共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Forest floor regeneration after fire in a holm oak forest was studied in a chronosequence in Catalonia (NE Spain). The sampled area represented situations of high fire disturbance because of the frequency of wildfires and the high impact of erosive processes. Forest floor bulk samples from the L, F and H layers were taken in 5 burned plots, aging from 0 to 35 years. They were analyzed for dry standing weight, and organic carbon and N content.Plant cover reached almost 100% two years after the fire. During the first 20 years, shrubs and herbs had the highest surface covering, and thereafter, holm oaks became dominant.Holm oak litterfall stabilized by the fourth year after burning.The major shrub species which were present in the chronosequence had two different patterns with respect to nitrogen: 1) a low litter C/N ratio (i.e. nitrogen fixing species); 2) a high litter C/N ratio.The litter decay coefficients were relatively high, allowing for a rapid structuration and formation of the L and F layers after the fire. Indeed, 95% of the maximum steady standing weight accumulates in 8–9 years. The pattern of cover in the different strata influenced the lateral distribution and variable accumulation of the forest floor layers and determined different turnover rates. 相似文献
3.
R. T. Busing 《Plant Ecology》1994,115(1):19-27
Relationships between canopy cover and tree regeneration were determined for various species in cove forests of the Great Smoky Mountains. Old-growth stands were sampled with six plots covering a total area of 4.8 ha. Each plot was subdivided into contiguous 10×10 m quadrats. Canopy cover overlying each of the 480 quadrats was characterized with three different indices based on visual estimates of cover. Influences of: (1) overlying cover, (2) proximate openings, and (3) total area of proximate openings on quadrat regeneration densities were determined. Most species reproducing by seed and some species reproducing by vegetative means had higher densities in quadrats with openings, but only the intolerants were highly dependent on gaps. Tsuga canadensis, a very shade-tolerant species, was one of the few species with abundant regeneration beneath dense canopy cover. In general, understory areas near gaps had somewhat higher regeneration densities than other areas with overlying cover. Several shade-tolerant species showed a positive regeneration density response to canopy openings and an ability to regenerate in gaps 0.01–0.03 ha in area. These openings were too small for intolerant species. Many species exhibited a positive response to total size of the proximate opening(s). A sharp increase in regeneration density with area of the opening(s) was evident at approximately 0.04 ha for the shade-intolerant species. 相似文献
4.
Abstract. Litter fall and decomposition in a Pinus halepensis forest was studied in order to help understand nutrient cycles in this ecosystem, threatened as it is by fire and tourism. The study was done over two years in an experimental forest stand at Cap des Pinar on Mallorca, Spain. The woodland area has not been disturbed for about 40 yr. Total litter fall amounted to 3.44 ton ha-1 yr-1 and 2.52 ton ha-1 yr-1 in the first and second year, and leaf fall to 2.00 ton ha-1 yr-1 and 1.93 ton ha-1 yr-1 respectively with a maximum in July. As to litter fall, there was a summer maximum for brown needles and kernels, a spring maximum for inflorescences and bud scales, and an autumn maximum for bark. Erratic maxima occurred for fall of green needles, cones and branches, linked to strong winds in winter. The total amount of litter mass on the forest soil reached 12.68 ton/ha: 5.75 ton/ha in the L organic horizon, 3.46 ton/ha needles, and 6.93 ton/ha in the F organic horizon. Weight loss from annual decomposition, measured using litter bags, was 18.1 % in year 1 and 26.8% in year 2. Over 365 days, an Olson (1963) decomposition rate of 0.045 %/day was found in year 1 and of 0.084 %/day for year 2. Decomposition half-time was 1529 for year 1 and 827 days for year 2. 相似文献
5.
