Influence of elevation on canopy transpiration of temperate deciduous forests in a complex mountainous terrain of South Korea

Background and aims

Variations in microclimate and soil characteristics on mountain slopes influence forest structure and function. Precipitation, incoming solar radiation and relative humidity change along a mountain slope. Equally, soil depth and the amount of stored soil moisture vary. The objective of this study was to examine the impacts of these factors on forest water use in mountainous terrains.

Methods

Transpiration of four temperate deciduous forest stands located at different elevations in South Korea was monitored with a sap flow technique throughout the growing season in 2010. The study sites were located on the north slope at 450 m (450 N), 650 m (650 N), and 950 m (950 N). To examine the effect of aspect, an additional site with a southern aspect was studied at 650 m (650S). All the sites were dominated by Quercus species, with leaf area index (L) ranging between 5 ? 6 m² m^?2.

Results

Rainfall increased, while air temperature (T _A ) and daytime vapor pressure deficit (D) decreased with increasing elevation. We did not observe any gradients in solar radiation (R _S ), soil moisture and sap flux density of the individual trees (J _st ) with an elevational gradient. Sapwood area (A _S ), i.e., hydro-active xylem area, and daily maximum tree water use (max TWU) increased non-linearly with increasing diameter at breast height (DBH). Neither A _S nor max TWU varied among tree species or along the elevation. The total annual canopy transpiration (E _C ) was 175, 115, 110, and 90 mm for 450 N, 650 N, 650S, and 950 N, respectively. E _C declined with increasing elevation as a result of decreasing length of the growing season, D, and T _A along the elevation. Significantly (P < 0.001) higher stomatal sensitivity to changes in D was found at the 950 N, leading to lower annual E _C and lower water use efficiency (WUE) at this elevation.

Conclusions

We conclude that differences in E _C exist along the mountain slope studied, corresponding to changing T _A , D, length of the growing season, and stomatal sensitivity to D, which should be considered when establishing forest catchment water balances.     

Holocene climate,fire and vegetation dynamics at the treeline in the Northwestern Swiss Alps

Treelines are expected to rise to higher elevations with climate warming; the rate and extent however are still largely unknown. Here we present the first multi-proxy palaeoecological study from the treeline in the Northwestern Swiss Alps that covers the entire Holocene. We reconstructed climate, fire and vegetation dynamics at Iffigsee, an alpine lake at 2,065 m a.s.l., by using seismic sedimentary surveys, loss on ignition, visible spectrum reflectance spectroscopy, pollen, spore, macrofossil and charcoal analyses. Afforestation with Larix decidua and tree Betula (probably B. pendula) started at ~9,800 cal. b.p., more than 1,000 years later than at similar elevations in the Central and Southern Alps, indicating cooler temperatures and/or a high seasonality. Highest biomass production and forest position of ~2,100–2,300 m a.s.l. are inferred during the Holocene Thermal Maximum from 7,000 to 5,000 cal. b.p. With the onset of pastoralism and transhumance at 6,800–6,500 cal. b.p., human impact became an important factor in the vegetation dynamics at Iffigsee. This early evidence of pastoralism is documented by the presence of grazing indicators (pollen, spores), as well as a wealth of archaeological finds at the nearby mountain pass of Schnidejoch. Human and fire impact during the Neolithic and Bronze Ages led to the establishment of pastures and facilitated the expansion of Picea abies and Alnus viridis. We expect that in mountain areas with land abandonment, the treeline will react quickly to future climate warming by shifting to higher elevations, causing drastic changes in species distribution and composition as well as severe biodiversity losses.     

