Nutrient Leaching from the Litter Layer after Clearfelling of Sitka Spruce Stands on Peaty Gley Soils

The nutrient dynamics in the litter layer of former Sitka sprucestands were examined from 0 to 7 years after clearfelling usingzero-tension lysimeters on a time series of sites 0, 2 and 5years after felling. The loss of most nutrients monitored inleachate was independent of the time from clearfelling. However,54 per cent (43 kg ha^–1) of the 7-year net loss of potassiumwas leached out of the litter layer in the first year. Also,nitrate losses, although small, increased after 5 years. Leachinglosses of NH₄-N, PO₄-P, K, Ca and H⁺ exceeded precipitationinputs. However, leaching losses were less than precipitationinputs for NO₃-N, Na and Mg. Nutrient losses from under brashswathes were generally greater than from clear strips.     

Nutrient Changes in Peaty Gley Soils after Clearfelling of Sitka Spruce Stands

The roots of second-rotation Sitka spruce (Picea sitchensis(Bong.) Carr.) planted on peaty gley sites are restricted tothe old litter (LFH) layer and are dependent on its decompositionfor availability of nutrients. A series of these sites of increasingage from felling were sampled to estimate changes in the nutrientcapital of the LFH horizon over time at Kielder Forest, Northumberland.Previous stand histories were reconstructed from stump data.Geographical, climatic, soil and mensurational data suggestedthat the use of a time series was justified. Nutrient capital in the LFH horizon generally declined overa 5 year period after clearfelling from approximately 997, 51and 83 kg ha^–1 to 676, 30 and 31 kg ha^–1 of N, Pand K, respectively. However, N concentration increased overa 5 year period from 11 mg g^–1 to 14 mg g^–1, P concentrationremained constant at about 0.6 mg g^–1, and K concentrationdecreased from 1.0 mg g^–1 to 0.7 mg g^–1. Nutrientconcentrations and contents of the LFH horizon were higher underthe brash (slash) swathes that resulted from the use of organizedfelling techniques than under clear strips devoid of brash. The patterned input of nutrient capital in brash as a resultof organized felling was also determined. Brash containing 219,20 and 71 kg ha^–1 of N, Pand K, respectively, was systematicallydistributed at a rate of 491 ha^–1 over 66 per cent ofthe site after harvesting. The needles and small branch fractionscontained 71 per cent of the N and 80 per cent of the P andK present in the brash.     

Denitrification of an Upland Forest Site

Rates of nitrogen loss through denitrification were monitoredfor standing forest and adjacent clear-felled areas locatedon a peaty-gley soil at Kershope Forest in the north of England,in two year-long studies. The rates of denitrification in soilcores brought back to the laboratory were determined using theacetylene (C₂H₂) block technique. An equation relating denitrificationto temperature was applied to derive an estimate for the monthlyloss of nitrogen via denitrification from the sites. In an additional study, half of the cores were incubated inthe absence of C₂H₂, so that an estimate of the ratio of emissionof N₂O/N₂ could be made. An annual loss of 1–3 kg N ha^–1 y^–1 was estimatedfor the standing forest while losses from the clearfelled siteswere estimated at 10–40 kg N ha^–1 y^–1 duringthe first 2 years after felling. This loss returned to pre-fellinglevels 4 years after felling. The results are discussed in relation to other studies of denitrificationin forest soils and to the rates of N₂O being lost to the atmosphereby UK forests.     

Effects of previous N fertilizations on soil‐water pH and N concentrations after clear‐felling and soil scarification at a Pinus sylvestris site

