Clearcut Plots Research Articles

Breeding Bird Responses to Silvicultural Treatments In the Klamath Province of Oregon

Abstract Silvicultural practices such as thinning are performed both for commodity production and to help achieve fuel reduction and biodiversity goals. Although there are several studies that have examined effects of clearcut harvest techniques on forest songbirds, few have examined the effects of thinning. We studied the response of songbirds to different silvicultural approaches to forest management. We experimentally manipulated three 80 to 110 y-old Douglas-fir stands to evaluate influences of commercial thinning and clearcut harvest silvicultural systems on populations of diurnal breeding birds in southwestern Oregon. We conducted 10 to 12 bird point count surveys in each stand between 1992 and 1994 (prior to treatment), and point count surveys of birds 6 times each year from 1998 through 1999 (subsequent to treatment). We found that relative abundance and species richness were highest in the uncut control plots, slightly lower in the thinned plots, and lowest in the clearcut plots. A species-by-spe...

Effects of clear-cutting on decomposition processes in leaf litter and the nitrogen and lignin dynamics in a temperate secondary forest

The effects of clear-cutting on the decomposition rate of leaf litter and on nitrogen (N) and lignin dynamics were investigated in a temperate secondary forest. Decomposition processes were examined over an 18-month period by the litterbag method and compared between a clear-cut site and an adjacent uncut control site using leaf litter from five dominant tree species (Clethra barvinervis, Quercus serrata, Camellia japonica, Ilex pedunculosa and Pinus densiflora). The decomposition rate for litter from C. barvinervis, Q. serrata and I. pedunculosa was significantly greater in the clear-cut plot than in the control plot, and there was no significant difference between plots for C. japonica and P. densiflora. Water content of litter was consistently lower in the clear-cut plot than in the control plot. Nitrogen mass increased after 6 months in the control plot, whereas no net increase of N was observed in the clear-cut plot. Nitrogen concentration increased with respect to accumulated mass loss of litter and was consistently lower in the clear-cut plot for all five species. The mass of lignin remaining in decomposing litter was generally lower in the clear-cut plot, but lignin concentration in decomposing litter was not significantly different between the clear-cut and control plots.

SLOPE ASPECT MODIFIES COMMUNITY RESPONSES TO CLEAR-CUTTING IN BOREAL FORESTS

Slope aspect modifies microclimate and influences ecological processes and spatial distribution of species across forest landscapes, but the impact of slope aspect on community responses to disturbance is poorly understood. Such insight is necessary to understand landscape community dynamics and resilience. We compared bryophyte (liverworts and mosses) communities in matched 0.02-ha plots of four boreal stand types in central Sweden: recently clear-felled and mature stands dominated by Norway spruce in south-facing and north-facing slopes. Differences between forests and clear-cuts were interpreted as effects of clear-cutting, and differences between south- and north-facing slopes as effects of aspect. In response to clear-cutting, bryophyte cover and composition changed more in south-facing slopes. Only one out of ten significantly declining species in south-facing slopes also declined significantly in north-facing slopes. North-facing slopes lost fewer bryophyte species, and among those, fewer forest species and fewer species associated with wood and bark. In north-facing slopes, the average proportions of mosses and liverworts shared between the forest and the clear-cut plot were 88% and 74%, respectively. Corresponding numbers for south-facing slopes were 79% and 33%. In addition, more bryophyte species were added in north- than south-facing slopes after clear-cutting, somewhat reducing the difference in compositional change between aspects. South- and north-facing mature forests differed in species composition, mostly due to higher richness of mosses in south-facing slopes. The smaller changes in bryophyte communities on north-facing slopes in response to clear-cutting have implications for ecosystem dynamics and management as high local survival may enhance landscape-level resilience.