Patterns of wood carbon dioxide efflux across a 2,000-m elevation transect in an Andean moist forest

During a 1-year measurement period, we recorded the CO₂ efflux from stems (R _S) and coarse woody roots (R _R) of 13–20 common tree species at three study sites at 1,050, 1,890 and 3,050 m a.s.l. in an Andean moist forest. The objective of this work was to study elevation changes of woody tissue CO₂ efflux and the relationship to climate variation, site characteristics and growth. Furthermore, we aim to provide insights into important respiration–productivity relationships of a little studied tropical vegetation type. We expected R _S and R _R to vary with dry and humid season conditions. We further expected R _S to vary more than R _R due to a more stable soil than air temperature regime. Seasonal variation in woody tissue CO₂ efflux was indeed mainly attributable to stems. At the same time, temperature played only a small role in triggering variations in R _S. At stand level, the ratio of C release (g C m^?2 ground area year^?1) between stems and roots varied from 4:1 at 1,050 m to 1:1 at 3,050 m, indicating the increasing prevalence of root activity at high elevations. The fraction of growth respiration from total respiration varied between 10 (3,050 m) and 14% (1,050 m) for stems and between 5 (1,050 m) and 30% (3,050 m) for roots. Our results show that respiratory activity and hence productivity is not driven by low temperatures towards higher elevations in this tropical montane forest. We suggest that future studies should examine the limitation of carbohydrate supply from leaves as a driver for the changes in respiratory activity with elevation.     

Environmental variables controlling soil respiration on diurnal, seasonal and annual time-scales in a mixed mountain forest in Switzerland

Studies on soil respiration in mountain forests are rather scarce compared to their broad distribution. Therefore, we investigated daily, seasonal and annual soil respiration rates in a mixed forest (Lägeren), located at about 700 m in the Swiss Jura mountains, during 2 years (2006 and 2007). Soil respiration (SR) was measured continuously with high temporal resolution (half-hourly) at one single point (SR_automated) and periodically with high spatial resolution (SR_manual) at 16 plots within the study site. Both, SR_automated and SR_manual showed a similar seasonal cycle. SR strongly depended on soil temperature in 2007 (R ² = 0.82–0.92), but less so in 2006 (R ² = 0.56–0.76) when SR was water limited during a summer drought. Including soil moisture improved the fit of the 2006 model significantly (R ² = 0.78–0.97). Total annual SR for the study site was estimated as 869 g C m^?2 year^?1 for 2006 and as 907 g C m^?2 year^?1 for 2007 (uncertainty <10% at the 95% confidence interval, determined by bootstrapping). Selected environmental conditions were assessed in more detail: (1) Rapid, but contrasting changes of SR were found after summer rainfall. Depending on soil moisture at pre-rain conditions, summer rain could either cause a pulse of CO₂ from the soil or an abrupt decrease of SR_automated due to water logging of soil pores. (2) Two contrasting winter seasons resulted in SR being about 60–70% (31.2–44.6 g C m^?2) higher during a mild winter (2007) compared to a harsh winter (2006). (3) Analysing SR for selected periods on a diurnal scale revealed a counter-clockwise hysteresis with soil surface temperatures. This indication of a time-lagged response of SR to temperature was further supported by a very strong relationship (R ² = 0.86–0.90) of SR to soil temperature with a time-lag of 2–4 h.     

Forest soil respiration reflects plant productivity across a temperature gradient in the Alps

Soil respiration (R _s) plays a key role in any consideration of ecosystem carbon (C) balance. Based on the well-known temperature response of respiration in plant tissue and microbes, R _s is often assumed to increase in a warmer climate. Yet, we assume that substrate availability (labile C input) is the dominant influence on R _s rather than temperature. We present an analysis of NPP components and concurrent R _s in temperate deciduous forests across an elevational gradient in Switzerland corresponding to a 6 K difference in mean annual temperature and a considerable difference in the length of the growing season (174 vs. 262 days). The sum of the short-lived NPP fractions (“canopy leaf litter,” “understory litter,” and “fine root litter”) did not differ across this thermal gradient (+6 % from cold to warm sites, n.s.), irrespective of the fact that estimated annual forest wood production was more than twice as high at low compared to high elevations (largely explained by the length of the growing season). Cumulative annual R _s did not differ significantly between elevations (836 ± 5 g C m^?2 a^?1 and 933 ± 40 g C m^?2 a^?1 at cold and warm sites, +12 %). Annual soil CO₂ release thus largely reflected the input of labile C and not temperature, despite the fact that R _s showed the well-known short-term temperature response within each site. However, at any given temperature, R _s was lower at the warm sites (downregulation). These results caution against assuming strong positive effects of climatic warming on R _s, but support a close substrate relatedness of R _s.     

