Temperate Broad-leaved Forest Research Articles

Species diffusion and niche differentiation of the warm temperate deciduous broad-leaved forest in its functional development process

Species diffusion and niche differentiation of the warm temperate deciduous broad-leaved forest in its functional development process

Attributes of Himalayan forest Ecosystems: they are not Temperate forests

This paper describes how Himalayan forests are different from temperate forests with which they are often clubbed. The principal forest types in Himalayas are dominated by evergreen trees with about one year leaf life span (e-leaf type), which include as dissimilar genera as Shorea, Pinus and Quercus. Though several taxa are common with temperate forests, functionally Himalayan forest ecosystems have values closer to tropical than temperate forest ecosystems. The Himalayan trees have tendency to reach their peak physiological activities during autumn when soil moisture is high due to the monsoon precipitation, sunny and fairly long days, and mild temperatures. In contrast, in temperate broadleaved forests, leaves begin to senesce with the beginning of autumn. Therefore, models that use data of temperate forests for predicting responses of Himalayan forests to global change would fail to make accurate predictions. Furthermore, models that focus on temperature and precipitation in Himalayas, would inaccurately predict about these forests because different forest types can occurs within same precipitation and temperature regimes in Himalayas. In many Himalayan tree species the regeneration strategy is geared to take advantage of monsoon, to the extent that their seeds show vivipary. Such species might be disturbed by climate change. The nutrient resorption efficiency during leaf senescence in Himalayan oaks is between 20-25% which are far lower than global averages for plants, 62.1% for N and 64.9% for P. Further, forest structure and distribution are variously modified by anthropogenic and natural disturbances, making predictions based on climate data of little value.

Complementarity in the use of nitrogen forms in a temperate broad-leaved mixed forest

Background: The complementary use of different forms of soil nitrogen (N) might lead to a higher productivity of mixed forests than monocultures, but convincing evidence for temperate mixed forests is scarce.Aims: We searched for species differences in N uptake rates and the preference for NH4+, NO3− or glycine among five temperate broad−leaved tree species (Acer pseudoplatanus, Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Tilia cordata) in a mature mixed stand.Methods: 15N tracer was added to the soil and its accumulation in fine root biomass was analysed after 10 min, 1 h and 1 d.Results: The estimated root uptake rates of the species were in the range of 5–46 µg N g−1 root h−1 for NH4+, 6–86 µg N g−1 h−1 for NO3− and 4–29 µg N g−1 h−1 for glycine during the first hour after tracer application. Carpinus, Tilia and Acer tended to prefer NH4+ over NO3−, while Fraxinus showed equal preference for both N forms and Fagus seemed to prefer NO3−.Conclusions: The five co-existing tree species differed in uptake rates and partly in their N form preference, but complementarity in the use of different N forms seems to be of minor importance in this forest because tree species appear to be rather flexible in their N form use.

Changes of preferential flow path on different altitudinal zones in the Three Gorges Reservoir Area, China

Liu, M., Du, W. and Zhang, H. 2014. Changes of preferential flow path on different altitudinal zones in the Three Gorges Reservoir Area, China. Can. J. Soil Sci. 94: 177–188. Preferential flow in soil macropores plays an important role in runoff control and soil and water conservation. The aim of this study was to investigate the distribution of preferential flow paths in the soil profile of various altitudinal belts, analyze its variation among different soil horizons, and define the cause of soil macropores. A dye tracer method combined with photographic analysis was conducted for four hillslope sites in the Three Gorges Reservoir Area of China (TGRA). The results show that stained area proportion, as well as its vertical distribution in soil sections, presented varied patterns due to changes of forest vegetation and soil type with altitude. Stained area ratio of soil profiles increased, while stained depth decreased with increasing altitude. For soil sections in the subalpine belt, mid-mountain belt, and low-mountain belt of TGRA, stained area ratios were 62, 42, and 45%, and stained depths were 52.4, 56.4, and 69.5 cm, respectively. For brown earth covered with subalpine temperate deciduous broad-leaved forest, stained area ratios were the largest, but dyed patches were concentrated in the humus horizon. For yellow earth covered with low-mountain warm coniferous forest, stained depth reached 69.5 cm, and stained patches existed in the total soil profile. Compared with forest soil, stained depth and stained area ratio of abandoned farmland in low-mountain belt were lower, and the depth of dye infiltration was even shallower.

