宁夏罗山自然保护区3种典型林分凋落物和土壤层水源涵养能力综合评估

森林凋落物层和土壤层是森林生态水文效应中的主要贡献层，对森林生态系统水土保持功能和水源涵养能力有重要影响。对比宁夏罗山自然保护区3种典型林分类型凋落物和土壤层水文效应的变化规律和水源涵养能力大小，为该地区的森林生态水文、水土保持和森林管理提供科学依据。以该自然保护区青海云杉纯林、油松纯林和青海云杉油松混交林为研究对象，运用称量、室内浸泡、环刀法和回归分析法对凋落物和土壤层的水文效应进行测定和拟合，并使用熵权法对二者的水源涵养能力进行评估。结果表明：（1）青海云杉油松混交林凋落物的总厚度和总储量显著高于青海云杉纯林和油松纯林（P<0.05），3种林分类型的半分解层的厚度和储量高于未分解层。（2）凋落物层最大持水量范围为63.29-95.08t/hm²，最大持水率范围为335.97%-353.85%，有效拦蓄量范围为34.09-63.92t/hm²，三者均为青海云杉油松混交林>云杉纯林>油松纯林。（3）3种林分类型的凋落物持水量（Q）与浸泡时间（t）呈对数函数关系，吸水速率（V）与浸泡时间（t）呈幂函数关系。（4）从3种林分类型的土壤物理性质和持水特性得出，3种林分类型的土壤层水文效应的等级排序为云杉油松混交林>油松纯林>青海云杉纯林。（5）凋落物层和土壤层的水源涵养能力大小为青海云杉油松混交林（0.43）>油松林（0.3）>青海云杉林（0.27）。综合来看，青海云杉油松混交林的凋落物层和土壤层的水源涵养能力最优，其次是纯林，说明混交林在水土保持和水源涵养方面比纯林更具优势。     

Late-glacial and Holocene vegetation history and dynamics as shown by pollen and plant macrofossil analyses in annually laminated sediments from Soppensee, central Switzerland

The palynostratigraphy of two sediment cores from Soppensee, Central Switzerland (596 m asl) was correlated with nine regional pollen assemblage zones defined for the Swiss Plateau. This biostratigraphy shows that the sedimentary record of Soppensee includes the last 15 000 years, i.e. the entire Late-glacial and Holocene environmental history. The vegetation history of the Soppensee catchment was inferred by pollen and plant-macrofossil analyses on three different cores taken in the deepest part of the lake basin (27 m). On the basis of a high-resolution varve and calibrated radiocarbonchronology it was possible to estimate pollen accumulation rates, which together with the pollen percentage data, formed the basis for the interpretation of the past vegetation dynamics. The basal sediment dates back to the last glacial. After reforestation with juniper and birch at ca. 12 700 B.P., the vegetation changed at around 12 000 B.P. to a pine-birch woodland and at the onset of the Holocene to a mixed deciduous forest. At ca. 7000 B.P., fir expanded and dominated the vegetation with beech becoming predominant at ca. 500¹⁴C-years later until sometime during the Iron Age. Large-scale deforestation, especially during the Middle Ages, altered the vegetation cover drastically. During the Late-glacial period two distinct regressive phases in vegetation development are demonstrated, namely, the Aegelsee oscillation (equivalent to the Older Dryas biozone) and the Younger Dryas biozone. No unambiguous evidence for Holocene climatic change was detected at Soppensee. Human presence is indicated by early cereal pollen and distinct pulses of forest clearance as a result of human activity can be observed from the Neolithic period onwards.     

Disturbance and regeneration dynamics of a mixed Korean pine dominated forest on Changbai Mountain,North-Eastern China

