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1.
? To elucidate the application of natural regeneration to the restocking of evergreen broad-leaved forests in the subtropics, the characteristics of a 20-year-old evergreen broad-leaved forest restocked by natural regeneration after clearcut-burning were studied in Okinawa, Japan. Within a 0.87 ha clearcut area with four 10 m × 10 m sampling plots, two burned and two unburned ones, the tree composition, tree species diversity and vegetation changes were investigated. ? The results showed that the species diversity, basal area and density of woody stems ? 1.0 m in height differed significantly among phanerophyte types, while they were not significantly different between the burned and unburned treatments. A vegetation census also revealed no obvious differences between the treatments. ? The primary dominant species, Castanopsis sieboldii, continued to dominate the secondary forest with a broad height distribution. ? The structural complexity and high tree species diversity of the regenerating forest after clearcut-burning provides no evidence of degeneration. We can predict that the regeneration forest may gradually develop into stands similar to pre-clearcut primary forest, and that natural regeneration may restore the high tree species diversity of the evergreen broad-leaved forests in Okinawa. 相似文献
2.
? The objectives of this study were to measure litterfall production of the four floodplain forest types and to analyze the relationship between litterfall (forest type, dominant species, and organic fractions) and flood pulses. ? Litterfall production was measured in two mono-specific stands of Salix humboldtiana or Tessaria integrifolia, respectively, and two mixed forests dominated by A. inundata or Nectandra angustifolia, during 1998 and the 2000–2002 periods. ? Mono-specific stands presented similar productivities (6.8 and 6.5 Mg dry matter ha?1 y?1, respectively), but differed significantly from the two other. The highest litterfall production was obtained during the large flood that occurred during 1998, decreasing later throughout the study period. Leaves were the dominant fraction of litterfall, followed by branches, flowers, and fruits. ? Only S. humboldtiana, T. integrifolia and A. inundata forests showed distinct patterns of litterfall production, depending on the flooding pulse. N. angustifolia did not show a distinctive litterfall pattern. ? The forests studied here presented patterns of litter production associated with the flood pulse according to its location along a topographic gradient, that controls the litter productivity of these forests. 相似文献
3.
? 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
4.
? Studies dealing with the estimation of biomass, site productivity and the contribution of forests to the global carbon balance require the use of allometric equations. There have been a great number of equations developed to estimate biomass components of trees and shrubs in various ecosystems. However, there are less literature compilations that address the calculations of biomass components. ? I report a total of 229 sets of allometric equations to estimate biomass components for 102 species in 72 different forest communities of arid, semi-arid, subtropical, tropical and temperate Latin-American ecosystems. ? The selection of the appropriate allometric model is a key element in the accurate estimation of biomass, stand productivity, carbon stocks and fluxes, and as a consequence, it is important to apply special effort to the selection and estimation of biomass equations. ? I also discuss statistical methods of parameter estimation and recommend the dissection of two conventional allometric equations when biomass studies are conducted on a wide range of diameters. In order to use nondestructive procedures of biomass estimation such as the fractal theory, the null hypothesis that the mean slope b value is equal to 2.67 was rejected for Latin American biomass species. ? This information is critical for the establishment of environmental projects that aim to estimate conventional parameters (i.e., productivity, habitat quality and fuel wood) as well as environmental features (i.e., stocks and fluxes of carbon and nitrogen). 相似文献
5.
? In Mediterranean forestry, it is important to improve knowledge about mixed stands dynamics, including their productivity. Previous studies have focused on the interactions between different species (competition, reduction of competition and facilitation) depending on site, species composition and structure. ? At the centre of this research are the possible differences between pure and mixed stands of Pinus sylvestris and Quercus pyrenaica in terms of density-growth relationships and volume growth per species. ? Using data from the second and third Spanish National Forest Inventory (606 plots), volume increment models for these species were fitted. Both species displayed a similar density-growth pattern for pure and mixed stands, with a maximum volume growth at maximum density. Volume increment per occupied area was also found to be greater in mixed stands as opposed to pure stands, suggesting a species interaction with reduced levels of competition in the former. However, the total volume growth was generally lower in mixed stands since the growth rate of oak is much lower. ? The results highlight the expedience of favouring P. sylvestris-Q. pyrenaica mixed stands with higher proportions of pine trees in order to gain the benefits of a more complex forest whilst retaining an acceptable level of wood production. 相似文献
6.