Seasonal dynamics of water use efficiency of typical forest and grassland ecosystems in China

We selected four sites of ChinaFLUX representing four major ecosystem types in China—Changbaishan temperate broad-leaved Korean pine mixed forest (CBS), Dinghushan subtropical evergreen broadleaved forest (DHS), Inner Mongolia temperate steppe (NM), and Haibei alpine shrub-meadow (HBGC)—to study the seasonal dynamics of ecosystem water use efficiency (WUE = GPP/ET, where GPP is gross primary productivity and ET is evapotranspiration) and factors affecting it. Our seasonal dynamics results indicated single-peak variation of WUE in CBS, NM, and HBGC, which were affected by air temperature (Ta) and leaf area index (LAI), through their effects on the partitioning of evapotranspiration (ET) into transpiration (T) (i.e., T/ET). In DHS, WUE was higher at the beginning and the end of the year, and minimum in summer. Ta and soil water content affected the seasonal dynamics of WUE through their effects on GPP/T. Our results indicate that seasonal dynamics of WUE were different because factors affecting the seasonal dynamics and their mechanism were different among the key ecosystems.

Seasonal patterns of litterfall in forest ecosystem worldwide

The seasonal litterfall plays an important role in the process of forest carbon and nutrient cycles. The current dynamic vegetation models use a simplified method to simulate seasonal patterns of litterfall, and assume that litterfall inputs distributed evenly through the year for deciduous trees or occur once during the start of year for evergreen trees. In this study, we collected more than 400 litterfall measurements for different forest ecosystems from existing literature and monographs, and analyzed the seasonal patterns of litterfall over the various forest types. The results showed that the total annual litterfall varied significantly by forest types in the range of 3–11Mgha−1y−1. The seasonal litterfall patterns had diverse forms and varied obviously among the forest types. For tropical forests, the litter peaks occurred mostly in spring or winter, corresponding to the drought season; for temperate broadleaved and needle-leaved evergreen forests, litter peaks could occur at various seasons; and for temperate deciduous broadleaved and boreal evergreen needle-leaved forests, litter peaks were observed in autumn. Global analyses showed that seasonal patterns of litterfall were determined by both the physiological mechanism and environmental variables.

Spatial pattern analysis of dominant species in Exochorda giraldii community in Xingtang Temple of Taiyue Mountains, Shanxi, China

Aims The Exochorda giraldii community is a secondary shrubland developed following destruction of warm temperate and deciduous broad-leaved forests. The objective of this study was to explore the distribution and in- ter-relationships of dominant species in E. giraldii communities in Taiyue Mountains, Shanxi, China. Methods Based on the vegetation survey data on a 50 m × 50 m plot, point pattern analysis (O-ring) and fractal analyses (including box-counting dimension analysis, information dimension analysis and correlation dimension analysis) were performed to determine the spatial patterns of dominant species in a E. giraldii community. Important findings In the E. giraldii community, most of the dominant species showed the characteristics of aggregated distribution at smaller scales. However, Periploca sepium and Spiraea salicifolia showed an aggrega- tion distribution at all scales. With increases in scale, the distributions of E. giraldii and Forsythia suspensa changed from aggregation to random and to uniform. Based on the point pattern analysis, the dominant species in the E. giraldii community showed aggregation distribution characteristics at different scales. The box-counting dimension analysis indicated that the ability of dominant species to occupy the space in the E. giraldii community was in the order of E. giraldii > F. suspensa > S. salicifolia > P. sepium. The information dimension analysis in- dicated that the degree of changes in pattern intensity of dominant species with scale in the E. giraldii community was in the order of P. sepium > S. salicifolia > E. giraldii > F. suspensa. The correlation dimension analysis showed that the spatial correlations of dominant species in the E. giraldii community was in the order of P. sepi- um > E. giraldii > F. suspensa > S. salicifolia. On a smaller scale, the E. giraldii population showed aggregated distribution; the F. suspensa population and the E. giraldii population had a positive correlation; the S. salicifolia population and the E. giraldii population had a positive correlation; the P. sepium population and the E. giraldii population had a negative correlation. Point pattern analysis and fractal analyses produced consistent results, re- vealing the spatial distribution patterns of secondary shrubs following destruction of the warm temperate and de- ciduous broad-leaved forests.

