杉木人工林林下植物物种β多样性的研究

应用β多样性测度公式对不同生长发育阶段和不同地位指数的杉木人工林林下植物进行定量分析。结果表明：不同生长发育阶段和不同地位指数的杉木人工林林下植物β多样性指数值存在明显差异,其中56年生老龄杉木林与3年生杉木幼林之间的林下植物β多样性指数值差异尤为9明显,并且随着人工林生长发育阶段越接近56年生老龄杉木林,其林下植物β多样性指数越小;各杉木林群落中,14地位指数的样地与18地位指数的样地间的林下植物β多样性指数值差异尤为明显。     

杉木人工林土壤真菌遗传多样性

为探明杉木人工林土壤真菌遗传多样性及其与环境因子的关系,采用454测序技术对土壤真菌的遗传多样性进行了分析,测定了黄丰桥林场杉木人工林土壤真菌的遗传多样性与环境因子的相关性。试验结果表明:①不同代数、林龄的杉木人工林土壤理化性质及林下植被多样性均有显著差异。第1代杉木幼林林土壤肥力较高,有机质、全N、速效K的均值分别为88.02g/kg、2.56 g/kg、84.96 mg/kg均高于第2代和第3代杉木幼林林,速效N和含水量的均值分别为22.86 mg/kg和26.28%低于其他样地。杉木幼林林下植被多样性最为丰富。②通过454测序技术分析发现第1代杉木幼林真菌Ace丰富度指数、Chao丰富度指数及群落遗传多样性指数均大于第2代杉木幼林和第3代杉木幼林。杉木人工林土壤中粪壳菌纲(Sordariomycetes)真菌为优势种群。不同栽培代数杉木人工林的真菌群落存在差异,其中块菌科(Tuberaceae)为第2代和第3代杉木林特有真菌,而不同发育阶段的杉木人工林的真菌群落差异不明显。③经RDA分析,杉木人工林土壤主要真菌群落受含水量、有机质、速效P、速效K影响较大。土壤真菌群落遗传多样性Shannon-Wiener多样性指数与林下植被多样性、土壤全N显著正相关,土壤真菌Chao指数与土壤真菌Shannon-Wiener多样性指数、土壤全N含量显著正相关。本研究表明不同栽培代数杉木人工林的真菌群落存在差异,土壤真菌群落与环境因子之间具有相关性。     

Impact of balsam fir flowering on pollen and foliage biochemistry in relation to spruce budworm growth, development and food utilization

The impact of balsam fir (Abies balsamea (L.) Miller) flowering on nutritional and allelochemical quality of pollen, current-year and one-year-old foliage is studied in relation to spruce budworm (Choristoneura fumiferana Clem.) (Lepidoptera: Tortricidae) growth, development and utilization of food and nitrogen. In the laboratory, using fresh food from the field, we simulated conditions of low larval population density, in which there is no current-year foliage depletion during the spruce budworm feeding period. Similarly, we simulated conditions of high larval population density when current-year foliage depletion occurs.Because of the high nutritive value of pollen (high amounts of amino acids and minerals, especially nitrogen; low monoterpene content), insects from flowering trees reached the fifth instar five days earlier than those from non-flowering trees, and had heavier dry- and nitrogen-weights at the beginning of the fifth instar. At budbreak, switching from pollen to current-year foliage negatively affected conversion efficiencies and digestibilities of food and nitrogen (AD; ADN; ECDN; ECI; ECIN). The switch from pollen to new foliage had a detrimental impact on fifth-instar survival and on newly-moulted sixth-instar dry- and nitrogen-weights. Moreover, during the fifth instar, balsam fir flowering reduced the nutritive value of current-year foliage, which in turn, might have contributed to the reduced larval growth. Nevertheless, during the sixth instar, balsam fir flowering affected the biochemistry of current-year foliage in ways that enabled larvae to compensate for their low fifth-instar biological performance; larvae also managed to reach pupal dry weight similar to larvae reared on non-flowering trees. Current-year foliage from flowering trees contained less nitrogen, total soluble sugars and total monoterpenes. Those foliar characteristics enabled larvae to increase food and nitrogen consumption rates (RCR; RNCR), because of lower repellency and/or post-ingestional feedback from monoterpenes.As for current-year foliage, balsam fir flowering reduced nitrogen, total soluble sugar and total monoterpene contents in one-year-old foliage during the sixth-instar feeding period. These characteristics enabled sixth-instar larvae, fed on old foliage from flowering trees, to have high relative food and nitrogen consumption rates (RCR; RNCR). Larvae were also able to reach higher relative growth rates (RGR) and relative nitrogen accumulation rates (RNAR) compared to larvae reared on one-year-old foliage from non-flowering trees. Finally, larvae on flowering trees had pupal dry weight similar to those from non-flowering trees, but reached the adult stage nine days earlier.Regardless the foliage type consumed by spruce budworm larvae during the sixth instar, pollen consumption during early larval stages reduced total development time, and thus exposure time to natural enemies. This phenomenon might increase larval survival. Balsam fir flowering changed the biochemistry of one-year-old and current-year foliages, but did not affect pupal dry weights of larvae reared on flowering trees compared to those reared on non-flowering trees. Thus, at low population density, spruce budworm populations in balsam fir flowering stands might be favoured over those in balsam fir non-flowering stands. In addition, when larvae consumed one-year-old foliage during the entire sixth instar, those on flowering trees are probably favoured over those on non-flowering trees. However, because flowering trees produce less new foliage than non-flowering trees, current-year foliage depletion may occur earlier on flowering trees than on non-flowering trees. Thus, at similar larval population density, larvae on flowering trees might have to feed on one-year-old foliage earlier than those on non-flowering trees. In that case, spruce budworm populations on non-flowering stands would be favoured over those on flowering stands.     

