共查询到20条相似文献，搜索用时 29 毫秒
1.
? 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
2.
? Fine-scale spatial and temporal establishment patterns of direct-seeded oaks on abandoned agricultural land have been little studied despite their potential importance for long-term stand structure. ? Here we periodically monitored seedling emergence and early growth of bur oak (Quercus macrocarpa Michx.) and red oak (Q. rubra L.) on an abandoned pasture, and tested the effects of herbaceous competition, rodents, and soil physicochemical properties. ? Herbaceous competition slightly decreased diameter growth, but rodents had little impact on establishment. Red oak seedlings emerged earlier than bur oak and in a greater proportion (92% vs. 56%). Seedling emergence and early growth of both species showed significant spatial structures that were partly explained by variation in soil physicochemical properties. Bur oak was more responsive to microenvironmental heterogeneity than red oak, yet much of the variation in emergence and growth of both species remained unexplained. ? This suggests that other factors, such as acorn size or genetic variability, may exert equal or greater control than microenvironmental heterogeneity over seedling emergence and early growth of these two oak species on abandoned pastureland. 相似文献
3.
? Cork oak mortality is a recurrent problem in southwestern Portugal. Despite the perception of increasingly visible damage in oak woodlands on drought-prone sites, the role of the various environmental factors in their decline is not clear. ? To describe the spatial patterns of cork oak (Quercus suber L.) mortality, a cork oak mortality index (MI) was determined for each landscape feature (agroforestry system, soil type, slope and aspect) using a GIS approach. To achieve this goal, a logistic regression model was formulated analyzing interactions between landscape attributes and allowing a prediction of cork oak mortality. ? Maximum values of MI were found in (i) shrublands and open woodlands with shrub encroachment (MI 6 and 3, respectively), where competition for soil water between tree and understory increases; and (ii) on lower slopes in the rounded hilltops and smooth hillsides or shallow soils where access to groundwater resources during summer drought is difficult. ? The model highlighted the importance of the agroforestry systems on cork oak mortality and may be used to identify sensitive areas where mitigation actions should be employed in a scenario of increasing drought severity in these Mediterranean ecosystems. 相似文献
4.
? The combined effect of water stress and light on seedlings of forest species is a key factor to determine the best silvicultural and afforestation practices in the Mediterranean area. ? The aims of this work was (1) to determine the optimal light level for the early development of cork oak seedlings under mild water stress and (2) to test if the combined effect of water stress and light followed the trade-off, the facilitation or the orthogonal hypothesis. ? Shade reduced instantaneous photosynthetic rates and water use efficiency in cork oak. However, seedlings grown under moderate shade (15% of full sunlight) were capable to accumulate similar amount of biomass than those grown under more illuminated environments by increasing their specific leaf area. Absolute differences in net photosynthesis between light treatments were higher in well watered than in water stressed seedlings. However, the impact of both factors on overall growth was orthogonal. ? We concluded that cork oak development is impaired under deep shade (5% of full sunlight) but it can be optimal under moderate shade (15% of full sunlight) even under moderate water stress. Implications of these patterns on regeneration, cultivation and afforestation of cork oak are discussed. 相似文献
5.
? Old oaks (Quercus robur L.) play an important role in the southern Scandinavian landscape by providing habitat for a wide range of species, a large proportion of them being currently on the National Redlists. ? To provide support for the management of these trees, we review data on oak mortality and formulate a mortality-driven stochastic model analysing interactions between mortality rate, oak recruitment rate into 100–150 age class, and amount of oaks older than 200 years. ? Empirical annual mortality rates varied between 0 and 13% with average 1.68%. Trees older 200 years had an average mortality rate of 1.1%. Oaks in the high density forests showed higher mortality (3.2%) as compared to the trees growing in the low density forests (1.2%). A 400-year long modelling exercises indicated that under current mortality rates (regular mortality being centred around 1% annually; and irregular mortality 7% with average return time of 13 years) the long-term maintenance of 20 trees older than 200 years per ha would require an input rate of 1 to 5 trees × year?1 × ha?1 into the 100–150 years old class. ? The modelling highlighted the importance of initial oak abundance affecting amount of old trees at the end of shorter (100 years) simulation period. 相似文献
6.