Diversity and species identity effects on fine root productivity and turnover in a species-rich temperate broad-leaved forest.

We investigated the evidence of belowground overyielding in a species-rich temperate broad-leaved forest with an ingrowth core study in 100 plots containing five common tree species (beech, lime, maple, hornbeam, ash) in mono-specific and 2-species or 3-species combinations. This design allowed separating diversity and species identity effects on root dynamics in a mature forest with long continuity. Fine root productivity was not significantly different between mono-specific and 2- or 3-species plots, whereas fine root turnover was significantly higher in the mixed than the mono-specific plots. Species identity effects on root turnover and root productivity were important. Ash achieved in the mixtures the highest fine root productivity and root turnover of all species; it is an apparent key species in this forest. Evidence in support of a diversity effect on fine root productivity and turnover was weak, however.

Impacts of Climate Change on Forest Ecosystems in Northeast China

This paper reviews the studies and research on climate change impacts on the forest ecosystems in Northeast China. The results show that in the context of global and regional warming, the growing season of coniferous forests has been increasing at an average rate of 3.9 d per decade. Regional warming favors the growth of temperate broad-leaved forests and has a detrimental effect on the growth of boreal coniferous forests. Over the past hundred years, the forest edge of the cool temperate zone in the southern Daxing’anling region has retreated 140 km northward. From 1896 to 1986, the northern boundary of broad-leaved forests in Heilongjiang province has extended northwestward about 290 km. Future climatic changes (until 2060) may lead to the northern deciduous needle forests moving out of China’s territory altogether. The occurrence cycles of pests and diseases have shortened; their distribution ranges have expanded. The life cycle of tent caterpillars (Malacosoma neustria testaceaMotschulsky) has shortened from 14–15 years in the past to 8–10 years now. The pine caterpillar (Dendrolimus tabulaeformisTsai et Liu), which has spread within western Liaoning province and the nearby areas, can now be found in the north and west. Lightning fires in the Daxing’anling region have significantly increased since 1987, and August has become the month when lightning fires occur most frequently. Overall, the net primary productivity (NPP) of forest in Northeast China has increased. The NPP in 1981 was around 0.27 Pg C, and increased to approximately 0.40 Pg C in 2002. With the current climate, the broad-leaved Korean pine forest ecosystem acts as a carbon sink, with a carbon sink capacity of 2.7 Mg C hm–2. Although the carbon sink capacity of the forest ecosystems in Northeast China has been weakened since 2003, the total carbon absorption will still increase. The forest ecosystems in Northeast China are likely to remain a significant carbon sink, and will play a positive role in the mitigation of climate change. CitationWang, X.-Y., C.-Y. Zhao, and Q.-Y. Jia, 2013: Impacts of climate change on forest ecosystems in Northeast China.Adv. Clim. Change Res.,4(4), doi: 10.3724/SP.J.1248.2013.230.