We used dendrochronological methods to study disturbance history of a mixed Korean pine (Pinus koraiensis Siebold et Zuccarini) dominated forest on the northern slope of Changbai Mountain, North Eastern China, over 1770–2000. Frequent small-scale canopy gaps and infrequent medium-scale canopy disturbances dominated natural disturbance regime in the forest, which did not experience stand-replacing disturbances over the studied period. Percentages of growth releases in subcanopy trees were below 6% in most decades, suggesting that disturbances initiating these releases were of low intensity. Strong winds were likely cause of moderate disturbance events. Two episodes with increased disturbance rates (19% and 13%) were dated to the 1920s and 1980s, timing of the 1980s event was consistent with a hurricane occurred in 1986 on the western slope of the Changbai Mountain. Age structure and growth release analyses revealed species-specific regeneration strategies of canopy dominants. Shade-intolerant Olga bay larch (Larix olgensis Henry) recruited mainly before the 1860s. Recruitment of moderately shade-tolerant P. koraiensis occurred as several regeneration waves (1820s, 1850s, 1870–1880s, 1930s, and 1990–2000s) of moderate intensity. Shade-tolerant Jezo spruce (Picea jezoensis Carr. var. komarovii (V. Vassil.) Cheng et L.K.Fu) and Manchurian fir (Abies nephrolepis (Trautv.) Maxim.) regenerated continuously over the last 220 and 130 years, respectively. Enhanced recruitment of P. koraiensis, P. jezoensis, and A. nephrolepis was observed during the 1930s and 1990s, coinciding with increased growth release frequency in the 1920s and 1980s, and suggesting disturbance events of moderate intensity. Our results indicate that the current disturbance regime of the mixed Korean pine dominated forest maintains coexistence of light-demanding and shade-tolerant species and that change in wind climate may be particularly important for future forest composition.     

Climate‐diameter growth relationships of black spruce and jack pine trees in boreal Ontario,Canada

To predict the long‐term effects of climate change – global warming and changes in precipitation – on the diameter (radial) growth of jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] B.S.P.) trees in boreal Ontario, we modified an existing diameter growth model to include climate variables. Diameter chronologies of 927 jack pine and 1173 black spruce trees, growing in the area from 47°N to 50°N and 80°W to 92°W, were used to develop diameter growth models in a nonlinear mixed‐effects approach. Our results showed that the variables long‐term average of mean growing season temperature, precipitation during wettest quarter, and total precipitation during growing season were significant (alpha = 0.05) in explaining variation in diameter growth of the sample trees. Model results indicated that higher temperatures during the growing season would increase the diameter growth of jack pine trees, but decrease that of black spruce trees. More precipitation during the wettest quarter would favor the diameter growth of both species. On the other hand, a wetter growing season, which may decrease radiation inputs, increase nutrient leaching, and reduce the decomposition rate, would reduce the diameter growth of both species. Moreover, our results indicated that future (2041–2070) diameter growth rate may differ from current (1971–2000) growth rates for both species, with conditions being more favorable for jack pine than black spruce trees. Expected future changes in the growth rate of boreal trees need to be considered in forest management decisions. We recommend that knowledge of climate–growth relationships, as represented by models, be combined with learning from adaptive management to reduce the risks and uncertainties associated with forest management decisions.     

Spatial and temporal variation in historic fire regimes in subalpine forests across the Colorado Front Range in Rocky Mountain National Park, Colorado, USA

Aim The historical variability of fire regimes must be understood in the context of drivers of the occurrence of fire operating at a range of spatial scales from local site conditions to broad‐scale climatic variation. In the present study we examine fire history and variations in the fire regime at multiple spatial and temporal scales for subalpine forests of Engelmann spruce–subalpine fir (Picea engelmannii, Abies lasiocarpa) and lodgepole pine (Pinus contorta) of the southern Rocky Mountains. Location The study area is the subalpine zone of spruce–fir and lodgepole pine forests in the southern sector of Rocky Mountain National Park (ROMO), Colorado, USA, which straddles the continental divide of the northern Colorado Front Range (40°20′ N and 105°40′ W). Methods We used a combination of dendroecological and Geographic Information System methods to reconstruct fire history, including fire year, severity and extent at the forest patch level, for c. 30,000 ha of subalpine forest. We aggregated fire history information at appropriate spatial scales to test for drivers of the fire regime at local, meso, and regional scales. Results The fire histories covered c. 30,000 ha of forest and were based on a total of 676 partial cross‐sections of fire‐scarred trees and 6152 tree‐core age samples. The subalpine forest fire regime of ROMO is dominated by infrequent, extensive, stand‐replacing fire events, whereas surface fires affected only 1–3% of the forested area. Main conclusions Local‐scale influences on fire regimes are reflected by differences in the relative proportions of stands of different ages between the lodgepole pine and spruce–fir forest types. Lodgepole pine stands all originated following fires in the last 400 years; in contrast, large areas of spruce–fir forests consisted of stands not affected by fire in the past 400 years. Meso‐scale influences on fire regimes are reflected by fewer but larger fires on the west vs. east side of the continental divide. These differences appear to be explained by less frequent and severe drought on the west side, and by the spread of fires from lower‐elevation mixed‐conifer montane forests on the east side. Regional‐scale climatic variation is the primary driver of infrequent, large fire events, but its effects are modulated by local‐ and meso‐scale abiotic and biotic factors. The low incidence of fire during the period of fire‐suppression policy in the twentieth century is not unique in comparison with the previous 300 years of fire history. There is no evidence that fire suppression has resulted in either the fire regime or current forest conditions being outside their historic ranges of variability during the past 400 years. Furthermore, in the context of fuel treatments to reduce fire hazard, regardless of restoration goals, the association of extremely large and severe fires with infrequent and exceptional drought calls into question the future effectiveness of tree thinning to mitigate fire hazard in the subalpine zone.     