Cumulative effects of nitrogen additions on litter decomposition in three tropical forests in southern China 总被引:2,自引:1,他引:2
A field-scale experiment with nitrogen (N) addition treatments was performed in three forest types – a pine (Pinus massoniana Lamb.) forest, a pine-broadleaf mixed forest (mixed) and a mature monsoon evergreen broadleaf forest (mature) – in tropical China. Two kinds of leaf litter, Schima superba Chardn. & Champ. and Castanopsis chinensis Hance, were studied using the litterbag technique after more than 2 years of continuous N additions. The objective of this study was to understand the cumulative effect of N addition on litter decomposition in the tropical forests and to determine if the initial effects of N addition changes over time. Results indicated that leaf litter decomposition was significantly faster in the mature forest than in the mixed or pine forests. The mean fraction of mass remaining after 12-months of decomposition was: mature (0.22) < mixed (0.50) < pine (0.51) for the two litters. Nitrogen addition significantly depressed litter decomposition in the pine forest and the mature forest, but had no significant effect in the mixed forest. These results suggest that N deposition has significant cumulative effect on litter decomposition. 相似文献
6.
Litter fall and litter decomposition in Pinus sylvestris forests of the eastern Pyrenees 总被引:2,自引:0,他引:2
Juli G. Pausas 《植被学杂志》1997,8(5):643-650
Abstract. Litter fall and litter decomposition were studied in four mature stands of Pinus sylvestris (Scots pine) in the eastern Pyrenees. The stands were located in environments differing in bedrock type and exposition and were studied for two years. Mass-loss during the first year of decomposition was compared with other European P. sylvestris forests and regressed with environmental variables (temperature and rainfall) and latitude. The results suggested that the mean amount of needle fall (1760 kg-ha-1·yr-1) was within the range reported for northern European stands. There were more differences in the amount of litter fall between the four stands than between the two years studied. However, the needle fall pattern over the year showed significant differences between years in three of the four stands. Litter decomposition was similar in all the stands and only the one in drier conditions showed a lower decomposition rate. On the European scale the decomposition rate was positively related to mean annual temperature and annual rainfall. However, regression analysis suggests that there are other factors, not taken into account in this study, that are important for predicting the decomposition rate. 相似文献
7.
The feedback between plant litterfall and nutrient cycling processes plays a major role in the regulation of nutrient availability and net primary production in terrestrial ecosystems. While several studies have examined site-specific feedbacks between litter chemistry and nitrogen (N) availability, little is known about the interaction between climate, litter chemistry, and N availability across different ecosystems. We assembled data from several studies spanning a wide range of vegetation, soils, and climatic regimes to examine the relationship between aboveground litter chemistry and annual net N mineralization. Net N mineralization declined strongly and non-linearly as the litter lignin:N ratio increased in forest ecosystems (r 2 = 0.74, P < 0.01). Net N mineralization decreased linearly as litter lignin concentration increased, but the relationship was significant (r 2 = 0.63, P < 0.01) only for tree species. Litterfall quantity, N concentration, and N content correlated poorly with net N mineralization across this range of sites (r 2 < 0.03, P = 0.17–0.26). The relationship between the litter lignin:N ratio and net N mineralization from forest floor and mineral soil was similar. The litter lignin:N ratio explained more of the variation in net N mineralization than climatic factors over a wide range of forest age classes, suggesting that litter quality (lignin:N ratio) may exert more than a proximal control over net N mineralization by influencing soil organic matter quality throughout the soil profile independent of climate. Received: 16 December 1996 / Accepted: 8 February 1997 相似文献
8.
大兴安岭北部原始老龄林内兴安落叶松幼苗种群的生命统计研究 总被引:6,自引:0,他引:6
天然落叶松老龄林每1个种子年后第2年,林地表面即会出现大量天然幼苗100-270株·m-2.幼苗发生时间集中,绝大多数在6月底.赤杨落叶松林幼苗发生较丛桦落叶松林和杜香落叶松林的迟.幼苗死亡时期也集中,主要在幼苗发生后的15天内.其间杜香落叶松林的幼苗死亡率为48%,3年内97%;丛桦落叶松林为29%和66%;赤杨落叶松林为33%和69%.7月以后发生的幼苗存活率很低,早期发生的幼苗占优势,死亡率低.丛桦落叶松林和杜香落叶松林幼苗的早期优势显著,尤其是杜香落叶松林.幼苗存活的年际变化很大,落叶松幼苗数量丛桦落叶松林>赤杨落叶松林>杜香落叶松林. 相似文献
9.