? Managed laurel forests in the Canary Islands have undergone clear-cutting with rotation periods of less than 30 y. Forest owners have recently requested a drastic reduction in the cutting interval. The effects of this new harvesting cycle on organisms like epiphytic bryophytes are not well known. ? This study investigates how time since last clear-cut, host species and characteristics of tree zones influence the biomass, cover and richness of epiphyte bryophytes in managed laurel forests in La Palma, Canary Islands. Four forest ages (8, 15, 25 and 60 y) and three host tree species (Erica arborea, Laurus novocanariensis and Myricafaya) were studied. ? Biomass, cover and richness of bryophytes increased through the chronosequence, both at the level of each plot and overall for L. novocanariensis. Most of the biomass (53%) and richness (81%) was concentrated in one of the tree species (L. novocanariensis), in plots for which 60 y had elapsed since the last clear-cutting. Trunks supported greater bryophyte biomass and richness than canopies, even in the oldest plots. ? Our results suggest that the current rotation periods used to manage laurel forests are insufficiently long to allow for complete reestablishment of epiphytic bryophyte assemblages. 相似文献
7.
? 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
8.
? In seasonally dry tropical forests deciduousness (leaflessness) is an important strategy of trees to survive in water stress period during summer. Deciduousness is a reflection of interacted effect of seasonal drought, tree characteristics and soil moisture conditions. ? The present study aims to document the diversity in leaf pheno-phases in terms of duration of deciduousness (which is reciprocal to growing season length), wood density, leaf mass per area (LMA) and leaf strategy index in 24 important tree species growing in the Vindhyan dry tropical forest in India. ? On the basis of phenological observations, the tree species were categorized into two main groups: leaf exchanging species exhibiting overlapping periods of leaf fall and leaf flush, and deciduous species whose timings of leaf flush and leaf fall differ resulting in a time lag (deciduousness) between the completion of leaf fall and initiation of leaf flush. Presence of wide range of deciduousness duration (from ca. a week to 7 months) among dry tropical trees indicates large variations in their growing season length. In the tree species studied, as the duration of deciduousness increased, leaf flushing period decreased significantly but leaf fall period showed little variation. ? Differing deciduousness in tree species exhibited substantial differences in their leafing (vegetative growth) pattern, as reflected by ratio of durations of leaf flush to leaf fall (leaf strategy index). Across different species, duration of deciduousness was significantly positively correlated with leaf strategy index, and significantly negatively correlated with both wood density and LMA. ? Wide variations in deciduousness, leaf strategy index, wood density and LMA in the 24 species investigated indicate considerable functional diversity in tree species growing in Vindhyan dry tropical region. Variation in seasonal duration of deciduousness among species is reflections of differences in tree functional traits like stem wood density, leaf strategy index and LMA. 相似文献
9.
? Mature, unmanaged forests in western North America provide important reference conditions for managers, yet little is known about fuel composition and the factors that influence fuel accumulation in such stands. Our objectives were to characterize fuels in a passively managed landscape of dry forests in central Oregon and identify environmental factors influencing fuel accumulation. ? Ordination techniques and analysis of variance revealed no statistical differences in total fuel loads across a wide range of environmental conditions. ? Individual fuel size classes, however, did vary by stand location and composition. Interior stands had more 1- to 100-h fuels and snags than stands at or near the edge, stands dominated by ponderosa pine had fewer small-diameter fuels and snags, lodgepole pine stands had more 1-h fuels and snags, and white fir stands had more 10-h fuels, duff, and snag basal area. ? Tree species, density and age, and years since last fire were the most important environmental variables, explaining 23% of the variation in fuels. ? Our results present further evidence that fuel composition is highly variable at many spatial and temporal scales. They also provide useful baseline information for managers of fire-prone western forests. 相似文献
10.
? 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
11.