Effects of logging in the southern boreal peatlands of Manitoba, Canada

To evaluate changes in surface water chemistry, peat, and the plant community in logged peatlands, we compared plots in 1–4 year old (class I) and 9–12 year old (class II) clearcuts with plots in wooded controls. Indicator species were significantly different between wooded and clear-cut plots but not between clear-cut plot age classes. Surface waters in class I clearcuts had significantly higher temperature and nutrients compared with controls, and this was attributed to warming of the soil, which resulted in faster decomposition and greater nutrient availability. Hummocks, important peatland plant microhabitats, were reduced in height in all clearcuts because of compaction and abrasion. These abiotic changes caused a shift in the plant community. Total plant diversity was approximately 30% higher on clearcuts and consisted primarily of herbs, particularly grasses. However, bryophyte and lichen diversity and cover was greatest in wooded controls. Picea mariana (Mill.) BSP regeneration was not compromised by clear-cutting and was greater in class II clearcuts. Greater diversity and cover of Salix species in class II clearcuts suggests stable shrub community formation, which may be persistent and may slow succession. The use of appropriate equipment to minimize site disturbances while the ground is frozen may reduce long-term shifts in the plant community.

A preliminary analysis of the response of an avian community to silvicultural treatments in the southern Cumberland Plateau, Alabama, USA

We simulated a shelterwood forest regeneration treatment by reducing basal area, and monitored the response of an avian community in oak-hickory forest on the southern Cumberland Plateau, northern Alabama, USA. We used five treatments: control (no removal), clear-cut (100% removal), and 25, 50, and 75% removal of basal area. Territory mapping was used to quantify bird community between mid-April and July of both 2002 and 2003. Microclimate variables were recorded at each plot. The residual basal area and canopy cover showed three distinct conditions after treatment: closed canopy, open forest, and clear-cut. The microclimate varied among treatments: air temperature was highest in clear-cut plots and lowest in control plots, whereas soil moisture had the opposite pattern. A total of 71 bird species were detected, with 36 of them defending territories. Territory density, species richness, and Shannon diversity index differed among the treatments; the relationship between these bird community indices and the level of basal area removal was quadratic, lowest in the clear-cut plots and highest in the intermediate levels. Although species richness was similar among the control, 25, 50, and 75% removal treatments, species composition varied. The richness difference among treatments became smaller in the second year post-treatment (2003) with an increase in bird density and richness occurring in the clear-cut plots.

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.

Nutrient and light availability to white spruce seedlings in partial and clearcut harvested aspen stands

White spruce is a commercially important tree species in Canada’s boreal forest, and studies are underway to determine the best conditions for planting nursery grown seedlings in the field. Here, we studied effects of low thinning (1/3 harvested), shelterwood (2/3 harvested), and clear-cut harvesting on soil chemical properties, on the growth and nutrition of white spruce seedlings, and on diffuse non-intercepted (DIFN) light levels at 75 cm above the soil surface. The study was conducted on a nutrient-rich clayey soil in the Abitibi region of Québec. DIFN light was lowest in non-harvested control plots and increased curvilinearly with basal area removal. Thus, DIFN light in clear-cut plots was more than twice the amount in shelterwood plots. At three years post-planting, significant linear relationships were found between DIFN light and seedling growth parameters, which were significantly higher in clear-cut than in other treatment plots. Harvesting treatments had no significant effects on soil chemical properties or on four indices of mineral N availability. Needle mass increased with harvesting intensity. Mg and K concentrations in current-year needles were lower in clear-cut than in other treatment plots. In previous-year needles, Ca concentration was higher and Mg concentrations lower in clear-cut plots, whereas as K concentration was higher in non-harvested control plots. Nutrient concentrations were nearly all sufficient in all harvesting treatments according to diagnostic norms established for white spruce. Relative nutrient content (mg nutrient needle–1) of current-year late-summer needles increased, whereas relative nutrient concentration (mg nutrient mg–1 needle) varied slightly, with increasing harvesting intensity, indicating that all nutrients were sufficient in all treatments. There were significant linear relationships between seedling growth and needle Ca, Mg and K concentrations. We conclude that light availability, rather than nutrient limitations, is the main determinant of white spruce seedling growth on these fertile soils.

