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1.
? 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
2.
? The Government of Papua New Guinea (PNG) has played a prominent part in recent negotiations for “rainforest nations” to be compensated for reducing greenhouse gas emissions from deforestation or forest degradation (DFD). ? A new report “The State of the Forests of Papua New Guinea” claims that rates of DFD in PNG are much higher than have previously reported. It suggests more than half of PNG’s remaining forests will have disappeared or be damaged beyond recovery by 2021. ? We argue that this claim is incorrect. The report overestimates the area of intact primary forest in 1972 and the impact of traditional land use practices on forest cover. Much of what the RSLUP report considers as deforestation is part of a cycle of traditional clearance for farming, fallow and regrowth that has been occurring for hundreds of years. ? The assumption that areas impacted by harvesting or shifting cultivation will inevitably degrade and become non-forest is also not supported by observation of cutover forest in PNG. A considerable proportion of cutover forest areas will recover carbon stocks after harvesting. ? It is argued that traditional land use practices and forest recovery processes need to be considered in assessing greenhouse gas emissions from deforestation and degradation in countries with complex land use histories such as PNG. 相似文献
3.
? 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
4.
? 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
5.
? Soil resources are heterogeneously distributed in terrestrial plant communities. This heterogeneity is important because it determines the availability of local soil resources. A forest fire may change the spatial distribution of soil nutrients, affecting nutrition and survival of colonizing plants. However, specific information on the effects of ecosystem disturbance on the spatial distribution of soil resources is scarce. ? We hypothesized that, on a short-term basis, wildfire would change the spatial patterns of soil N and P availability. To test this hypothesis, we selected two Pinus canariensis forests burned in 2005 and 2000, respectively, and a third forest that was unburned since at least 1990 (unburned). We incubated ionic exchange membranes (IEMs) in replicated plots to estimate soil N and P availability and characterized the spatial pattern using SADIE (Spatial Analysis by Distance Indices). ? Mineral N, NO3-N and PO4-P availability, and aggregation and cluster indices for all nutrients were higher in the 2005 wildfire plots than in the 2000 wildfire and unburned plots. ? Our results suggest that surviving plants or new individuals becoming established in a burned area would find higher soil resources, but also higher small-scale heterogeneity in nutrients, which may have a major impact on the performance of individual plants and on the forest structure and dynamics. 相似文献
6.
? Growing concerns about fires and the increase of fire frequency and severity due to climate change have stimulated a large number of scientific papers about fire ecology. Most researchers have focused on the short-term effects of fire, and the knowledge about the long-term consequences of fires on ecosystem nutrient dynamics is still scarce. ? Our aim was to improve the existing knowledge about the long-term effects of wildfires on forestlabile N concentrations. We hypothesized that fires may cause an initial decline in organic and inorganic N availability, and in the amount of microbial biomass-N; this should be followed by the recovery of pre-fire N concentrations on a long-term basis. We selected a fire chronosequence in Pinus canariensis forests on La Palma Island (Canary Islands, Spain). These forests are under low anthropogenic atmospheric deposition, and forest management is completely lacking; wildfires are therefore the only significant disturbance. Soil samples were collected during the winter and spring at 22 burned and unburned plots. ? Fire produced a significant decrease in microbial biomass N, mineral N and dissolved organic N. Almost 20 y after fire, pre-fire levels of N concentrations had not recovered. ? These results demonstrate that P. canariensis forest soils have a lower resilience against fire than expected. The magnitude of these observed changes suggests that pine forest wildfires may induce long-term (2 decades) changes in soil and in plant primary production. 相似文献
7.
