不同植被类型下红壤pH和交换性酸的剖面特征

研究湘南红壤丘陵区11种植被类型下施肥区域和未施肥区域红壤剖面(0～100 cm)pH及交换性酸的变化特征.结果表明: 施肥区域0～60 cm土层土壤的pH大小顺序为茶园<花生地<柑橘园,交换性酸含量大小为花生地≤柑橘园<茶园;种植茶树和花生后,表层(0～40 cm)相对底层(60～100 cm)均产生酸化,pH分别降低0.55和0.17,而种植柑橘后,土层间无显著差异.未施肥区域中,植被恢复区0～40 cm土层pH大小为白檵木林≤湿地松林<板栗园<白茅草地,交换性酸含量大小为白茅草地<板栗园<白檵木林≤湿地松林;天然林区0～20 cm土层中次生林和油茶林的pH均显著低于马尾松林0.34和0.20个单位,马尾松林和次生林交换性酸含量显著低于油茶林.与裸地相比,未施肥区域除白茅草地外,其他植被类型均加速了表层土壤酸化,其中天然次生林酸化最严重,pH降低0.52;未施肥区域除天然次生林外,其他植被类型均提高了深层土壤pH,其中白茅草地提升效果最显著,pH升高0.43.无论施肥区域还是未施肥区域,整体上随着土层深度的增加,植被类型或施肥对土壤酸度的影响越来越小.     

Soil properties and crop performance on a kaolinitic Alfisol after 15 years of fallow and continuous cultivation

A long-term field experiment was established on a kaolinitic Alfisol in Ibadan, Nigeria, in 1972. The land was cleared manually from secondary forest and used for (i) continuous no-till cropping with maize (Zea mays L.) and maize/cassava (Manihot esculenta Crantz) intercropping, (ii) planted fallow of guinea grass (Panicum maximum Jacq.), leucaena (Leucaena leucocephala de Wit), and pigeon pea (Cajanus cajan Millsp.), and (iii) natural bush regrowth in a randomized complete block design with three replications. At the end of 15 years, the fallow plots were cleared manually and cropped with maize for three years. The chemical and physical soil properties and crop performance of the newly-cleared plots were compared with those under 15 years of continuous cultivation. A total of 26 woody species were identified on the bush regrowth plots. Above-ground biomass accumulation of the bush plots was 157 Mg ha^-1 containing 1316 kg N ha^-1. Guinea grass, leucaena and natural bush regrowth plots had comparable organic C concentrations (approximately 20 g kg^-1) in the surface soil (0 to 10 cm) after 15 years. The organic C concentration in the surface soil under pigeon pea was the lowest (9.5 g kg^-1) among the four fallow treatments. Soil under 15 years of continuous no-till maize with and without residue mulch, respectively, contained approximately half (10 g kg^-1) and a quarter (5.7 g kg^-1) of the organic C under natural bush or guinea grass fallow. The levels of exchangeable Ca, K, Mg and effective cation exchange capacity (ECEC) were lower in the soils under continuous cultivation than in those under natural bush and planted fallow. Soil acidification occurred in soils under continuous cropping as depicted by the lower pH values and greater exchangeable Al and Mn concentrations compared to the fallow plots. Grain yield of maize (3 to 5 Mg ha^-1) without fertilizer application in the plots newly cleared from natural bush, guinea grass and leucaena fallow was comparable with that of continuous no-till maize with residue mulch and chemical fertilizer (N, P, K, Mg, Zn) applications. Among the four fallow treatments, maize grain and stover yields were the lowest in plots cleared from pigeon pea fallow.     

An experimental study of the impacts of understorey forest vegetation and herbivory by red deer and rodents on seedling establishment and species composition in Waitutu Forest, New Zealand

