Recovery of carbon and nutrient pools in a northern forested wetland 11 years after harvesting and site preparation

We measured the change in above- and below-ground carbon and nutrient pools 11 years after the harvesting and site preparation of a histic-mineral soil wetland forest in the Upper Peninsula of Michigan. The original stand of black spruce (Picea mariana), jack pine (Pinus banksiana) and tamarack (Larix laricina) was whole-tree harvested, and three post-harvest treatments (disk trenching, bedding, and none) were randomly assigned to three Latin square blocks (n = 9). Nine control plots were also established in an adjoining uncut stand. Carbon and nutrients were measured in three strata of above-ground vegetation, woody debris, roots, forest floor, and mineral soil to a depth of 1.5 m. Eleven years following harvesting, soil C, N, Ca, Mg, and K pools were similar among the three site preparation treatments and the uncut stand. However, there were differences in ecosystem-level nutrient pools because of differences in live biomass. Coarse roots comprised approximately 30% of the tree biomass C in the regenerated stands and 18% in the uncut stand. Nutrient sequestration, in the vegetation since harvesting yielded an average net ecosystem gain of 332 kg N ha⁻¹, 110 kg Ca ha⁻¹, 18 kg Mg ha⁻¹, and 65 kg K ha⁻¹. The likely source for the cations and N is uptake from shallow groundwater, but N additions could also come from non-symbiotic N-fixation and N deposition. These are the only reported findings on long-term effects of harvesting and site preparation on a histic-mineral soil wetland and the results illustrate the importance of understanding the ecohydrology and nutrient dynamics of the wetland forest. This wetland type appears less sensitive to disturbance than upland sites, and is capable of sustained productivity under these silvicultural treatments.     

Modelling the effects of forest management intensification on base cation concentrations in soil water and on tree growth in spruce forests in Sweden

The study investigated the effects of forest residue extraction on tree growth and base cations concentrations in soil water under different climatic conditions in Sweden. For this purpose, the dynamic model ForSAFE was used to compare the effects of whole-tree harvesting and stem harvesting on tree biomass and the soil solution over time at 6 different forest sites. The study confirmed the results from experimental sites showing a temporary reduction of base cation concentration in the soil solution for a period of 20–30 years after whole-tree harvesting. The model showed that this was mainly caused by the reduced inputs of organic material after residue extraction and thereby reduced nutrient mineralisation in the soil. The model results also showed that whole-tree harvesting can affect tree growth at nitrogen-poor forest sites, such as the ones in northern Sweden, due to the decrease of nitrogen availability after residue removal. Possible ways of reducing this impact could be to compensate the losses with fertilisation or extract residue without foliage in areas of Sweden with low nitrogen deposition. The study highlighted the need to better understand the medium- and long-term effects of whole-tree harvesting on tree growth, since the results suggested that reduced tree growth after whole-tree harvesting could be only temporary. However, these results do not account for prolonged extraction of forest residues that could progressively deplete nutrient pools and lead to permanent effects on tree growth.

     

Structure and composition of streamside management zones following reproduction cutting in shortleaf pine stands

Streamside management zones (SMZs) in the Ouachita Mountains of Arkansas and Oklahoma are frequently established along headwater ephemeral and intermittent streams to protect water quality, provide wildlife habitat, and increase landscape diversity. To better understand the function of these riparian forest corridors, we characterized the tree density and composition, forest floor mass, and downed woody debris volume within SMZs located in undisturbed, mature, upper mid-slope shortleaf pine stands and then compared these attributes to those in upland portions of these stands. In addition to evaluate the impact of upland forest harvesting on these riparian corridors, we compared the amounts and distribution of forest floor, downed woody debris (DWD), snags, and windthrows in SMZs within shortleaf pine stands that had been clearcut, had a shelterwood harvest, and had no recent management activity (uncut stands). Total tree and hardwood basal area was significantly higher (4.4 and 4.2 m² ha⁻¹) while forest floor mass was significantly lower (0.5 kg m⁻²) in the SMZs than in the upland portion of the undisturbed stands. Five years following the reproduction cuttings tree basal area, DWD volume, and forest floor mass within SMZs did not significantly differ among stands that had or had not been harvested. Snag density was significantly lower within SMZs that occurred in clearcut stands compared to those in the uncut or shelterwood stands. Harvesting activities that retain few or no residual trees appear to increase the degradation of snags. This study provided evidence that clearcutting may also increase the risk of windthrow in SMZs as well. There was little difference in the distribution of forest floor within SMZs regardless of whether the stand was harvested or the type of harvesting that occurred in the stand. However, DWD amounts were higher near the SMZs edge than in the interior of the SMZs with the greatest differences in distributions in stands that were clearcut.     