? Mixed coniferous, subalpine forest communities in the Rocky Mountains are historically dense and have experienced infrequent, high-severity fire. However, many of these high-elevation stands are thinned for a number of perceived benefits. ? We explored the effects of forest stand density on ecosystem properties in subalpine forests in Colorado, USA, 17–18 y after forests were managed for timber. ? Forest structure significantly altered the composition and chemical signature of plant communities. Previously managed stands contained lower density of overstory trees and higher ground cover compared to paired reference stands. Foliar phenolic concentration of several species was negatively related to basal area of overstory trees. Furthermore, reductions in stand density increased total foliar phenolic:nitrogen ratios in some species, suggesting that gap formation may drive long-term changes in litter quality. Despite significant changes in forest structure, reductions in stand density did not leave a strong legacy in surface soil properties, likely due to the integrity of soil organic matter reserves. ? Changes in forest structure associated with past management has left a long-term impact on plant communities but has only subtly altered soil nutrient cycling, possibly due to trade offs between litter decomposability and microclimate associated with reductions in canopy cover. 相似文献
8.
? Forest certification sets requirements for minimizing the impacts of logging on the natural structure and floristic composition of forests. ? We assessed the impact of certification by comparing the floristic composition of 52 taxa of trees and shrubs in the treefall gaps of certified, conventionally managed and protected forests in northern Honduras. ? The highest abundance of light-benefiting taxa was found in certified forests, whereas conventionally managed forests were floristically more similar to natural forests. The environmental conditions measured in certified gaps were not favourable for a natural forest floristic composition. ? Past logging may have altered the species composition in certified forests relatively more than in conventionally managed forests. This implies that the need for restoration operations should be considered in certification requirements, along with landscape-level planning to enhance post-logging recovery. 相似文献
9.
? Assessment of forest sustainability requires reliable soil quality indicators. The present study evaluated the use of several potential such indicators in forests in the Basque Country under different types of management, involving: (i) species change and (ii) heavily mechanised forest operations. ? Five adjacent forest stands were selected for study: (i) two unmanaged forests (Quercus robur, Fagus sylvatica) and one (40-year-old) Pinus radiata plantation, to investigate the effect of species change; and (ii) a chronosequence of mechanised radiata pine plantations (3 and 16 years old), to investigate heavy mechanisation. ? Several physical, chemical and biological parameters were analysed in the mineral soil. Species change could not be assessed with chemical parameters, but parameters related to organic matter indicated the disturbance caused by heavy mechanisation. The Least Limiting Water Range was a good indicator of soil physical degradation induced by heavy mechanisation. Biological parameters proved sensitive indicators: (i) the fungal phospholipid fatty acid biomarker 18:2ω6 for species change; and (ii) the ratio of Gram-positive/Gram-negative bacteria for heavy mechanisation. Nevertheless, these parameters are complementary, and monitoring programmes should include physical, chemical and biological parameters. ? Further studies are required to assess natural boundaries of variation in soil quality indicators, and their resistance and resilience. 相似文献
10.
? Although accumulation of decomposing litter temporarily removes nutrients from active circulation, it creates a medium that is more suitable for nutrient uptake where soil conditions are unfavorable. ? A pot experiment was conducted using labeling of isotopically exchangeable phosphate ions of the soil and applying the dilution principle to accurately assess the contribution of the forest floor to P nutrition of maritime pine seedlings (Pinus pinaster Aït.). Three-week-old maritime pine seedlings were planted in pots containing either mineral soil (MS) or mineral soil covered with a forest floor layer (MS+FF). ? After 130 d, P uptake was still insignificant in the MS treatment while the P content of the seedlings in the MS+FF treatment increased tenfold with respect to the initial P content. In the latter treatment, the forest floor contributed 99.1% of the P supply to pine seedlings. ? The higher P uptake from the forest floor than from the mineral soil may be explained by its lower ability to retain inorganic P, which enabled a higher concentration of inorganic P to be maintained in solution. 相似文献
11.
? 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
12.
