Early seed fall and seedling emergence: precursors to tropical restoration

We explore processes of seed immigration and seedling recruitment before an experimental rainforest restoration matures enough to affect either. Twenty-four 30 × 30-m plots were fenced in 12 ha of pasture in 2006. Seeds were collected in ninety-six 1-m⁻² seed traps; recruits were censused in ~12,000 m² in which establishment was allowed. We tested effects of distance from forest, living trees, and stumps of trees cut during site preparation on seed rain in 2007 and effects of these and soil depth on recruits through June 2008. Seed fall and recruitment were not correlated with distance to forest 90–400 m away, nor to living shade trees outside the 160 × 485-m experimental grid. Recruitment differed for animal- and wind-dispersed species in a topographically complex landscape. Recruitment of wind-dispersed species was random with respect to soil depth or distance to recent stumps. Recruitment of animal-dispersed species was multimodal; partial correlations with number of stumps within 30 m of plots were significant with soil depth held constant (P < 0.025), as were correlations of recruitment with soil depth with number of stumps held constant (P < 0.01). Animal-dispersed recruits were often not conspecifics of adults that had been cut, indicating a legacy of attraction by fruiting trees of animals bearing seeds from distant sources. Ecological implications are that recruitment in pastures released from grazing reflects a mix of widely scattered wind-dispersed pioneers and, where animal-dispersed trees exist, multi-modal and decidedly non-random recruitment of pioneer and later successional animal-dispersed trees from seed banks.     

Seasonal variation in oxygen isotope composition of waters for a montane larch forest in Mongolia

Measurements of water oxygen isotopic composition were conducted in the 2003 growing season for a montane larch (Larix sibirica Ledeb.) forest in northern Mongolia, a transitional area from the south Siberian taiga to the Asian steppe. Oxygen isotopic composition of foliar water and its daily variability were found to be sensitive to atmospheric evaporative demand. During most of the growing season, water sources used by larch trees were from the upper 30-cm surface layer of the soil when precipitation input was large, and were from the deeper layer when the water supply at the upper soil layer was limited. The Keeling plot method suggested that the forest returned soil water to the atmosphere predominantly by means of canopy transpiration during the peak growth period (in August).     

Contrasting responses of seedling and sapling densities to livestock density in the Mongolian forest-steppe

The past and present regeneration of Siberian larch (Larix sibirica) was studied in the forest-steppe of the Mongolian Altai, an area which has experienced an increase in annual mean temperature by 2.1 °C since 1940 and is subjected to grazing by mixed herds of livestock owned by pastoral nomads. Past regeneration was reconstructed from tree rings and present regeneration was analyzed by surveying seedlings, sapling-sized trees and the occurrence of viable larch seeds in the soil seed bank. Forest regeneration occurred throughout the twentieth and the early twenty-first centuries in the forest interiors, but ceased after the late 1970s at forest edges. The density of sapling-sized larch trees decreased with livestock density linearly in the interior and exponentially at the edge. Most sapling-sized trees had visible damage from livestock browsing, which also manifested in wood-anatomical anomalies. By contrast, the densities of 1- and 2-year old seedlings increased with livestock density at the forest edge, suggesting that seedlings in this habitat benefitted from the reduction in competition intensity due to livestock grazing. This relationship also suggests that larch seedlings, in contrast to sapling-sized trees, were avoided by the livestock, as otherwise removal by the herbivores should have counteracted the promotion due to reduced competition. Near-consistency of the correlations of total livestock and goat densities with sapling and seedling densities suggests that the control of larch regeneration is primarily a function of goat density, which have tripled in the Mongolian livestock during the past 20 years for economic reasons.     

