红河州老阴山天然林下植被组成及生物多样性

通过对云南省红河州老阴山5种在天然林栽培条件影响下产生的次生植被树种的森林种类、盖度、密度分布等方面进行作了全面调查,采用Shannon-Wiener指数、Simpson指数、Pielou指数等森林生物多样性指数，将结合植被物种资源总丰度来研究现有5种植被类型和天然林植被群落类型模式下的植被物种数量分布组成、演化方式规律和森林种群植物资源分布多样性。研究发现线柏林的林下植被生物种群及其多样性物种含量分布最为全面丰富；草本植物的物种类型中则以禾本科植物种类最多,其次的类型为蔷薇科；林下生物多样性指数的主要因子为地表干扰；通过回归分析和生长痕迹发现同一水热条件下，灌木层生长周期有区别于乔木层、草本层。     

滇中半湿润常绿阔叶林群落类型演替的植物多样性调查与保护

滇中地区半湿润常绿阔叶林是其垂直带上重要的植被类型。采用典型样地调查法,对其主要群落类型及破坏后的森林群落类型进行植物生物多样性调查结果认为,元江栲林和高山栲林是该区域顶级群落,破坏后产生的次生群落类型主要为云南松林、旱冬瓜林、华山松林。对不同演替阶段的物种多样性、保护物种多样性、群落结构完整性、群落的涵养水源和保持水土能力进行评价,并对当前生态保护存在的问题进行分析,提出保护建议。     

湖南低丘区不同植被类型组成、结构及碳贮量评价研究

以湖南省低山丘陵区典型人工植被、天然次生林、荒草地群落为研究对象,分析了不同类型生态系统地上部分的组成、结构,并从生态系统尺度上,估算了不同植被覆盖类型的碳贮量。结果表明：天然次生林物种多样性恢复最快、垂直结构复杂、系统的碳贮能力最强,人工林群落的结构相对比较简单、物种多样性相对较低、碳贮能力一般,而荒草地群落的结构最简单、物种多样性最低、碳贮能力也最差。研究结果对于评价湖南省森林生态系统的生态服务功能有的参考价值。     

句容市仑山典型森林群落物种多样性特征

采用典型样地取样法,对句容市仑山典型森林植被进行了调查。仑山森林植被发现有维管植物90科200属350种,其中,裸子植物5科12属17种,被子植物79科180属325种,蕨类植物6科8属8种。该森林为人为干扰后形成的天然次生林,部分地段为人工林,依据主要树种组成可划分为6种森林群落类型:马尾松+构树+冬青混交林、落叶栎林、盐肤木林、枫杨林、杉木林和竹林。群落类型不同,植物物种的丰富度、多样性指标存在一定的差异。由于种群竞争以及人为干扰、有害生物入侵等外界因素的影响,部分森林群落出现退化,应因地制宜地采取抚育措施对森林进行结构改造,促使仑山森林植被朝着健康、稳定、和谐的方向发展。     

苏州市上方山森林植被分类及其群落学特征

利用典型样地取样法,对苏州上方山国家森林公园森林群落进行了调查,对该区森林植被类型进行了划分,并对不同植被类型的物种多样性特征进行了分析。依据相关文献,上方山森林植被可以划分成5个植被型亚纲, 6个植被型组(植被型),11个群系,16个群丛。以马尾松为主体的暖性针叶林和枫香林、栓皮栎林、白栎林3种落叶阔叶林在本区分布最广,也具有丰富的竹林资源。由于立地条件和种群竞争的共同作用,不同植被类型的物种丰富度、多样性指标存在一定差异。湿地松林群落内阔叶树种组成稳定,个体竞争和缓,湿地松感病较少,在未来一定时期内可能长期存在,应加以保护和利用;马尾松林则日渐衰败,建议有选择地逐步清除病木,并采取合理的营林技术措施,促进其朝着稳定的落叶阔叶林或落叶常绿阔叶混交林演替。     

