Effect of CCC on the morphology and growth potential of containerised silver birch seedlings

The objective of the experiment described here was to assess the effect of the synthetic growth regulator CCC on the quality of containerised silver birch seedlings. The time course of stem elongation during the growing season, the morphology and size of the seedlings at the end of the growing season, and the growth potential after winter storage were measured and the following results obtained: (1) Stem height, root-collar diameter and total dry weight of the seedlings were decreased by CCC. (2) Stem-height:root-collar-diameter ratio was slightly decreased and root weight ratio was increased by CCC. (3) Stem flexibility was not significantly affected by CCC, although it was significantly correlated with total plant dry weight and with the stem-height:root-collar-diameter ratio. (4) Root-growth potential was decreased at high doses of CCC while shoot growth potential was not affected.     

Genetic and environmental determinants of silver birch growth and herbivore resistance

Plant growth and herbivore resistance is affected by both environmental and genetic factors. The aim of this study was to examine (1) whether genotype explains variation in herbivore resistance, plant growth and tolerance of feeding within natural silver birch populations, (2) whether there is significant interaction between birch genotype and environment or the study year, and (3) whether there are defence costs in field grown juvenile silver birch saplings. The 22 genotypes studied were assigned insect exposure and insect removal treatments in two different environments. Resistance to insect herbivory was measured as the amount of undamaged leaves of the saplings and tolerance of feeding as a difference in relative height increment of the saplings between insect exposure and removal treatments in relation to the amount of damage (i.e. opposite number of resistance). Our study shows that a local silver birch population has substantial genotypic variation in resistance to insect herbivores and this variation is not affected by the environment or the study year. Genotypic variation was not observed for tolerance of feeding. We also showed that, in contrast to genotypic variation in resistance, the genotypic variation in growth among silver birch genotypes strongly depended on the environment, i.e. silver birch genotypes have a high degree of phenotypic plasticity in their growth. Therefore, defence costs in terms of lower growth rate appear to be highly dependent on the environment. To conclude, our results indicate that silver birch populations have a good potential to adapt to possibly increasing herbivory in boreal forests in warmer future climates.     

Initial seedling emergence of hairy birch and silver birch on abandoned fields following different site preparation regimes

Experiments were carried out at four sites in Sweden to investigate the possibility of establishing hairy birch (Betula pubescens Ehrh.) and silver birch (Betula pendula Roth) on abandoned fields using natural regeneration and (or) direct seeding. The effects of six soil preparation methods (no preparation, ordinary ploughing, rotary cultivation, deep ploughing, inverted ground, removal of top-soil) and five additional treatments (no treatment, herbicide, peat litter, wood-ashes, slaked lime) on seedling emergence percentages (SEP) and vegetation cover percentages (VCP) were studied. SEP-values were estimated in June (SEP(J)) and October (SEP(O)). The experimental designs used were: 1) split-plot design with whole plots in a randomized complete block design (RCBD); 2) RCBD. The SEP-values observed with no preparation were close to 0% while the SEP-values obtained with mechanical soil preparation methods mostly were much higher (p0.014). Seedbeds with top-soil in the surface, created by ordinary ploughing or rotary cultivation, and seedbeds with mainly bare mineral soil in the surface, created by deep ploughing, inverted ground or removal of top-soil, obtained SEP-values of equal merit on silty soils, reaching SEP(O)-values up to 15%. The latter seedbeds obtained the best results on sandy soil, with as high SEP(O)-values as 47% after removal of top-soil. Seedbeds with top-soil in the surface were quickly colonized by ground vegetation, reaching VCP-values between 70% and 100%. Herbicide spraying with glyphosate and application of peat litter to the seedbed surface promoted seedling emergence. However, herbicide spraying before soil preparation was of little effect when followed by mechanical soil preparation.     

