Fire and other variables as determinants of forest/fynbos boundaries in the Cape Province

Abstract. Forests in the southwestern Cape are restricted to sheltered stream banks and patches of rock scree owing to protection from recurrent fire and the more favourable soil moisture conditions in these habitats. The effects of a prescribed burn on 17 March 1987 on the forest / fynbos boundaries in the Swartboskloof catchment are described. No evidence of erosion of the forest edge was recorded, although this could be ascribed to the low intensity of the fire. Soil properties, primarily pH and aluminium and available phosphorus levels, differed markedly between forest and fynbos. It is argued, however, that this is a result, not a cause of vegetation change. Light extinction levels and soil moisture availability after the fire were lower in the fynbos than in the forest, and are considered to preclude incursions of forest species into fynbos of a low post-fire age.     

广东南澳岛植被恢复过程中的群落动态研究

 以广东南澳岛的1个草坡、4个人工林和3个次生林群落为对象,采用时空互代的方法,将这8个群落当作植被恢复中的不同阶段,研究各群落的群落结构、生物量、叶面积指数和土壤养分等,进而研究了南澳岛退化生态系统植被恢复的过程和机理。随着植被的恢复进程,群落的阳性种类逐渐减少,中生性种类逐渐增加。物种多样性、均匀度、生态优势度和β多样性指数分析表明南澳岛植被恢复过程群落组成结构的复杂性依退化草坡→人工林→次生林逐渐增加。南澳岛退化草坡、10年生人工林、15年生人工林和次生林的生物量分别为4.81t·hm-2、45.18t·hm-2、100.39t·hm-2和88.34t·hm-2,叶面积指数分别为1.04、3.81、5.89和6.52,凋落物贮量分别为0.42t·hm-2、3.20t·hm-2、3.70t·hm-2和4.90t·hm-2。南澳岛植被恢复过程中土壤有机质、全氮和速效磷和交换性K含量逐渐增加。由于海岛的生境、大风和暴雨的影响,海岛植被恢复的格局不同于大陆,而其恢复速度也较慢。根据本研究结果,提出了人工促进海岛植被恢复的途径。     

Acceleration of vegetation succession on eroded land by reforestation in a subtropical zone

Based on field investigations in the East River basin in Guangdong Province, south China, the processes of vegetation development and vegetation succession on bare slopes with high erosion rates are studied. Different reforestation measures have been applied to the slopes, which have resulted in very different processes of vegetation development and succession. On an experimental plot with burned forest but surviving roots, the vegetation restored naturally and quickly because there was little soil erosion. However, in the plots suffering from long-term severe soil erosion, natural vegetation recovery on these barren slopes is very slow. After 26 years, a barren slope has only been partly colonized by poorly developed vegetation composed of heliophilous herbages and scattered shrubs. On the other hand, plantation of some selected wood species on the slope land has dramatically accelerated the vegetation recovery and succession. The plots were reforested with plantation of Acacia auriculiformis in the early 1980s. Twelve years later, the vegetation cover of the artificial forests reached 90% and an understory vegetation community consisting of local species had naturally developed. Reforestation with suitable strategies may control erosion and greatly accelerate vegetation succession in the eroded slope land in the subtropical zones.     

浦东滩涂中型土壤动物群落结构及土质酸碱度生物评价分析

1999年,对上海浦东滩涂4类不同酸碱度土壤中的中型土壤动物进行了调查。应用物种丰富度,个体数多度,多样性指数和均匀度4个群落参数,并结合种类研究,讨论了土壤动物群落结构与不同酸碱度土壤的关系。结果表明,土壤中弹尾目和蜱螨目对不同酸碱度土壤反应敏感。弹尾目的3个群落参数和蜱螨目的4个参数均很好地反映与土壤反应敏感。弹尾目的3个群落参数和蜱螨目的4个参数均很好地反映与土壤pH的关系,相关系数分别在0．9以上和0．85左右,在pH相差较大的情况下,可以区分不同酸碱度的土壤。弹尾目的符Tao(Paranura sp.)可用于评价酸碱度较接近的土壤,球角Tao(Hypogastrura sp.）可用于评价酸碱度相差较大,高pH或环境条件较恶劣的土壤。     

