The mechanisms by which whole-tree harvesting affect growth of second-rotation Sitka spruce (Picea sitchensis (Bong.) Carr.) were studied for 2 years on a stagnohumic gley soil in Kielder Forest, Northumberland. The full factorial experiment included treatments with harvest residues (±R), fertiliser additions (±F), and herbicide (±H), giving a total of eight treatments in three replicate blocks. Fertiliser and herbicide treatments increased foliage nutrient concentrations which were above those expected to limit growth of young Sitka spruce. The removal of harvest residues decreased height growth in both years (p<0.05). Soil temperature fluctuations at 10 cm depth increased during the year in whole-tree harvested plots. Soils were warmer in spring and summer and cooler in autumn where residues had been removed and this response was considered most likely to favour tree growth. However, the removal of harvest residues increased mean annual windspeed at 30 cm above groundlevel by 40%. The sheltering effect of residues increased with increasing windspeed (r=0.87). The most likely cause of reduced growth after whole-tree harvesting on this exposed upland site was considered to be the removal of shelter from around the newly planted seedlings.

Three experiments were established in the 1990s to examine the impact of complete residue (brash) and above-ground biomass removal (i.e. ‘whole-tree harvesting’, WTH) at clearfelling on the subsequent growth and yield of replanted Sitka spruce (Picea sitchensis). The sites were of varying fertility; two would now be considered to be of ‘medium’ risk for brash removal, while one would be a ‘high’-risk site. The interactions between brash removal and regular remedial fertilizer applications and weed control regimes were also investigated at each site. After 10 years, trees had been successfully established at all sites, and in most cases, the treatments were close to canopy closure.

It is necessary to assess the effects of removing nutrient-rich harvest residues (brash) from clearfell sites because there is a growing market for this brash as bioenergy. The aim of this study was to use stable isotope techniques in a model system to trace nutrients released by decomposing brash. Labelled biomass was obtained by growing Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings with a generous or poor nutrient supply containing elevated 15N, 41K, 26Mg, and 44Ca. This biomass was used in two subsequent studies. In this study (Part I of II), the above-ground biomass was harvested and placed on soil in a pot containing a newly planted seedling. Soils from two forests, Ae and Teindland, of contrasting nutritional status were used. A full destructive harvest was undertaken after one growing season. Enriched 15N, 41K, 26Mg, and 44Ca were recovered in the new seedlings. The percentage contribution from labelled biomass to new tree growth was small, but discernible. The N contribution from labelled biomass to new trees was greater in Ae soil, but the base cation contribution was greater in Teindland soil. Results are discussed with reference to the initial nutrient concentrations of each soil. The elevated 15N, 41K, 26Mg and 44Ca in new seedlings indicate that nutrients in brash can make a direct contribution to new tree growth. The success of this model system will provide guidance for the application of similar techniques in field experiments.

Potassium (K) and magnesium (Mg) are essential macro-nutrients, but little is known about how they are cycled within plants. Stable isotope studies have shown that the internal cycling of nitrogen (N) is independent of current nutrient supply in temperate tree species. This is ecologically significant because it allows trees to produce rapid shoot growth in spring independent of current soil N uptake. We used stable isotopes to quantify N, K and Mg in new shoots of Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings and to compare the relative contributions from current uptake and internal cycling. Two-year-old Sitka spruce seedlings were labeled with (15)N, (41)K and (26)Mg in an abundant or a limited supply for one growing season. The trees were repotted in the subsequent dormant season to prevent further root uptake of enriched isotopes and provided with an abundant or a limited supply of unlabeled nutrients until they were harvested in early summer of the following year. The supply was switched for half the trees in the second year to create four nutrient regimes. Enrichment of (15)N, (41)K and (26)Mg in current-year growth was attributed to internally cycled N, K and Mg uptake from the previous year. The internal cycling of N, K and Mg in new growth was significantly affected by the first-year nutrient treatments. The second-year nutrient supply affected the growth rates of the trees, but had no effect on the amounts of N, K or Mg contributed from internal cycling. Thus, internal cycling of K and Mg in Sitka spruce are, like that of N, independent of current nutrient supply.

