Whole-tree Harvesting Research Articles

Soil erosion under different harvesting managements in steep forestlands from northern Spain

In spite of the high risk of erosion, highly mechanized operations, in which humus layer removal and down-slope ploughing are practised, are often employed to prepare steep forestlands for planting. The purpose of this study was to evaluate the effect on soil loss of three post-harvesting management systems usually used in a mountainous region of northern Spain. The techniques evaluated were (a) conventional stem-only harvesting, (b) whole-tree harvesting and humus layer removal and (c) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. Soil erosion was measured in a total of 39 recently clear-felled Pinus radiata plantations over the period between the stand harvesting and establishment of understorey vegetation. They were located on slopes with gradients of between 40 and 50 per cent. For all treatments the associated runoff–rainfall ratios were high, indicating inherent low permeability of the soil. Intense site preparation resulted in considerable decreases in soil organic matter and increases in bulk density, which decreased the hydraulic conductivity and subsequently produced higher runoff. These deteriorations of soil properties delayed the establishment of pioneer vegetation thus extending the period of high erosion. In the ploughed soils, the higher soil erodibility and the removal of slash and vegetation cover resulted in a four-fold increase of soil losses when compared with no mechanical site preparation. The results indicate that, in order to maintain the soil productivity, and for conservation purposes, harvesting management should minimize the soil disturbances and maintain the slash and vegetation cover. Copyright © 1999 John Wiley & Sons, Ltd.

Soil erosion under different harvesting managements in steep forestlands from northern Spain

In spite of the high risk of erosion, highly mechanized operations, in which humus layer removal and down-slope ploughing are practised, are often employed to prepare steep forestlands for planting. The purpose of this study was to evaluate the effect on soil loss of three post-harvesting management systems usually used in a mountainous region of northern Spain. The techniques evaluated were (a) conventional stem-only harvesting, (b) whole-tree harvesting and humus layer removal and (c) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. Soil erosion was measured in a total of 39 recently clear-felled Pinus radiata plantations over the period between the stand harvesting and establishment of understorey vegetation. They were located on slopes with gradients of between 40 and 50 per cent. For all treatments the associated runoff–rainfall ratios were high, indicating inherent low permeability of the soil. Intense site preparation resulted in considerable decreases in soil organic matter and increases in bulk density, which decreased the hydraulic conductivity and subsequently produced higher runoff. These deteriorations of soil properties delayed the establishment of pioneer vegetation thus extending the period of high erosion. In the ploughed soils, the higher soil erodibility and the removal of slash and vegetation cover resulted in a four-fold increase of soil losses when compared with no mechanical site preparation. The results indicate that, in order to maintain the soil productivity, and for conservation purposes, harvesting management should minimize the soil disturbances and maintain the slash and vegetation cover. Copyright © 1999 John Wiley & Sons, Ltd.

Sources of stream sulfate at the Hubbard Brook Experimental Forest: Long-term analyses using stable isotopes

Sulfur deposition in the northeastern U.S. has been decreasing since the 1970s and there has been a concomitant decrease in the SO42− lost from drainage waters from forest catchments of this region. It has been established previously that the SO42− lost from drainage waters exceeds SO42− inputs in bulk precipitation, but the cause for this imbalance has not been resolved. The use of stable S isotopes and the availability of archived bulk precipitation and stream water samples at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire provided a unique opportunity to evaluate potential sources and sinks of S by analyzing the long-term patterns (1966–1994) of the δ34S values of SO42−. In bulk precipitation adjacent to the Ecosystem Laboratory and near Watershed 6 the δ34S values were greater (mean: 4.5 and 4.2l, respectively) and showed more variation (variance: 0.49 and 0.30) than stream samples from Watersheds 5 (W5) and 6 (W6) (mean: 3.2 and 3.7j; variance: 0.09 and 0.08, respectively). These results are consistent with other studies in forest catchments that have combined results for mass balances with stable S isotopes. These results indicate that for those sites, including the HBEF, where atmospheric inputs are ≤10 kg S ha−1 yr−1, most of the deposited SO42− cycles through the biomass before it is released to stream water. Results from W5, which had a whole-tree harvest in 1983–1984 showed that adsorption/desorption processes play an important role in regulating net SO42− retention for this watershed-ecosystem. Although the isotopic results suggest the importance of S mineralization, conclusive evidence that there is net mineralization has not yet been shown. However, S mass balances and the isotopic result are consistent with the mineralization of organic S being a major contributor to the SO42− in stream waters at the HBEF.