Site preparation of abandoned fields and early establishment of planted small-sized seedlings of silver birch

Field experiments at two sites in Sweden investigated the possibility of establishing silver birch (Betula pendula Roth) on abandoned fields by planting small (5–10 cm tall) seedlings. The effects of five modes of soil preparation (no preparation, rotary cultivation, deep ploughing, soil inversion, and removal of topsoil) with or without preliminary herbicide weed control on seedling performance were studied for three growing seasons following plantation. Both a split-plot design and a randomized block design were used to evaluate the experiments. Where there was no site preparation, seedling survival was close to nil. The highest seedling survival rates on the site with sandy soil were obtained on sites prepared by removing topsoil, or by transposing it by deep ploughing. On the site with silty soil, the best survival was observed on sites created by soil inversion or rotary cultivation. The tallest seedlings were found on sites with topsoil retained within the soil profile. Herbicide application with glyphosate promoted seedling survival and seedling height in combination with no soil preparation, but was of little effect when followed by mechanical soil preparation.     

The effects of species mixture on the growth and yield of mid-rotation mixed stands of Scots pine and silver birch

The effect of tree species mixture on stand volume yield and on tree-species-specific diameter and height growth rates were analysed in managed mixed stands of Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Ehrn.).Data were obtained from 14 repeatedly measured stands located in Southern Finland on mineral soil sites with varying admixture of Scots pine and silver birch. Statistical analysis was carried out for studying the effect of species mixture on the development of stand characteristics. For the analysis, the plots were categorised into three groups (plot types) according to the species dominance. In order to analyse species-specific growth rates, individual-tree mixed linear growth models for tree diameter and height growth were developed for both tree species.The results clearly show that the yield of the managed mid-rotation, mixed stands was greater for stands dominated by Scots pine than for stands dominated by birch, and the stand volume increment decreased with an increasing proportion of silver birch. Analysis of diameter and height growth by tree species revealed that the main reason for this pattern is the negative impact of birch competition on the growth of pine trees. The increase in diameter of pine was clearly hampered if the proportion of birch was high. An abundance of birch also slightly decreased the growth in height of Scots pine, although the effect was less than on diameter growth. Species mixture did not affect the diameter growth of birch but did have a significant effect on height development. Height growth of birch was considerably greater in pine-dominated stands than in birch-dominated stands. In pine-dominated mixed stands, the height growth of birch was quite close to that of dominant pine trees, and birches can endure in competition with pines for light.The results apply for even-aged and single-storey managed stands, where stocking density and structure are controlled with pre-commercial and commercial thinnings. The results are not applicable to unmanaged mixed stands undergoing self-thinning. This study provides new information on mixed stands from a silvicultural perspective, which can be applied in decisions involving the management of mixed stands.     

Stress resistance levels change little during dormancy in ash,sessile oak and sycamore seedlings

The physiological status of ash (Fraxinus excelsior L.), sessile oak (Quercus petraea (Matt.)) and sycamore (Acer pseudoplatanus L.) seedlings sampled from nurseries in Ireland between October and May, 1995/1996 and 1996/1997 was investigated. The results of heat treatments applied to taproots in vitro and evaluated using root electrolyte leakage (REL) indicated that sycamore was more easily damaged than the other species but lift date effects were small in all species. Dormancy release began later each year in ash (mid-November) than in oak or sycamore (late October to early November). The results of the REL and other data indicated that there was little change in stress resistance from November to about March (and April for some parameters). Sycamore was most active (highest shoot xylem pressure potential, REL, and root growth potential) during the winter, suggesting that adverse handling during this period is likely to reduce plant quality than in ash or oak. Field performance was good regardless of lifting/planting date.     