? The physical properties of wood and the associated variations within and between trees were evaluated by analysing 770 small specimens of clear wood from 11 Pinus sylvestris L. trees thinned from 3 plantations. ? Within-tree variations in basic density or volumetric shrinkage increased with cambial age and decreased with increasing ring width. The effect of the height in the stem on wood properties was considered indirect and height was not included as an explanatory variable in the mixed models proposed to estimate basic density and volumetric shrinkage. ? The models had random components for the intercept parameter and explained 52.5% of the total variance in basic density and 56% of the total variance in volumetric shrinkage. Linear shrinkage in the direction of the grain was extremely variable. ? Between-tree variation and between-plot variation in the physical properties of wood were high, considering that all trees sampled were growing in similar sites and stands. It would then be desirable to predict physical properties of wood on living trees in order to use the quality of wood as a criterion for timber tree selection in thinnings. 相似文献
12.
? We describe the distribution and the ecology of three Armillaria species observed in silver fir (Abies alba) forests of the Pyrenees. ? We surveyed the presence and abundance of Armillaria above and belowground in 29 stands. Isolates were identified by the PCR-RFLP pattern of the IGS-1 region of their ribosomal DNA. We measured several ecological and management parameters of each stand in order to describe Armillaria infected sites. ? Armillaria cepistipes was the most abundant of three species observed. Armillaria gallica was dominant in soils with a higher pH and at lower elevations. Armillaria ostoyae seemed to be more frequent in stands where A. alba recently increased its dominance relative to other forest tree species. Thinning activities correlated with an increased abundance of Armillaria belowground. In 83% of the stands the same Armillaria species was observed above and belowground. ? It seems that in a conifer forest, A. cepistipes can be more frequent than A. ostoyae, a virulent conifer pathogen. Since logging is related to a higher abundance of Armillaria in the soil, the particular Armillaria species present in a given stand could be considered an additional site factor when making management decisions. 相似文献
13.
? Litterfall and litter chemistry are key factors for the assessment of forest floor properties. A long-term study on litterfall, litter chemistry and forest basal areas was carried out in an old-growth temperate forest, northeastern China. ? The objective of this study was to test whether forest floor properties in the old-growth forest remain relatively constant. ? Litterfall increased significantly over the past 27 y but litterfall of various litter components showed different temporal trends. Changes in proportions of various litter components, combined with the inherent chemistry differences among them, made litter carbon (C): nitrogen (N) and lignin:N ratios increase at an average rate of 0.19 and 0.16 per year, respectively, suggesting a decreasing trend in the forest floor C and N cycling rates. Changes in dominant tree species biomass significantly affected their corresponding foliar litter production and proportions in the total litterfall and therefore played a dominant role in regulating the developing trends of litter chemistry and quantity in this forest floor. ? Our study indicated that forest floor properties in the old-growth forest still showed a directional change and this was mainly caused by the intrinsic changes rather than yearly climatic fluctuation. 相似文献
14.
? In the 1940s–1950s, large limba (Terminalia superba Engl. & Diels) plantations were established in the Democratic Republic of Congo to reduce the pressure on the natural forests. ? The objective of this study was to evaluate the potential of these long-rotation plantations as production forests (timber) and carbon sinks. ? Five different plantations, between 50 and 58 years old, were sampled. Over a sample surface of more than 73 ha, the diameter above buttresses of 2 680 trees, bole height of 265 trees and tree height of 128 trees was measured. ? To estimate the commercial volume, a nonlinear power law regression was used (R 2 = 0.95). A power law variance function was applied to counter heteroscedasticity of the residual plot. Estimates of commercial tree and stand volume at 50 to 58 y were 5.6 ± 4.1 m3 and 183.9 ± 135.0 m3 ha?1. Stand volumes appear low but are explained by a large decrease in tree density. However, the mean volume increment of 3.2–3.7 m3 ha?1 y?1 corresponds well with teak plantations of a similar age. For limba, aboveground biomass and carbon estimates of this study (resp. 108.4 and 54.2 Mg ha?1) differ significantly from those of existing aboveground biomass models (resp. 135.7–143.9 Mg ha?1 biomass and 67.9–72.0 Mg ha?1 C). All aboveground biomass and carbon estimates for T. superba stands were lower than for the estimates of young fast-growing plantations like Tectona grandis L. f., Eucalyptus spp. and Acacia spp. (≤ 30 y). 相似文献
15.