Introduced mammalian herbivores are changing the structure and composition of New Zealand’s forest ecosystems and may modify forest succession after natural disturbances. We studied how introduced ungulates (red deer and feral pigs) and rodents (rats and house mice) affected the rate of recovery (i.e. the engineering resilience) of the forest understorey following artificial disturbance. We imposed disturbances by clearing understorey vegetation dominated by Blechnum ferns in forests on relatively fertile alluvium and elevated infertile marine terraces, and recorded recovery of vegetation (seedling establishment, species composition, cover and volume) in herbivore exclosures and controls. Seedlings quickly established on cleared plots: after 2 years, numbers of woody seedlings and ground cover of vascular plants relative to initial values were similar on cleared and uncleared treatments. Volume of plant biomass <2 m remained low on cleared subplots. Ungulates significantly reduced the re-establishment of woody seedlings ≥ 10 cm tall: only one seedling reached this height outside exclosures, compared with 29 seedlings inside. The number of seedlings <10 cm tall, expressed relative to numbers present pre-clearing, was not significantly affected by ungulates. The species composition of regenerating vegetation was more similar (Jaccard index) to pre-clearing understorey vegetation inside ungulate exclosures than outside. No consistent effect of rodents (primarily house mice) on seedling establishment or species composition was detected after 2 years, and rodent exclosures did not significantly affect survival of seedlings (Griselinia littoralis and Aristotelia serrata) planted as an index of rodent herbivory pressure. No significant differences in vegetation recovery were apparent between forest types. Rapid seedling recruitment in the absence of understorey vegetation and the presence of herbivores provided evidence that understorey vegetation competes with seedlings for light. Ungulate effects were consistent with other experiments that showed herbivores reduced the rate and altered the trajectory of vegetation regrowth after disturbance.     

Relations of soil properties to topography and vegetation in a subtropical rain forest in southern Taiwan

Soil chemical properties for a subtropical rain forest in the Nanjenshan Reserve, southern Taiwan, were examined to determine soil-landscape and soil-vegetation relationships. Soil sampling sites were separated into four groups based on landscape features and exposure to the prevailing northeasterly monsoon winds. Corresponding vegetation types were delimited along the first DCA axis. The forest showed a drastic change both in structure and floristic composition along the wind-stress gradient. Redundancy analysis (RDA) showed that both topographic variables and vegetation types were needed to explain the variation in soil data. Soil properties that differed significantly among landforms were pH, available N, CEC, exchangeable Al, K, Ca and Mg. Levels of pH, exchangeable Ca and Mg increased in a downslope direction, and exchangeable Al tended to be higher in the upper slope soils. These trends pointed to the importance of slope processes in redistribution of soil minerals. The main differences in soil properties attributed to the influence of the occupying vegetation were apparently aspect dependent. The contents of available N, exchangeable K, and CEC in the 0–40 cm depth of soils under windward low-stature (mostly sclerophyllous) forest were consistently lower compared to those under the leeward forest. For a given catena, however, soil variability associated with vegetation differences seemed to be confounded by the slope processes.     

Nutrient content of the moist tropical forest of Ghana

Summary The total weight of vegetation on an area of just over 1 acre of old secondary forest in the moist forest zone of Ghana has been determined, and found to be equivalent to roughly 150 tons per acre dry weight. The nutrient content of each component of the vegetation was also determined and showed that the amounts of the major nutrients immobilised in the vegetation were: N, 1,800 lb./acre; P, 120 lb./acre; K, 800 1b./acre; Ca, 2,400 lb./acre; Mg, 350 lb./acre. The corresponding amounts of nutrients in the top foot of soil supporting the vegetation were: total N, 4,100 lb./acre; available P, 11 lb./acre; exchangeable K, 580 lb./acre; exchangeable Ca, 2,300 lb./acre; exchangeable Mg, 330 lb./acre. About half the nutrients stored in the vegetation were contained in readily combustible material, and except for N would be released to the soil if the forest were cleared and burnt for cultivation. The quantity of roots and the amounts of nutrients contained in them were not sufficiently great to make an important addítion to the nutrient supply in the soil during subsequent cultivation. Of the total quantity of roots supporting the vegetation 85.5 per cent by weight were within 1 foot of the soil surface.     

Effects of different Rhododendron control methods in eastern beech (Fagus orientalis Lipsky) ecosystems in the western Black Sea region of Turkey

