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1.
? Within the alpine treeline ecotone tree growth is increasingly restricted by extreme climate conditions. Although intra-annual stem growth recorded by dendrometers can be linked to climate, stem diameter increments in slow-growing subalpine trees are masked by changes in tree water status. ? We tested the hypothesis that intra-annual radial stem growth in Pinus cembra is influenced by different climate variables along the treeline ecotone in the Austrian Alps. Dendrometer traces were compared with dynamics of xylem cell development to date onset of cambial activity and radial stem growth in spring. ? Daily fluctuations in stem radius reflected changes in tree water status throughout the treeline ecotone. Extracted daily radial increments were significantly correlated with air temperature at the timberline and treeline only, where budburst, cambial activity and enlargement of first tracheids also occurred quite similarly. A close relationship was detected between radial increment and number of enlarging tracheids throughout the treeline ecotone. ? We conclude that (i) the relationship between climate and radial stem growth within the treeline ecotone is dependent on a close coupling to atmospheric climate conditions and (ii) initiation of cambial activity and radial growth in spring can be distinguished from stem re-hydration by histological analysis. 相似文献
2.
? Temperature is suggested to determine the upper limit of tree life. Therefore, future climate warming may be of importance for tree distribution within the European Alps, where low temperatures limit carbon metabolism. ? We focused on the effects of air and soil temperature on net photosynthesis (P n) of Pinus cembra an evergreen climax species of the timberline ecotone of the Central Austrian Alps. Light response and temperature response curves were estimated along an altitudinal gradient ranging from the forest limit up to the krummholz limit in both summer and fall. ? In general, P n was significantly lower in fall as compared to summer. Nevertheless, independent from season mean P n values tended to increase with elevation and were positively correlated with root zone temperatures. The specific leaf area by contrast declined with increasing elevation. Furthermore, the temperature optimum of net photosynthesis declined with increasing elevation and was positively correlated with the mean maximum air temperature of the 10 days prior the date of measurement. ? Thus, our findings appear to reflect a long-term adaptation of the photosynthetic apparatus of Pinus cembra to the general temperature conditions with respect to elevation combined with a short term acclimation to the prevailing temperature regime. 相似文献
3.
? Most studies of tree-growth and climate report positive responses to global warming in high latitudes and negative responses at lower ones. ? We analyzed tree-ring width of Pinus nigra Arn. along a 500 km latitudinal transect in the Iberian Peninsula to study the temporal trend and climate forcing in tree radial growth during the last century. ? Tree growth was enhanced by cool summers and moist cold seasons. Increased moisture stress has decreased tree growth rates. However, we present evidence of growth increases in some trees in all sampled populations after 1980’s. Climate change negatively (positively) affected between 72% (5%) of trees in the southern populations and 40% (25%) in the north Trees with positive growth trends were favored by winter temperatures and their abundance was inversely correlated with forest productivity. ? Our findings add evidences of tree growth divergence in the Mediterranean basin and show the gradual transition between forests where positive (temperate and boreal) and negative (Mediterranean) growth trends dominate. 相似文献
4.
? The aim of this work was to examine the anatomy and functioning of secondary xylem in stems in relation to the decline of European ash (Fraxinus excelsior L.). ? We tested the hypothesis that declining trees show changes in the structure of wood, which result in impaired water transport. ? Anatomical analyses were carried out on wood samples (comprising all annual rings formed during the 30 years life of the analysed trees) collected at breast height from the main stem of healthy, weakened and dead ash trees. The width of annual wood increments, the diameter and density of earlywood vessels were measured and the theoretical hydraulic conductivity index through the secondary xylem calculated by application of Hagen-Poisseuille’s formula. ? Anatomical characteristics changed both with the age of trees and in response to unfavorable factors. The largest vessels were observed in healthy trees, which implied that they had the highest hydraulic conductivity index, whereas trees considered to be in decline produce smaller vessels and hence had reduced conductivity. 相似文献
5.