Summary Vaccinium myrtillus (deciduous) and V. vitis‐idaea (evergreen) are ericaceous shrubs adapted to low‐nitrogen environments. Their comparative responsiveness to N supply was determined in relation to both N storage and developmental constraints. Plants were grown with high or low N in sand culture to condition their N storage, and their growth measured during the first flush of a second year when plants from each treatment were again supplied either high or low N. 15N‐labelling was used to quantify remobilization of N taken up in the first year for growth in the second. In both species, the growth response to external N availability was mediated through a change in the number of buds, initially present, which produced shoots, with no alteration of the number of leaves per shoot; but the magnitude of the response was smaller in the evergreen species. The second flush of growth took place more rapidly in V. myrtillus than in V. vitis‐idaea, and depended on both external and internal N supply, in terms of the number of shoots produced and the number of leaves per shoot. The amount of labelled N remobilized by both species depended on the level of N reserves, and on the number of initial buds which produced shoots. In V. myrtillus, the total amount of N remobilized to new growth was significantly affected by external N supply. Since the total amount of N remobilized is independent of external N availability during spring growth, this result implies that the age of the N remobilized depended on the number of buds that produced shoots. We explain this result by the perennial nature of N storage in V. myrtillus and the age range of the pool of buds coming into growth each year on an individual plant. Nitrogen remobilization and the growth response to N supply were closely linked with the pattern of bud activation. Species‐specific growth responses to N supply in spring were better explained by developmental constraints on growth than by the ability to store and re‐use N.

Red alder and Balsam Spire poplar were planted in May 1989 as single stems at 1.0 m spacing on a converted agricultural site in central Scotland. Biomass production, canopy structure and light interception were quantified and the effects of coppicing and of planting at wider (1.5 m) spacing were determined. Bowles hybrid willow was grown as coppice planted at 1.0 in spacing and its canopy characteristics compared with those of coppiced alder and poplar.Total above-ground biomass at 5 years old, ranged from 51 to 81 Mg ha(-1) dry matter with an average annual production of 10 Mg ha(-1) dry matter. Coppicing reduced poplar and alder biomass by 26% and 47%, respectively. Planting at the wider spacing reduced stocking density by 56% and led to a 35% reduction in biomass. Both coppicing and planting at wider spacing increased root:shoot ratios and leaf weight ratios in alder and poplar and reduced the seasonal interception of photosynthetically active radiation (PAR) for 2 years. Light interception was most influenced by early canopy development due to the annual distribution of PAR. Treatment effects on net photosynthesis were due, primarily, to changes in canopy structure affecting light levels.After 3 years light interception was similar across all treatments suggesting that planting at wider spacing or early coppicing would require additional weed control for one more growing season. (C) 2002 Elsevier Science Ltd. All rights reserved.

The effect of N supply on plant growth and leaf demography of a deciduous and an evergreen Ericaceae was studied in relation to their internal cycling of N. Mature ramets of Vaccinium myrtillus (deciduous) and Vaccinium vitis-idaea (evergreen) were established in sand culture for 1 year with an adequate supply of a balanced nutrient solution. During one growing season, the plants were given two levels of N supply enriched with 15N and eight sequential destructive harvests were taken. Recovery of unlabelled N in the new shoot was used to determine the remobilization of N from storage. Initially, growth was unaffected by N supply. After May, High N enhanced growth for both species but the nature of their growth response differed. For both species, new shoot biomass and leaf number increased but root biomass production was affected for V. myrtillus only. Whole plant biomass production was similar for both species under High N, but was greater for V. vitis-idaea under Low N. The amount of N remobilized to support new shoot growth was similar for the two species and was independent of N current supply. N was remobilized predominantly from previous year leaves for V. vitis-idaea and from previous year stems and roots for V. myrtillus. The contribution of remobilization to new shoot N was similar for the two species, but depended on N supply. Remobilization was faster in V. myrtillus, but lasted longer in V. vitis-idaea. The results are discussed in relation to species growth in N-poor environments, focusing on the extent to which species-differences in the dynamic of N remobilization and growth may explain their adaptation to constant and/or changeable N supply.