Intensive weed control and plot preparation practices have become a critical and integral part of productive beech forest management in Turkey’s coastal Black Sea region (BSR). This study was conducted in an eastern beech forest of 100+ year old in the BSR to evaluate ecosystem effects of three different experimental Rhododendron ponticum understory control methods with a randomised block design, including manual grubbing, foliar and cut stump spraying with imazapyr (Arsenal) and foliar and cut stump spraying with triclopyr (Garlon). Untreated vegetation plots served as controls. Evaluation of these treatments included their effects on understory and forest floor biomass and nutrients (C, N, P, S, K, Ca and Mg) and effects on soils, including bulk density, pH, soil nutrients (C, N, P and S), exchangeable cations (K, Ca and Mg) and soil cation exchange capacity (CEC). Grubbing and imazapyr treatments had greatly reduced the amount of understory biomass 5 years after application (P = 0.002). Triclopyr treatment also had a major effect on understory vegetation control, but by 5 years later, about 10% of the rhododendron originally present on these plots had gradually re‐sprouted and partially covered the plots. Five years after woody vegetation control treatments, at the 0‐ to 20‐cm depth, treatments did not appear to affect soil bulk density, pH and CEC. For the upper 20‐cm soil depth, the exchangeable soil K concentration at the 10‐ to 20‐cm depth on triclopyr‐treated plots was 33% higher than on grubbing plots, and it was twice that of imazapyr application plots. Imazapyr plots had almost 11 times more dead organic matter on the forest floor than there was on grubbing plots. Forest floor C concentrations on imazapyr plots were 26 and 14% greater than those on grubbing and triclopyr plots, respectively. Total ecosystem (forest floor + understory + soil exchangeable) Ca content was 50% higher on imazapyr plots than that on triclopyr plots, while the ecosystem K pool on imazapyr treatment plots was 27% lower than that on triclopyr plots. Herbicides can be used as an alternative for achieving some forest management objectives when other vegetation control methods are not feasible or economical. It is recommended that vegetation control not be used on steep slopes because of greater risk of soil erosion. There may be benefits in encouraging slash disposal by fire after imazapyr treatments, thus removing recalcitrant understory residues left on the forest floor and releasing the essential nutrients within them.     

Soil and vegetation response to thinning White Cypress Pine (Callitris glaucophylla) on the North Western Slopes of New South Wales, Australia

Dense White Cypress Pine (Callitris glaucophylla J. Thompson and L.A.S. Johnson) regrowth occurs frequently across previously cleared landscapes in New South Wales (NSW), and is thought to adversely affect agricultural production and to cause land degradation. The NSW Native Vegetation Act (2003) requires that management of native vegetation including pre-1990 regrowth must ‘improve or maintain’ site condition, yet there is currently limited information regarding techniques for the optimum management of C. glaucophylla in this regard. We conducted a preliminary study to examine floristic composition, soil condition (to 50 cm) and carbon storage under ‘Dense’ (dense regrowth), ‘Thinned’ (dense regrowth thinned 2000/2001) and ‘Un-colonised’ (pasture not yet recolonised by C.␣glaucophylla) plots on private lands in NSW. Reduced tree density from thinning resulted in increased biomass of the remaining individual trees. Un-colonised plots had significantly more groundcover than thinned plots, which had significantly more groundcover than dense plots. Differences in plant diversity however, were explained by site factors rather than land use. Soils in the dense plots were the most acid but soil pH was significantly higher in thinned plots and pH was highest in soil of the un-colonised plots. Mean values for carbon, nitrogen, sulphur and extractable phosphorus varied among sites, although each were significantly more abundant in the mineral soil of dense and thinned plots compared with un-colonised plots, suggesting that thinning had had a minimal effect on the soil parameters assessed. Accounting for all site components, site carbon storage was significantly higher in dense and thinned plots compared with un-colonised plots due to elevated levels of soil and litter carbon as well as the presence of trees. The results indicate that thinning dense C. glaucophylla can maintain and (by some measures) improve site condition. However, given the variability in some of the parameters assessed, further study across a wider range of soil types and rainfall gradients is proposed.     

Disturbance regimes as determinants of seed banks in coastal dune vegetation of the southeastern Cape

Soil-stored seed banks of grassland, fynbos and thicket, all growing on calcareous dunes and each subject to different disturbance regimes, were examined. Seed banks were determined from counts of germinants from 50 soil cores from each type. Aboveground estimates of plant species cover in 10 1-m² plots were used in determining vegetation/seed bank similarities. There was no evidence for seed bank densities to be markedly higher in the most frequently disturbed community (grassland -4273 seeds/m²) than the least disturbed community (thicket - 3417 seeds/m²). Highest similarity between seed bank and above-ground vegetation composition in terms of species and growth form/life-span classes was recorded for grassland (CC = 50%). Lowest similarity (CC = 13%) was found in the less frequently disturbed thicket where no seeds of climax trees were recorded in the seed bank. A fynbos community on a north-facing (warm, dry) slope had intermediate-sized seed banks (1683 seeds/m²) with intermediate vegetation/seed bank similarity (CC = 46%). However, on the south-facing slope, which has a large post-fire ephemeral herb component, seed banks were larger (4518 seeds/m²) but less similar to above-ground vegetation (CC = 39%o). Ordination (DCA) of vegetation data from the four communities was different from an ordination of their seed bank data. Fynbos shrub species were absent from seed banks of both grassland and thicket, even though secondary succession proceeds from grassland, through fynbos to thicket. Their seed banks appear less persistent than those of European heath or Californian chaparral shrubs.     