? Decay resistance of larch (Larix sp.) to fungi was evaluated on heartwood samples belonging to 3 species (L. decidua, L. kaempferi and their hybrid), 3 races of European larch (polonica, sudetica and alpine), 13 wood lots (populations) and 313 trees. ? Larch wood appeared, on average, as moderately durable although a high variability was observed. At the sample level as well as at the mean individual tree level, durability ranged from class 1 to 5 according to EN 350-1 standard. At the population level, larch wood varied from ‘durable’ to ‘slightly durable’. Genetics played a major role in decay resistance at the species, provenance and tree levels. Environmental factors such as the position of heartwood samples and the age of trees were also identified as a source of variability. ? The most durable wood was not necessarily from old native alpine stands of European larch: some young larches from faster growing lowland origins also produced durable wood. ? Genetic improvement of larch wood durability appeared therefore likely by the selection of the best populations for decay resistance as well as from the selection of individuals. 相似文献
6.
? Understanding tree mortality processes across time requires long term studies. Spatiotemporal patterns of mortality in a 200 years-old mono-layered Norway spruce stand were evaluated to determine what factors affected individual-tree mortality. ? We performed an analysis on two surveys (1993 and 2005) in a 1-ha permanent plot in the Paneveggio forest (Eastern Italian Alps). Tree diameter and age distribution between surveys were compared. We examined spatial patterns of living and dead trees before 1993, in 1993 and in 2005 using univariate and bivariate Ripley’s K(d) function, and a kernel estimator of local crowding. A logistic model was used to assess the effects of diameter, age, recent growth and competitive pressure on tree mortality. ? Spatial pattern analysis indicated mortality was associated to tree neighbourhood (neighbour effect at 2–5 m). An increment of regularization of tree spatial pattern occurred due to density-dependent mortality. Logistic regression showed tree diameter and recent growth were determinant on mortality risk during the monitoring period. ? Even if the stand is relatively aged, mortality dynamics are those typical of stem exclusion stage. Mortality was related to competitive dynamics, and small suppressed trees with slow growth rate had higher probability to die. 相似文献
7.
? Because all microclimatic variables change with elevation, it is difficult to compare plant performance and especially photosynthetic capacity at different elevations. Indeed, most previous studies investigated photosynthetic capacity of low- and high-elevation plants using constant temperature, humidity and light but varying CO2 partial pressures (P CO 2). ? Using gas exchange measurements, we compared here maximum assimilation rates (A max) at ambient and constant-low-elevation P CO 2for two temperate tree species along an altitudinal gradient (100 to 1600 m) in the Pyrénées mountains. ? Significant differences in A max were observed between the CO2 partial pressure treatments for elevations above 600 m, the between-treatment differences increasing with elevation up to 4 μmol m?2 s?1. We found an increase in A max with increasing elevation at constant-low-elevation P CO 2 but not at ambient P CO 2 for both species. Given a 10% change in P CO 2, a proportionally higher shift in maximum assimilation rate was found for both species. ? Our results showed that high elevation populations had higher photosynthetic capacity and therefore demonstrated that trees coped with extreme environmental conditions by a combination of adaptation (genetic evolution) and of acclimation. Our study also highlighted the importance of using constant CO2 partial pressure to assess plant adaptation at different elevations. 相似文献
8.
? Tree age is one of the most important factors to affect the natural durability of wood. ? The purpose of this study was to determine the natural termite resistance of heartwood and sapwood of teak (Tectona grandis Linn. fil.) for trees aged 8, 30 and 51 years. Reticulitermes speratus Kolbe was employed as a test termite using a no-choice feeding method. ? The heartwood and sapwood of all of the trees tested exhibited antitermitic activity. Based on the mean mass loss due to termite activity, the sapwood and heartwood regions of 8-year-old trees are the most susceptible to termites while the heartwood regions of the 30-year-old trees showed termite resistance similar to the termite resistance of 51-year-old trees. ? The mass loss is moderately correlated with n-hexane extractive content, total extractive content, brightness and redness of the wood. 相似文献
9.