Harvesting Effects on Long‐Term Changes in Nutrient Pools of Mixed Oak Forest

AbstractThe effects of sawlog harvesting (SAW) vs. whole‐tree harvesting (WTH) on C and nutrient budgets of a mixed oak forest near Oak Ridge, TN, were assessed by sampling soils and vegetation just prior to and 15 yr after harvesting. Fifteen years after harvest, large woody residues in the SAW treatment lost >80% of their mass and nutrient content. Greater concentrations of Ca, K, and Mg were found in both foliage and soils in the SAW treatment than in the WTH treatment, but there were no signs of deficiency in these nutrients and no differences in growth due to treatment. There were nod eclines in exchangeable Ca2+ in the WTH treatment, and the increases in soil exchangeable Ca2+ pools in the SAW watersheds were approximately equal to the amount of Ca2+ released by decomposing residues. On the other hand, no treatment effects on soil C, vegetation biomass, species composition, vegetation N or P concentration, soil bulk density, or soil N were found 15 yr after treatment. Contrary to what has been speculated on regarding the basis of nutrient budgets, this study showed no detrimental effects of WTH on productivity or soil nutrient status (i.e., reductions from preharvest conditions). The results did show, however, that nutrients (especially Ca) from logging residues are largely retained in soils and reflected in elevated foliar nutrient concentrations.

Long-term base cation mass balances for Swedish forests and the concept of sustainability

Data from the Swedish Forest Inventory was used to calculate mass balances for base cations Ca, Mg and K for Swedish forests. Using lysimeter and forest survey soil analyses to estimate present base cation leaching from the root zone reveals that weathering plus base cation deposition is not sufficient to support both, the present base cation leaching rate and the present rate of uptake caused by stem growth. Calculations suggest that 96% of the productive forested area may have higher rates of removal than supply for one or more base cation. Under a best-case scenario, assuming less pollution, the present growth rate and 100% efficiency in uptake of available nutrients, the area with more removal than supply would still be at least 30% of the total area. Forest soils are being depleted at a rate where the exchangeable reservoirs have high risk of being severely depleted in the next few decades in central and southern Sweden. During 1983–1985 the depletion rate is calculated to be, on the average, 0.33 keq ha−1 year−1. The weathering rate and present base cation deposition can sustain growth at a level where (80–85)×106m3 stemwood year−1 can be harvested. Any harvested growth beyond this volume must be sustained by artificial means. For whole-tree harvesting without base cation return, the calculations indicate that it would significantly increase the base saturation depletion rate to an average of 0.62 keq ha−1 year−1, and risk depletion of the soil in less than one-to-two rotation periods almost anywhere in Sweden. The calculations stress the importance that sustainable forest management must include the management of nutrient fluxes and reservoirs.

Assessing soil calcium depletion following growth and harvesting of Sitka spruce plantation forestry in the acid sensitive Welsh uplands