遗传改良对杉木针叶和种实性状的影响

为揭示遗传改良对主要造林用材树种叶和种实性状的影响,阐明性状的变异趋势,该研究以杉木第4轮育种的精选树(改良群体)、四省五地的表型优树与古树(未改良群体)为对象,调查了218个无性系的针叶和种实性状指标,采用方差分析和多重对比方法研究遗传改良对杉木及不同类型杉木的表型差异,并通过相关性分析探究遗传改良对杉木针叶和球果部分表型性状的影响,以及利用主成分分析和聚类分析进行了分类。结果表明:(1)未改良群体的针叶长、针叶宽和出籽率分别比改良群体小13.28%、10.81%和33.90%,其他性状表现为未改良群体大于改良群体,差异在10.90%～27.03%之间。未改良群体球果长、球果宽和出籽率的变异系数,分别比改良群体大9.14%、12.73%和15.38%。(2)球果长、球果宽、苞鳞长和苞鳞宽4个性状,在未改良群体中仅有球果长和球果宽(0.931)、苞鳞长和苞鳞宽(0.622)之间呈极显著正相关,经遗传改良后,该4个性状两两之间均呈显著或极显著正相关。(3)四川雅安(SCYA)的球果长和球果宽的性状比改良群体大48.83%和53.26%,安徽黄山(AHHS)的百粒重比改良群体大16.92%。(4)遗传改良导致松张型球果的杉木比例降低,紧包型和反翘型球果的杉木比例增加。综上认为,杉木的遗传改良导致球果大小下降,改变了不同针叶和球果类型的比例,同时会改变针叶性状和种实性状的相关性,将为杉木种质资源评价和未来多目标育种提供依据。     

Habitat use of nightjar (Caprimulgus europaeus) in an Austrian pine forest

The Steinfeld in Lower Austria supports a population of European Nightjar (Caprimulgus europaeus) which was extensively studied during 1997 and 1998. The study area encompassed a pine forest of 20 km². The population densities of 1.05 and 1.25 territories/km², respectively, lies within the range found in central European populations. Annual monitoring until 2001 has shown the population to be stable. To gain an insight into habitat use of the species, various habitat-related parameters were measured inside and outside the territories, namely structure of trees, density of trees, structure of undergrowth vegetation and structure of clearings. Discriminant analysis was applied to assess the factors responsible for habitat choice of the Nightjar population. The findings showed that the Nightjars territories were frequently centered on a large clearing with an area of at least 0.7 ha. Clearings less than 50 m wide were not colonized. The requirement for a minimum width of a clearing in addition to a minimum area probably relates to better hunting conditions. Nightjars prefer trees where the lower edge of the crown is on average 4.38 m higher than at control points so that males can churr from dead branches immediately below the canopy. Such trees were found on the edge of clearings in the forest, and the edge of a clearing thus had a pronounced effect on the quality of a territory. In contrast to reports in the literature, neither the proportion of bare patches of ground nor the average height of undergrowth vegetation was found to be decisive for territory selection.     