In vitro cytotoxicity, α-glucosidase inhibition, antioxidant, and free radical scavenging activities of Illicium griffithii Hook. f. & Thoms fruits

Illicium griffithii is a medicinal tree species of the temperate broad-leaved forests of North East India; its fruits are used in the pharmaceutical and spice industries. The fruits are used medicinally to treat cough, sinusitis, toothache, regurgitating, dyspepsia, abdominal pain, and food poisoning and are considered carminative, stomachic, and glactagogic. The present study was aimed to evaluate the cytotoxicity, α-glucosidase inhibitory potential, antioxidant, and free radical scavenging activities of hexane, ethyl acetate, and methanol extracts of I. griffithii fruits. Ethyl acetate extract (EAE) exhibited 78.7 % toxicity at the dose of 500 μg/ml with IC50 value of 300 μg/ml against A549 human adenocarcinoma lung cancer cell line, 50 % α-glucosidase inhibition at 810.32 ± 1.28 μg/ml concentration, and potent scavenging activity at 1,000 μg/ml on DPPH (91.12 % ± 2.08), CUPRAC (2.384 ± 0.03), reducing power (0.847 ± 0.02), lipid peroxidation (55.52 % ± 1.56), hydroxyl (75.83 % ± 1.47), and DMPD (76.12 % ± 1.35). It additionally showed maximum activity at 300 μg/ml on total antioxidant activity (0.290 ± 0.04 GAE mg/g) and FRAP (2.150 ± 0.23 mM Fe2+/g). The results demonstrated that EAE possessed marked activity in all the tested biological parameters. On further fractionation, EAE gave an active fraction F3. Two phenolic compounds were isolated and identified (3,4-dihydroxybenzoic acid and 3,4,5-trihydroxybenzoic acid) from this fraction for the first time. I. griffithii showed promising cytotoxic and antioxidant activities.

Is randomized branch sampling suitable to assess wood volume of temperate broadleaved old-growth forests?

Old-growth forests are characterized by the presence of large and very large trees. The estimation of their wood volume and biomass is essential in order to monitor the ecological processes in these stands and their contribution to carbon cycle. However, conventional wood volume estimation techniques based on mensuration of stem diameter at breast height and tree height is most often unfeasible for large and very large trees in old-growth forests because volume models or tables are usually elaborated from trees of smaller size grown up in regularly managed forest stands. Random Branch Sampling (RBS) is often proposed as a possible estimation alternative under such conditions. Starting from the ground level some of the parts of the main trunk and of the branches are sampled and measured to estimate the overall wood volume (or other biophysical variables). The application of RBS in old-growth forests, where tree cutting is usually forbidden or very difficult, requires that the crown of the tree can physically be reached to measure the sampled parts. We argue that under such conditions it is usually preferable to fully measure all the components of the tree crown because RBS estimates are not precise if based on only one sampling path and that, on the other hand, measuring the main trunk and all the branches by tree-climbing consumes the same time as replicating several RBS paths on the same tree. To demonstrate our hypothesis we selected 16 large beech trees located in the old-growth forest of Mount Cimini in Central Italy. Using a modern tree-climbing approach the main trunk and all the branches were measured and recorded in the field. The database was used to simulate RBS paths. Real values from volume census were contrasted with estimates based on RBS. On the whole, RBS estimates based on one single path prove to be highly imprecise. Even for trees characterized by a rather regular form, at least three RBS paths should be repeated on the same tree to maintain the relative standard error under or near 15%. This paper introduces the problem and describes the experimental test. The results are discussed under the perspective of standardized application of the proposed methodology.

Soil C and nutrient stores under Scots pine afforestations compared to ancient beech forests in the German Pleistocene: The role of tree species and forest history

In the diluvial lowlands of northern Germany, the Netherlands and northern Poland, an estimated ∼5 Mio ha of Scots pine plantations (Pinus sylvestris) has been established on sandy soil in the last 250years replacing the former temperate broad-leaved forests after extended periods of cultivation in the Middle Ages. We examined the effect of variable stand continuity of pine plantations (recent vs. ancient: 51–128 vs. >230years) on the soil organic carbon (SOC) store and soil nutrient capital in comparison to ancient beech forests (>230years of continuity) which represent the potential natural forest vegetation. Recent and ancient pine stands had c. 75% larger organic layer C stores than ancient beech forests, while the total C stock in the soil (organic layer and mineral soil to 100cm) was ∼25% larger in the beech forests due to higher C concentrations in 0–50cm depth of the mineral soil. The soil stores of Ntot were ∼50% and the exchangeable Ca, K and Mg pools about three times larger under beech than under the pine stands. Resin-exchangeable P was enriched in the soils under ancient pine stands probably due to manuring in the past. After clear-cut and long cultivation, it may take >230years of forest presence to restore the greatly reduced mineral soil C and N pools. The C and N sequestration potential of the soils appeared to be particularly small under pine indicating a pronounced tree species (pine vs. beech) effect on soil C and N dynamics. We conclude that, in the face of rising greenhouse gas emissions, the limited soil C and nutrient storage potential of Scots pine plantations on sandy soils needs consideration when selecting suitable tree species for future forestry.