Abstract. A simple mass balance has been used to estimate soil calcium depletion during the growth of a 50 year old Sitka spruce crop on acid, base-poor peaty podzol soils in upland Wales. Growth of the crop will deplete the soil calcium reserve by an amount (205 kg Ca ha-1) approximately equivalent to the exchangeable calcium pool to the bottom of the profile and equal to 14% of the total soil calcium reserve to the bottom of the B horizon. Despite these predictions, measurements of exchangeable calcium show no differences beneath mature forest and acid grassland, implying that i) weathering rates in forest soils are greater than long-term estimates and predictions by the PROFILE soil chemistry model ii) the trees can access other sources of calcium or iii) there are significant errors in the mass balance. Following stem-only harvesting, growth of a 50 year old second rotation crop will lead to further depletion of soil calcium, but this amount (79 kg Ca ha-1), is less than for a second rotation crop following whole-tree harvesting (197 kg Ca ha-1). After the first crop, stem-only harvesting would allow a further 18 rotations before depletion of the total calcium reserve to the bottom of the B horizon. Whole-tree harvesting would allow for seven rotations after the first crop. These calculations assume that all sources of calcium are equally available to the crop. This can only be resolved by dynamic modelling of the calcium cycle at the ecosystem scale based on appropriate field measurements. The potential for significant soil acidification is therefore greater following whole-tree harvesting and, in line with current recommendations (Nisbet et al., 1997), this technique should probably be avoided on acidic, nutrient-poor soils unless remedial measures are included to enhance the soil base cation status.

Effects of organic matter removal on the soil food web: Forestry practices meet ecological theory

We examine the long-term effects of removing forest harvesting residues (above-ground whole-tree harvesting; WTH) in the soil food web, using data from two different experiments on slash removal and addition in Sweden. Removal of harvesting residues had negative effects on the abundances of animals at higher trophic positions and on more mobile animals. Predators such as gamasid mites, spiders and staphyliniid and cantharid beetles decreased by 30–50% after WTH at both sites. Microbidetritivorous dipterans and fungivorous Collembola decreased at the pine site, but not at the more productive spruce site. Enchytraeids and nematodes were usually not affected by WTH. No differences in fungal and bacterial biomass were found. The removal of organic matter had fairly long-term, of the order of decades, effects on the soil food web. The effects were quantitative rather than qualitative. No functional groups disappeared after WTH. Our findings do not support the hypothesis that soil food webs are entirely donor-controlled. The more pronounced effects of WTH at higher trophic positions indicates that the major interactions in the food webs we have studied are reciprocal, i.e., that consumers to some degree control the density of their resources.

Variations in mineral nutrient and C distribution in the soil and vegetation compartments of five temperate tree species in NE Sweden

The influence of five tree species on soil acidity and the distribution of carbon and nutrients between biomass and soil were studied in an experiment with 27-year-old stands in three replicates on set-aside farmland in NE Sweden. The five tree species were: Picea abies L. Karst., Pinus sylvestris L., Pinus contorta Dougl., Betula pendula Roth, and Larix sibirica Ledeb. Total tree biomass was 11 kg dw m −2 in B. pendula and L. sibirica, 10 kg dw m −2 in P. abies, and 8 kg dw m −2 in the pines. The foliage of P. abies had a more than eight times higher quantity of Ca, and a more than twice as high quantity of dry weight, Mg, K, P and N, as the foliage of any of the other species. Concentrations of Ca in foliage, branches and stems generally decreased in the order P. abies> B. pendula> L. sibirica, P. sylvestris, P. contorta. The highest amounts of Mg, K, P and N in the stems were found in B. pendula and L. sibirica. The results suggest that the choice of tree species may have a pronounced influence on the rate of nutrient removal both in case of whole-tree harvest and stem-wood harvest, also at similar rates of stem-wood biomass production. However, compared to the large differences found between the species in Ca and K contents of the above-ground part of the trees, the corresponding differences in depletions that were detected in the `non-harvestable' pools of these elements were smaller. (Non-harvestable pool: total element amounts in coarse tree roots and field vegetation and litter/organic layer, plus exchangeable element amounts in the A horizon). No significant species-related differences in soil pools of C or acidity were found. In the combined litter and organic layer, a significant difference in pH was found; about half a unit higher for B. pendula and P. abies than for P. contorta and L. sibirica.