Chemical composition of forest floor and consequences for nutrient availability after wildfire and harvesting in the boreal forest

In boreal forests of eastern Canada, wildfire has gradually been replaced by clearcut harvesting as the most extensive form of disturbance. Such a shift in disturbance may influence the chemical properties of the forest floor and its capacity to cycle and supply nutrients, with possible implications for forest productivity. We compared the effects of stem-only harvesting (SOH), whole-tree harvesting (WTH) and wildfire on the chemical composition of forest floor organic matter and nutrient availability for plants, 15–20 years after disturbance in boreal coniferous stands in Quebec (Canada). The forest floor on plots of wildfire origin was significantly enriched in aromatic forms of C with low solubility, whereas the forest floor from SOH and WTH plots was enriched with more soluble and labile C compounds. The forest floor of wildfire plots was also characterized by higher N concentration, but its high C:N and high concentration of ¹⁵N suggest that its N content could be recalcitrant and have a slow turnover rate. Total and exchangeable K were associated with easily degradable organic structures, whereas total and exchangeable Ca and Mg were positively correlated with the more recalcitrant forms of C. We suggest that the bulk of Ca and Mg cycling in the soil–plant system is inherited from the influx of exchangeable cations in the forest floor following disturbance. The buildup of Ca and Mg exchangeable reserves should be greater with wildfire than with harvesting, due to the sudden pulse of cation-rich ash and to the deposition of charred materials with high exchange capacity. This raises uncertainties about the long-term availability of Ca and Mg for plant uptake on harvested sites. In contrast, K availability should not be compromised by either harvesting or wildfire since it could be recycled rapidly through vegetation, litter and labile organic compounds.     

Variance components of the respiration rate and chemical characteristics of soil organic layers in Niepołomice Forest, Poland

Respiration rates and chemical characteristics of soil organic layers were measured at 40 experimental plots, 5 sampling sites per plot, in a moderately polluted Niepoomice Forest, S. Poland. The respiration rate was positively related to pH, water content and concentrations of Ca and K, and negatively to N_tot, Zn and Pb (p < 0.001 for all variables). No significant correlation was found between the respiration rate and Na, Cu or Cd (p > 0.25 in all cases). The regression model explained 73% of the total variance. Analysis of variance components revealed that ca. 35% of the total variance in the respiration rate can be explained by the vegetation types covering the area: oak-hornbeam vs. pine-oak forests. The next 40% was explained by the variability between sampling plots and the remaining 25% by within-plot variability among sampling sites. Similar results were obtained for water content. The variance in pH was split 30%:39%:31% between vegetation types:plots:sampling sites. No variance in Ca and Na was explained by the forest type, and approximately half of the variance was due to between-plot and half to within-plot variability. In contrast, potassium concentration differed between forest types (58% variance explained), more than 25% of total variance was due to between-plot variability and only 15% due to within-plot variability. For Zn the results were 1%, 66% and 33%, for Cu 0%, 38% and 62%, for Pb 48%, 18% and 34%, and for Cd 0%, 33% and 67%, respectively. The study clearly shows (1) substantial variance in some soil characteristics between sampling sites and (2) a different split of variance among spatial scales for different soil characteristics.     

The effect of fallow and continuous cultivation on the chemical and physical properties of an alfisol in western Nigeria

Summary Soil properties under continuous cropping were compared with those under planted fallows and natural bush regrowth for three years after forest clearing. The cropping treatments consisted of continuous maize with and without stover returned as surface mulch, continuous soybean, and maize and cassava intercropped. The fallow treatments included pigeon pea, leucaena, Guinea grass and natural bush regrowth.In the continuous soybean and unmulched maize plots, soil organic matter and pH declined rapidly; whereas the mulched maize plots maintained a soil organic matter level comparable to the fallow treatments. To maintain soil organic matter in the surface soil at a level comparable to soil under secondary forest, two to three applications of a total amount of 16 MT/ha/annum of dry plant materials (maize stover or grass) are required when the material is applied as surface mulch.In the cropped plots, favorable physical characteristics in the surface soil were also maintained when sufficient plant residue was returned; whereas the deterioration of subsoil structure of the forest soil occurred in all cropping treatments.Guinea grass fallow has a distinct advantage in recycling mineral nutrients and maintaining soil physical properties and organic matter. It is suggested that soils may be planted with a combination of Guinea grass and pigeon pea fallow for one or two years after three or four years of arable cultivation.IITA Journal Paper No. 65 IITA Journal Paper No. 65     

