Tree-ring analysis and conifer growth responses to increased atmospheric CO2 levels

Summary Tree-ring data of naturally grown connifers were analyzed to evaluate the possibility of enhanced tree growth due to increased atmospheric CO₂. Tree cores were obtained from 34 sites in four different climatic regions in the northern hemisphere. In each of the four regions, the sampling sites were located along ecological gradients between the subalpine treeline and low elevations and, sometimes, the arid forest border. Growth trends after 1950, when the atmospheric CO₂ concentration increased by more than 30 l·l^-1 indicate an increase in ring-widths at eight of the 34 sites. These chronologies were from sites which moderate temperature or water stress. In four cases the growth increase in the post-1950 period coincided with favorable climatic conditions. In the remaining four cases, the growth increase exceeded the upper bound response expected from CO₂ enrichment experiments with seedling conifer species. Therefore, increased growth in any of the tree-ring chronologies examined could not be solely attributed to higher atmospheric CO₂ concentrations.Major financial supporters: Swiss National Science Foundation (application no. 1.869-0.83); Swiss Federal Institute of Forestry Research, 8903 Birmensdorf, Switzerland; other financial supporters: Carbon Dioxide Research Division, U.S. Department of Energy under subcontract no. 11X-57507V with Martin Marietta Energy Systems, IncOperated by Martin Marietta Energy Systems, Inc., under contract DE-AC05-840R21400 with U.S. Department of Energy     

Climate change and vegetation response

This study, as many other current investigations in palaeoecology is focused on the long-term dynamics of vegetation and the extent to which they are controlled by climate change. Climate and classes of climate change are defined and reviewed, and examples cited of vegetation response. The concepts of vegetation, plant community and equilibrium are examined, with particular emphasis on theories on short term dynamics developed by ecologists working with temperate and boreal forests. Vegetation response to climate change can be modified by anthropogenic factors, topographic diversity and soils, life-cycle characteristics and hysteresis.I am grateful for comments on an earlier version of this paper by Keith Bennett, Les Cwynar and Glen MacDonald, and I particularly appreciate the useful remarks by Colin Prentice.I am grateful for comments on an earlier version of this paper by Keith Bennett, Les Cwynar and Glen MacDonald, and I particularly appreciate the useful remarks by Colin Prentice.     

Vegetational pattern near alpine timberline as affected by fire-snowdrift interactions

Conclusions In the central Rocky Mountains, flat areas or gentle slopes just below climatic timberline exhibit a vegetational pattern consisting of ribbon forests and snow glades lying across the path of the prevailing winds. The pattern is the result of removal of snow by wind from the open areas and its deposit in a great drift about 60 to 100 m in from the windward edge of the forest. This drift remains too long during the summer for tree growth. Consequently, the vegetation in the drift area is a wet or moist subalpine meadow occupying the snow glade and, in effect, breaking the forest into ribbon-like patches. The source area for the snow may be natural climax tundra, tundra which has replaced burned subalpine forest, or subalpine meadow of edaphic origin. The ribbon-forest and snow-glade pattern can be expected just below climatic timberline wherever plateaus or gentle slopes are exposed to heavy snowfall, strong winter winds, and cool summers. Destruction of such ribbon forests by fire or cutting will result in new snowdrift patterns and the long-lasting replacement of the forest by alpine or subalpine meadow vegetation.

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Zusammenfassung In den zentralen Rocky Mountains zeigen flache Gebiete oder sanfte Hänge gerade unterhalb der klimatischen Baumgrenze eine Pflanzendecke, die aus Streifenwald ribbon forests und Schnee-Lichtungen besteht, die quer auf die vorherrschende Windrichtung stehen.Dieses Muster wird dadurch verursacht, daß der Schnee durch den Wind von den offenen Stellen weggeweht, und etwa 60–100 m vom Wald gegen den Wind wieder deponiert wird. Diese Schneehaufen bleiben im Sommer zu lange erhalten, um Baumwuchs zu erlauben. Deshalb entsteht dort eine nasse oder feuchte Alpenwiese, die den Wald in Streifen zerbricht. Diese Streifenwald-Schnee-Lichtung Vegetation kann man dort erwarten, wo unterhalb der klimatischen Baumgrenze Plateaux oder sanfte Neigungen starkem Schneefall, heftigen Winterwinden und kühlen Sommern ausgesetzt sind.Durch Feuer oder Schlag wird dieser Waldtyp in Alpine oder Subalpine Wiese umgewandelt.

