渡区域的植被景观,虽然基带以上各植被带暖温带特色很明显,但其植被属性应是北亚热带的。     

佛坪国家自然保护区地面生苔藓植物物种多样性

通过对秦岭南坡佛坪国家自然保护区地面生苔藓植物的调查,采用相似性系数、重要值、多样性指数对其进行物种多样性的研究。结果表明:29个样地内地面生苔藓植物共33科69属189种,包括苔类植物7科8属15种和藓类植物26科61属174种,其中青藓科是最优势的科。落叶阔叶栎(Quercus)林下地面生苔藓植物的物种多样性最高,其次是落叶阔叶桦(Betula)林带、竹林、针叶林和沟谷岩石,杜鹃(Rhododendron)灌丛带的最低。落叶阔叶栎林带和落叶阔叶桦林带的种相似性最高,杜鹃灌丛与其它植被带的种相似性都很低。研究表明秦岭南坡的佛坪国家自然保护区内,低山地区的落叶阔叶栎林带是该地区苔藓植物多样性的分布中心,是物种多样性保护的关键地带;亚高山地区杜鹃灌丛带的苔藓植物物种多样性虽然不高,但种类明显不同于别的地带,所以也应是苔藓植物多样性保护值得注意的地带。     

The effects of reindeer grazing on the composition and species richness of vegetation in forest–tundra ecotone

We conducted an 8-year exclosure experiment (1999–2006) in a forest–tundra ecotonal area in northwestern Finnish Lapland to study the effects of reindeer grazing on vegetation in habitats of variable productivity and microhabitat structure. The experimental sites included tundra heath, frost heath and riparian habitats, and the two latter habitats were characterized by hummock-hollow ground forms. The total cover of vegetation, cover of willow (Salix spp.), dwarf birch (Betula nana), dwarf shrubs, forbs and grasses (Poaceae spp.) increased in exclosures in all habitats. The increase in the total cover of vegetation and in the covers of willow and dwarf birch tended to be greatest in the least productive tundra heath. Opposing to the increase in the dominant vascular plant groups, the cover and species number of bryophytes decreased in exclosures. We conclude that the effects of reindeer grazing on vegetation composition depend on environmental heterogeneity and the responses vary among plant groups. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Plant carbon allocation drives turnover of old soil organic matter in permafrost tundra soils

Carbon cycle feedbacks from permafrost ecosystems are expected to accelerate global climate change. Shifts in vegetation productivity and composition in permafrost regions could influence soil organic carbon (SOC) turnover rates via rhizosphere (root zone) priming effects (RPEs), but these processes are not currently accounted for in model predictions. We use a radiocarbon (bomb‐¹⁴C) approach to test for RPEs in two Arctic tall shrubs, alder (Alnus viridis (Chaix) DC.) and birch (Betula glandulosa Michx.), and in ericaceous heath tundra vegetation. We compare surface CO₂ efflux rates and ¹⁴C content between intact vegetation and plots in which below‐ground allocation of recent photosynthate was prevented by trenching and removal of above‐ground biomass. We show, for the first time, that recent photosynthate drives mineralization of older (>50 years old) SOC under birch shrubs and ericaceous heath tundra. By contrast, we find no evidence of RPEs in soils under alder. This is the first direct evidence from permafrost systems that vegetation influences SOC turnover through below‐ground C allocation. The vulnerability of SOC to decomposition in permafrost systems may therefore be directly linked to vegetation change, such that expansion of birch shrubs across the Arctic could increase decomposition of older SOC. Our results suggest that carbon cycle models that do not include RPEs risk underestimating the carbon cycle feedbacks associated with changing conditions in tundra regions.     

Impacts of succession and grass encroachment on heathland Orthoptera

For the conservation of biodiversity, heathlands present important ecosystems throughout Europe. The formerly widespread habitats are nowadays restricted to small and isolated remnants. Without land use heathland vegetation undergoes succession and, in addition, the increasing amount of atmospheric nitrogen deposition has resulted in an encroachment of grasses. In the present study we analysed the effects of succession and grass encroachment on Orthoptera in a coastal heathland on the Baltic island of Hiddensee, Germany. Vegetation, microclimate, soil humidity and Orthoptera were sampled in the five main stages of heathland succession, namely grey dunes, dwarf-shrub heath, grassy heath, heath with shrubs, and birch forest. Vegetation and environmental parameters showed strong differences among the successional stages. Orthoptera species richness was highest in transitional stages. The high proportion of grasses offer favourable habitat conditions for graminivorous, chorto- and thamnobiont species. Orthoptera density was highest in grey dunes. Threatened and specialised species were restricted to the young stages grey dunes and dwarf-shrub heath. Hence, in order to maintain a high diversity of Orthoptera in heathlands, maintaining different successional stages is of critical importance and this should be integrated into heathland management practices.     