Persistence of balsam fir and black spruce populations in the mixedwood and coniferous bioclimatic domain of eastern North America

The boreal ecocline (ca 49°N) between the southern mixedwood (dominated by balsam fir) and the northern coniferous bioclimatic domain (dominated by black spruce) may be explained by a northward decrease of balsam fir regeneration, explaining the gradual shift to black spruce dominance. 7,010 sample plots, with absence of major disturbances, were provided by the Quebec Ministry of Forest, Fauna, and Parks. The regeneration (sapling abundance) of balsam fir and black spruce were compared within and between the two bioclimatic domains, accounting for parental trees, main soil type (clay and till) and climate conditions, reflected by summer growing degree‐days above 5°C (GDD_5), total summer precipitation (May–August; PP_MA). Parental trees and soil type determined balsam fir and black spruce regeneration. Balsam fir and black spruce, respectively, showed higher regeneration in the mixedwood and the coniferous bioclimatic domains. Overall, higher regeneration was obtained on till for balsam fir, and on clay soils for black spruce. GDD_5 and PP_MA were beneficial for balsam fir regeneration on clay and till soils, respectively, while they were detrimental for black spruce regeneration. At a population level, balsam fir required at least 28% of parental tree basal area in the mixedwood, and 38% in the coniferous bioclimatic domains to maintain a regeneration at least equal to the mean regeneration of the whole study area. However, black spruce required 82% and 79% of parental trees basal area in the mixedwood and the coniferous domains, respectively. The northern limit of the mixedwood bioclimatic domain was attributed to a gradual decrease toward the north of balsam fir regeneration most likely due to cooler temperatures, shorter growing seasons, and decrease of the parental trees further north of this northern limit. However, balsam fir still persists above this northern limit, owing to a patchy occurrence of small parental trees populations, and good establishment substrates.     

Genetic variation of Marchalina hellenica (Hemiptera: Margarodidae) sampled from different hosts and localities in Greece

Random amplified polymorphic DNA (RAPD) analysis was applied to 120 individuals of Marchalina hellenica (Gennadius) representing six populations collected in northern, central and southern mainland Greece. One population was sampled on one species of fir tree and the others on two species of pine trees. Four random decamer primers were used to evaluate genetic variation among the populations examined. The results revealed intra- and interpopulation polymorphism both related to host type and region of origin. Phylogenetic analysis based on genetic distances estimated by the RAPD frequencies revealed an important genetic differentiation in samples collected on fir trees in southern Greece and to a lesser extent in samples from pine trees in central and northern Greece. Furthermore, considerable subdivision and restricted gene flow among the populations examined were observed. The results are discussed in relation to the biology and geographical distribution of M. hellenica in Greece.     

Silver fir and Douglas fir are more tolerant to extreme droughts than Norway spruce in south‐western Germany

Improving our understanding of the potential of forest adaptation is an urgent task in the light of predicted climate change. Long‐term alternatives for susceptible yet economically important tree species such as Norway spruce (Picea abies) are required, if the frequency and intensity of summer droughts will continue to increase. Although Silver fir (Abies alba) and Douglas fir (Pseudotsuga menziesii) have both been described as drought‐tolerant species, our understanding of their growth responses to drought extremes is still limited. Here, we use a dendroecological approach to assess the resistance, resilience, and recovery of these important central Europe to conifer species the exceptional droughts in 1976 and 2003. A total of 270 trees per species were sampled in 18 managed mixed‐species stands along an altitudinal gradient (400–1200 m a.s.l.) at the western slopes of the southern and central Black Forest in southwest Germany. While radial growth in all species responded similarly to the 1976 drought, Norway spruce was least resistant and resilient to the 2003 summer drought. Silver fir showed the overall highest resistance to drought, similarly to Douglas fir, which exhibited the widest growth rings. Silver fir trees from lower elevations were more drought prone than trees at higher elevations. Douglas fir and Norway spruce, however, revealed lower drought resilience at higher altitudes. Although the 1976 and 2003 drought extremes were quite different, Douglas fir maintained consistently the highest radial growth. Although our study did not examine population‐level responses, it clearly indicates that Silver fir and Douglas fir are generally more resistant and resilient to previous drought extremes and are therefore suitable alternatives to Norway spruce; Silver fir more so at higher altitudes. Cultivating these species instead of Norway spruce will contribute to maintaining a high level of productivity across many Central European mountain forests under future climate change.     

