Mature Spruce Research Articles

Energy and CO2 exchange in an undisturbed spruce forest and clear-cut in the Southern Taiga

Effects of clear cutting and other forest disturbances on surface radiative properties and the energy and CO2 fluxes between land surface and the atmosphere can vary significantly depending on local climatic and moisture conditions, forest structure and species composition, soil properties and many other factors. In this study we analyzed the influence of clear-cutting on the energy, water vapor and CO2 fluxes in the still very poorly investigated part of the boreal forest community in the European part of Russia. This issue has become particularly relevant due to intensified logging in the region during recent decades. The sensible (H) and latent (LE) heat, as well as CO2 fluxes were continuously measured at recently clear-cut and undisturbed mature spruce forest sites using eddy covariance technique during the first growing season following harvest. Because of their close location they are characterized by similar meteorological conditions. The results of our field measurements showed that the clear-cut strongly influenced the energy balance and CO2 fluxes between the land surface and atmosphere. Energy fluxes (LE and H) at the undisturbed forest site were consistently larger than at the clear-cut throughout the period of measurements. The Bowen ratio (β=H/LE) varied significantly over time, though was similar at both sites. Whereas H was almost equal to LE at both sites in spring, the LE significantly exceeded H over the summer (β≈0.2 - for mature spruce forest and β = 0.4 - for clear-cut). The mean β for the entire period was similar (β≈0.5) at both sites. Analysis of CO2 fluxes showed that the clear-cut was a consistent source of CO2 to the atmosphere. Net ecosystem exchange (NEE) at the clear-cut averaged 3.3 ± 1.3 gC∙m−2∙d-1 (±1 SD), while average NEE at the undisturbed mature forest was close to zero (0.1 ± 1.9 gC∙m−2∙d-1). Differences in NEE were mainly governed by differences in gross primary productivity (GPP) between sites (7.0 ± 4.1 gC∙m−2∙d-1 and 4.1 ± 3.0 gC∙m−2∙d-1, for the undisturbed forest and clear-cut, respectively). Total ecosystem respiration (TER) did not significantly (p < 0.05) differ between sites (7.1 ± 3.6 gC∙m−2∙d-1 at the undisturbed mature forest and 7.4 ± 3.4 gC∙m−2∙d-1 at clear-cut). TER at the undisturbed forest showed higher sensitivity to changes in soil temperature, whereas GPP at the clear-cut was characterized by higher light-use efficiency. Our measurements showed that TER rates were relatively high in the southern taiga in comparison with other boreal sites where CO2 fluxes were previously investigated.

Isotopic response of run‐off to forest disturbance in small mountain catchments

AbstractStable water isotopes were applied to trace hydrological processes in an undisturbed (mature spruce forest) and a nearby disturbed (deforested from a bark beetle outbreak) lake catchments in the Czech Republic. Both catchments are situated above 1,000 m a.s.l. within the Šumava National Park and have similar environmental conditions. The isotopic compositions of precipitation, creeks, springs, and lakes were sampled at 3‐week intervals over one hydrological year. Water inputs to catchments were derived from isotopically similar local precipitation, whereas run‐off was found to have different isotopic signatures. Creeks in the undisturbed catchment had ~1‰ and ~7‰ higher δ18O and δ2H with ~2‰ lower d‐excess than in the disturbed catchment. The d‐excess in creeks of the undisturbed catchment was more pronounced, particularly during snowmelt, and highly heterogeneous as compared with the disturbed catchment. Creeks in the undisturbed catchment were mainly fed by precipitation during the warm period (May–October), whereas creeks in the disturbed catchment were mostly fed by precipitation during the cold period (November–April). Estimated mean transit times of creeks and springs were ~6 months, except for two creeks in the undisturbed catchment, which had residence times of ~1 year. Although evaporation and transpiration fluxes were apparently reduced in the disturbed catchment, transpiration ratios were similar for both catchments. The difference in isotope signatures between catchments was attributed to the altered role of the forest canopy in temporal water distribution, which produced changes in the water cycle, potentially influencing important biogeochemical processes.