Holocene vegetation history and tree-line changes on a north–south transect crossing major climate gradients in southern Norway—evidence from pollen and plant macrofossils in lake sediments

Long-term tree-line fluctuations have been studied using pollen and plant macrofossils preserved in lake sediments from three sites on an oceanic to continental transect in southern Norway. After deglaciation the early Holocene vegetation developed from an open pioneer herb-dominated vegetation into dwarf-shrub heath with shrubs, which was soon colonised by Betula and later also by Pinus sylvestris at the two lower sites. Maximum tree-line altitudes occurred in the early-to mid-Holocene. P. sylvestris reached 100–150 m higher than at present in continental areas, and 35–100 m higher on the west coast during the Holocene. Betula pubescens grew at altitudes that today reach 1300 m a.s.l. in Jotunheimen and 800 m a.s.l. in western Norway. The Pinus forest was at the two southwestern sites mixed with Betula and Alnus was closer to the sites between 8500 and 7500 cal years BP. A shift from mixed pine-birch woodland to birch woodland is seen from ca. 4300 cal years BP with the development of a sub-alpine birch belt followed by further recession of the birch forest. On the west coast, birch dominated only during the last 500–1000 years. Further decrease of woodland and opening of the landscape in the last 2000 years occurred due to climatic change and human impact such as sheep and cattle grazing.     

Coastal heathland succession influences butterfly community composition and threatens endangered butterfly species

Succession has a strong influence on species diversity and composition of semi-natural open terrestrial ecosystems. While several studies examined the effects of succession on butterflies in grassland and forest ecosystems, the response of heathland butterflies to succession had not been investigated so far. To address this issue we sampled butterfly abundance and environmental parameters on the Baltic island of Hiddensee (NE Germany) along a gradient of coastal heathland succession from grey dunes to birch forest. Our results provide evidence that succession of coastal heathland has a strong influence on butterfly diversity, abundance, and species composition. Thereby grass and tree encroachment present the main threats for heathland butterflies. Diversity and abundance of butterflies were highest in shrub-encroached heath directly followed by early stages of coastal heathland succession (dwarf-shrub heath, grey dune). Both observed threatened species (Hipparchia semele, Plebeius argus) were negatively affected by succession: abundance decreased with increasing vegetation density (both species) and grass cover (P. argus); consequently, the two later successional stages (shrub, birch forest) were not occupied. Our findings highlight the importance of the preservation of early stages of coastal heathland succession for endangered butterfly species. For coastal heathland management we therefore suggest to maintain early successional stages by sheep grazing, mowing or, in case of high nutrient contents, intensive techniques such as sod-cutting or choppering. To a lower extend shrub-encroached sites should also be present, which might be beneficial for overall species richness.     

Study of changes in life zone distribution in north-east China by climate–vegetation classification

Life zones and their changes in distribution in north-east China were studied based on climate–vegetation relationships. The warmth index (WI) and aridity index (the ratio of evaporation [evaporation rate, ER] to precipitation) were used to represent the site condition. The typical site condition of each vegetation type was determined as the classification criterion. The boundaries of the four potential vegetation zones were estimated based on the combinations of WI and ER in relation to vegetation (i.e. cold-temperate conifer forest zone, temperate broad-leaved conifer mixed forest zone, warm-temperate deciduous forest zone, and temperate steppe zone). The distribution changes in vegetation zone caused by human activities were estimated by comparing the potential vegetation with the actual one. The percentage cover of forest has shrunk from about 70% to the present 27%. About 23% of the study area was replaced by agricultural vegetation and industrial use. Nearly half of the region could have been covered by broad-leaved conifer mixed forest which was shrunk to a small area, less than 5% of the region. The broad-leaved deciduous forest zone in the southern part could have occupied about 7% of the area, and had almost no virgin stand.     

N-fertilization and disturbance impacts and their interaction in forest-tundra vegetation

The interaction of environmental perturbations is an important, although a seldom studied feature, when evaluating factors influencing plant community structure and potential changes in the vegetation. Since environmental perturbations commonly occur in concert, there is a need for experimental investigations in which single, combined and interactive effects of environmental factors are studied. We studied interactive effects of N-fertilization (40 kg N ha^?1 year^?1) and disturbance, i.e. removing the vegetation and soil organic layers, in the forest-tundra ecotone in northern Finland during 2002–2005. Plant abundances were measured in a coniferous forest, mountain birch forest and tundra heath. Both N-fertilization and disturbance reinforced the proportion of deciduous (Vaccinium myrtillus) and the graminoids (i.e. Deschampsia flexuosa and Carex sp.) at the expense of evergreens in vegetation. N-fertilization also enhanced the post-disturbance recovery of graminoids. Vegetation recovery was slow in the tundra heath, where N-fertilization decreased the abundance of the evergreen Empetrum nigrum ssp. hermaphroditum. Although the changes in vegetation due to the N-fertilization and disturbance could be detected, they did not change the initial dominance of plant functional types. Taken together, our results suggest that increasing N affects the rate rather than direction of recovery after disturbance. Moreover, plant communities differ in terms of their capabilities to respond to multiple perturbations which should be taken into account when evaluating future vegetation responses under changing environment in at high-latitude and high-altitude ecosystems.     