Estimation of nutrient removals in stem-only and whole-tree harvesting of Scots pine, Norway spruce, and birch stands with generalized nutrient equations

Whole-tree harvesting (WTH), where logging residues are removed in addition to stems, is widely practised in Fennoscandian boreal forests. WTH increases the export of nutrients from forest ecosystems. The extent of nutrient removals may depend on tree species, harvesting method, and the intensity of harvesting. We developed generalized nutrient equations for Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karsten), and birch (Betula pendula Roth and Betula pubescens Ehrh.) stands to be able to calculate the amounts of nitrogen, phosphorus, potassium, and calcium in stems and above-ground biomass (stem and crown) as a function of stand volume. The equations were based on Fennoscandian literature data from 34 pine, 26 spruce, and 5 birch stands, and they explained, depending on the tree species and nutrient, 61–99% and 56–87% of the variation in the nutrient amounts of stems and above-ground biomass, respectively. The calculations based on the equations showed that nutrient removals caused by stem-only harvesting (SOH) and WTH per harvested stem m³ were smaller in pine than in spruce and birch stands. If the same volume of stem is harvested, nutrient removals are, in general, nearly equal at thinnings and final cuttings in SOH, but larger in thinnings than final cuttings in WTH. If the principal aim is to minimize the nutrient removals per harvested stem m³, the harvesting should be done at mature pine stands. The effect of biomass removal on overall site nutrient status depends on site-specific factors such as atmospheric deposition, weathering of minerals, and the size of the nutrient pools in the soil.     

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.     

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.     

日本北海道北部寒温带森林流域林冠层凋落物及其养分归还量的景观格局(英文)

Within a forested watershed at the Uryu Experimental Forest of Hokkaido University in northern Hokkaido, overstory litterfall and related nutrient fluxes were measured at different landscape zones over two years. The wetland zone covered with Picea glehnii pure stand. The riparian zone was deciduous broad-leaved stand dominated by Alnus hirsuta and Salix spp., while the mixture of deciduous broadleaf and evergreen conifer dominated by Betula platyphylla, Quercus crispula and Abies sachalinensis distributed on the upland zone. Annual litterfall averaged 1444, 5122, and 4123 kg.hm^-2·a^-1 in the wetland, riparian and upland zones, respectively. Litterfall production peaked in September-October, and foliage litter contributed the greatest amount （73.4%-87.6 %） of the annual total litterfall. Concentrations of nutrients analyzed in foliage litter of the dominant species showed a similar seasonal variation over the year except for N in P glehnii and A. hirsuta. The nutrient fluxes for all elements analyzed were greatest on riparian zone and lowest in wetland zone. Nutrient fluxes via litterfall followed the decreasing sequence： N （11-129 kg.hm-2.aq） 〉 Ca （9-69） 〉 K （5-20） 〉 Mg （3-15） 〉 P （0.4-4.7） for all stands. Significant differences were found in litterfall production and nutrient fluxes among the different landscape components. There existed significant differences in soil chemistry between the different landscape zones. The consistently low soil C：N ratios at the riparian zone might be due to the higher-quality litter inputs （largely N-fixing alder）.     