Changes in nutrient distribution in forests and soils of Walker Branch watershed,Tennessee, over an eleven-year period

Changes in vegetation, litter, and soil nutrient content were measured in selected plots on Walker Branch watershed, Tennessee, from 1972–73 to 1982. The watershed has been allowed to revert to forest since 1942, before which it consisted of small subsistence farms and woodland pastures. Changes in Ca status were of particular interest because initial nutrient cycling characterizations indicated that net Ca accumulation in vegetation could have caused large decreases in soil exchangeable Ca²⁺ within 20 years.Decreases in forest floor and subsoil (45–60 cm) N, exchangeable Ca²⁺, and Mg²⁺ content were noted in several plots from 1972 to 1982. Surface soils (0–15 cm) showed either no change or, in some cases (e.g., N and exchangeable K⁺ in certain plots), increases over the 11-year period. Reductions in forest floor and subsoil exchangeable Ca²⁺ and exchangeable Mg²⁺ on cherty, upper slope oak-hickory and chestnut oak forests were most striking. The changes in Ca²⁺ are thought to be due primarily to high rates of Ca²⁺ incorporation into woody tissues of oak and hickory species. Reductions in forest floor and subsoil exchangeable Mg²⁺ could not be accounted for by woody increment; leaching may have played a major role in causing these decreases. Changes in P and exchangeable K⁺ were variable, with both increases and decreases.There were significant increases in exchangeable Al³⁺ in both subsoils and surface soils of certain plots, but these were not accompanied by decreases in exchangeable base cations or consistent decreases in pH. Dissolution of interlayer Al from 2:1 clays may be the cause of the exchangeable Al³⁺ increases.These results suggest a general decline in fertility, especially with regard to Ca and Mg in those forests with low soil Ca and Mg supplies. Monitoring of further changes (if any) in these ecosystems will continue as the currently aggrading forests approach steady state.     

Vegetation of tuscan ultramafic soils in relation to edaphic and physical factors

Vegetation and soil sampling were carried out in 80 plots located in five different ultramafic (serpentine) sites of Tuscany, central Italy. The physical and chemical features of each plot were determined and the species composition and cover recorded. The exchangeable fraction of soil metals was analysed because it gives a measure of their concentrations available to plants. The plots were classified by cluster analysis and ANOVA was used to compare the environmental variables of the groups of plots. Canonical correspondence analysis was used to detect the principal factors for gradients of species composition within the plant communities. A higher content of exchangeable metals was found under the more evolved and structured plant communities, suggesting that serpentine vegetation of Tuscany is not strongly limited by soil metals, such as chromium, cobalt, nickel and magnesium, typically associated with ultramafic soils. The low nutrient content of the soils and drought stress mainly due to topographical features, appear to have a more significant role in determining the typical scattered vegetation of the Tuscan ultramafics.     

Vegetation succession after fire in sclerophyll woodland communities in south-eastern Australia

The dynamics of vegetation regeneration after burning were examined in three dry sclerophyll communities near Canberra, in south-eastern Australia. Changes in seedling and regrowth populations were followed in permanent quadrats during the first two years after burning, compared with both the preburn vegetation and population changes over the same period in adjacent, unburnt plots. All species represented either by living plants in the tree and shrub strata and/or by seed in the soil and litter prior to burning regenerated during the first year after the fire treatments. No new species invaded the areas after burning. Species varied in their regenerative strategy and recovered after the fires either by germination of seed residual in the soil and ash or released from trees after burning, by regrowth from surviving vegetative organs, or by a combination of germination and regrowth. Both seedling input and the vegetative recovery of populations were higher during the first than second year after burning. The vegetative multiplication and seed gertnination of many species were stimulated by fire. It was concluded that the regeneration of the communities studied, as well as the post-fire recovery of numerous different communities reported in the literature, closely resembled an initial floristic composition model. It is considered that the process of vegetation redevelopment after a disturbance (i.e. secondary succession) will be influenced greatly by the species composition at the time of disturbance, and by the type of disturbing agent. A single model would not be expected to adequately describe secondary succession following disturbance by agents imposing different stress conditions on a community.     