The effect of whole-tree harvesting on microclimate during the restocking of three upland forest sites in the UK was studied from January 1994 to November 1999. Mean soil temperatures at 0.1 m depth were greater during summer months and reduced during winter months at all three sites in whole-tree harvested treatments compared to those where harvest residues were retained on site. Whole-tree harvesting also affected mean shoot temperatures (0.3 m above ground level) at each of the three sites and, for much of the time, the effects on shoot temperatures were the reverse of those observed for the soil. In comparison to conventional harvesting, shoots on whole-tree harvested plots tended to be cooler in spring and summer whereas the same shoots were warmer during winter. Whole-tree harvesting increased mean wind speeds measured at 0.3 m by around 40% at each of the three sites during the first year after replanting. This effect diminished to 26, 20 and 5% over the following 3 years at the one site studied for the longest period, located in Kielder Forest, Northumberland. The biomass of 4-year-old Sitka spruce trees was greater on whole-tree harvested plots at two sites where growth was increased by fertiliser applications but was not affected by harvesting treatment at the more fertile third site in which no response to fertiliser was observed.

Use of Mg-26 and K-41 as tracers allows the quantification of the uptake and internal cycling of Mg and K in plants. Application of thermal ionisation mass spectrometry (TIMS) used for a plant experiment is discussed here. Firstly, the sensitivity of the Mg-26/Mg-24 ratio to the amount of Mg loaded onto the mass spectrometer filament was assessed. Using NIST SRM-980 and amounts of Mg from 0.2 to 1.2 mu g, no significant difference in the Mg-26/Mg-24 value after correction for isotope fractionation was observed. Analysis of SRM-980 produced a corrected mean Mg-26/Mg-24 value of 0.13960 +/- 0.00006 (n = 10) close to the certified range (0.13932 +/- 0.00026). Control of fractionation during K analysis by TIMS is important for accurate isotope determinations. Fractionation profiles for NIST SRM-985 using filament loadings of 1 and 5 mu g K were plotted and, with the higher loading, produced a more stable K-39/K-41 value. Conversion of K from a chloride to an iodide had no significant effect on the measured ratio. The SRM-985 mean K-39/K-41 value was 13.916 +/- 0.034, higher than the certified range (13.8566 +/- 0.0063). Analysis of natural Mg-26 and K-41 levels in needles, stem wood, stem bark, fine roots and coarse roots from Scots pine allowed the precision of the analysis to be defined. This information, in conjunction with a simple model, was used to discuss the design of a tracer study in plants using Mg-26 and K-41. Predicted whole tree K-39/K-41 and Mg-26/Mg-24 values from a 95 day experiment were then calculated and compared with the actual values measured using TIMS.

Stem injection of 15N-labeled ammonium sulfate was used to determine effects of pruning on canopy nitrogen dynamics in open-grown Pinus radiata D. Don in New Zealand. Trees were planted in July 1990 and the isotope introduced in December 1994. Tree crowns were divided into three zones: base section, from which branches of pruned trees were removed; mid section, between the pruned zone and the height of the trees at the start of the year in which they were pruned; and top section, which grew predominantly after the isotope was applied. Pruning removed 32% of the green crown length, representing 75% of foliage biomass. Needles were sampled from each region of the crown until July 1996. Branch growth was used to predict foliage biomass for each sampling occasion. Approximately 45% of the applied isotope was recovered from needles sampled in December 1994 (1 week after application and immediately before pruning), two-thirds of which occurred in needles in the base section. Thereafter, changes in isotope content of needles in the base section of unpruned trees largely reflected foliage biomass fluctuations and dilution of the isotope by continued uptake from the unlabeled soil nitrogen pool. Recovery of isotope in needles from the mid-crown section increased by 58 and 86% from December 1994 to July 1995 in control and pruned trees, respectively. Within this crown section, there was evidence of isotope translocation from old to new needles, with both isotope dilution and efflux observed in the needle cohorts that had been present at the time the isotope was applied. Therefore, isotope dynamics did not reflect the dynamics of the total nitrogen pool in the mid-crown section. By July 1996, a small proportion of the applied isotope was recovered from the new foliage formed in the top section of the crown. Within the top section, isotope dynamics closely matched total nitrogen fluxes. Pruning the lower crown did not affect nitrogen dynamics elsewhere in the crown for the following 18 months.

