Natural regeneration of Picea abies on small clear-cuts in SE Norway

The objective was to study the influence of vegetation cover, humus depth, microrelief and distance to seed tree edge on natural regeneration of Norway spruce (Picea abies (L.) Karst.) in five small clear-cuts on bilberry woodland in southeastern Norway. The impact of the vegetation was considered at tree different scales: at the growing point, in the nearest square decimetre around the seedlings and at a 1 m² scale. Most of the regeneration (95%) developed in 1996, after a rich seed year in 1995. The microhabitat was of crucial importance to seedling establishment. Litter, Sphagnum spp. and Polytrichum commune were good substrates for establishment, while areas dominated by Deschampsia flexuosa, Dicranum spp. and Pleurozium schreberi had very few seedlings. Seedling survival after five growing seasons was slightly better in litter than in Sphagnum and other mosses, but the differences were not statistically significant. Increasing humus depth had a positive influence on regeneration, probably due to shallow soils at the sites. Even though depressions covered only 4.9% of the ground, 24.1% of the seedlings occurred here. Survival was, however, lower in depressions than in the other microrelief classes. Distance to the seed tree edge had a significant influence on establishment, with more seedlings establishing close to the edge.     

Effects of different soil treatments on growth and net nitrogen uptake of newly planted Picea abies (L.) Karst. seedlings

Five soil treatments in a 4-year-old clearcut in southern Sweden affected biomass increase and net nitrogen uptake by planted Norway spruce (Picea abies (L.) Karst.) seedlings through their on net mineralisation and root growth. The patch soil treatments studied were: (i) soil inversion in an old clearcut; (ii) mineral soil from the clearcut remaining, (iii) mineral soil from the clearcut with fertiliser application during the first season; (iv) mineral soil from a nearby uncut forest replacing the clearcut mineral soil; and (v) an untreated control. Growth increased in seedlings in treatments (i) and (iii), but growth in soil treatments with humus removal was not better than that of seedlings in untreated soil. High N uptake early in the first growing season resulted in increased growth during this season in contrast to late N uptake that resulted in a high N concentration in the seedlings after the first growing season. This in turn led to a high growth rate during the next growing season. Generally, both root growth and net N mineralisation were positively correlated to N uptake in the soil treatments. Therefore, a combination of low net N mineralisation and poor root growth as a result of high soil density appears to explain the low N uptake in seedlings in undisturbed soil. The importance of competition with field vegetation for N and water was not clear. Net mineralisation was larger in soil treatments where the humus layer was retained than where it was removed. Net N mineralisation in soil from old clearcuts was the same as in soil from fresh clearcuts.     

Germination and seedling growth of Quercus (section Erythrobalanus) across openings in a mixed-deciduous forest of southern New England, USA

In this study three species of the genus Quercus section Erythrobalanus (Quercus coccinea, Quercus rubra, Quercus velutina) were investigated. All occur together as canopy trees in forests of southern New England. Acorns of each Quercus species were planted in plots located in five zones that represent a range of forest gap/canopy conditions that can occur within a southern New England forest. These five zones were demarcated adjacent to and across large openings of two physiographic sites—valley and ridgetop. Experiments were designed to monitor germination and initial growth of seedlings for the first three growing seasons. During the start of the first growing season germination was monitored. At the end of the first growing season measurements of height and number of flushes were taken and destructive samples of seedlings made for dry mass of root, stem and leaves. At the end of the third growing season height was recorded for surviving seedlings. Comparisons were made of germination and growth of seedlings located in the different gap/canopy conditions.

Results demonstrated clear differences in patterns of germination and early growth among species and among gap/canopy conditions of the sites. All species showed an increased lag in germination with reduced amounts of light. Highest growth and flushing rate were in the center conditions of the openings for all species during the first growing season. Quercus rubra had the greatest height growth the first growing season but a lower number of flushes than Q. velutina and Q. coccinea. In comparison with the other species, Q. rubra had the greatest total dry mass in most gap/canopy conditions after the first growing season. However, Q. velutina had the greatest total dry mass in the center of the ridgetop opening. In almost all gap/canopy conditions Q. velutina had greater proportions of dry mass allocated to roots compared with the other species.