? The short-term effect of organic residue management on the growth and nutrition of Pinus pinaster Ait. seedlings, and on nutrient leaching and chemical properties of an acid soil was assessed through a lysimeter experiment. Treatments included absence, placement on the soil surface, and incorporation into the soil (with and without legume cover cropping) of organic residues (forest floor litter or forest floor litter plus harvest residues). ? Residues placed on the soil surface enhanced seedling growth. Organic residues reduced nutrient losses (NO 3 ? , Ca and Mg) and resulted in nutrient accumulation in the soil. Harvest residues positively affected K seedling nutrition status and enhanced K soil accumulation. ? Legume cover cropping reduced soil nutrient losses (N, Ca, Mg and K) during the early stage of seedling growth; it also improved seedling nutrition status (N and P), but without any effect on growth. ? Harvest residues plus forest floor litter placed on the soil surface was the most appropriate management to both reduce nutrient losses through leaching and increase height of seedlings at the end of the experimental period (two years). 相似文献
13.
? 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
14.
? This study describes the scenarios of likely development of carbon pools in managed forest ecosystems of the Czech Republic. The analysis was based on a matrix scenario model (EFISCEN), adopting a novel parameterization based on forest stand site types and forest typology. The model was constrained by practical management rules as prescribed by the Czech Forestry Act and used to assess production potential for the next five decades under three management and three climate scenarios. The analysis provided data on carbon pool development, including both tree biomass and soil compartments. ? For the tested scenarios of sustainable forest management (wood removals not exceeding increment) the model indicated a slight increase of soil carbon pool. For the possibly largest removals (maximum sustainable felling scenario), soil carbon stabilized within two or three decades reaching a mean value of about 8.1 kg/m2 for. At the same time, the mean carbon stock held in biomass reached about 10.2 kg/m2 including belowground parts. No decline of soil carbon was observed for any of the tested scenarios. ? We conclude that it is reasonable to assume that soil carbon is not a source of carbon under the current management constraints as implemented in the Czech forestry practice. 相似文献
15.
? Carabid beetles were investigated at five different forest types in the Ibaizabal basin (northern Spain). The landscape is characterized by the presence of remnants of native forest surrounded by conifer plantations. ? Carabids were trapped in 52 stands of mixed forest, beech forest, holm oak forest, mixed pine and Monterey pine plantations in 2005 and 2006. The main objectives of the study were: compare carabid diversity, recognise the characteristic species, and study the effects of ecological variables on carabid assemblages in the different forest types. ? No significative differences in species abundance, richness and diversity were found among the studied forests. Most of the trapped beetles were identified as forest generalists, nevertheless some native and non-native forest specialist species were also found. Distribution of carabid communities overlapped and, except for beech forest, no specific communities were distinguished. Altitude, percentage of grass coverage and temperature were the main variables influencing species distribution. ? The results suggest high habitat homogeneity, caused by regeneration in pine plantations of the indigenous understorey, and by poor habitat quality in native forest (patchy remnants enclosed in conifer plantations). This situation could explain the similar carabid diversity. 相似文献
16.
? Risk assessment of ozone effects on forests is gradually moving from concentration-based exposure metrics to a more complicated approach that requires modelling of ozone fluxes to trees. ? This study reviews the status of the DO3SE stomatal flux model employed within the Convention on Long-range Transboundary Air Pollution, describing a range of applications and identifying major research needs, especially in the context of support that could be provided by the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests. ? The most urgent development need for DO3SE is the modelling of the soil moisture status and its effect on stomatal conductance. Furthermore, the data related to the physical characteristics and the seasonal dynamics of physiological activity of vegetation continue to pose problems. ? There is a clear need for more extensive validation of models and risk estimates using more rigorous statistical procedures and comparisons with flux networks and satellites. ? The current large-scale forest monitoring activities provide only limited possibilities for flux modelling, but could be enhanced by introducing a new monitoring strategy outlined here. 相似文献
17.