The study describes effects of clear‐felling and soil scarification on the N concentration and pH of soil water in experimental plots previously supplied with different doses of N. The experiment is situated in central Sweden in a former Pinus sylvestris L. stand. Over a 20‐yr period, plots were fertilized three times with ammonium nitrate, resulting in total doses of 360, 720, 1080, 1440 and 1800 kg N ha^‐1. Soil water was sampled at a depth of 40–50 cm using suction lysimeters, and analysed for N and pH. The study covers one growing season before clear‐felling and six and four growing seasons after clear‐felling and soil scarification, respectively. Statistically significant (p < 0.05) elevations in total N and nitrate‐N concentrations were noted in the fourth to the sixth growing seasons after clear‐felling in the plots that had received 1800 kg N ha^‐1, and in the fifth and sixth seasons in the plots that had received 1440 kg N ha^‐1. Ammonium‐N concentrations were not significantly affected. After clear‐felling, total N and nitrate‐N increased with time at a higher rate in the plots that had received 1440 and 1800 kg N ha^‐1 doses compared with the control. In the sixth post‐cutting season, the nitrate‐N concentration was 0.26 mg l^‐1 in the control and between 0.51 and 4.0 mg l^‐1 in the various fertilized plots. Before clear‐felling, a linear relationship between pH and fertilizer dose was absent. After clear‐felling, negative relationships prevailed, but they differed significantly from the pre‐cutting relationship only during the fourth, fifth and sixth post‐cutting seasons. In the sixth post‐cutting season, the pH was 6.0 in the control, and 6.1, 5.7, 5.6, 5.2 and 4.3 in the plots supplied with 360, 720, 1080, 1440 and 1800 kg N ha^‐1 doses, respectively. The absolute difference in pH between the sixth growing season after clear‐felling and period before clear‐felling increased linearly with increasing fertilizer dose (p < 0.05, R ² = 0.79). Before clear‐felling, nitrate‐N was elevated only in the plots that had received 1800 kg N ha^‐1. After clear‐felling, nitrate‐N seemed to increase in all fertilized plots, but the increase began first in the plots receiving the highest fertilizer dose. It was not until the fifth and sixth growing seasons after clear‐felling that nitrate‐N concentrations appeared elevated in all fertilized plots compared with the control. It seems likely that nitrification caused the increases in nitrate‐N because nitrate‐N accounted for most of the variation in pH in the fourth to the sixth growing seasons. Disc trenching was simulated around some of the lysimeters so that 50% of the soil was disturbed. This did not significantly affect the N concentration or pH of the soil water during the first 4 yrs after scarification.     

Water and element fluxes during the regeneration of Norway spruce with European beech: Effects of shelterwood-cut and clear-cut

The regeneration of mature Norway spruce with European beech using the shelterwood silvicultural system is a good example of continuous cover forestry. In contrast, the regeneration may also start with clear-cut plots, which often occur after calamities like wind-throw or bark beetle attack. During regeneration the forest ecosystem becomes a highly dynamic system. Nutrient losses from the soil may occur as the element turnover is affected by the reduced nutrient uptake of forest trees as well as the enhanced mineralisation and nitrification due to higher soil temperature and soil moisture. Continuous cover forestry may help to reduce these nutrient losses. In order to test this, we investigated water and element fluxes of two chronosequences. The first investigated regeneration in the shelterwood system, while the second concerned itself with regeneration on clear-cut plots. In a shelterwood-cut about 30% of the mature spruce trees are removed and young beech trees are planted. Some 10 years later a secondary felling is carried out and at age 20 of the beech regeneration the final harvest of the mature trees occurs. Thus, the studied time steps were (a) the first 5 years after the initial cut and planting, (b) 10-year-old beech regeneration after the second shelterwood cut and (c) 20-year-old beech regeneration after the final harvest.Our results indicate that nutrient losses with seepage water – especially nitrogen, calcium and magnesium – occur during the first years after the clear cut and, to a lesser extent, after secondary felling on the selective-cut plot. This may temporarily affect seepage water quality due to elevated nitrate concentrations, which reached values of more than 100 mg l⁻¹. In the time span between planting and an age 20 of the beech regeneration, total losses of nitrogen from the main rooting zone reach 230 kg ha⁻¹ after clear cut. Preliminary estimates of the total nitrogen loss in the shelterwood system range between 150 and 230 kg ha⁻¹ indicating either significantly lower or equal losses of nutrients. In the second case, however, element output is distributed more equally over the 20-year-period than after clear felling where 85% of the nitrate leaching occurs during the first 3 years.     

