Current growth differences of Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and birch (Betula pendula and Betula pubescens) in different regions in Sweden

Abstract

The choice of species in forestry is important, and a real issue as large areas of wind-damaged forest land in southern Sweden need to be regenerated. To compare the growth potential between the most common tree species in Sweden, ratios between site quality derived from site index values determined with site properties were used. A regression function to determine site index for birch from site properties was used to complement the known relationships between site properties and site index for spruce and pine. In large regions of Sweden the distribution of site quality classes was calculated to compare the special characteristics and demands of the three species. On average, the growth difference for pine compared to spruce was about 60% in southern Sweden and 95% in northern Sweden. Corresponding figures between birch and spruce were 40% and 60%. Birch was expected to produce around 60% of pine in northern Sweden and about 70% in southern Sweden. However, it must be stressed that the comparison is based on survey data encompassing mainly naturally regenerated birch, whereas spruce and pine are mainly planted.     

Browsing by large herbivores on Scots pine (Pinus sylvestris) seedlings in mixture with ash (Fraxinus excelsior) or silver birch (Betula pendula)

Abstract

Food selection by large herbivores occurs at a hierarchy of scales, for example landscape, patch or plant. Several hypotheses regarding food plant selection on patch or plant level have been developed. In this cafeteria-type design field experiment, conducted during one winter immediately after planting, we tested the effect of species mixture on browsing by large herbivores (mainly roe deer) on Scots pine seedlings in mixture with seedlings of ash (highly preferred) or silver birch (less preferred). Browsing on Scots pine was not affected by species mixture, neither in terms of the number of browsed pines nor browsing intensity. Instead, browsed biomass was positively and significantly correlated to the total biomass available for browsing. Also, there were differences due to species, with ash being most browsed (44.6%), followed by Scots pine (18.9%) and silver birch (11.6%). Browsed biomass per browsed seedling, however, was largest for Scots pine. In addition, browsed seedlings were initially taller compared to unbrowsed seedlings for all species. The main management implication in this study is that the species mixture did not influence large herbivore browsing on Scots pine seedlings. Hence, removing or discouraging more (or less) attractive browse species in early stages of pine regeneration activities seems unnecessary from the point of large herbivore browsing.     

Effect of Temperature on the Induction of Bud Dormancy in Ecotypes of Betula pubescens and Betula pendula

The purpose of this study was to determine the influence of temperature applied during short day-induced budset on induction of dormancy in six ecotypes of Betula pubescens Ehrh. and two ecotypes of Betula pendula Roth. Seedlings were grown in a phytotron at constant temperatures of 9–21°C under a 12 h photoperiod (SD) during dormancy induction. Induction of dormancy was monitored by following bud flushing and shoot growth after transfer to long photoperiod conditions (24 h) at 18°C. Chilling requirement was studied in seedlings exposed to 10 weeks of SD. In both species induction of bud dormancy developed most rapidly at 15–18°C, and both 9–12°C and 21°C delayed the induction of dormancy. Raising the temperature (from 9 to 21°C) applied during induction of dormancy significantly increased the chilling requirement. These responses were noted for all ecotypes tested, but in general the northern ecotypes entered dormancy more quickly than the southern ones. No such trend was recorded for chilling requirement, although a B. pubescens ecotype from Iceland and another from the coast of northern Norway appeared to require a longer chilling treatment than the other ecotypes. In conclusion, induction and depth of bud dormancy in birch are significantly affected by temperature conditions and these effects may explain some of the annual variation in dormancy and chilling requirement observed in nature.     

Improvement of Betula pendula by clonal and progeny testing of phenotypically selected trees

Abstract

Field tests, each including 39–83 Swedish plus-tree clones of silver birch (Betula pendula Roth) planted on 10 different sites in the southern part of Sweden, were evaluated at up to 10 years of age. The main conclusions can be summarized as follows. Growth traits were mostly under strong genetic influence, and showed substantial genetic variation and high potential genetic gain. Survival did not seem to be a trait of genetic importance. The genetic correlation between growth and growth cessation was weak, suggesting that it should be possible to find clones combining high growth and early autumn growth. Non-significant transfer effects for clones of different origin and weak G×E interaction were found, indicating that southern Sweden can be treated as a single utilization zone and that few sites are needed for genetic tests. Strong genetic age×age correlations were detected, suggesting that short test periods could be used.     