Two‐yr‐old Scots pine (Pinus sylvestris) seedlings were grown in sand culture for 1 yr with a generous supply of a balanced nutrient solution. Trees were repotted into clean sand in February 1998 and given either a reduced or adequate nutrient supply containing enriched 15N, 41K and 26Mg to label nutrient uptake during spring 1998. Trees doubled their biomass during the experiment. Whole‐tree net photosynthesis was reduced by 43% after 95 d in trees that received the lower nutrient supply (P < 0.001), although differences in biomass between the two treatments were less pronounced. Remobilization contributed 83, 82 and 52% of the N, K and Mg, respectively, used to support growth of new tissues in trees that received reduced nutrient supply. Those receiving the higher nutrient supply still obtained 44–59% of nutrients used for spring growth of new tissues from remobilization. Current nutrient supply had no significant effect on the amount of N or Mg remobilized to new tissues but K remobilization was less in trees that received the lower nutrient supply (P = 0.025). The importance of remobilization in young trees and problems associated with quantifying internal cycling of nutrients are discussed.

Vector analyses have been used to examine the effects of harvest residues on the growth of Sitka spruce planted 18 months after clearfelling a first rotation of the same species. Four treatments were imposed at the time of planting: retention of all residues; retention of fine twigs and foliage; placement of coarse branch material onto plots; and removal of all harvest residues. Sample trees were harvested each year for five years after planting and the biomass and nutrient contents of whole crowns were quantified.Harvest residues had a large effect on mean tree height (p < 0.001). Coarse and fine components produced similar increases when compared to plots with no residues although the response to fine material occurred earlier. After five years, residues had increased mean tree height by 40%. Residues also increased the mean dry weight per tree although the response to coarse material was not significant until the age of five years, at which time trees in residues had 166% more biomass (p< 0.001). Tree growth was greatest where both forms of residue were retained on site.Interpretation of vector nomograms, foliage concentrations and concentration ratios indicated that the growth response was unlikely to he related to changes in nutrient supply for the first two years of treatment. Early treatment effects may have been mediated through changes in weed competition or microclimate. After three years, treatment effects were likely to have been related to altered nutrient supply, particularly those for nitrogen and potassium. According to vector analyses, potassium was not limiting tree growth in whole-tree harvested plots although foliage levels were below critical levels for young Sitka spruce and potassium : nitrogen ratios indicated a nutrient imbalance in these plots. Such an imbalance may arise from the rapid loss of potassium from decomposing harvest residues accompanied by a more gradual release of nitrogen that may relate more closely to the nutrient demand of newly planted trees.The contention that vector analyses allow a standardized comparison between treatments without confounding with other factors has to be questioned. In the present study, different interpretations resulted from analyses based on comparing samples of different age-classes or from different canopy positions. The method has also been shown to be very sensitive to the choice of critical test statistic used in assessing each vector component. We conclude that vector analyses can provide a useful visualization of treatment effects on tree growth and nutrition, Its relevance to the assessment of sustainable forest management is limited by the need to have treatment comparisons available and interpretations should be corroborated by other evidence before firm conclusions can be drawn. (C) 1999 Elsevier Science B.V. All rights reserved.

A comparison of biomass production from single stems and coppice has been carried out in Lanarkshire, Scotland. The site comprises a noncalcareous gley at 210 m above sea level and has a cool, temperate climate with 1100 mm precipitation.Red alder (Alnus rubra Bong,) and balsam spire poplar (Populus balsamifera var. Michauxii (Henry) x Populus trichocarpa var. Hastata (Dode) Farwell) were grown at 1.0 m spacing as coppice or single stems and at 1.5 m spacing as single stems only. Common osier willow (Salix viminalis L.) was also grown as coppice at 1.0 m spacing. Trees were planted in May 1989 and the coppice was cut back in the winter following planting. High mortality occurred in the red alder following coppicing and this reduced the stocking by 50%.Biomass production ranged from 2.0 to 8.4 Mg ha(-1) y(-1) in 1992 and this had increased to between 6.5 and 10.7 Mg ha(-1) y(-1) by 1995. Production from coppice and single stems was similar in 1992. By 1995, coppice production was 28% less than single stems due, in part, to a decrease in willow productivity from 1992 onwards. Although individual trees were larger at wider spacing, productivity per hectare was reduced.Analysis showed that a single regression model using basal area explained 91% of the variation in woody biomass per tree for all treatments and for all years. (C) 1999 Elsevier Science Ltd. All rights reserved.