Seasonal dynamics of damage to small-leaved lime trees by phyllophagous arthropods

The seasonal dynamics of damage to the small-leaved lime Tilia cordata by phyllophagous arthropods was monitored in Izhevsk in 1999–2002. The work was carried out in 15 test plots, 10 model trees being selected within each plot. From May 30 to September 10, damage to leaves was assessed every ten days in the same model branch selected from the lower layer in the northern part of the crown. The complex of phyllophagous arthropods of the small-leaved lime includes 33 species from 17 families and 7 orders.     

Phytohormones in needles of healthy and declining silver fir (Abies alba Mill.): I. Indole-3-acetic acid

 Levels of indole-3-acetic acid (IAA) were determined in needles from silver fir (Abies alba Mill.) trees in the northern Black Forest. IAA was quantified by gas chromatography (GC) as 1-heptafluorobutyryl-IAA-methylester (HFB-IAA-ME) using electron capture detection. Prior to GC analysis, extensive purification of needle extracts was performed employing two HPLC steps. Peak identity of HFB-IAA-ME was confirmed by combined gas chromatography-mass spectrometry in selected samples. Levels of IAA in needles belonging to different needle age-classes exhibited a cyclic seasonal pattern with highest concentrations in winter and lowest levels in spring when bud-break occurred. Such a cyclic seasonal pattern of IAA levels was also observed in needles from declining fir trees or fir trees suffering from a strong sulfur impact (S-impact) in the field due to a local SO₂ source. Levels of IAA increased with increasing needle age. This age dependency of IAA concentrations was most pronounced in late autumn when IAA levels were high and nearly disappeared in spring when IAA levels reached their minimum. In needles from declining fir trees or fir trees suffering from a strong S-impact in the field, IAA levels hardly increased with increasing needle age. It is suggested that in healthy trees high levels of IAA protect older needles from abscission and that the considerable losses of older needles of declining fir trees or of fir trees under S-impact are a consequence of the low levels of IAA found in older needles of such trees. Received: 4 May 1995 / Accepted: 29 August 1995     

Analysis of ovipositional environment using Quantification Theory Type I: the case of the butterfly, Luehdorfia puziloi inexpecta (Papilionidae)

The habitat of Luehdorfia puziloi inexpecta was analyzed by using Quantification Theory Type I, a method for quantifying qualitative data. The investigation area was divided into 92 small sections and was surveyed for its environmental characteristics such as type of trees, tree trunk girth, condition of undergrowth, geography, aspect of slope, and amount of food plants. Environmental factors suitable for oviposition were analyzed using the area density of eggs in each section as the external criterion. The results showed the order of importance of environmental factors to be: aspect of slope > amount of food plants > tree type = tree trunk girth > condition of undergrowth > geography. A slope facing northeast, rich in food plants, with deciduous trees of trunk girth larger than 40 cm, with undergrowth below 30 cm and along a ridgeline was the most preferable habitat for the butterfly.     

Spatial Organization of the Bird Population in the Middle Taiga of the Western Siberian Plain

Based on long-term route surveys, the bird population is studied in the least ornithologically investigated subzone of western Siberia, in the middle taiga all along its length from the Trans-Ural region to the Yenisei valley and in all types of landscapes. It is established that the species richness of the birds and the population density increase under replacement of dark coniferous species with small-leaved species, the impact of the floodplain regime and eutrophic swamping, and an increase in mosaicism and productivity of biocoenoses. It is noted that a decrease in the number of species and individuals in bird communities is associated with the replacement of dark coniferous small-leaved forests by pine forests or wooded mesotrophic and eutrophic bogs and then upland bogs. It is shown that the frequent trends of impoverishment of bird communities are determined by industrial and residential transformation of landscapes and the transition from land habitats to water ones.     