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The research was supported by National Science Foundation Grant GB-1219 and the Duke University Council on Research.     

Studies on forest health and vegetation changes in Greece under the effects of climate changes

Greece, as part of the Mediterranean Basin, is projected to be among the most vulnerable countries to climate change. It is therefore quite urgent to adapt forest management to the changing climate in order to enhance biodiversity and to enable the conservation of healthy and productive forests. In the framework of the project LIFE+ AdaptFor (www.life-adaptfor.gr), an effort was made to understand the ecological responses and the vulnerability of forest ecosystems in the face of climate change; the overall aim of the project is the development and implementation of appropriate adaptation strategies. Four study areas were selected where changes in vegetation, quite likely attributed to climate change, have already been observed (dieback of Scots pine and Greek fir, intrusion of conifers in broadleaved forests). To investigate the synergism of climatic parameters’ alterations in the development of the occurring phenomena, time series of temperature and precipitation for the period 1950–2009 were produced and parameters of forest status were investigated, including mapping of vegetation changes through remote sensing. The findings support the hypothesis that climate change has an impact on forest health; the dieback of tree species can be attributed to outbreaks of pathogens (fungi and insects) which are associated with climatic parameters. However, the intrusion of conifer species into broadleaved forests showed no direct connection to climatic parameters, something that needs to be further investigated. In all cases, insufficient or inappropriate management practices applied in the areas exacerbated the occurring phenomena.     

Terrestrial transects for global change research

The International Geosphere-Biosphere Program has proposed a set of large-scale terrestrial transects to study the effects of changes in climate, land use, and atmospheric composition (global change) on biogeochemistry, surface-atmosphere exchange, and vegetation dynamics of terrestrial ecosystems. The transects ( 1000 km) will be located along existing environmental and land use intensity gradients that span transitions between biomes in regions likely to be widely affected by forcing from components of global change or where the impacts of global change are likely to feed back to affect atmospheric, climatic, or hydrologic systems. Experimental studies on the transects will examine short-term changes in ecosystem function and biosphere-atmosphere interaction in response to variation in primary controlling variables. A hierarchy of modeling approaches will develop predictions of long-term changes in biome boundaries and vegetation distribution. The proposed initial set of IGBP terrestrial transects are located in four key regions: (1) humid tropical forests undergoing land use change, (2) high latitudes including the transition from boreal forest to tundra, (3) semi-arid tropical regions including transitions from dry forest to shrublands and savannas, and (4) mid latitude semi-arid regions encompassing transitions from shrubland or grassland to forests. We discuss here the rationale and general research design of transect studies proposed for each of these priority regions.GCTE Focus 1 Office     

A numerical phytoclimatic classification of China

The relationship is examined between vegetation and climate using climatic variables collected from 644 meteorological stations located throughout China. Multivariate methods are applied directly to the raw climatic data in order to define climatic clusters and to examine the relationship between the clusters and vegetation types. This approach is based on the concept of multidimensional climatic space defined by the combination of climatic variables. Phytoclimatic classes are defined on the basis of the distribution of vegetation types in climatic clusters and a new phytoclimatic classification of China is proposed. Patterns of climatic changes between neighbouring phytoclimatic classes are described. Two indexes of the influence of climate on vegetation are proposed based on discriminant analysis.     