After 3 years, greatest height growth in any of the gap/canopy conditions was recorded for all three species in the center of the valley site. Under this condition Q. rubra had significantly greater growth than Q. velutina and Q. coccinea. Quercus rubra also had significantly greater height growth and survival beneath the canopy conditions of the valley site than the other species. On the ridgetop site regeneration failed to establish beneath canopy conditions that provided low amounts of light. Quercus velutina showed greatest height growth after three years in the center and edge conditions of the ridgetop opening compared with the other species. Environmental influences that determine species germination and growth performance are suggested.     

Density-dependent effects of northern hardwood competition on selected environmental resources and young white spruce (Picea glauca) plantation growth, mineral nutrition, and stand structural development – a 5-year study

The effects of competition from red raspberry (Rubus idaeus L.) and northern hardwood tree species on white spruce (Picea glauca (Moench) Voss) seedlings were examined on a clearcut site of the boreal mixedwood forest of the Bas-Saint-Laurent region of Quebec, Canada. A controlled experiment involving a gradient of five vegetation densities on the basis of the leaf area index (LAI) was established in a completely randomized plot design with six replications. Each of the five levels of vegetation cover (including vegetation-free plots) were examined to evaluate how they affected environmental factors (quantity and quality of light reaching the spruce seedlings, and soil temperature), spruce growth (height, basal diameter, volume index, and above-ground biomass), spruce mortality, browsing damage, spruce foliar mineral nutrition, as well as the stand structural development, during the first 5 years after seedling planting.

Each spruce growth variable analyzed in this study, according to a RMANOVA procedure, followed a negative hyperbolic form of density dependence of competitive effects. Loss of growth in young white spruce plantations in competition with northern hardwoods is likely to occur with the first few competitors. In cases where higher levels of competing vegetation were maintained over time, loss of spruce growth was extremely severe, to an extent where the exponential growth character of the young trees has been lost. At the end of the fifth year, spruce growing with no interference were larger in mean total above-ground biomass by a factor of 9.7 than those growing with the highest level of vegetation cover. Spruce did not develop a strategy of shade avoidance by increasing tree height, on the contrary. Spruce mortality differed among treatments only in the fifth year, indicating that early evaluation of spruce survival is not a strong indicator of competitive effects, when compared to diameter growth. Spruce foliar N and Ca contents were significantly reduced by the first level of competing vegetation cover, while K increased with the density of the vegetation cover, and P and Mg were not affected. Nitrogen nutrition of young white spruce planted on recently disturbed sites is discussed in relation to the potential root discrimination of this species against soil nitrate, a reaction observed by Kronzucker et al. [Kronzucker, H.J., Siddiqi, M.Y., Glass, A.D.M., 1997. Conifer root discrimination against soil nitrate and the ecology of forest succession. Nature London 385, 59–61]. The effects of hardwood competition indicate a prevalence of competition for light over a competition for nutrients, as revealed by the substantial increase in the h/d ratio of white spruce. Two indicators, h/d ratio and the quantity of light received at the tree seedling level, are suggested as a basis for the management of hardwood competition in a white spruce plantation.

Analysis of the stand structural development indicates that spruce height distribution was affected only by moderate or dense cover of vegetation, while diameter distribution, when compared to competing vegetation-free plots, was affected by the lowest level of vegetation cover. This study shows that competition influenced the stand structural development in the same way as genetic and micro-site factors by aggravating the amplitude of size inequality. The impact of hardwood competition is discussed in view of reaching an equilibrium between optimal spruce plantation growth and benefits from further silvicultural treatments, and maintaining hardwood species known to improve long term site quality, within a white spruce plantation.     