Influence of climate change,fire and harvest on the carbon dynamics of black spruce in Central Canada

The results of EFIMOD simulations for black spruce (Picea mariana [Miller]) forests in Central Canada show that climate warming, fire, harvesting and insects significantly influence net primary productivity (NPP), soil respiration (Rs), net ecosystem production (NEP) and pools of tree biomass and soil organic matter (SOM). The effects of six climate change scenarios demonstrated similar increasing trends of NPP and stand productivity. The disturbances led to a strong decrease in NPP, stand productivity, soil organic matter (SOM) and nitrogen (N) pools with an increase in CO₂ emission to the atmosphere. However the accumulated NEP for 150 years under harvest and fire fluctuated around zero. It becames negative only at a more frequent disturbance regime with four forest fires during the period of simulation. The results from this study show that changes in climate and disturbance regimes might substantially change the NPP as well as the C and N balance, resulting in major changes in the C pools of the vegetation and soil under black spruce forests.     

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.     

Effects of forest residue harvesting on short-term changes in soil solution chemistry

Short-term (three to four years) effects of forest harvesting on soil solution chemistry were investigated at two Norway spruce sites in southern Norway, differing in precipitation amount and topography. Experimental plots were either harvested conventionally (stem-only harvesting, SOH) or whole trees, including crowns, twigs and branches were removed (whole-tree harvesting, WTH), leaving residue piles on the ground for some months before removal. The WTH treatment had two sub-treatments: WTH-pile where there had been piles and WTH-removal, from where residues had been removed to make piles. Increased soil solution concentrations of NO₃–N, total N, Ca, Mg and K at 30?cm depth, shown by peaks in concentrations in the years after harvesting, were found at the drier, less steep site in eastern Norway after SOH and WTH-pile, but less so after WTH-removal. At the wetter, steeper site in western Norway, peaks were often observed also at WTH-removal plots, which might reflect within-site differences in water pathways due largely to site topography.     

Changes in microclimate after stand conversion in two northern hardwood stands

Changes in air temperature, soil temperature, and soil moisture were monitored for 5 years in two northern hardwood stands after whole-tree harvesting and conversion to red pine (Pinus resinosa Ait.) plantations. Soil temperatures at a depth of 5 cm and maximum air temperatures 2 m above the soil surface were increased 5–25% after stand conversion. Soil moisture content at a depth of 5 cm was increased by 10–20% in one stand but not in the other. Differences in stand, soil, and topographical characteristics between the two stands did not have any apparent effect on the magnitude of air or soil temperature changes after stand conversion. However, higher initial stand density and soil water holding capacity appeared to be related to increased soil moisture content at one of the sites. The increased soil temperatures after conversion were not only a result of the removal of the northern hardwood canopy but also the removal and redistribution of the forest floor caused by whole-tree harvesting. Five years after stand conversion air temperature, soil temperature, and soil moisture showed no evidence of recovering from initial post-harvest levels.     

Recovery of Soil pH,Cation-exchange Capacity and the Saturation of Exchange Sites from Stemflow-induced Soil Acidification in Three Swedish Beech (Fagus sylvatica L.) Forests

Stemflow water acidifies the soil in beech stands impacted by atmospheric deposition. To investigate whether the soil recovers from acidification, stemflow was experimentally removed. A horizon material was sampled at a distance of 10 - 250 cm from the stems. Before the onset of the experiment, there were stemflow - induced gradients in the saturation of exchange sites with K⁺, H⁺ and Na⁺ that were larger near the stems, while the pHKCl, the cation - exchange capacity, and the saturation with Ca2⁺, Mg2⁺ and Mn2⁺ were smaller. After 8 yrs of recovery, the pHKCl and the saturation with Ca2⁺ and Mg2⁺ had increased close to the stems, while the saturation with Na⁺, H⁺, Mn2⁺ and 2⁺ and the C/N ratio had decreased. With some exceptions, e.g. base saturation, the recovery was not complete after 8 yrs. Soil far from stems had also changed similarly, probably because of the ongoing decrease in overall deposition in southern Sweden.     

Impact of management on nutrients,carbon, and energy in aboveground biomass components of mid-rotation loblolly pine (Pinus taeda L.) plantations

Context

To sustainably manage loblolly pine plantations for bioenergy and carbon sequestration, accurate information is required on the relationships between management regimes and energy, carbon, and nutrient export.