Indicative response of <Emphasis Type="Italic">Oxysternon festivum</Emphasis> Linné (Coleoptera: Scarabaidae) to vegetation condition in the basin of the Orinoco river,Venezuela

A good indicator species should be easy to sample, identify and measure, and be informative about its ecological context. We analysed data from a nation-wide dung beetle survey in Venezuela in order to assess the indicative response of Oxysternon festivum (Coleoptera: Scarabaeinae) to vegetation and climatic condition in the Orinoco river basin. Our approach consisted of two steps: estimating habitat suitability (HS) from historical records and mean environmental conditions, and analysing four different properties measured during a nationwide survey (occurrence, total abundance, individual body size, and total biomass), in relationship with HS and current environmental covariates measured from remote sensors. O. festivum population status could not be completely explained by historical or current conditions alone, but rather by combinations of both. It was strongly associated with forest vegetation, but abundance, biomass and body size increased under harsher (hotter and drier) climatic conditions. Thus, O. festivum seems to be sensitive to changes in vegetation cover, but tolerant to certain levels of perturbance, where it probably replaces other, more sensitive species. Fully understanding the role of O. festivum requires the analysis of its relationships to other species. We strongly recommend the development of similar protocols for the analysis of other potential ecological indicator species, drawing information from historical and contemporary sources and exploiting the available statistical tools to reveal complex patterns. Given the high diversity of dung beetles, and the growing interest in this group, several candidates will probably be found in most tropical countries.     

BIOME系列模型: 主要原理与应用

 基于过程的平衡态陆地生物圈模型-BIOME系列及其动态发展(LPJ-DGVM: Sitch et al.,2000) 已经成为模拟大尺度(全球至区域)的植被地理分布、净第一性生产力和碳平衡以及预测气候变化对陆地生态系统潜在影响的有效工具。本文综述了BIOME系列模型的发展过程,包括每个模型的主要原理、优点和缺陷,论述了模型在国际以及我国全球变化研究中的应用,并简单讨论了模型未来发展的趋势。以植物功能型作为基本研究单元,BIOME系列模型的控制因素从单纯的生物气候变量和生态生理限制因子(BIOME1),发展     

Fragmentation Impairs the Microclimate Buffering Effect of Tropical Forests

Background

Tropical forest species are among the most sensitive to changing climatic conditions, and the forest they inhabit helps to buffer their microclimate from the variable climatic conditions outside the forest. However, habitat fragmentation and edge effects exposes vegetation to outside microclimatic conditions, thereby reducing the ability of the forest to buffer climatic variation. In this paper, we ask what proportion of forest in a fragmented ecosystem is impacted by altered microclimate conditions driven by edge effects, and extrapolate these results to the whole Atlantic Forest biome, one of the most disturbed biodiversity hotspots. To address these questions, we collected above and below ground temperature for a full year using temperature sensors placed in forest fragments of different sizes, and at different distances from the forest edge.

Principal Findings

In the Atlantic forests of Brazil, we found that the buffering effect of forests reduced maximum outside temperatures by one third or more at ground level within a forest, with the buffering effect being stronger below-ground than one metre above-ground. The temperature buffering effect of forests was, however, reduced near forest edges with the edge effect extending up to 20 m inside the forest. The heavily fragmented nature of the Brazilian Atlantic forest means that 12% of the remaining biome experiences altered microclimate conditions.

Conclusions

Our results add further information about the extent of edge effects in the Atlantic Forest, and we suggest that maintaining a low perimeter-to-area ratio may be a judicious method for minimizing the amount of forest area that experiences altered microclimatic conditions in this ecosystem.     

Development and regional differentiation of the European vegetation during the Tertiary

The Tertiary vegetation of Europe evolved from paratropical to warm-temperate and temperate forms in response to a progressive, non-linear, climatic cooling. Its vegetational forms are composed mainly of two separate ecological units: the evergreen, laurophyll paleotropical geoflora and the deciduous, broad-leaved Arctotertiary geoflora. The development of the Tertiary climate and its interaction with the vegetation are convincingly indicated by the geoflora's migration; the changes in its composition; and the development of the Tertiary forest, swamp, and aquatic plant communities. The paleotropical geoflora is characterized in the upper Cretaceous to the upper Miocene by paratropical rain forest, subtropical rain and laurel forests, temperate laurel forests and edaphically-mediated formation of laurel-conifer forests. The Arctotertiary geoflora advanced into Europe in waves since the Paleocene and formed the basis for the Tertiary mixed mesophytic forests. These can be divided into warm-temperate rain forests, oak-hornbeamchestnut or mixed beech-oak-hornbeam forests, and edaphic formations such as bottomland and swamp forests. Beginning in the lower Cretaceous, the hydrophytic vegetation developed independently of the forest vegetation and formed very diverse herbaceous fresh water, swamp, salt water, and coastal formations. Considerable differences in composition allow to separate floral regions and provinces in Eurosiberia. Instead of three ill-defined floral regions in the Paleocene, there are four well-defined floral regions in the Pliocene. A Mediterranean region cannot be recognized, although Mediterranean (eumesogeic) floral elements appear in the Eocene/Oligocene and thereafter. The Mediterranean sclerophyll forests probably arose after the destruction of the laurophyll forests during the Pleistocene.     