匈牙利刺槐改良与经营(英文)

刺槐是 17世纪初由北美引入欧洲的第一批林木树种 .刺槐之所以在世界快速传播 ,归功于其对环境条件的广泛适应能力 ,易于培育的特性 ,结实频繁、结种量大 ,萌蘖力强 ,种苗保存率高而且速生高产 ,同时又是优良的蜜源植物 .事实上 ,很少有什么病虫对其造成伤害 .刺槐是匈牙利现有林分中最重要的成林树种之一 ,它覆盖 2 0 %的林地 .匈牙利的刺槐的木材产量占全国产量的 18% .鉴于许多国家对培育刺槐的兴趣越来越浓 ,在此将匈牙利的经验和研究结果整理成文 ,期望在刺槐课题方面有所裨益     

Microsite patterns of conifer seedling establishment and growth in a mixed stand in the southern Alps

In many forests of the Alps, permanent forest cover and, therefore, its continuous renewal is the main silvicultural goal. Regenerating these forests must be based on a sound understanding of the ecology of the tree species in question. The regeneration of silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) Karst.) in the upper montane zone of the southern central Alps has so far received little attention. The aim of this study was, therefore, to characterize the ecological niche for the establishment and growth of silver fir and Norway spruce seedlings in this zone. The study was conducted as a case study on a plot of 1.5 ha in the upper montane zone of southern Switzerland, at an altitude of 1380 m. The basal area of the mixed Norway spruce–silver fir stand was 43.7 m² ha⁻¹. Seedlings were censused on 375 plots of 1.0 m² area. Seedling density was 1.30 ± 4.25 m⁻² (mean ± standard deviation) for Norway spruce and 0.87 ± 1.50 m⁻² for silver fir. Logistic regression models were used to test the effect of microsite characteristics on seedling occurrence, and general linear models for effects on seedling height growth and biomass increment. Most seedlings received less than 10% light (photosynthetic photon flux density) as compared to values in the open. Silver fir occurrence was positively related to microsites at the edge of canopy trees, but unrelated to ground cover type, light and micro-relief. Norway spruce occurrence was only, and positively, related to the presence of mosses. Height growth and biomass increment of seedlings of both species were only loosely correlated with microsite conditions. Seedlings without canopy cover grew faster than those under canopy cover, probably as a result of light and moisture limitations under the canopy of adult trees. Diffuse radiation was positively correlated with average annual biomass increment of silver fir, but not of Norway spruce seedlings. In general, the results suggest that silver fir seedlings have less specific microsite requirements than Norway spruce seedlings in terms of ground cover. They are also more shade tolerant, and therefore, grow faster than Norway spruce in low-light environments of the upper montane zone of the southern Alps. While the microsite concept can be helpful in designing silvicultural operations, it has limitations when only patch characteristics that are easy to assess are used, and others neglected. Finally, our study suggests that counting the number of green shoots is a promising method to quickly and non-destructively estimate the biomass of a great number of small seedlings.     

Inoculation of Picea abies (L.) Karst. seedlings with vegetative inocula of ectomycorrhizal fungi Suillus bovinus (L.: Fr.) O. Kuntze and Inocybe lacera (Fr.) Kumm.

Perlite-peat substrate (2:1 v:v) fumigated with Basamide was inoculated with vegetative inocula (a mixture of perlite and peat moistened with the MMN liquid medium) of ectomycorrhizal fungi Suillus bovinus (isolate TUZ 105) and Inocybe lacera (isolate X/14) immediately before seeding with Norway spruce (Picea abies [L.] Karst.) in a nursery bed. Suillus inoculum was applied at rates of 0.5; 1.0; 1.5 and 2.0 litres per m², Inocybe inoculum at rates of 0.5 and 1.5 litres per m². At the end of the first growing season, all inoculation treatments showed a significantly greater mycorrhizal infection of bareroot seedlings compared to that found in both fumigated and unfumigated controls. The ectomycorrhizal 1-year-old seedlings were transplanted into containers. At the end of the second year, ectomycorrhizal infection of the 2-year-old container-grown seedlings was considerably less than that of the 1-year-old barerooted seedlings, probably as a consequence of too high fertility and/or insufficient porosity/aeration of pure peat moss medium. There was no difference in seedling growth between inoculated and uninoculated seedlings throughout the experiment.     