Effect of Soil Compaction and Biomass Removal on Soil CO2 Efflux in a Missouri Forest

Forest disturbances associated with harvesting activities can affect soil properties and soil respiration. A soda‐lime technique was used to measure soil carbon dioxide (CO2) efflux rates in clearcut plots of a Missouri oak‐hickory (Quercus spp. L.—Carya spp. Nutt.) forest 4 years after being treated with two levels of forest biomass removal and two levels of compaction, both separate and in combinations, and an uncut control. Respiration rates were measured twice a month from mid‐April through October. Soil CO2 efflux rates were significantly (p<0.001) higher in uncut control plots than in clearcut plots, but differences between biomass removal or soil compaction treatments were not significant. Soil CO2 efflux rates were positively correlated with soil temperature. The lack of difference between soil CO2 efflux rates in weed control and no weed control subplots suggests that several more years may be required for regenerating clearcut plots to produce soil respiration rates similar to those in uncut control plots.

The Response of Conifer and Broad-Leaved Trees and Shrubs to Wildfire and Clearcut Logging in the Boreal Forests of Central Labrador

Abstract To assess the differences between forest management and natural disturbance, we retrospectively compared crown cover of woody plant species between burned and clearcut sites after 5, 14, and 27 years of succession. All 16 sites had been dominated by black spruce (Picea mariana) before disturbance. We found no difference in species richness between disturbance types, but richness was lowest on 5-year-old sites for both disturbances. Burned and clearcut sites differed in the cover of woody plant species, differences increasing slightly with time since disturbance. Both balsam fir (Abies balsamea) and black spruce were more abundant on 14- and 27-year-old clearcut plots than burned plots. Black spruce cover was always greater than fir, but the spruce:fir ratio on clearcut plots was lower than on burned plots. Our data suggest that fire and clearcut logging affect postdisturbance succession differently. Contrary to other studies, logging resulted in more commercially valuable black spruce than fire, and broad-leaved woody plants were not in greater abundance on logged sites. However, the persistence of fir through logging suggests that the resulting forest would be of lower commercial value than a pure black spruce forest. North. J. Appl. For. 22(1):35–41.

Influence of Cutting Method on Stand Growth in Sawtimber Oak Stands

Abstract Many upland oak forests in the eastern United States are approaching economic and biological maturity. A study was established in 1981–1984 in three central Connecticut forests to examine the effects of six distinct cutting methods (shelterwood, diameter limit, multiaged crop tree, high grading, silvicultural clearcut, forest preserve) on stand growth and dynamics in sawtimber oak stands. Board-foot volumes (International 1/4) averaged 8.4 mbf/ac before the initial harvest. Sixty-nine percent of sawtimber trees had butt-log grades of 2 or better. Volume growth was significantly lower on high grading plots (36 bf/ac/year) than on the forest preserve, diameter limit, shelterwood, and multiaged crop tree plots (∼214 bf/ac/year) through two cutting cycles. Total board-foot yield (final volumes plus harvested volumes) for the silvicultural clearcut plots (7.3 mbf/ac) was significantly lower than for uncut, shelterwood, and diameter limit cuts, 12.3, 12.5, and 13.0 mbf/ac, respectively. This study showed that three distinct cutting methods: shelterwood, multiaged crop tree, and forest preserve resulted in similar stand volume growth rates in sawtimber oak stands. The first two methods can be used by landowners who wish to generate income to offset expenses. The choice will depend on the aesthetic and regeneration goals of the landowner. Diameter-limit cutting also had similar volume rates, but it was necessary to lower the diameter limits for the second cutting cycle to maintain economically viable harvests. As a consequence, residual stand structure after the second cutting cycle was similar to that for the high grading plots. Although high grading had the highest harvested volume during the first cutting cycle, low quality of residual trees and depressed stand growth rates indicate it is not a viable option for long-term forest management. North. J. Appl. For. 22(1):59–67.