Warming and the dependence of limber pine (Pinus flexilis) establishment on summer soil moisture within and above its current elevation range

Continued changes in climate are projected to alter the geographic distributions of plant species, in part by affecting where individuals can establish from seed. We tested the hypothesis that warming promotes uphill redistribution of subalpine tree populations by reducing cold limitation at high elevation and enhancing drought stress at low elevation. We seeded limber pine (Pinus flexilis) into plots with combinations of infrared heating and water addition treatments, at sites positioned in lower subalpine forest, the treeline ecotone, and alpine tundra. In 2010, first-year seedlings were assessed for physiological performance and survival over the snow-free growing season. Seedlings emerged in midsummer, about 5–8 weeks after snowmelt. Low temperature was not observed to limit seedling photosynthesis or respiration between emergence and October, and thus experimental warming did not appear to reduce cold limitation at high elevation. Instead, gas exchange and water potential from all sites indicated a prevailing effect of summer moisture stress on photosynthesis and carbon balance. Infrared heaters raised soil growing degree days (base 5 °C, p < 0.001) and August–September mean soil temperature (p < 0.001). Despite marked differences in vegetation cover and meteorological conditions across sites, volumetric soil moisture content (θ) at 5–10 cm below 0.16 and 0.08 m³ m^?3 consistently corresponded with moderate and severe indications of drought stress in midday stem water potential, stomatal conductance, photosynthesis, and respiration. Seedling survival was greater in watered plots than in heated plots (p = 0.01), and negatively related to soil growing degree days and duration of exposure to θ < 0.08 m³ m^?3 in a stepwise linear regression model (p < 0.0001). We concluded that seasonal moisture stress and high soil surface temperature imposed a strong limitation to limber pine seedling establishment across a broad elevation gradient, including at treeline, and that these limitations are likely to be enhanced by further climate warming.     

Global patterns and predictors of stem CO2 efflux in forest ecosystems

Stem CO₂ efflux (E_S) plays an important role in the carbon balance of forest ecosystems. However, its primary controls at the global scale are poorly understood and observation‐based global estimates are lacking. We synthesized data from 121 published studies across global forest ecosystems and examined the relationships between annual E_S and biotic and abiotic factors at individual, biome, and global scales, and developed a global gridded estimate of annual E_S. We tested the following hypotheses: (1) Leaf area index (LAI) will be highly correlated with annual E_S at biome and global scales; (2) there will be parallel patterns in stem and root CO₂ effluxes (R_A) in all forests; (3) annual E_S will decline with forest age; and (4) LAI coupled with mean annual temperature (MAT) and mean annual precipitation (MAP) will be sufficient to predict annual E_S across forests in different regions. Positive linear relationships were found between E_S and LAI, as well as gross primary production (GPP), net primary production (NPP), wood NPP, soil CO₂ efflux (R_S), and R_A. Annual E_S was correlated with R_A in temperate forests after controlling for GPP and MAT, suggesting other additional factors contributed to the relationship. Annual E_S tended to decrease with stand age. Leaf area index, MAT and MAP, predicted 74% of variation in E_S at global scales. Our statistical model estimated a global annual E_S of 6.7 ± 1.1 Pg C yr⁻¹ over the period of 2000–2012 with little interannual variability. Modeled mean annual E_S was 71 ± 43, 270 ± 103, and 420 ± 134 g C m² yr⁻¹ for boreal, temperate, and tropical forests, respectively. We recommend that future studies report E_S at a standardized constant temperature, incorporate more manipulative treatments, such as fertilization and drought, and whenever possible, simultaneously measure both aboveground and belowground CO₂ fluxes.     

