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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 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
3.
? 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
4.
? 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
5.
? Primary forests in the seasonally dry tropical regions of Mexico are disappearing under land-use pressure, creating a mosaic of secondary forests of different ages. ? In this study we measured the aboveground litterfall phosphorus (P) fluxes, litter-layer and soil P pools to compare the P cycles in primary and secondary seasonally dry tropical forests. Our hypothesis was that the previous agricultural land use of secondary forests would bring about a lower P flux in the litterfall, lower soil P pool, and higher nutrient resorption proficiency than in primary forests, as well as an increase of relative amounts of available P provided by the soil with forest aging. ? The expected litterfall P flux increase in the secondary forest following a previous agricultural land use did not occur. Phosphorus return to the soil by aboveground litterfall was unaffected by the succession stage of the forest. In addition, the total soil P pool did not change with forest age. However, available soil P (bicarbonate P-inorganic and P-organic pools) and hydroxide inorganic P pools were higher in primary than in secondary forest soils. Phosphorus concentration in litterfall increased significantly with forest age, suggesting that P is cycled more efficiently (by a higher nutrient resorption proficiency) when soil available P is less abundant. Despite these differences among forests, the results of our study gave evidence that P requirements by plants in primary and secondary forests are sufficiently met by the accumulation of dissolved (water extractable) P in the forest floor during the dry season and by soil bicarbonate-P pools. ? Our study on the effects of land cover change on P cycling, following the discontinuation of agricultural practices, leads to the conclusion that this ecosystem P dynamics will vary depending on the successional stage of the forests, and is strongly influenced by the seasonal rainfall pattern which determines plant-available P. 相似文献
6.
Background This study was designed to evaluate the internal nutrient cycling of litterfall in different elevation subtropical forests of Central Taiwan. Methods The litterfall of evergreen hardwoods at three elevations, specifically Mt. Peitungyen (2,078?m), Hui-Sun experimental forest (HSEF) (1,066?m), and Lienhauchi (782?m) in central Taiwan, was collected monthly using traps and sorted into leaves, twigs, reproductive litter, and miscellaneous material. In addition, the litter on the forest floor was collected trimonthly. All the samples were weighed and measured for C, N, P, K, Ca, and Mg concentrations and fluxes from March 2009 to February 2010. Results The annual litterfall productions were 6.58, 8.24, and 9.17?Mg?ha ?1?year ?1 at Mt. Peitungyen, HSEF, and Lienhauchi, respectively. At more than 60?%, leaves were the main component of the total litterfall. There was smallest decomposition constant (0.487) at Mt. Peitungyen. The nutrient fluxes increased as elevation decreased. The litterfall correlated positively with rainfall at Lienhauchi, with temperature at HSEF, and with temperature and rainfall at Mt. Peitungyen. Conclusion The annual litterfall decreased with an increase in elevation. The turnover rate was faster at HSEF than at Mt. Peitungyen. Thus, the forest managers should pay more attention to understand and monitor plant community responses to global warming and nutrient loss. 相似文献
7.
? 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
8.
? From the summit downslope a granitic inselberg in French Guiana, soils and vegetation evolve from bare granite covered by cyanobacteria, to a savannah-type vegetation on thin patchy sandy accumulations, then to a low forest on shallow young soils and to a high forest on deep highly weathered ultisols. ? We have used element budgets and Sr isotopic variations in soils and plants to investigate the mineral nutrient supply sources of the different plant communities. ? Granite and atmospheric deposition have 87Sr/86Sr ratios of 1.3 and 0.71, respectively. The 87Sr/86Sr ratio of cyanobacteria (0.72) suggests granite weathering by cyanobacteria crusts. The 87Sr/86Sr ratio of the savannah-type vegetation is 0.73 and varies between 0.75 and 0.76 in the low and high forest leaf litter regardless of soil depth, age and degree of impoverishment. ? These almost constant ratio suggest that forest Sr comes from rainwater and from the summit of this inselberg, where it is released and redistributed along the slope, by surface flow, lateral redistribution of litter, and mineral particles. However, because of its very low content in the rock and soils, Ca is supplied to plants by atmospheric deposition. 相似文献
9.