Canopy disturbance patterns and regeneration of Quercus species in two Ohio old-growth forests 总被引:6,自引:0,他引:6
This study was conducted to determine the abundance of Quercus species, the spatial pattern of Quercus regeneration, the current canopy disturbance pattern, and their interrelationship in two old-growth deciduous forests in Ohio (Goll Woods and Sears-Carmean Woods). Acer saccharum and Fagus grandifolia had the greatest density and basal area in both forests, yet the largest trees (by basal area) present at each site were Quercus spp. Quercus spp. appeared to be decreasing in abundance in both sites. Though Quercus seedlings were common, few Quercus saplings or subcanopy trees were present. The current disturbance regimes were dominated by small canopy gaps created by death of 1–2 trees; canopy gaps 100 m2 in size were rare and only 2.5–2.8% of the forest area was covered by recognizable canopy gaps. No significant differences in the density of Quercus seedlings or saplings were found between gaps and non-gap areas at either site. Though no significant barrier to seedling establishment appeared to exist, the present disturbance regimes are not well suited for the growth of Quercus into the subcanopy size class or the recruitment of Quercus into the canopy. The most frequent gapmakers in Goll Woods were Tilia americana and Acer saccharum, and those in Sears-Carmean Woods were A. saccharum and F. grandifolia. The species most frequent as gap fillers were A. saccharum (in both sites) and F. grandifolia (in Goll Woods). These results suggest that A. saccharum will continue to increase in abundance, and Quercus decrease in abundance, in these two old-growth stands. 相似文献
10.
In two consecutive years, we analysed the effect of litter quality, quantity and decomposability on soil N at three characteristic
sites of the Patagonian Monte. We assessed (i) concentrations of N, C, lignin and total phenolics and the C/N ratio in senesced
leaves as indicators of litter quality of three species of each dominant plant life form (evergreen shrubs and perennial grasses),
and (ii) N, and organic-C concentrations, potential N-mineralisation and microbial-N flush in the soil beneath each species.
Rate constants of potential decomposition of senesced leaves and N content in decaying leaves during the incubation period
were assessed in composite samples of the three sites as indicators of litter decomposability. Further, we estimated for each
species leaf-litter production, leaf-litter on soil, and the mass of standing senesced leaves during the senescence period.
Senesced leaves of evergreen shrubs showed higher decomposability than those of perennial grasses. Leaf-litter production,
leaf-litter on soil, and the mass of standing senesced leaves differed significantly among species. The largest variations
in leaf-litter production and leaf-litter on soil were observed in evergreen shrubs. The mass of standing senesced leaves
was larger in perennial grasses than in evergreen shrubs. Nitrogen, organic C and potential N-mineralisation in soil were
higher underneath evergreen shrubs than beneath perennial grasses, while no significant differences were found in microbial-N
flush among life forms. The initial concentrations of C, N and total phenolics of senesced leaves explained together 78% of
the total variance observed in the dry mass loss of decaying leaves. Litter decomposition rates explained 98%, 98%, 73%, and
67% of the total variance of soil N, organic C, net-N mineralisation, and microbial-N flush, respectively. We concluded that
leaf-litter decomposition rates along with leaf-litter production are meaningful indicators of plant local effects on soil
N dynamics in shrublands of the Patagonian Monte, and probably in other similar ecosystem of the world dominated by slow growing
species that accumulate a wide variety of secondary metabolites including phenolics. Indicators such as C/N or lignin concentration
usually used to predict litter decomposability or local plant effects may not be adequate in the case of slow growing species
that accumulate a wide range of secondary metabolites or have long leaf lifespan and low leaf-litter production. 相似文献
11.