Physiological and field growth responses of oak seedlings to warm storage

The effect of warm storage (15°C) for 0, 15 or 31 days, applied after cold storage until April, and date of lifting to cold storage on the physiological condition and field performance of two-year-old oak seedlings (Quercus robur L.) was investigated. Assessments before planting included plant moisture status, root and shoot dry weight, root growth potential (RGP), while after planting root growth, shoot growth phenology, shoot and root dry matter accumulation and stem quality were assessed. Warm storage effects were large, but lift date effects were small. Warm storage for 31 days reduced height and diameter growth, stem quality, total biomass, root growth, and reduced stem quality in the field, but 15 days storage had a smaller effect. Warm storage delayed bud break and shoot growth cessation but survival was unaffected. The depletion of food reserves during storage and low moisture availability might have caused shoot dieback leading to the development of poor quality stems. There was evidence that dry weight fraction of both the shoot tip and the taproot provided good information on the quality of the stock before planting. RGP was also a good indicator of quality. Electrolyte leakage readings from fine and taproots were not reliable indicators of plant quality.     

Early performance of native birch (<Emphasis Type="Italic">Betula</Emphasis> spp.) planted on cutaway peatlands: influence of species,stock types and seedlings size

The poor reputation of birch in Ireland is gradually changing, and the interest shown in it by foresters is growing, as is the recognition of the many advantages that this genus offers, especially from an afforestation and ecosystem development point of view. The potential of native birch species was investigated on industrial cutaway peatlands in the Irish midlands. Field experiments were established to evaluate differences (in terms of survival, growth attributes and form) between B. pendula and B. pubescens, between bare-root and container planting, and between small and medium size seedlings. After five growing seasons, B. pendula was found to be the superior species especially on well drained and shallow peat sites. Bare-root B. pendula will grow faster with reasonable form but containerised birch may be favoured on more difficult sites (with deeper and wetter peat). Larger seedlings performed better, regardless of species. This study demonstrated good growth potential for planted birch on cutaway peatlands and that this species should be integrated in further planting programmes.     

Biomass production, foliar and root characteristics and nutrient accumulation in young silver birch (Betula pendula Roth.) stand growing on abandoned agricultural land

The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics of a 8-year-old silver birch (Betula pendula) natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current annual production after eight growing seasons was 31.2 and 11.9 t DM ha⁻¹, respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass of the stand. Carbon sequestration in tree biomass reaches roughly 17.5 t C ha⁻¹ during the first 8 years. The biomass of the fine roots (d < 2 mm) was 1.7 ± 0.2 t DM ha⁻¹ and 76.2% of it was located in the 20 cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7 m² m⁻² and specific leaf area (SLA) 15.0 ± 0.1 m² kg⁻¹. The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared with the lower part. The short-root specific area (SRA) in the 30 cm topsoil was 182.9 ± 9.5 m² kg⁻¹, specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry mass unit of short roots were 145.3 ± 8.6 m g⁻¹, 58.6 ± 3.0 kg m⁻³ and 103.7 ± 5.5 tips mg⁻¹, respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6, 25.0 and 56.6 kg ha⁻¹, respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7 kg ha⁻¹ yr⁻¹ (55 and 27%), respectively, of which 29.1 kg ha⁻¹ N and 2.8 kg ha⁻¹ P were accumulated in the above-ground part of the stand.     

Influence of different nursery container media on rooting of Scots pine and silver birch seedlings after transplanting

Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) seedlings were grown in containers filled with growth media based on medium-textured sphagnum peat, coarse perlite and fine sand. The seedlings were then planted into fine and coarse sandy soils in 2.2 l pots, which were subjected to two water-content treatments (only one for birch). After the seedlings had grown five weeks in a greenhouse, rooting into the surrounding soil and shoot growth were measured. Addition of perlite and sand to peat medium slightly affected rooting; thus suggesting minor effects on seedling establishment. However, nitrogen concentration of the seedlings varied between growth media and correlated positively with rooting into the soil. The particle size and water content of the soil affected considerably rooting of the seedlings. Seedling height at the time of planting did not affect rooting or shoot growth. The fact that the fewest out-grown roots occurred in the dry fine sandy soil, suggests that dry soil together with high strength and resistance to root penetration reduce rooting and water uptake by container seedlings most and may thus cause water and nutrient stresses to seedlings after outplanting.     