Effects of P,K, and liming on soil pH,Al, Mn,K, and forage barley dry matter yield and quality for a newly-cleared Cryorthod

Forage barley dry matter yield and quality, as well as soil pH, Al, and Mn were monitored in response to P, K, and lime application on a newly cleared Typic Cryorthod (Orthid Podzol). The overall yearly yield level was affected by precipitation. Without liming soil acidification occurred after three years of production. The liming rate of 2.2 Mg.ha⁻¹ was found optimal for maintaining initial pH levels (5.66) and increasing forage barley yields. It was also found optimum for K and P utilization for these first years of production. Soil pH dropped an average of 0.33 units over the three years on unlimed P plots and 0.46 units over 4 years on K plots. Phosphorus and K fertilization increased N utilization and resulted in decreased soil acidification. Phosphorus availability was greater in the first year of cropping than in subsequent years, this was likely due to the effects of higher available moisture, liming release of native P, and effects of initial fertilization. There was a 148% increase in total dry matter yield and an 85% increase in protein yield of forage barley with P application. Liming increased total forage barley yields an average of 69% and total protein yields 48%. Reduced barley yields in unlimed plots were due to low soil pH. After two years of cultivation, unlimed plots contained exchangeable Al and soluble Mn levels reported toxic for other soils. The higher liming rates of 4.4 and 6.6 Mg.ha⁻¹ reduced soluble Mn to near critically low levels. soil Al and Mn were highly correlated to pH. Soil exchangeable Al, Mn, and soluble Mn along with tissue Al were inversely correlated to percentage yield. The average yield respone to three levels of applied K, increased from zero initially to 67% by the fourth year. Total dry-matter production increased 32% and total protein yield increased an average of 32% and total protein yield increased an average of 15% with K fertilization over four years. About 60% of the yield response occurred between the 0 and 22kg K.ha⁻¹ rates. Initial soil exchangeable K levels were not maintained even at the highest 66kg K.ha⁻¹ treatment. Soil exchangeable Al and soluble Mn were elevated with dropping pH. Soil K reserves and resupply of exchangeable K in these soils over the long term will be an important factor in crop production.     

皖南黟县次生灌草丛生物量的研究

本文对地处中亚热带的安徽黟县次生灌丛和灌草丛以及常绿阔叶幼林共9个样地的生物量进行了研究。结果表明:黟县常绿阔叶幼林、次生灌丛和灌草丛的地上部分为81.74、16.83和5.28t/ha。所调查的5个群落类型的地上部分生物量和生产力可回归成线性方程Y=3.88+0.14X,净生产力随生物量的增加而提高。     

Air humidity,soil moisture and soil chemistry as determinants of the herb layer composition in European beech forests

Question: What role does air humidity play as an environmental factor for the abundance and distribution of temperate woodland herbs? Location: Beech forests on calcareous soils in southern lower Saxony, central Germany. Methods: The abundance of woodland herb species and total herb cover were investigated in 60 plots with contrasting exposure, slope angle and relief type. On all plots, air humidity, air temperature, soil moisture, photosynthetically active radiation, pH (H₂O) and concentration of salt‐exchangeable Ca, Mg and K were measured. Species‐environment relationships were analysed with multiple regression analysis and CCA. Results: Air humidity (RH), soil moisture and the concentration of exchangeable Ca and K, but not light, C/N ratio and the concentration of exchangeable Mg were identified as the most important abiotic factors influencing the cover of the most abundant plant species and total herb cover. RH varied substantially across the different forest floor site types and influenced species abundance independent of soil moisture. In several species (including Mercurialis perennis and Impatiens noli‐tangere), RH was found to be a key environmental factor. Other species such as Aegopodium podagraria and Lamiastrum galeobdolon depended more on elevated soil moisture, while RH was less important. Conclusions: This study showed that the distribution of widespread temperate woodland herb species depends on high air humidity, and that certain sensitive species do not occur at sites with reduced air humidity even though soil moisture is high. Thus, high air humidity and ample soil moisture are key abiotic factors in beech forests on calcareous soils. Shade level (PAR) was found to be of secondary importance.     