? Today’s forest managers face a number of important challenges involving an increasing need for precise estimates of forest structure and biomass, potential productivity or forest growth. The objective is to develop a model for potential productivity in a mountainous region of Spain. The model combines climatic, topographic and lithological data using a variant of a traditional biophysical model: the Paterson index. ? In a first approach, the climatic productivity is assessed by modelling the required parameters using different geostatistical techniques and software supported by GIS. A second approach includes the correction of the former productivity classes considering the different lithological facies. The potential forest productivity model involves the integration of both models. ? Finally, data from the National Forest Inventory (NFI) are used to compare the real and potential yield data within different regions of the studied area. ? The results of these analyses demonstrate the usefulness of the model, particularly in mountainous regions, where no significant differences are found between the data from the NFI and the model, but they also show the discrepancies between the estimates and real data when the latter are considered for different tree species, diameter classes or management. 相似文献
16.
? 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
17.
? Stand structure indices would appear to be good surrogate measures for biodiversity in forest ecosystems. ? The vertical structure of Pinus sylvestris L. stands in Central Spain was analysed in order to evaluate their structural diversity. A comparison between two forests with similar ecological conditions but managed under different silvicultural systems was conducted in order to analyse changes in diversity at different stages of stand development. Height diversity was quantified using two non-spatially explicit indices (Shannon’s index and STVI) as well as two spatially explicit indices (Gadow’s differentiation index and the Structure complexity index). A new diversity index was then proposed, based on the sum of square roots of height differences (SQRI). ? Correlations between all vertical structure indices were highly significant. All indices showed that height diversity was greater in the forest with the longer regeneration period and where less intensive thinnings were applied throughout the rotation. Diversity was highest in uneven-aged stands and in the period between the regeneration stage and the first thinning. Thinning from below accounted for the decrease in vertical structure complexity throughout the rotation in even-aged stands. ? The results show that height distribution along with successional stage data enhance the analysis of vertical diversity since structural complexity is highly related to the silvicultural practices that are carried out at different ages. 相似文献
18.
? Simulation tools, based on individual tree growth and mortality models can produce the most detailed predictions of forest stand development under different management schedules. These models allow the manager to predict the development of any type of stand (even- and uneven-aged, and pure and mixed stands). ? Different model approaches and predictors are required for pure even-aged or mixed uneven-aged forest stands. This study developed and compared two sets of models which enable tree-level simulation of the development of pure and mixed stands of Pinus brutia in north-east Greece. The first set of models for even-aged forestry consists of site index models, diameter growth models, tree height models, and mortality models. The second set, which is for uneven-aged forestry, uses a past growth index instead of a site index. ? The simulations and overall fitting statistics suggest that the two types of models provide realistic and accurate predictions of forest stand development and allow one to simulate the development of complex Pinus brutia stand structures in Dadia National Park forests. ? The advantages of the two approaches are discussed and it is suggested that the growth index is an effective predictor of site quality and the set of models which used such variable as predictor performed in a similar way as the models using site index, which require more information and a given stand structure (even-aged). 相似文献
19.
? Wood density is a characteristic of major interest. Usually, it is used as an indicator of wood quality; however, in the context of global change, it is increasingly used for biomass and carbon storage estimations. X-ray computer tomography is a method which enables quick estimates of wood density after applying a calibration procedure. ? A review of the literature is presented in this article. Most of the previous studies have been performed in the 80’s or at the beginning of the 90’s. ? In this study, the relationship between wood density and Hounsfield numbers was investigated using a recent medical scanner. A linear relationship was fitted using a calibration data set which consisted in tropical wood samples representing a large range of densities ranging between 133 and 1319 kg m?3, and then validated using an independent data set (mainly temperate tree species). The fitted relationships were very strong (R 2 > 0.999), whichever the tested scanner settings, with slight but significant effects of the current voltage and reconstruction filters. The RMSE values computed from the validation data set ranged between 5.4 and 7.7 kg m?3 for densities ranging between 364 and 821 kg m?3. ? In conclusion, this method of calibration enables the use of a medical scanner to obtain maps of wood density, in a fast and non destructive way, and with a very good accuracy. Very interesting perspectives are opened regarding biomass distribution within trees. 相似文献
20.
? 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
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