Natural regeneration status of commercial mangrove species (Rhizophora apiculata and Bruguiera gymnorrhiza) in the mangrove forest of Tanjung Bungin, Banyuasin District, South Sumatra

In the mangrove forest areas of Sumatra, Rhizophora apiculata (Bl.) and Bruguiera gymnorrhiza (L.) Lmk., the two most economically important commercial species of mangrove trees, have been intensively exploited for their valuable wood and tannin since the Dutch colonization in the 16th century. The mangrove forest areas of Tanjung Bungin, Banyuasin District, South Sumatra belong to the production forest. Typical Rhizophora-dominated stands were sampled from two inundation classes (Watson, 1928, III and IV) of the virgin mangrove forest of Tanjung Bungin. The sampling method used a 20 × 10-m quadrat for tress. A 5 × 5-m subplot and a 1 × 1-m sublot, for saplings and seedlings respectively, were made in each of the main plots at 10-m intervals. The distribution pattern of R. apiculata and B. gymnorrhiza seedlings studied indicates that regeneration of R. apiculata by seedling establishment is generally sufficient to ensure local propagation in inundation III subplots where Acrostichum aureum is absent. Due to the abundance of A. aureum as a weed in inundation IV zones, the regeneration of both commercial mangrove species is inadequate. This has given rise to considerable concern for their survival. Finally, the presence of regenerating virgin mangrove forest in Tanjung Bungin provides strong argument for this area to be set aside as a conservation area.     

Influence of nutrient supply on spring frost hardiness and time of bud break in Norway spruce (Picea abies (L.) Karst.) seedlings

When spring frosts occur on recently planted forest sites, severe damage may occur to the seedlings. The aim of the present study was to test how different low levels of nutrient concentrations in Norway spruce (Picea abies (L.) Karst.) seedlings affected spring frost hardiness and time of bud break. Seedlings were grown in a greenhouse for one season and supplied with fertiliser containing 22, 43 and 72 mg N l^–1, respectively. The treatments resulted in needle nitrogen concentrations ranging from 0.9 to 1.8% in autumn. After winter storage at 0 °C, bud break was recorded on seedlings growing in the greenhouse, outdoors and in growth chambers at 12 °C and at 17 °C. Freezing tests were performed on seedlings directly removed from winter storage and following one week growth in the greenhouse. Seedlings receiving fertiliser with 43 mg N l^–1 had less freezing injury than the two other fertilisation treatments in the present study. The earliest bud break occurred in seedlings receiving 72 mg N l^–1.     

The effects of limestone and of limestone plus NPK fertilization on the soil and mass balance of a spruce stand (Picea abies (L.) Karst.) in the Vosges mountains

Calcareous amendment and/or fertilization trials were carried out in a declining 66-year-old Norway spruce (Picea abies (L.) Karst.) stand in the Vosges mountains (northeast France, altitude 1100 m) in 1985. The aim was to test tree response to nutritional deficiencies (Ca + Mg) and to alleviate soil acidity. In 1988, experimental equipment was set up to collect atmospheric input (bulk precipitation, throughfall) and soil seepage water. The soils are podzolic (‘ocre-podzolique’), derived from an acid-poor granitic bedrock (‘granite du Valtin’). The soils are coarsely textured, hence very porous. They are very acid (pH 3.4 in the A₁ horizon, and pH 4.1 in the Bs horizon). The cation exchange capacity (CEC) is highly saturated in exchangeable acidity: 86% in the A₁ horizon. Ca²⁺ + Mg²⁺ saturation is very low (<10% in A¹ and <1% in the subsoil). Liming and fertilization significantly increase soil pH, base cation saturation and decrease soil acidity, especially in the surface horizons.

Bulk precipitation is dilute and acidic (pH 4.5); ion concentration of the precipitation greatly increases after passing through the tree canopy. Dry deposition is moderate and has values in the lower range reported for Europe.

Nitrification produced large amounts of NO₃⁻-N and H⁺ ions in the O layer and organo-mineral horizons. Nitrate and aluminium dominate the chemical composition of the soil see-page water.

