Role reversal in the stand dynamics of an angiosperm–conifer forest: Colonising angiosperms precede a shade-tolerant conifer in Afrotemperate forest

In mixed angiosperm–conifer forests worldwide, infrequent landscape-level catastrophic disturbances create a mosaic of persistent and different aged forest stands in the landscape with varying levels of dominance by the conifer component. In the ‘temporal stand replacement model’ (TSRM), disturbance creates conditions favouring a colonising cohort that is replaced by a suite of relatively shade-tolerant canopy species, which establish following the synchronous senescence of the pioneer canopy. In most southern hemisphere mixed angiosperm–conifer forests, with the exception of those in southern Africa, the establishing cohort is usually a large and very long-lived (550–650 years) conifer that is gradually replaced by angiosperms. As an explanation of the apparent dominance of the conifer Podocarpus latifolius, we examine the efficacy of the TSRM in mixed Afrotemperate forests where the establishing cohort is not a conifer. Forest succession in Afrotemperate forests was deterministic with the successive replacement of species determined first by their establishment success in shaded environments, and second, by their relative longevity. Several angiosperm species that were common canopy dominants established a pioneer cohort but were gradually replaced by P. latifolius, a shade-tolerant species. Continuous regeneration beneath the angiosperm canopy by P. latifolius eliminates synchronous canopy senescence, a key feature of the TSRM, as a mechanism driving the temporal replacement of canopy species. Senescing angiosperms created canopy gaps that were colonised by grasses and ferns, which suppressed canopy tree regeneration. In contrast, with continuous regeneration beneath the shaded canopy, P. latifolius gains a critical advantage over angiosperms at gap formation. Thus, in the absence of fairly large-scale natural disturbances, conifers come to dominate Afrotemperate forests. Commensurate with the latter, conifers in Podocarpus-forest were dated to approximately 320 years, more than 100 years older than the oldest P. latifolius in angiosperm-dominated forest. Tree life-history differences (shade tolerance, longevity) and the time since disturbance drive successional change from an angiosperm-dominated system to a stage dominated by P. latifolius. In general, the TSRM is a plausible explanation for the observed canopy tree structure and dynamics in mixed Afrotemperate forests. South African Afrotemperate forest is unusual among other southern hemisphere mixed angiosperm–conifer forests in that a suite of angiosperm canopy species, rather than a single conifer species, forms the colonising cohort.     

Modelling soil organic carbon turnover in improved fallows in eastern Zambia using the RothC-26.3 model

Scarcity of simple and reliable methods of estimating soil organic carbon (SOC) turnover and lack of data from long-term experiments make it difficult to estimate attainable soil C sequestration in tropical improved fallows. Testing and validating existing and widely used SOC models would help to determine attainable C storage in fallows. The Rothamsted C (RothC) model, therefore, was tested using empirical data from improved fallows at Msekera in eastern Zambia. This study (i) determined the effects of nitrogen fixing tree (NFT) species on aboveground organic C inputs to the soil and SOC stocks, (ii) estimated annual net organic C inputs to the soil using the RothC, and (iii) tested the performance of RothC model using empirical data from improved fallows. Soil samples (0–20 cm) were collected from coppicing and non-coppicing fallow experiments in October 2002 for determination of SOC by LECO CHN-1000 analyser. Data on surface litter, maize and weed biomasses, and on weather, were supplied by the Zambia/ICRAF Agroforestry Project. Measured SOC stocks to 20 cm depth ranged from 32.2 to 37.8 t ha⁻¹ in coppicing fallows and 29.5 to 30.1 t ha⁻¹ in non-coppicing fallows compared to 22.2–26.2 t ha⁻¹ in maize monoculture systems. Coppicing fallows accumulated more SOC (680–1150 g m⁻² year⁻¹) than non-coppicing fallows (410–789 g m⁻² year⁻¹). While treatments with NFTs accumulated more SOC than NFT-free systems, SOC stocks increased with increasing tree biomass production and tree rotation. For food security and C sequestration, coppicing fallows are a potentially viable option.     

