Treeline Research Articles

Perceptions of cultural ecosystem services of tree-based green infrastructure: A focus group participatory mapping in Zagreb, Croatia

Urban green infrastructure provides city dwellers numerous benefits. Among them, cultural ecosystem services (CES) are distinguished by being easily perceived and essential for people and their well-being. However, not all CES are equally easy to perceive, resulting with some of the CES categories being weakly explored. Research on CES also rarely considers elements of urban green infrastructure other than parks and forests. Therefore, there is a lack of research on different components of urban green infrastructure, especially tree-based, perceived in relation to CES. This paper presents the results of focus group participatory mapping implemented with citizens in the city districts of Zagreb on the perception of five selected CES categories in various types of urban green infrastructure. Our results show that participants perceived 13 different types of tree-based urban green infrastructure as providers of CES. We also distinguish patterns in the perception of CES categories and their connection with types of tree-based urban green infrastructure. Tree lines are perceived as providers of aesthetical experiences. Furthermore, forests and park forests are perceived in relation to place attachment and recreational activities, while parks are versatile and provide all explored CES. Other types that emerged as important were greenways, greenery around residential buildings and educational institutions, which provokes rethinking of a careful planning of the entire repertoire of urban green infrastructure.

Root distribution and properties of a young alley-cropping system: effects on soil carbon storage and microbial activity

In agroforestry systems, the root distributions and properties of the annual and perennial vegetation are poorly known, although they are recognized for fostering soil carbon (C) stocks through annual root-derived C inputs and by altering microbial activity. This study aimed to evaluate the potential contribution of roots from the understory vegetation strip (UVS) and the crop to top- and subsoil C stocks (0–100 cm) to a 3-year-old agroforestry system of the alley-cropping type. Root biomass, chemical composition, functional traits and anatomical structure were assessed in parallel to a characterization of soil physicochemical and microbiological properties, including enzymatic activity, at different depths and locations perpendicular to the tree line. The root biomass and properties were heterogeneous in the young alley-cropping system due to the presence of different plant communities and the heterogeneity of the soil mineral N content according to the location perpendicular to the tree line. The soil microbiological properties and organic C stocks did not vary horizontally at this stage of agroforestry but should be monitored through multiple-time samples to confirm a differentiation in subsequent years suggested by the tight link between root stoichiometry and microbial extracellular enzymatic activities that we found. Altogether, our results suggested that increasing the root biomass in topsoil in agroforestry systems positively contributes to increasing soil organic C stocks, but in deeper soil layers, an increase in litter inputs with a high C:N ratio might accentuate microbial N limitations and limit soil C storage.

Plant Diversity of Mts. Oligirtos and Farmakas (NE Peloponnisos, Greece) with Emphasis on Their Endemic Flora.

Greece is known to be a biodiversity hotspot. Though the plant diversity of Peloponnisos, the southernmost part of the Greek mainland, has been well-studied during the past 200 years, there are still gaps in our knowledge. To this end, the flora of the neighboring mountains Oligirtos and Farmakas was investigated, with a total of 740 and 762 taxa (species and subspecies) recorded, respectively, of which 635 and 756 for the first time. Ten species or subspecies were previously not known from Peloponnisos. Endemics correspond to 10.2% and 8.9% of the total flora and are predominately hemicryptophytes and entomogamous. Almost half of them produce capsules. The number of endemics per 2 × 2 km grid cell reveals that their highest number is found in areas of high elevation, and corresponds to habitats above the tree line, or to the limestone cliffs vegetation. No less than 62 endemic plant taxa of Mt. Oligirtos and 58 of Mt. Farmakas are threatened. A comparison of Mts. Oligirtos and Farmakas with five neighboring mountains shows that elevation correlates positively with the number of regional or bi-regional endemics but not with local or narrow endemics. The importance of mountainous regions for plant conservation is stressed.