滨海盐沼湿地植被净初级生产力变化对土壤因子的响应

以辽河三角洲滨海盐沼湿地为研究区,基于遥感数据、气象数据、野外调查和实验室分析数据,采用CASA模型模拟并分析该区域植被净初级生产力（Net Primary Productivity,NPP）的变化特征,利用统计分析方法定量分析土壤因子对植被NPP的影响。结果表明：（1）研究区植被NPP空间分异显著,区域变异系数为43.71%,且同种植被类型内部NPP也变化显著;（2）N、P和K对芦苇NPP的限制形式是协同限制,且随土壤电导率的增加呈抛物线形式,因子敏感性从大到小依次为K、P和N;营养限制程度从大到小依次为K、N和P;（3）土壤水盐对芦苇NPP的影响也基本符合抛物线模式,芦苇NPP对土壤电导率的敏感性和土壤电导率对芦苇NPP的影响程度都大于土壤含水量,且土壤含水量越高,芦苇NPP对土壤电导率的敏感性越低。本文最终得出只有各土壤因子达到组合最优时,芦苇NPP才最大,这对滨海盐沼湿地植被的管理和保护具有重要意义。     

Sensitivity of Soil Restoration Indicators during Páramo Succession in the High Tropical Andes: Chronosequence and Permanent Plot Approaches

The aim of this study was to analyze indicators of soil restoration during secondary succession in a heterogeneous valley in the high tropical Andes. A combination of chronosequence and permanent plot methods was used to detect changes in this heterogeneous matrix. Thirty-six plots with different fallow times (1–9 years) and four noncultivated plots with natural vegetation (páramo) were sampled twice in a 3-year interval (1996 and 1999). The following soil properties were determined: total C and N, pH, exchangeable bases, cation exchange capacity, and microbial biomass N (MB-N). Using the chronosequence approach, successional increases in soil pH and Mg were detected, pointing to these variables as indicators of soil restoration during the fallow period. Comparing the noncultivated páramo with the fallow plots, a significant decrease in MB-N was found, suggesting that this is a sensitive agricultural disturbance indicator. The permanent plot analysis failed to detect successional trends in any of the study variables, probably as a result of a lack of sensitivity of the indicators used within the 3-year interval. Nevertheless, a strong acidification was detected by the permanent plot method when fallow plots were cultivated. We conclude that the size of important soil components such as total soil organic matter or microbial biomass is not a sensitive soil restoration indicator in these heterogeneous mountain systems but that other integrative variables such as pH could be more sensitive to successional changes in key soil processes (e.g., nitrification or nutrient losses).     

A comparison of fynbos and non-fynbos coenoclines in the lower Gamtoos River Valley,southeastern Cape,South Africa

Patterns in the relative importance of structural attributes and growth forms along fynbos and non-fynbos coenoclines were studied to test the hypothesis that there would be less structural variation in the former because the overriding influence of low levels of soil nutrients would be manifest in a great deal of structural convergence in fynbos. The coenoclines were ranged along identical environmental gradients of increasing altitude, rainfall and soil moisture and decreasing climatic variability. Results showed that along the entire fynbos coenocline vegetation was structurally a small-leaved sclerophyllous shrubland with a graminoid understorey and, usually, a large-leaved (proteoid) shrub overstorey. Fynbos structure was interpreted largely as a response to low levels of soil nutrients. Non-fynbos vegetation ranged from mixed succulent-sclerophyllous and spiny large-leaved thicket at lower altitudes to tall mesic forest at the upper end of the gradient. Non-fynbos structure was explained in terms of variations in soil moisture and climate. An analysis of the biogeographical affinities of sample floras at sites along the coenoclines showed that fynbos vegetation was dominated by taxa endemic to the Cape phytochorion, although phytochorological mixing was pronounced at the lower altitude sites. The level of local endemism in the fynbos coenocline was relatively high; nearly all endemics were Cape fynbos taxa and their incidence increased with increasing altitude. These data indicate that fynbos vegetation has had a lengthy history in the southeastern Cape and that high altitude sites would have comprised a refuge for Cape taxa during unfavourable climatic periods. Non-fynbos vegetation ranged from dry subtropical Tongaland-Pondoland thicket with a strong Karoo-Namib component to temperate Afromontane forest. Levels of endemism were lower than the fynbos coenocline and decreased with increasing altitude. The high number of karroid endemics found in both coenoclines at low altitudes suggests that karroid vegetation would have been more widespread in the past, probably during the last glacial which was considerably drier than the present Holocene interglacial.