? Development of both somatic and gametic embryogenesis has many applications in clonal forestry and genetic improvement, for instance as mass-propagation of genetically improved plants and production of pure lines through doubled-haploid plant regeneration from gametic embryos. ? The goal of this work was to improve growth, maturation and plantlet regeneration of cork oak (Quercus suber L.) embryos from both somatic and gametic origin. ? Activated charcoal promoted a significant increase in growth in terms of relative size and weight of both somatic and doubled-haploid embryos, as well as a more efficient control of secondary somatic embryogenesis during development. A significant interaction was also observed with amino acid nutrition. While some amino acids (i.e., glutamine, arginine or asparagine) did not show significant differences with the controls, a mixture of these three amino acids or gamma amino butyric acid stimulated embryo growth. The highest survival rate during acclimation of plantlets from both somatic and doubled-haploid origin was obtained when the embryos had been previously cultured on basal medium with 3% sucrose and 1% activated charcoal for two months at 4 °C and germinated on medium supplemented with 6-benzylaminopurine and indole-3-butyric acid. ? We obtained more than 900 cork oak plantlets acclimated from several embryogenic lines, with a high survival rate, demonstrating that this methodology is applicable for large scale plantlet production. We also report the first regeneration of doubled-haploid plantlets in cork oak. 相似文献
7.
? 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
8.
? Oak powdery mildew severity (Erysiphe alphitoides) is usually mild in Europe because epidemics start late in spring, at the end of the first oak growth unit maturation. However, the disease can occasionally be very severe when strong infection occurs early during the development of the first growth unit, suggesting that host-pathogen synchrony in spring could be a critical factor in disease severity. ? We studied the timing of ascospore production in a given environment for four E. alphitoides populations sampled from SW France to the Czech Republic to determine whether this trait shows variation within Europe. ? Timing of ascospore production was clearly influenced by environmental factors as chasmothecia from a single origin showed very different dates of optimal ascospore production when transferred for overwintering in locations with different climate. In common garden experiments, no differences were observed between populations for the date of optimal ascospore production. ? Results suggest little genetic differentiation for timing of ascospore production for E. alphitoides populations across Europe and therefore a lack of local adaptation to their host phenology. Availability in ascospore inoculum is limited during host budburst, explaining the low infection usually observed on the first oak growth unit. 相似文献
9.
?The study aimed at clarifying basic life traits (fecundity, mortality and development) of Monochamus galloprovincialis, the vector of Bursaphelenchus xylophilus, the causative agent of the Pine Wilt Disease, in Portugal. ? Mating and oviposition experiments were conducted on P. sylvestris logs under laboratory conditions during two years. Larval development was followed outdoors. ? Fecundity was high, with 138.2 eggs per female. ? For the first time, the number of larval instars (4) in M. galloprovincialis was recognized and instars were described. ? Informations are provided on the shape and size of the larval galleries. Boring of galleries in sapwood and heartwood started at the third instar. All instars could overwinter but adults emerged simultaneously resulting in a univoltine life cycle for the majority of the individuals. ? An obligatory diapause in the forth instar was assumed. However, 8.1% of the insects had a two year development. ? Important differences in mortality were noted between the two experimental years, which could be explained by differences on the size of the breeding logs. ? There is a high biological proximity between M. galloprovincialis populations in France and those in Portugal and Northern Europe. However, a higher fecundity and longevity was observed in France, as well as a higher percentage of insects with a two year development, compared with portuguese populations. 相似文献
10.