A Deep-Learning Extraction Method for Orchard Visual Navigation Lines

Orchard machinery autonomous navigation is helpful for improving the efficiency of fruit production and reducing labor costs. Path planning is one of the core technologies of autonomous navigation for orchard machinery. As normally planted in straight and parallel rows, fruit trees are natural landmarks that can provide suitable cues for orchard intelligent machinery. This paper presents a novel method to realize path planning based on computer vision technologies. We combine deep learning and the least-square (DL-LS) algorithm to carry out a new navigation line extraction algorithm for orchard scenarios. First, a large number of actual orchard images are collected and processed for training the YOLO V3 model. After the training, the mean average precision (MAP) of the model for trunk and tree detection can reach 92.11%. Secondly, the reference point coordinates of the fruit trees are calculated with the coordinates of the bounding box of trunks. Thirdly, the reference lines of fruit trees growing on both sides are fitted by the least-square method and the navigation line for the orchard machinery is determined by the two reference lines. Experimental results show that the trained YOLO V3 network can identify the tree trunk and the fruit tree accurately and that the new navigation line of fruit tree rows can be extracted effectively. The accuracy of orchard centerline extraction is 90.00%.

Mapping snow depth and volume at the alpine watershed scale from aerial imagery using Structure from Motion

Time series mapping of snow volume in the mountains at global scales and at resolutions needed for water resource management is an unsolved challenge to date. Snow depth mapping by differencing surface elevations from airborne lidar is a mature measurement approach filling the observation gap operationally in a few regions, primarily in mountain headwaters in the Western United States. The same concept for snow depth retrieval from stereo- or multi-view photogrammetry has been demonstrated, but these previous studies had limited ability to determine the uncertainties of photogrammetric snow depth at the basin scale. For example, assessments used non-coincident or discrete points for reference, masked out vegetation, or compared a subset of the fully snow-covered study domain. Here, using a unique data set with simultaneously collected airborne data, we compare snow depth mapped from multi-view Structure from Motion photogrammetry to that mapped by lidar at multiple resolutions over an entire mountain basin (300 km2). After excluding reconstruction errors (negative depths), SfM had lower snow-covered area (∼27%) and snow volume (∼16%) compared to lidar. The reconstruction errors were primarily in areas with vegetation, shallow snow (< 1 m), and steep slopes (> 60°C). Across the overlapping snow extent, snow depths compared well to lidar with similar mean values (< 0.03 m difference) and snow volume (± 5%) for output resolutions of 3 m and 50 m, and with a normalized median absolute deviation of 0.19 m. Our results indicate that photogrammetry from aerial images can be applied in the mountains but would perform best for deeper snowpacks above tree line.

Recent increase in autumn temperature has stabilized tree growth in forests near the tree lines in Chilean Patagonia

AbstractIt is widely accepted that global warming is affecting forests near the tree line by increasing tree growth in these cold‐limited environments. However, since about 1970, a reduction in tree growth near the tree line has been observed in response to warming and increased drought stress. This reduction in tree growth has been mainly reported in forests of the northern hemisphere but less studied in southern forests. In this study, we investigated tree populations of Nothofagus pumilio located near the arboreal altitudinal limit in the central Patagonian Andes (45–47° S, Aysén region, Chile). In this region, warming has been accompanied by increased drought conditions since the 2000s. We explored whether this climatic variability has promoted or reduced tree growth at the regional scale in tree lines of these broadleaved temperate forests of central Patagonia. We constructed tree‐ring chronologies and determined common growth patterns and trends, and then analyzed the influence of recent climate. We detected a significant change in the slope of regional growth trends between the periods 1955–1985 and 1985–2015. We found that positive growth trends in the period 1955–1985 were associated with warmer and drier springs. However, after 1985, we found a stabilization in N. pumilio growth associated with a steady increase in temperature in autumn. Our results support the idea that more frequent warm autumns, with very thin or no snow cover, have stabilized tree growth due to water deficit at the end of the growing season of N. pumilio. The predicted climate change scenario of increasing temperatures and drought in central Patagonia may increase competition among trees for water, particularly at the end of the growing season. Consequently, we could expect a decreasing forest growth trend in central Patagonia, potentially impacting forest dynamics of these southern forests.