Due to economic needs, a process of abandonment of unfavourably situated areas and intensified cultivation on favoured areas
has taken place in the alpine region. This abandonment not only means the loss of a cultural landscape based on centuries
of care but also interference with an established ecological balance. We wanted to investigate the impact of land-use, such
as mowing, fertilisation and irrigation and the effects of abandonment on the O-horizon type, quantity and quality. Therefore,
we selected areas with different types of land use but with equivalent site conditions in the Passeier Valley (Bolzano-South
Tyrol province) for investigation. The areas studied were as follows: an organically fertilised and irrigated, intensively
managed hay meadow mown once a year; an organically fertilised, intensively managed hay meadow mown once a year; a lightly
managed hay meadow mown every second year; a lightly managed hay meadow mown every 3–4 years; an area densely covered with
dwarf shrubs abandoned 10 years ago; and a reforested area abandoned 30 years ago. These selected areas represent different
intensities of land use or stages of succession. On these areas, vegetation, phytomass, litter quantity, humus type, O-horizon
quantity, litter decomposition and C and N storage, were analysed in detail. Abandonment causes the percentage of coverage
with grasses and herbs to decrease from 100 to 10%, while lignified species increase from 0 to 90%. This leads to growth of
the phytomass pools, which in turn causes an increase in the annual litter quantity (from 117 to 525 g m−2). Significant changes in litter quality in the case of reduced use or abandonment increases the litter’s resistance to decomposition,
decreasing overall decomposition. Litter quantity and quality then have a significant impact on the O-horizon quantity. This
increases strongly with decreasing intensity of land use or longer times since abandonment (115–1,180 g m−2). This leads to a significant increase of C and N storage and a change in O-horizon type ranging from no definite O-horizon
or mull O-horizons on regularly used areas to moder on abandoned areas. 相似文献
12.
Leaf-litter and changing nutrient levels in a seasonally dry tropical hardwood forest,Belize, C.A. 总被引:3,自引:0,他引:3
Summary Total above ground plant biomass in a 45 year old seasonally dry tropical hardwood forest was estimated to be approximately 56,000 kg/ha oven dry weight. Nutrients immobilized in the standing vegetation were: N, 203 kg/ha; P, 24 kg/ha; K, 234 kg/ha; Ca, 195 kg/ha; Mg, 47 kg/ha; Na, 9 kg/ha; Mn, 1 kg/ha; Cu, 0.5 kg/ha; Zn, 3 kg/ha; Fe, 4 kg/ha. Total nutrients returned each year through the litter were: N, 156 kg/ha; P, 9 kg/ha; K, 59 kg/ha; Ca, 373 kg/ha; Mg, 32 kg/ha; Na, 5 kg/ha; Mn, 1 kg/ha; Al, 21 kg/ha; Zn, 0.3 kg/ha; Fe, 9 kg/ha. Half of the nutrients immobilized in the standing vegetation were found in the leaves and are returned annually to the soil. Although litter fall is interrupted during the year, the mean nutrient content of the litter was high –5.2%.A decomposition rate of 0.48 percent per day was considered high for a seasonally dry tropical hardwood forest. Fluctuations in soil nutrient levels showed a sharp increase at the start of the rainy season. Later during the dry season nutrient levels decreased to concentrations similar to what they were just prior to the rainy season. Soil organic matter levels were very high –20% in the top 12 cm. 相似文献
13.
14.
In 1994, 234 fungal species were listed for protection under the Survey and Manage Programme (SMP) guidelines of the Northwest Forest Plan (NWFP), an area encompassing 9.7 M ha of federal land in the states of Washington, Oregon, and northern California. The fungal species were presumed rare, associated with late-successional old-growth forests, and in need of protection not afforded by the major elements of the NWFP, including a vast system of forest reserves. The SMP guidelines thus called for protecting known sites while gathering information through surveys to learn more about species rarity, distribution, habitat requirements, and persistence concerns. If new information revealed that a species was not rare, not associated with late-successional old-growth forests, or that other aspects of the NWFP guidelines provided for their persistence (e.g. adequate protection provided by forest reserves), the species could be removed from the programme. The first assemblage of known site records from fungal herbaria yielded approximately 3500 records for all listed species. After 12 y of survey the total number of records increased four-fold to approximately 14400 records. Fifty-five percent of species were found at 20 or fewer sites and considered rare; 42 % were found at ten or fewer sites. Over the life of the programme, 39 species were removed from the programme primarily because they were no longer considered rare; many were found at several hundred sites throughout the NWFP area. Mapped distributions of known sites varied among species. When viewed across species, however, known sites were well distributed throughout the NWFP area, thus indicating the importance of the entire NWFP area in maintaining this diverse array of fungi. The NWFP relies on a system of late-successional forest reserves to act as a coarse-filter conservation approach to provide protection for late-successional species. Ninety percent of fungal species had some portion of their known sites within reserves, but only 34 % of total sites occurred within reserves. Thus, for the rarest species, applying a fine-filter conservation approach that protects known sites outside of reserves becomes an important aspect of species protection. The SMP became a costly and controversial aspect of the NWFP and underwent several administrative revisions including attempts to end the programme in 2004 and 2007. Regardless of costs and controversy, this conservation programme represents an unprecedented attempt to conserve rare fungal species at a regional scale. One of the more important lessons learned is the absolute need for professional mycologists to develop long-term partnerships with resource managers and other scientists, and apply mycological expertise to complex species and habitat conservation issues in an interdisciplinary setting. 相似文献
15.