Interception and Fog Drip Estimates in Fragmented Mountain Forests

Forest interception is a major loss of water balance in mountain catchments, reducing the recharge of water resources. Fog precipitation occurring at higher elevations can reduce this loss by saturating the vegetative surface and dripping down to the soil surface. In 2015–2017, detailed observations of canopy throughfall and fog drip were performed in the upper plain of the Jizera Mountains (North Bohemia, Czech Republic). In the warm season (May–October), the interception loss of 106 mm was found in investigated mature spruce stand at 975 m a.s.l., i.e., 16% of the gross precipitation (662 mm). In 51 days a year, the forest interception was affected by a canopy fog drip. Hypothetically, by a negligible fog drip, the mean seasonal interception calculated by the Gash analytical model (225 mm) was 34% of the ‘open field’ rainfall. The fog drip volume (119 mm) was confirmed by the Slinn model (128 mm, + 9%), while the relatively simple models of Gallagher and Vermeulen significantly underestimated results by −23 and − 38%. Therefore, the Slinn model was employed to calculate daily fog drip over an annual cycle in heavy fragmented forest stands over 1 km2 of an experimental catchment. We found only slightly increased fog drip (up to 10%) within 30 m of the forest edge, reflective of the relatively high forest fragmentation (an absence of large homogenous stands and sharp edges). Four basic canopy classes (from mature spruce stands to herbaceous cover) were distinguished. The mean annual fog drip was PF = 81 mm (i.e., 7% of the gross precipitation) and fog drip reached 7–8% of the mean annual gross precipitation, or 10–12% of the mean annual runoff. In addition, the winter fog drip of up to 60% confirmed previous findings from this area.

Severity of Overstory Mortality Influences Conifer Recruitment and Growth in Mountain Pine Beetle-Affected Forests

The severity of lodgepole pine mortality from mountain pine beetle outbreaks varies with host tree diameter, density, and other structural characteristics, influencing subcanopy conditions and tree regeneration. We measured density and leader growth of shade-intolerant lodgepole pine, shade-tolerant Engelmann spruce, and very shade-tolerant subalpine fir regeneration beneath stands that experienced moderate and high overstory lodgepole pine mortality (average 40% and 85% of total basal area) a decade earlier. Lodgepole comprised &gt;90% of the overstory basal area and mature spruce and fir were present in both mortality levels, though live basal area and disturbance history differed. Post-beetle outbreak recruitment was high in both mortality levels, but there were more lodgepole in high than moderate mortality plots (1140 stems ha−1 vs. 60 stems ha−1) and more subalpine fir in moderate than high mortality plots (4690 stems ha−1 vs. 2870 stems ha−1). Pine advance regeneration, established prior to outbreak, was more dense in high mortality than moderate mortality sites (930 stems ha−1 vs. 310 stems ha−1), but the trend was generally the opposite for the other conifers. Lodgepole recruitment increased and subalpine fir decreased with greater forest floor light availability. All species grew faster in high mortality areas than their counterparts in moderate mortality areas. However, in high mortality areas pine grew faster than the more shade tolerant species, and in moderate mortality areas spruce and fir grew faster than pine. These species-specific responses to the degree of overstory mortality will influence future stand composition and rate of forest recovery after mountain pine beetle outbreaks.

Barbastelle bats in a wind farm: are they at risk?