鄂西三峡库区主要森林植被空间分布及影响因素

根据系统的野外调查数据和历史数据分析,结果表明:鄂西三峡库区主要森林植被类型在空间上分布不均匀,且分布分散,森林植被的空间分布具有明显的垂直地带性。同时分析了自然因素、人为因素等不同因素对鄂西三峡库区森林植被空间分布的影响方式和强度,初步揭示了鄂西三峡库区主要森林植被空间分布的原因。     

罗布泊及周边地区植物区系和植被特征兼论植被的恢复与保护

在对罗布泊及周边地区植物和植被资源广泛调查的基础上,分析了该区植物的区系成分,阐述了该区的植被类型及其物种组成、结构,计算了主要群落的物种丰富度及多样性,研究了该区主要植被类型的演替规律。结果显示:罗布泊及其周边地区共有种子植物27科53属74种,其中包括栽培植物2种,省级保护植物7种,生活型以草本植物占绝对优势,木本植物以灌木为主,乔木树种极少。该区藜科(Chenopodiaceae)和禾本科(Poaceae)种类最多,单种科和单种属占较大的比例。该区区系成分分布最多的为世界广布类型,其次为北温带分布类型和地中海区、西亚至中亚地区分布类型。该区主要群落类型有胡杨林群落、多枝柽柳灌丛、芦苇群落、花花柴群落、黑果枸杞群落、铃铛刺灌丛群落、骆驼刺群落、沙拐枣群落等,这些群落物种丰富度和多样性指数偏低、结构简单、物种组成单一,符合典型荒漠生态系统的特点。通过对胡杨更新表和群落的结构分析,部分胡杨林群落处于退化阶段、部分胡杨林更新正常,群落退化的原因就是由于水资源的极度匮乏,提出了该区的植被保护与恢复的建议:进一步规划好当地水资源的利用。     

吉林蛟河阔叶红松林树种空间分布格局及其种间关联性

【目的】群落水平上研究28个物种在不同尺度下种群空间分布格局及其种间空间关联性,明确温带森林群落物种共存与生物多样性维持机制。【方法】基于吉林蛟河阔叶红松林30 hm~2动态监测样地数据,运用空间点格局分析方法,分别采用完全空间随机零模型和异质性泊松零模型分析不同尺度种群空间分布格局及其种间关联性。【结果】基于完全空间随机零模型的种群空间分布格局分析显示,本研究中的28个物种均表现出空间聚集格局,表明总体空间分布格局的非随机性;基于异质性泊松零模型的种群空间分布格局分析结果表明聚集分布格局主要出现在较小尺度(0~10 m),随研究尺度增加,种群聚集所占比例迅速降低,随机分布和均匀分布成为主要的分布格局类型;分离和部分重叠类型是主要的种间关联类型,混合种间关联类型所占比例较低;多数尺度上,种间相互排斥所占比例高于种间相互吸引,表明不同物种个体之间在空间上趋向于分离,种间个体直接相互作用的机会少,表现为种间分离格局。【结论】本研究表明种内聚集和种间分离是该研究群落主要空间构型,物种间的空间分离减弱种间竞争,阻止或减缓竞争优势物种对竞争劣势物种的竞争排除作用有利于维持物种共存,促进生物多样性维持。     

浑河上游植被群落特征及其生态适应性

以浑河上游植被为研究对象,运用二元指示种分析法(TWINSPAN)对研究地区植被进行群落分类,对各群落类型特征进行分析。在提出河岸带植被生态功能适应性指标的基础上,对河岸带植被进行了生态功能适应性分组。研究发现,浑河上游河岸带植被可划分为香蒲草丛、球子蕨草丛、灯心草草丛、柳属灌丛、珍珠梅灌丛、核桃楸阔叶混交林、家榆阔叶混交林、长白落叶松林和油松林等9个群落类型,群落类型表现出突出的多样性特征,且物种组成复杂;研究地区9个群落类型可以划分为强入侵性功能组、弱入侵性功能组和高逃避性功能组3个生态适应性功能组,不同生态适应性功能组的群落中的主要物种具有明显的不同的生态对策。     