Variations in phenology and growth of European white birch (Betula pendula) clones

Phenology can have a profound effect on growth and climatic adaptability of northern tree species. Although the large interannual variations in dates of bud burst and growth termination have been widely discussed, little is known about the genotypic and spatial variations in phenology and how these sources of variation are related to temporal variation. We measured bud burst of eight white birch (Betula pendula Roth) clones in two field experiments daily over 6 years, and determined the termination of growth for the same clones over 2 years. We also measured yearly height growth. We found considerable genetic variation in phenological characteristics among the birch clones. There was large interannual variation in the date of bud burst and especially in the termination of growth, indicating that, in addition to genetic effects, environmental factors have a strong influence on both bud burst and growth termination. Height growth was correlated with timing of growth termination, length of growth period and bud burst, but the relationships were weak and varied among years. We accurately predicted the date of bud burst from the temperature accumulation after January 1, and base temperatures between +2 and -1 degrees C. There was large clonal variation in the duration of bud burst. Interannual variation in bud burst may have important consequences for insect herbivory of birches.     

Long-term dynamics of leaf and root decomposition and nitrogen release in a grey alder (Alnus incana (L.) Moench) and silver birch (Betula pendula Roth.) stands

The decomposition of the leaf litter, fine roots (d?<?2?mm) and coarser roots (2?≤?d?<?5?mm) of grey alder and silver birch, as well as of α-cellulose sheets using the litterbag method was studied in two experimental stands on Podzoluvisol soils in Southern Estonia. For both tree species, the coarser roots decomposed faster than the fine roots, (p?<?.05), tree species did not affect the decomposition rate of the roots (p?>?.5). The nitrogen (N) input to soil from aboveground litter was multiple times higher than the N flux from roots. The remaining relative ash-free mass of the leaves of grey alder and silver birch after three and a half years was similar. After 11 years the remaining relative ash-free mass of the fine and coarser roots of grey alder still accounted for around 10% of the initial value. For silver birch the remaining value was around 20% after 9 years. The litterbag method to underestimates in fertile soils the decomposition of organic matter and thus did not reflect the actual dynamics of decomposition.     

Transgenic Betula pendula expressing sugar beet chitinase IV forms normal ectomycorrhizae with Paxillus involutus in vitro

Abstract

Mycorrhizal fungi contain chitin in their cell walls and may be influenced by transgenic chitinases. This study examined the ability of a transgenic tree, silver birch (Betula pendula Roth), constitutively expressing the sugar beet chitinase IV gene, to form ectomycorrhizae with Paxillus involutus (Batsch) Fr. Eight transgenic lines showing varying levels of sugar beet chitinase IV expression and the non-transgenic control plants were inoculated by P. involutus in vitro, and the morphology of the mycorrhizae, mycorrhization efficiency and shoot and root fresh weights were studied. All the transgenic birch lines were able to form normal ectomycorrhizae containing distinctive mantles and Hartig nets. The level of sugar beet chitinase IV expression had no significant influence on mycorrhizal colonization. The only significant differences between transgenic and control plants were detected in weight parameters. According to these results, the expression of sugar beet chitinase IV in silver birch is not deleterious to formation of ectomycorrhizae between birch and P. involutus.     

Prediction of individual tree growth in managed stands of mixed Picea abies (L) Karst,and Betula pendula Roth & Betula pubescens Ehrh.

