Spruce Plantations Research Articles

Constitutive and inducible chemical defences in nursery-grown and naturally regenerated Norway spruce (Picea abies) plants

Nursery-grown Norway spruce Picea abies seedlings are often heavily attacked by the pine weevil Hylobius abietis on clear-cuts the first years after planting. Because the seedlings are not resource-limited during the growing phase in the nursery they are expected to invest less in defence than naturally regenerated seedlings already present on the clear-cuts. The latter have had to cope with various environmental stressors that could make them invest more in defence. We tested if naturally regenerated plants have stronger chemical defences than nursery-grown plants. Nursery-grown plants were planted in-between naturally regenerated plants on fresh clear cuts, and phenolic and terpene compounds in the stem bark were measured after one growing season. To test both constitutive and inducible defences, plants were either wounded, painted with methyl jasmonate (MeJA) to induce defences, or given a combination of both treatments. Growth and pine weevil attacks of the plants were registered.Nursery-grown plants had higher total concentrations of phenolic compounds and lower concentrations of terpenes than naturally regenerated plants. These opposite responses were reflected in very different compound profiles in the two plant types. We suggest the differences between plant types to be results of differences in plant age, stress level, genetic origin or possibly a combination of these factors. Most compounds showed no response to wounding, MeJA-treatment or wounding and MeJA-treatment combined, but the terpenes 3-carene, eucalyptol, limonene and para-cymene had higher concentrations in MeJA-treated nursery-grown plants than in control plants. These compounds are known to be effective in conifer resistance against weevils and bark beetles. Overall, 27% of our 400 study plants had signs of pine weevil damage after 3 ½ months in the field. However, treatment or plant type had no significant effect on whether plants were attacked or not and this might have been a result of the relatively low overall level of attacks in this study. Further studies are needed to disentangle the importance of plant age, stress level, genetic origin and resource availability for chemical defence mechanisms of young Norway spruce plants, as strengthening the natural resistance of nursery plants may be increasingly important in a future with less pesticide use.

Precommercial Thinning Increases Spruce Yields in Boreal Mixedwoods in Alberta, Canada

A few studies in young mixedwood stands demonstrate that precommercial thinning of aspen at early ages can improve the growth of spruce and increase stand resilience to drought. However, information on tree and stand responses to thinning in older mixedwood stands is lacking. To address this need, a study was initiated in 2008 in Alberta, Canada in 14 boreal mixedwood stands (seven each at ages 17 and 22). This study investigated growth responses following thinning of aspen to five densities (0, 1000, 2500, 5000 stems ha−1 and unthinned (control)). Measurements were collected in the year of establishment, and three and eight years later. Mortality of aspen in the unthinned plots was greater than in the thinned plots which were not significantly different amongst each other. Eight years following treatment, aspen diameter was positively influenced by thinning, while there was no effect on aspen height. The density of aspen had no significant effect on the survival of planted spruce. Spruce height and diameter growth increased with both aspen thinning intensity and time since treatment. Differentiation among treatments in spruce diameter growth was evident three years from treatment, while differentiation in height was not significant until eight years following treatment. Yield projections using two growth models (Mixedwood Growth Model (MGM) and Growth and Yield Projection System (GYPSY)) were initialized using data from the year eight re-measurements. Results indicate that heavy precommercial aspen thinning (to ~1000 aspen crop trees ha−1) can result in an increase in conifer merchantable volume without reducing aspen volume at the time of harvest. However, light to moderate thinning (to ~2500 aspen stems ha−1 or higher), is unlikely to result in gains in either deciduous or conifer merchantable harvest volume over those of unthinned stands.