Chemical and seasonal controls on the dynamics of dissolved organic matter in a coniferous old-growth stand in the Pacific Northwest,USA 总被引:1,自引:0,他引:1
Soil organic matter (SOM) is the largest terrestrial C pool, and retention and release of dissolved organic matter (DOM) cause formation and loss of SOM. However, we lack information on how different sources of DOM affect its chemical composition, and how DOM chemical composition affects retention. We studied seasonal controls on DOM production and chemical controls on retention in soils of a temperate coniferous forest. The O horizon was not usually the dominant source for dissolved organic C (DOC) or N (DON) as has been reported for other sites. Rather, net production of both DOC and DON was often greater in the shallow mineral soil (0–10 cm) than in the O horizon. DOM production in the shallow mineral soil may be from root exudation as well as turnover of fine roots and microflora in the rhizosphere. In the field, the two acid fractions (hydrophobic and hydrophilic acids) dominated the soil solution at all depths. A major portion of net production and removal of total DOC within the soil column was explained by increases and decreases in these fractions, although a shift in chemical composition of DOM between the O and mineral soil horizons suggested different origins of DOM in these layers. A larger loss of the free amino fraction to deep soil water at this study site than at other sites suggested lower retention of labile DON. Field DOM removal measurements suggest that field-measured parameters may provide a good estimate for total DOM retained in mineral soil. 相似文献
16.
Over the past decade an increasing amount of research has sought to understand how the diversity of species in an ecosystem
can influence fluxes of biologically important materials, such as the decomposition of organic matter and recycling of nutrients.
Generalities among studies have remained elusive, perhaps because experimental manipulations have been performed at relatively
small spatial scales where site-specific variation generates patterns that appear idiosyncratic. One approach for seeking
generality is to perform parallel experiments at different sites using an identical species pool. Here we report results from
a study where we manipulated the diversity of leaf litter from the same six dominant tree species in the litter layer of three
forested ecosystems. These ecosystems spanned a 300 km latitudinal transect in Wisconsin, USA, and were characterized by a
large gradient in temperature and moisture, and thus, rates of decomposition. After allowing combinations of one, two, four,
and six species of leaf litter to decompose for 1 year, we found that increasing leaf litter richness led to slower rates
of decomposition and higher fractions of nitrogen lost from litter. Across all sites, climate and initial litter chemistry
explained more of the variation in decomposition rates than did litter richness. Effects of leaf litter diversity were non-additive,
meaning they were greater than expected from the impacts of individual species, and appeared to be strongly influenced by
the presence/absence of just 1–2 species (Tilia americana and Acer saccharum). The rate of decomposition of these two species was highly site-specific, which led to strong negative effects of litter
richness only being observed at the southernmost sites where T. americana and A. saccharum decomposed more quickly. In contrast, litter diversity increased nitrogen loss at the northernmost sites where decomposition
of T. americana was notably slowed. Our study shows that species diversity affected at least one of the two litter processes at each site
along this 300-km gradient, but the exact nature of these effects were spatially variable because the performance of individual
species changed across the heterogeneous landscape. 相似文献
17.
Masashi Ohsawa 《Ecological Research》2008,23(1):11-20
The relationships between coarse woody material (CWM) and the diversity of three saproxylic beetle families (Cerambycidae,
Melandryidae, and Curculionidae) were investigated. These three families responded differently toward the quality and quantity
of CWM. The species richness of cerambycid beetles increased in forests with more CWM in the early stage of decomposition.