Logging residue removal after thinning in Nordic boreal forests: Long-term impact on tree growth

The aim of this study was to determine the effect of whole-tree harvesting (WTH) on the growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as compared to conventional stem harvesting (CH) over 10 and 20 years. Compensatory (WTH + CoF) and normal nitrogen-based (CH + F or WTH + F) fertilisation were also studied. A series of 22 field experiments were established during 1977-1987, representing a range of site types and climatic conditions in Finland, Norway and Sweden. The treatments were performed at the time of establishment and were repeated after 10-13 years at 11 experimental sites. Seven experiments were followed for 25 years.Volume increment was on average significantly lower after WTH than after CH in both 10-year periods in the spruce stands. In the pine stands thinned only once, the WTH induced growth reduction was significant during the second 10-year period, indicating a long-term response.Volume increment of pine stands was 4 and 8% and that of spruce stands 5 and 13% lower on the WTH plots than on CH during the first and the second 10-year period, respectively. For the second 10-year period the relative volume increment of the whole-tree harvested plots tended to be negatively correlated with the amount of logging residue. Accordingly, the relative volume increment decreased more, the more logging residue was harvested, stressing the importance of developing methods for leaving the nutrient-rich needles on site.If nutrient (N, P, K) losses with the removed logging residues were compensated with fertiliser (WTH + CoF), the volume increment was equal to that in the CH plots. Nitrogen (150-180 kg ha⁻¹) or N + P fertilisation increased tree growth in all experiments except in one very productive spruce stand. Pine stands fertilised only once had a normal positive growth response during the first 10-year period, on average 13 m³ ha⁻¹, followed by a negative response of 5 m³ ha⁻¹ during the second 10-year period. The fertilisation effect of WTH + F and WTH + CoF on basal area increment was both smaller and shorter than with CH + F.     

The effect of afforestation on soil carbon dioxide emissions in blanket peatland in Ireland

We studied the effect of afforestation on soil CO₂ emissionsin blanket peat. The study sites were as follows: two undrainedblanket peatland sites, six sites which had been drained andafforested 3, 19, 23, 27, 33 and 39 years previously, and twoforest sites which were clearfelled in summer 1996. Soil CO₂emissions were measured using the soda-lime method during 13sampling campaigns throughout 1997. Each campaign consistedof two consecutive 24-h measurements. Comparison of the averageannual CO₂ emission revealed no clear pattern in relation tosoil type and suggests that afforestation does not always leadto an increase in soil CO₂ emissions. In the most recently forestedsite, CO₂ emissions were 1.7 t C ha^–1 a^–1 and drainagehad failed to lower the water-table sufficiently to cause alarge increase in CO₂ emissions. In the 19-, 23-, 27- and 33-year-oldsites soil CO₂ emissions were 1.0–1.4 t C ha^–1 a^–1and were similar to, or lower than, levels in the undrainedsites. In the 39-year-old site average CO₂ emissions were 2.6t C ha^–1 a^–1. In the clearfelled sites CO₂ emissionswere lower at between 1.4 and 1.6 t C ha^–1 a^–1.Root respiration appears to account for a large proportion ofCO₂ emissions, and blanket peat, despite drainage, is resistantto decay. It is concluded that losses of soil C are compensatedby C uptake by the trees.     

Is the productivity decline in Norway spruce following whole-tree harvesting in the final felling in boreal Sweden permanent or temporary?

The growing demand for renewable energy sources in Sweden has resulted in an increased use of forest biomass that now includes logging residues. However, concern has been raised that the moderate increase in biomass removal associated with whole-tree harvesting results in a significant increase in nutrient removal, which in turn has a negative effect on future forest growth. Productivity over 31 years in planted Norway spruce (Picea abies (L.) Karst) in northern Sweden following three different harvest intensities is reported from a field experiment with exceptionally large growth reductions following whole-tree harvest. The three harvest intensities were applied in a randomized block design with four blocks: (i) conventional stem-wood harvest up to a top diameter of 5 cm (CH); (ii) whole-tree harvest of all above-stump biomass (WTH); (iii) branch and stem harvest with needles left on site (BSH). Recovery rate of biomass was almost 100% and the logging residues left were evenly spread over the 25- by 25-m experimental plots. Stand growth was negatively affected by WTH: basal area after 31 years was significantly lower following WTH (10.5 m² ha⁻¹) as compared to CH (14.0 m² ha⁻¹, p = 0.005) and BSH (14.2 m² ha⁻¹p = 0.003). Annual height growth of a sub-sample of trees (10 undamaged trees per plot, or 40 per treatment) was used to estimate and compare long-term effects on site productivity. This showed that stand growth loss resulted from a significant but temporary reduction in site productivity on WTH plots over a 5-year period (years 8-12, 1984-1988). Nitrogen is the major growth-limiting nutrient in boreal Swedish forests, and the N-content of needles during that period suggests that the temporal reduction in site productivity (i.e., stand growth) was primarily due to increased nitrogen loss with WTH.     