The effect of whole-tree harvest on phosphorus cycling in a northern hardwood forest

A small watershed ecosystem at the Hubbard Brook Experimental Forest in New Hampshire was whole-tree harvested in the dormant season; all trees greater than 10 cm diameter were removed. This harvest removed 50 kg P/ha, five times more P than the bole-only clearcut of an adjacent watershed. The P content of branches and twigs was nearly twice that of stem wood and bark, which contributed to the intensity of P removal. The amount of P removed in harvest was small compared to total P in the mineral soil (1600 kg/ha) but large compared to the pools of P in the living vegetation (70 kg/ha) and the forest floor (85 kg/ha). Negligible P was lost in streamwater and sediment (0.2 kg P/ha over 3 years), although export of other nutrients increased dramatically. Although leaching of P from the forest floor to the mineral soil in the first 2 years after logging was higher in harvested sites than in undisturbed forest, the increase in P leaching (0.7 kg P/(ha yr)) was much less than the estimated decrease in P uptake from the forest floor (4.8 kg/(ha yr)), suggesting a 70% decline in net P mineralization in the forest floor. Even in areas where P uptake by regrowing vegetation was quite high, calculated net P mineralization was 40% lower in the first 2 years of growth than in the undisturbed forest. Revegetation was rapid: in the first 2 years after logging, P in biomass had accumulated to 3% of the uncut forest; uptake was 12% of that in the uncut forest. Whether intensive biomass removals could induce P deficiency in future rotations is unknown.

Nutrient removals with harvesting and by deep percolation from white birch (Betula papyrifera [Marsh.]) sites in central Newfoundland

The effects of conventional stem-only and whole-tree harvesting on nutrient losses in biomass removal and in leachate fluxes over a 3-yr period after cutting three white birch stands in central Newfoundland were determined. Losses of nutrients in biomass were proportionately greater with more intensive harvesting as tree components with higher nutrient concentrations (branches, foliage) were removed. Stem-only harvesting removed 126, 9, 51, 126 and 23 kg ha–1 of N, P, K, Ca and Mg in biomass, respectively. Whole-tree harvesting led to a 19% increase in biomass removal as compared to stem-only harvesting, but nutrient removals with whole-tree harvesting increased by 127% for N, 138% for P, 151% for K, 72% for Ca and 90% for Mg. Nutrient losses in deep percolation of soil solution during the first 3 yr after harvesting were generally greater following stem-only than whole-tree harvesting. This may be the result of increased leaching from slash, increased mineralization beneath slash, and retardation by slash of the successional vegetation that could act as a nutrient sink. In the first 3 yr following harvesting, leaching losses after whole-tree harvesting were 4, 0.2, 8, 23 and 7 kg ha–1 of N, P, K, Ca and Mg, respectively, as compared with 9, 0.1, 7, 28 and 9 kg ha–1 of N, P, K, Ca and Mg after stem-only harvesting. Nutrient losses in leachate were generally small compared to losses in biomass removal. Key words: Intensive harvesting; slash; nutrient budget; sustainable site productivity; Betula papyrifera (Marsh.)

Effects of soil compaction and chipped aspen residue on aspen regeneration and soil nutrients

The effects of soil compaction and depth of chipped aspen residue on aspen regeneration, plant community development, decomposition, and nutrient cycling were tested on an Orthic Gray Luvisol in the Lower Foothills of Alberta. Twenty-seven 100-m × 15-m plots were established in 1992. Three depths of chipped aspen residue (0, 1–5 cm and >10 cm) and three levels of compaction (no compaction, 6 and 16 skidder passes) were applied following whole-tree harvesting in 1993. Sixteen skidder passes and chip residue depths >10 cm resulted in reduced plant cover and aspen sucker densities for at least 2 yr following treatment. Nutrient concentrations of the chip residue and surface organic horizon (LFH) were similar for the three compaction treatments. The initial total nitrogen (N) concentration of the chipped aspen residue was 3.6 g kg−1. Ammonium (NH4+-N) concentrations in the LFH of the chip residue treatments, particularly at the >10-cm residue depth, were lower compared with the no-residue treatment. However, adequate N apparently was available to the aspen suckers and understory vegetation as the NH4+-N concentration remained higher than in the LFH before harvesting. Compaction and woody residue applications had only short-term (3 yr) effects on soil properties, plant community development and aspen suckering at this site when clear-cut harvesting was done in the fall with low soil moisture content. Key words: Ammonium, aspen regeneration, wood residue, compaction