东灵山林区不同森林植被水源涵养功能评价

森林植被发挥着涵养水源的作用,主要表现在以下几个方面:对降水的截留与再分配;调节河川径流,调节林内小气候,减小林内地表蒸发,改善土壤结构,减少地表侵蚀等. 通过对几种林分各层拦蓄降水和保土功能指标定性评价的基础上,用综合评定法对不同林分水源涵养和保土功能进行综合评价,选择出综合功能最好的林分,以期为北京山区的生态环境建设、植被恢复与保护提供一定的依据。在测定东灵山4种森林植被林冠层、枯枝落叶层和土壤层蓄水和土壤保持功能指标的基础上,采用综合评定法对4种森林植被水源涵养和土壤保持功能进行了评价。结果表明:各植被类型的林冠层截留各不相同,在雨季(6-9 月份) 辽东栎林的截留率最大,华北落叶松的最小;枯落物最大持水深以辽东栎林的最大,油松的最小;土壤水文特性各异,0-80 cm 土层平均容重以落叶阔叶林的最小,华北落叶松的最大;稳渗速率以落叶阔叶林的最大,油松的最小,初渗速率以辽东栎林的最大,油松的最小。不同林分水源涵养和土壤保持综合能力由大到小顺序为落叶阔叶混交林、辽东栎林、华北落叶松林、油松林。常绿阔叶灌丛水源涵养和土壤保持综合能力评价值(0.1039) 比其它植被类型少3个数量级,说明其水源涵养和土壤保持功能明显优于其它植被类型。由此可见,树种组成丰富、林下灌草盖度高、枯落物储量多的落叶阔叶混交林水源涵养和土壤保持能力最强,优于单一的阔叶林,而油松林最差。     

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。     

Long-term persistence of aspen – a key host for many threatened species – is endangered in old-growth conservation areas in Finland

Large, dead and dying European aspens (Populus tremula L.) host many threatened species in Fennoscandian boreal forests. Large aspen trees have mostly disappeared and are being harvested from the managed forests that cover 95% of the forest area in Finland. Due to the small area protected (4.1%), the aspen-associated species may encounter major difficulties in the protected areas if aspen trees disappear due to natural forest succession. The availability of aspens was assessed in the old-growth conservation area network in eastern Finland. We mapped all the living and dead aspens in 15 protected old-growth forests. The total number of counted trees was 32 903 individuals. Current amounts of living (2.7 m³/ha) and especially dead aspens (2.8 m³/ha) in the protected areas were higher than in the surrounding managed forests (1.1 and 0.1 m³/ha for living and dead trees, respectively). However, while saplings (dbh<5 cm) occur in most of the areas (12 individuals/ha on average) they survive poorly and young aspen cohorts (5 cm <dbh<15 cm) are lacking or are very rare. The most likely reason for the poor sapling survival is high browsing pressure by the mammalian herbivores, especially the moose. The moose population has increased many times in Finland during the past decades. The poor regeneration of aspens implies that the value of the old-growth conservation areas for aspen-associated species will face a serious bottleneck within a few decades when the currently middle-aged tree cohorts disappear. If the current high browsing pressure and lack of natural disturbances continue the obligatory aspen-associated species may disappear both locally and regionally from the network of the protected areas.     

Recent drought stress leads to growth reductions in Larix sibirica in the western Khentey,Mongolia

Trends in air temperature and precipitation in the forest‐steppe ecotone of the western Khentey, northern Mongolia were studied and related to stem increment and shoot water relations in Mongolia's most common tree species, Siberian larch (Larix sibirica). The area has been subject to a significant increase of summer temperature and a decrease of summer precipitation during the last 47 years. Tree‐ring width series from >400 larch trees show a strongly decreasing annual increment since the 1940s. The onset of this decrease is independent of the age of the trees and, therefore, can be attributed to the increasing aridity in the 20th century. Simultaneously to the declining annual increment, regeneration of Siberian larch decreased as well; today regeneration is virtually lacking in the larch forests on mountain slopes of the western Khentey. Measurements of shoot water potentials during the growing season exhibited daily minimum water potentials close to the point of zero turgor for extended periods. The drought stress indicated by these results is in line with the current low annual increment. Trees in the forest interior were more severely stressed and grow more slowly than trees at the forest line to steppe. This is attributable to the recent increase in aridity, as the stand density and probably also the trees themselves in the forest interior are adapted to moister conditions, whereas the trees at the forest edge have always been exposed to a more extreme microclimate. The progressing increase in aridity during the 21st century that is predicted for the western Khentey, suggests a future decline of larch forests. A widespread increase of aridity predicted for most parts of the Mongolian forest belt, suggests even a supra‐regional decline of larch.     