The individual tree growth in stands of mixed Norway spruce (Picea abies (L.) Karst.) and birch (Betula pendula Roth & Betula pubescens Ehrh.) is estimated using basal area and height growth functions for each species separately. The individual tree growth models are distant dependent and the number, size and proximity of neighbours are expressed as size‐ratio competition indices. The competition indices were calculated using a basal area factor gauge to define competitors. The tree growth functions are based on data from nine mixed stands of Norway spruce and birch. The recursive multivariate regression approach is used. The growth functions have standard deviation about the function/standard deviation about the mean (sf/sm) values between 31 and 61% and the evaluations made with root mean square error (rmse) give estimates which vary between 8 and 45 % of the observed mean value. These values are comparable with the precision reported in other studies. In the present investigation the distant dependent indices are important independent variables. It seems suitable to describe the change in growth conditions from retarded to released growth by means of size ratio competition indices. For birch, a positive effect on growth is obtained the more the total competition consists of Norway spruce. For Norway spruce a negative effect on growth is obtained the more the total competition consists of Norway spruce. The lower competitors have a positive effect on the growth of the spruce trees. The interpretation should be that it is better to have a small competitor than a larger one, not that small competitors as such have a positive effect on growth of Norway spruce.     

冀北山地亚高山地区阴坡白桦中幼龄林生长状况分析

为进一步提高林分质量,实现森林可持续经营的目的,在野外调查的基础上,采用对优势木和平均木解析的方法,研究了冀北山地亚高山地区阴坡中幼龄白桦林不同发育阶段的生长变化规律。结果表明：在0～20a间,树高、胸径、材积均处于高速生长的时期,并且从3个指标来看,优势木均比平均木达到最快生长的时期早,并通过对3个指标的平均生长量和连年生长量的对比分析,得出白桦优势木在10～15a间生长速度最快,平均木在15～20a间生长速度最快。速生期后,林分进入平稳生长的时期,连年生长量逐渐降低,平均生长量趋于平缓,并继续进入慢生期。     

Effects of red alder and paper birch competition on juvenile growth of three conifer species in southwestern British Columbia

We examined the effects of competition from red alder (Alnus rubra Bong.) and paper birch (Betula papyrifera Marsh.) on the growth of western redcedar (Thuja plicata Donn), western hemlock (Tsuga heterophylla Sarg.), and Douglas-fir (Pseudotsuga menziesii Franco) at a site near Maple Ridge, British Columbia, Canada. At this site, the three coniferous species and two broadleaf species had been planted in 1999 as part of a long-term experiment examining effects of broadleaf density on conifer growth. Red alder and paper birch were planted alone and as a 50:50 mixture at four densities (0, 277, 556, and 1150 stems ha⁻¹).     

Isolation of genes up-regulated by copper in a copper-tolerant birch (Betula pendula) clone

Suppression subtractive hybridization (SSH) was used to isolate genes differentially expressed following exposure to copper (Cu) in a naturally selected Cu-tolerant birch (Betula pendula Roth.) clone originating from a disused lead/zinc smelter. Of the 352 cDNA fragments initially isolated, 108 were up-regulated by Cu, of which 55 showed over twofold induction by macroarray analysis. Searches against protein databases (Blastx) and sequence analysis provided the tentative identity of 21 genes. Three fragments lacked homology to any sequences in the databases. Most of the identified genes are involved in cellular transport, regulation or cell rescue and defense. Several genes have not previously been reported to be up-regulated by Cu, e.g., plasma intrinsic protein 2, glutamine synthetase and multi-drug resistance-associated protein (MRP4). The expression of MRP4, a vacuolar sorting receptor-like protein and an unidentified gene was studied in more detail by quantitative real-time PCR. These genes showed stronger up-regulation by Cu in the roots and shoots of the Cu-tolerant birch clone compared with a less tolerant clone. Clear clonal differences in gene expression were observed, e.g., for the regulator of chromosome condensation family protein, DnaJ protein homolog, vacuolar sorting receptor-like protein and MRP4. These findings contribute to our understanding of Cu tolerance in birch, a pioneer plant in metal-contaminated soils.     