Predicted scarcity of suitable habitat for alpine plant communities in northern Japan under climate change

AbstractQuestionAlpine vegetation is sensitive to climate change, with shifts in species ranges, changes in community composition, and an upward shift in the forest limit over decades. Under climate change, habitats suitable for alpine vegetation will progressively decrease in scale, making their protection and conservation particularly important. In the Taisetsu Mountains of Japan, alpine vegetation has changed remarkably during the last decade. The aim of this study was to estimate the distribution of habitats suitable for alpine and subalpine vegetation types (snowbeds, shrubs, and alpine heathland/fellfield) and competing vegetation types (Sasaspp. and subarctic forest), while considering uncertainties in future predictions and climate scenarios.LocationTaisetsu Mountains, Daisetsuzan National Park, Hokkaido (northern Japan).MethodsWe estimated the habitat area suitable for each vegetation type from current vegetation maps on the basis of the predictions by three global climate models (GCMs) under two climate change scenarios (RCP2.6 and RCP8.5) using five habitat suitability models (HSMs) in two periods (2046–2050 and 2096–2100). We also compared the performances of the HSMs.ResultsMean summer temperature and snow‐cover period had significant effects on the distribution of all vegetation types. The estimated distribution area for suitable habitat did not differ markedly among GCMs and HSMs. Under the RCP2.6 scenario, habitats suitable for snowbeds and alpine heathland/fellfield drastically decreased overall but were preserved in some regions. Under the RCP8.5 scenario, however, subarctic forest almost completely replaced alpine and subalpine vegetation types over time.ConclusionsOur projections indicate that the severity of future climate change will determine whether or not habitats suitable for alpine vegetation will remain. Monitoring the dynamics of endemic and rare species for the effects of global warming should be the priority for adaptation strategies to enable timely conservation measures.

Leaf litter breakdown along an elevational gradient in Australian alpine streams.

The breakdown of allochthonous organic matter, is a central step in nutrient cycling in stream ecosystems. There is concern that increased temperatures from climate change will alter the breakdown rate of organic matter, with important consequences for the ecosystem functioning of alpine streams. This study investigated the rate of leaf litter breakdown and how temperature and other factors such as microbial and invertebrate activities influenced this over elevational and temporal gradients. Dried leaves of Snow Gum (Eucalyptus pauciflora) and cotton strips were deployed in coarse (6 mm), and fine (50 μm) mesh size bags along an 820 m elevation gradient. Loss of mass in leaf litter and cotton tensile strength per day (k per day), fungal biomass measured as ergosterol concentration, invertebrate colonization of leaf litter, and benthic organic matter (mass and composition) were determined. Both microbial and macroinvertebrate activities were equally important in leaf litter breakdown with the abundance of shredder invertebrate taxa. The overall leaf litter breakdown rate and loss of tensile strength in cotton strips (both k per day) were greater during warmer deployment periods and at lower elevations, with significant positive relationships between mean water temperature and leaf breakdown and loss of tensile strength rate, but no differences between sites, after accounting for the effects of temperature. Despite considerably lower amounts of benthic organic matter in streams above the tree line relative to those below, shredders were present in coarse mesh bags at all sites. Ergosterol concentration was greater on leaves in coarse mesh bags than in fine mesh bags, implying differences in the microbial communities. The importance of water temperatures on the rate of leaf litter breakdown suggests the potential effects of climate change‐induced temperature increases on ecological processes in such streams.

