海南麻竹林凋落物及养分动态研究

研究了海南麻竹林凋落物量及其养分动态.结果表明:麻竹林凋落物全年总量为6 862.8 kg·hm-2.N、P、K、Ca、Mg的年归还量分别为74.847、3.264、25.921、45.924、11.902kg·hm-2,大小顺序为:N＞Ca＞K＞Mg＞P,养分总的年归还量是161.858kg·hm-2·a-1.凋落物分解失重率达95%的分解期为11.59个月,每年产生的凋落物全部归还于土壤.     

米老排12年生人工林养分积累及其分配特征

为揭示米老排生长过程中养分元素积累特点和分配规律,采用Monsic分层切割法,对广西高峰林场12年生(中龄林)米老排人工林的5种养分元素(N、P、K、Ca、Mg)的含量进行测量,分析其林分的积累量及分配特征。结果表明:(1)米老排不同器官养分元素含量依次为树叶树皮树枝树根树干;各器官养分元素含量表现为:树叶、树干和树根NKCaMgP;树枝为KCaNMgP;树皮为KNCaMgP。(2)米老排人工林养分总储量为1 310.36 kg/hm2,其中乔木层养分储量为1 177.74 kg/hm2,占总养分储量的89.88%;草本层、灌木层以及凋落物层的养分积累量分别为2.92 kg/hm2、3.93 kg/hm2和125.77 kg/hm2,分别占林分总积累量的0.20%、0.30%和9.60%。(3)乔木层养分元素年净积累量为98.15 kg/(hm2·a),各器官的年净积累量顺序为树干树枝树根树叶树皮。(4)米老排人工林乔木层每积累1 t干物质需要5种养分元素7.63 kg,其养分元素利用效率低于杉木,但明显高于马占相思、湿地松和灰木莲人工林。     

速生阶段秃杉与杉木人工林营养元素积累及其分配特征

对广西南丹山口林场相似立地条件下速生阶段(11年生)的秃杉与杉木(第2代)人工林5种营养元素(N、P、K、Ca和Mg)的含量、积累量、年净积累量和分配进行了研究。结果表明,秃杉与杉木不同器官中营养元素含量排序均为树叶干皮树枝树根干材,林木各器官营养元素含量均以N最高,其次是Ca和K,Mg和P最低。秃杉人工林分营养元素贮存量为573.40kg.hm-2,明显高于杉木人工林(330.33kg.hm-2),其中乔木层、林下植被层和凋落物层分别为517.97、11.05和47.05kg.hm-2,分别占林分营养元素积累量的89.91%、1.92%和8.17%。5种营养元素贮存量在秃杉与杉木人工林乔木层的分配均为树叶树枝干材干皮或树根。秃杉人工林营养元素平均年净积累量为47.09kg.hm-.2a-1,是杉木人工林(26.55kg.hm-.2a-1)的1.77倍。秃杉的营养元素利用效率低于杉木,但明显高于马尾松、刺槐和马占相思。     

杉木人工林凋落物C,N,P归还量对氮沉降的响应

为探讨亚热带森林对氮沉降增加的响应,在12年生的杉木人工林中开展4种水平的模拟氮沉降试验,分N0(对照),N1,N2,N3等4种处理,氮沉降量分别为0,60,120,240kg·hm-2a-1。模拟氮沉降2年后,4种不同氮沉降水平杉木人工林的年凋落量分别为1008.83,1164.10,1147.30和976.47kg·hm-2,表明低中氮处理(N1,N2)在一定程度上增加森林凋落物量,而高氮处理(N3)则表现出一定的抑制作用。叶凋落物中C,N元素含量随氮沉降水平的增加而增加,而C/N则呈不断下降的趋势。经不同氮沉降处理后,凋落物C元素的归还量分别为474.70,544.07,538.55和474.02kg·hm-2,N元素的归还量分别为7.21,8.56,9.03和9.04kg·hm-2,P元素的归还量分别为1.17,1.24,1.32和1.09kg·hm-2,说明与N0处理相比,氮沉降显著提高N元素的归还量,而N1,N2处理提高C,P元素归还量,N3处理对C归还量影响不明显,但降低P的归还量。     

