江西次生米槠林组成结构及生产力研究

在江西次生米槠林群落中，有这束植物３７科６１属７６例，其中乔灌森林４科４属５９种，草本８科１０属１０种，层外植物５科７属种。林分直径分布，幼龄林呈倒“Ｊ”型，壮龄林近似于正态分布；种群或林分直径分布用Ｌｏｇｉｓｔｉｃ方程预估。次生米储林有较高的生产力，４０年生林分，平均胸么达２７．１ｃｍ，平均树高达１７．０ｍ，蓄积达３８９．２６ｍ＾３／ｈｍ＾２。     

杉木及其人工林自身特性对长期立地生产力的影响

本文系统地研究并综合了有关杉木及其人工林自身特性对长期立地生产力的影响的研究资料,认为杉木及其人工林自身的特性存在许多对地力维护不利的因素：（1）杉木凋落物发生晚,大量凋落物发生在14－15a前后;（2）杉木枯死枝叶具宿存特性,10－15a期间大部分枯死枝叶在树上,影响枯死枝叶的分解;（3）杉木凋落物养分含量低,如N含量只有阔叶树的30％－50％,因此枯落物营养元素积累低;（4）凋落物分解速率慢,分解速度在45％以下,而宿存于树上的枯死枝叶分解速率更慢;（5）杉木为速生树种,尤其在15a年前生长量大,吸收养分多,而养分归还少,杉木人工林养分循环速率不及40％;（6）杉木人工林培育密度较大,在15a前很少有林下植物生长,在20a后才有较好的林下植被发育,人工林长期处在单一的群落结构,很难发挥林下植被对地力的维护和改良作用。从现有的研究资料看,杉木及其人工林自身对地力维护有不利影响,是引起杉木林地土壤肥力及长期生产力下降的重要因素之一。     

A study on the productivity and cost of cable logging in Turkey

Tower yarders have recently been introduced to forestry in Turkey. Clarification of the productivity and cost of logging using the tower yarder is often requested because the cost for machinery is a significant factor in all calculations concerning mechanized operations. Machines are often extremely expensive compared with the low cost of labor in developing regions. In this study, a new logging system using a tower yarder was compared with a conventional system using a stationary yarder in terms of productivity and cost. The research was conducted in the northeast of Turkey, in 1989 and 1992. The productivity of the tower yarder and the stationary yarder was found to be 5.655 m³/h and 5.002 m³/h, respectively. Harvesting cost was analyzed based on observed productivity. The harvesting costs of the tower yarder and the stationary yarder were found to be 47,410 TL/m³ and 17,553 TL/m³, respectively. With the tower yarder, the machine cost reached 93.1 % of the harvesting cost while the machine cost using the stationary yarder reached 71.1%. A part of this paper was orally presented at the 3rd Annual Meeting of the Japan Forest Engineering Society (1996).     

The relationship between length of fallow and crop yields in shifting cultivation: a rethinking

Rethinking the relationship between length of fallow and crop yields inshifting cultivation?The theory that a correlation between shortened fallow periods and yielddecline in shifting cultivation exists is questioned in this paper. Thisrelationship has been taken for granted, and because it shows that shiftingcultivation will break down under pressure, it has partly been responsible fornegative government views on shifting cultivation. Yield levels in shiftingcultivation are influenced by a wide range of biophysical, socioeconomic, andcultural factors and it is difficult to isolate fallow length as a singledetermining factor. A total of 330 studies were reviewed and fifteen withempirical data were chosen for in-depth analysis. Although most of the empiricalstudies support the theory, the data sets are often ambiguous and importantparameters are insufficiently taken into account. Several studies found norelationship between fallow length and yield, but these also lack information toverify the validity of the data. It is concluded that empirical studiesfocussing on this problem are needed to fully understand this relationship anddevelop feasible scenarios for the numerous attempts at modelling shiftingcultivation development. Moreover, the use of gloomy `breakdown' scenarios asjustification for improving shifting cultivation should be avoided.     

黄土丘陵区金矮生苹果园土壤水分有效性及生产力分级

在半干旱黄土高原丘陵沟壑区,采用Li-Cor6200便携式光合仪和Li-Cor1600便携式稳态气孔计,对9年生金矮生苹果树的净光合速率、蒸腾速率、水分利用效率、气孔导度、胞间C02浓度和气孔限制值与土壤水分的定量关系进行了研究;以光合作用生理参数为指标对苹果园土壤水分有效性及生产力进行了分级与评价。结果表明：苹果园的土壤相对含水量在21．5％以下为“无效水”;21．5％～46．5％为“低产低效水”;46．5％～65．0％为“中产高效水”;65．0％～75．0％为“高产中效水”;75．0％～79．0％,为“中产低效水”;79．0％以上也属于“低产低效水”。依据干旱与半干旱地区农林业生产以提高水分利用效率为核心的土壤水分管理思想,确定金矮生苹果园适宜的土壤相对含水量为46．5％～65．0％;最佳土壤相对含水量为65．0％左右,此土壤水分可使苹果树达到获得高产高效的生产水平,称之为“高产高效水”。     