Factors causing spatial heterogeneity in soil properties, plant cover, and soil fauna in a non-reclaimed post-mining site

This study explored processes responsible for environmental heterogeneity at a man-made post-mining landscape formed by heaping of homogeneous overburden in longitudinal “waves”. Soil chemistry (pH; conductivity; total C; total, available, and water-soluble P; and available K, Na, and Ca), the distribution of woody and herbaceous plants, litter quantity, and the distribution of soil fauna were studied along a100-m transect. Heterogeneity between waves was very low, and only available P and biomass of herbaceous plants differed among waves. In contrast, all investigated parameters except of total and available P and fauna density differed among position inside waves. Woody plants were more numerous on the wave tops and slopes than on the bottoms. Distribution of shrubs between waves affect between-waves distribution of other parameters, namely soil C_ox, as waves with more shrubs have larger litter input and more soil carbon.     

黄土高原森林草原区退耕地植被自然恢复与土壤养分变化

研究了黄土高原森林草原区退耕地植被自然恢复过程与土壤养分变化.结果表明,在显域生境下,植被自然演替过程虽然趋向于该区原有植物群落类型,但经过40～0年的时间,仍未形成灌丛或稀树等群落,分布较多的仍是长芒草、铁杆蒿、白羊草、大针茅和达乌里胡枝子等群落类型.从植被恢复时间对土壤养分变化的影响来看,除全P外(P＞0.0),有机质、全N、速效氮、速效钾的变化极显著(P＜0.001),速效磷变化较显著(0.0＜P＜0.01),并随植被恢复时间的延长而呈增加趋势.除恢复时间外,养分含量变化也随土壤剖面深度而变化,其中除全P含量变化较显著外(P＜0.0),其余各养分含量变化都达极显著水平(P＜0.001).土壤养分变化具有明显的表聚性.相关分析表明,土壤有机质、全N、有效氮与速效钾相互间相关极显著(P＜0.001),而与全P与速效磷相关性不明显(P＞0.0),全P与速效磷二者相关性也不明显(P＞0.0).     

植被砍伐对土壤养分的影响

研究了不同砍伐频率下,香港、深圳和鹤山研究样地山坡地Ｎ、Ｐ、Ｋ含量的差异．不同采样地之间,养分全量和有效量差异显著．在尚未砍伐的山坡地,土壤养分含量显著高于经常砍伐的山坡地．未伐土壤的Ｎ含量顺序为香港样地＞深圳样地＞鹤山样地．下层土壤Ｐ的含量高于上层土壤．深圳样地常代土壤养分含量高于鹤山．结果建议采用最适砍伐频率和在最适季节砍伐,以便减少砍伐产生的不利影响．     

Vegetation study as a generator for population biological and physiological research on salt marshes

The paper deals with some views on the phytocoenose in relation to the functioning of vegetation and its plant-species populations in space and time. From these viewpoints the study of vegetation is seen as a field of tension between the organismic and reductionistic approaches. Both have their value, provided any dogmatism is avoided and either can be applied to the other.In the field of vegetation structure characteristic features of life-form spectra and species distribution, inversion phenomena in zonation, and community architecture in relation to production and decomposition are discussed. In this connection some remarks are made on habitat and niche differentiation with respect to the phytocoenose concept.Vegetation dynamics are discussed in relation to the introduction of Spartina anglica, the frequency of flooding by the tides, different environmental disturbances caused by heavy winter frost, rainfall and hot and dry periods, as well as to human interferences for agricultural and civil-technical purposes.It is suggested that salt-marsh plants may have found refuge areas in inland habitats as well as on more southerly coastal sites during glaciations.Nomenclature follows Tutin et al. (1964–1980).The author wishes to thank his collaborators Messrs B. P. Koutstaal and W. de Munck for much fieldwork, and Mrs M. J. van Leerdam-de Dreu and Messrs A. A. Bolsius and J. A. van den Ende for the preparation of text and figures.Communication No. 302 of the Delta Institute for Hydrobiological Research.     