Liming induces a considerable rise in the soil solution pH and the base cations (Ca²⁺ + Mg²⁺) and decreases nitrate and aluminium substantially. Liming alone seems to lower the rate of nitrification. Addition of fertilizers increases the deep drainage of base cations which could reduce the long term efficiency of liming.

Improvement of tree health-status accords with the positive effects of liming and/or fertilization on the soil's solid phase and solution.     

Effects of planting time on pine weevil (Hylobius abietis) damage to Norway spruce seedlings

Feeding by pine weevil (Hylobius abietis L.) causes severe damage to newly planted conifer seedlings in most parts of Scandinavia. We investigated the effect of planting time and insecticide treatment on pine weevil damage and seedling growth. The main objective was to study if planting in early autumn on fresh clear-cuts would promote seedling establishment and reduce the amount of damage caused by pine weevil the following season. The experiment was conducted in southern Sweden and in south-eastern Norway with an identical experimental design at three sites in each country. On each site, Norway spruce seedlings with or without insecticide treatment were planted at four different planting times: August, September, November and May the following year. In Sweden, the proportion of untreated seedlings that were killed by pine weevils was reduced when seedlings were planted at the earliest time (August/September) compared to late planting in November, or May the following year. This pattern was not found in Norway. The average length of leading shoot, diameter growth and biomass were clearly benefited by planting in August in both countries. Insecticide treatment decreased the number of seedlings killed or severely damaged in both Norway and Sweden.     

Modelling the distribution of wood properties along the stems of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as affected by silvicultural management

In this work, empirical ring-based models were developed to predict the distribution of early wood percentage, wood density and fibre length along the stems of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as affected by silvicultural management. The performance of the ring-based models was also compared for Scots pine and Norway spruce with corresponding disc-based (cross-sectional) models. Moreover, both models were integrated with example simulations by a process-based growth and yield model to analyze how management, such as thinning, affects the growth and wood properties of Scots pine trees over a rotation as an average for the tree stem, but also along the stem.The ring-based models built for annual early wood percentage (explained by ring width), air dry wood density (explained by early wood percentage and cambial age) and fibre length (explained by radial growth percentage and cambial age) predicted reasonably well the wood properties both at an intra-ring level, but also at a cross-sectional level. These predictions were also reasonably well in line with corresponding cross-sectional predictions by the disc-based models (which predicted the properties based on the number of annual rings and diameter at breast height and/or the cross-section being considered and temperature sum). The example simulations also demonstrated that both models predicted slightly lower wood density for dominant trees compared to dominated ones grown in thinned and unthinned Scots pine stands over a rotation. Unlike the disc-based model, the ring-based model predicted, on average, higher early wood percentage in dominant trees than in dominated ones. However, fibre length was not significantly affected when the averages of the whole stems were predicted, and this held true for both ring- and disc-based models.In summary, the incorporation of empirical ring-based wood property models into a process-based growth and yield model, offers a means to study in detail how environmental conditions, forest structure and management affect the quantity and properties of stem wood produced over a rotation. The disc-based wood property models used in this work are based on data with large geographical and genetic variation, and therefore may turn out to be more applicable for predicting future wood and fibre resources at a regional and national level. This kind of integrated use of wood property models with a process-based growth and yield model could help us to evaluate the forest resources under current and changing climate.     

Thinning intensity effects on carbon and nitrogen stores and fluxes in a Norway spruce (Picea abies (L.) Karst.) stand after 33 years