Carbon, nitrogen and phosphorus in volcanic soils following afforestation with native birch (Betula pubescens) and introduced larch (Larix sibirica) in Iceland

Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth) and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed to a slow accumulation of organic matter. Soil N concentrations and soil P_tot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material (400 Mg soil ha⁻¹ in 0–10 cm depth and 600 Mg soil ha⁻¹ in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average 23.6 Mg ha⁻¹ in the upper soil layer and 16.9 Mg ha⁻¹ in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha⁻¹ year⁻¹ in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha⁻¹ in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass of the growing trees. Soil P_tot pools were in average 220 and 320 kg P ha⁻¹ in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence on the availability of N and P to the trees. Responsible Editor: Hans Lambers.     

Culturable microfungi inhibitory to Armillaria rhizomorph formation from Fagus sylvatica stump roots and soil

Culturable fungi from 28 fungal communities were isolated from soil, rhizosphere and thick (1 cm diam.) roots of living beech (Fagus sylvatica) trees and their stumps 1–3 years after felling. All fungi were morphotyped and identified morphologically. The frequency of fungi was 2–5× greater in stumps than in living trees. The diversity of fungi was similar in living trees and stumps. The majority of fungal species that occurred at greater frequency on/in roots of stumps reduced the growth of Armillaria ostoyae and to a smaller extent of A. gallica rhizomorphs in a soil substrate in vitro. It is suggested that the mycobiota of roots may constrain the colonization of F. sylvatica by A. ostoyae rather than by A. gallica. The significance of these findings in the epidemiology of Armillaria in beech forests is discussed.     

Cutting of lichen trees: a survival strategy used before the 20th century in northern Sweden

Sami reindeer herders in northern Fennoscandia have historically cut trees with high quantities of arboreal lichens to feed their animals during harsh winters. In this study we analysed temporal and spatial patterns of lichen-tree cuttings of Scots pine in a remote forest landscape in northern Sweden. We wanted to test the hypothesis that repeated cutting of such trees may have had long-lasting effects on the forest ecosystem that are still discernable today. Our analyses included an inventory of remaining lichen-tree stumps, and a field survey of forest variables to relate structural variation within the forest to these cuttings. We used dendrochronological methods to date stumps and reconstruct forest structure. Our results show that more than 7,000 trees were cut for this purpose over a period of almost 300 years within an area covering 6 km². Lichen-tree cutting was most intense during the late 18th century when ca. 600–1,000 trees were cut during each decade. We did not detect any significant relationship between past lichen-tree cutting and present small-scale forest heterogeneity, and suggest that this might be due to the small size of the cut trees and the long time elapsed since most of the cuttings. We conclude that vestiges such as stumps from lichen-tree cutting are highly valuable for our understanding of past land use. Furthermore, since they are located in an unlogged and very old forest, this highlights the need to acknowledge the interconnectedness between ecological and cultural values of such forests and the need to identify and protect them.     

Plasticity in gas‐exchange physiology of mature Scots pine and European larch drive short‐ and long‐term adjustments to changes in water availability

Adjustment mechanisms of trees to changes in soil‐water availability over long periods are poorly understood, but crucial to improve estimates of forest development in a changing climate. We compared mature trees of Scots pine (Pinus sylvestris) and European larch (Larix decidua) growing along water‐permeable channels (irrigated) and under natural conditions (control) at three sites in inner‐Alpine dry valleys. At two sites, the irrigation had been stopped in the 1980s. We combined measurements of basal area increment (BAI), tree height and gas‐exchange physiology (Δ¹³C) for the period 1970–2009. At one site, the Δ¹³C of irrigated pine trees was higher than that of the control in all years, while at the other sites, it differed in pine and larch only in years with dry climatic conditions. During the first decade after the sudden change in water availability, the BAI and Δ¹³C of originally irrigated pine and larch trees decreased instantly, but subsequently reached higher levels than those of the control by 2009 (15 years afterwards). We found a high plasticity in the gas‐exchange physiology of pine and larch and site‐specific responses to changes in water availability. Our study highlights the ability of trees to adjust to new conditions, thus showing high resilience.     