A shallow water record of the onset of the Messinian salinity crisis in the Adriatic foredeep (Legnagnone section, Northern Apennines)

The Legnagnone section (North-eastern Apennines) represents one of the few shallow water records of the onset of the Messinian salinity crisis. Here we present a detailed description of a ~200kyr time interval encompassing the pre-/syn-evaporitic transition based on a multidisciplinary approach, integrating sedimentological, bio-magnetostratigraphical, palaeontological and stable isotope data. Such a shallow water setting is potentially more sensitive to the palaeoenvironmental change leading to the MSC than the more often studied deeper Mediterranean basin. The aquatic palaeoenvironmental reconstruction proposed here is based on the study of foraminifer, ostracod and mollusc assemblages. It depicts a change from infralittoral (20–50m) to inner circalittoral environment (60–100m) that, since 6.12Ma, was progressively affected by a reduction of oxygen at the sea floor punctuated by short-lived anoxic events. At least three cooling events have been recognized on the basis of relative abundance data in mid to high altitude pollen, which, before 6.03Ma, are in phase with abundance peaks of Turborotalia spp., a taxon indicating eutrophic and cool surface waters. The absence of stress-tolerant benthic foraminifers during these peaks points to strong ventilation episodes triggered by a generally cooler climate. The proximity of a deltaic system and the consequent riverine input probably caused a salinity decrease of the surface waters, hindering the proliferation of planktonic foraminifers in the water column, which prevalently occur in short influxes and disappear at ca. 6Ma. Our results suggest that the onset of the crisis occurred during a phase of relative sea level high stand, whereas no evidences of sea level drop can be envisaged. The palaeoclimatic reconstruction based on palynological data indicates the dominance of a “subtropical humid forest” vegetation type, where fresh water swamps are well represented. From 6.03Ma onward, the transition to the salinity crisis is marked by more pronounced cyclical expansions of the temperate broad-leaved deciduous forest, along with herbaceous taxa. The establishment of the strongly evaporative condition at the crisis onset is not associated with major vegetational changes towards drier conditions, but linked to a sudden increase of δ18O and the disappearance of benthic foraminifers just prior to the deposition of the 1st laminated carbonate, which represents the base of the Primary Lower Gypsum unit.

Diurnal and Seasonal Variations in Soil Respiration in a Temperate Broad-Leaved Korean Pine Forest, China

LI-6400-09 soil CO2 flux chamber (LI-COR, NE USA) and Subtraction method were used to investigate the diurnal and seasonal variations of soil respiration and the contribution of root respiration to total soil respiration in a temperate broad-leaved Korean Pine forest ecosystem, China. Soil temperatures at 5 cm depth were recorded by Hobo thermal recorder (at 1 h interval) and year-round soil respiration and the contribution of root could be calculated based the Q10 relationship. The results indicated that: Diurnal variations of total soil respiration (TRs) and root-severed soil respiration (RRs) were highly associated with variations of soil temperature at 5 cm depth in a day. total soil respiration, root-severed soil respiration (RRs) and root respiration (Rs) followed a similar seasonal trend that varied markedly during the growing season with high rates in summer and low rates in spring and autumn, coinciding with summer wet and high temperature, and in spring and autumn, with the lower temperature. The mean rates of TRs, RRs and Rs was 3.68, 2.02 and 1.63 µmol m-2 s-1, which were 1392.63, 764.43 and 616.84 g C m-2 y-1 respectively from May to September in 2004. TRs, RRs and Rs were exponentially correlated with temperature during growing season. However, there were no correlations between soil respiration and soil volumetric moisture. The Q10 values for TRs, RRs and Rs were 2.40, 2.42 and 2.50 respectively. The root was a major component of soil respiration, accounting for from 29.3 to 58.7% of the total soil respiration from May to September in 2004. The year-round mean of TRs, RRs and Rs were 1.95, 1.07 and 0.81 µmol m-2 s-1, which were 737.94, 404.92 and 306.53 g C m-2 y-1 respectively. Root respiration contributed 41.0% to the annual total soil respiration.