森林防火是小五台山自然保护区的首要任务

小五台山保护区始建于1983年11月,初建为省级,2002年7月经国务院批准晋升为国家级。保护区位于河北省张家口市蔚县、涿鹿县南部山区,群山环抱、山峦叠嶂,植被繁茂、物种丰富,是我国同纬度森林植被最好、森林垂直分布最典型的区域,主要保护对象是臭冷杉、褐马鸡等珍稀野生保护动植物及其群落。     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Defoliation by the Needle-shortening Pine Gall Midge,Thecodiplosis brachyntera,on Pines in Central Sweden

An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Boron in forest trees and forest ecosystems

This review critically examines the role of boron (B) in forests in view of recent findings on B nutrition and the continuing occurrence of B deficiency. Many perceptions about the role of B in plants and its uptake and mobility have been altered since the last review on B in forest trees in 1990. Now there is evidence for a fundamental role of B in the formation of the pectic structure in primary cell walls in plants, and further roles in membrane function are being explored. In plants, channel-mediated B uptake, active B uptake and B uptake by mycorrhizas have been shown, B transporters have been identified, and B retranslocation has been shown. We explore these findings and their consequences on forest trees and on ecosystems that they dominate. Particular emphasis is placed on B retranslocation and B in mycorrhizal symbiosis, given their importance in trees.     

Survival and Growth of Picea abies Regeneration after Shelterwood Removal with Single- and Double-grip Harvester Systems

Three stands in Sweden were followed for 7 yrs to study the survival and growth of Norway spruce [Picea abies (L.) Karst.] regeneration after shelterwood removal with single- and double-grip harvester systems. The height of all seedlings within circular plots was recorded before and after final cutting. The tallest seedling and one randomly selected seedling on each circular plot were permanently marked and their annual height growth was measured each year during the period 1993-1999. No significant differences between single- and double-grip harvester systems were found with respect to their effects on regeneration density, survival or annual height growth. The annual height growth of the individual seedlings after shelterwood removal was significantly correlated with seedling height before shelterwood removal. Significant differences were found in annual height growth between seedlings with high and low vitality. Logging damage did not affect the annual height growth. Several practical conclusions were drawn. First, the choice of harvester system does not affect seedling height growth or survival after shelterwood removal. Secondly, the removal of a 200 m³ shelterwood with 200 stems ha^-1 does not seem to constitute a serious problem for seedling survival and growth. Finally, estimated vitality and seedling height both seem to be fairly good predictors of postrelease survival and growth.     

Development of Pinus sylvestris Main Stems Following Three Different Precommercial Thinning Methods in a Mixed Stand

Reducing competition by point cleaning may be an attractive alternative to conventional precommercial thinning in forestry. In this study, survival and development of main stems of Scots pine (Pinus sylvestris L.) following point cleaning were examined in a mixed stand of mainly Scots pine and birch (Betula pendula Roth and Betula pubescens Ehrh.) in northern Sweden. Treatments studied were: no precommercial thinning, conventional precommercial thinning, point cleaning of all secondary stems, and point cleaning of only the secondary stems that were higher than the main stem, within a radius of 0.8 m from the main stem, respectively. A randomised complete block design with three replicates was used. Measurements taken 13 growing seasons after these treatments showed that conventional precommercial thinning was the best treatment for retaining Scots pines as main stems. However, conventional precommercial thinning resulted in the poorest timber quality of the remaining Scots pines in terms of stem taper, thickest branch diameter and relative live crown height. In conclusion, point cleaning has to be followed by a complementary cleaning operation if the objective is to retain Scots pines as main stems in such mixed stands.