? We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate. ? Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth. ? High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes. ? Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak. 相似文献
10.
? To investigate the effect of climate on radial growth in young plantation grown teak (Tectona grandis L.), growth ring width was measured in 105 trees and correlated to precipitation and temperature data. ? The social status of trees within the stand was also determined and cross-sectional area (CSA) for the trunk correlated to the proportion of heartwood (HW) within the tree. HW develops asymmetrically in leaning stems of some conifer species, but it is not known if this phenomenon also occurs in broadleaf species. Therefore, we measured HW proportion in leaning and straight stems, along with the number of growth rings in the HW. ? Annual ring width depended strongly on mean monthly temperature during the rainy season and the most significant relationships were found corresponding to the months of June and July. With regard to the weaker relationship between precipitation and radial growth, correlations were highest during the period of bud-break at the beginning of the rainy season. ? The very high stand density affected radial growth, particularly in suppressed trees, which responded little to thinning operations. HW formation was greatest in dominant trees, and was highly regressed with stem CSA. ? Therefore, rapid growth of young stands should be encouraged by reducing stand density. Asymmetric HW formation occurred in both leaning and straight trees, and was significantly greater along the upper sides of leaning stems. It is probable that this eccentric HW formation is linked to mechanical loading on the tree. 相似文献
11.
? Direct assessment of modulus of elasticity (MOE) on standing trees is attractive for breeders to evaluate genotypes prior to selection: this can be done using the Rigidimeter, a bending-based measurement device. ? In this study, we tested its reliability to properly rank genotypes by relating trunk MOE with MOEs estimated with a vibrating analysis system (Bing) on different types of conditioned wood specimens from the same trees (boards and standardised 2×2×30 cm-clear-wood specimens). One hundred and ten trees from different genotypes of hybrid larch (Larix × eurolepis) were tested. ? Mean trunk MOE was 7 300 MPa with a similar value obtained for sawn boards. Clear-wood specimens MOE increased from pith to bark from less than 6 000 MPa to nearly 9 000 MPa. Moderate correlations (r = 0.48–0.61) were found at the individual tree level between trunk MOE and MOE of wood samples. ? Single specimen MOE was shown to be strongly related to a linear combination of trunk MOE and sample position. ? At the genotype mean level, trunk MOE was highly correlated with wood samples MOE (r = 0.80–0.91). Ranking of genotypes based on trunk MOE was mostly consistent with that based on standardised specimens. ? It was concluded that besides other operational advantages which are discussed, the Rigidimeter is a valuable tool for breeders to routinely evaluate and rank genotypes for stiffness prior to further selection. 相似文献
12.
? The pith represents the central part of the cross-section of a tree trunk and it is composed of primary parenchyma tissue. And its eccentricity is associated with the presence of reaction wood, which affects trunk straightness, and diminishes the quality of the logs and products. ? Gmelina arborea trees (8 to 14 years old) from fast growth plantations in Costa Rica were sampled with the purpose of determining diameter, eccentricity and pith percentage as well as pith distance from the real centre of the cross section. These pith parameters were also evaluated in relation to management intensity (intensive, moderate and unmanaged), climate (dry and wet tropical) and tree height. ? Pith diameter varies from 0.15 to 1.10 cm and is located at 6 cm, at its maximum, around the real centre of the cross section. Percentage eccentricity might reach values of up to 26.5% and this parenchyma tissue represents between 1 and 5% of the total tree diameter. ? The level of management had a significant effect on the eccentricity and percentage of the pith, while the climate significantly affected the pith percentage and the distance of pith from the real centre of the cross section. Tree height affected significantly all the parameters evaluated. 相似文献
13.