Effects of phenological change on ecosystem productivity of temperate deciduous broad-leaved forests in North America

Effects of phenological change on ecosystem productivity of temperate deciduous broad-leaved forests in North America

Response of microbial respiration from fine root litter decomposition to root water content in a temperate broad-leaved forest

Microbial respiration from plant litter decomposition is sensitive to soil water status; however, its response to water status remains ambiguous, particularly in the litter of fine roots. We investigated the effect of fine-root water content on microbial respiration after 468 days of decomposition in forest soil for two diameter classes (0-0.5 and 0.5-2 mm) of Quercus serrata and Ilex pedunculosa in central Japan. Direct measurement of microbial respiration from root litter resulted in a range of 0.015-3.52 nmol CO2 g −1 s −1 . Microbial respiration in both diameter classes and species decreased linearly with decreasing root water content. These changing patterns of microbial respiration did not differ significantly between the diameter classes of either species, indicating that microbial respiration was regulated by the moisture of root litter, and not by characteristics associated with diameter class or species. In contrast, the carbon to nitrogen ratio and mass loss of the root litter differed significantly between diameter classes in both species. These findings suggest that along with chemical and morphological properties of fine root litter, the changes in root water content should also be considered as a viable factor in microbial activity variations. Drying-wetting cycles of fine roots could lead to sensitive responses of microorganisms during the short term, leading to variation in the decomposition rate of fine root litter over the long term. This study provided insight into the potential impact of microbial physiological performance on heterotrophic respiration and fine root decomposition under the varying root water content.

Rhizosphere effects of tree species – Large reduction of N2O emission by saplings of ash, but not of beech, in temperate forest soil

Previous research has shown that N2O emissions from forest soils can vary considerably with forest type. It is not yet known whether these variations are mainly reflecting differences between needle-leaved and broad-leaved forests or if there are also flux differences among different broad-leaved tree species. Furthermore, it remains unclear if these differences are merely caused by species-specific leaf litter effects, or whether root-related traits are also influential. We conducted two laboratory experiments with soil from a temperate broad-leaved forest to examine the effects of ash saplings (Fraxinus excelsior L.) on N2O emissions at ambient and high nitrate availability (experiment A), and to compare the effects of ash, beech (Fagus sylvatica L.) and ash/beech mixture on N2O emissions (experiment B). In both experiments, a large reduction in N2O efflux was found for the ash treatments as compared to root-free soil (by 94% at ambient nitrate availability and by 98% after the addition of 200 kg N ha−1 KNO3). The suppressing effect of ash saplings was larger than the stimulating effect of nitrate addition on N2O emissions. Soil planted with beech saplings tended to reduce N2O emissions as well, but the non-significant effect was much smaller than the ash effect. Our study provides evidence that species-specific rhizosphere effects can have a substantial influence on the emission of greenhouse gases from forest soils, which have to be considered in addition to leaf litter effects.