? Tree recruitment in Mediterranean savannas is generally hampered, in contrast with the original oak forests where these savannas are derived from. We asked whether this difference in recruitment success can be explained by differential post-dispersal survival. For one year we monitored experimentally cached holm oak acorns in a savanna — forest ecosystem in Central Spain, and recorded cache pilferage, type of pilferer, boar rooting, seedling emergence, seedling survival and the cause of mortality. ? Cache pilferage was significantly lower in savanna (8%) than in forest (21%). However, the higher cache survival was more than offset by lower seedling emergence and, particularly, by nine times higher seedling mortality in savanna, mainly due to desiccation. Wild boar rooting did not differ between experimental caches and controls without acorns, indicating that individual cached acorns do not trigger rooting activity. ? Our results indicate that the difference in post-dispersal survival between savanna and forest is due to lower emergence and, primarily, higher seedling mortality in savanna, not to higher cache pilferage. Absence of safe sites such as shrubs, abundantly present in the forest, may well explain the lack of recruitment in the savanna. Management measures appear necessary for long-term persistence of Mediterranean savannas in general. 相似文献
11.
? In forests, the substitution of broadleaf species by conifers can reduce biodiversity because coniferous forests generally provide less diverse vascular understories than broadleaf forests. However, in some cases, former pine plantations might be useful for restoring native forests. We compared plant species composition on the plot scale in natural beech and mixed oak forests with that in plantations of Pinus radiata. Links between plant diversity and landscape parameters (patch size, fractal dimension and distance to the nearest patch of the same type) were investigated. ? The objective of this study was to evaluate the use of pine plantations for restoring native diversity in a zone where native forests are very fragmented. ? Similar to oak forests, plant diversity in pine plantations was high, mainly due to the presence of generalist species. Some species characteristic of oak forests also appeared in pine plantations, suggesting the onset of natural forest regeneration. ? These results suggest that pine plantations could be used to promote natural regeneration of original oak forests. Moreover, residual native stands should be conserved as important sources of native species and their seeds. 相似文献
12.
? The density and identity of tree neighbourhood is a key factor to explain tree mortality in forests, especially during the stem exclusion phase. ? To understand this process, we built a logistic model for mortality in a spatially explicit context, including tree and neighbourhood predictors. Additionally, we used this model to build mortality risk frequency distributions. Finally, we tested this model against a random mortality model to predict the spatial pattern of the forest. ? Annual mortality rate was high for pedunculate oak (Quercus robur, 6.99%), moderate for birch (Betula celtiberica, 2.19%) and Pyrenean oak (Q. pyrenaica, 1.58%) and low for beech (Fagus sylvatica, 0.26%). Mortality risk models for pedunculate oak and birch included stem diameter, tree height, canopy position and neighbourhood. Mortality was affected by the specific nature of the neighbourhood showing a clear competitive hierarchy: beech > pedunculate oak > birch. Models based on random mortality and logistic regression model were able to predict the spatial pattern of survivors although logistic regression predictions were more accurate. ? Our study highlights how simple models such as the random mortality one may obscure much more complex spatial interactions. 相似文献
13.
? Most of the edible forest mushrooms are mycorrhizal and depend on carbohydrates produced by the associated trees. Fruiting patterns of these fungi are not yet fully understood since climatic factors alone do not completely explain mushroom occurrence. ? The objective of this study was to retrospectively find out if changing tree growth following an increment thinning has influenced the diversity patterns and productivity of associated forest mushrooms in the fungus reserve La Chanéaz, Switzerland. ? The results reveal a clear temporal relationship between the thinning, the growth reaction of trees and the reaction of the fungal community, especially for the ectomycorrhizal species. The tree-ring width of the formerly suppressed beech trees and the fruit body number increased after thinning, leading to a significantly positive correlation between fruit body numbers and tree-ring width. ? Fruit body production was influenced by previous annual tree growth, the best accordance was found between fruit body production and the tree-ring width two years previously. ? The results support the hypothesis that ectomycorrhizal fruit body production must be linked with the growth of the associated host trees. Moreover, the findings indicate the importance of including mycorrhizal fungi as important players when discussing a tree as a carbon source or sink. 相似文献
14.