Carbon pools and sequestration in forest ecosystems in Britain

British vegetation is estimated to contain 113.8 million tC,80 per cent of which is in forests and woodlands (91.9 milliontC). Sitka spruce plantations, although covering 21.4 per centof the forest/woodland area, contain only 8.2 per cent of theforest/woodland carbon, because the plantations are young andhave an average of only 14.1 tC ha^–1. Broadleaved woodlandsin Britain have an average of 61.9 tC ha^–1 and contain46.8 per cent of the total carbon in all vegetation. A breakdownis given of the carbon density (tC ha^–1) and content ofdifferent tree species. A carbon density map of Britain highlightsthe concentration of carbon in the broadleaved woodlands insouthern England and in the large conifer plantations in southernScotland and northern England. Carbon storage in the trees, products, litter and soil can beevaluated in terms of long-term equilibrium storage or short-termrate of storage. These two components vary among forest typesin Britain and globally. Plantations harvested at the time ofmaximum mean annual increment (MAI) will not store as much carbonas mature, old-growth forests on the same site unless they havelong-lasting products and/or are very fast growing. Maximumequilibrium carbon storage is generally achieved by harvestingat the time of maximum MAI when the lifetime of products exceedsthe time to maximum MAI. Undisturbed peatlands sequester CO₂and emit CH₄, and may be greenhouse neutral. When peatlandsare drained and planted with trees, they stop emitting CH₄ andstore carbon in the trees, forest litter, forest soil and woodproducts. However, these greenhouse gas ‘gains’are offset by the oxidation to CO₂ of the peat, and the gainsare exceeded by CO₂ losses when 20–40 cm depth of peathas been oxidized. Forests in Britain are currently sequestering1.5–1.7 million tC a^–1 in trees, 0.3–0.5 tCa^–1 in litter and 0.5 million tC a^–1 in wood products,totalling about 2.5 million tC, equivalent to about 1.5 percent of the carbon currently emitted by burning fossil fuelsin the UK. In order to maintain the current forest carbon sink,the forest area needs to continue to expand at about 25 000ha a^–1 of upland conifers or 10 000 ha a^–1 of poplarson good land.     

Whole tree harvesting can reduce second rotation forest productivity

The practice of harvesting forest residues is rapidly increasing due to rising demand for renewable energy. However, major concerns have been raised about the sustainability of this practice and its net impact on productivity, in particular through negative effects on the growth of subsequent tree crops. We measured height, diameter at breast height (DBH) and tree spacing density on 23-year-old second rotation stands of Sitka spruce (Picea sitchensis), following whole tree harvesting (WTH—of all above ground biomass, by cable crane) or conventional stem-only harvesting (CH) of the first rotation crop. Overall, WTH reduced tree DBH by 10.3% (p = 0.017), with weaker evidence that it may have reduced height (by 8.2%, p = 0.164) and stand basal area (by 15.3%, p = 0.101). However, treatment effects differed greatly between individual blocks and, analysed separately by block, significant differences (WTH plot trees smaller than CH plot trees) were most notable in the two more exposed south-facing blocks (where, in both cases, p < 0.01 for height and p < 0.05 for basal area). Variation in productivity between the experimental plots cannot simply be attributed to preharvesting site environment – no correlation was found between first rotation and second rotation productivity – nor was treatment effect explained by differences in tree spacing density. Treatment effects can be attributed to the removal of three to four times larger quantities of N, P and K in the tree biomass by WTH than by CH of the first rotation crop, combined with greater competition with tree natural regeneration and other vegetation in WTH plots during the early stages of the second rotation. Soil moisture was higher in WTH plots but there was no evidence that WTH increased soil acidity or aluminium mobility nor that it decreased soil organic matter. The results also highlight the complexities of predicting the effect of harvesting treatment on future productivity, even within single-age, single-species forests. The study demonstrates the risk that WTH can reduce second rotation productivity of conifer forests in acidic upland sites, and that this practice will only be sustainable with appropriate interventions to overcome shortage of nutrients and high levels of vegetation competition.     