Vegetation management with glyphosate has little impact on understory species diversity or tree growth in a sub boreal spruce plantation – A case study

Abstract

In central British Columbia (BC), forest management practices have altered natural stand development pathways by controlling “non commercial” tree species and other competing species with the objective of maximizing crop tree growth. This potentially decreases overall diversity within the stand. We conducted a retrospective study on a 13-year-old stand to investigate the impacts of vegetation management with glyphosate on tree growth, species diversity and forest health in central BC. Results revealed that spruce was marginally taller than birch in the herbicide treated area and significantly shorter than birch in the untreated area. There was no difference in spruce diameter at breast height (DBH) and mean stem volume by treatment. White pine weevil attack was significantly reduced in the untreated area. In total, 133 plant species were recorded from 2002 to 2006, but 30% of the species present in 2002 were not present in 2006. Species' richness and alpha diversity were similar between treatments but beta diversity was relatively low indicating little treatment effect. There was a greater occurrence and abundance of “weedy” and pioneer species in the herbicide-treated area. Overall, this study suggests that glyphosate application does not remove all birch and showed minimal or no impact on under-story vegetation. Therefore, a move away from broadcast vegetation control to spot control where warranted could result in better tree growth, improved forest health and structural diversity.     

塔河林业局林火对植被的影响

针对大兴安岭地区塔河林业局不同林型下,不同火烧强度的火烧迹地的森林植被更新及恢复情况进行了调查研究。结果表明：（1）针叶林过火迹地上,落叶松幼苗较少,阔叶树萌条更新强度同火烧程度成正比;火烧前生长有白桦、赤杨的林地上,火烧后阔叶树成为主导树种,林相完全发生变化。（2）重度火烧下有利于天然更新,促使白桦、山杨萌生。中度火烧最初形成以杨桦为优势树种的阔叶林,后逐渐演变为针阔混交林。轻度火烧有利于针叶林的更新。（3）火烧后不同林型下灌木草本植被种类变化不同。从盖度方面来看,杜鹃落叶松林型中林下灌木草本更新最为良好。     

秦岭太白山桦林的稳定性

本文论述了桦林的稳定性。文中认为桦林地质时期和现代都可形成地带性森林,它是凉温湿润气候的顶极群落,分布在暖温带落叶阔叶林与湿冷生针叶林之间的凉温湿润地带。因此这类林的区系组成无论地质时期或现代,都是以暖温带落叶阔叶林和寒温带针叶林的混合成分为特征。     

秦岭太白山桦林的稳定性

本文论述了桦林的稳定性。文中认为桦林地质时期和现代都可形成地带性森林,它是凉温湿润气候的顶极群落,分布在暖温带落叶阔叶林与湿冷生针叶林之间的凉温湿润地带。因此这类林的区系组成无论地质时期或现代,都是以暖温带落叶阔叶林和寒温带针叶林的混合成分为特征。     

A study on the vegetation in the east side of Helan Mountain

This paper analyzed the vegetation data obtained from a field survey conducted in the East Side of Helan Mountain, China, to reveal the features of mountainous vegetation growing in a transitional zone between the steppe and desert regions. Detrended correspondence analysis (DCA) was applied to the process of analysis, to clarify the spatial variation of floristic composition of the vegetation in the lower mountain range.The preliminary results obtained from the analysis are: (1) There are 53 vegetation formations existing in the area, following the China's criteria of vegetation classification system. (2) Those vegetation types compose a vertical vegetation spectrum in the East Side of Helan Mountain due to the climatic gradient caused by elevation variation. The spectrum consists of 4 zones. They are, from the foot up to the peak in turn, mountain steppe zone, mountain open forest and steppe zone, mountain coniferous forest zone, and alpine bush and meadow zone. The mountain coniferous forest zone can be further divided into two subzones: Pine forest subzone and Spruce forest subzone. (3) Most of the vegetation types show clear xeromorphic features due to the base zone of the vertical vegetation spectrum lying in the arid region of China. (4) The distribution of vegetation types and flora is sensitive and susceptible to the moisture condition that the vertical vegetation spectrum has quite different expressions between northern and southern exposures. (5) Floristic composition of the vegetation shows a northern temperate feature. The families that are rich in species in the area include Gramineae, Compositae, Leguminosae, Chenopodiaceae, Rosaceae and others, most of which are abundant in herbaceous species. (6) The variation of the ecological conditions from the north to the south also leads to the differentiation of vegetation and its floristic composition in the area. (7) The broad-leaved forest can not form a forest zone in the vertical vegetation spectrum. This may be a special characteristic of the spectrum sitting on a transitional zone between the steppe and desert regions.     