宜昌市郊不同龄级柏木人工林下植物组成与多样性变化

对宜昌市郊3个不同龄级柏木人工林林下植物物种组成和多样性变化的研究,结果表明,从幼龄林、中龄林到近熟林,林下灌木层由耐旱及强阳性种趋向耐旱性较强及中性种,且乔木种逐渐增加;林下草本层由以栗褐苔草和铺地龙为主趋向以蕨类为主;灌木层和草本层物种数量、香农—威纳指数、均匀度指数均呈增加趋势,而生态优势度呈下降趋势。说明实施封育恢复后柏木人工林呈进展演替趋势,但仍处于演替早期阶段。     

Linking alternative food sources to winter habitat selection of herbivores in overbrowsed landscapes

During winter, ungulates in boreal forests must cope with high energetic costs related to locomotion in deep snow and reduced forage abundance and quality. At high density, ungulates face additional constraints, because heavy browsing reduces availability of woody browse, the main source of forage during winter. Under these severe conditions, large herbivores might forage on alternative food sources likely independent of browsing pressure, such as litterfall or windblown trees. We investigated the influence of alternative food sources on winter habitat selection, by studying female white-tailed deer (Odocoileus virginianus) living in 2 landscapes with contrasted browse abundance, recently logged and regenerated landscapes, in a population at high density and on a large island free of predators. We fitted 21 female white-tailed deer with Global Positioning System (GPS) collars and delineated winter home ranges and core areas. We measured snow conditions in different habitat categories and sampled vegetation in the core areas and in the rest of the home ranges to determine how forage abundance, protective cover, and snow conditions influenced habitat selection within the home range. In both landscapes, deer were less likely to use open habitat categories as snow accumulated on the ground. At a finer scale, deer inhabiting the regenerated landscape intensively used areas where balsam fir cover was intermediate with greater balsam fir browse density than in the rest of the home range. In the recently logged landscape, deer were more likely to be found near edges between clear-cuts and balsam fir stands and in areas where windblown balsam fir trees were present; the latter being the most influential variable. Although balsam fir browse was sparse and mainly out of reach in this landscape, deer increased the use of areas where it was present. Our results offer novel insights into the resource selection processes of northern ungulates, as we showed that access to winter forage, such as woody browse and alternative food sources, depends on climatic conditions and stochastic events, such as abundant compacted snow or windthrows. To compensate for these scarce and unpredictable food supplies, deer selected habitat categories, but mostly areas within those habitat categories, where the likelihood of finding browse, litterfall, and windblown trees was greatest. © 2011 The Wildlife Society.     

不同林地清理方式对杉木人工林生态系统的影响

在杉木中心产区福建尤溪建立径流场,进行不同林地清理方式对杉木人工生态系统影响的６ａ定位研究结果表明：炼山清理迹地导致林地严重的水土流失,炼山后的６ａ中要地的水、土、肥人分别达８７６７．３２ｍ＾３／ｈｍ＾２、３８．００ｔ／ｈｍ＾２、５２３．１６ｋｇ／ｈｍ＾２,分别是不炼山林地的３．１０、１９．７０、６．１０倍。两种清理方式林地流失量差异随时间推移逐年缩小,于第６年趋于一致,炼山具有短期激效效应,经雨     

The effect of logging and slash-burning on the nutrient content of douglas fir

Summary Foliar analyses of Douglas fir needles was made in an attempt to evaluate soil fertility and productivity changes caused by logging and slash-burning. No statistically significant differences were found between means of nitrogen, potassium, phosphorus, calcium, and magnesium values of Douglas fir needles from trees growing on logged and logged and slash-burned areas. No nutrient deficiencies appeared in the needles from either area. Needle nutrient contens is compared with regional results in an attempt to estimate optimum levelt for Douglas fir trees. The importance of foliar analyses in determining soil fertility and productivity is discussed and avenues of approach for future studies are suggested.     

EFFECTS OF POPULATION STRUCTURE AND CONE PRODUCTION ON OUTCROSSING RATES IN ENGELMANN SPRUCE AND SUBALPINE FIR

Variation in the mating systems of Engelmann spruce and subalpine fir was examined in two adjacent subpopulations in the Colorado Front Range. Multilocus outcrossing rates were estimated from analysis of allozyme variation in embryo and megagametophyte tissue. The overall multilocus outcrossing rate of 0.93 for spruce was significantly higher than the outcrossing rate of 0.89 for fir. Outcrossing rates varied from 0.73 to 0.97 for spruce and from 0.65 to 0.94 for fir when trees of each species were grouped according to age, size, spatial distribution, maternal heterozygosity, cone production, and year of sampling. In both spruce and fir, trees with higher levels of male-cone production and/or more clumped spatial distribution had lower outcrossing rates. Temporal variation in outcrossing rates within subpopulations, examined only in spruce, was less than variation between subpopulations. Male-cone production was significantly correlated with tree size, and regression analyses revealed that the highest outcrossing rates are expected on trees that are medium to large in size, rather than the largest trees in the forest. The results show that, while there is some temporal variation, patterns of male cone production and spatial distribution of individuals are the most important factors influencing outcrossing levels in these wind-pollinated forest trees.     