We need to know if and how western barbastelles Barbastella barbastellus are affected by wind farming in Sweden. This is because wind turbines are frequently constructed in barbastelle habitats and yet there is no national guideline on how the arising conflict should be handled. We studied the movement, behavior and mortality of a barbastelle population at a wind farm in southern Sweden, using radio-telemetry, automatic bat detectors and carcass searches. The tagged bats (6 males and 8 females) roosted mainly under loose bark of dead oak trees and foraged in patches of mature deciduous woodlands or pockets of mature spruce trees within 15 km of the roosts. Extensive areas of young spruce plantation, open farmland and lakes were not used for roosting or foraging but were crossed by commuting bats. Continuous recordings with bat detectors frequently picked up barbastelles at forest edges 30 m from the turbines, but rarely over the turbine pads within 10 m from the turbines and never at heights of 30 and 100 m at the turbine towers. Barbastelles were apparently not attracted to the wind turbines and did not seem to interact with them in any way. Carcass searches under 10 wind turbines at 1-week intervals over three summers did not reveal any dead barbastelles, although three other species were recovered. We conclude that wind farming is not nessarily incompatible with effective conservation of barbastelles in Sweden, but instead of focusing on wind turbines, effors should concentrate on (a) preservation and restoration of mature, age-structured deciduous woodlands and spruce forests, including very small and isolated patches, which provide food and roosts, and probably also (b) avoidance of outdoor lighting in areas used by barbastelles. Designating large circular buffer zones around each known or suspected colony according to current practice would be inefficient or meaningless in our case, because barbastelles use extensive home ranges and switch roost frequently. We argue that barbastelle management must be applied on a landscape scale.

Growth recovery of mature Norway spruce and European beech from chronic O3 stress

Elevated O3 levels can strongly impair the health and vitality of forest ecosystems. Free-air exposure systems reveal that forest tree and stand growth can be reduced strongly under chronic O3 stress. Detailed knowledge of the effect of O3 exposure on photosynthesis, carbon sequestration, allometry and growth during chronic stress is available. However, knowledge of growth response after O3 reduction is scarce. Here, we analyse the growth of mature Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) in the free-air O3 fumigation experiment at Kranzberg Forest. We compare tree growth over a 9-year period (2008–2016) after exposure to O3 (2000–2007). During 2 × O3 exposure, the annual basal area growth of Norway spruce and European beech decreased by 24 and 32%, respectively. After cessation of 2 × O3 exposure, the annual basal area growth of Norway spruce and European beech not only recovered but exceeded the growth of the trees in the control condition by 14 and 24%, respectively. The growth resilience and resistance of trees previously exposed to 2 × O3 towards drought stress and late frost was hardly lower than that of the trees in the control condition. The capacity for growth recovery even after long-term chronic O3 stress emphasizes the strong beneficial effect of air pollution control on the health of forest ecosystems and on the global land carbon sink.

Underplanted silver fir and common beech cause changes in root stratification and morphology in mature spruce stands

Underplanted silver fir and common beech cause changes in root stratification and morphology in mature spruce stands

Effects of Forest Practices on Water Resources Recharge in the Boreal Climate

The aim of this study was to evaluate effects of forestry practices on water resources in the middle-boreal zone of central Finland. The long-term research was performed at Kivesvaara experimental plots (64∘28′ N, 27∘33′ E) and Oijusluoma small catchments (65∘50′ N, 29∘0′ E), with a detailed snow observation at Paljakka (65∘26′ N, 26∘26′ E). Forestry practices included clear-cut, shelterwood and seed cutting with different techniques of soil preparation and reforestation. The clear-cut (particularly by the total biomass harvest including stump removal) has increased the water yield (a positive feedback). But, on the other hand, it has caused a drop in retention and lag-time, and an increase of peak-flows, as well as increasing mobility of nitrogen and phosphorus. Thus, the clear-cut of mature spruce stands (Picea abies) increased the groundwater recharge by 63 mm (i.e., 24%), and the total biomass harvest of one-half of the experimental catchment increased the water yield by 44 mm (i.e., 15%) during three years after the harvest. A significant increase in contents of nitrogen persisted in groundwaters more than 25 years after the clear-cut, and 10 years after the natural regeneration (shelterwood or seed cutting). During the monitored period of 28 years, the total output of nitrogen from subsequent forest plantations ranged from 12 to 21 tons per hectare (i.e., exceeding 5–9 times the output from control mature spruce stands). By natural regeneration, the ten-year mean load of nitrogen exceeded 2.5–5 times the load at control plots. After the total biomass harvest (a whole tree and stump removal), the mean annual outflow of nitrogen and phosphorus was 5.4 and 0.11 k g h a −1 (exceeding 2.5 and 1.8 times the pre-treatment stream-flow). These results confirmed the hypothesis of a significant impact of forest practices on water resource control in the boreal forest biome.