嘉陵江上游低山暴雨区3种不同植被类型氮循环研究

本文通过对嘉陵江上游低山暴雨区不同植被类型的初步研究。不同植被类型的氮库总储量分别为：6 787.27 kg.hm-2、7 115.39 kg.hm-2、6 951.06 kg.hm-2。其中不同植被类型中活体生物量分别为：136.43 kg.hm-2、210.40 kg.hm-2、169.66 kg.hm-2,凋落物层分别为：31.06 kg.hm-2、38.96 kg.hm-2、40.05 kg.hm-2,土壤（0-40cm）中分别为：6 619.73 kg.hm-2、6 866.03 kg.hm-2、6 741.35 kg.hm-2。不同植被类型土壤中的氮分别占总储量的97.53%、96.50%、96.98%,活体生物量分别占2.01%、2.96%、2.44%,而凋落物层分别仅占0.46%、0.55%、0.58%。结果表明,低山暴雨区3种不同植被类型的N主要分布在土壤中,而在活体生物量和凋落物层中只占很少的一部分。3种不同植被类型树干径流的氮含量分别为：0.44 kg.hm-2、0.553 kg.hm-2、0.851kg.hm-2,林分穿透雨氮含量分别为：12.649 kg.hm-2、12.551 kg.hm-2、13.291 kg.hm-2,地表径流氮的输出量分别为：0.55 kg.hm-2、0.55 kg.hm-2、1.27 kg.hm-2。不同植被类型氮的生物循环：湿地松林吸收量、存留量、归还量、循环系数分别为：37.561 kg.hm-2.a-1、6.497 kg.hm-2.a-1、31.064 kg.hm-2.a-1、82.703%,刺槐林吸收量、存留量、归还量、循环系数分别为：48.976 kg.hm-2.a-1、10.019 kg.hm-2.a-1、38.957 kg.hm-2.a-1、79.543%,混交林吸收量、存留量、归还量、循环系数分别为48.127 kg.hm-2.a-1、8.079 kg.hm-2.a-1、40.048kg.hm-2.a-1、83.213%。吸收量、存留量均是刺槐林〉混交林〉湿地松林,归还量是混交林〉刺槐林〉湿地松林。结果表明,3种植被类型处于良好的养分积累状态,有利于系统的稳定持续发展。     

会同广坪林区降雨和杉木林内雨的养分含量

对会同广坪林区的大气降雨、水库水、小河水及杉木林内雨的养分含量进行了5个水文年的定位监测.结果表明水库水、小河水中的10种养分元素N、P、K、Ca、Mg、Fe、Cu、Mn、Zn、Si,有的含量高于降雨,而有的含量低于降雨;降雨中各养分元素按含量高低排列顺序为K＞Zn＞Ca＞Org-N＞NH4-N＞NO3-N＞Si＞Mg＞Mn＞P;林内雨中P、K、Ca、Mg、Fe、Cu、Mn、Zn、Si元素含量均比降雨高;从林冠层淋洗的养分量为79.475 kg*hm-2a-1;从林内雨直接进入林地土壤的养分总量为161.957 kg*hm-2a-1,其中以Ca元素最高,为73.71 kg*hm-2a-1,为外界补充杉木幼林地土壤养分的主要来源,对加速杉木林的养分循环和促进林木生长,具有重要的生态作用.该项研究可为杉木林的持续经营,生态环境保护提供科学依据.     

西藏色季拉山冷杉林生态系统的养分循环

对西藏色季拉山急尖长苞冷杉林生态系统的养分循环进行了研究,结果表明:养分的总存留量为35 41kg·hm-2·a-1,总归还量为54 89kg·hm-2·a-1,年吸收总量为90 3kg·hm-2·a-1。冷杉林分具有养分低循环利用特征。大气降水主要补充N、Ca、Fe等元素,而凋落物主要补充P、K、Fe等元素,其中Fe元素是净增加的。冷杉林生态系统养分年输入量均大于年输出量,说明该森林生态系统处于良好的养分积累阶段。林地土壤(不包括凋落物层)的养分年输出量(除N、Fe、Mg元素外)稍大于年获得量,土壤年净亏损不大,但K的亏损较严重。冷杉林分的养分利用效率以及土壤养分利用指数均表明,林分对N的需求最大,对Fe的需求最少。     