Climate response,migrational lag,and pollen representation: The problems posed by Rhododendron and Acer

Views have changed as to the relative importance of climate change and human activity on the composition of Holocene temperate forest. The ‘climate school’ maintains that temperate arboreal taxa responded swiftly to changes in Holocene climate, irrespective of dispersal mechanism, with no evidence for migrational lag or for human influence; taxa moved individualistically according to their climate response. This paper tests these tenets in two case studies. The present‐day distributions of Rhododendron and Acer in Europe are compared with earlier records, and discussed in the context of migrational lag and pollen‐climate response. Distributional data emphasise the importance of humans as a vector in aiding the spread of both Rhododendron ponticum and some Acer species in the very late Holocene. Arguably, the species concerned have exhibited extreme migrational lag; they re‐open the question as to whether the natural distributions of temperate arboreal species are in equilibrium with climate.     

Untangling the causes of vegetation change in a 5,300 year pollen record at Tiniroto Lakes,Gisborne, New Zealand

To address potential causes of disturbances in recent New Zealand vegetation a sediment core from Tiniroto Lakes near Gisborne was used to reconstruct the local history of ecological disturbance and vegetation dynamics. Our approach was to examine the pattern and rate of vegetation change, against known disturbances, in order to identify different causes of disturbance. Despite intermittent disturbances, a steady transformation of vegetation dominates the period from c. 4,900 to c. 2,300 cal. yrs b.p. This is a time of climatic amelioration, with increasing precipitation suggested by the decline of light-adapted taxa, together with the establishment of forest. After c. 2,300 cal. yrs b.p., vegetation change becomes much more irregular, and apparently driven by disturbances, including unusual ones, such as earthquakes. In contrast to earlier disturbances, later vegetation responses are typified by a reduction of forest species and the establishment of semi-open vegetation, which persists for decades. This dichotomy suggests that a change in disturbance regime, especially in terms of fire, characterises the period after c. 2,300 cal. yrs b.p. The rises of fire frequency and of intensity at that time could be a result of severe droughts under climate extremes associated with intensified ENSO frequencies.     

Forest fire dynamics during the early and middle Holocene along the southern North Sea basin as shown by charcoal evidence from burnt ant nests

Based on a dataset of 434 radiocarbon dates and charcoal data from burnt abandoned ant nests which were formerly interpreted as Mesolithic hearth-pits, the correlation between short periods of abrupt climatic cooling and increased forest fires during the early and middle Holocene is studied. Despite dating calibration limits, the results indicate a clear synchronicity between the 9.3 ka event and widespread and repeated forest fires which occurred in a coniferous woodland environment dominated by Pinus sylvestris (pine). It is argued that the cold and dry climatic conditions resulted in an overall desiccation of pines, which became prone to wildfires. A similar correlation is tentatively suggested for the 8.2 ka event, though changing climate first affected vegetation by reintroducing pines followed by increased wildfires. Indications of forest fires possibly caused by humans only appear around 6,400/6,200 uncal bp, corresponding to the final stage of hunter-gatherers along the southern North Sea basin.     