? It is widely believed that distance-independent tree models fail to take into account the complexity of mixed stands due to the fact that spatial structure often has a greater impact on growth and dynamics in mixed stands than in pure stands. On the other hand, distance-dependent tree models are difficult to use because they require a map of the stand, which is not only very costly but also impracticable in a routine management context. ? This paper reports the development of a model bridging distance-dependent and distanceindependent tree models, and that is designed to simulate the growth of a mixed forest. The model used distributions of the number of neighbours to reconstruct tree neighbourhoods and compute the competition indices needed as inputs to the growth model. ? Data were collected from a mixed forest of sessile oak and Scots pine in central France. The study showed that local competition indices explained a significant proportion of growth variability and that intraspecific competition was greater than interspecific competition. The model based on neighbourhood distributions gave consistent predictions compared to a distance-dependent model. ? This type of model could be used instead of distance-dependent models in management contexts. 相似文献
15.
? We studied mortality rates of birch, small-leaved linden, pedunculate oak, Norway maple, black alder, common ash and Norway spruce, assessed through two inventories of 12 664 trees in the unmanaged mixed deciduous forests of Oranienbaum Park, northwestern Russia, in 1981 and 2003. ? Our objectives were to evaluate if (a) long-term mortality rates vary among species, and if (b) crown condition, age and tree size affect the probability of mortality. ? Over this period, tree mortality rates in the park varied annually from 1 to 3% for healthy and moderately healthy trees, and from 3.9 to 9.3% for declining trees. The lowest mortality rates were observed for small-leaved linden and oak (0.8 and 1.0%, respectively), and the highest rate for birch (2.7%). We found (1) a significant and consistent association between tree condition and the probability of mortality, and (2) significantly higher mortality rates in smaller trees of ash, maple and oak. ? The effect of species-specific biology on mortality rates in the Oranienbaum Park was largely overridden by the “health status” and environmental conditions of the trees (e.g. degree of crown shading). The observed rates were similar to the estimates from natural temperate deciduous forests in both Europe and North America, indicating similar intensity of mortality in these ecosystems under natural conditions. 相似文献
16.
? Radial and height growth chronologies from 150-year-old and 50-year old Scots pine stands, both located near to the northern timberline in Laanila, Finland (68° 30′ N, 27° 28′ E), were cross-correlated with each other and with mean temperatures of various temperature periods defined as months, days or growing-degree-days. ? The height-growth chronology correlates significantly with radial growth at lags 1 and 2, and radial growth with height growth at lag 2 when the effect of temperature is omitted. On average, low and high growth years represent cool and warm average growing seasons. The summer temperatures (June, July and August) affect most on growth, but height and radial growth do have a different set of effective temperature periods. Furthermore, July temperature variation affects stronger height than radial growth. ? Those years with low height/radial-growth ratio, i.e. relatively higher current year’s radial than next year’s height growth, do have lower growth and cooler-than-average July temperature whereas those years with high height/radial-growth ratio do have clearly warmer mid-summer temperatures. 相似文献
17.
? Interspecific differences in tree growth patterns with respect to biotic and abiotic factors are key for understanding forest structure and dynamics, and predicting potential changes under climate change. ? Repeated observations from the Spanish Forest Inventory (SFI) were used to parameterize maximum likelihood estimators of tree growth as a function of tree size, competition indices and climate for Pinus pinaster, P. sylvestris, Quercus ilex and Q. pyrenaica. ? Significant responses to both biotic and abiotic factors were found, with interspecific differences in species performance along competition, temperature and precipitation gradients. Q. ilex was the species most tolerant to competition while P. pinaster was the species most sensitive to climatic variation. Species relative positions shifted along gradients of these factors with rank reversals in species performance along size, competition and climatic gradients. ? The results based on average growth matched previous forestry classifications and experimental studies on relative growth rate (RGR). ? When examining growth along studied abiotic and biotic gradients, a mismatch was found between species performance ranks as predicted by our models and information derived from previous knowledge. Those discrepancies highlight the relevance of ontogeny and environmental heterogeneity in defining species performance along competition gradients. 相似文献
18.