The present paper deals with C and N storage in soil and vegetation, litter fall and CO₂ efflux from the soil 32–33 years after early thinning in a Norway spruce (Picea abies (L.) Karst.) stand in order to evaluate the effect of thinning regime on C sequestration. At 22 years old, the stand was reduced from 3190 to 2070, 1100 and 820 trees per hectare in four replicates. The N2070 treatment represents the recommended start density in practical forestry, while the other represent a moderate to large reduction in tree number at the present stand age. Aboveground biomass was estimated from single tree measurements of diameter and height based on allometric functions. Litter fall was collected during one and a half years and soil respiration was measured on five occasions during one summer. Ground vegetation was mapped and sampled for biomass, C and N determination. A significant decrease in aboveground tree (including stump-root system) C storage of 27% and 22% due to thinning was found in the N820 and N1100 treatments, respectively, compared to the N2070 treatment. Ground vegetation C storage was little affected by treatment, while litter fall C showed a non-significant decrease in the N820 and N1100 treatments compared to the N2070 treatment. Soil respiration was significantly lower in parts of the summer in the N2070 treatment compared to the N820 treatment. The reason for this is still unexplained since no differences in soil temperature, soil moisture or litter fall chemistry was found between the treatments. No significant treatment effects on humus and mineral soil C storage could be detected. With the present soil variability, the time period of 32 years is probably too short to detect soil C differences due to thinning. The N storage followed the same pattern as for C.     

Effects of root trenching of overstorey Norway spruce (Piceaabies) on growth and biomass of underplanted beech (Fagussylvatica) and Douglas fir (Pseudotsugamenziesii) saplings

In Central Europe, the conversion of pure Norway spruce stands (Picea abies [L.] Karst.) into mixed stands with beech (Fagus silvatica L.) and other species like e.g. Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) is accomplished mainly by underplanting of seedlings beneath the canopy of overstorey spruce trees after partial cutting treatments what means exposure to shade and below-ground root competition by the overstorey to the seedlings. Particularly about the second factor, our knowledge is limited. Therefore, we carried out a below-ground competition exclusion experiment by root trenching and investigated the effects on soil resources, growth, and biomass partitioning of underplanted beech and Douglas fir saplings under target diameter and strip cutting treatments. The exclusion of overstorey root competition by trenching increased the soil water potential in the second year that had a fairly dry growing season and led to significantly higher foliar concentrations of most nutrients, particularly in Douglas fir, indicating an amended nutrient supply. Both improvements were accompanied by an increase in length and diameter increment of the underplanted saplings, appearing in both species only after having surpassed a species-specific threshold light value (Douglas fir 16% of above canopy radiation, beech 22%). We also found significant interactions between trenching and light for specific fine root length and further biomass and morphological parameters. Judged by the much steeper increase in height and diameter growth with increasing light after release from below-ground competition, Douglas fir saplings appeared to be more sensitive to root competition than beech saplings what conforms to older findings for beech. According to our results, a strip cutting seems to be more appropriate than a target diameter cutting treatment to replace a pure spruce stand by a mixed stand with beech and Douglas fir.     

Regeneration in windthrow areas in hemiboreal forests: the influence of microsite on the height growths of different tree species

Natural regeneration of windthrow areas is an important issue when planning forestry measures after forest disturbances. Seedling recruitment was investigated in storm-damaged hemiboreal mixed forests in eastern Estonia. The establishment and growth of seedlings from natural regeneration was registered for tree species in soil pits and in mounds of uprooted trees in stands that were either heavily or moderately damaged. Seedling growth is expected to be better in large but shallow soil pits created by uprooted Norway spruce [Picea abies (L.) Karst.] and poorer in small but deep pits created by the hardwoods in the area, silver birch (Betula pendula Roth.) and European aspen (Populus tremula L.). The most abundant regenerating species was birch. Pits hosted larger seedling numbers than mounds, due to soil instability in mounds. Rowan (Sorbus aucuparia L.) showed significantly faster growth than the other seedling species. Norway spruce pits were preferred to pits of other species by both birch and spruce seedlings. Black alder [Alnus glutinosa (L.) J. Gaertn.] did not show a preference for pits of a certain species of uprooted tree. Both spruce and rowan preferred hardwood mounds over spruce mounds. Storm severity also affected species composition: birch predominantly occurred on pits and mounds in heavily disturbed areas, while spruce was more abundant in the moderately damaged areas. The effects of advance regeneration and surrounding stands on seedling microsite preferences should be considered in future research and subsequent management recommendations.     