Seasonal and within-stem variations of neutral lipids in silver birch (Betula pendula) wood

Neutral lipids were analyzed in stem wood of a 7-year-old clone and in five 35-70-year-old mature trees of silver birch (Betula pendula Roth). In young trees and in mature wood of old trees, the free fatty acid fraction comprised less than 5% of the concentration of triacylglycerols (TG). The concentration of free linoleic acid was lowest in March when the young trees were dormant and highest during midsummer and September. In mature trees, the TG concentration increased toward the pith, indicating that living parenchyma cells close to the pith have a large TG storage capacity. The TG concentration (mean 0.51 +/- 0.02% of wood dry mass) remained constant throughout the year in young trees, whereas the concentration of beta-sitosterol, the dominant free sterol (mean 82.5 +/- 0.4% of total free sterols), decreased during spring and early summer when the temperature gradually increased, and increased during autumn when the trees became dormant. In young trees, we detected a seasonal interconversion between the free and esterified forms of beta-sitosterol and campesterol, and within the steryl ester fraction between squalene and betulaprenol-7. The concentration of esterified sterols/isoprenoids was exceptionally high, especially in the inner regions of mature stem wood (mean 0.6 +/- 0.03% of wood dry mass). No heartwood formation was detected.     

Photosynthesis and canopy characteristics in genetically defined families of silver birch (Betula pendula)

Net photosynthetic rates (A) of leaves in upper and lower crown layers (A(upper) and A(lower)), leaf area index (LAI), mean tilt angle (MTA), several leaf characteristics, and volume growth were observed in fast- and slow-growing families of a 14-year-old full-sib and half-sib family progeny test of Betula pendula Roth. Each measure of net photosynthetic rate was calculated after correcting measured net photosynthesis for the effects of environmental variables. The differences in A(upper) and LAI among families were significant. The proportions of the total variance assigned to family for A(upper), A(lower) and LAI were 33.64, 28.93 and 54.99%, respectively. The mean A(upper) and LAI of the fast-growing families were significantly higher than those of the slow-growing families, whereas the mean A(lower) of the fast-growing families was significantly lower than that of the slow-growing families. There were also significant differences among families in leaf size, leaf shape, and the ratios leaf fresh weight/area and leaf dry weight/area. Between 27.55 and 54.55% of the total variance in these characteristics could be assigned to the family effect. Volume growth was positively correlated with A(upper) and LAI, but it was most strongly correlated with A(upper) x LAI.     

Dependence of dormancy release on temperature in different origins of Pinus sylvestris and Betula pendula seedlings

The chilling requirement of rest completion and the high temperature requirement of growth initiation were determined in three origins of silver birch (Betula pendula Roth.) seedlings and five origins of Scots pine (Pinus sylvestris L.) seedlings. In both the pine and birch the chilling requirement was highest in maritime Scottish origins and lowest in the most continental Finnish and Russian origins. The requirement for southern mountainous Spanish and Bulgarian pine origins was in between. In terms of the high temperature requirement, there were no clear differences between origins. These results suggest that owing to their high chilling requirement, which prevents the beginning of growth and the loss of frost hardiness during the frost‐exposed season, origins from a maritime climate could be the most tolerant under climatic warming.     

Long-term photosynthetic acclimation to increased atmospheric CO(2) concentration in young birch (Betula pendula) trees

To study the long-term response of photosynthesis to elevated atmospheric CO(2) concentration in silver birch (Betula pendula Roth.), 18 trees were grown in the field in open-top chambers supplied with 350 or 700 &mgr;mol mol(-1) CO(2) for four consecutive growing seasons. Maximum photosynthetic rates, stomatal conductance and CO(2) response curves were measured over the fourth growing season with a portable photosynthesis system. The photosynthesis model developed by Farquhar et al. (1980) was fitted to the CO(2) response curves. Chlorophyll, soluble proteins, total nonstructural carbohydrates, nitrogen and Rubisco activity were determined monthly. Elevated CO(2) concentration stimulated photosynthesis by 33% on average over the fourth growing season. However, comparison of maximum photosynthetic rates at the same CO(2) concentration (350 or 700 &mgr;mol mol(-1)) revealed that the photosynthetic capacity of trees grown in an elevated CO(2) concentration was reduced. Analysis of the response curves showed that acclimation to elevated CO(2) concentration involved decreases in carboxylation efficiency and RuBP regeneration capacity. No clear evidence for a redistribution of nitrogen within the leaf was observed. Down-regulation of photosynthesis increased as the growing season progressed and appeared to be related to the source-sink balance of the trees. Analysis of the main leaf components revealed that the reduction in photosynthetic capacity was accompanied by an accumulation of starch in leaves (100%), which was probably responsible for the reduction in Rubisco activity (27%) and to a lesser extent for reductions in other photosynthetic components: chlorophyll (10%), soluble protein (9%), and N concentrations (12%) expressed on an area basis. Despite a 21% reduction in stomatal conductance in response to the elevated CO(2) treatment, stomatal limitation was significantly less in the elevated, than in the ambient, CO(2) treatment. Thus, after four growing seasons exposed to an elevated CO(2) concentration in the field, the trees maintained increased photosynthetic rates, although their photosynthetic capacity was reduced compared with trees grown in ambient CO(2).     