Seasonal dynamics of arginine ammonification in forest soils of Norway spruce pure stands under different silvicultural practices

Abstract Effects of seasonal dynamics and silvicultural practice on ammonification of arginine, one of the proteinogenic amino acids, were assessed in surface organic H-horizon of three Norway spruce pure stands in medium altitudes (600 - 660 m a.s.l.). Contents of ammonium ions NH4 + measured monthly in the field and contents of NH4 + after laboratory incubation of these samples with arginine were taken as dependent variables in ANOVA and in linear regression model using generalised linear model. The aim of the analyses was to determine the significance of decomposition of this amino acid in H-horizon of forest soils and to determine categorical and continuous predictors which influence intensity of the ammonification. Laboratory experiments confirmed its close link to seasonal dynamics, as well as to forest management; however the last mentioned was firstly found as less significant when compared within whole season. As regards to seasonal dynamics in forest soils, the highest amount of ammonium ion was released in May and the lowest in July. As regards to the silvicultural practice applied, more ammonium ion was released under mature spruce monoculture, especially in August and May; in the young stands, the method of thinning had no effect on the ammonium ion release. However, the arginine ammonification was found to be influenced by ammonium nitrogen content (slight, less significant negative correlation) and by soil water content (stronger positive significance), especially in the stand with thinning from below. This was concluded to be caused by changes in stand microclimate in function of the silvicultural practice.

Communities of oribatid mites (Acari: Oribatida) of naturally regenerating and salvage-logged montane spruce forests of Šumava Mountains

AbstractThe main aim of this study was to describe and compare communities of oribatid mites of selected areas in montane spruce forests near Březník in the Šumava National Park, where different management strategies were used after the spruce dieback caused by massive bark beetle gradation more than 15 years ago. Naturally regenerating and salvage-logged areas were compared. Significant differences were found in the oribatid mite community composition between differently managed areas. The oribatid mite community in naturally regenerating areas was in better shape and its abundance and species composition was similar to the community of a control area in a mature and healthy spruce forest.

Impacts of fire on non-native plant recruitment in black spruce forests of interior Alaska

Climate change is expected to increase the extent and severity of wildfires throughout the boreal forest. Historically, black spruce (Picea mariana (Mill.) B.S.P.) forests in interior Alaska have been relatively free of non-native species, but the compounding effects of climate change and an altered fire regime could facilitate the expansion of non-native plants. We tested the effects of wildfire on non-native plant colonization by conducting a seeding experiment of non-native plants on different substrate types in a burned black spruce forest, and surveying for non-native plants in recently burned and mature black spruce forests. We found few non-native plants in burned or mature forests, despite their high roadside presence, although invasion of some burned sites by dandelion (Taraxacum officinale) indicated the potential for non-native plants to move into burned forest. Experimental germination rates were significantly higher on mineral soil compared to organic soil, indicating that severe fires that combust much of the organic layer could increase the potential for non-native plant colonization. We conclude that fire disturbances that remove the organic layer could facilitate the invasion of non-native plants providing there is a viable seed source and dispersal vector.

Volatile Organic Compounds Emitted by Fungal Associates of Conifer Bark Beetles and their Potential in Bark Beetle Control.