Logging residues and ground vegetation in nutrient dynamics of a clear-cut boreal forest

In this thesis are studied the role of decomposing logging residues and developing ground vegetation in nutrient dynamics of a clear-cut area. The main aims were to study how much nutrients are released from logging residues during the first three years after clear-cutting and what is the role of ground vegetation in the retention of nutrients on site after clear-cutting. The study was conducted in eastern Finland in a Norway spruce dominated mixed forest, part of which was clear-cut and part left uncut. The decomposition of Norway spruce (Picea abies (L.) H. Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth) logging residues i.e. foliage, fine roots (diameter 2 mm) and branches (diameter 1 cm), were studied using the litterbag method. Aboveand below-ground biomass of the ground vegetation was sampled on one uncut plot and two clear-cut plots one year before and five years after clear-cutting. In total, 33 % of the dry mass and C, 49 % of P, 90 % of K and 8 % of Ca were released from logging residues in three years, but there was no net release of N because more N accumulated in the roots and branches than was released from the foliage. The loss of mass, C, P and K was greatest during the first year, whereas there was no net release of Ca until the third year. Most of the released nutrients originated from the foliage. Total ground vegetation biomass and nutrient pools decreased after clear-cutting to one half or even lower, but returned to precutting levels within 4-5 years, and the pools of P and K became even larger. In the first year after clear-cutting more N and Ca accumulated in the logging residues than were stored in the ground vegetation. The results indicate that logging residues are a potential source of the elevated dissolved C and P, K and Ca observed in surface waters soon after clear-cutting, but are not a net source of N during the first three years. The ground vegetation is capable of taking up only a small fraction of the nutrients that are released from logging residues during the first two years after clear-cutting and the decomposing dead ground vegetation is a potential source of leached nutrients. The results suggest that nutrients released from logging residues are initially retained on site primarily through soil processes and microbial immobilization. Solely microbial immobilization in logging residues can initially play a more important role in the retention of N and Ca than the ground vegetation. Ground vegetation, however, recovers rapidly from clear-cutting and it becomes thereafter a significant nutrient sink.

Effects of a clearcut on the net rates of nitrification and N mineralization in a northern hardwood forest, Catskill Mountains, New York, USA

The Catskill Mountains of southeastern New York receive among the highest rates of atmospheric nitrogen (N) deposition in eastern North America, and ecosystems in the region may be sensitive to human disturbances that affect the N cycle. We studied the effects of a clearcut in a northern hardwood forest within a 24-ha Catskill watershed on the net rates of N mineralization and nitrification in soil plots during 6 years (1994–1999) that encompassed 3-year pre- and post-harvesting periods. Despite stream NO3− concentrations that increased by more than 1400 μmol l−1 within 5 months after the clearcut, and three measures of NO3− availability in soil that increased 6- to 8-fold during the 1 st year after harvest, the net rates of N mineralization and nitrification as measured by in situ incubation in the soil remained unchanged. The net N-mineralization rate in O-horizon soil was 1– 2 mg N kg−1 day−1 and the net nitrification rate was about 1 mg N kg−1 day−1, and rates in B-horizon soil were only one-fifth to one-tenth those of the O-horizon. These rates were obtained in single 625 m2 plots in the clearcut watershed and reference area, and were confirmed by rate measurements at 6 plots in 1999 that showed little difference in N-mineralization and nitrification rates between the treatment and reference areas. Soil temperature increased 1 ± 0.8 °C in a clearcut study plot relative to a reference plot during the post-harvest period, and soil moisture in the clearcut plot was indistinguishable from that in the reference plot. These results are contrary to the initial hypothesis that the clearcut would cause net rates of these N-cycling processes to increase sharply. The in situ incubation method used in this study isolated the samples from ambient roots and thereby prevented plant N uptake; therefore, the increases in stream NO3− concentrations and export following harvest largely reflect diminished uptake. Changes in temperature and moisture after the clearcut were insufficient to measurably affect the net rates of N mineralization and nitrification in the absence of plant uptake. Soil acidification resulting from the harvest may have acted in part to inhibit the rates of these processes.

