Height development of Betula pubescens following precommercial thinning by breaking or cutting the treetops in different seasons

Topping, i.e. cutting or breaking the treetops of secondary stems, may be an attractive alternative to traditional precommercial thinning. The survival and height development of downy birch (Betula pubescens Ehrh.) after topping were examined over three growing seasons in two dense, naturally regenerated stands, 3.1–3.5 m high, in northern Sweden. The topping was performed in experiments with a two-factor randomized complete block design, as follows. Three treatments were applied to individual secondary stems (top-breaking at half the sample tree mean height, top-cutting at half the sample tree mean height, and traditional cutting just above ground) at each of three times: winter, spring and summer (in frozen, dormant and growing conditions, respectively). A control (no treatment) was also included. The survival rate was lowest for traditionally cut stems and for stems cut in growing conditions. Height development after three growing seasons was significantly affected by time of treatment, the height growth being lowest after treatment in growing conditions, but not by treatment. Height growth of control stems was not significantly different from height growth in any combination of treatment and time of treatment, after three growing seasons. However, control stems had the greatest leading shoot length in the third growing season.     

浅谈白桦苗木的培育技术

论述了白桦的形态特征、白桦的采种技术、育苗技术及田间管理;对从事白桦苗木的培育技术人员有一定的指导作用。     

小兴安岭白桦林降水转化过程元素特征分析

为了探究小兴安岭白桦林生态系统在降水转化过程中养分循环及养分平衡的变化特征,采用生态系统野外长期定位观测和采样的方法,并利用ICP发射光谱分析仪对小兴安岭白桦林穿透雨、树干径流以及林外雨中的K、Ca、Si、Mg和Mn共5种养分元素进行了测定,结合白桦林对大气降雨的截留再分配比例,计算了白桦林内各元素的输入量,结果表明:1)大气降雨中各养分元素年均质量浓度Ca为最高(10.807 mg/L),Mn最低(0.069 mg/L),其排序为Ca＞K＞Si＞Mg＞Mn;大气降雨中养分输入量排序与养分年均质量浓度有相同排序规律;2)穿透雨与树干径流中的各元素年均质量浓度规律一致,均为Ca＞K＞Mg＞Si＞Mn;与大气降雨相比,穿透雨和树干径流中养分元素的年均浓度均有不同幅度的增长;3)大气降雨中除Ca元素外,其他元素的变异系数均大于1,其中K的变异系数最大(1.514),Ca的变异系数最小(0.827);白桦林穿透雨、树干径流中Mg元素变异系数均为最大,分别为0.989和0.827,最小变异系数分别为Si(0.46)和Mn(0.459);与大气降雨相比,穿透雨和树干径流中各养分元素的变异系数均小于降雨中该元素的变异系数;4)白桦林各元素年净输入量为K＞Mg＞Si＞Mn＞Ca,且Ca元素的年净输入量为负值。      

红松人工用材林近自然经营技术的研究

以“近自然林业”为指导思想。采用实验生态学的方法,经过６ａ的伐孔实验证实了林隙对红松更新生长的有利作用,确定出树高与林隙孔径比为１：１～４：３时较利于林隙内红松的生长。据此通过理论生态学的方法,得出了５种地位级上单位面积不同白桦高度及白桦－红松经营复合体中白桦株数、林隙个数、林隙孔径、不同直径大小的红松株数及每个林隙中不同大小的红松株数等技术指标,为红松人工用材林的持续经营提供了科学的依据。     

大兴安岭不同演替阶段白桦种群光合生理生态特征

应用LI-6400光合作用测定系统,研究了大兴安岭不同演替阶段白桦光合生理生态学特征。结果表明:无论是最大净光合速率,还是表观最大量子效率,非演替顶极群落中的白桦[(7 79μmol/(m2·s)、0 0698mol/mol)]都大于演替顶极群落中的白桦[(7 59μmol/(m2·s)、0 0457mol/mol)],这表明非演替顶极群落中白桦的实际光合能力和潜在光合能力都大于演替顶极群落中的白桦。2个不同演替阶段中白桦的光饱和点相差不大,但是演替顶极群落中白桦的光补偿点却低于非演替顶极群落,这表明演替顶极群落中白桦的呼吸作用有所下降。此研究结果揭示了大兴安岭顶极群落中白桦退出主林层的生理生态学机制。     