Water table decline alters growth and survival of Salix gooddingii and Tamarix chinensis seedlings

In the western United States, many native riparian forests are declining downstream from dams and diversions, primarily due to a lack of successful regeneration of native species. Conceptual models have been described that incorporate stream flow characteristics that promote successful regeneration of western riparian Populus seedlings. However, these models need to be calibrated for additional species and specific stream characteristics. In this study, we examined the growth and survival of two dominant Sonoran desert riparian tree species, a native Salix gooddingii, and an exotic, Tamarix chinensis, to simulated water table declines at rates of 0, 1, 2, and 4 cm/day. Salix seedlings performed best in the 0 cm/day treatment in which the soil was saturated and showed decreasing survival and growth with increasing rates of water table decline. Root-to-shoot ratios were high for Salix, but root elongation rates were low with an emphasis on lateral root development. This root growth pattern may be an adaptation to habitat where Salix typically grows, near the stream channel where the water table is shallow but the likelihood of flood scour is high. Lateral root development may help to protect Salix seedlings from late season flood scour. Tamarix seedlings showed consistently high survival across all treatments and had the greatest growth in the 0 and 1 cm/day treatments. Tamarix seedlings had greater root elongation rates in response to water table decline relative to the control, with the greatest elongation in the 1 cm/day treatment. Greater root elongation rates and higher drought tolerance allowed Tamarix seedlings to persist in dry soils where Salix seedlings died. Differences in growth and survival of these two species in response to water table decline will need to be incorporated into management practices to promote successful native riparian tree regeneration.     

Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations

Soil pH declined from 5.9 to 5.0 in 8 years beneath plantations of Eucalyptus saligna (Sm.) in Hawaii. In stands of Albizia falcataria, (L.) Fosberg, the soil pH change was more dramatic, declining from 5.9 to 4.6. We measured several components of soil acidity beneath four mixtures of the two tree species to gain insight on the processes responsible for the decline in soil pH. These components were studied using an empirical method of comparing acid quantity, degree of neutralization (depletion of base cations), and acid strength. The decline in soil pH differed between species as a result of differences in the degree of neutralization of the soil exchange complex; the larger decrease in soil pH under Albizia was produced by greater acidification of the exchange complex. Empirical titration curves suggested that differences in acid strength moderated the divergence in soil pH beneath the species. Had the acids accumulating in the soil under Albizia been as strong as those in the Eucalyptus soil, the difference in soil pH would have been greater. Though the two species had contrasting effects on soil pH, the differences in degree of neutralization, responsible for the pH decline, were small compared with differences in the amount of cations stored in tree biomass. Continued supply of nutrient cations (from weathering or fertilization) will ultimately control both the extent of soil pH decline and the level of productivity sustained by the forest.     

Effect of Reforestation Methods on Pine Weevil (Hylobius abietis) Damage and Seedling Survival

Örlander, G.1 and Nilsson, U. (Swedish University of Agricultural Sciences, The Southern Swedish Forest Research Centre, Asa Forest Research Station, S-360 30 Lammhult, Sweden and Swedish University of Agricultural Sciences, The Southern Swedish Forest Research Centre, Box 49, S-230 53 Alnarp, Sweden). Effect of reforestation methods on pine weevil (Hylobius abietis) damage and seedling survival. Received Feb. 16, 1998. Accepted Sept. 15, 1998. Scand. J. For. Res. 00: 000-000, 199X. Damage to Norway spruce (Picea abies (L.) Karst.) seedlings by the large pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), was monitored in relation to clear - cutting age and silvicultural treatments in southern Sweden. New clear - cuttings were established on four sites during five consecutive years, and seedlings were planted on them from 1989 through 1993. In total, 31 774 seedlings were planted on 20 clear - cuttings. The measures evaluated were seedling insecticide treatment, application of herbicide to ground vegetation, scarification (mound) and planting late in the season. In addition, the effects of slash removal and seedling type were studied. The pine weevil was, by far, the dominant damaging agent. Planting without insecticide or soil treatment on fresh, one- or two - year - old clear - cuttings resulted in a mean level of weevil - caused mortality exceeding 60%. The results indicate that the risk of serious damage by pine weevils remains high until the clear - cuttings reach four or five years of age. Killing the vegetation with herbicide had no effect on pine weevil damage. Slash removal decreased damage on older clear - cuttings, but the effect was small. Scarification (mounding) strongly reduced damage. On fresh clear - cuttings the mean mortality caused by pine weevils in mounded plots was 13%, whereas it was 77% in the controls. The mounding effect varied between sites and clear - cuttings of different ages. Late planting (10 June instead of 1 May) reduced damage on two- and three - year - old clear - cuttings. Three - year - old, bare - rooted seedlings were not damaged as seriously as two - year - old, containerized ones, but the effect was probably due to the larger size of the bare - rooted seedlings. Non - lethal injury resulted in reduced seedling growth. Damage by pine weevils varied between years and within growing seasons. However, on fresh, one- and two - year - old clear - cuttings, damage was severe enough to cause high mortality during all studied years.     