Aims

The effects of cultural intensity and planting density were investigated with respect to energy, carbon, and essential nutrients in aboveground biomass of mid-rotation loblolly pine plantations, and the effects of harvesting scenarios on export of nutrients were tested.

Methods

Destructive biomass sampling of a 12 years-old loblolly pine culture/density experiment, and analysis of variance were used to assess the effects of cultural intensity (operational vs. intensive) and six planting densities ranging from 741 to 4,448 trees ha^?1. Two harvesting scenarios (stem-only vs. whole-tree harvesting) were assessed in terms of energy, carbon, and nutrient export.

Results

The concentrations of energy, carbon, and nutrients varied significantly among stem wood, bark, branch, and foliage components. Cultural intensity and planting density did not significantly affect these concentrations. Differences in energy, carbon and nutrient contents among treatments were mainly mediated by changes in total biomass. Nutrient contents were affected by either cultural intensity or planting density, or both. Stem-only harvesting removed 71–79 % of aboveground energy and carbon, 29–45 % of N, 28–44 % of P, 44–57 % of K, 51–65 % of Ca, and 50–61 % of Mg.

Conclusions

Stem-only harvesting would be preferred to whole-tree harvesting, from a site nutrient conservation perspective.     

六盘山华北落叶松林降水转化中的阳离子通量变化特征

在六盘山香水河小流域的华北落叶松人工林样地,测定了2011年生长季降水转化过程中的大气降水、穿透水、干流、枯落物渗透水和主根系层(30 cm土层)土壤渗透水的pH值与多种阳离子的浓度及通量变化.结果表明:林外降水的pH值平均为7.13,转化为穿透雨和干流后降为6.73和6.00,转化为枯落物渗透水和土壤渗透水后回升为6.87和7.28.在降水转为由穿透雨和干流组成的林下降水后,绝大多数阳离子的浓度都不同程度地增大,但Zn2+浓度下降;虽然林冠截持使林下降水的数量减小,但由于雨水对林冠的离子交换及淋洗,林下降水的多数阳离子通量都比林外降水明显增大,K+、Mg2+、H+、Mn2+、Cu2+、Fe3+由林外的17.23、12.51、0.06、0.09、0.13、0.19 mmol·m-2分别上升到林下的141.87、32.93、0.10、0.68、0.24、0.56 mmol·m-2,但Na+、Ca2+、Zn2+的通量分别由林外的33.73、112.91、2.05 mmol·m-2减小为林内的30.70、75.75、1.10 mmol·m-2.在枯落物层渗透水中,绝大多数阳离子的浓度都不同程度地下降,仅Mg2+浓度微弱上升;受枯落物截持部分降水及雨水中阳离子与枯落物交换的影响,枯落物渗透水中所有阳离子的通量都比林下降水明显减小,K+、Na+、Mg2+、Ca2+、H+、Mn2+、Cu2+、Zn2+、Fe3+分别降至83.06、12.30、23.96、65.73、0.04、0.12、0.09、0.13、0.32 mmol·m-2.在主根系层土壤渗透水中,一些阳离子(K+、Mn2+、Cu2、Fe3+)的浓度下降,另一些阳离子(Na+、Mg2+、Ca2+、Zn2+)的浓度则上升,尤其Ca2+浓度显著上升;Na+、M2+、Ca2+、Mn2+、Zn2+的通量比枯落物渗透水增大,其值分别为37.49、62.83、202.41、0.22、1.05 mmol·m-2,但K+、Cu2+、Fe3+的通量比枯落物渗透水减小,其值分别为27.14、0.07、0.09 mmol·m-2.相对于林外降水的阳离子输入通量,林冠层对多数阳离子(除Na+、Ca2+、Zn2+)的通量为净淋出(增加)作用,枯落物层对多数阳离子(除K+、Mg2+、Mn2+、Fe3+)的通量为净固定(减少)作用,主根系层土壤对盐基离子(Na+、K+、Mg2+、Ca2+)和Mn2+的通量为净淋失(增大)作用,但对其他阳离子(H+、Cu2+、Zn2+、Fe3+)的通量为净固定(减少)作用.     