Effect of thawing regime on growth and mortality of frozen-stored Norway spruce container seedlings planted in cold and warm soil

One-year-old frozen-stored Norway spruce (Picea abies (L.) Karst.) container seedlings were planted in a controlled environment providing an air temperature of 22°C and soil temperature of 9±1 or 18±1°C. At planting the root plugs were either frozen or had been thawing for 4 days at 9°C. During a 5-week growing period, in both cold and warm soil the root growth and height growth were less in frozen-planted seedlings than in thawed seedlings. In addition, frozen-planting delayed bud burst and increased mortality. Soil temperature, however, had no effect on bud burst or mortality. Low soil temperature retarded root growth of seedlings thawed before planting but resulted in both retarded root growth and height growth if root plugs were frozen when planted. These results indicate that planting Norway spruce seedlings with frozen root plugs constitutes a considerable risk for successful forest regeneration at soil temperatures normally prevailing in Fennoscandia in spring or early summer especially if the soil is dry at the time of the planting.     

Effects of log storage and drying on birch (<Emphasis Type="Italic">Betula pendula</Emphasis>) wood proanthocyanidin concentration and discoloration

In conventional drying, sawn birch (Betula sp.) timber darkens and reddens from the inside while the layer a few millimetres under the yellowish surface remains light in color. Lack of information concerning the chemical basis of the discoloration hinders the development of a reliable solution for this problem. In this study, the role of soluble proanthocyanidins in discoloration of birch wood was investigated because the polymerization and oxidation of these compounds are known to yield insoluble reddish compounds. Different periods of log storage affected the synthesis of soluble proanthocyanidins during conventional drying. Concentration of proanthocyanidins also correlated with changes in the color of birch wood. Discoloration appeared differently in conventionally dried and vacuum-dried wood, which indicates that the discoloration mechanism in these drying methods may differ chemically, and/or the compounds that take part in discoloration may be different at different drying temperatures.     

Differences in soil properties in adjacent stands of Scots pine, Norway spruce and silver birch in SW Sweden

Soil properties were compared in adjacent 50-year-old Norway spruce, Scots pine and silver birch stands growing on similar soils in south-west Sweden. The effects of tree species were most apparent in the humus layer and decreased with soil depth. At 20-30 cm depth in the mineral soil, species differences in soil properties were small and mostly not significant. Soil C, N, K, Ca, Mg, and Na content, pH, base saturation and fine root biomass all significantly differed between humus layers of different species. Since the climate, parent material, land use history and soil type were similar, the differences can be ascribed to tree species. Spruce stands had the largest amounts of carbon stored down to 30 cm depth in mineral soil (7.3 kg C m⁻²), whereas birch stands, with the lowest production, smallest amount of litterfall and lowest C:N ratio in litter and humus, had the smallest carbon pool (4.1 kg C m⁻²), with pine intermediate (4.9 kg C m⁻²). Similarly, soil nitrogen pools amounted to 349, 269, and 240 g N m⁻² for spruce, pine, and birch stands, respectively. The humus layer in birch stands was thin and mixed with mineral soil, and soil pH was highest in the birch stands. Spruce had the thickest humus layer with the lowest pH.     

Effects of coppicing on the root and stump carbohydrate dynamics in birches

Whole birch stems were cut off in order to determine how coppicing affects root and stump starch, glucose, fructose and sucrose concentrations and their correlation with shoot regeneration capacity. The Betula pubescens Ehrh. and B. pendula Roth studied included intact trees, trees that had been coppiced 8 years earlier, trees coppiced at the beginning of the experimental season, and birches that had been coppiced twice, 8 years earlier and at the beginning of the experimental season. Carbohydrate accumulation differed between 8 years earlier coppiced and intact trees. Recent coppicing clearly decreased the starch and sugar concentrations of the roots, which were often highest in the thin roots. The concentrations of these compounds in the stumps were always low, although the carbohydrate concentrations of stumps, in particular, correlated with shoot regeneration capacity. Starch was the most labile of the carbohydrates measured and most clearly reacted to coppicing. Differences in starch- and sugar-reserve dynamics indicate a difference between these birch species in the use and replenishing of root and stump reserves. This information may also be of help when the effects of other stresses, for example, severe animal damage or burning, on the regrowth of young birch stands are estimated.     