Gap formation, microsite variation and the conifer seedling occurrence in a subalpine old-growth forest, central Japan

To evaluate the effects of canopy gaps and forest floor microsites (soil, fallen logs, root-mounds, buttresses and stumps) on regeneration of subalpine forests, the gap regeneration and seedling occurrence of conifers (Abies mariesii, Abies veitchii, Picea jezoensis var. hondoensis and Tsuga diversifolia) were studied in two stands of a subalpine old-growth forest, central Japan. The percentage of gap area to total surveyed area was 11.2–11.3% in the stands. Gap regeneration was not common for P. jezoensis var. hondoensis and T. diversifolia. In contrast, gap regeneration by advanced regeneration was relatively common for Abies. Seedling occurrence of P. jezoensis var. hondoensis and T. diversifolia was restricted on elevated surfaces such as stumps and root-mounds, while Abies seedlings could occur on soil as well as on elevated surfaces. Rotten stumps were the most favorable microsites for conifer seedling occurrence, which covered small area in the forest floor. Although canopy gaps were not always favorable for seedling occurrence, all conifer seedlings were larger under canopy gaps than under closed canopy. Canopy gaps and forest floor microsites clearly affected seedling occurrence and growth of conifers. This suggests that regeneration of conifers is related to the difference of growth advantage under canopy gaps and favorable microsites for seedling occurrence.     

Canopy transpiration of mountain mixed forest as a function of environmental conditions in boundary layer

The canopy transpiration of mountain mixed forest was investigated during summer 2006 at research plot Smrekovec in Tatra National Park in Slovakia after heavy windstorm in November 2004 on the area of 12,000 hectares. The research plot is situated in untouched forest at altitude 1249 m on the southern-east oriented slope. The forest is mixed with 80% of spruce trees and 20% of larch trees with rich under storey vegetation, 120 years old, 7th altitudinal vegetation stage. Whole tree sap flow based on up to dated stem tissue heat balance method was continuously measured in nine 120-years old larch and spruce trees. Stem basal area was used for tree-canopy up-scaling. Meteorological parameters were measured on the top of eddy stuff tower above investigated forest. Two virtual monocultures were assumed for characterizing of both species. The sap flow and tree transpiration were calculated for the whole measured period for both spruce and larch virtual forests.     

Influence of moss and lichen spatial mosaics on radial growth of Gmelin larch (Central Evenkia)

The results of research studies on the influence of high moss-and-lichen mosaicity typical for the northern taiga in Central Evenkia on the dynamics of radial growth of Gmelin larch trees (Larix gmelinii (Rupr.) Rupr.) are reported. Three sample plots were laid out in the larch ledum–cowberry–green moss forest on the northwest facing slope (8°–10°) in close proximity to each other; they differed in the proportions of area occupied by the principal components of a moss–lichen cover (Aulacomnium turgidum, Pleurozium schreberi, Cladonia rangiferina, and Hylocomium splendens), spatial distribution, and thermal properties of seasonally thawed soil layers. The worst thermal soil properties under the current climatic conditions have determined the comparatively low radial growth of trees in the sampling area, reduced response to air-temperature variations in the period of preseason cambium activity and at the beginning of the radial growth period, and heightened the response to this factor at the end of a season.     

大兴安岭森林火烧后不同演替阶段土壤细菌多样性动态

【目的】研究我国最大的林区之一——大兴安岭森林火烧后不同演替阶段土壤细菌多样性动态,为天然林保护工程对于生物多样性的影响增添新的认识。【方法】以空间替代时间的方法分析大兴安岭森林演替对于土壤细菌多样性动态的影响。大兴安岭森林火烧后典型的自然演替序列为火烧迹地(LG-BA)、灌丛(SHR)、白桦林(BP)、白桦落叶松混交林(BP-LG)、落叶松林(LG-OM)。在演替序列的每个典型样地上采集0-10 cm土样,采用Illumina Mi Seq高通量测序技术测定土壤细菌群落组成及其多样性。【结果】细菌操作分类单位(OTU)数量从少到多的顺序为火烧迹地落叶松白桦混交林灌丛落叶松林白桦林。随着森林演替,多样性指数Simpson先增高后降低;Shannon指数先增加后减少再增加;OTU的丰度变化比较平缓,表明物种变化较小。在各演替阶段中,土壤细菌种类主要有变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)、放线菌门(Actinobacteria)和浮霉菌门(Planctomycetes),4个门的种类含量随演替顺序都呈现先增加后减少的趋势。主成分分析表明不同演替阶段土壤细菌群落存在一定的差异性。冗余分析表明有机质(SOM)、全氮(TN)、全磷(TP)和p H对于土壤细菌群落变化有影响。【结论】随着森林演替,大兴安岭地区土壤细菌种类和生物多样性会发生变化,其变化与土壤化学成分和p H有关。     