? Understanding the effects of tree species diversity on biomass and production of forests is fundamental for carbon sequestration strategies, particularly in the perspective of the current climate change. However, the diversity-productivity relationship in old-growth forests is not well understood. ? We quantified biomass and above-ground production in nine forest stands with increasing tree species diversity from monocultures of beech to stands consisting of up to five deciduous tree species (Fagus sylvatica, Fraxinus excelsior, Tilia spp., Carpinus betulus, Acer spp.) to examine (a) if mixed stands are more productive than monospecific stands, (b) how tree species differ in the productivity of stem wood, leaves and fruits, and (c) if beech productivity increases with tree diversity due to lower intraspecific competition and complementary resource use. ? Total above-ground biomass and wood production decreased with increasing tree species diversity. In Fagus and Fraxinus, the basal area-related wood productivity exceeded those of the co-occurring tree species, while Tilia had the highest leaf productivity. Fagus trees showed no elevated production per basal area in the mixed stands. ? We found no evidence of complementary resource use associated with biomass production. We conclude that above-ground productivity of old-growth temperate deciduous forests depend more on tree species-specific traits than on tree diversity itself. 相似文献
10.
? 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
11.
? The effect of nitrogen (N) deposition on the decomposition of pine (Pinus massoniana) needles in a tropical pine plantation was studied. The pine needles with two different nutrient status (nutrient-rich and nutrient-poor) were used, followed by 3-levels of N treatments (Control: no N addition, Low- N: 5 g N m?2 y?1, and Medium-N: 10 g N m?2 y?1 experimental inputs), which had been applied for 26 months continuously before this experiment and continued throughout the decomposition measurement. ? The main objective was to test the hypothesis that decomposition of nutrient-rich needles would be more sensitive to cumulative N deposition than the decomposition of nutrient-poor needles. ? Nitrogen addition had negative effect on mass loss, and the release of N and P from decomposing nutrient-rich needles but little or no effect on the decomposition of nutrient-poor needles. In addition, a negative effect in the initial decomposition phase and a positive effect in later decay stages were found on C release. The negative effect was stronger on nutrient-rich needles than on nutrient-poor needles, but the reverse was true for the positive effect. ? Our results suggest that response of litter decomposition to N deposition may vary depending on the nutrient status of the litter. 相似文献
12.
? Density dependence is a major mechanism for shaping plant communities. However, its role in regulating diverse, mixed natural tree communities is less certain. ? In this study we investigated density-dependent effects in a large-scale (25 ha) old-growth temperate forest in northeastern China. Spatial patterns of neighborhood distribution in the plot were analyzed using various methods for inferring competition, including (1) pair correlation function to determine spatial patterns of pre-mortality and post-mortality and (2) neighborhood analysis of individuals to examine the extent to which tree survival is correlated with other covariates. ? Results showed that, for common species, 3 of 5 canopy species and 3 of 8 midstory and understory species were random in mortality. Negative density-dependent mortality was not found when trees reach 1 cm in DBH. There was no significant correlation for canopy species between tree survival and conspecific abundance, but largely positive correlations for midstory and understory species. In contrast, tree survival was found to negatively correlate with conspecific basal area for most species, indicating strong intraspecific competition. No strong interspecific density dependence was found in the forest. 相似文献
13.
? 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
14.
? Context The amount and chemistry of litterfall have been known to strongly vary among the years with important implications for ecosystem nutrient cycles, but there are few quantitative data describing such variations. ? Aims We studied the climatic implications on the variation in litterfall and its C and N input to soil in two distinct European coniferous forests. ? Methods Year-to-year variations in canopy litterfall were measured in a Scots pine stand (Hyytiälä, Finland) over 13 years, and a Douglas fir stand (Speulderbos, The Netherlands) over 3 years. ? Results Important inter-annual variations in litterfall were observed in Scots pine. Litterfall was mainly driven by leaf senescence; however, premature needle fall was observed in high wind speed and early frost events. The seasonal variation in litterfall was characterized by a maximum in September in Scots pine, and by a biphasic variation pattern in Douglas fir, in May and November. Lower seasonal variations and lower annual average in litterfall N content were observed in Scots pine. ? Conclusion Significant inter- and intra-annual variations in litterfall and chemistry and between the sites were demonstrated; and it depended on year-to-year differences in climate and extreme weather events. 相似文献
15.