? The effect of climatic variables (temperature and precipitation) on radial growth of the Mediterranean Maritime pine (Pinus pinaster Ait.) was studied using dendrochronological techniques in the Iberian Peninsula. ? Ten tree-ring width chronologies, along the central distribution area of the species, were built. Chronology variability was analysed using Principal Component Analysis (PCA) for the period 1952–2005. ? The first principal component (PC1) explained 56% of tree-growth variability. Tree-growth association with climate was analysed at regional and local scales using correlation coefficient and bootstrapped response functions. ? Radial growth at both scales was positively correlated with rainfall during and prior to the growing season at all sites, and with summer rainfall before the growing season at five sites. Mean temperature effect changed according to the sampling site, from non-significant at the highest sites to significant (positive relationship in winter) at the lowest sites. Growth season temperature also had a negative effect. ? The Kalman filter was applied to estimate changing association between growth and climate over-time. Results suggested a change in association, initiated in the 80s, from non-significant to significant (*p < 0.05) at six of the sampling sites. ? Pinus pinaster is an accurate species for analysing tree-growth association with climate and for studying plant behaviour under global change conditions. 相似文献
14.
? Eperua grandiflora, which is widely distributed in the French Guiana forest region, shows high variability in decay resistance. Further information concerning this wood quality parameter is necessary, but standard testing methods are complex and time-consuming. We assessed the use of colorimetry to determine durability in heartwood samples from a range of trees. ? Eperua grandiflora colour parameters were measured using a CIELAB system, revealing that the tree effect was greater than the radial position and height effects. ? The wood samples were exposed to Coriolus versicolor and Antrodia sp. according to two European standards (En 350-1 and XP CEN TS 15083-1). Eperua grandiflora is more susceptible to brown rot. These two standards did not give the same durability classes. The high variation in natural durability was due to the tree effect. ? These two properties were found to be correlated and the assessment also distinguished the extreme durability classes but they are not sufficient to classify the class of durability of this species. 相似文献
15.
? The effect of two weeds (grasses and broom, Cytisus scoparius) competition on the growth and functional traits of European beech saplings (Fagus sylvatica) was investigated in an experimental plantation in the French Massif central. ? We hypothesized that grasses would have a much more harmful effect than broom on beech growth through strong competition for soil water and nitrogen. ? A randomized block design was used with three separate blocks, each possessing three types of vegetation; grasses (mainly Agrostis capillaris, Holcus mollis and H. lanatus), broom, and bare soil as a control. ? Two years after plantation beech sapling growth was significantly greater in bare soil than with competition from grasses, and was intermediate on broom. Growth was positively correlated with beech leaf nitrogen content (Nm) and xylem water potential (Ψx). N and Ψx were dependent, with nitrogen uptake probably decreasing with increasing drought. There was no clear correlation between growth and light transmitted 10 cm below the apex of the saplings. ? Beech leaf mass on an area basis (LMA) was correlated with the three resource variables (water, nitrogen and light) and with growth, confirming that LMA is a sensitive functional trait integrating the degree of stress experienced by the saplings. ? The results suggest that broom is less competitive than grasses and, if properly managed on a sufficiently well-watered site, can generate satisfactory conditions for beech establishment and growth. 相似文献
16.
? Although comparisons between methods of selecting trees for site index estimates are well documented in the literature, little is known on mortality rates of different canopy tree cohorts used for that purpose. ? This study was initiated to test the hypothesis that the mortality rates of top height trees are lower than those of codominants only or a combination of codominant and dominant trees. To test this hypothesis, we used records from a network of permanent sample plots in Québec and studied the fate of different cohorts of site trees for five different species. ? Our results did not show clear evidence of lower mortality rates for top height trees. Instead we found that depending on the species, top height trees have lower (Populus tremuloides, Pinus banksiana), higher (Picea mariana, Abies balsamea) or equal mortality rates (Betula papyrifera) than codominant trees or codominant and dominant trees combined. ? These results suggest a tendency for shade intolerant species to maintain lower top height tree mortality rates over time when compared to shade tolerant species. In the latter case, it is also shown that spruce budworm epidemics (Choristoneura fumiferana) did not change the pattern of mortality rates of site trees of A. balsamea. 相似文献
17.