Dramatic diversity losses in epiphytic lichens in temperate broad-leaved forests during the last 150 years

Comparing data of epiphytic lichen diversity in semi-natural broad-leaved forests in north-western Germany from the 19th to early 20th centuries with recent inventories revealed strong changes, even though forest structure and tree species composition had changed only little. In three study areas, between 55% and 70% of the species became rarer during the 100–150-year long observation period. In the spatially extended study areas Weser-Ems Lowlands and Solling Mountains, 36% or 39% of the species, respectively, could not be rediscovered in the recent survey. Considering that species might have been overlooked during revisitation, the extinction rate was estimated to be 28% in the Weser-Ems Lowlands and 30% in the Solling Mountains based on a estimated probability for recovering the species of 75% in crustose lichens and 90% in foliose and fruticose lichens. The main causes of the species decline are thought to be forest management (especially the reduction of overmature and decaying trees), the reduction of soil moisture and, with it, air humidity due to drainage as well as the deposition of acidifying and fertilizing substances from the atmosphere. Lichens specialized on rain-sheltered bark furrows and cavities of old trees or smooth, shady bark or moist thick-stemmed deadwood in the forest interior have suffered the strongest declines, including the epiphyte flora of Fagus sylvatica, Central Europe’s most abundant native forest tree species. Only few lichens which benefit from nitrogen deposition, global warming or the acidification of bark due to sulphur dioxide pollution have spread.

Carbon isotopic signature of CO2 emitted by plant compartments and soil in two temperate deciduous forests

The carbon isotope composition of the CO2 efflux (δ13CE) from ecosystem components is widely used to investigate carbon cycles and budgets at different ecosystem scales. δ13CE, was considered constant but is now known to vary along seasons. The seasonal variations have rarely been compared among different ecosystem components. We aimed to characterise simultaneously the seasonal dynamics of δ13CE in different compartments of two temperate broadleaved forest ecosystems. Using manual chambers and isotope ratio mass spectrometry, we recorded simultaneously δ13CE and δ13C of organic matter in sun leaves, current-year twigs, trunk bases and soil in an oak and a beech forest during 1 year. In the two forests, δ13CE displayed a larger variability in the tree components than in the soil. During the leafy period, a pronounced vertical zonation of δ13CE was observed between the top (sun leaves and twigs with higher values) and bottom (trunk and soil with lower values) of the ecosystem. No correlation was found between δ13CE and δ13C of organic matter. Causes for these seasonal variations and the vertical zonation in isotope signature are discussed. Our study shows clear differences in values as well as seasonal dynamics of δ13CE among different components in the two ecosystems. The temporal and local variation of δ13CE cannot be inferred from organic matter signature or CO2 emission rates.

Climate change, growing season water deficit and vegetation activity along the north–south transect of eastern China from 1982 through 2006

Abstract. Considerable work has been done to examine the relationship between environmental constraints and vegetation activities represented by the remote sensing-based normalized difference vegetation index (NDVI). However, the relationships along either environmental or vegetational gradients are rarely examined. The aim of this paper was to identify the vegetation types that are potentially susceptible to climate change through examining their interactions between vegetation activity and evaporative water deficit. We selected 12 major vegetation types along the north–south transect of eastern China (NSTEC), and tested their time trends in climate change, vegetation activity and water deficit during the period 1982–2006. The result showed significant warming trends accompanied by general precipitation decline in the majority of vegetation types. Despite that the whole transect increased atmospheric evaporative demand (ET0) during the study period, the actual evapotranspiration (ETa) showed divergent trends with ET0 in most vegetation types. Warming and water deficit exert counteracting controls on vegetation activity. Our study found insignificant greening trends in cold temperate coniferous forest (CTCF), temperate deciduous shrub (TDS), and three temperate herbaceous types including the meadow steppe (TMS), grass steppe (TGS) and grassland (TG), where warming exerted more effect on NDVI than offset by water deficit. The increasing growing season water deficit posed a limitation on the vegetation activity of temperate coniferous forest (TCF), mixed forest (TMF) and deciduous broad-leaved forest (TDBF). Differently, the growing season brownings in subtropical or tropical forests of coniferous (STCF), deciduous broad-leaved (SDBF), evergreen broad-leaved (SEBF) and subtropical grasslands (STG) were likely attributed to evaporative energy limitation. The growing season water deficit index (GWDI) has been formulated to assess ecohydrological equilibrium and thus indicating vegetation susceptibility to water deficit. The increasing GWDI trends in CTCF, TCF, TDS, TG, TGS and TMS indicated their rising susceptibility to future climate change.