Spatial and temporal variation of seepage water chemistry after femel and small scale clear-cutting in a N-saturated Norway spruce stand

The chemistry of seepage water was studied before and after small scale clear-cutting and femel cutting (removing 20% of the trees) between 1999 and 2002 at the Hoglwald site in southern Bavaria. The interventions were performed in February 2000 on mature, N-saturated Norway spruce (Picea abies (L.) Karst.) stands with high NO3− concentrations before felling. Seepage water was collected with suction cups at 40 cm soil depth in the following treatments: (I) a mature stand (control), (II) a femel-cut, and (III) a clear-cut. In the femel cut subvariants were created with suction cups (plots) at varying distances from pre-selected spruce, which were later removed. The femel treatment was replanted with beech (Fagus sylvatica L.) saplings. On the clear-cut, subvariants of planted beech (close to the stem, interstem area), planted spruce (interstem), or natural spruce regeneration were investigated. Clear-cutting caused high NO3− peaks (average values up to 2750 µM) during 2000 and 2001 in all planted tree subvariants during times of comparatively low water fluxes. In contrast to peak concentrations, flux weighted yearly average concentrations showed different trends. In 2000, flux weighted yearly average NO3− concentrations were significantly elevated, but only on the subvariants of the interstem area, which covered in the clear-cut plot ca. 62% of the area. However, the subvariant close to the stem (31% of clear-cut area), or the natural spruce regeneration subvariant (6% of clear-cut area) exhibited no significant felling effect. With respect to the whole treatment area, this resulted in no significant felling effect as compared with the control. In the next year (2001), flux weighted yearly average NO3− concentrations were not significantly affected by clear-cutting, while the concentrations were even reduced for all of the clear-cut subvariants in 2002. On the subvariant natural spruce regeneration, NO3− concentrations remained below the European limit of drinking water (806 µM) during almost the whole investigation period. Selective cutting resulted in slightly reduced NO3− concentrations in 2000 and 2001 on the femel treatment. However, no significant effect could be detected for any subvariant in the femel-cut, even not for the subvariant with suction cups closest to the felled spruce. In contrast to many other investigations, clear-cutting did not increase the NO3− problem on the treatment to a relevant extend. Quite contrary, a decline in NO3− concentrations to values below the EU level for drinking water and levels below the control and femel treatment just 2 years after cutting were observed. Al3+ concentrations showed nearly the same trend as NO3−, while Ca2+, Mg2+, and K+ concentrations were affected to a lesser degree. Only in 2002 was Ca2+ significantly lower on the clear-cut as compared to the femel treatment, but not compared to the control. Mg2+ increased in 2000 on the clear-cut subvariants in the interstem area, but decreased in the years 2001 and 2002. Changes could be observed for K+ only periodically on some subvariants, but not for the whole treatment area. Concentrations of SO42−, Na+, and Cl− were reduced after clear-cutting and remained nearly unchanged after femel cutting.

The effects of harvest intensity and seedbed type on germination and cumulative survivorship of white spruce and balsam fir in northwestern Quebec

The effects of different harvest intensities, including uncut, 1/3 and 2/3 partial cuts, clearcuts with and without slash, were investigated on the germination and cumulative survivorship of white spruce and balsam fir over 2 consecutive years. We also investigated the regenerative capacity of both species on three different seedbeds across all harvest intensities. The seedbeds included were mineral, humus, and organic soil. At the germination stage, both species were strongly affected by seedbed type (p &lt; 0.032). The germination rates of fir seeds in partial cuts were significantly greater than clearcut treatments, but spruce remained unaffected at this stage by harvest intensity. The addition of slash improved the germination rates of fir relative to the clear-cut plots without slash. The germination rates the following year were reduced on mineral soil for spruce. The cumulative survivorship at the end of the third summer still showed a significant seedbed response for both species (p &lt; 0.007) and a significant harvest response for fir (p &lt; 0.005). The cumulative survivorship of the second fir cohort was no longer affected by either harvest or seedbed type. Spruce, however, was still affected by seedbed type (p = 0.006). The data from this study provide us with a more detailed description of the fate of cohorts recruited following a harvest operation. Still, what remains to be studied is the fate of these cohorts over the next 5–10 years.