Influencing factors on early vegetation restoration in burned area of Pinus pumila – Larch forest

Pinus pumila (Dall.) Regel, a rare conifer and key species in high latitude and high altitude mountains, has an important role in soil and water conservation. This evergreen shrub grows 3–6 m high in P. pumila – larch (Larix gmelini) open forest at altitudes of 800–1200 m in the Greater Kingan Mountain Range (Daxing’an Mountain). Forest fires are major natural hazards to P. pumila – larch forest. The unique ecological role of this community gives important theoretical and practical significance to research on P. pumila – larch forest restoration after fires. Literature concerning factors influencing early vegetation restoration in burned areas in this habitat is sparse. We studied these factors, especially those related to P. pumila seedling establishment. The results showed fires in P. pumila – larch forest usually resulted in severe burns. Typically almost no P. pumila survived after fires. Nearly all ground fuels were consumed. Second growth after fires exhibited low species richness. The dominant tree/shrub seedlings found after fires were birch (Betula platyphylla) and larch, with small number of P. pumila. Other shrub seedlings found were Ledum palustre, Vaccinium vitis-idaea, Betula fruticosa, and Rubus arcticus. The main herb species found were Deyeuxia langsdorffii, and Chamaenerion angustifolium. Important factors influencing early vegetation restoration after fires included seed dispersal, fire size, and site condition. Seed dispersal in birch and larch is higher than in P. pumila; more seedlings of birch and larch were found in burned areas than seedlings of P. pumila. Most seeds germinated in the first year following a fire. The extent of the burned area influences seedling distribution patterns, especially in species with limited seed dispersal ability. Birch and larch seedlings were evenly distributed in the entire burned area, while seedlings of P. pumila were found only at the fire edge. No P. pumila seedlings were found more than 50 m away from seed source trees. Site condition significantly influenced seed germination and growth in birch and larch; these seedlings only grew well in burned areas with good site conditions (shallow slopes, thick soils, etc.). They did not grow well in burned areas with poor site conditions (steep slopes, thin soils, etc.). However, P. pumila seedlings could grow well in burned areas with either good or poor site conditions. The strong vitality of P. pumila seedlings gives this species an enormous ecological advantage in soil conservation and environmental restoration and conservation. We conclude that the main factor influencing seedling establishment in P. pumila is its weak seed dispersal ability. Although the P. pumila seeds can germinate in all burned areas, natural regeneration rarely restores burned areas to the original P. pumila – larch forest. Planting seeds and/or seedlings may facilitate burned area restoration to P. pumila – larch forest. Because P. pumila seedlings grow very slowly, the restoration process may take decades.     

Root system development of Larix gmelinii trees affected by micro-scale conditions of permafrost soils in central Siberia

Spatial distributions of root systems of Larix gmelinii (Rupr.) Rupr. trees were examined in two stands in central Siberia: an even-aged stand (ca. 100 yrs-old) and a mature, uneven-aged (240–280 yrs-old) stand. Five larch trees of different sizes were sampled by excavating coarse roots (diameter > 5 mm) in each stand. Dimensions and ages of all first-order lateral roots were measured. Micro-scale conditions of soil temperature and soil water suction (each 10 cm deep) were also examined in relation to earth hummock topography (mound vs. trough) and/or ground floor vegetation types (moss vs. lichens). All larch trees developed superficial root systems, consisting of the aborted short tap root (10–40 cm in soil depth) and some well-spread lateral roots (n= 4-13). The root network of each tree was asymmetric, and its rooting area reached about four times the crown projection area. Lateral roots generally expanded into the upper soil layers of the mounds where summer soil temperature was 1–6°C higher than inside nearby troughs. Chronological analysis indicated that lateral root expansion started successively from lower to upper parts of each aborted tap root, and some lateral roots occurred simultaneously at several decades after tree establishment. The process of root system development was likely to be primarily linked with post-fire dynamics of rhizosphere environment of the permafrost soils.     