江苏省植被区划

 本文简要论述江苏省自然环境特点和植被地理分布规律,并探讨了植被区划的原则与依 据。笔者认为：该省原为我国森林分布地区,所以森林植被应是植被区划的重要依据,农作物植被似不宜作为区划的依据。由于江苏面积较小,而且现存自然植被占地太小,故区划只分三级。制订的江苏植被区划系统,包括2个植被区域、3个植被地带和10个植被区,并分别作了简要叙述。     

Vkgetation analysis along a successional gradient from heath to oak forest

At Hjelm Hede in Denmark where an oak shrub is invading into a heathland the successional process has been studied on poor sandy outwashed plain. The study used a transect through a successional gradient from open heath to oak shrub where vegetation, major topsoil parameters and tree characteristics were analysed. The study enables us with spatial variation of key parameters to combine numerous detailed studies from the same site into an overall picture of changing vegetation and soil parameters reflecting the succession, which has been documented previously. The data were analysed by the use of Detrended Correspondence Analysis (DCA). Along the gradient from heath to forest the thick mor layer of the heathland soil decomposed, the CM ratio decreased from 25 to 15, pH increased and ammonium became available for the plants during a time span of approximately 120 years. The vegetation on the open heath was typical Danish inland heath vegetation dominated by Calluna vulgaris, Empetrum nigrum and Deschampsiaflexuosa. Under the young oak shrub the vegetation was dominated by Deschampsia Jexuosa, Trientalis europaea , and Maianthemum bijiolium. In the oldest and most forest like parts of the shrub a vegetation dominated by Holcus mollis, Anemone nemomsa and Stellaria holostea was found. Woody chamaephytes were replaced first by hemicryptophytes and later by geophytes. The vegetation's Ellenberg values indicated an increase in nitrogen availability and a decrease in acidity and light availability through secondary succession.     

Habitat distribution and conservation of land bird populations in northern Norway

About 300 km line transect censuses of breeding land birds were made in northern Norway in 1974–76. The data (1020 pairs in 26 samples) were grouped into seven major habitats: stony ground and oceanic heath (C1), continental dry heath (C2). "'2Calcarius heath", dry peatland, wet peatland (C5), meagre and average birch forest, and rich birch forest (C7). Bird density ranged from 22 pairs km⁻² (C2) to 364 pairs km⁻² (C7), but most habitats had 67–96 pairs km⁻². The bird communities are described.
Defining the Optimal habitat for a species as the maximum-density habitat, the 43 species observed were found to comprise three major groups: tundra species (optimal habitat C1), peatland species (C5) and forest species (C7). Species whose central range includes northern Norway had a broader habitat amplitude than those with a southern or a very northern distribution. A new index was devised for the evaluation of the conservational importance of a habitat or a species. From the North European standpoint. C1 is certainly the most important habitat in northern Norway, as C1 supports many species which are rare in other parts of North Europe. However, population trends should also be taken into account when conservational preferences are judged.     

Species richness and phylogenetic diversity of seed plants across vegetation zones of Mount Kenya,East Africa

Mount Kenya is of ecological importance in tropical east Africa due to the dramatic gradient in vegetation types that can be observed from low to high elevation zones. However, species richness and phylogenetic diversity of this mountain have not been well studied. Here, we surveyed distribution patterns for a total of 1,335 seed plants of this mountain and calculated species richness and phylogenetic diversity across seven vegetation zones. We also measured phylogenetic structure using the net relatedness index (NRI) and the nearest species index (NTI). Our results show that lower montane wet forest has the highest level of species richness, density, and phylogenetic diversity of woody plants, while lower montane dry forest has the highest level of species richness, density, and phylogenetic diversity in herbaceous plants. In total plants, NRI and NTI of four forest zones were smaller than three alpine zones. In woody plants, lower montane wet forest and upper montane forest have overdispersed phylogenetic structures. In herbaceous plants, NRI of Afro‐alpine zone and nival zone are smaller than those of bamboo zone, upper montane forest, and heath zone. We suggest that compared to open dry forest, humid forest has fewer herbaceous plants because of the closed canopy of woody plants. Woody plants may have climate‐dominated niches, whereas herbaceous plants may have edaphic and microhabitat‐dominated niches. We also proposed lower and upper montane forests with high species richness or overdispersed phylogenetic structures as the priority areas in conservation of Mount Kenya and other high mountains in the Eastern Afro‐montane biodiversity hotspot regions.