Long-term changes in bryophyte diversity of central European managed forests depending on site environmental features

Cryptogamic diversity is a reliable indicator of the state of forest ecosystems. In this study we analysed the variations in both bryophyte species richness overall and number of hemerophobic bryophyte species in Central European managed forests over a 20-year time span, based on data collected in 132 plots scattered across Poland. We tested differences in species richness among five temporal replicates, as well as among site types grouped based on elevation a.s.l., dominant tree species and stand age. The analyses revealed no significant trend in species richness across years. Meanwhile, species richness significantly increased along with elevation a.s.l., especially in broadleaved forests. No significant difference in species number between spruce and pine dominated stands emerged for mature stands, while there was a strong difference for young stands, with spruce forest hosting a much higher number of species. Species richness exhibited a slight, but not significant, increase over time in broadleaved forests, no significant variations in pine dominated stands and significant fluctuations in spruce dominated stands, yet without a significant trend. Out of the tested drivers, dominant tree species exhibited the strongest impact on species community composition. Number of hemerophobic and strongly hemerophobic species did not undergo significant variations across years either. The lack of bryophyte diversity trends highlighted in this study suggests Central European managed forests are in an equilibrium sate, maintained by the opposing effects of climate changes, on one side and of more sustainable forest management and pollutant deposition decline, from the other.

     

The Transpiration Rate of Unhardened, Hardened, and Dehardened Seedlings of Spruce and Pine

Tissue injuries in winter are sometimes interpreted as caused by drought damages. The possibility that the tolerance of conifers of winter and spring conditions is increased through decrease in transpiration rate has been little investigated. The transpiration rate of 3 or 6 months old unhardened, hardened, and dehardened seedlings of Pinns silvestris L. and Picea abies (L.) Karst. was assessed gravimetrically, at 20°C. The transpiration rates of seedlings of spruce and pine which had been hardened for 3 months were about ¹/₂ the rates of dehardened seedlings. Transpiration during a dehardening period increased at different rates in pine and spruce. After a dehardening period of 3–5 days the transpiration rate of spruce reached a maximum, whereas pine reached the maximum transpiration rate after a dehardening period of 10–14 days. Transpiration of seedlings of spruce and pine hardened for 3 months showed only a very slight reaction to light and darkness. This indicated that stomata of hardened seedlings remained closed. The results are discussed in connection with frost and drought injuries in pine and spruce during early spring.     

凉水自然保护区松鼠和星鸦贮食生境选择差异

2003 年9 月30 日～2005 年10 月8 日,在黑龙江凉水国家级自然保护区,应用样方调查法, 采用Vanderploeg和Scavia 选择系数Wi和选择指数Ei作为衡量指标,对松鼠和星鸦贮食生境选择进行了研究。结果表明, 二者贮食生境选择优先顺序略有不同,松鼠偏爱的贮食生境依次是: 云杉林、原始红松林、人工红松林、针阔混交林、人工云杉林、白桦林、针叶混交林、人工落叶松林、阔叶混交林、冷杉林和其它。星鸦对贮食生境的偏爱程度依次为: 人工红松林、原始红松林、云杉林、人工云杉林、针阔混交林、阔叶混交林、白桦林、针叶混交林、人工落叶松林、冷杉林和其它。在对贮食微生境因子的选择利用上, 二者大致相同,只是在对优势灌丛的选择上略有差异, 松鼠优先选择在狗枣猕猴桃优势灌丛内贮藏红松种子, 而星鸦优先选择在刺五加优势灌丛内贮食。松鼠和星鸦贮食生境选择的差异将对随后的红松天然更新过程产生不同的影响。     