Long-Term Trends of Hazel Grouse (Tetrastes bonasia) in the Bohemian Forest (Šumava), Czech Republic, 1972–2019

The population dynamics of Hazel Grouse were studied by presence/absence recording at stationary sites along fixed routes (110 km) in the central part of Šumava (Bohemian Forest, Czech Republic) from 1972 to 2019. The 100 km2 study area covered altitudes between 600 m (Rejštejn) and 1253 m above sea level (Mt. Sokol). Our database contained indices of Hazel Grouse occupancy: positive sites/visited sites for a yearly increasing number of Hazel Grouse occurrence sites (n = 134) for 48 years. We used a loglinear Poisson regression method to analyze the long-term population trend for Hazel Grouse in the study area. In the period from 1972 to 2006 we found a stable Hazel Grouse population (p = 0.83). From 2006–2007 to 2019, the population index dropped (−3.8% per year, p < 0.05). This decline is assumed to be influenced by habitat loss due to succession, resulting in older, more open forest stands, by strongly increasing forestry and windstorm “Kyrill”, followed by clear cutting, bark beetle damage, and the removal of pioneer trees in spruce plantations, which diminished buds and catkins, the dominant winter food of Hazel Grouse. The influence of disturbance by increasing tourist activities and/or predation is also discussed. Our results could help to optimize the conservation efforts for Hazel Grouse in the Bohemian Forest.

Trade-offs across densities and mixture proportions in lodgepole pine-hybrid spruce plantations

Monocultures tend to yield higher total stand volumes and are simple to manage. Yet, mixed species stands may result in similar stand volumes while providing benefits such as mitigating damage from insects and disease. To understand the effects of stand density and species mixture and their interactions on stand yield, tree size and morphology, and damage in monocultures and mixtures, we analyzed a 25-year-old experiment in interior British Columbia, Canada. The lodgepole pine (Pl)-interior hybrid spruce (Sx) experiment included three densities—1000, 1500, and 2000 stems per hectare (SPH)—and five species mixtures—1:0, 3:1, 1:1, 1:3, and 0:1 Pl:Sx. Results 25 years after stand establishment showed that stand volume was significantly larger with an increasing proportion of Pl across all stand densities. Pl had 10% larger diameters in the 1000 SPH than in the 2000 SPH and when mixed with Sx (1:1). Pl had larger crowns in mixtures regardless of density. Mixture proportion did not affect gall rust incidence or stem form in Pl, but reduced attack in Sx by spruce weevil. Our findings suggest that mixing Pl-Sx and high planting density decrease weevil attacks in Sx, which reduce loss in timber quality. Yet, Pl quality may decrease when mixed with Sx, due to larger Pl crowns. These results may be used to improve the implementation of management strategies that decrease trade-offs between yields, desired market tree sizes, and timber loss from pest and pathogens, while making the stands more resilient to further climate change impact.

Management options for the conversion of allochthonous coniferous forest patches towards more natural species composition in the Vorpommersche Boddenlandschaft National Park, NE Germany

The conversion of coniferous tree plantations towards natural self-regenerating forests is one of the targets of forestry in Europe and particularly desirable in national parks. The aim of this study was to evaluate the effectiveness of different conversion approaches (conducted once) on natural forest development in man-made spruce plantations. We studied the effects of three distinct management options (partial-cutting [PC], clear-cutting with timber removal [CC] and clear-cutting with timber remaining [CCr]) six years after application on tree regeneration (sapling identity, abundance, height, browsing intensity) and understorey species composition in former spruce plantations within the Vorpommersche Boddenlandschaft National Park in Northeastern Germany. An unmanaged spruce [M] and near-natural beech [N] stands were considered as local references. The sites differed significantly in tree regeneration and understorey species composition. The abundance of native tree saplings was highest at site CCr, their height did not differ among sites, while browsing intensity was most pronounced at site CC. Understorey species composition of all management options was equally dissimilar to site N. However, site CCr contained more species that are typically abundant in local beech forests. Clear-cutting of spruce plantations with dead wood remaining on site favoured the natural regeneration of native trees and understorey vegetation compared to clear-cutting with timber removal, partial-cutting and no management. Herbivore browsing detrimentally affected tree regeneration independent of the treatment. Clear-cutting with timber removal promoted the dominance of competitive herbaceous species that may hamper long-term forest regeneration. We conclude that progression of site CCr appears to proceed fastest towards natural forest conditions. Further long-term data is required to derive clear trends regarding time and direction of forest regeneration. Keywords: forest conversion, spruce plantations, beech forest, natural tree regeneration, understorey species composition, deer browsing

Disentangling the effect of topography and microtopography on near-ground growing-season frosts at the boreal-temperate forest ecotone (Québec, Canada)