Litter leachate as a potential selector of woody species germination at alpine treeline

ABSTRACT The advancement of upper forest limits is driven by environmental conditions, but our current understanding overlooks the attributes of habitats and germination ability of woody species. Habitats, through plant litter, impact the competitive relation of germination and seedling growth. The aims of this study were to identify the selective effect of six litter leachates on the germination of indigenous Norway spruce (Picea abies) and nonindigenous dwarf pine (Pinus mugo) and compare the germination rates of the species. We collected plant litter and seeds from the (sub)alpine belt of the Hrubý Jeseník Mts. (the Eastern Sudetes Mts.; the Czech Republic). We evaluated the effect of plant litter leachates from alpine heathlands, wind-swept alpine grasslands, subalpine tall-herb plants, Pinus mugo scrub, subalpine Vaccinium vegetation, and Norway spruce clonal groups on germination process under standard light and temperature conditions. The germination of Norway spruce was inhibited by the litter leachate from subalpine tall-herb vegetation mainly dominated by Calamagrostis villosa, whereas that of dwarf pine was not. The other five litter leachates had no significant effect on the both. Under standard conditions, the germination time of dwarf pine is on average one day faster. These results suggest that most of the litter leachates examined may have small impacts on the germinability and germination time of Norway spruce and dwarf pine, but litter from the subalpine tall-herb vegetation can act as a filter that influences the seedling composition of the woody species.

Intensification of ENSO frequency drives forest disturbance in the andes during the holocene

The biodiverse montane forests of the tropical Andes are today frequently disturbed by rainfall-driven mass movements which occur mostly during extreme El Niño events. Over the coming decades these events are projected to double under the 1.5 °C global warming scenario. The consequent increased rainfall and mass movement events likely present an elevated risk to millions of people living in the Andes. However, the impact of more frequent rainfall extremes remains unclear due to a lack of studies that directly link past changes in El Niño-Southern Oscillation (ENSO) frequency to forest and landscape disturbance patterns. Here, we present the first Holocene palaeoecological record from Laguna Pallcacocha, southern Ecuador, a key site for El Niño reconstructions. We demonstrate that for the past 10,000 years plant taxa indicative of recolonization – such as Alnus acuminata – covary with El Niño-induced flood layers in the lake. An amplified forest disturbance pattern is observed in the late Holocene, suggesting enhanced slope instability following deforestation. The temporal pattern is not explained by tree line fluctuations or human impact, while the latter does amplify the impact of ENSO on landscape disturbance. Spatial correlations between modern ENSO and precipitation are consistent with a regional comparison of Holocene records of landscape disturbance. Our results indicate that climate extremes, such as those associated with future intensification of El Niño, combined with ongoing land use change will increase the frequency of mass movements elevating risks for millions of people in the Andes.

Land-use intensification reduces multi-taxa diversity patterns of Small Woodlots Outside Forests in a Mediterranean area

Land-use intensification exacerbates landscape fragmentation, increasing the negative effects on biodiversity. In this context, the biodiversity value of Trees Outside Forests (TOF; scattered trees, tree lines and small woodlots) is often overlooked by landscape planning and conservation programs, which typically focus on protecting larger and more intact areas. More empirical studies on taxa inhabiting TOF are needed to support and promote their conservation in human-altered lands.However, we are not aware of any study focusing on multiple taxa living in small woodlots outside forests (SWOFs) in the Mediterranean basin. We investigated how diversity patterns of multiple taxa in SWOFs respond to a land-use intensification gradient, from natural areas to more disturbed ones (agricultural and urban areas), in a Mediterranean biodiversity hotspot.We explored the influence of land-use types on species richness and composition of vascular plants and six ground-dwelling invertebrate groups (pseudoscorpions, spiders, darkling beetles, rove beetles, ground beetles, and ants). Species composition was more sensitive than species richness to land-use change, highlighting the need to consider a suitable measure for interpreting ecological processes. We observed a strong influence of land use embedding SWOFs on the mean composition and beta diversity of taxa: land-use intensification led to a general homogenization of diversity patterns, especially among agricultural and urban areas. In our study area, vascular plants responded more sensitively to land-use change than invertebrates. For most invertebrates: the higher the land-use intensity, the lower the species composition dissimilarity due to the dominance of good dispersers or disturbance-tolerant species. More vagile species and disturbance-tolerant species can move across open habitats and colonize new areas, reducing compositional differences and potentially boosting species pools. We demonstrated that SWOFs play a key role in supporting viable populations of invertebrates, also in human-altered lands, underlining the need to promote their conservation in this Mediterranean fragmented landscape to avoid homogenization from driving a generalized biodiversity loss.