Observations on the life cycle and pathogenicity of Paralongidorus maximus in a forest nursery in Scotland

Soil samples from a forest nursery growing Scots pine were collected at monthly intervals at five different depths during 1975 and examined for Paralongidorus maximus: 49% occurred at the 10–19 ^cm depth. The fluctuation in the numbers of the larval stages suggested that a complete life cycle from egg to adult probably took more than 1 yr. Growth in the second year after planting and overall height of Scots pine seedlings was inversely related to the numbers of P. maximus. In a glasshouse experiment using varying numbers of P. maximus the growth of Scots pine and European larch but not of Sitka spruce were decreased by increasing numbers of nematodes. A possible relationship between P. maximus, Cylindro-carpon destructans and the death of small numbers of Scots pine is discussed.     

Regenerative and age dynamic of spruce population in pine plantations under conditions typical for spruce development

We have studied the natural regeneration of spruce (Picea abies L.) under a canopy of pine (Pinus sylvestris L.) on loamy soils. Spruce survival and growth depend on the duration of the regeneration period from the creation of the plantation and the local conditions formed as a result of uneven thinning of pine and spruce canopy. The formation of spruce population is mainly determined by trees that regenerated upon intensive thinning of 20- to 40-year-old pine trees. Spruce regeneration may be enhanced by timely cleaning cutting in pine plantations. The first one, done at the age of 15–20 years, favors pine growth and spruce regeneration. At the normal reproduction of spruce population under the canopy of 80-year-old pine plantations, the second spruce layer is formed. Trunk reserve in this layer is 20–25% of the reserves of the first layer. After its formation, the light regime in the forest depends greatly on the space volume occupied by spruce crowns. Their percentage is especially high at the relative height equal to 0.4–0.7 of the mean spruce height in the second layer. Smaller spruce trees may exist for a long time period, but their development is slowed down and they die at the undergrowth stage. When the plantation is 150 years old, the reserves of spruce trees regenerated under the canopy of pine comprise one-third of the total reserves of the plantation. If the growing conditions are favorable for spruce (C₃), the stability and productivity of pine-spruce plantations exceed those of the pure spruce plantations. The reasonability of natural spruce regeneration for the creation of pine-spruce plantations under C₃ conditions should be substantiated with the consideration of their designation, ages of cuttings, and the possibility of plantation creation and sanitary cuttings according to the valid regulations.     

Late-Glacial and Postglacial Vegetation and Associated Environment in Jianghan Plain

Pollen percentage and influx diagrams were prepared from two cores in Jianghan Plain, and studied by means of Fuzzy cluster and radiocarbon dating. This paper reports that there was a cool-temperate evergreen coniferous forest in late-glacial epoch, representing that the climate was cold and wet. In Holocene, the hypsithernaal interval took place about 9100–3500 year B. P. and the maximum was about 8000 year ago. At that time, the vegetation, was that of an evergreen and deciduous broad-leaf mixed forest, and the climate was warmer and damper than that of present. It also shows that the history of vagetational development and climate chenges in this area in the past 21900 years can be divided into five stages: (1). During 21000--10000 year B. P., the vegetation was one of the cool-temperate evergreen coniferous forest, dominated by Abies. The climate was cold and wet. (2) During 10000–9100 year B. P., the vegetation was that of the coniferous and deciduous broad-leaf mixed forest, consisting of Pinus. Quercus, Ulmus and Liquidambar, with a mild and cool climate. (3) During 9100–3500 year B. P., the mixed forest of evergreen and deciduous broad-leaf was predominant, consisting of Cyclobalanopsis, Fagus, Castanopsis, Castanea, Pterocarya, Quercus and Ulmus. The palaeoecological environment was warm and damp. (4) During 3500–2400 year B. P., there was deciduous broad-leaf, consisting of Quercus, Pterocarya, Liquidambar. and Pinus. The climate was droughter and cooler than that of stage(3). (5) During 2400 year B. P. to present, the broad-leaf forest, consisting of Quercus, Fagus, Liqui-dambar and Castanea, was dominant. The climate was warm and damp.     