特殊立地条件——铺装条件下的植物种植

园林植物经常种植在某些特殊的地方,特殊的种植条件或者限制植物当前的生长,或者植物的生长引起某些特殊的问题。作者论述了铺装地面上栽植树木的特点和技术,以及影响根系与铺装之间冲突的原因并设计了解决方法;回顾了国内外一些景观状况,对以后铺装下的植物种植提出了建议。     

林木非生物胁迫抗性基因工程研究进展

干旱、极端温度和盐害等非生物胁迫因子是制约林木生长的重要因素。由于林木生长周期长, 且抗逆机制极为复杂, 长期以来, 如何改良林木对非生物胁迫的抗性一直是育种学家的难题。然而, 随着基因工程技术的发展, 人们可以在基因水平上改造林木, 提高其抗逆能力。文中主要介绍了林木抗逆基因工程的研究进展, 探讨了目前基因工程技术应用于林木抗逆育种研究存在的问题, 并对其应用前景进行了展望。     

河南新县古树名木资源评价及保护

新县境内现存古树名木资源16科26属28种,计3349株,为河南省古树资源较丰富的县;在分析评价该县古树名木资源的基础上,提出科学保护的建议。     

张家口市园林树木害虫危害规律与防治对策

为全面了解张家口市区园林树木害虫的种类、分布及其危害规律,给防治提供理论依据,作者采用踏查和标准地调查的方法对张家口市区内主要街道、公园及城郊周边绿化的园林树木害虫进行了全面调查。结果表明,张家口园林树林害虫群落共有5个目20个科38种,优势种集中于天牛、蚧虫、卷叶蛾等类群及天幕毛虫、舞毒蛾等。并对不同类群的害虫提出了综合防治对策。     

Effects of previous forest types and site conditions on species composition and abundance of naturally regenerated trees in young <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> plantations in northern Japan

Naturally regenerated trees in young Cryptomeria japonica plantations were investigated in 141 quadrats of 10 × 50 m within a watershed of 1,000 ha, and factors affecting their composition and abundance were examined. The species composition of naturally regenerated trees was classified into four types. Dominant species were Swida controversa, Magnolia hypoleuca and Pterocarya rhoifolia in Type A1, Betula maximowicziana, M. hypoleuca, Quercus crispula and Castanea crenata in Type A2, Q. serrata and C. crenata in Type B1, and Pinus densiflora in Type B2. The results of path analysis showed significant influences of previous forest type and geology among the factors that correlated with the species composition of naturally regenerated trees; previous forest type in particular showed a higher absolute path coefficient value. Species composition types of naturally regenerated trees corresponded to the previous forest types: Types (A1 and A2) corresponded to the natural forests composed of Thujopsis dolabrata var. hondai, Fagus crenata, Aesculus turbinata, etc., Type B1 corresponded to the secondary Q. crispula and Q. serrata forest, and Type B2 corresponded to the secondary P. densiflora forest, respectively. The abundance of naturally regenerated trees was strongly affected by geology; i.e., plantations on soft-sedimentary dacitic tuff contained great amounts of colonizing P. densiflora trees.     

Effect of wide spacing on tree growth, branch and sapwood properties of young Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] in south-western Germany

The influence of stand density on Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] is conceptually understood, but for wide spacings not well quantified, particularly in Europe. This study used 41 trees from 7 different locations in south-western Germany to compare important tree- and branch-level attributes across three different densities, namely 100, 200, and 1,200 stems ha⁻¹. In general, there were only a few tree and branch attributes that were significantly different between the 100 and 200 ha⁻¹ densities. Crown projection area and diameter of the thickest branches were the most important differences between the 100 and 200 ha⁻¹ densities. The most obvious and significant differences in this study were between 100 and 1,200 ha⁻¹ densities, where nearly every examined tree and branch attributes were statistically significant. However, relative sapwood area, the number of branches, branch angle, and the occurrence of spike knots were insensitive to stand density. Although the two lowest stand densities in this study represent rather extremely wide spacings, these results still have important implications for the development of effective thinning regimes for Douglas-fir in south-western Germany. Important management recommendations from this study include thinned stands should be maintained to at least 200 stems ha⁻¹ to maintain high log quality and stand stability. Furthermore, even at stand densities exceeding more than 1,200 trees ha⁻¹ planted trees, artificial pruning may even be necessary to produce high quality logs.     

毛竹纯林留养阔叶树后土壤理化性质的研究

对闽侯县荆溪镇仁洲村毛竹纯林留养阔叶树林与毛竹纯林的土壤理化性质的分析研究结果表明：毛竹留养阔叶树后,土壤容重、毛管持水量、总孔隙度及非毛管孔隙度等物理性状都得到了改良;林地土壤有机质含量增加,土壤全氮、水解氮及有效磷等养分指标普遍比毛竹纯林土壤高。由此可知毛竹留养阔叶树能更好的培肥土壤,提高林分水源涵养力,改善土壤的理化性质。     

古茶树体内的寄生虫——金针虫

金针虫是叩甲幼虫的通称,广泛分布于世界各地,为害农作物、林木、中药材、牧草等,是一类重要的害虫.文章报道了金针虫在云南无量山为害古茶树的案例,介绍了金针虫的形态特征、为害及生活习性、防治措施等内容,供广大茶树植保工作者和茶农参考.