Modeling potentially sustainable biomass productivity in jack pine forest stands

A steady-state mass balance model (ForSust), developed to simulate potentially sustainable levels of tree biomass growth and related nutrient uptake dynamics, was applied to 17 jack pine sites across Canada. The model simulates potential tree biomass growth based on nutrient inputs from estimated atmospheric deposition (N, Ca, Mg, K) and soil weathering (Ca, Mg, K), and matches the resulting nutrient supply rates with calculated nutrient demand. Nutrient demand calculations are based on nutrient concentrations in wood, bark, branches, and foliage. Specifically, the model simulates sustainable annual increment (SAI) of biomass growth for stem-only and whole-tree (aboveground biomass) harvesting, and for recurring forest fire conditions. Calculated SAI levels were compared with field-estimated mean annual increments for aboveground forest biomass (MAI). For recurring forest fires, it was found that SAI values, as simulated, corresponded with the MAI field estimates in general. For whole-tree harvesting, SAI was lower than MAI for most but not all sites. For stem-only harvesting, SAI corresponded with MAI, but there was a greater scatter between SAI and MAI values than what appeared to be the case for the recurring forest fire scenario. Key words: Jack pine; whole-tree, stem-only harvesting; steady-state mass balance; forest biomass; N, Ca, Mg, K growth limitations; atmospheric deposition

Long-Term Effects of Logging Residue Addition and Removal on Macroarthropods and Enchytraeids

The long-term effects of logging residue addition and removal on soil macroarthropods and enchytraeids were examined in a Scots pine Pinus sylvestris L. stand in central Sweden. The study was performed 15-18 years after the treatments had been applied after clear-cutting in 1976. In comparison with plots receiving roughly twice the normal amount of residues, removal of logging residues (above-ground whole-tree harvesting) resulted in decreases in the total numbers of Collembola (springtails), gamasid mites, spiders, predatory insects and dipterous larvae, whereas no significant effects on enchytraeids and diplopods could be detected. Few effects on single species of Collembola and Gamasida were found. The composition of the soil fauna community, as well as food web structure, were significantly affected by whole tree harvesting, but the effects were quantitative rather than qualitative-most organism groups decreased, but the relative importance of different groups did not change markedly. Over the 4 years studied, community predictability (specifically, constancy) at the levels of higher taxa, functional groups and species did not differ substantially between the treatments. Predictabilities of higher taxa and functional groups were higher than predictability of species of Collembola and gamasid mites. Values of community predictability were similar to those found in other studies of forest soil fauna. It is concluded that whole tree harvesting may result in long-term decreases in the abundances of many soil animal groups. The possible impact of decreased abundances of fungivores and predatory arthropods on nutrient cycling and site productivity is discussed. It is argued that the direct effects of these changes on nitrogen mineralization are likely to be small. However, the possibility that the soil fauna may be involved in a positive feedback loop towards lower site productivity means that the observed long-term decreases in several organism groups should be of concern, at least on sites dominated by internal nutrient dynamics.

Forest Management Effects on Surface Soil Carbon and Nitrogen

AbstractChanges in surface soil C and N can result from forest management practices and may provide an index of impacts on long‐term site productivity. Soil C and N were measured over time for five watersheds in the southern Appalachians: two aggrading hardwood forests, one south‐ and one north‐facing, undisturbed since the 1920s; a white pine (Pinus strobus L.) plantation planted in 1956; and two regenerating hardwood forests, a whole‐tree harvest in 1980, and a commercial sawlog harvest in 1977. Soils on harvested watersheds were sampled before and for ≈15 yr after harvest. Surface soil C concentration on the undisturbed watersheds varied significantly among sample years. Concentrations fluctuated on the south‐facing and decreased on the north‐facing watershed. The pattern for total N was similar. Total N decreased significantly on the north‐facing but was stable on the south‐facing watershed. In the white pine plantation, C increased while N concentrations decreased during the 20‐yr period. Soil C and N concentrations generally declined the first year following whole‐tree harvest. Fourteen years after cutting, C remained stable, while N was greater compared with reference watershed soils. The commercial sawlog harvest resulted in large increases in surface soil C and N concentrations immediately after cutting. Carbon levels remained elevated 17 yr following cutting. Our data suggest that the forest management practices examined do not result in long‐term decreases in soil C and N. However, the high interannual variation on all watersheds suggests that care must be taken in selecting control sites to determine long‐term treatment impacts.