Cuttings of balsam spire hybrid poplar (Populus trichocarpa var. Hastata Henry x Populus balsamifera var. Michauxii (Dode) Farwell) were grown in sand culture and irrigated every 2 (W) or 10 (w) days with a solution containing either 3.0 (N) or 0.5 (n) mol nitrogen m(-3) for 90 days. Trees in the WN (control) and wn treatments had stable leaf nitrogen concentrations averaging 19.4 and 8.4 mg g(-1), respectively, over the course of the experiment. Trees in the Wn and wN treatments had a similar leaf nitrogen concentration, which increased from 12.0 to 15.8 mg g(-1) during the experiment. By the final harvest, mean stomatal conductances of trees in the wN and wn treatments were less than those of trees in the Wn and WN treatments (1.8 versus 4.6 mm s(-1)). Compared to the WN treatment, biomass at the final harvest was reduced by 61, 72 and 75% in the Wn, wN and wn treatments, respectively. At the final harvest, WN trees had a mean total leaf area of 4750 +/- 380 cm(2) tree(-1) and carried 164 +/- 8 leaves tree(-1) with a specific leaf area of 181 +/- 16 cm(2) g(-1), whereas Wn trees had a smaller mean total leaf area (1310 +/- 30 cm(2) tree(-1)), because of the production of fewer leaves (41 +/- 6) with a smaller specific leaf area (154 +/- 2 cm(2) g(-1)). A greater proportion of biomass was allocated to roots in Wn trees than in WN trees, but component nitrogen concentrations adjusted such that there was no Wn treatment effect on nitrogen allocation. Compared with WN trees, rates of photosynthesis and respiration per unit weight of tissue of Wn trees decreased by 28 and 31%, respectively, but the rate of photosynthesis per unit leaf nitrogen remained unaltered. The wN and Wn trees had similar leaf nitrogen concentrations; however, compared with the Wn treatment, the wN treatment decreased mean total leaf area (750 +/- 50 cm(2) tree(-1)), number of leaves per tree (29 +/- 2) and specific leaf area (140 +/- 6 cm(2) g(-1)), but increased the allocation of biomass and nitrogen to roots. Net photosynthetic rate per unit leaf nitrogen was 45% lower in the wN treatment than in the other treatments. Rates of net photosynthesis and respiration per unit weight of tissue were 48 and 33% less, respectively, in wN trees than in Wn trees.

Effects of nitrogen supply and drought stress were studied in two separate glasshouse experiments using young cuttings of Balsam Spire poplar (Populus balsamifera var. Michauxii (Henry) x Populus trichocarpa var. Hastata (Dode) Farwell.) grown in sand culture. In the nitrogen experiment, trees received either 1 (N1) or 9 mol N.m(-3) (N9) applied every 2 days. In the drought experiment, all trees received 3 mol N.m(-3), applied every 2 days for well-watered trees (WW) and every 10 days for drought-stressed trees (WS). Low nitrogen supply and drought stress both reduced tree growth and increased dry matter allocation to roots. Treatment effects upon nitrogen allocation were small due to changes in component nitrogen concentrations. Leaf area per tree was reduced in stressed treatments, although the effects upon leaf number, weight, and specific leaf area differed between treatments. Whole-plant respiration decreased in N1 and WS trees due to a reduction in total biomass and lower rates of respiration per unit tissue. In N1 trees, root respiration per unit tissue decreased whereas in WS trees, it was shoot respiration per unit tissue that decreased. The likely reasons for these differences are discussed.