Productivity of Closely-spaced Young Poplar on Agricultural Soils in Britain

Recent ideas on ‘silage’ and ‘fuel’forestry call for more information on the total harvestablewoody dry matter produced by hardwoods grown at very close spacingsin fertile soils and coppiced every few years. Yields of oven-driedstems and branches (S and B) are presented here for Populustrichocarpa Torr. and Gray, clone ‘Fritzi Pauley’.Plantings in Bedfordshire at 21 600 trees ha^–1 had a meanannual increment (M.A.I._SB) of 5.2 t ha^–1 y^–1 overfive years, and plantings in the Cambridgeshire fens at 1480trees ha^–1 produced 4.8 t ha^–1 y^–1 over sixyears. Fan-shaped spacing experiments, established in Midlothianby inserting cuttings through black polythene into nursery soilwith added fertilizers, gave 4.6 t ha^–1 y^–1 at theend of the first year and about 7 t ha^–1 y^–1 oneyear after coppicing, but only with over 250 000 stems ha^–1producing closed canopies with leaf area indices of about 4.Similar spacing experiments planted without fertilizer on farmlandin Gloucestershire, Suffolk, Argyll and Midlothian gave averageM.A.I._SB values of 6.5–7.0 t ha^–1 y^–1 afterthree years with over 25 000 trees ha^–1 and similar valuesafter five years with over 10 000 trees ha^–1. Peak currentannual increments (C.A.I._SB) averaged 10–12 t ha^–1y^–1. The maximum M.A.I._SB, attained in Gloucestershire,was 10.0 t ha^–1 y^–1 at age 5 with over 20 000 treesha^–1, with maximum C.A.I._SB values of about 14 t ha^–1y^–1 at age 4; M.A.I._SB values of about 11.5 t ha^–1y^–1 were anticipated at this site by age 6–8. Equivalentstem volumes are given. As expected, trees subjected to competitionaccumulated greater proportions of their woody biomass in stemsrather than branches. Biomass yields of fully-stocked young hardwood stands are independentof planting density. In Britain, M.A.I._SB values of 6–8t ha^–1 y^–1 can be obtained over 1 or 25 years byplanting 250 000 or 2000 trees ha^–1, using vigorous Populusspp, Salix spp or Nothofagus procera on good sites. Advantages and problems of ‘silage’ forestry arediscussed, and it is considered that hardwood fuel coppicescould not meet more than about 2% of national energy needs. The reciprocals of individual tree weights were linearly relatedto planting density.     

Nitrogen critical loads for spruce plantations in Wales: is there too much nitrogen?

We have used the mass balance approach for calculating nitrogencritical loads (CL(N)) to avoid eutrophication for Sitka spruceplantation forestry in Wales. The various approaches for assigningvalues to the parameters in the mass balance equation are discussedwith particular reference to the soil nitrogen immobilizationvalue. A CL(N) value of 11 kgN ha^–1 a^–1 was calculatedfor an intensively studied site in Wales of Yield Class 14 ona freely draining acid soil. If this site is assumed to representa typical spruce stand, application of the CL(N) value meansthat 97 per cent of the area of coniferous forest in Wales,which is predominantly Sitka spruce, is currently receivingnitrogen deposition in excess of the CL(N). The area of coniferousforest at risk is reduced to 72 per cent if the proposed empiricalCL(N) for managed acidic coniferous forests to prevent ecologicalchanges (10–20 kgN ha^–1 a^–1) is applied andto 45 per cent if the empirical CL(N) to prevent nitrogen saturation,nitrate leaching and depletion of soil base cations is applied(10^–25kgN ha^–1 a^–1). Irrespective of the choiceof CL(N) values, the implications of critical load exceedanceneed urgent investigation. Available information at presentindicates that the main known consequence of chronic atmosphericnitrogen deposition to coniferous forest ecosystems is enhancednitrate and associated aluminium leaching to freshwaters. Thereis insufficient information regarding the potential adverseeffects of eutrophication of soils and waters and of impactson tree health and production.     