Effects of different levels of biomass removal in thinning on short‐term production of pinus sylvestris and picea abies stands

Effects of harvest intensity in thinnings on the productivity of the remaining stands were studied in two Scots pine (Pinus sylvestris L.) and two Norway spruce (Picea abies (L.) Karst.) stands in Sweden. Treatments were: conventional stem wood harvest with short‐wood system (CH); whole‐tree harvest (WTH); whole‐tree harvest + compensation fertilization with NPK (WTH + F). No significant treatment differences in basal area increment could be detected during the first 10 yrs after harvest. However, in all four stands mean basal area increment was lower on WTH plots than on CH plots. The effects of WTH + F were inconsistent. The results indicate that WTH could be practiced in thinnings without significant short‐term production losses in Scots pine and Norway spruce stands in Sweden. However, it is to early to draw any definite conclusion on long‐term effects of WTH on site productivity.

Soil solution concentrations on three white birch sites in central Newfoundland following different harvesting intensities

Three white birch stands of differing site quality (good, intermediate, rich) in central Newfoundland were monitored using porous cup lysimeters to study changes in nutrient concentrations (NH 4N, NO 3N, PO 4P, K, Ca, Mg, pH) in the soil solution following stem only and whole tree harvesting. Ammonium concentrations on the good and intermediate sites were not greatly affected by cutting, but stem only (STO) harvesting on the rich site led to increased concentrations that persisted for 3 y. Nitrate concentrations increased more on the intermediate than on the good site, but increases were smallest on the richest site. This was attributed to a combination of uptake by more vigorous advance regeneration (mainly alders) on the rich site, as well as wetter soil conditions that limited nitrification. Phosphorous concentrations were not greatly affected by harvesting. Potassium concentrations increased immediately after harvesting as K leached from slash on the STO treatments, plant remains and the forest floor, and decreased as these sources were depleted. Vegetation uptake and leaching associated with movement of NO 3N were also controlling mechanisms on some sites. Calcium and Mg concentrations were correlated, and initially increased with harvesting, but on the richest two sites decreased below control stand levels after whole tree harvesting (WTH) at the end of 3 y. Movement of Ca and Mg was associated with NO 3N on sites where there was a significant increase in NO 3N concentrations following harvesting. Acidity decreased on the good site, increased after STO, but decreased after WTH on the intermediate site, and increased after both intensities of harvesting on the rich site. Nutrient concentrations in the soil solution were generally higher when slash was retained in STO treatments rather than removed in WTH treatments. This was attributed to a combination of increased mineralisation beneath the slash, increased leaching from the slash, and decreased plant uptake. In general, the soil solution data suggest that harvesting effects last for no more than 3 y for most nutrients on these birch sites in Newfoundland, and that whole tree harvesting generally had less impact on nutrient concentrations than stem only harvesting. However, this does not necessarily mean that net losses from sites were less with WTH, as this does not take into account nutrient fluxes or nutrient removals in slash.

A strategy to develop a guide for whole-tree harvesting of Sitka spruce in Great Britain

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.