The importance of whole-tree harvesting of Sitka spruce (Picea sitchensis (Bong.) Carr.) in Great Britain is likely to increase rapidly in the next 30 years. Large areas of marginal agricultural land were planted with Sitka spruce from 1960 to 1980 and this is likely to be harvested on a 50–60 year rotation. Increased mechanisation of harvesting operations has led to the frequent removal of whole trees from the site and there is concern over the implications of such forest management operations for long-term site fertility. This paper describes an integrated approach to be used in Britain to develop a decision support system (DSS) to provide long-term predictions of the impact of whole-tree harvesting on site fertility across a range of site types. The approach to be taken will make use of a wide range of data available from conventional yield tables, field and laboratory experiments which have examined various aspects of growth and nutrient cycling in Sitka spruce. This information will be used to calibrate a hybrid computer simulation model capable of simulating ecosystem dynamics. The parallel development of an ecological site classification system will provide a framework within which the model can be applied to generate a series of decision rules to be incorporated into a DSS. A key feature of the strategy employed is the establishment of a series of long-term field experiments which will test model predictions across the spectrum of sites to which the DSS will be applicable. Provision is also made to ensure that feedback will be obtained to compare research output with operational performance. Finally, an approach is suggested by which the DSS could be integrated within a geographic information system (GIS) to provide a spatial context for the output which will be relevant to the wider forest industry, planning authorities and policy makers.

A regression model developed to predict the general yield class (GYC, maximum mean annual volume increment) of Sitka spruce (Piceasitchensis (Bong.) Carrière) from a range of site factors has been used to assess the potential impact of climate warming on the growth of Sitka spruce in Scotland. The model was interfaced with a geographic information system to predict and map the GYC of Sitka spruce across Scotland under a number of climate change scenarios. GYC was predicted to increase by 2.8 m3•ha−1•year−1 per °C rise in temperature when a uniform temperature increase was assumed during the year. A more likely assumption is a greater warming during winter months, and under such a scenario the increase in mean GYC was predicted to be 2.4 m3•ha−1•year−1•°C−1 because of a negative correlation between growth rate and mean winter temperature. When assessed in terms of land area capable of supporting a GYC greater than 18 m3•ha−1•year−1 (a value likely to provide an internal rate of return of approximately 6%), this area was predicted to almost double within the next 20 years with a similar increase occurring during the subsequent 40 years.

Stem analysis has been used to examine the effects of two harvesting techniques upon growth of second rotation Sitka spruce planted in 1981 on a peaty gley site of low fertility in Kielder Forest, Northumberland. The effect of NPK fertilizer upon tree growth on conventionally harvested plots was also determined. Weed competition was reduced by hand weeding and the application of herbicides. Repeated measures analysis was used to identify the time at which significant growth responses occurred.Whole-tree harvesting reduced mean tree volume from 1986 onwards while the addition of fertilizer to conventionally harvested plots increased volume growth from 1990. By 1993, whole-tree harvesting had decreased mean tree volume by 32 per cent and the addition of fertilizer to conventionally harvested plots had increased mean tree volume by 13 per cent.Observed treatment effects are most likely due to the increased removal of nutrients during whole-tree harvesting. The release of nutrients from decomposing residues is expected to meet uptake requirements for approximately 7-9 years following replanting. Effects of shelter and weed competition should also be considered on sites where herbicides have not been used to control ground vegetation. Repeated measures analysis and the use of suitable growth functions provide powerful analytical tools to examine historical treatment effects derived from stem analysis.

Seasonal relationships between N supply, tree growth, and partitioning of both N and P have been studied in young trees using 15N and 32P isotopes. Three-year-old clonal cuttings of Sitka spruce (Piceasitchensis (Bong.) Carr.) were grown for 2 years in sand irrigated with a nutrient solution containing either 1.0 mol N•m−3 (low N) or 6.0 mol N•m−3 (high N). In the first year, trees received 2-week pulses of 15N and 32P to label current nutrient uptake during either a period of rapid spring growth or shortly after bud set in summer. In the second year, trees that had been preconditioned to a low-N supply received 3-week pulses of 15N at either the low rate of application or at the high rate to simulate a single application of N fertilizer. In spring of the first year, N treatment had no effect upon tree growth. Low-N trees increased the partition of 15N uptake to roots, but the partition of 32P was not affected by N supply and was similar to the partition of 15N in the high-N treatment. At the time of the later pulse, however, growth was affected by N supply and 32P partitioning to roots increased to match the partition of 15N in the low-N treatment. During the second year, the additional 15N given to Low-N trees to simulate fertilizer application was partitioned predominantly to current shoots and roots. Results are discussed in relation to the processes of internal cycling and the partition of nutrients taken up by larger trees.