Primary succession of subarctic vegetation and soil on the fast‐rising coast of eastern Hudson Bay,Canada

Aim The objectives of the study are: (1) to evaluate the dynamics of the maritime tree line and forest limit of white spruce, Picea glauca, within the dual framework of primary succession induced by the rapid post‐glacial land emergence on the eastern coast of Hudson Bay and the impacts of recent and past climate changes; and (2) to determine the time lapse between land emergence and seedling, tree, and forest establishment in the context of the primary chronosequence occurring on rising, well‐drained sandy beaches and terraces. Location The study area was located on the eastern coast of Hudson Bay (56°20′ N, 76°32′ W) in northern Québec, Canada. Methods We evaluated the colonization dynamics of white spruce as seedlings, tree‐line trees and primary‐forest trees at eight sites distributed along a 200‐km latitudinal gradient based on a mean land emergence rate of 1.2 m century^?1. A 30‐m wide by 140–300‐m long quadrat was positioned at random at the centre of each site. The elevation above sea level, position and age of all individuals of spruce present in the quadrat areas were determined, and the soils of each chronosequence were described. Results The main stages of primary succession along the emerging coast were common to all the sites, regardless of latitude, but occurred at different elevations above sea level (a.s.l.). White spruce seedlings colonized near‐shore beaches 2 m a.s.l., whereas the tree line and forest limit tended to form only at about 3–4 m and 4–8 m a.s.l., corresponding approximately to 180–825 years and 310–1615 years after land emersion, respectively. White spruce establishment at the tree line occurred about 50 years ago. Climatic conditions at this time were probably more favourable to tree colonization than when the species established at the forest limit. Soil formation was influenced primarily by distance from the seashore and elevation above sea level, with podzolization being accelerated by white spruce cover. Main conclusions The current tree‐line and forest‐limit positions on the rising coast of eastern Hudson Bay correspond to ecological limits established during the course of primary succession within a context of changing climatic conditions. The recent establishment of trees at the tree line and forest limit at relatively old coastal sites is associated with warmer conditions over the last 100 years. Although white spruce was present nearby, coastal sites were devoid of trees before the 20th century.     

Spatial and temporal variations in boreal forest fire frequency in northern Alberta

Abstract. Spatial and temporal variations in fire frequency in the boreal forest of Wood Buffalo National Park (WBNP) were assessed using forest stand age, fire scar and historical data. I test the hypotheses that (1) fire frequency is higher in jack pine forests and aspen forests than in black spruce forests and white spruce forests, (2) these variations in fire frequency can be related to the mean waterbreak distance (MWD) around a site and (3) fire frequency has changed over the past 300 years. The fire cycles (the time required to burn an area equal in size to the entire study area) in jack pine forests (39 years) and in aspen forests (39 years) were significantly shorter than those in black spruce forests (78 years) and in white spruce forests (96 years). The length of the fire cycle varies inversely with the MWD around a site, and the MWD was significantly higher in jack pine and aspen forests than in black or white spruce forests. It is suggested that covariations between soil type and the MWD influence, respectively, variations in forest dominant and fire frequency. A change in fire frequency at 1860 was apparent in the fire history for all of WBNP, the black spruce dominated stands, and the near and medium MWD classes. The fire cycle estimates for these classes were all significantly shorter during the period 1750 to 1859 (fire cycles = 25–49 years) than they were in the period 1860 to 1989 (fire cycles = 59–89 years). The possible roles of changes in climate and aboriginal burning practices in causing the temporal change in fire frequency are discussed.     

Foraging activity and dietary spectrum of wood ants (Formica rufa group) and their role in nutrient fluxes in boreal forests

Abstract 1. We monitored three different‐sized wood ant (Formica aquilonia Yarrow) mounds over a 3‐year period in Finnish boreal forests dominated by Norway spruce (Picea abies Karst.), to assess the seasonal temperature dependency of ant activity. Additionally, we also monitored Norway spruce trees around the mounds for descending honeydew foragers. 2. The amount of collected honeydew and prey and its composition, as well as the carbon (C), nitrogen (N), and phosphorus (P) in honeydew and invertebrate prey was also investigated. 3. The number of warm days (average temperature above 20 °C) and the amount of precipitation differed among the years. Ant activity at the mounds (but not on the trees) was highly correlated with air temperature throughout the ant‐active season (May–September), but ant activity in spring and autumn was lower than in summer at similar temperatures. During all 3 years, honeydew played a major role in wood ant nutrition (78–92% of dry mass). Invertebrate prey was mainly Diptera (on average 26.2%), Coleoptera (12.5%), Aphidina (9.3%), and Arachnoida (8.5%). 4. The total amounts of C, N, and P input brought into the ant mounds in the form of food (both honeydew and prey) on the stand level were 12.6–39.0, 1.6–4.6 and 0.1–0.4 kg ha^?1 year^?1, respectively, which is equivalent to 2–6%, 12–33% and 27–58% of the fluxes in annual needle litterfall in typical boreal Norway spruce forests. Thus, wood ants can play a significant role in short term and local N and P cycling of boreal forest ecosystems.     

