双柏县桉树及其混交林生长过程的研究

对双柏7年生纯桉树林和桉树与黑荆树混交林中桉树树高、胸径、材积生长过程的研究表明,桉黑混交对7年生桉树的高粗及材积生长未表现出明显的影响,但对土壤 N、P、K 营养元素的含量变化有较大影响,对防止病虫害的发生、发展有一定的作用。提出改进桉树经营管理的建议。     

不同有机肥对尾叶桉生长的影响

通过对比 4 种不同有机肥对尾叶桉（Eucalyptus urophylla）胸径、树高和地径的影响，分析不 同 N、 P、 K 含量的有机肥对桉树生长的影响，筛选出最有利桉树生长的有机肥种类。结果表明：处理 D 即 N : P : K 为 15 : 5 : 11 时对桉树的胸径和地径增长促进效果最好；处理 C 即 N : P : K 为 9 : 11 : 10 时对 桉树树高的增长效果最好。     

桉树幼林施肥肥效的研究

2001-2003年,在湖南省郴州市苏仙区卜里坪村林场,对桉树幼林地进行不同肥料品种、不同施肥剂量的肥效研究.结果表明:施用N2K肥对桉树幼林生长不利,产生负面作用;P2K2,N2P1,P2肥对按树生长有较好的肥效;N1P2K1混合施用肥效最佳,树高达4.73 m,比对照的增加132%,胸径4.50 cm,比对照的增加133%,差异达显著水平.肥料最佳配比剂量为每株尿素65 g,过磷酸钙430 g,氯化钾25 g.     

桉树人工林施肥技术研究

分析了同肥料种类、不同施肥方式对桉树生长的影响,以获取提高桉树种植率的有效施肥技术,能够为实现可持续发展奠定良好的基础。结果表明:与纯化肥组合相比,无机复混肥的施肥效果更为显著;当基肥种类、数量以及其他因素特定时,基肥方式对桉树生长起着至关重要的促进作用,N︰P︰K为15︰5︰11的比例的施肥效果更为显著,桉树的生长量可以最高值,同时也可以去获取较高的经济效益。为此,提出了N︰P︰K为15︰5︰11的施肥比例更能够为桉树提供一个良好的生长环境,以加快桉树生长速度,提高生长质量。     

桉树与乡土阔叶树种混交林的初期生长效应

以红锥（Castanopsis hystrix）、米老排（Mytilaria laosensis）2种广西乡土阔叶树种为混交树种,对不同混交模式下桉树与红锥、米老排的林木生长情况进行了分析。研究结果表明：在桉树与米老排（3∶1）混交模式下,桉树树高、胸径生长量明显高于桉树纯林。而混交模式下,红锥生长量增加,而米老排生长量降低。初步认为,混交能促进桉树生长,但最佳混交造林模式因混交树种而异。     

东山县丘陵山地桉树与马占相思混交造林试验研究

针对桉树经营中潜在的生态问题,开展了桉树与马占相思混交造林研究,进行了桉树与马占相思1∶1(行状)和4∶4(带状)混交以及桉树纯林为对照的试验研究,结果表明:桉树与马占相思混交促进了桉树生长和土壤条件的改善,提高了土壤肥力,而在桉树-马占相思混交林中,桉树与马占相思采取带状混交对于桉树和马占相思的生长都有较大的提高作用,并且改善土壤理化性质的作用也更大。     

3种肥料养分释放特性及对桉树生长响应研究

对3种不同养分比例的CF、NW、FH肥料进行养分释放研究,并在N、P、K养分总量相同的情况下,比较了3种肥对于不同试验林地内桉树生长的影响.结果表明:NW肥对P、K的缓释效果要好于CF和FH肥.NW肥对树高生长量的影响要大于其余两种肥.CF肥则有利于胸径和叶绿素的增长.     

丘陵地桉树无性系人工林生长调查

采用标准地法,对广西南宁市南部丘陵地2.25～2.67年生的桉树无性系人工林进行了调查研究。结果表明:林木平均保存率为89.3%,平均年蓄积生长量达30.0 m3/(hm2.a),林木径阶以10 cm居多,其次是12 cm径阶,二者合计占80%。林分生长量与无性系种类、林地坡位有一定关系,无性系的生长排序为DH33-29>DH33-26>DH33-28,坡位排序为下坡位>中坡位>上坡位,但差异均较小。林地土壤有效N含量对桉树生长影响显著,含量少的林地桉树生长量显著低于含量多的林地。林地土壤有效N、P、K含量普遍不足,林地施肥应充分考虑N、P、K养分,以满足桉树生长对各种元素养分的需要。     

桉树福建柏混交造林效果分析

为了探索闽南地区桉树人工林混交造林模式,2010年在福建省安溪白赖国有林场开展了桉树福建柏混交(混交比例为2桉∶8福建柏)造林试验,并与桉树纯林、福建柏纯林对比。5 a的试验结果表明:混交林中桉树胸径、树高、材积的生长量都大于桉树纯林,增益可达39.2%、16.1%、109.5%以上;混交林中福建柏的平均胸径、平均树高、单株材积生长分别比纯林减少了25.9%、10.7%、46.8%,但树高生长也超过速丰林标准的14.7%。说明桉树与福建柏混交存在着生长相互促进作用,是种间关系较为协调并且具有较高生产力的混交模式,可以在生产上推广应用。     