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
16.
? Liming is a forestry practice used to counteract forest decline in acidic soils. It consists of direct Ca and Mg input to forest soil, which restores tree mineral nutrition, but also modifies microbial communities in soil. The aim of this study was to assess the effects of liming on both belowground (ectomycorrhizal root tips) and aboveground (epigeous sporocarps) fungal communities. ? Results showed that the modification of soil chemical properties (pH, and Ca-Mg contents versus total free Al and Fe concentrations) was a stronger factor of ECM community structuring than tree host. The species appearing in limed plots were ubiquist or known as good competitors and replaced acidophilic and stress species. ? At the sporocarp level, tree host was a stronger factor of community structuring than soil chemical properties associated with liming. On the whole, there was a shift in the community composition from a typical acidophilic forest fungal community of medium altitude in the untreated plots to a less typical one, with the reduced dominance of acidophilic fungi while many late-stage forest species appeared. ? We finally suggest a marker species (Russula ochroleuca) to assess both above and belowground effects of liming on ectomycorrhizal communities. 相似文献
17.
? The quality of monitoring is defined by its ability to provide data that (i) allow estimates of the status of the target resource with defined precision level, (ii) permit change detection with defined power, and (iii) are comparable through space and time. To achieve these requirements a Quality Assurance (QA) perspective is essential. ? To what extent QA was considered and data quality achieved in international forest monitoring programmes in East Asia and Europe? What is missing? ? Past and present QA activity in forest monitoring in East Asia and Europe revealed that most attention was given to evaluate and promote comparability of measurements, with special emphasis on analytical chemistry. Much less attention was given to field sampling and to the overall monitoring design. QA approaches were unbalanced among the various investigations, and several problems with data comparability remained over years. ? Despite considerable work on data quality control, parts of the monitoring process are still poorly covered by QA and revealed weaknesses in design and implementation. More comprehensive, formal and stringent QA procedures are necessary in international monitoring initiatives. Steps currently being undertaken for a more comprehensive QA approach are presented. 相似文献
18.
? 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
19.
? Chestnut stands (Castanea sativa Mill.) for fruit production, in Northern Portugal, are subjected to frequent soil tillage operations, which is considered a threat for the system sustainability. ? The effects of replacement of conventional tillage by the no-tillage system in chestnut stands on decomposition and nutrient dynamics of leaf litter and burs were evaluated, using the litterbag methodology. Amounts of mass and nutrients in the organic layers, and chemical characteristics of the 0–20 cm top soil layer were assessed after eight years. ? The mass loss and release of N, P, Ca and Mg from both leaves and burs buried in the soil were faster than from those placed on the soil surface. Burs decomposed and released nutrients more slowly than leaf litter. The no-tillage system led to the formation of organic layers, which retained great amounts of N (249.2 kg ha?1) and Ca (215.5 kg ha?1). Such a management system increased the concentration of organic C and nutrients in the 0–5 cm top soil layer, but significant differences were only observed for exchangeable Ca. ? The no-tillage system may enhance organic C accumulation regarding the conventional system, due to the increment in both organic and mineral soil layers. 相似文献
20.
? The aim of this work was to analyze how the forest structure affects the risk of wind damage at the landscape level in a boreal forest. ? This was done by employing: (i) Monte Carlo simulation technique for generating landscapes with different age class distributions, proportions of open areas (gaps), and tree species composition; and (ii) a mechanistic wind damage model, HWIND, for predicting the critical wind speeds at downwind stand edges of open areas (gaps) for risk consideration. The level of risk of wind damage observed at the landscape level was significantly affected by the presence of gaps and old stands. Even a slight increase in the proportion of gap areas or older stands had a significant impact on the total length of edges at risk. As a comparison, variation in species composition (Scots pine and/or Norway spruce) had much smaller impact on the risk of damage. ? In conclusion, the effects of forest structure on the risk of wind damage should especially be considered by forest managers in day-to-day forest planning in order to reduce the risk of wind damage both at the stand and landscape level. 相似文献
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