Water Chemistry Profiles under Four Tree Species at Gisburn, NW England

A study was made of the changes and variation in the chemistryof rainwater passing through the different strata of separateecosystems of four tree species (oak, alder, spruce and pine)on the same site at Gisburn (Bowland Forest), north-west England.Waters were sampled as rain, throughfall, forest-floor leachateand soil waters from both the A and B/C horizons; and analysedfor NH₄-N, NO₃-N, PO₄-P, K, Ca, Mg, Na, Al, SO₄-S, Cl, totalorganic carbon and pH. Species differences — often markedones — appear to exist in the concentrations of most solutesin most strata. The between-species differences in throughfallchemistry provide little guide to the chemistry of waters lowerdown the profile: the forest floor is a particularly importantsource of further species differences, e.g. variation in NO₃production and the resulting effects on acidity and other ions. The chemistry of the soil waters provides some indication ofpossible drainage losses, although the question of which horizonacts as the source of drainage waters on this site remains unanswered.The levels of H and Al, in particular, are very different betweenthe upper mineral soil (A horizon) and the lower B/C horizon.In general, and based on these concentration data only, oakis associated with smallest potential solute losses, pine thegreatest. Received 13 February 1990.     

Harvesting of logging residues affects diameter growth and pine weevil attacks on Norway spruce seedlings

Removal of logging residues causes significant nutrient losses from the harvesting site. Furthermore, collection of residues into piles could lead to small-scale differences in establishment conditions for seedlings. We studied the effects of stem-only (SOH) and aboveground whole-tree harvesting (WTH) on Norway spruce (Picea abies) seedling growth and pine weevil (Hylobius abietis) damage at two sites (SE and W Norway). We also compared two planting environments within the WTH plots (WTH-0: areas with no residues, WTH-1: areas where residue piles had been placed and removed before planting). In practice, one-third of the residues were left on site after WTH. After three growing seasons there were no differences for height or diameter increment between SOH and WTH (WTH-1 and WTH-0 combined) treatments. However, relative diameter increment was largest for WTH-1 seedlings and lowest for WTH-0 seedlings. Few seedlings sustained pine weevil attacks at the W Norway site, with no differences among treatments. At the SE Norway site, the percent of seedlings damaged by pine weevils and average debarked area were significantly higher after WTH (82% and 3.3?cm²) compared to SOH (62% and 1.7?cm²). We conclude that WTH may lead to spatial differences in establishment conditions.     

Nutrition management of cedar and hemlock plantations in coastal British Columbia

Recent re-measurements of silvicultural trials in conifer plantations on nutrient-poor cedar-hemlock (CH) cutovers on northern Vancouver Island have confirmed co-limitation by nitrogen and phosphorus. Repeated fertilization increased volumes of both cedar and hemlock on CH sites (at 2,500 stems ha^?1) by about 100 m³ ha^?1 relative to unfertilized plots 22 years following initial fertilization, and increased the productivity of regenerating conifers to a level approximating that of neighbouring hemlock-amabilis fir (HA) sites. More surprising was the response to fertilization on the more-productive HA sites. After 22 years, cedar in fertilized HA plots had produced an extra 180 m³ ha^?1 compared to unfertilized HA plots, while hemlock had produced an extra 250 m³ ha^?1 in fertilized plots (at 2,500 stems ha^?1). Thus, contrary to expectations, the greatest volume responses of both hemlock and cedar to fertilization occurred on the good (HA) sites rather than on the poor (CH) sites. Ecological studies of CH and HA sites supported the hypothesis that the poor nutrient supply and productivity of CH sites is a long-term consequence of excessive moisture, and that the two site types bracket a critical ecological threshold of moisture, aeration and redox.     

Replacement of wildfire by whole-tree harvesting in jack pine forests: Effects on soil fertility and tree nutrition

Large areas of northern coniferous forests once naturally maintained by stand-replacing wildfires have shifted to an anthropogenic disturbance regime of clearcut harvesting followed by natural or artificial regeneration, with unknown consequences for soil biogeochemical processes. We used a comparative approach to investigate the effects of whole-tree harvesting (WTH) vs. stand-replacing wildfire (WF) on soil C and nutrient availability, and nutrition and growth of the succeeding stand, in jack pine (Pinus banksiana) forests of northern Lower Michigan. We compared total carbon (C), total nitrogen (N), potential N mineralization, and extractable phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) among stands regenerated via WTH or WF in two age classes (4–7 years and 12–18 years). We also measured jack pine foliar nutrition and height growth in these same stands, as well as estimating the contribution of legacy dead wood to ecosystem nutrient capital in young stands. We found some evidence in support of our hypothesis that WTH would leave behind greater pools of soil C and N, but lower pools of P and base cations. However, the differences we observed were confined entirely to surface organic horizons, with the two disturbance regimes indistinguishable when viewed cumulatively to our maximum sampling depth of 30 cm. Estimates of nutrient pools in legacy wood inherited by young jack pine stands were also small in comparison to total soil pools (ranging from 1 to 9% depending on the element), suggesting that decomposition and nutrient release from this material is not likely to result in noticeable differences in soil fertility later in stand development. Similar levels of soil nutrients between WTH- and WF-origin stands were reflected in our measures of jack pine foliar nutrition and height growth, which were both unaffected by mode of stand origin. Results from this study suggest that soil nutrient levels following WTH fall within the natural range of variation produced by WF in these jack pine forests; however, comparison with a similar study on boreal jack pine suggests that latitudinal effects on O-horizon nutrient capital may influence the degree to which WTH matches the effects of WF on soil nutrient availability.     