Permanent landscape attributes such as topography (elevation [m]) and microtopography (local variation in elevation [cm]) can increase the risk of cold air drainage down-slopes and in microtopographic depressions, causing important temperature gradients that generate localized growing-season frosts. Since most studies on growing-season frosts are restricted to the northern parts of the boreal forest or to mountainous areas, their negative consequences on tree productivity at the boreal-temperate forest ecotone is often ignored. We quantified the intensity and probability of growing-season frosts at the boreal-temperate forest ecotone in regard to topographic and microtopographic landscape attributes, which were extracted from airborne LiDAR surveys. In situ air temperature was measured for two summers (2016–2017) with 252 temperature loggers installed in two 18-years-old spruce plantations established in both temperate and boreal mixedwood forests. Growing-season frosts were more intense and probable at the boreal mixedwood forest site compared to the temperate forest site. Still, at both sites, when growing-season frost occurred, air temperature could vary by 4 °C along the elevation gradient of 15 m, often reaching sub-zero values at low elevation while reaching above-freezing values at high elevation. The importance of microtopography on the risk of sub-zero temperatures increased where frost events were less likely to occur such as at the temperate forest and at high elevation. Considering that growing-season frosts can considerably reduce tree productivity, the effects of both topography and planting microsite should be considered when determining where to establish plantations in the landscape and to determine suitable frost-free planting microsites within a plantation.

Modeling of growth and development of modal fir and spruce stands in Middle Siberia

At present, a significant area of Siberian dark coniferous forests is characterized by a significant decrease in resistance due to recurrent forest fires, mass reproduction of insect pests and diseases, which leads to their natural degradation and death. However, the intensity of the growth processes of the coniferous stand under certain forest conditions persists in the long term. Therefore, the creation of regression models of the course of forest growth with the identification of forest conditions is very important both from the point of view of practice and environmental monitoring. The object of the study was the stands of Siberian fir (Abies sibirica Ledeb) and Siberian spruce (Picea obovate Ledeb) of bonitet classes III-IV, growing in the conditions of the West Siberian southern taiga plain forest region on the territory of the Yenisei forestry of the Krasnoyarsk Territory. The initial data for studying the processes of natural growth of fir and spruce plantations were the materials of the mass inventory of 11097 units. As a result of the work carried out for modal fir-spruce stands, concentrated in the territory of Central Siberia (Yenisei forestry of the Krasnoyarsk Territory), regression models of the growth course have been developed, which make it possible to predict the dynamics of taxation indicators and reproduce the succession picture of the development of stands.

Effects of Sitka spruce masting on phenology and demography of siskins Spinus spinus

Masting behaviour of Sitka spruce Picea sitchensis may influence Eurasian siskin Spinus spinus breeding ecology as breeding siskins specialize on spruce seeds. We caught siskins and other small passerines over 16 years using mist nets adjacent to large plantations of mature Sitka spruce. We sexed, aged, measured and weighed the birds and collected feather samples from fledglings to measure nitrogen and carbon stable isotope ratios. Siskins departed in late summer, and returned, and bred earlier in years of higher cone abundance. Nitrogen and carbon isotopes indicated that siskins fed their chicks on Sitka spruce seeds in most years, and more so in years of high cone production. More siskins were caught following heavy rainfall, when the cones had closed, encouraging the birds to seek alternative food sources. Fledglings were not heavier or larger in years with higher cone crops but were more numerous. However, the age ratio of siskins caught the following year was unaffected by cone crop. Given their reliance on Sitka spruce seeds, climate change may have a major impact on siskin numbers by altering the availability of Sitka spruce seeds, either through changes in masting patterns or cone opening, or due to climate-related changes in forestry practices. Siskins represent a valuable study system to conservation ecology, where a native species is ecologically reliant on introduced taxa.

Keeping mixtures of Norway spruce and birch in production forests: insights from survey data

ABSTRACT Admixtures of birch in Norway spruce plantations are being promoted as a means to increase habitat and species diversity. The implications of this mixture were analysed with regional survey data from southern Sweden. Permanent sample plots from the Swedish National Forest Inventory (NFI), with Norway spruce and admixture of birch, were used to describe the temporal trends in the admixture, regarding species composition and competitive strength. Observations from thinned plots show a higher harvest removal in birch (35%) than for Norway spruce (19%). Observations without thinnings in the period before measurement showed that individual birch tree growth was lower compared to Norway spruce and it decreased even more with increasing stand age and competition. In addition, a complementary field survey, with multiple distributed sample plots in each stand, was used to detect within-stand variation of species composition and density. Although within-stand heterogeneity was larger in mixed stands in terms of species composition, it was not different from Norway spruce monocultures in terms of stand density. These two surveys show that the admixture of birch, for several reasons, decreases over stand age and although birch increases tree species diversity, it does not necessary imply a change in density.