尾巨桉萌芽林土壤肥力变化及施肥研究

通过林地调查和室内分析化验,结果表明广西钦州市桉树二代萌芽林林地土壤酸性、有机质、全N、水解N、全K、速效K含量均降低;土壤磷素含量降低,全P含量为0.28～0.38g.kg-1、有效P含量为0.3～1.1mg.kg-1;Cu、B的含量也降低,且B含量偏低,仅为0.01～0.03 mg.kg-1。针对上述结果,提出了相应的测土配方施肥方案。分别以普通HA桉树肥、桉树专用肥、鸡粪+普通复合肥和钦州市林科所桉树配方复混肥4种肥料进行施肥对比试验,寻找最佳施肥方式。试验表明:尾巨桉施肥肥效明显,施用几种肥料对桉树二代萌芽林生长量均有显著促进作用,不同种类的肥料对桉树二代萌芽林前期生长量的肥效差别主要受肥料总养分含量、N、P、K百分含量及养分的合理配比影响。不同处理萌芽林分间的保留株数、树高、胸径、材积及蓄积均达极显著水平,钦州市林科所桉树配方复混肥较适合当地桉树二代萌芽林林木生长,3年生单株材积及蓄积量分别达到0.076 m3.株-1、105.396 m3.hm-2。     

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.     

Biogeochemical impacts of clearfelling and reforestation on blanket-peatland streams: II. major ions and dissolved organic carbon

Streams and drains in blanket-peatland forest in western Ireland were sampled weekly over 5 years, 1996–2000, using continuous, depth-proportional passive sampling. Analysis was for pH, alkalinity by Gran titration, anions by IC, metals by ICP, aluminium speciation by loaded-resin exchange, and dissolved organic carbon (DOC) by absorbance at 320 nm.

Effects of felling are identified graphically from two forest drains whose catchments (both about 1 ha) were clearfelled, and partial clearfelling of one larger catchment (somewhat over 1 km²), in summer 1999. Calcium concentrations and alkalinity were increased in the drain- and streamwater from the felled areas. The pH was increased in drains, while in the larger stream, pH range decreased while the mean increased. Phosphorus increased markedly with clearfell, in the absence of recent fertilising, and also increased with fertilising; these results are reported in an accompanying paper. Ammonium-nitrogen concentrations were increased in the two drains with felling, and temporarily decreased in the larger stream. Nitrate increased in some cases. Potassium and manganese concentrations also increased. Concentrations of DOC and organic monomeric aluminium increased gradually, subject to a continuing strong annual cycle. There were no clearfelling effects on concentrations of solphate, suspended solids or inorganic monomeric aluminium. In the two drains (fully clearfelled), concentrations of sodium, chloride and magnesium, and conductivity, were all reduced after felling. Fertilising effects other than for phosphorus were indistinct.

Effects of the combined clearfell–reforestation treatment were testable statistically, using randomised intervention analysis, between two larger streams (1 km²) as a treatment–control comparison. There were statistically significant positive responses in streamwater concentrations of nitrate, potassium, calcium, DOC and aluminium fractions. The implications for management practice depend on whether the loss of nutrients is sustainable for future crop productivity, and whether critical limits and loads of receiving ecosystems are exceeded.     

Effect of Drought on Growth and Mortality of Actively Growing Norway Spruce Container Seedlings Planted in Summer

Survival, root egress and height growth of 13-month-old actively growing Norway spruce ( Picea abies (L.) Karst.) container seedlings exposed to preplanting drying treatments (0, 4, and 8 days) and postplanting drought periods (1, 2, 3, and 4 weeks) were studied in the field between 5 July and 18 August 1999. The mortality of seedlings increased and the height growth and root egress decreased throughout the postplanting drought period. Postplanting performance was also affected by preplanting drying treatments. The results indicate that no risk of excessive mortality and growth restrictions occurs when actively growing seedlings are planted in summer, provided that seedlings are well watered before planting and the drought period does not exceed 3 weeks.     

Rehabilitation of diseased cacao fields in Peru through shade regulation and timing of biocontrol measures

The objective of this case study was to test the effectiveness of biocontrol for the rehabilitation of abandoned, diseased (moniliasis, witches' broom and black pod) cocoa and to develop testable hypotheses regarding the effect of shade and biocontrol timing. Three trial fields differed in their shade regimes. Biocontrol was administered starting either at flowering or pod filling. Disease incidence and yield were compared with cultural control alone. Biocontrol reduced moniliasis from 49% to 25%, independent of the shading regime and application time. Witches' broom was most severe without shade and unaffected by biocontrol. No significant effects on black pod were observed. Although biocontrol increased percentage healthy fruit independent of shading and timing, only the shaded plot with biocontrol from flowering onwards responded with increased yield. Our hypothesis is: 'In the rehabilitation of abandoned cacao, only fields under sustainable shade management and early onset of biocontrol can realise their production potential.' This revised version was published online in June 2006 with corrections to the Cover Date.