Early growth and photosynthetic responses to light in seedlings of three tropical species differing in successional strategies

Containerized seedlings of three commercially important tropical species were grown under four different light treatments [i.e., 100 (open site), 45, 22 and 10% sunlight] for 130 days. Light-saturated photosynthesis (A _max) and light saturation estimates (LSE) reflected the species successional status with Terminalia superba Engl. and Diels, the pioneer species showing largest mean A _max and LSE at 100% sunlight, whereas at 10% sunlight, it showed the lowest A _max and LSE. At 22% sunlight, Cedrela odorata L., an intermediate successional species had greater A _max and LSE than Mansonia altissima A. Chev., a non-pioneer light demander and T. superba. T. superba had the lowest relative growth rate (RGR) at 10% sunlight and greatest net assimilation rate (NAR) at 100% sunlight; although a higher RGR at this light level was not seen for this species. Strong and positive linear mean A _max–mean NAR relationship of C. odorata and T. superba indicated that differences in leaf photosynthetic rates of the two species were reflected in their NAR, which increased with increasing light. At final harvest, superior biomass production was found at 45% sunlight for all the species. Seedling responses in specific leaf area, leaf area ratio, leaf mass ratio and root mass ratio were typically those found along a light gradient. At the 100% sunlight, intrinsic water-use efficiency (WUE), F _v/F _m and final root system of the plants was generally superior in T. superba but at 10% sunlight, WUE was inferior in T. superba when compared to C. odorata and M. altissima, reflecting the respective species’ short-term acclimation to high or low light. Results of this study may have practical use in screening tropical tree species for use in plantation forestry.     

Root growth and hydraulic conductivity of southern pine seedlings in response to soil temperature and water availability after planting

Comparison of the root system growth and water transport of southern pine species after planting in different root-zone environments is needed to guide decisions regarding when, and what species to plant. Evaluation of how seed source affects root system responses to soil conditions will allow seed sources to be matched to planting conditions. The root growth and hydraulic conductivity of three sources each of shortleaf, loblolly and longleaf pine seedlings were evaluated for 28 days in a seedling growth system that simulated the planting environment. Across species, an increase in root-zone temperature alleviated limitations to root growth caused by water stress. In the coldest temperature, longleaf pine maintained a higher hydraulic conductivity compared to shortleaf and loblolly pine. Without water limitation, the root growth and hydraulic conductivity of shortleaf and loblolly pine were superior to that of longleaf pine, but as water availability decreased, the root growth of longleaf pine surpassed that of loblolly pine. Hydraulic conductivities of the seed sources differed, and differences were attributed to either new root growth, or an increase in the efficiency of the root system to transport water.     

Effects of thinning on growth of six tree species in north-temperate forests of Lithuania

This paper summarises the results from 35 years-observed thinning experiments on 256 permanent sample plots in 10–60 year-old stands of ash, aspen, birch, oak, pine and spruce in Lithuania. Thinning enhanced crown projection area increment of residual trees. The largest effect was observed in stands of aspen and birch (growth increase by 200%), followed by ash and oak (over 100%), and spruce and pine (about 80%). Thinning also promoted dbh increment, especially in younger stands, and the increase of dbh increment was positively correlated with the thinning intensity. The strongest reaction was exhibited by oak and aspen, while ash, birch and conifers reacted to a lower extent. Low and moderate intensities of thinning stimulated volume production in younger stands while the opposite was observed in older stands with increasing removals. Spruce stands exhibited relatively strongest increase of volume increment and pine, –the weakest, while the effect on deciduous species was intermediate. The results demonstrate that significant increase in volume increment is achievable with thinning of only young forest stands, e.g. 10–20 year-old pine, birch and ash, or 10–30 year-old oak, aspen and spruce.     