湖北省引种原生种源和次生种源日本落叶松生长比较研究

以湖北省从国内引种的日本落叶松次生种源和从日本引种的原生种源材料为对象,利用7a生生长数据对这两部分材料在湖北省的生长情况进行了比较研究。结果表明:原生种源的胸径、树高生长分别是次生种源的1.8、1.6倍,次生种源和原生种源内各种源间胸径和树高的生长差异均达到显著或极显著水平;原生种源比次生种源具有更高的遗传变异性,通过选择获得的遗传增益分别是次生种源的4.75和2.38倍。     

山地麻竹笋用林生态系统生物量、生产力及能量结构

对南靖林场5a山地麻竹林生物量、生产力及能量结构进行了研究,结果表明,麻竹林现存生物量、能量贮量和移出林外利用的生产力随林龄的增大而增大,3a以后竹林地下部分生物量、能量贮量大于地上部分生物量,林下植被生物量和能量随竹龄增大而减小,1、2a竹林林下植被能量贮量高于麻竹林层;麻竹林各组分的热值为17 2059～20 2806kJ·g-1,灌木的最高,地表残留物的最低。     

Adaptive responses of<Emphasis Type="Italic">Acer ginnala,Pyrus ussuriensis and Prunus davidiana</Emphasis> seedlings to soil moisture stress

One-year-old seedlings of Amur maple (Acer ginnala Maxim), Ussurian pear (Pyrus ussuriensis Maxim) and David peach (Prunus davidiana Carr) were planted in pots in greenhouse and treated with four different soil moisture contents (75.0%,61.1%, 46.4% and 35.4%). The results showed that net photosynthesis rate (NPR), transpiration rate (TR) and stomatal conductance (Sc) of seedlings of the three species decreased with the decease of soil moisture content, and Amur maple seedlings had the greatest change in those physiological indices, followed by Ussurian pear, David peach. Amur maple and Ussurian pear seedlings also presented a decrease tendency in water use efficiency (WUE) under lower soil moisture content, whereas this was reversed for David peach. Under water stress the biomass allocation to seedling root had a significant increase for all the experimental species. As to root/shoot ratio, Amur maple seedlings had the biggest increase, while David peach had the smaliest increase. The leaf plasticity of Amur maple seedlings was greater, the leaf size and total leaf area decreased significantly as the stress was intensified. No significant change of leaf size and total leaf area was found in seedlings of Ussurian pear and David peach. It was concluded that Amur maple was more tolerant to soil moisture stress in comparison with David peach and Ussurian pear.     

Establishment and growth potential of fuelwood species in northeastern Mexico

Fifteen multipurpose tree species native and introduced to the matorral (low dry shrubland and forest) of the Gulf Coastal Plain in north-eastern Mexico were planted in monoculture in four randomized blocks. Measurements of various growth parameters and volume of trees over the first five years were evaluated. Eucalyptus camaldulensis, E. microtheca, Leucaena leucocephala (exotic species) and Parkinsonia aculeata (native species) performed best while Prosopis glandulosa, Helietta parvifolia and Acacia rigidula (native species) did not establish well due to biotic problems which arose under plantation conditions. Acacia farnesiana, A. wrightii and two Pithecellobium spp. (native species) showed high yields which is of great interest since their multipurpose potential is the best of all fifteen species. These species could be of great importance in rehabilitating badly degraded parts of the matorral before such areas deteriorate to an irreversible desertified condition.

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Resumen Para cuantificar el crecimiento y la productividad de las plantas leñosas, quince especies nativas e introducidas con caracteristicas multipropósito fueron plantadas en monocultivo en una zona de matorral de la Planicie Costera del Golfo Norte de México a partir de 1984. Durante cinco años de medición continua sobre diferentes parámetros de crecimiento, fueron evaluados los resultados sobre el comportamiento y productividad (volumen de la madera) de las especies. Eucalyptus camaldulensis, E. microtheca, Leucaena leucocephala (especies exóticas) y Parkinsonia aculeata (especie nativa) presentaron los mejores crecimiento en altura y en volumen en comparación con Prosopis glandulosa, Helietta parvifolia y Acacia rigidula (especies nativas). El desarrollo de Acacia farnesiana, A. wrightii y ambos Pithecellobium spp. (especies nativas) se puede considerar bastante bueno. Estas últimas especies son de gran interés como potencial forestal y forrajero. Todas las especies ensayadas son de suma importancia en la rehabilitación de matorral degradado y en el manejo silvicola de estos vastos recursos.