Conifer bark beetles attack and kill mature spruce and pine trees, especially during hot and dry conditions. These beetles are closely associated with ophiostomatoid fungi of the Ascomycetes, including the genera Ophiostoma, Grosmannia, and Endoconidiophora, which enhance beetle success by improving nutrition and modifying their substrate, but also have negative impacts on beetles by attracting predators and parasites. A survey of the literature and our own data revealed that ophiostomatoid fungi emit a variety of volatile organic compounds under laboratory conditions including fusel alcohols, terpenoids, aromatic compounds, and aliphatic alcohols. Many of these compounds already have been shown to elicit behavioral responses from bark beetles, functioning as attractants or repellents, often as synergists to compounds currently used in bark beetle control. Thus, these compounds could serve as valuable new agents for bark beetle management. However, bark beetle associations with fungi are very complex. Beetle behavior varies with the species of fungus, the stage of the beetle life cycle, the host tree quality, and probably with changes in the emission rate of fungal volatiles. Additional research on bark beetles and their symbiotic associates is necessary before the basic significance of ophiostomatoid fungal volatiles can be understood and their applied potential realized.Electronic supplementary materialThe online version of this article (doi:10.1007/s10886-016-0768-x) contains supplementary material, which is available to authorized users.

Assessment of the Main Natural Disturbances on Norwegian Forest Based on 20 Years of National Inventory.

The re-measurement of permanent forest inventories offers a unique opportunity to assess the occurrence and impact of forest disturbances. The present study aims at exploring the main forest damages in Norway based on the extensive data of several consecutive national forest inventories during the period 1995–2014. Five of the most common disturbance agents in Norway are selected for analysis: wind, snow, browsing, fungus and insect damage. The analyses focuses on the frequency and variation along time, the average damage at stand level and the spatial patterns of damage occurrence, resulting in a characterization of the damage produced by disturbances in Norway. The highest damage occurrences by disturbance agent are due to browsing, snow and wind. Snow presents a decreasing temporally trend in damage frequency in the studied period. By forest type, mature and intermediate birch forest are found to be more affected by snow damage, whereas mature spruce forest is by wind damage. The results from this study provide support to the hypothesis that damages by autumnal moth (Epirrita autumnata) on birch are more common in mature stands. No major attacks from bark beetle (Ips typographus) are found, probably related to the lack of major storm damages in the period. Forest types susceptibility to fungus has no apparent variation over time except in the last years, as increased occurrence is observed on mature spruce stands probably correlated with warmer than average periods. Browsing damage causes the most severe losses, as expected, in young stands, and is allocated mainly on the most productive forests. Although some of the disturbances present locally moderate effects, the results show no major disturbances threatening Norwegian forests in the studied period. Finally, the Norwegian national forest inventory demonstrates its reliability as a basis to understand the occurrence and effects of major natural disturbances.

White Spruce Growth and Wood Properties over Multiple Time Periods in Relation to Current Tree and Stand Attributes

The relationships between white spruce radial increment and wood properties were investigated in relation to tree and stand attributes using data from mature white spruce stands in the boreal forest of western Canada that experienced a range of shelterwood treatments. The model with the highest predictive ability was radial increment (adj-R2 = 67%) and included crown attributes, diameter at breast height (DBH), average height of competitors, and a climate index. Radial growth was positively related to live crown ratio, whereas wood density and modulus of elasticity were negatively correlated to the crown attribute. Tree slenderness had a significant negative effect on wood density and modulus of elasticity, as it reflects the mechanical stability requirement of the tree. The models consistently improved when using annual averages calculated over longer periods of time. However, when the annual averages were calculated using time periods of 5–10 and 10–20 years prior to sampling, the predictive ability of the models decreased, which indicated that the current tree and stand conditions were the best predictors of growth and wood properties up to five years prior to sampling. This study suggests that crown length equal to 2/3 of the tree height might represent an optimal balance between radial growth and wood quality.

Effect of salicylic acid on protease and urease activity in soils under Norway spruce pure stands

This study tested the hypothesis that soil protease and urease activity is inhibited by salicylic acid. This was tested in soils from spruce monocultures of different ages and treated by different forest management methods at the Rajec-Němcice Ecosystem Station. Surface organic H-horizons from three study plots were sampled: a mature spruce monoculture of 105 years and two young spruce monocultures of 33 years, one of which was thinned from above and the other thinned from below. Statistically significant differences between the measured values confirm that young stands are sensitive to the presence of 2-hydroxybenzoic acid as a phytotoxic substance. The results of this study do not conclusively show whether the effect of salicylic acid on protease activity inhibition increases when the protease activity itself is high. The impact of salicylic acid on soil urease activity was not clearly evident either.