A review of the vascular plant flora of the Cairngorms Connect project area, Scotland, and some possible implications of forest expansion to the natural tree line

Cairngorms Connect, a partnership of four adjoining land owners, is committed to a 200-year vision to enhance and restore habitats, species and ecological processes across a 592 km2 area within the Cairngorms National Park. This will be achieved by, inter alia, expanding woodland to its natural altitudinal limit, including high altitude sub-alpine scrub. All or parts of six native Caledonian pinewoods occur here, c.26% of the national total. Ancient, semi-natural woodland within the Cairngorms Connect area is 43% of the National Park total. Modelling of the extent of potential-natural woodland (sensu Peterken, 1981, 1996) indicates that below 600 m all terrestrial habitats are potentially capable of supporting some degree of tree and scrub cover. 899 vascular plant taxa have been recorded here, of which 693 are native to the area. 7.6% of native taxa are endemic to Great Britain (and Ireland) or to Scotland; these are mainly Hieracia (Hawkweeds). Of the native taxa, 23% are of national, and 11% of regional conservation concern. Few native taxa are widespread within the Cairngorms Connect area, most are local or rare. 40% of native taxa have been recorded in five or less monads (1 km squares), with 16% recorded from just a single monad. 12% of native taxa are associated with shaded locations or semi-shade (Ellenberg Light values 3-5). 51% of taxa are found in partial shade to well lit locations (values 6 and 7) and 37% of taxa in well lit to fully lit locations (values 8 and 9). Native taxa with Light values of 6-7 are the most frequent in 92% of monads with more than 10 recorded taxa. 65% of taxa of national conservation concern favour well lit to fully lit locations (Light values 8-9). Shading of plants, at altitudes below the potential tree line, is strongly influenced by the extent of woodland and scrub and its structure, and by herbivore grazing levels determining height and structure of the field layer. To achieve forest expansion to the natural tree line by natural regeneration will require sustained low levels of grazing and browsing, for decades, or longer. This is already leading to a taller field layer and an increased density of tree regeneration. 40% of native taxa may be negatively impacted, if existing and new woodland becomes dense with a high level of shading. Of these 'at risk' taxa, 50% have maximum height less than 50 cm and may be especially at risk from sustained periods of low grazing. Limited disturbance and lack of open sites and bare ground for seedling recruitment is another potential constraint on vascular plants. The issue of vegetation succession and shading, leading to possible loss of plant diversity is likely to be much less of an issue at altitudes around and above the tree line. Here there are likely to be benefits, with possible expansion of tall herb communities.

Red foxes enhance long‐term tree growth near the Arctic treeline

AbstractRecent climate warming is expected to increase tree growth and productivity, substantially altering ecological function and boundaries in northern ecosystems. Although climate largely determines the range and growth of trees in any biome, variations in microsite conditions can influence growth on a finer scale. Red foxes (Vulpes vulpes) are found in most terrestrial ecosystems and are considered ecosystem engineers through their denning activities. Added soil nutrients from prey remains, feces, and urine could benefit tree growth on dens in subarctic regions by alleviating soil nutrient limitations. We examined growth in white spruce (Picea glauca) trees growing on eight red fox dens and paired control sites at the Arctic treeline. Radial growth was 55% higher for trees on dens than on control sites between 1897 and 2017, despite similarities in tree ages and densities. This enhanced growth was more pronounced in younger trees, consistent with the decrease in growth with age among all trees. By promoting tree growth near the treeline, red foxes may act as hotspots for tree reproduction. Although the impacts on tree growth largely depend on the spatial distribution of dens, predators can create distinct microhabitats across the landscape, leading to increased vegetation productivity, persisting over many decades.