Root characteristics and growth potential of container and bare-root seedlings of red oak (<Emphasis Type="Italic">Quercus rubra</Emphasis> L.) in Ontario,Canada

Root characteristics and field performance of container and bare-root seedlings of red oak (Quercus rubra L.) were compared during the first growing season after planting. Sixty seedlings of each stock type were planted on a clearfell and weed-free site near Restoule, Ontario. Twenty-four additional seedlings from each stock type were compared at the start of the study in terms of shoot and root parameters. Measurement of root and shoot parameters were repeated at three dates during the first growing season in the field. The root systems of container stock had a larger number of first order lateral long roots and were significantly more fibrous than bare-root stock. These differences were sustained throughout the first growing season. In terms of field performance, container seedlings had 100% survival and achieved significant increases in both biomass and shoot extension. Bare-root seedlings suffered 25% mortality, significant shoot dieback and more variable growth. The mean relative growth rate (RGR) of container seedlings increased throughout the study period to a maximum of 30 mg/g/day, whereas the mean RGR of bare-root stock remained close to or below zero. Overall, the container seedlings proved less prone to transplanting shock than the bare-root seedlings, most likely due to favourable root architecture and the pattern of root development. Further work may be warranted in container design, growing regimes and root architecture to fully realise the potential of container systems for the production of high quality red oak seedlings across a range of site conditions.     

Evaluation of three root growth potential techniques with tree seedlings

Three growing systems commonly used to evaluate root growth potential (RGP) are soil, hydroponic, and aeroponic culture. Aeroponic RGP testing is a relatively new technique that has not been adequately compared to conventional methods. This paper reports the results of an experiment designed to compare the amount and variability of root growth of jack pine seedlings in soil, hydroponic, and aeroponic culture. New root length in aeroponic culture was significantly greater at 10, 14, 17, and 21 days and was less variable than that in soil and hydroponic culture. However, the patterns of root growth over time in the three systems are strongly related, so the testing methods provide the same diagnostic information. Root zone temperature differed significantly among locations within each system, but the actual differences were small and did not significantly affect root growth.     

Effect of planting density on plant growth and camptothecin content of Camptotheca acuminata seedlings

C. acuminata seedlings cultivated in greenhouse were transplanted into the fields with 5 designed planting densities (11, 16, 25, 44 and 100 plants·m⁻²) in May of 2004 and were harvested in the middle of September of 2004. The seedling growth indexes including plant height and crown width, biomass allocation, camptothecin (CPT) content and CPT yield of different organs (young leaf, old leaf, stem, and root) were studied. For the 5 selected planting densities, the plant biomass, height, crown width, and total leaf area ofC. acuminata seedlings all showed highest values at the planting density of 25 plants·m⁻². CPT content in young leaves was higher than that in other organs of seedlings and presented an obvious change with the variation of planting densities and with the highest value at density of 100 plants·m⁻², while for other organs no significant variation in CPT content was found with change of planting density. The accumulation of CPT was enhanced significantly at the planting density of 25 plants·m⁻². It is concluded that for the purpose to get raw materials with more CPT fromC. acuminata, the optimal planting density ofC. acuminata seedlings should be designed as 25 plants·m⁻². Foundation item: This paper was supported by the National Natural Science Foundation of China (No. 3970086) and Heilongjiang Province Foundation for Distinguished Youth Scholars (JC-02-11) Biography: Wei Huan-yong (1978-), male, Graduate in College of Life Sciences, Northeast Forestry University, Harbin 150040, P. R. China. Responsible editor: Zhu Hong