Wood Ash Application Reduces Bryophyte Cover and Changes Species Composition in a Norway Spruce (Picea abies) Plantation

Return of wood ash from power plants to plantations makes it possible to recycle nutrients, counteract acidification, and to reduce economically costly waste deposition of the wood ash. However, current legislation restricts the amount of wood ash that can be applied and it is desirable to increase the allowed application dose, if possible, without negative effects on the plantation ecosystems. Here, we applied wood ash in levels corresponding to 0, 3, 9, 15, 30, and 90 t ash ha−1 and monitored the effect of the different ash doses on bryophytes in a Norway spruce (Picea abies) plantation with a dense bryophyte cover dominated by Hypnum jutlandicum, Dicranum scoparium, and Pleurozium schreberi. We used two complementary methods, image analysis, and pinpoint registration during a three-year period. To our knowledge, we are the first to apply this combined effort, which provides a much more exhaustive description of the effects than the use of each method separately. Moreover, the inclusion of a wide range of different wood ash levels enabled us to establish detailed dose-response relationships, which previous authors have not presented. The bryophyte cover decreased with increasing ash level with concomitant changes in species composition. At ash doses above the currently allowed 3 t ha−1, the ash significantly reduced the bryophyte cover, which only re-established very slowly. With increasing wood ash dose, the dominating species changed to Brachythecium rutabulum, Ceratodon purpureus, and Funaria hygrometrica. We conclude that application of more wood ash in spruce plantations than currently allowed will reduce total cover of bryophytes and cause a pronounced change in bryophyte species composition. These changes will in particular harm bryophyte species with specific environmental requirements and generally impair the bryophyte cover as habitat for invertebrates and its economic value for moss harvesting.

Potential of Beauveria bassiana application via a carrier to control the large pine weevil

The large pine weevil (Hylobius abietis) is an important pest of freshly planted coniferous trees. Feeding damage to conifer seedlings can be prevented by protecting the seedlings (mechanically or chemically), or by reducing H. abietis abundance. The entomopathogenic fungus Beauveria bassiana has promise for H. abietis control. To test the effects of the B. bassiana-colonized carriers (25 mm in diameter and colonized by strain AMEP20) on H. abietis adults that move into forest clearances, we performed several experiments. These included an experiment in Petri dishes under laboratory conditions, an experiment in cages with Norway spruce seedlings under semi-natural conditions, and a field experiment. Infection by B. bassiana and mortality of H. abietis was confirmed in all three experiments. The total mortality rate in all Petri dishes with B. bassiana carriers after 14 days was 74% (80% with fresh carriers; 68% with carriers that had been treated with UV light; 82% for carriers that had been frozen; 45% for adults that were exposed to carriers for only 24 h; and 95% for carriers that had been stored at 4 °C for 2 months). The mortality of H. abietis adults was affected by the absence/presence of carriers in the cages with spruce plants. The number of dead adults after 4 weeks of treatment in forest clearing were higher in plots with carriers than in the control plot. Mortality was highest for adults trapped in the plot with carriers on trap barks (58%), followed by the plot with carriers and an attractant (48%), and followed by the plots with carriers without an attractant (35%).The results suggest that carriers colonized by the entomopathogenic fungus B. bassiana could be suitable for reducing H. abietis abundance in forests. The results indicated that H. abietis adults may be infected by B. bassiana after only a short exposure to carriers. The B. bassiana-colonized carrier is ready-to-use, i.e., it could be immediately produced and applied.