小兴安岭三种林型叶面积指数的估测

利用Winscanopy2006冠层分析仪测定2009年7月初至11月初小兴安岭白桦次生林、谷地云冷杉林、阔叶红松林的有效叶面积指数(LAI_e),并将经过木质部分所占比率、冠层水平集聚和簇内集聚校正的11月初LAI_e作为真实叶面积指数(LAI_t),结合凋落物法测定3种林型的LAI_t及其季节动态.结果表明： 调查期间,白桦次生林的LAI_e在7月达到峰值(2.21),谷地云冷杉林、阔叶红松林的LAI_e在8月达到峰值,分别为2.57、2.68.白桦次生林、谷地云冷杉林、阔叶红松林的LAI_t均在7月达到峰值,分别为3.44、3.86、6.93;相对于本文探讨的方法,光学仪器所测定的LAI_e在最高叶面积指数期分别低估33.1%、32.9%、66.0%;而在整个调查期内,谷地云冷杉林和阔叶红松林LAI_e平均低估22.8%和56.5%,白桦次生林平均高估13.2%.
     

Total, organic and extractable-P in humus and soil beneath Sitka spruce planted in pure stands and in mixture with Scots pine

Total, organic and extractable P were measured in the humus and underlying soil to 10 cm depth beneath Sitka spruce (SS) and mixed Sitka spruce and Scots pine (SS+SP) stands planted on upland heath. The humus beneath SS+SP contained significantly (p<0.01) greater amounts of total and organic-P than that in SS and the mixed stands had more effectively retained approximately 87 per cent of previously applied fertilizer-P, totalling 100 kg P ha^–1, compared with 70 per cent in SS. Despite the larger amounts of total-P in the mixed plots 0.01 M CaCl₂ extractable molybdate reactive phosphorus (MRP) was significantly (p<0.05) greater in SS+SP humus only during March and April. Greater concentrations of MRP were released from the humus and soil during July and August at a mean rate of 58 g P ha^–1 day^–1. This coincided with drying of the soil during the summer and the rate of release, attributed to death of fine roots and microorganisms, was 4 to 30 times greater than reported values for rates of net mineralization of P from forest soils.     

Pollen AnalysiS and Paleoenvironment Study of Late Pleistocene in Daganba,Guizhou Province

In this paper, the division of the two pollen zones is discussed based on the results of pollen and spores analysis and 14C dating in the Daganba area, Zhijin County, central Guizhou Province. Zone Ⅰ represents a forest of mixed evergreen-deciduous broad-leaved trees closed subtropic mountain and dominated by Fagus, Quercus, Cyclobalanopsis, Carpinus and Castanea (Castanopsis, Lithocarpus) together with Pinus, Tsuga and Abies till 23000 yr B.P. It stands for the Dali interstadial climate, cool and moist. Zone Ⅱ vegetation adopted dry climate. During the time from 23000 yr B. P. to the fullglacial period the forest cowered and the fern extended. The pioneer trees such as Pinus, Betula began to grow towards the end of the dry phase. The genus Fagus is of great importance in studing ecology and geography of the flora. The retirement and growth of Fagus forest reveals the paleoenvironment changes.     