马尾松林下补植阔叶树后森林凋落物量、养分含量及周转时间的变化

在25年生的马尾松林下分别补植拉氏栲、青栲、闽粤栲、格氏栲和苦槠,形成针阔混交异龄林。补植16年后,对上述5种混交林类型及马尾松纯林的森林凋落物量、养分含量及周转时间进行研究。上述5个混交群落和马尾松纯林的年凋落物量分别为6149·1、7533·2、6741·1、7151·5、8041·7和3442·8kg·hm-2。各混交群落总凋落物量的季节动态呈双峰型,第1次峰值出现在2—4月份,第2次峰值出现在8、9月份。在凋落物组成中,枯叶占绝对优势,占凋落物总量的50%~71%,其余依次为枯枝6%~26%、树皮9%~19%、果实和其他组分5%~17%。各混交群落中来自马尾松的凋落物占50%~58%,来自阔叶树的凋落物占42%~50%,且两者的组成有明显差异。凋落物各组分的养分含量存在较大差异,N、P、K、Ca、Mg的含量范围分别为3·25~12·98、0·24~0·97、0·37~6·55、12·77~35·40、2·35~6·10g·kg-1。各林分类型凋落物中养分元素的年归还总量为Ca>N>Mg>K>P。5个混交林群落及马尾松纯林凋落物中的养分年归还总量分别为238·05、213·77、223·93、289·90、304·12和142·01kg·hm-2。6个群落的森林地被物现存量分别为8448·0、15565·8、11993·7、12718·6、6974·2和5020·0kg·hm-2,其中L层在各群落中所占比例分别为47·2%、59·6%、51·3%、61·0%、85·4%及86·3%,平均为61·7%。森林地被物中各养分元素的含量在群落和组分之间存在明显差异,但总的趋势表现为Ca>N>Mg>K>P。最后,通过对年凋落量和林地凋落物积累量的比较分析,上述6个群落的凋落物周转时间预测值依次为0·76、1·42、0·97、1·17、0·84及1·52年,其中枯枝的周转时间明显大于枯叶,且马尾松的枯叶和枯枝的周转时间普遍大于阔叶树。     

毛竹、杉木人工林生态系统碳平衡估算

采用CID-301PS光合测定仪,对湖南会同林区毛竹和杉木人工林土壤CO2排放动态进行观测,并结合现存生物量调查,对其生态系统碳平衡特征进行估算.结果表明:毛竹和杉木林生态系统碳贮量分别为144.3和152.52 t·hm-2,并且其碳贮量空间分布格局基本一致,土壤层是主要部分,其次为乔木层,凋落物层和林下植被层所占比例最小.毛竹林土壤层有机碳贮量占76.89%,乔木层占22.16%,凋落物和林下植被层分别占0.51%和0.41%;杉木林土壤层碳贮量占62.03%,乔木层占34.99%,凋落物和林下植被层分别占2.28%和0.70%.毛竹林和杉木林生态系统年固定CO2总量分别为38.87和26.95 t·hm-2a-1,但其每年以土壤异养呼吸和凋落物呼吸的形式排放CO2的量分别为24.35和15.75 t·hm-2a-1,毛竹林和杉木林生态系统年净固定CO2的量分别为14.52和11.21 t·hm-2a-1,折合成净碳量分别为3.96和3.07 t·hm-2a-1.     

南亚热带6种人工林凋落物的初步研究

2006年5月至2007年4月在广西凭祥市中国林科院热带林业实验中心伏波实验场,采用塑料网框收集法对米老排、西南桦、红椎、火力楠、马尾松、杉木6种人工林分凋落物的凋落量及凋落节律进行了研究,结果表明:不同树种林分凋落物的动态变化规律不同,凋落量也各异.在6种林分中,叶、杂物的凋落量以米老排最高,分别达4 748.23、1 881.07 kg·hm-2·a-1,西南桦最低,分别为2 641.32、153.88 kg·hm-2·a-1;枝凋落量以马尾松最高,达902.94 kg·hm-2·a-1,杉木最低,仅149.93 kg·hm-2·a-1.林分的年总凋落量也以米老排最高,达7 095.76kg·hm-2·a-1,西南桦最低,仅3 309.05 kg·hm-2·a-1,米老排林分的年总凋落量是西南桦的2.14倍,而红椎、杉木、马尾松、火力楠4种林分的年总凋落量比较相近,为5 555.61～5 864.87 kg·hm-2·a-1,相差不足6%.6种林分年总凋落量的差异极显著,多重比较显示,米老排与另外5个树种比较都达到了极显著差异,红椎和杉木与西南桦、火力楠、马尾松比较达极显著差异;火力楠、马尾松与西南桦比较达极显著差异.     

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.