Do thinnings influence biomass and soil carbon stocks in Mediterranean maritime pinewoods?

The effects of silvicultural treatments on carbon sequestration are poorly understood, particularly in areas like the Mediterranean where soil fertility is low and climatic conditions can be harsh. In order to improve our understanding of these effects, a long-term thinning experiment in a stand of Mediterranean maritime pine (Pinus pinaster Ait.) was studied to identify the effects of thinning on soil carbon (forest floor and mineral soil), above and belowground biomass and fine and coarse woody debris. The study site was a 59-year-old pinewood, where three thinnings of differing intensities were applied: unthinned (control), moderate thinning and heavy thinning. The three thinning interventions (for the managed plots) involved whole-tree harvesting. The results revealed no differences between the different thinning treatments as regards the total soil carbon pool (forest floor + mineral soil). However, differences were detected in the case of living aboveground biomass and total dead wood debris between unthinned and thinned plots; the former containing larger amounts of carbon. The total carbon present in the unthinned plots was 317 Mg ha^?1; in the moderately thinned plots, it was 256 Mg ha^?1 and in the case of heavily thinned plots, 234 Mg ha^?1. Quantification of these carbon compartments can be used as an indicator of total carbon stocks under different forest management regimes and thus identify the most appropriate to mitigate the effects of global change. Our results indicated that thinning do not alter the total soil carbon content at medium term, suggesting the sustainability of these silvicultural treatments.     

Silicate mineral weathering rate estimates: Are they precise enough to be useful when predicting the recovery of nutrient pools after harvesting?

Are current estimates of silicate minerals weathering rates precise enough to predict whether nutrient pools will recover after forest harvesting? Answering this question seems crucial for sustainable forestry practices on silicate dominated soils. In this paper, we synthesize estimated Ca and K weathering rates (derived using seven different approaches) from a forested area in northern Sweden (the Svartberget-Krycklan catchment) to evaluate the precision of weathering rate estimates. The methods were: mass-balance budgets (catchment and pedon-scale); long-term weathering losses inferred from weathered soil profiles (using zirconium as a conservative tracer); strontium isotopes (⁸⁶Sr/⁸⁵Sr) as proxy for catchment export of geogenic Ca; climate based regressions; a steady-state, process-based weathering model (PROFILE) and a dynamic, conceptual catchment geochemistry model (MAGIC). The different methods predict average weathering rates of 0.67 ± 0.71 g Ca m⁻² year⁻¹ (mean ± stdev) and 0.39 ± 0.38 g K m⁻² year⁻¹, suggesting a cumulative weathering release during a forest rotation period of 100 years that is the same magnitude as losses induced by forest harvesting at the end of the period. Clearly, forestry practices have the capacity to significantly alter the long-term nutrient status of the soil and cation concentrations in soil-water runoff. However, the precision in weathering estimates are lower than that needed to distinguish between effects on nutrient pools by different forest practices (complete-tree harvesting versus conventional stem only harvest). Therefore, we argue that nutrient budgets, where weathering rates play a crucial role, cannot be used as basis for resolving whether different harvesting techniques will allow nutrient pools to recover within one rotation period. Clearly, this hampers the prerequisite for sound decision making regarding forestry practices on silicate mineral dominated soils.     