Climate change simulations in Alpine summer pastures suggest a disruption of current vegetation zonation

Alpine summer grazing areas (high-altitude pastures) represent hotspots of biodiversity and high cultural heritage values. Low density forests (Alpine Larix decidua and/or Pinus cembra forests) and species-rich open land (Alpine and boreal heaths, siliceous Alpine and boreal grasslands) are protected according to the Flora-Fauna-Habitat-directive of the European Union. These habitats are threatened by the accelerated mountain climate warming and the expected upslope shift of vegetation zones. With climate change, tree growth accelerates and montane species spread to higher altitudes. The fate of low density larch forests, alpine heathlands and grasslands is unclear. We used the process-based wooded pasture model WoodPaM to simulate large-scale and long-term dynamics of the forest and tree line under several land-use scenarios and climate change. The simulation results for the central Alpine summer grazing area Furggtal (Canton Valais, Switzerland) showed a plausible projection of the upslope migration of vegetation zones due to climate warming in the very long-term. For the upcoming centuries however, the existing vegetation zonation was disrupted by the intermixing of tree species during the migration process. This unexpected result emerged from the process-based modelling of tree species specific dispersal and establishment in interaction with livestock grazing. This effect was most pronounced in simulations of grazing abandonment and current low intensity grazing of free ranging livestock, which failed to buffer climate change effects. The establishment of paddocks and thereby intensified grazing on the current pastures on the valley floor promised the conservation of valuable open habitats. We conclude that the ongoing rapid upslope shift of climate zones in mountain regions might not be followed by a similar shift of vegetation zones. Widespread colonisation processes might lead to a period dominated by very dynamic vegetation communities that might not zone along climatic gradients as it was in the past of comparable stable climate. Climate change may therefore impact more like disturbance on alpine ecosystems rather than to drive continuous range shifts. During this disruptive transformation, adapted grazing management in summer pastures can help to maintain continuity for valuable habitats but would require subsidies to establish infrastructure and to increase livestock numbers. • Rapid warming disturbs the ecological balance among larch forests, Alpine grasslands, and livestock grazing. • The upslope shift of climate zones in mountain regions might not be followed by a continuous shift of vegetation zones. • During a disruptive transformation period, colonisation processes might be dominated by dynamic vegetation communities. • Climate change might therefore impact like disturbance on Alpine ecosystems. • Adapted grazing management in summer pastures can help to maintain continuity for valuable habitats.

Remarkable Variation in the Process of Hg Accumulation in Timberline Forests Indicates an Aggravated Hg Burden in Alpine Forests Under Climate Warming

AbstractSignificant knowledge gaps in mercury (Hg) cycling challenge our ability to assess the effectiveness of the Minamata Convention on Mercury in reducing human and wildlife Hg exposure due to the complicated impacts of climate change. In this study, we comprehensively quantified the Hg spatial distribution and determined the Hg stable isotopes to understand the Hg sources and accumulation pathways in forests along the timberline ecotone, an ecosystem that provides an early bellwether of global warming effects. Our results show that although there were subtle variations in meteorological and environmental conditions among the <50 m elevation variation, a spruce to shrub vegetation structure shift led to a distinct decrease in vegetation and soil Hg pool sizes by 36%–56% along the timberline ecotone. Further Hg isotopic evidence verified that vegetation‐induced atmospheric Hg0 deposition was the main source for Hg accumulation in soils, and the source contribution of such input decreases from 73% to 45% along the timberline ecotone. Our results indicate that if global warming induced a spruce tree line upward shift, it would significantly promote the atmospheric Hg burden, thus resulting in a conspicuous “Hg hotspot”. We recommend further studies to assess the Hg ecological risk promoted by global warming in alpine ecosystems.