The richness of saproxylic curculionids increased in stands with more tree species. No clear trend was evident for melandryid
diversity. The CWM differed in quality and quantity among three forest types [middle-aged larch (Larix kaempferi [Lamb.] Carrière) plantation, secondary forest, and old-growth forest] and between two forest-management practices (thinning
and long rotation). Forest type and management practices affected CWM and the number of tree species, and CWM and the number
of tree species influenced the diversity of saproxylic families differently. Because each decomposition stage is considered
to be important for saproxylic beetles at the species level, a constant supply of CWM is necessary to maintain a suitable
balance of CWM through these decomposition stages in forests to maintain the diversity of saproxylic beetles. 相似文献
18.
Shin-Ichi Yamamoto 《Ecological Research》1995,10(1):31-39
Gap characteristics and gap regeneration were studied in three old-growth stands of subalpine coniferous forests in the northern
Yatsugatake and the northern Akaishi mountains, central Japan. With the results of the present study and those of a previous
study conducted in another locality, general features of gap characteristics and gap regeneration behavior of major tree species
in subalpine coniferous forests of central Japan were summarized and discussed. Of the total 237 gaps investigated in the
14.48 ha of forested area, the percentage gap area to surveyed area, gap density and mean gap size were 7.3%, 17.2 ha−1, and 43.3 m2, respectively. The gap size distributions were similar among stands and showed a strong positive skewness with a few large
and many small gaps; gaps <40m2 were most frequent and those >200 m2 were rare. Gaps due to the death of multiple canopy trees comprised 44.7% of the total ones. Canopy trees died in various
states; standing dead (42.6%) or trunk broken (43.7%) were common and uprooted (12.2%) was an uncommon type of death of canopy
trees. These figures indicate that general features of gap characteristics in this forest type are the low proportion of gap
area and the high proportions of small gap size and multiple-tree gap formation. In general, shade-tolerantAbies frequently, andTsuga, infrequently, regenerate in gaps from advance regenerations recruited before gap formation, whilePicea and shade-intolerantBetula possibly regenerate in gaps from new individuals recruited after gap formation. Gap successors of conifers occurred in a
wide range of gap size and did not show the clear preference to species specific gap size. In old-growth stands without large-scale
disturbance (≥0.1 ha in area) of subalpine coniferous forests of central Japan, major tree species may coexist with their
different gap-regeneration behaviors and, probably, different life history traits. 相似文献
19.
Decomposition of branch litter of four angiosperm and one conifer species was studied over a two-year period. Litter species and the corresponding forest type are: (i) Shorea robusta, sal forest at 329 m; (ii) Lyonia ovalifolia, mixed-pine broadleaf forest at 1 350 m; (iii) Pinus roxburghii, pine forest at 1 750 m; (iv) Quercus leucotrichophora, mixed oak-pine forest at 1 850 m; and (v) Quercus lanuginosa, mixed oak forest at 2 150 m. The weight loss ranged from 44–89%. Litter moisture and air temperature had significant positive effect on decomposition. The decomposition rate decreased with an increase in altitude and was inversely related with lignin content. Linear combinations of lignin content with rainfall and with temperature indicated significant interactive influence on decomposition.Authorities for plant names are given in Table 1.We gratefully acknowledge financial support from the Department of Science and Technology, Government of India. 相似文献
20.
Summary Creosobebush (Larrea tridentata) fine litter was treated with either the general biocide HgCl2 and CuSO4 or water (controls) and buried 5 cm beneath the soil surface in the northern Chihuahuan Desert. The treated litter showed significantly less mass loss than controls during the three month summer-autumn field study; controls lost about 20% of the original mass while treated litter lost less than 2%. In addition, the total nitrogen content of the control litter increased from an initial concentration of about 14.08 g kg-1 to 17.62 g kg-1 dry weight by the end of the study, while treated litter nitrogen content decreased to 13.30 g kg-1. Results suggest abiotic processes other than leaching have little effect on the decomposition of buried litter in this environment. 相似文献