Phosphorus release from forest harvesting on an upland blanket peat catchment

The aim of this study was to investigate the release of phosphorus (P) to receiving waters resulting from harvesting 34-year-old lodgepole pine trees in an upland peat catchment. The study site was within a 25.3-hectare (ha) area, and was drained by a stream that received flows from ploughed furrows, mainly, via collector drains, and discharged directly to the salmonid Shrahrevagh River, Burrishoole, Co. Mayo, Ireland. The study site was divided into two parts: the upstream part was left intact and the downstream part was harvested in early Autumn 2005 following implementation of forest guidelines. Good management practices such as proper use of brash mats and harvesting only in dry weather were implemented. Two instrumented stations were established – one just upstream (US) and the other just downstream (DS) of the clearfelled area. The measurement of P concentrations at the two stations commenced in May 2005, two months before the harvesting started. The daily mean P concentration at the DS station increased from about 6 μg L⁻¹ of total reactive phosphorus (TRP) during pre-clearfelling to 429 μg L⁻¹ in August 2006. By October 2009, four years after clearfelling, the P concentrations at the DS station had returned to pre-clearfelling levels. In the first three years after harvesting, up to 5.15 kg ha⁻¹ of TRP was released from the harvested catchment to the receiving water; in the second year alone, 2.3 kg ha⁻¹ of TRP was released. Linear regression can be used to describe the relationship between TRP load and water discharge. About 80% of the total phosphorus (TP) in the study stream was soluble and more than 70% of the P release occurred in storm events, indicating that traditional buffer strips with widths of 15–20 m might not be efficient for P immobilization. The P concentrations were affected by antecedent weather conditions and highest concentrations occurred during storm events following prolonged drought periods. The water extractable phosphorus (WEP) contents in the soil were significantly higher below windrow/brash material than in brash-free areas, and whole-tree harvesting should be studied as one of the means to decrease P export from blanket peats.     

Contribution of understory vegetation to minimizing nitrate leaching in a Japanese cedar plantation

Understory vegetation may affect nitrate (NO₃ ⁻) leaching, even in coniferous forests. Our objective was to estimate the contribution of understory vegetation to nutrient cycling, especially nitrogen, in a Japanese cedar (Cryptomeria japonica) stand. We therefore cut down and removed understory vegetation in one plot of the stand (the cutting plot) to compare nutrient budgets in the cutting plot with those in a control plot in which understory vegetation was allowed to grow. We also examined neutralization of the acid produced due to an increase in NO₃ ⁻ leaching. A monitoring study on precipitation and soil-percolated water was carried out in both plots. When the understory vegetation was cut down, NO₃ ⁻ flux at a soil depth of 10 cm increased remarkably in summer, with values significantly higher than those in the control plot. This resulted in an increase in proton load associated with N transformation ([H⁺]load). The increase in [H⁺]load enhanced mobilization of Ca²⁺, Mg²⁺, and SiO₂ ([SiO₂]mob). In addition, the correlations between [SiO₂]mob and mobilization of each base cation were distinct in the cutting plot. These results indicated that the acids produced because of N transformation were buffered not only by ion exchange but also by chemical weathering. The contribution of understory vegetation to minimizing NO₃ ⁻ leaching suggested that understory vegetation might reduce the risk of N saturation because of chronic atmospheric N inputs.     

The influence of partial timber harvesting in riparian buffers on macroinvertebrate and fish communities in small streams in Minnesota,USA

Relatively few evaluations of aquatic macroinvertebrate and fish communities have been published in peer-reviewed literature detailing the effect of varying residual basal area (RBA) after timber harvesting in riparian buffers. Our analysis investigated the effects of partial harvesting within riparian buffers on aquatic macroinvertebrate and fish communities in small streams from two experiments in northern Minnesota northern hardwood-aspen forests. Each experiment evaluated partial harvesting within riparian buffers. In both experiments, benthic macroinvertebrates and fish were collected 1 year prior to harvest and in each of 3 years after harvest. We observed interannual variation for the macroinvertebrate abundance, diversity and taxon richness in the single-basin study and abundance and diversity in the multiple-basin study, but few effects related to harvest treatments in either study. However, interannual variation was not evident in the fish communities and we detected no significant changes in the stream fish communities associated with partially harvested riparian buffers in either study. This would suggest that timber harvesting in riparian management zones along reaches ≤200 m in length on both sides of the stream that retains RBA ≥ 12.4 ± 1.3 m² ha⁻¹ or on a single side of the stream that retains RBA ≥ 8.7 ± 1.6 m² ha⁻¹ may be adequate to protect macroinvertebrate and fish communities in our Minnesota study systems given these specific timber harvesting techniques.