Osmotic stress affects physiological responses and growth characteristics of three pistachio cultivars

Pistachio (Pistacia vera L.) has a high tolerance to drought and soil salinity. Although adult pistachio trees are well known to be drought tolerant, the studies on physiological adaptation of pistachio cultivars to drought are limited. Therefore, three pistachio cultivars, i.e., Akbari, Kaleghochi, and Ohadi were subjected to three osmotic drought stress treatments: control (?0.1 MPa), moderate (?0.75 MPa) and severe drought (?1.5 MPa) stress using PEG 6000 for a 14-day period. All drought stress treatments decreased net photosynthesis (P _n), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), and transpiration rate (E), but Ohadi maintained better its photosynthetic capacity compared to Akbari and Kaleghochi. Maximum quantum yield of PSII photochemistry (F _v /F _m), effective PSII quantum yield (ΦPSII) and photochemical quenching (qP) were also reduced. The chlorophyll fluorescence parameters indicated that Akbari was more susceptible to the applied drought stress. Drought stress levels decreased chlorophyll pigments, fresh weight, stem elongation, leaf nitrogen content (N), leaf water potential and increased water use efficiency (WUE). Proline increased strongly under drought stress for Akbari. After 2 weeks of stress a recovery of 2 weeks was applied. This period was insufficient to fully restore the negative effects of the applied stress on the studied cultivars. Based on the reduction of photosynthesis and the increase of the proline content Akbari seems more sensitive to the applied drought stress.     

Increasing relevance of spring temperatures for Norway spruce trees in Davos,Switzerland, after the 1950s

Key message

Relevance of spring temperatures for tree-ring growth steadily increased since 1950s. Closely linked tree-ring growth and net CO ₂ exchange driven by spring temperatures.

Abstract

We investigated long-term (over 100 years) tree-ring width (TRW) variabilities as well as short-term (10 years) variations in net ecosystem productivity (NEP) in response to climate to assess the driving factors for stem growth of Norway spruce in a subalpine forest at Davos in Switzerland. A tree-ring width index (TRWi) chronology for the period from 1750 to 2006 was constructed and linked with climate data from 1876 to 2006, and with NEP available for the period from 1997 to 2006. Based on TRWi, we found that only two out of the 257 years exhibited extreme negative TRWi, compared to 29 years with extreme positive anomalies, observed mainly in recent decades. Annual temperature, annual precipitation, as well as autumn and winter temperature signals were well preserved in the TRWi chronology over the last 130 years. Spring temperatures became increasingly relevant for TRWi, explaining less than 1 % of the variation in TRWi for the period from 1876 to 2006, but 8 % for the period from 1950 to 2006 (p = 0.032), and even 47 % for 1997–2006 (p = 0.028). We also observed a strong positive relationship between annual TRWi and annual NEP (r = 0.661; p = 0.037), both strongly related to spring temperatures (r = 0.687 and r = 0.678 for TRWi and NEP, respectively; p = 0.028; p = 0.032). Moreover, we found strong links between monthly NEP of March and annual TRWi (r = 0.912; p = 0.0001), both related to March temperatures (r = 0.767, p = 0.010 and r = 0.724, p = 0.018, respectively). Thus, under future climate warming, we expect stem growth of these subalpine trees and also ecosystem carbon (C) sequestration to increase, as long as water does not become a limiting factor.     

Tree growth,cambial phenology,and wood anatomy of limber pine at a Great Basin (USA) mountain observatory

Key message

Anatomical features of Pinus flexilis under warmer and drier conditions along an altitudinal transect revealed a shorter growing season and shifts in the timing of wood formation.

Abstract

Future climate change driven by greenhouse warming is expected to increase both frequency and severity of drought events and heat waves. Possible consequences for forest ecosystems include changes in foundation species and extended die-off phenomena. We investigated tree growth under the set of biotic and abiotic conditions, and their interactions, that are expected in a drier and warmer world using mountain observatories designed to capture elevation gradients in the Great Basin of North America. Stem cambial activity, wood anatomy, and radial growth of limber pine (Pinus flexilis) were examined at two different elevations using automated dendrometers and repeated histological microcores in 2013–2014. Mean annual temperature was 3.7° cooler at the higher site, which received 170 mm year^?1 of precipitation more than the lower site. Mean air temperature thresholds for xylogenesis computed using logistic regression were 7.7 and 12.0 °C at the higher and lower site, respectively. No differences in the onset date of cambial activity were found under such naturally contrasted conditions, with the global change analog provided by the lower site. Growing season was shortened by increasing drought stress at the lower site, thereby reducing xylem production. Stem expansion was only detectable by automated dendrometers at the higher site. Using elevation to simulate climatic changes and their realized ecosystem feedbacks, it was possible to express tree responses in terms of xylem phenology and anatomical adaptations.