A comparison of two different biodiversity assessment methods in LCA—a case study of Swedish spruce forest

Purpose Lately, there has been a growing interest in how to include biodiversity in life cycle assessment (LCA). The aim of this study was to compare two impact assessment methods, with regard to their applicability on a regional level and their feasibility in terms of data availability, through applying them to a case study. MethodsThe methods tested were those developed by de Baan et al. (2013a), based on species richness, and Lindner et al. (2014), based on ecosystem indicators. These were applied to commercially managed spruce forest in the south of Sweden. For the species-based method, characterization factors (CFs) were based on species richness of vascular plants in the region, calculated for two different stages in the production cycle, before and after felling, and using two different types of semi-natural reference situations. The key feature in the ecosystem approach was a set of indicators of prerequisites for biodiversity, based on expert knowledge, and the reference situation applied was the hypothetic maximum biodiversity quality in the region. Results and discussionThe results showed that both methods were applicable for biodiversity assessment at regional level. All methodological requirements, such as species data and expert opinion, were available. To obtain enough data for the species richness method, data on vascular plants from two administrative regions was needed. When biodiversity was assessed before felling and using the spruce reference situation, the conventional spruce forestry studied was shown to have positive impact on biodiversity. All other results showed negative impacts on biodiversity. The positive impact indicated by the species richness method was probably due to the small difference in species richness between the mature spruce forest assessed and the available spruce forest reference situation. ConclusionsThe study shows that the two methods are applicable on a regional level, although data availability was a constraint in the species richness method by de Baan et al. (2013a). The choice of reference situation, and when in the production cycle assessment was made, led to considerable differences in the characterization factors generated.

Long-term landscape changes in a subalpine spruce-fir forest in central Utah, USA

In Western North America, increasing wildfire and outbreaks of native bark beetles have been mediated by warming climate conditions. Bioclimatic models forecast the loss of key high elevation species throughout the region. This study uses retrospective vegetation and fire history data to reconstruct the drivers of past disturbance and environmental change. Understanding the relationship among climate, antecedent disturbances, and the legacy effects of settlement-era logging can help identify the patterns and processes that create landscapes susceptible to bark beetle epidemics. Our analysis uses data from lake sediment cores, stand inventories, and historical records. Sediment cores were dated with radiometric techniques (14C and 210Pb/137Cs) and subsampled for pollen and charcoal to maximize the temporal resolution during the historical period (1800 CE to present) and to provide environmental baseline data (last 10,500 years). Pollen data for spruce were calibrated to carbon biomass (C t/ha) using standard allometric equations and a transfer function. Charcoal samples were analyzed with statistical models to facilitate peak detection and determine fire recurrence intervals. The Wasatch Plateau has been dominated by Engelmann spruce forests for the last ~10,500 years, with subalpine fir becoming more prominent since 6000 years ago. This landscape has experienced a dynamic fire regime, where burning events are more frequent and of higher magnitude during the last 3000 years. Two important disturbances have impacted Engelmann spruce in the historical period: 1) high-grade logging during the late 19th century; and (2) a high severity spruce beetle outbreak in the late 20th century that killed >90 % of mature spruce (>10 cm dbh). Our study shows that spruce-dominated forests in this region are resilient to a range of climate and disturbance regimes. Several lines of evidence suggest that 19th century logging promoted a legacy of simplified stand structure and composition such that, when climate became favorable for accelerated beetle population growth, the result was a landscape-scale spruce beetle outbreak. The lasting impacts of settlement-era landscape history from the Wasatch Plateau, UT may be relevant for other areas of western North America and Europe where sufficient host carrying capacity is important in managing for resistance and resilience to outbreaks.