Pure and mixed forest plantations with native species of the dry tropics of Costa Rica: a comparison of growth and productivity

In Costa Rica, most reforestation trials with native species were established in the tropical humid regions. In the dry tropics, research on the performance of native species in forest plantations is incipient and trials comparing pure and mixed designs are limited. This paper presents the results of two experimental plantations with native trees in pure and mixed plots in the dry tropics of Costa Rica. The growth and productivity of 13 native species in pure and mixed plantations was compared with Tectona grandis (L.f.) Lam., an exotic species broadly used in the region. In a plantation of relatively slower growing species, measurements taken at 68 months of age resulted in Samanea saman (Jacq.) Merril. and Dalbergia retusa Hemsl. demonstrating the best growth, followed by Astronium graveolens Jacq. and Swietenia macrophylla King. Measurements in a plantation of relatively faster growing species, at 68 months of age, showed that growth of Schizolobium parahyba (Vell.) Blake was greatest in the pure and mixed plots, followed by Terminalia oblonga (Ruiz & Pav.) Steud., Anarcadium excelsum (Bert. & Balb. ex Kunth) Skeels and Pseudosamanea guachapele (Kunth) Harms. The native species grew better in the mixed plots. The pure plots of T. grandis (L.f.) Lam. were the most productive, compared to all species and the mixture of species. Plantations of T. grandis (L.f.) Lam. seem to be well adapted to the region and are certainly a commercially interesting alternative. Nevertheless, mixed plantations with native species would contribute more to sustainable management, because while single-species plantations do not provide a great range of goods and services when compared to the natural forest, mixed plantations are likely to increase this range of benefits.     

Influence of a high Mn supply on Norway spruce (Picea abies (L.) Karst.) seedlings in relation to the nitrogen source

Effects of 3, 25, 100, 200 and 800 microM Mn on biomass and pigment, starch and nitrate concentrations were studied in Norway spruce (Picea abies (L.) Karst.) seedlings grown with either NO(3) (-) or NH(4) (+) as the sole nitrogen source. After 77 days of exposure to 800 microM Mn, shoot growth had ceased in about 50% of the seedlings independently of the N source. Despite high Mn concentrations in roots and shoots of the Mn-treated seedlings, no visible symptoms of Mn toxicity were evident. The rate of root elongation was decreased by treatment with >/= 200 microM Mn when N was supplied as NO(3) (-), but not when it was supplied as NH(4) (+). This difference could be attributed to the higher Mn concentrations in root tips of the NO(3) (-)-grown seedlings compared with the NH(4) (+)-grown seedlings. In Mn-treated seedlings, the concentration of Mg, and to a lesser extent that of Ca, decreased. Depletion of these elements might account for the observed growth depression. Potassium concentrations were similar in the control and Mn-treated seedlings. Treatment of seedlings with 800 microM Mn for 50 days led to several physiological changes: starch accumulated, the concentrations of nitrate and phenolic compounds increased, pigment concentrations decreased, and in vivo nitrate reductase activity in roots was reduced.