The generalized multiplicative model for viability selection at multiple loci

Selection due to differential viability is studied in an n-locus two-allele model using a set indexation that allows the simplicity of the one-locus two-allele model to be carried to multi-locus models. The existence condition is analyzed for polymorphic equilibria with linkage equilibrium: Robbins' equilibria. The local stability condition is given for the Robbins' equilibria on the boundaries in the generalized non-epistatic selection regimes of Karlin and Liberman (1979). These generalized non-epistatic regimes include the additive selection model, the multiplicative selection model and the multiplicative interaction model, and their symmetric versions cover all the symmetric viability models.Research supported by grant no. 11-7805 from the Danish Natural Science Research Council, by NIH grant GM 28016, by a fellowship from the Research Foundation of Aarhus University, and by a visiting fellowship from the University of New England, N.S.W.     

Changes of the forest-savanna boundary in Brazilian Amazonia during the Holocene revealed by stable isotope ratios of soil organic carbon

The possibility of ecosystem boundary changes in northern Brazilian Amazonia during the Holocene period was investigated using soil organic carbon isotope ratios. Determination of past and present fluctuations of the forest-savanna boundary involved the measurement of natural ¹³C isotope abundance, expressed as ¹³C, in soil organic matter (SOM). SOM ¹³C analyses and radiocarbon dating of charcoal fragments were carried out on samples derived from soil profiles taken along transects perpendicular to the ecotonal boundary. SOM ¹³C values in the upper soil horizons appeared to be in equilibrium with the overlying vegetation types and did not point to a movement of the boundary during the last decades. However, ¹³C values obtained from deeper savanna and forest soil layers indicated that the vegetation type has changed in the past. In current savanna soil profiles, we observed the presence of mid-Holocene charcoals derived from forest species: fire frequency at that time was probably greater, and more extensive savanna may have resulted. Isotope data and the presence of these charcoals thus suggest that the forest-savanna boundary has shifted significantly in the recent Holocene period, forest being more extensive during the early Holocene than today. During the middle Holocene, the forest could have strongly regressed, and fires appeared, with a maximum development of the savanna vegetation. At the beginning of the late Holocene, the forest may have invaded a part of this savanna, and fires occurred again.     

Climatic impacts on the vegetation of eastern North America during the past 2000 years

Pollen diagrams from seven lakes with annually laminated sediments sampled at 40-year intervals are analyzed to isolate the climatic effects from other effects on the long-term dynamics of vegetation during the past 1000–2000 years along a transect from Maine to Minnesota. Principal components analysis is used to reduce the dimensionality of the pollen data. The pollen records from all lakes show long-term trends, medium frequency oscillations, and higher frequency fluctuations. The long-term trend is associated with the neoglacial expansion of the boreal forest. The mechanism causing this replacement is a change in frequency of air masses in the area. The medium-frequency oscillations are also associated with climate changes, the most recent of which is the ‘Little Ice Age’. The climate-related mechanism causing the medium-frequency changes may be changes in disturbance frequency. The higher frequency fluctuations may also be related to disturbance. This analysis of pollen diagrams into time scales of variation has enabled the separation of climate from other factors affecting vegetation dynamics. By comparing the principal components across a transect of sites it proved possible to interpret the climatic effects on vegetation at most sites and not only at range boundaries and ‘sensitive’ sites.     

Global vegetation productivity response to climatic oscillations during the satellite era

Climate control on global vegetation productivity patterns has intensified in response to recent global warming. Yet, the contributions of the leading internal climatic variations to global vegetation productivity are poorly understood. Here, we use 30 years of global satellite observations to study climatic variations controls on continental and global vegetation productivity patterns. El Niño‐Southern Oscillation (ENSO) phases (La Niña, neutral, and El Niño years) appear to be a weaker control on global‐scale vegetation productivity than previously thought, although continental‐scale responses are substantial. There is also clear evidence that other non‐ENSO climatic variations have a strong control on spatial patterns of vegetation productivity mainly through their influence on temperature. Among the eight leading internal climatic variations, the East Atlantic/West Russia Pattern extensively controls the ensuing year vegetation productivity of the most productive tropical and temperate forest ecosystems of the Earth's vegetated surface through directionally consistent influence on vegetation greenness. The Community Climate System Model (CCSM4) simulations do not capture the observed patterns of vegetation productivity responses to internal climatic variations. Our analyses show the ubiquitous control of climatic variations on vegetation productivity and can further guide CCSM and other Earth system models developments to represent vegetation response patterns to unforced variability. Several winter time internal climatic variation indices show strong potentials on predicting growing season vegetation productivity two to six seasons ahead which enables national governments and farmers forecast crop yield to ensure supplies of affordable food, famine early warning, and plan management options to minimize yield losses ahead of time.     