The incidence of mistletoe (<Emphasis Type="Italic">Viscum album</Emphasis> ssp. <Emphasis Type="Italic">abietis</Emphasis>) on silver fir (<Emphasis Type="Italic">Abies alba</Emphasis>) in Croatia

The research on incidence of mistletoe (Viscum album ssp. abietis) on silver fir (Abies alba) was carried out in natural fir stands in Croatia. In the area of Gorski Kotar 32.8 % of the examined dominant fir trees were infected with mistletoe. The mistletoe incidence was presented according to the damage degrees of silver fir from 0 (healthy trees) to 4 (dead trees), rated by the crown defoliation and needle discoloration. With the increase of incidence, mistletoe spreads more onto more vital, i.e. less damaged trees. In the Dinaric Alps 28.6% of the examined fir trees were infected, this percentage amounting to 27.1% for the mountainous regions between the Sava and Drava rivers. The site and stand parameters (exposure, elevation, site quality, forest community and crown closure) were analysed in order to establish whether there was a correlation between these parameters and mistletoe incidence. There was a negative correlation between the elevation and mistletoe incidence. Among the compartments with a closed stands there were considerably less compartments with higher mistletoe incidence than among compartments with a sparsely closed and understocked stands. The other analysed site and stand parameters individually had no significant influence on mistletoe incidence. The correlation of silver fir mortality in 2004 and mistletoe incidence in 2002/03 was analysed, and their strong correlation was established. Mistletoe could be considered as a bioindicator of silver fir decline, and probably a significant contributor to that decline. In the areas where mistletoe incidence is great it can be presumed that silver fir is significantly damaged.     

Ecogeographical characteristics of the seed-bearing capacity and natural regeneration of pine on the fire-sites in pine forests of Transbaikalia

The paper presents the results of the studying of the parameters of post-fire structure and seed-bearing capacity of tree stands, factors of surface medium (thickness of burnt duff, projective cover of herb and moss vegetation) as well as number, vitality, and age structure of self-seeded Scots pine (Pinus sylvestris L.) and accompanying small-leaved species in the Lower Selenga pine forest massif of the forest-steppe in Southwestern Transbaikalia. The seed harvests were 1.5–2 times higher than in the geographically replacing forest types in the forest-steppe of West Siberia, and vitality of the undergrowth of the pine under the canopy of fire-affected stands was extremely low. It is shown that the pine reforests successfully on the fire-sites in the zone of insemination from the forest walls and on the thin fire-sites in the cowberry-rhododendron pine forests, where it is 2–3 times more abundant than in forest-steppe of the West Siberia. The reforestation is insufficient on the fire-sites in the bearberry-lichen pine forests.     

Little change in the fir tree-line position on the southeastern Tibetan Plateau after 200 years of warming

? As one of the world's highest natural tree lines, the Smith fir (Abies georgei var. smithii) tree line on the southeastern Tibetan Plateau is expected to vary as a function of climate warming. However, the spatial patterns and dynamics of the Smith fir tree line are not yet well understood. ? Three rectangular plots (30 m × 150 m) were established in the natural alpine tree-line ecotone on two north-facing (Plot N1, 4390 m asl; Plot N2, 4380 m asl) and one east-facing (Plot E1, 4360 m asl) slope. Dendroecological methods were used to monitor the tree-line patterns and dynamics over a 50-yr interval. ? The three study plots showed a similar pattern of regeneration dynamics, characterized by increased recruitment after the 1950s and an abrupt increase in the 1970s. Smith fir recruitment was significantly positively correlated with both summer and winter temperatures. However, Smith fir tree lines do not show a significant upward movement, despite warming on the Tibetan Plateau. ? The warming in the past 200 yr is already having a significant impact on the population density of the trees, but not on the position of the Smith fir tree line.