Context Anthropogenic activity has increased the level of atmospheric CO 2, which is driving an increase of global temperatures and associated changes in precipitation patterns. At Northern latitudes, one of the likely consequences of global warming is increased precipitation and air humidity. Aims In this work, the effects of both elevated atmospheric CO 2 and increased air humidity on trees commonly growing in northern European forests were assessed. Methods The work was carried out under field conditions by using Free Air Carbon dioxide Enrichment (FACE) and Free Air Humidity Manipulation (FAHM) systems. Leaf litter fall was measured over 4 years (FACE) or 5 years (FAHM) to determine the effects of FACE and FAHM on leaf phenology. Results Increasing air humidity delayed leaf litter fall in Betula pendula, but not in Populus tremula?×? tremuloides. Similarly, under elevated atmospheric CO 2, leaf litter fall was delayed in B. pendula, but not in Alnus glutinosa. Increased CO 2 appeared to interact with periods of low precipitation in summer and high ozone levels during these periods to effect leaf fall. Conclusions This work shows that increased CO 2 and humidity delay leaf fall, but this effect is species-specific. 相似文献
18.
? Empirical observations suggest that in pure even-aged forests, the mean diameter of forest trees (D, diameter at breast height, 1.3 m above ground) tends to remain a constant proportion of stand height (H, average height of the largest trees in a stand) divided by the logarithm of stand density (N, number of trees per hectare): D = β(H ? 1.3)/ ln(N). ? Thinning causes a relatively small and temporary change in the slope β, the magnitude and duration of which depends on the nature of the thinning. ? This relationship may provide a robust predictor of growth in situations where scarce data and resources preclude more sophisticated modelling approaches. 相似文献
19.
? Two decades after the launching of the monitoring program of forest ecosystems in Europe (ICP forests), a unique data set is now available regarding the foliar nutritional status of the main broad-leaved species growing in much-diversified sites (soil, climate). ? This study focuses on the foliar concentration time series (1993 to 2005) of the French (RENECOFOR), Walloon and Luxemburg broad-leaved plots. The aim is to show long-term trends while taking the inter-plot and inter-annual variability into account. ? Two kinds of statistical processing were used to analyze the data on foliar chemistry: principal component analysis (PCAs) and linear mixed models. In general, the main temporal trends reveal a decrease in the foliar P concentration and a decrease in the foliar Ca concentration, except for European beech on acid soils. ? These temporal patterns confirm the trends previously observed and could be explained by the joint actions of several processes that influence tree nutrition in the long term: tree age, N and S deposition, harvesting and climate. 相似文献
20.
? A discriminant study based on samples taken from high and low yielding oleoresin trees of two Greek populations, Chalkidiki and Euboia, was carried out. Oleoresin of Pinus halepensis Mill. was characterised by GC/MS analysis. ? The objectives of this study were: (i) to identify in detail the composition of the oleoresin of P. halepensis and in particular of high yielding trees (plus trees) (ii) to investigate a potential relationship between the oleoresin compounds and the oleoresin yield and (iii) to investigate any correlations among the compounds. ? About forty monoterpenes, sesquiterpenes and diterpenes were identified as main compounds representing 97.40% of the analyzed oleoresin. α-Pinene, methyl abietate, abietic acid, palustric acid, isopimaric acid and neoabietic acid were the major compounds. Efficient discrimination was achieved between the two populations and between the two groups of trees (high and low yielding). In both cases, the differentiation was due to the quantitative variability of certain compounds. High positive correlations were found among certain compounds. ? The results suggest that the oleoresin profile is a useful tool for the discrimination of trees according to their provenance or their oleoresin yield. 相似文献
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