Litter Production in Western Washington Douglas-Fir Stands

Litter production by Douglas-fir stands ranging in age from22 years old to 160 years old, is discussed. Typical leaf litterproduction was 2100 kg ha^–1 yr^–1 while total litterwas 2500 kg ha^–1 yr^–1. Annual fall of leaf litterincreases up to about 40 years of age and then becomes fairlyconstant while total litter continues to increase because ofwood production, although this increase may be quite irregular.Average nutrient returns to the forest floor are 21, 3, 7, 32,4, and 7 kg ha^–1 yr^–1 for N, P, K, Ca, Mg, and Mnrespectively.     

Alley cropping on an Ultisol in subhumid Benin Part 3: nutrient budget of maize, cassava and trees

An alley cropping experiment was conducted from 1986 to 1992 near Cotonou, Benin Republic on a field previously used as four-year bush-fallow. A no-tree control was compared with Leucaena leucocephala (Lam.) de Wit and Cajanus cajan (L.) Millsp. grown in 4 m distant hedgerows. In the same experiment, application of 90-39-75 kg ha^-1 NPK fertiliser vs. no fertiliser and maize-cassava intercropping vs. rotation of sole crops was also tested. Topsoil samples (0–30 cm) were taken initially and again after four and six years. Alley cropping enhanced nitrogen recycling relative to the no-alley control by 253 kg haha^-1 yr^-1 for Leucaena and 131 kg ha^-1 yr^-1 for Cajanus in the overall average but a maximum of 22 kg N ha^-1 yr^-1 was recovered in total crop exports. Apparent fertiliser-N recovery increased from a low average of 14% in the first year to 66% in the second year up to a maximum of 109% in the no-tree control in the last year. Soil nutrient depletion during the six years was significant for all nutrients except P, K falling from 0.5 to 0.1 cmolc kg^-1 soil and N from 0.08 to 0.05%. Hedgerow accumulation of N in the topsoil- plant system calculated as difference to a no-tree control was only 18 to 37 kg ha^-1 yr^-1 during the first four years after clearing, increasing to 208 kg in Leucaena and 111 kg ha^-1 yr^-1 in Cajanus without NPK during the last two years. During the first four years, average N, K, Ca and Mg losses from the topsoil-plant system of 223 kg, 160 kg, 176 kg and 80 kg ha^-1 yr^-1 were high but probably stored in the subsoil because corresponding leaching losses were only 10, 1, 15 and 6 kg ha^-1 yr^-1 at 150 cm depth during the second to fourth cropping year. Beyond the fourth year, markedly reduced nutrient losses from the topsoil and stable food crop yields in no-tree plots suggest that continuous maize-cassava cropping using balanced rates of mineral fertiliser is producing sustainable yields with almost closed nutrient cycles of the soil-plant system on our site. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Amount and Nutrient Content of Litter Fall under Sitka Spruce on Poorly Drained Soils

Litter fall was collected every three months for four yearsfrom twenty-one vigorous (Yield Class 18–20 m³ ha^–1y^–1) and sixteen less vigorous (Yield Class 10–12)plots of Sitka spruce on gleyed soils in Northern Ireland. Forty-fourper cent of all litter fell in the June-August quarter, andlitter fall was heaviest in years when there was green spruceaphis attack. Beneath YC 10–12 crops, both rate and quantityof litter fall was less and nutrient concentrations were lower,than under YC 18–20 crops. As the pool of organic matterand nutrients on the forest floor was greater under trees ofYC 10–12, poor growth was associated with a slow organicmatter and nutrient turnover.