Current and Future Fire Regimes and Their Influence on Natural Vegetation in Ethiopia

Fire is a major factor shaping the distribution of vegetation types. In this study, we used a recent high resolution map of potential natural vegetation (PNV) types and MODIS fire products to model and investigate the importance of fire as driver of vegetation distribution patterns in Ethiopia. We employed statistical modeling techniques to estimate the distribution of fire and the PNVs under current climatic conditions, and used the calibrated models to project distributions for different climate change scenarios. Results show a clear congruence between distribution patterns of fire and major vegetation types. The effect of climate change varies considerably between climate change models and scenarios, but as general trend expansions of moist Afromontane forest and Combretum–Terminalia woodlands were predicted. Fire-prone areas were also predicted to increase, and including this factor in vegetation distribution models resulted in stronger expansion of Combretum–Terminalia woodlands and a more limited increase of moist Afromontane forests. These results underline the importance of fire as a regulating factor of vegetation distribution patterns, and how fire needs to be factored into predict the possible effects of climate change. For conservation strategies to effectively address conservation challenges caused by rapid climate shifts, it is imperative that they not only consider the direct influence of climate changes on the vegetation, species species, or biodiversity patterns, but also the influence of future fire regimes.     

Late Quaternary vegetation, fire and climate dynamics of Serra do Araçatuba in the Atlantic coastal mountains of Paraná State, southern Brazil

Late Quaternary vegetation, fire and climate dynamics were studied by pollen and charcoal analysis on a sediment core from near the summit of the Serra do Araçatuba at 1500 m elevation, part of the Serra do Mar coastal mountains of Paraná State, southern Brazil. Three radiocarbon dates indicate that clay and peat were deposited in a shallow basin during the last 14,880 b.p. Accumulation was probably continuous, but sedimentary gaps during the dry mid Holocene cannot be excluded. During late-glacial times the upper coastal mountain were covered with grassland, reflecting relatively dry and cold climatic conditions. Large areas of natural grasslands remained in the upper mountain region during the Holocene. Only after 2000 b.p. did Araucaria forest trees, specially Ilex, some Atlantic forest trees as well as the pioneer Myrsine move to higher elevations, reflecting markedly wetter climatic conditions. This expansion stopped and the forest areas were reduced significantly by human activities during about the last 200–300 years. The modern grassland vegetation of the uppermost mountains may reflect the natural setting, but may also partly result from post-Columbian human activities. Fires were rare during the late Pleistocene and even less frequent during the early and mid Holocene. During the wettest recorded period of the late Holocene fires increased markedly and are therefore most probably of anthropogenic origin.     

Stand-scale reconstruction of late Holocene forest succession on the Gdańsk Upland (N. Poland) based on integrated palynological and macrofossil data from paired sites

This study concerns the stand-scale palaeoecological reconstruction of the subsequent stages of late Holocene vegetation development on habitats recently covered by beech-dominated woodland in the southern Baltic region. The data, based on pollen, non-pollen palynomorphs, macrofossil and charcoal analyses from two close-lying sites, demonstrated that each of the subsequent late Holocene shifts in dominating forest communities took place because of human impact coupled with climatic events or episodic human-made disturbances. Shifts from the Tilia dominated forest to the Quercus-Corylus plant community at around 3300 bc was most probably driven by the coupled effect of climate change and human activity. Human impact was the primary driver of the final Corylus decline and concurrent major Carpinus expansion at c. 460 bc, and the Carpinus decline followed by Fagus expansion at c. ad 900. Carpinus had been lingering on the edge of a major expansion in the local forest for at least 2,500 years while Fagus had persisted in a small admixture for no fewer than 1,500 years before becoming important forest constituents. Our data illustrate the role of episodic disturbances as turning points that initiate long-term vegetation changes.