大兴安岭白桦低质林改造后土壤肥力的综合评价1）

以大兴安岭白桦低质林为研究对象,通过对白桦低质林进行不同林窗、不同带宽诱导改造,应用灰色关联度法综合分析不同模式改造后的林分土壤肥力的各个指标。研究表明,所有的诱导改造对土壤肥力均有改善作用。白桦低质林林窗诱导改造中土壤肥力综合评价最高的是20 m×20 m（ G4）为0．849;不同带宽的诱导改造中最高的是14m （S3）为0．733。综合评价白桦低质林改造模式土壤肥力质量的改造效果,林窗诱导改造优于带状诱导改造模式。     

Functions for estimating aboveground biomass of birch in Norway

A suite of regional allometric aboveground biomass functions were derived for Betula pubescens and Betula pendula for Norwegian conditions. The data consisted of 67 trees sampled throughout Norway. A total of 14 component functions were developed for total aboveground, total stem, stemwood, stem bark, live crown, live branch, leaf, and dead branch biomass using combinations of diameter at breast height and height as predictor variables. Application of the derived functions to existing local southern Norwegian mountain birch and regional Swedish biomass datasets indicated an overall good predictive ability of the developed functions. However, the functions produced slight underestimates, suggesting that the respective birch populations had differing biomass allocation patterns. When the developed functions were applied to Norwegian National Forest Inventory data, they produced slightly higher biomass stock and stock change estimates than what is obtained using existing Swedish functions. The higher estimates were evident in the north, central, and western part of Norway, while estimates were similar in southeastern Norway where growing conditions are most similar to Swedish conditions. The analysis indicates that the derived functions are the best available for regional birch biomass stock and stock change estimation in Norway.     

Birch stands growth increase in Western Siberia

Birch (Betula pendula Roth) growth within the Western Siberia forest-steppe was analyzed based on long-term (1897–2006) inventory data (height, diameter at breast height [dbh], and stand volume). Analysis of biometry parameters showed increased growth at the beginning of twenty-first century compared to similar stands (stands age = 40–60 years) at the end of nineteenth century. Mean height, dbh, and stem volume increased from 14 to 20 m, from 16 to 22 cm, and from ～63 to ～220 m³/ha, respectively. Significant correlations were found between the stands mean height, dbh, and volume on the one hand, and vegetation period length (r_s = 0.71 to 0.74), atmospheric CO₂ concentration (r_s = 0.71 to 0.76), and drought index (Standardized Precipitation-Evapotranspiration Index, r_s = ?0.33 to ?0.51) on the other hand. The results obtained have revealed apparent climate-induced impacts (e.g. increase of vegetation period length and birch habitat drying due to drought increase) on the stands growth. Along with this, a high correlation of birch biometric parameters and [CO₂] in ambient air indicated an effect of CO₂ fertilization. Meanwhile, further drought increase may switch birch stand growth into decline and greater mortality as has already been observed within the Trans-Baikal forest-steppe ecotone.     

白桦木材侵染菌侵染材的化学分析

白桦木材在自然和人工干燥过程中易受真菌类微生物的侵染产生色变,在一定程度上降低了白桦木材的加工利用价值。本文针对白桦木材侵染菌侵染试材的化学成分变化进行分析,以期为白桦木材生物变色防治提供参考。首先对白桦木材侵染菌进行分离、纯化与鉴定,确定侵染白桦试材的侵染菌的基本类型,然后进行白桦试材接菌,最后对白桦侵染菌侵染木材的化学成分进行测定。结果表明,与未侵染素材相比,侵染菌侵染试材中苯醇抽提物含量、1%NaOH抽出物含量、热水抽出物含量和多戊糖含量均较高,而纤维素及木素含量较低。这表明侵染菌在适宜的条件下会侵蚀白桦木材细胞壁组织,造成纤维素和木素等主要成分含量的降低,导致木材组分的破坏。同时,侵染菌的存在会造成白桦木材抽提物组分中的显色及助色物质的含量变化,以致木材产生不同程度的变色。