? Eight-year old trees from two Eucalyptus globulus Labill. clones planted across three different sites in Tasmania, Australia, were sampled for wood and kraft pulp/handsheet properties. ? Site had a significant effect on all measured properties. Compared with the poor site (Parkham) the wood from the good site (West Ridgley) had on average 11 % lower wood density. The poor site had also greater microfibril angles, shorter fibres at lower pulp yields. ? The handsheets produced with pulp from the poor site resulted in comparatively higher bulkiness, lower burst, lower tear and tensile indices, lower zero span tensile strength, but higher opacity, higher light scattering and higher surface roughness. Significant height effects were found with all wood properties, and also with tear index, zero span tensile strength and opacity. ? Discriminant analysis showed that for 76 out of 100 handsheets the raw material source, i.e. growth site, could be predicted correctly using a set of handsheet properties with tear index and bulk index being most prominent. ? This is unique evidence that site conditions are strongly reflected in handsheet properties produced from Eucalyptus pulp. 相似文献
19.
? Water and carbon fluxes, as measured by eddy covariance, climate, soil water content, leaf area index, tree biomass, biomass increment (BI), litter fall and mortality were monitored for 10 successive years in a young beech stand in Hesse forest (north-eastern France) under contrasting climatic and management conditions. ? Large year-to-year variability of net carbon fluxes (NEE) and to a lesser extent, of tree growth was observed. The variability in NEE (coefficient of variation, CV = 44%) was related to both gross primary production (GPP) and to variations in total ecosystem respiration (TER), each term showing similar and lower interannual variability (CV = 14%) than NEE. Variation in the annual GPP was related to: (i) the water deficit duration and intensity cumulated over the growing season, and (ii) the growing season length, i.e. the period of carbon uptake by the stand. Two thinnings occurring during the observation period did not provoke a reduction in either GPP, water fluxes, or in tree growth. Interannual variation of TER could not be explained by any annual climatic variables, or LAI, and only water deficit duration showed a poor correlation. Annual biomass increment was well correlated to water shortage duration and was significantly influenced by drought in the previous year. ? The relationship between annual NEE and biomass increment (BI) was poor: in some years, the annual carbon uptake was much higher and in others much lower than tree growth. However this relationship was much stronger and linear (r 2 = 0.93) on a weekly to monthly time-scale from budburst to the date of radial growth cessation, indicating a strong link between net carbon uptake and tree growth, while carbon losses by respiration occurring after this date upset this relationship. ? Despite the lack of correlation between annual data, the NEE and BI cumulated over the 10 years of observations were very close. ? On the annual time-scale, net primary productivity calculated from eddy fluxes and from biological measurements showed a good correlation. 相似文献
20.
? This review considers potential effects of atmospheric change and climate warming within the timberline ecotone of the Central European Alps. After focusing on the impacts of ozone (O3) and rising atmospheric CO2 concentration, effects of climate warming on the carbon and water balance of timberline trees and forests will be outlined towards conclusions about changes in tree growth and treeline dynamics. ? Presently, ambient ground-level O3 concentrations do not exert crucial stress on adult conifers at the timberline of the Central European Alps. In response to elevated atmospheric CO2 Larix decidua showed growth increase, whereas no such response was found in Pinus uncinata. Overall climate warming appears as the factor responsible for the observed growth stimulation of timberline trees. ? Increased seedling re-establishment in the Central European Alps however, resulted from invasion into potential habitats rather than upward migration due to climate change, although seedlings will only reach tree size upon successful coupling with the atmosphere and thus loosing the beneficial microclimate of low stature vegetation. ? In conclusion, future climate extremes are more likely than the gradual temperature increase to control treeline dynamics in the Central European Alps. 相似文献
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