Millennial land use explains modern high‐elevation vegetation in the submediterranean mountains of Southern Europe

AbstractAimPinewood decline and scrubland expansion are major features of Late Holocene vegetation history in the Cantabrian Range. However, the drivers of this remarkable vegetation shift remain to be investigated. Here, we aim at disentangling the role of past land use and climate in shaping the high‐elevation Cantabrian landscape during the past two millennia.LocationCantabrian Range (northern Iberia).TaxaPinus sylvestris, Betula, Ericaceae, Juniperus, Poaceae.MethodsWe conducted high‐resolution multiproxy palaeoecological analyses (pollen, plant macrofossils, microscopic charcoal and dung fungi) on lake sediments from Lago del Ausente to reconstruct vegetation, fire occurrence and grazing through time. The chronology is based on 14C (terrestrial plant macrofossils) and 210Pb dating, and Bayesian age‐depth modelling (‘rbacon’). We carried out cross‐correlation analysis to quantify vegetation responses to fire.ResultsBetween 250 and 900 CE, the vegetation above 1700 m a.s.l. consisted of subalpine scrubland and scattered P. sylvestris trees/stands. Pinewoods with Betula were widespread at slightly lower elevation. This vegetation was resilient to moderate fire disturbance associated with limited pastoral activities. In contrast, enhanced fire occurrence alongside heavier pastoralism led to the demise of pinewoods and their replacement with Betula stands, subalpine scrublands, and meadows between 900 and 1100 CE. Later, the subalpine scrubland‐birch tree line did not respond to Little Ice Age cooling. However, further intensification of transhumant herding between 1300 and 1860 CE (‘La Mesta’) triggered birch decline and the establishment of the modern treeless landscape.Main conclusionsThe extant high‐elevation vegetation of the Cantabrian Range is largely the legacy of intensive land use starting more than one millennium ago. Recurrent and severe fires to promote pasturelands led to the regional extirpation of the previously widespread Pinus sylvestris. Future management should aim at preserving the valuable cultural open landscape of mountain scrubland and meadows and also at restoring patches of ancient pine‐birch woodlands.

Contributions of climate, vegetation and soil to the alpine sediment carbon accumulation rate in central China since the Middle Holocene

Large amounts of carbon in alpine sediments have been expected to be sensitive to climate change, but how carbon accumulation responds to climate change remains unclear. Thus, we explored the impact of different factors on the carbon accumulation rate (CAR) of alpine sediments by combining a variety of climatic variables, vegetation data and erosion indicators based on two alpine sediment successions on Taibai Mountain, the highest peak in central and eastern mainland China. One succession is near the modern treeline (Paomaliang Swamp, PML) and the other is located at the upper forest line (Sanqing Chi, SQC, a small lake). We used our previously published organic carbon content data and for the first time calculated the CAR, and further used pollen and physicochemical indicators to quantify the contributions from climate, vegetation and soil. We found that their contributions varied during different periods and between the two sediment successions. For the PML succession, from 5850 to 4000 calendar years before present (cal. a BP), the CAR was low, which was related to low annual temperatures, low vegetation cover and strong soil erosion. From 4000 to 2400 cal. a BP, a high CAR coincided with high annual temperatures, high vegetation cover and weak soil erosion. From 2400 to 200 cal. a BP, the CAR decreased, mainly attributed to low vegetation cover. Local vegetation cover had major impacts on the CAR in the SQC succession during the Middle–Late Holocene. In general, the local factor interpretation rate in SQC (83%) was higher than that of PML (47%), related to the vegetation stability of continuous forest and the treeline. This study highlights the important role of the local environment in determining carbon accumulation in the alpine region.