Changes in the Biogeochemistry of Potassium following a Whole‐Tree Harvest

AbstractA whole‐tree harvest (WTH) was conducted at the Hubbard Brook Experimental Forest, New Hampshire, in 1983–1984 to evaluate changes in the loss and supply of nutrients such as K in response to clear‐cutting. The WTH removed 554 mmol m−2 associated with forest biomass. During the first 2 yr following the WTH, there were marked increases in concentrations and fluxes of K in drainage waters (stream efflux 24 mmol m−2 yr−1), coinciding with elevated losses of NO3−. While these losses decreased within 3 yr, concentrations and fluxes of K remained high in Bs2 horizon soil water and streamwater (10.5 mmol m−2 yr−1) for 10 yr relative to the reference watershed (4.8 mmol m−2 yr−1). Soil exchangeable K pools increased within 3 yr after the WTH. In the high‐elevation zone of the watershed, soil pools returned to near‐preharvest values after 8 yr. In the remainder of the watershed, exchangeable K pools decreased after 8 yr but remained about 20% above preharvest pools. The increase in exchangeable K in the mineral soil probably contributes to the long‐term pattern of elevated K concentrations in streamwater after the WTH. Although stream and WTH removal of K (8.5 mmol m−2 yr−1) was large in comparison to preharvest exchangeable K pools (284 mmolc m−2), the increased release of K from mineralization of soil organic matter and weathering resulted in an increase in K on the soil exchange complex (43 mmol m−2 yr−1 in the first 8 yr). The increase in exchangeable K provided an available pool of K for the regrowing vegetation.

Organic Matter Decomposition following Harvesting and Site Preparation of a Forested Wetland

AbstractOrganic matter accumulation is an important process that affects ecosystem function in many northern wetlands. The cotton strip assay (CSA) was used to measure the effect of harvesting and two different site preparation treatments, bedding and trenching, on organic matter decomposition in a forested wetland. A Latin square experimental design was used to determine the effect of harvesting, site preparation, and relative position within the wetland on organic matter decomposition at soil depths of 5, 10, and 20 cm. Repeated measures analysis of variance was used to test for treatment effects on organic matter decomposition, soil temperature, and soil oxidation depth. Cellulose decomposition increased at each soil depth as site disturbance increased, with bedding > trenching > whole‐tree harvest > reference. The cellulose decomposition response was correlated with changes in soil temperature; the temperature coefficient Q10 equaled 6.0, which is greater than previously reported values. Position within the wetland relative to an adjoining river affected the decomposition and soil oxidation depth. Because the rate of decomposition is strongly controlled by temperature, higher rates of organic matter decay are expected to continue on harvested and regenerated sites until canopy closure reduces soil temperature.

Effects of different forest harvest intensities on the pools of exchangeable cations in coniferous forest soils

Effects of harvest intensity on exchangeable cations (1 M NH4Cl extracts) were examined in four coniferous forest soils in Sweden, 15–16 years after clear-felling. Logging residues were harvested at three intensities, applied experimentally in a randomized block design (n = 4): (i) conventional stem-only harvest, (ii) branches and stems harvested but needles left on the ground and (iii) whole-tree harvesting where all above-stump biomass was harvested. Two of the sites were located in northern Sweden, and the other two were in southern Sweden. In each region one site was occupied by a pure Scots pine stand (Pinus sylvestris L.) and the other by a pure Norway spruce stand (Picea abies (L.) Karst.).Whole-tree harvesting resulted in a lower level of base saturation, especially in the humus layer. Compared with base saturation levels in the stem-only harvest treatment, the reductions were 19%, 16% and 8% at the southern sites with spruce and pine and at the northern spruce site, respectively. At the northern pine site no significant treatment effect was detected. Analyses across all study sites of element pools in the humus and 0–20 cm mineral soil layers indicated that reductions in base saturation generally were associated with depletions of exchangeable pools of K, Ca and Mg. In addition, effective cation exchange capacity per unit area was in general lower after whole-tree harvesting compared with the other treatments. Effects on exchangeable pools of Mn and Zn were similar to those observed for base cations. Exchangeable pools of acidic cations were generally not affected, but at the southern sites pools of acidic cations increased with harvest intensity. No significant differences in soil pH(H2O) were detected between treatments.A relatively high proportion of the Ca left on site in the form of slash was recovered in the soil ca. 15 years after felling. This was not the case for K. Furthermore, the nutrient load recovered in the soil was lower at the southern site with Norway spruce than at the other sites. Apart from these inter-site differences, the results were consistent across all study sites.