Tree growth and competition in a post-logging Quercus mongolica forest on Mt. Sobaek, South Korea

Secondary woodlands in South Korea cover most mountains from low to middle elevations. While general patterns of forest succession are well understood, little is known about mechanisms of stand recovery after disturbance. We examined the spatio-temporal variations in establishment, growth, size inequality, and mode of competition among trees in a 50-year-old post-logging Quercus mongolica-dominated stand. We further compared the growth and stem allometry of single trees, presumably of seed origin, with multi-stemmed trees resprouting from stumps. Q. mongolica formed the upper canopy 16–22 m tall, 88.3% of total stand basal area, and 36.2% of total stem density, with most trees established during the first post-logging decade (51.2% were resprouts). During the first three decades, the Q. mongolica recruits grew exponentially, and disproportionately more in diameter than few older reserved trees left after the last cutting. This substantially decreased size inequality. The reverse trend was observed from 1994 to 2004: larger trees grow more, indicating an increasing asymmetry of competition for light. Neighborhood analysis revealed that when target trees had more or larger neighbors, their exponential phase of growth was reduced and maximum size was decreased. After the 50 years of stand development, more than 70% of Q. mongolica showed growth decline as a result of competitive stress, and mortality was about 30%, concentrated in smaller size classes. Compared to single stems, resprouts within clones do not seem to compete less asymmetric as might be expected based on studies of clonal herbaceous plants and physiological integration within genets. As Q. mongolica was also negatively affected by competition from woody species currently prevailing in the lower tree stratum (Tilia amurensis, Acer mono, Fraxinus rhynchophylla, Acer pseudosieboldianum), we predict the stand will become increasingly dominated by these more shade-tolerant trees.     

An inventory of forest relicts in the pastures of Southern Tibet (Xizang A.R., China)

An inventory of isolated tree stands surrounded by desert pastures in Southern Tibet (A.R. Xizang, China) revealed more than 50 sites with vigorous trees of Juniperus convallium Rehder & E.H. Wilson and Juniperus tibetica Kom and additional more than 10 records where juniper trees had been destroyed between 1959–1976. The tree stands are not restricted to any specific habitat, and occur within an area stretching 650 km westwards from the current forest border of Southern Tibet. The trees are religious landmarks of the Tibetan Buddhists. The highest trees were found at an elevation of 4,860 m. Vegetation records, rainfall correlations and temperature data collected by local climate stations and successful reforestation trials since 1999 indicate that forest relicts fragmented through human interference could regenerate if current cattle grazing and deforestation practices are halted. The drought line of Juniperus forests in Southern Tibet is approximately 200–250 mm/a. A first pollen diagram from Lhasa shows forest decline associated with the presence of humans since at least 4,600 yr BP. The currently degraded commons developed in the last 600 yr. To date, no findings of remains of ancient forests in the Central Tibetan Highlands of the Changtang have been reported.     

Pine stumps act as hotspots for seedling regeneration after pine dieback in a mixed natural forest dominated by <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>

Over the past few decades, rural forest ecosystems in Japan have experienced dynamic vegetation changes due to forest dieback and changes in land use, leading to the loss of local species populations and biodiversity. The aim of this study was to evaluate the importance of pine (Pinus densiflora) stumps and logs for tree seedling regeneration in a mixed natural forest in Kyoto Prefecture, Japan, that had previously experienced severe pine dieback, and to determine which factors most greatly affect seedling establishment. Seedlings of 17 tree species were recorded on pine stumps and logs in later stages of decay, among which Chamaecyparis obtusa and Rhododendron reticulatum were most dominant. Both of these species had a greater density on pine stumps than on logs or soil, despite stumps covering less than 0.5% of the study area. In addition, the seedling densities of both species were positively associated with moss cover on coarse woody debris, but negatively associated with wood pH. Brown rot in the sapwood and heartwood, which occurred more frequently in stumps than in logs, also positively associated with the seedling densities of both species. Predictive modelling showed that C. obtusa seedlings exhibited a stronger response to pH in stumps than in logs. Therefore, since brown-rotted wood is acidic due to fungal decay activities, brown-rotted pine stumps may present hotspots of C. obtusa seedling regeneration at the study site.