     

Simulating seasonal and inter-annual variations in energy and carbon exchanges and forest dynamics using a process-based atmosphere�Cvegetation dynamics model

The present paper shows simulated results of seasonal and inter-annual variations in energy and carbon exchanges and forest dynamics in a sub-boreal deciduous forest using a fully coupled atmosphere?Cvegetation interaction model [multilayered integrated numerical model of surface physics-growing plants interaction (MINoSGI)]. With careful adjustment of site-specific eco-physiological parameters, MINoSGI reproduced successfully stand biomass?Ctree density relationship based on the forest inventory data for 7 years (1999?C2005) and seasonal and inter-annual variations in energy and CO₂ fluxes measured by means of eddy covariance technique for 3 years (2003?C2005) in the sub-boreal forest, northern Japan. In addition, MINoSGI estimated annual evapotranspiration (E _vt) at 328.6 ± 25.8 mm year^?1, net primary production (NPP) at 372.1 ± 31.5 gC m^?2 year^?1 and net ecosystem exchange (NEE) at ?224.2 ± 32.2 gC m^?2 year^?1. We found the estimate of annual NEE in our site lies among the estimates at other forest stands with the almost same climatic conditions in northern Japan, although the tree species and stand age of these forests are different from those of our site. Overall, MINoSGI was found useful to present simultaneous simulations of forest dynamics, surface energy, and carbon exchanges of a forest stand in the future from micro-meteorological and ecophysiological points of view.     

Variability of indices of macronutrient availability in soils at different spatial scales along an elevation transect in tropical moist forests (NE Ecuador)

The availability of key plant nutrients may change with elevation in tropical mountains due to altitudinal gradients in temperature and moisture which affect pedogenesis and nutrient cycling. In a transect from upper lowland to montane forests in NE Ecuador, we tested the hypotheses that (1) the availability of P is low in low-elevation forests but increases upslope, while the availability of N is relatively high at low elevations but decreases with elevation, and (2) increasing amounts of calcium, magnesium and potassium are stored on top of the soil with progressive humus accumulation toward higher elevations, likely to improve nutrient availability. In each 20 plots in undisturbed natural forest at 500, 1000, 1500 and 2000 m?a.s.l., we measured in situ N net mineralization and nitrification rate (N_NM and N_NI, buried bag method), plant-available phosphorus (P_a, resin-bag method), and salt-exchangeable calcium, potassium and magnesium concentrations (Ca_ex, K_ex, Mg_ex) in the organic and mineral topsoils. N_NM and N_NI, and the Ca_ex, K_ex and Mg_ex concentrations were much more variable at the plot level than across the four elevations, while P_a varied equally at small and large spatial scales. P_a increased more than 10fold from 500 to 2000 m. The net release of nitrate dominated over ammonium at all elevations. While mass-related N_NM and N_NI rates and also organic matter C/N ratio in the topsoil remained invariant along the slope, N_NM and N_NI rates per ground area decreased by about 40% from 500 to 2000 m. Thus, the N_NM/P_a ratio decreased markedly with elevation proving our first hypothesis. In support of the second hypothesis, the pools of Ca_ex, Mg_ex and K_ex in the organic layers increased with elevation, demonstrating the key role that organic topsoil horizons are playing for forest nutrition at high elevations. We suggest that the large difference in N versus P availability of tropical (upper) lowland and montane forests is likely to be a key factor influencing the species composition and productivity along tropical mountain slopes.     