The ecological importance of fallowing to swidden (slash and burn) agriculture is well known. Cyclic agroforestry systems which emphasize utilization of the fallow cycle should, where appropriate, consider the ecologic processess of site recovery, so as not to impair the productivity of the subsequent swidden cycle. this artical discusses the ecologic ‘fit’ of a cyclic swidden-fallow management scheme into swidden cultivation and fallow succession. Such a fit suggests a reciprocally reinforcing situation between this agroforestry design and processes involved in site recovery. Observed among some indigenous and colonist inhabitants of the Peruvian Amazon, this system produces fallow crops and products, while enhancing site nutrient recovery. The economic benefits of this scheme have recently been reported (Denevan and Padoch, n.d.) while the ecologic attributes involved in promoting site recovery have not; primarily these include: - Less destruction of the nutrient cycling root-mat in the swidden cycle, and its quicker re-formation in the fallow cycle.
- Discouraging the establishment of exotic, pantropical weeds and grasses such as imperata, while encouraging the colonization of local, early successional species.
- Encouraging the earlier establishment of woody plants in abandoned swiddens.
- A natural litterfall higher in nutrients than in unmanaged fallows.
- Additions of ‘slash’ litterfall higher in nutrient content than natural litterfall in the proximity of valuable managed plants.
- The increased capacity of the managed stand to scavenge limiting nutrients such as N and P from, and leach unneeded quantities of non-limiting nutrients such as K, Ca and Mg to, thoughfall.
- Increasing the alkalinity of throughfall, possibly resulting in less soil cation leaching in managed fallows.
- Staggering seed production, germination and maturation times of the rapid nutrient sycling softwood trees.
- Increasing the spontaneously occuring abundance of valuable fallow plants with management of successive fallow cycles, thereby possibly reducing the labor requirement, and increasing the value of this agroforestry scheme over time.
相似文献
18.
? 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
19.
? Stand harvesting and regeneration were usually considered to be a critical phase for the sustainability of forest soils. The present study concerned the effects on soil chemical fertility of the clear-cutting of a highly productive Douglas-fir stand aged 67 years that was clear-cut with no disturbance. ? Results showed that soil changes were rapid in the three-year period following the cutting. The forest floor mass considerably decreased and the mineral soil showed a limited but real acidification. Soil losses represented 4% of the available nutrients over a depth of 60 cm for N, 22% for K, 25% for Ca and 32% for Mg. Only P increased by 11%. Due to the spatial variability of forest soils, and despite regular re-sampling, confidence intervals were large and difficult to reduce. ? The reversibility of the effects of the clear-cutting and its consequences on soil functions depend on the element: it should not be a problem for C, N and K, which would recover when the biological cycle is re-established once again in the young stand. Phosphorus is not at issue since it changes form in the soil. The depletion of Ca, and to a lesser extent of Mg, is of some concern as a result of limited soil reserves, the limited flux of cations from the mineral changes in the soil, the relatively large part of Ca and Mg in the forest floor, and the negative input-output budgets for those elements. ? The duration of the impact of the clear-cutting on soil requires medium-term observations because it cannot be deduced from the current knowledge of this ecosystem. 相似文献
20.
? Seedling banks of woody species established under closed canopy have received little consideration in coppice forests despite their potential importance for natural regeneration. ? This study aimed to evaluate the influences of canopy composition and of distance from the nearest forest edge on the abundance and species richness of the seedling bank, for different ecological groups of seedlings (age, successional status and dispersal vector) in 68 fragmented coppice stands. ? Seedlings were found in 67 stands, with 19 species identified. Eight species present as older seedlings were lacking as first-year old seedlings, suggesting temporal variability of species recruitment. Seedling abundances of species with low-dispersal ability were positively correlated with the abundances of their conspecific adults. Seedling abundance of mid-successional species was negatively correlated with the distance from the nearest forest edge, while mid-to-late successional species seedling abundance presented the opposite pattern. ? Our results showed that woody species were able to establish frequently under closed canopy in these fragmented coppices and form a seedling bank which may be used for natural regeneration. 相似文献
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