Biomass of external mycelium of ectomycorrhizal fungi in Norway spruce stands in Poland

&lt;p&gt;Biomass of extramatrical mycorrhizal mycelium (EMM) was examined under canopies of mature Norway spruce trees grown in different forest stands in Poland. Two mountain forest sites (Brenna and Salmopol), one upland site (Zwierzyniec) and one lowland site (Mirachowo) have been investigated, using sand-filled mesh-bags method. The in-grow mesh-bags were buried in the soil for 12 months (since October up to the next October) or for 4 months (since June up to October) at four depths at each site: 5, 15, 30 and 45 cm (Brenna and Salmopol) or 60 cm (Zwierzyniec and Mirachowo). The mycelium biomass was estimated from the ergosterol content determined in the mesh-bags. The results indicated significant differences in EMM production and their vertical distribution between the mountain and the upland and lowland forest sites. The lowest EMM biomass was found at the experimental plot in the mountainious site Brenna. Considerable decrease of EMM biomass with the soil depth was recorded after 12 months of the mesh-bags incubation in soil in the upland and lowland sites, while in the mountain forests decrease of the EMM biomass in the lower soil depths diminished more gradually EMM biomass determined in the mesh-bags placed in soil at the upper 5 and 15 cm tended to be higher after 4 months than after 12 months of incubation period. Such results suggest that the time necessary for evaluation of EMM biomass in soil may be limited to the summer–autumn months, when the production of EMM is the highest. Variable stress factors can influence decreased ectomycorrhizal mycelium production and/or their destruction. Further research in different forest types and regions are needed for better understanding factors determining EMM biomass production and surviving in soil.&lt;/p&gt;

Windthrow and growth response following a spruce budworm inspired, variable retention harvest in New Brunswick, Canada

Forest management regimes increasingly focus on the emulation of natural disturbance events, e.g., fire or insect outbreaks, to help increase ecosystem sustainability. We determined the residual stand response to a variable retention harvest inspired by spruce budworm (Choristoneura fumiferana (Clemens)) outbreaks in New Brunswick, Canada. Our objectives were to analyze the differences between surviving residual trees and those that succumbed to windthrow and to quantify growth release. The treatment was based on harvesting the estimated spruce budworm outbreak mortality, i.e., 90% of mature balsam fir (Abies balsamea (L.) Mill., 60% of mature spruce (Picea spp.), and no hardwoods. Windthrow increased with the proportion of trees harvested and averaged 52% over 7–9 years in these stands with high balsam fir – spruce content. One-third of 42 harvested plots sustained &gt;30% windthrow, whereas 73% of 11 similar unharvested plots had &lt;10% windthrow. Balsam fir had higher windthrow than spruce at 53% and 41%, respectively. Windthrown balsam fir trees had significantly larger diameters at breast height (DBH, 1.3 m), larger heights, and smaller crown ratios than surviving residual trees. Substantial growth release occurred, with DBH increment of residual trees 48%–64% greater than trees in unharvested plots. Balsam fir and intolerant hardwoods exhibited the largest growth response. We suggest that future spruce budworm inspired harvests in stands with high balsam fir – spruce content use two or three entries about 5 years apart to reduce windthrow.

Cyclic dynamics of a boreal southern red-backed vole population in northwestern Quebec

In Fennoscandia, red-backed vole populations (Myodes spp.) often show regular fluctuations of abundance of 3- to 5-year periods. In contrast, only a few populations show evidence of cyclic fluctuations in North America. From 2001 to 2009, we livetrapped southern red-backed voles (Myodes gapperi) in 3 mature jack pine and 3 mature black spruce forest stands in the Muskuchii hills region, Quebec, Canada. We found that their density fluctuated (up to 41-fold) with a cyclical pattern and 4-year periods. Our study is the first to demonstrate cyclic dynamics in a southern red-backed vole population found in the boreal forest of North America. Regular pulse of food or heavy predation may be responsible for the fluctuations of southern red-backed voles. Furthermore, vole cycles may help elucidate the factors driving the irruptions of owls in the boreal forest.