Spatial variation in vegetation structure coupled to plant available water determined by two-dimensional soil resistivity profiling in a Brazilian savanna

Tropical savannas commonly exhibit large spatial heterogeneity in vegetation structure. Fine-scale patterns of soil moisture, particularly in the deeper soil layers, have not been well investigated as factors possibly influencing vegetation patterns in savannas. Here we investigate the role of soil water availability and heterogeneity related to vegetation structure in an area of the Brazilian savanna (Cerrado). Our objective was to determine whether horizontal spatial variations of soil water are coupled with patterns of vegetation structure across tens of meters. We applied a novel methodological approach to convert soil electrical resistivity measurements along three 275-m transects to volumetric water content and then to estimates of plant available water (PAW). Structural attributes of the woody vegetation, including plant position, height, basal circumference, crown dimensions, and leaf area index, were surveyed within twenty-two 100-m² plots along the same transects, where no obvious vegetation gradients had been apparent. Spatial heterogeneity was evaluated through measurements of spatial autocorrelation in both PAW and vegetation structure. Comparisons with null models suggest that plants were randomly distributed over the transect with the greatest mean PAW and lowest PAW heterogeneity, and clustered in the driest and most heterogeneous transect. Plant density was positively related with PAW in the top 4 m of soil. The density-dependent vegetation attributes that are related to plot biomass, such as sum of tree heights per plot, exhibited spatial variation patterns that were remarkably similar to spatial variation of PAW in the top 4 m of soil. For PAW below 4 m depth, mean vegetation attributes, such as mean height, were negatively correlated with PAW, suggesting greater water uptake from the deep soil by plants of larger stature. These results are consistent with PAW heterogeneity being an important structuring factor in the plant distribution at the scale of tens of meters in this ecosystem.     

Vegetation succession at the abandoned Ogushi sulfur mine, central Japan

We surveyed plant community development at the abandoned Ogushi sulfur mine. We found seven communities dominated by the following respective species: Deschampsia flexuosa, Miscanthus sinensis, shrub willow, Gaultheria miqueliana–Betula ermanii, Sasa senanensis–Betula ermanii, willow–Betula ermanii, and Sasa kurilensis–Abies veitchii. We examined the succession of these communities, in which younger communities of low height and ground cover contained seedlings of the successive communities that were taller and had higher ground cover. To understand the development of these different communities, we surveyed damage from mining pollution and effects of immature soils formed by landslides. The average pH (H₂O) was 4.12, and aluminum concentrations were not sufficiently high to damage plant growth, except in areas where sulfur had been mined. The organic carbon and nitrogen content in soil samples were very low because of a delay in soil development caused by a large landslide in 1937. Hence, succession was positively correlated with the soil development stage. The delay in soil development after a large landslide influenced the seven successional steps of the plant communities, but mineral poisons at the abandoned Ogushi sulfur mine had no effect on succession.     

Spatial structure of genetic variation and primary succession in the pioneer tree species Antirhea borbonica on La Réunion

In habitats where colonization and extinction are recurrent, the distribution of gene frequencies among patches of suitable habitat may reflect the age structure of different populations. In this study, we quantify population genetic structure for a pioneer tree species, Antirhea borbonica, in a chrono-sequence of primary succession on the lava flows of the Piton de La Fournaise volcano (La Réunion). Using microsatellite loci and amplified fragment length polymorphism (AFLP) markers, we quantified genetic variation within and among populations for early- and late-succession populations in a landscape where extinction and recolonization are recurrent (the ‘Grand Brûlé’) and for late-succession populations in a more stable landscape. This study produced three main results. First, we detected no evidence that founder events increase genetic differentiation among colonizing populations; F_ST values among early- and among late-succession populations were similar. Second, we found no evidence for isolation by distance; genetic distance was not correlated with spatial distance within and among populations. Third, F_IS values are consistently high in all populations, despite the fact that A. borbonica populations are functionally close to dioecy and thus expected to have an outcrossing mating system. Multiple colonization events from different sources may limit differentiation among young populations and spatial isolation may enhance differentiation among late-succession populations. Ecological processes acting during colonization may create the conditions for spatial aggregation within pioneer populations, and thus contribute to the high F_IS values.     