Sufficient conditions for rapid range expansion of a boreal conifer

Unprecedented modern rates of warming are expected to advance boreal forest into Arctic tundra1, thereby reducing albedo2–4, altering carbon cycling4 and further changing climate1–4, yet the patterns and processes of this biome shift remain unclear5. Climate warming, required for previous boreal advances6–17, is not sufficient by itself for modern range expansion of conifers forming forest–tundra ecotones5,12–15,17–20. No high-latitude population of conifers, the dominant North American Arctic treeline taxon, has previously been documented5 advancing at rates following the last glacial maximum (LGM)6–8. Here we describe a population of white spruce (Picea glauca) advancing at post-LGM rates7 across an Arctic basin distant from established treelines and provide evidence of mechanisms sustaining the advance. The population doubles each decade, with exponential radial growth in the main stems of individual trees correlating positively with July air temperature. Lateral branches in adults and terminal leaders in large juveniles grow almost twice as fast as those at established treelines. We conclude that surpassing temperature thresholds1,6–17, together with winter winds facilitating long-distance dispersal, deeper snowpack and increased soil nutrient availability promoting recruitment and growth, provides sufficient conditions for boreal forest advance. These observations enable forecast modelling with important insights into the environmental conditions converting tundra into forest.

Contrasting water sources used by a coniferous forest in the high-altitude, southeastern Tibetan Plateau

Forest trees use various water sources to adapt to environmental conditions in mountainous regions. However, water resources variances along elevational gradients are not clearly understood. This limits the assessment of the ecosystem responses to climate change. In this study, stable oxygen and hydrogen isotopes were used to investigate the spatiotemporal patterns of water sources for Faber's fir in a humid high-altitude elevational gradient (ranging between 2800 m.a.s.l. and 3700 m.a.s.l.) on the southeastern Tibetan Plateau. The results indicated that 27 ± 8.3 % of the xylem water was from previous winter snowmelt between May and June. In contrast, almost all xylem water was from current summer precipitation between July and October. Faber's fir at the lower elevation (2800 m.a.s.l.) primarily relied on water derived from winter precipitation during May and June. Yet, trees located near the tree line (3700 m.a.s.l.) were mostly dependent on current precipitation over the entire growing season. However, when statistically analyzing data from all seven different elevation gradients in this study, the contribution of winter precipitation to xylem water was not elevation dependent. Precipitation contributed to a large proportion (59.86 % ± 33.43 %) of xylem water between May and October. Meanwhile, no linear contribution ratio of precipitation to trees was identified in this high-altitude elevational gradient. The replenishment of soil water and the soil water storage determine the spatiotemporal patterns of water sources. Climate change has the possibility of reducing winter precipitation at high altitudes on the Tibetan Plateau. Thus, tree water use at different altitude gradients will play varied roles in influencing the evolution of forest composition under ongoing climate change.

Long-term spatiotemporal dynamics in a mountain birch (Betula pubescens ssp. czerepanovii) forest in south-east Norway.

Mountain birch forest covers large areas in Eurasia, and their ecological resilience provides important ecosystem services to human societies. This study describes long-term stand dynamics based on permanent plots in the upper mountain birch belt in SE Norway. We also present forest line changes over a period of 70 years. Inventories were conducted in 1931, 1953, and 2007. Overall, there were small changes from 1931 up to 1953 followed by a marked increase in biomass and dominant height of mountain birch throughout the period from 1953 to 2007. In addition, the biomass of spruce (Picea abies) and the number of plots with spruce present doubled. The high mortality rate of larger birch stems and large recruitment by sprouting since the 1960s reveal recurrent rejuvenation events after the earlier outbreak of the autumnal moth (Epirrita autumnata). Our results demonstrate both a high stem turnover in mountain birch and a great ability to recover after disturbances. This trend is interpreted as regrowth after a moth attack, but also long-term and time-lagged responses due to slightly improved growth conditions. An advance of the mountain birch forest line by 0.71 m year-1 from 1937 to 2007 was documented, resulting in a total reduction of the alpine area by 12%. Most of the changes in the forest line seem to have taken place after 1960. Regarding silviculture methods in mountain birch, a dimension cutting of larger birch trees with a cutting interval of c. 60 years seems to be a sustainable alternative for mimicking natural processes.