Drivers of temperature sensitivity of decomposition of soil organic matter along a mountain altitudinal gradient in the Western Carpathians

Mountain forest soils contain an important stock of carbon. Their altitudinal gradient can serve as a model for research on the potential risk of increased emission of carbon dioxide to the atmosphere, in a positive feedback of global warming. Using soil samples collected at three elevations (600, 900, and 1200 m a.s.l.) from five separate slopes of the Carpathian Mountains (Poland), we studied the effects of soil physical, chemical and microbial properties controlling the temperature sensitivity (Q₁₀ values) of organic matter decomposition in forest soils. Data of soil basal respiration rate measured in laboratory conditions at six different temperatures (5, 10, 15, 20, 25 and 30 °C) were fitted to a Gaussian function. The modelled soil respiration rates differed between altitudes at temperature exceeding 15 °C, and the respiration rate of soil from 1200 m a.s.l. was higher than in soils from the two lower elevations. Based on the modelled respiration values, we calculated Q₁₀ values in the low (Q₁₀L, 0–10 °C), medium (Q₁₀M, 10–20 °C) and high (Q₁₀H, 20–30 °C) temperature ranges. The Q₁₀ values did not differ between elevations. Q₁₀L and Q₁₀M were negatively related only with the C:N ratio. Temperature sensitivity of decomposition of soil organic matter was not affected by bacterial activity and functional diversity (assessed using Biolog^® ECO plates), microbial biomass or community structure (inferred from phospholipid fatty acid assays). Our findings support a kinetics-based theory of the higher temperature sensitivity of more chemically recalcitrant soil organic matter, put forward by other authors.     

Root functioning in tropical high-elevation forests: Environmental vs. biological control of root water absorption

Lowered temperatures may reduce the root water uptake of tropical trees at high elevations through several mechanisms; however, field studies to test their relevance are lacking. We measured sap flux density (J) in small-diameter tree roots across a 2000-m elevation transect in a tropical mountain forest for quantifying the effects of temperature (T_a), VPD and soil moisture (θ) on root water flow and uptake at different elevations. Recently developed miniature heat balance-sap flow gauges were applied to roots of about 10 mm in diameter in mountain forest stands at 1050, 1890 and 3060 m a.s.l. in the Ecuadorian Andes and the measured flow was related to anatomical properties of the root xylem. Between 1050 and 3060 m, mean J decreased to about a third. VPD was the most influential environmental factor controlling J at 1050 and 1890 m, while T_a was the key determinant at 3060 m. Large vessels were absent in the root xylem of high-elevation trees which resulted in a 10-fold decrease of theoretical hydraulic conductivity (k_h^theor) between 1050 and 3060 m. We conclude that both physical limitations (reduced VPD, increased viscosity of water) and biological constraints (large decrease of k_h^theor) result in a significantly reduced J and root water uptake of the trees in high-elevation tropical forests.     

Vegetation and environment of the Rødalen alpine area, Central Norway, with emphasis on the early Holocene

Detailed pollen analysis and pine megafossils from the immediate area of Rødalen in Central Norway have revealed new knowledge of Holocene alpine environments. A period of about 1,000 years characterised by pioneer herbs, dwarf-shrubs (Betula nana, Empetrum) and Juniperus followed the Holocene climatic amelioration. Local birch forest became established around 10.3 ka b.p., ca 150 years earlier than the local pine rise. Pine dominated at 1,100 m a.s.l. from 9.9 to 8.5 ka b.p., followed by birch forests until 1.3 ka b.p. when deforestation occurred. Slightly after 6 ka b.p., pine forests disappeared from the valley floor (930 m a.s.l.), an area that today is dominated by birch forest. Three short-lasting vegetational set-backs at ca 10.7, 10.5 and 10.3 ka b.p. may indicate climate oscillations. A temporary reduction of local forests reflects the Erdalen 2/9.7 ka b.p. event. The influence of the 8.2 event, superimposed on a cooling trend, lasted ca 400 years and involved a two-step vegetational regression: (1) A strong reduction of pine forests due to cooling and (2) reduction of alder due to cold and drought. Winter stress preventing pine regeneration may have caused scarcity of pine megafossils from the latter period. In the early Holocene, vegetation in the present alpine region was not in equilibrium with temperature development. It is suggested that the birch forest establishment lagged by about 1,000 years due to drought, whereas winter stress may have delayed the establishment of pine even longer.     