广西木论喀斯特森林土壤养分水平与植被及地形的关系

研究了广西木论喀斯特森林原生植被和次生植被的土壤养分特征,测定了陡坡、缓坡、洼地3种主要地形内林地0～5 cm表层土壤中的有机质(SOM)、氮、磷、钾含量,以及它们在石土面、土面两类主要小生境间的差异.结果表明:林分成熟度高、优势种不明显的原生林积累了高水平的SOM,缓坡石土面最高,达345 g kg-1,洼地的含量较低,但仍在80 g kg-1以上;土壤全氮(TN)、碱解氮(AN)含量也较高.以红背山麻杆(Alchornea trewioides)、广西野桐(Mallotus conspuyrcatus)、伞花木(Eurycorymbus cavderiei)等为优势种的次生林,物种多样性较原生林低,SOM、TN、AN含量也低,缓坡石土面和土面小生境的SOM分别为110 g kg-1和77 g kg-1,是原生林的32%和35%,下降幅度最大,其次为陡坡,而洼地的差异不明显.全磷(TP)、有效磷(AP)、全钾(TK)、有效钾(AK)含量在两林型间差异无明显规律.原生林和次生林土壤养分含量(除TK外)以缓坡>陡坡>洼地;但次生林中三者间无显著差异.同类型样地内小生境土壤养分含量(除TK外)均为石土面含量高于土面.     

太行山区不同植被群落土壤微生物学特征变化

为评价太行山区不同植被群落土壤微生物学特征,比较分析了针阔混交林、针叶混交林、针叶纯林、落叶阔叶纯林、灌丛和裸露地6种不同植被群落中的土壤微生物区系、微生物生物量和呼吸强度等指标的变化.结果表明,6种不同植被群落土壤中的微生物学特征存在较大差异. 灌丛地在微生物数量和微生物生物量两项指标中均为最高,其余植被群落在这两项指标中的顺序从大到小依次为落叶阔叶纯林＞针阔混交林＞针叶纯林＞针叶混交林＞裸地,土壤呼吸强度也有相似的变化趋势.在进行退化山地的植被恢复时,应充分重视生态系统的自然恢复能力.     

Dynamic and static views of succession: Testing the descriptive power of the chronosequence approach

Chronosequence and permanent plot studies are the two most common methods for evaluating successional dynamics in plant communities. We combined these two approaches by re-sampling an old-field chronosequence at Cedar Creek Natural History Area (Minnesota, USA) to: (1) measure rates of secondary succession; and (2) to test the ability of the chronosequence approach to predict actual successional dynamics over a 14-year survey interval. For each of 19 chronosequence fields we calculated four complimentary indices of succession rate for community changes that actually occurred within each of these fields between 1983 and 1997. We found that measures of compositional dissimilarity, species turnover, and the change rates of perennial and native species cover over this 14-year period were all negatively correlated with field age, indicating that the rate of successional change in these old-fields generally declines over time. We also found that data collected from the initial static chronosequence survey (1983) accurately predicted many of the observed changes in species abundance that occurred between 1983 and 1997, but was a poor predictor of changes in species richness. In general, chronosequence re-sampling confirmed the validity of using the chronosequence approach to infer basic patterns of successional change.     

菠萝-甘蔗轮作的土壤生态效应

通过2000～2002年进行菠萝-甘蔗轮作田间试验,研究了菠萝、甘蔗轮作对甘蔗土壤生态的影响。结果表明：菠萝甘蔗轮作田与甘蔗连作田比较,能明显地改善土壤的通气和蓄水性,加速速效性养分的释放;增强土壤酶活性;增加土壤微生物总量(一般好气性细菌、真菌、放线菌);有益的氨化细菌和硝化细菌成倍增加,而无益的厌氧性细菌、反硝化细菌则受到抑制;固氮菌数量小且变化不大。菠萝-甘蔗轮作对甘蔗土壤生态环境的改善其实质在于：菠萝、甘蔗轮作后,由于其作物种类的不同导致土壤结构的改善和土壤微生物种类和数量增多,土壤生物活性增强,并导致土壤速效养分的增加。