Decomposition and nutrient release from logging residues after clear-cutting of mixed boreal forest

Elevated dissolved carbon (C), nitrogen (N) and phosphorus (P) concentrations are frequently observed in surface water soon after clear-cutting of boreal coniferous forests. It has been suggested that they originate from the fine logging residues whose decomposition may be accelerated as a result of changes in soil temperature and moisture conditions. In the present study, the decomposition rate and release of C, N, and P from Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karsten) and silver birch (Betula pendula Roth.) logging residues (fine roots ∅≤2 mm, branches ∅≤10 mm and foliage) were investigated during three years with the litterbag method in a clear-cut area and in an adjacent Norway spruce dominated, mixed boreal forest in eastern Finland (63°51′ N, 28°58′ E, 220 m asl). The mass loss of the logging residues decreased in the order: foliage > roots > branches. Birch leaves were the only fraction that showed significantly higher losses of mass and C at the clear-cut plot than at the forest plot; otherwise there was no tendency for accelerated decomposition or mineralization at the clear-cut plot. After three years the initial C pool in the logging residues had declined by 33% and that of P by 49% but there was no net release of N as more N accumulated in roots and branches than was released from foliage. The results indicate that 1) logging residues release relatively large and rapid fluxes of CO2 to the atmosphere 2) are potential source of elevated P in surface waters soon after clear-cutting 3) are not a net source of N immediately after clear-cutting.

Temperature sensitivity of mineral N transformation rates, and heterotrophic nitrification: possible factors controlling the post-disturbance mineral N flush in forest floors

A major forest disturbance such as clearcutting may bring on a flush of mineral N in organic forest floor horizons, but the magnitude of this flush can vary markedly from one ecosystem to another. For example, it was previously established that clearcutting in a high elevation Engelmann spruce-subalpine fir (ESSF) ecosystem results in significantly higher NH 4 + and NO 3 − concentrations, whereas clearcutting in an old-growth coastal western hemlock (CWH) ecosystem has little effect on mineral N dynamics. We hypothesized that the higher mineral N flush observed in the ESSF ecosystem is due to a greater temperature sensitivity of mineral N transformation rates, and to a lower proportion of heterotrophic nitrifiers, compared to the CWH ecosystem. To test these two hypotheses, we sampled forest floors several times over the growing season from clearcut and old-growth plots in both ecosystems, and measured gross mineral N transformation rates at field temperatures and at 10 °C above field temperatures, as well as with and without acetylene to inhibit autotrophic nitrifiers. Gross NH 4 + transformations rates ranged between 20 and 120 μg N (g forest floor) −1 day −1 at the ESSF site, and between 15 and 40 μg N (g forest floor) −1 day −1 at the CWH site. Higher temperature increased gross NH 4 + transformation rates in forest floor samples at both sites, but the average Q 10 value was higher at the ESSF site (3.15) than at the CWH site (1.25). Temperature sensitivity at the ESSF site was greater in clearcut plots ( Q 10=4.31) than in old-growth plots ( Q 10=1.98). Gross NO 3 − transformation rates ranged between 10 and 32 μg N (g forest floor) −1 day −1 at the ESSF site, and between 10 and 24 μg N (g forest floor) −1 day −1 at the CWH site, but there were no significant effects of temperature or clearcutting on gross NO 3 − transformation rates at either site. Likewise, there were no significant differences in the proportion of heterotrophic nitrifiers between sites. Overall, our results support the view that the temperature sensitivity of microbial processes may explain the magnitude of the NH 4 + flush in some coniferous ecosystems, but we lack the evidence relating the magnitude of the NO 3 − flush to the proportion of heterotrophic nitrifiers.

Release of potassium, calcium, iron and aluminium from Norway spruce, Scots pine and silver birch logging residues

Potassium (K), calcium (Ca), iron (Fe) and aluminium (Al) release from Norway spruce (Picea abies Karsten), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) logging residues (fine roots, foliage and small branches) were studied by means of litterbags over a period of three years in clear-cut area and adjacent uncut Norway spruce dominated mixed boreal forest in eastern Finland (63°51′ N, 28°58′ E, 220 m a.s.l) to determine the amounts and rates of release for these elements and to evaluate whether clear-cutting accelerates mineralization. Almost all K was released from logging residues already during the first year. Calcium was released from foliage and roots but accumulated in branches. Most of the roots Fe and Al content were released during three years while the absolute amounts of Fe and Al in branches and foliage generally increased with decomposition. The results indicate that mineralization is slightly accelerated as a result of clear-cutting since K from foliage and branches of all studied tree species and Ca from pine and spruce roots was released significantly faster at the clear-cut plot than at the forest plot. In three years the initial K pool in the logging residues declined by 90%, Ca by 8%, Fe by 55% and Al by 61% in the clear-cut area. These results indicate that Ca is retained a long time; but Fe, Al and in particular, K are soon released from logging residues. Fine roots of the logged trees release large amounts of Fe and Al and can significantly affect Fe and Al fluxes.