干旱胁迫对高山柳和沙棘幼苗光合生理特征的影响

为了解干旱河谷-山地森林交错带植物光合生理特征对干旱胁迫的响应。以交错带两种典型植物高山柳(Salix paraqplesia)和沙棘(Hippophae rhamnoides)为研究对象,研究其在不同程度的干旱胁迫条件下植株气体交换参数的日变化特征。干旱胁迫显著降低了两种植物叶片数、叶面积、叶片生物量、比叶面积、色素含量、净光合速率(Pn)、气孔导度(gs)和气孔限制值(Ls)等与光合生理过程密切相关的叶片指标,但增大了胞间CO₂浓度(Ci)和内禀水分利用效率(WUEi)。植物叶片的气体交换参数(如:Pn和gs)日变化并未完全随着光合有效辐射的增强和温度的升高而增加,全天以11:00最大,"午休"现象明显。相对而言,沙棘在干旱胁迫条件下表现出相对较高的叶面积、Pn、gs和WUEi,具有相对更强的适应干旱环境的能力,而高山柳对干旱胁迫更为敏感。     

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.     

干旱胁迫对高山柳和沙棘幼苗光合生理特征的影响

为了解干旱河谷-山地森林交错带植物光合生理特征对干旱胁迫的响应。以交错带两种典型植物高山柳(Salix paraqplesia)和沙棘(Hippophae rhamnoides)为研究对象,研究其在不同程度的干旱胁迫条件下植株气体交换参数的日变化特征。干旱胁迫显著降低了两种植物叶片数、叶面积、叶片生物量、比叶面积、色素含量、净光合速率(Pn)、气孔导度(gs)和气孔限制值(Ls)等与光合生理过程密切相关的叶片指标,但增大了胞间CO₂浓度(Ci)和内禀水分利用效率(WUEi)。植物叶片的气体交换参数(如:Pn和gs)日变化并未完全随着光合有效辐射的增强和温度的升高而增加,全天以11:00最大,"午休"现象明显。相对而言,沙棘在干旱胁迫条件下表现出相对较高的叶面积、Pn、gs和WUEi,具有相对更强的适应干旱环境的能力,而高山柳对干旱胁迫更为敏感。     

Role of coarse woody debris in the carbon cycle of Takayama forest,central Japan

Coarse woody debris (CWD) is an important component of the forest carbon cycle, acting as a carbon pool and a source of CO₂ in temperate forest ecosystems. We used a soda-lime closed-chamber method to measure CO₂ efflux from downed CWD (diameter ≥5 cm) and to examine CWD respiration (R _CWD) under field conditions over 1 year in a temperate secondary pioneer forest in Takayama forest. We also investigated tree mortality (input to the CWD pool) from the data obtained from the annual tree census, which commenced in 2000. We developed an exponential function of temperature to predict R _CWD in each decay class (R ² = 0.81–0.97). The sensitivity of R _CWD to changing temperature, expressed as Q ₁₀, ranged from 2.12 to 2.92 and was relatively high in decay class III. Annual C flux from CWD (F _CWD) was extrapolated using continuous air temperature measurements and CWD necromass pools in the three decay classes. F _CWD was 3.0 (class I), 17.8 (class II), and 13.7 g C m^?2 year^?1 (class III) and totaled 34 g C m^?2 year^?1 in 2009. Annual input to CWD averaged 77 g C m^?2 year^?1 from 2000 to 2009. The budget of the CWD pool in the Takayama forest, including tree mortality inputs and respiratory outputs, was 0.43 Mg C ha^?1 year^?1 (net C sink) owing to high tree mortality in the mature pioneer forest. The potential CWD sink is important for the carbon cycle in temperate successional forests.