Effect of growing site,sampling date,wood location in trunk and drying method on concentration of soluble proanthocyanidins in Betula pendula wood,with special reference to wood colour

Proanthocyanidins (PAs), which are common phenolic compounds in plants, are considered to be mainly defensive compounds against different kinds of stress, e.g. herbivory. In addition to increasing after stress, they may condense and/or oxidize to form coloured compounds when cells die, which may affect both the resistance of xylem to rot and its colour. This is important in the mechanical wood industry. The effects of some biological factors (growing site, sampling date, wood location in the trunk) on the concentration of soluble PAs (sPAs) were studied in fresh and dried birch wood. Those factors that affected sPA concentration most were sampling date and radial location. Drying method also had a great effect on the sPA concentration, which in turn correlated with the colour of the wood.     

Origin of the acetylated structures present in white birch (Betula pendula Roth) milled wood lignin

The occurrence and nature of acetate groups in the milled wood lignin (MWL) isolated from birch (Betula pendula Roth) has been addressed by spectroscopic (2D-NMR) and chemical degradative (derivatization followed by reductive cleavage, DFRC) methods. Considerable amounts of acetate groups were present in the MWL preparation. However, 2D-NMR analysis indicated that the lignin polymer is not extensively acetylated and that the major part of the acetate groups is attached to the xylan moieties present in the MWL preparation. Nevertheless, evidence of the presence of minor acetylation of the γ-carbon of the lignin side chain (<3% of both syringyl and guaiacyl lignin units) was provided by DFRC analysis.     

Effects of copper and cadmium on uptake and leakage of K(+) in birch (Betula pendula) roots

Uptake and leakage experiments were performed to study the effects of copper and cadmium on K(+) fluxes in birch (Betula pendula Roth) roots. Labeled rubidium ((86)Rb(+)) was used as a tracer for K(+). Plants were pretreated with Cu or Cd (0, 2, 5 or 25 microM) for 0-300 min and then transferred to radiolabeled nutrient solution (150 microM K(+)) with or without 2,4-dinitrophenol (DNP) to separate the effects of heavy metal on active and passive K(+) influxes. Passive K(+) influx was decreased by pretreatment with Cu but was only slightly affected by pretreatment with Cd. Pretreatment with 2 microM Cu increased active K(+) influx, whereas pretreatment with 25 microM Cu decreased active K(+) influx and intermediate Cu concentrations (5 microM) did not affect active K(+) influx. The pretreatment effects of Cu on active and passive K(+) influxes increased with increasing pretreatment time. During the first hour, pretreatment with Cd decreased active K(+) influx with increasing pretreatment time, whereafter recovery began. To measure K(+) efflux, birch plants were loaded with (86)Rb(+) for 7 days before being exposed to Cu or Cd (0, 1, 3, 5 or 10 microM) in unlabeled nutrient solutions for 24 h. Net efflux of K(+) was measured as (86)Rb(+)-activity in the nutrient solutions 24 h after a heavy metal had been introduced. Efflux of K(+) increased with increasing Cu or Cd concentration in the unlabeled nutrient solution.The data indicate that Cu and Cd affected K(+) influx differently and that recovery mechanism(s), which were induced shortly after heavy metal introduction, counteracted the heavy-metal induced inhibition of active K(+) influx. Efflux of K(+) from plant roots over a 24-h period indicated that Cu and Cd had similar effects on K(+) efflux. There was no evidence of a recovery mechanism counteracting the heavy-metal-induced inhibition of K(+) efflux.