Mineral N availability for conifer growth following clearcutting: responsive versus non-responsive ecosystems

We compared mineral N concentrations, potential net mineralization rates and gross N mineralization rates in the forest floor of 4-year-old clearcut plots and adjacent mature forest stands, in three distinct coniferous ecosystems in British Columbia (coastal low elevation, coastal montane, interior montane). Our data showed that clearcutting has no effect on forest floor mineral N dynamics in some coniferous ecosystems, and significant effects in others. Among “responsive” sites, we noted contradictory effects of clearcutting on some of the measured N variables. Furthermore, the effects of clearcutting on potential net mineralization were not consistent with changes in gross production rates of mineral N. We discuss these observations in light of our knowledge of the ecology of each site, of the various sources and sinks of mineral N, and of the biotic and abiotic factors controlling mineral N dynamics. Our results suggest that generalizations cannot be made on the effects of clearcutting on mineral N supply to conifer seedlings, as these can lead to incorrect interpretations of ecosystem dynamics, with serious policy-relevant ramifications for the forest industry.

Carbon sequestration in trees and regrowth vegetation as affected by clearcut and partial cut harvesting in a second-growth boreal mixedwood

Ecosystem biomass and C sequestration and cycling were measured in a mature, budworm-ravaged, second-growth boreal mixedwood stand subjected to clearcut and partial cut harvest treatments. Ninety permanent sample plots, distributed among fifteen 10 ha blocks, were established in 1993 and remeasured shortly after harvest and, again, 5 years later to ascertain C removals, as well as post-harvest ingrowth and upgrowth. In addition, litter bags and litter traps were installed and ground vegetation and forest floor samples were collected to monitor changes in ecosystem C pools and fluxes as affected by harvesting. The harvested blocks were quickly reoccupied by a thriving ground species regrowth, followed by a prolific trembling aspen thicket. Despite this, 5-year growth per area on control plots exceeded that on either partial cut or clearcut plots. Annual C assimilation rates in the post-harvest period were similarly significantly higher on control (3.1 Mg ha −1 per year) than on partial cut (1.8 Mg ha −1 per year) or clearcut (0.3 Mg ha −1 per year) plots. When growth was expressed as a function of biomass, the order reversed indicating the young growth to be the more vigorous. The forest floor lost little mass during the post-harvest period. Further, leaf litter decomposition was slower on clearcut plots than in uncut forest. Results suggest that ecosystem C pools and fluxes are rapidly reconstituted following harvest. If harvesting were to occur, ecosystem C assimilation in boreal mixedwood forest would be maximized under partial cutting.

Similarity of small mammal abundance in post-fire and clearcut forests

To test the assumption that forest harvesting can maintain wildlife through emulating natural disturbance, we compared small mammal abundance between seven post-fire and nine clearcut plots representing three ages since disturbance (4, 14 and 27 years). On each site, two Victor snap traps were placed at 100 stations on 10×10 grids spaced 20 m apart. Clethrionomys gapperi were more abundant in clearcut plots, likely due to abundant coarse woody debris. This difference decreased through time. No other species differed between disturbance types. In both burned and clearcut plots, the abundance of C. gapperi was lowest on 14-year-old sites while Microtus pennsylvaticus and Sorex cinereus peaked at 14 years. At the meso-scale (plot-level), grass, herbs, and coarse woody debris explained 53% of the variation in small mammal abundance. At the micro-scale (individual trapsite), several variables showed statistical significance, yet only 13% of the variation in small mammals was explained. This was reduced to 4% when the spatial component of ecological variation was controlled. This suggests that our small mammals are coarse-grained foragers and fine-scale vegetation descriptions have little ability to explain small mammal abundance. We conclude that the coarse-filter approach to forest management by emulating natural disturbances can maintain small mammal communities in central Labrador.