Vertical transport of dissolved organic C and N under long-term N amendments in pine and hardwood forests

At the Harvard Forest, Massachusetts, a long-term effort is under way to study responses in ecosystem biogeochemistry to chronic inputs of N in atmospheric deposition in the region. Since 1988, experimental additions of NH₄NO₃ (0, 5 and 15 g N m^–2 yr^–1) have been made in two forest stands:Pinus resinosa (red pine) and mixed hardwood. In the seventh year of the study, we measured solute concentrations and estimated solute fluxes in throughfall and at two soil depths, beneath the forest floors (Oa) and beneath the B horizons.Beneath the Oa, concentrations and fluxes of dissolved organic C and N (DOC and DON) were higher in the coniferous stand than in the hardwood stand. The mineral soil exerted a strong homogenizing effect on concentrations beneath the B horizons. In reference plots (no N additions), DON composed 56% (pine) and 67% (hardwood) of the total dissolved nitrogen (TDN) transported downward from the forest floor to the mineral soil, and 98% of the TDN exported from the solums. Under N amendments, fluxes of DON from the forest floor correlated positively with rates of N addition, but fluxes of inorganic N from the Oa exceeded those of DON. Export of DON from the solums appeared unaffected by 7 years of N amendments, but as in the Oa, DON composed smaller fractions of TDN exports under N amendments. DOC fluxes were not strongly related to N amendment rates, but ratios of DOC:DON often decreased.The hardwood forest floor exhibited a much stronger sink for inorganic N than did the pine forest floor, making the inputs of dissolved N to mineral soil much greater in the pine stand. Under the high-N treatment, exports of inorganic N from the solum of the pine stand were increased >500-fold over reference (5.2 vs. 0.01 g N m^–2 yr^–1), consistent with other manifestations of nitrogen saturation. Exports of N from the solum in the pine forest decreased in the order NO₃-N> NH₄-N> DON, with exports of inorganic N 14-fold higher than exports of DON. In the hardwood forest, in contrast, increased sinks for inorganic N under N amendments resulted in exports of inorganic N that remained lower than DON exports in N-amended plots as well as the reference plot.     

Stand dynamics,regeneration patterns and long-term continuity in boreal old-growth Picea abies swamp-forests

Abstract. The occurrence of macrofossil charcoal (long axis > 0.5 mm) and Picea abies (Norway spruce) pollen in peat stratigraphies, in combination with size and age data from 2976 P. abies trees were used to analyse ecosystem continuity and stand-structure in ten old-growth swamp-forests in northern Sweden. All stands were dominated by P. abies, a species whose abundance increased westwards in Sweden between 3000 and 2000 yr B.P. In three stands no macrofossil charcoal was found and the maximum age of the peat, determined by ¹⁴C dating, varied from 1800 to 3600 yr B.P. In the other seven stands the number of levels containing charcoal varied from 1 to 23, but only between 1 and 7 levels were found after the appearance of spruce. Here the maximum age of the peat varied from 400 to 7900 yr B.P. The ten stands had an all-sized stand structure and a stand continuity of ca. 300 yr. The shape of the age structure was similar to an inverse J-curve. This indicates a continuous recruitment over time in a self-perpetuating ecosystem. In a short-term perspective (< 300 yr), the swamp-forests are characterized by individual trees continually emerging while others are dying. it is suggested that internal dynamics of continuous small-scale disturbances in combination with local site-specific factors determine the structure of these forests. in a long-term perspective, some of the present spruce swamp-forests within the northern boreal zone have functioned as true fire-free refugia since the establishment of P. abies populations while others have been affected by recurring fires, although not as frequently as forests on surrounding drier sites. The hypothesis that Scandinavian spruce swamp-forests in general have functioned as true longterm fire-free refugia is thus modified by the present results.     

秦岭地区不同林分土壤微生物群落代谢特征

利用BIOLOG微孔板法研究了秦岭山脉的锐齿栎(Quercus aliena var.acutidentata)、油松(Pinus tabuliformis)、华山松(Pinus armandii)、松栎混交、云杉(Picea asperata)6个林地5种典型林分土壤微生物群落代谢特征。发现:(1)5种典型林分中,华山松的平均颜色变化率(AWCD)最高,然后是锐齿栎1云杉油松锐齿栎2松栎混交。位于不同林场的锐齿栎林地土壤AWCD值差异较大;(2)土壤微生物功能多样性指数与平均颜色变化率表现一致,6种林分之间差异显著,且不同的林分土壤微生物对6种碳源利用差异较大。(3)主成分分析显示各土壤微生物功能多样性具有显著差异,其综合因子得分为华山松锐齿栎1油松云杉锐齿栎2松栎混交。(4)冗余分析表明土壤p H、有机质、全氮、碱解氮、速效磷和速效钾的综合作用对土壤微生物群落功能多样性有显著影响,其中速效磷和p H与土壤微生物功能多样性最密切。