Explaining landscape preference heterogeneity using machine learning-based survey analysis

ABSTRACT We conducted a national survey on a high-quality internet panel to study landscape preferences in Norway, using photos as stimuli. We examined preference heterogeneity with respect to socio-demographic characteristics and latent topics brought up by the respondents, using ordinal logistic regression and structural topic modelling (STM), a machine learning-based analysis. We found that pasture landscapes are the most favoured (55%), while densely planted spruce forests are the least favoured (8%). The contrast was particularly strong between eastern and western Norway, between men and women, and between young and old. STM revealed that the choices were mainly driven by the preference for landscape openness, especially by women. Other important drivers were concerns regarding reforestation of former farmlands, aesthetic properties, forest management, biodiversity issues, and cultural values. Our results suggest that landscape policies may clash with socio-cultural preferences, and failure to account for these may undermine the success of a policy.

Exploring the potential of two-aged white spruce plantations for the production of sawlog volume with simulations using SORTIE-ND

The main objective for even-aged plantation (EAP) management of producing sawlog material has driven practices towards low initial planting densities and lower post thinning densities. For semi-shade tolerant species, the resulting stand density potentially leaves enough growing space for the introduction of a second cohort of trees in the understory, making it a two-aged plantation (TAP). TAPs could have many silvicultural benefits, especially in sensitive areas where intensive treatments associated with EAPs are incompatible with local management objectives. White spruce (Picea glauca) is a good candidate species for modeling TAPs because it is the most widely planted tree species in Canada and has proven tolerance to understory planting. SORTIE-ND, a single-tree spatially explicit growth model was used to explore the yield of variable density and rotation length scenarios when each white spruce cohort is introduced mid rotation, compared to traditional even-aged management. All TAP scenarios tested produced more sawlog volume and more merchantable volume than equivalent densities of EAPs. The lowest density tested, 400 stems ha-1 planted every 35 years, had the highest sawlog yields (3.23 m3 ha-1 yr-1). Considering smaller size products changes the optimum TAP scenario but maintains the advantage over EAPs.

Allometric Equations for Estimating Biomass and Carbon Stocks in Afforested Open Woodlands with Black Spruce and Jack Pine, in the Eastern Canadian Boreal Forest

Allometric equations use easily measurable biometric variables to determine the aboveground and belowground biomasses of trees. Equations produced for estimating the biomass within Canadian forests at a large scale have not yet been validated for eastern Canadian boreal open woodlands (OWs), where trees experience particular environmental conditions. In this study, we harvested 167 trees from seven boreal OWs in Quebec, Canada for biomass and allometric measurements. These data show that Canadian national equations accurately predict the whole aboveground biomass for both black spruce and jack pine trees, but underestimated branches biomass, possibly owing to a particular tree morphology in OWs relative to closed-canopy stands. We therefore developed ad hoc allometric equations based on three power models including diameter at breast height (DBH) alone or in combination with tree height (H) as allometric variables. Our results show that although the inclusion of H in the model yields better fits for most tree compartments in both species, the difference is minor and does not markedly affect biomass C stocks at the stand level. Using these newly developed equations, we found that carbon stocks in afforested OWs varied markedly among sites owing to differences in tree growth and species. Nine years after afforestation, jack pine plantations had accumulated about five times more carbon than black spruce plantations (0.14 vs. 0.80 t C·ha−1), highlighting the much larger potential of jack pine for OW afforestation projects in this environment.

The feasibility of ash and spruce forest plantations in the Northeast of Iran

In the present study, the feasibility of planting ash (Fraxinus excelsior L.) and spruce (Picea abies L.) tree species was investigated for rehabilitation of the Toroq Watershed in the northeast of Iran. The estimated land suitability indices ranged from 23.95 to 71.05, and 22.47 to 69.38 for ash and spruce plantations by parametric approach, categorized into moderately suitable (S2) in the east to not suitable (N) in the middle and western parts of the study area. The values of land indices by the AHP approach varied between 35.45 to 94.09 and 34.67 to 83.98 for ash and spruce plantations ranging from highly suitable (S1) in the east to moderately suitable (S2) in the middle and scattered parts in the east and not suitable (N) in the north and southwest of the basin. The results showed that the most important limitations were climate, elevation, soil depth, and soil texture. The regression coefficient (R2) of land suitability indices between parametric and AHP approaches for the two spices was 0.894 and 0.866 respectively. The results of the two models revealed that the moderately suitable class S2 is dominant for ash and spruce plantations in the eastern parts of the basin, while the middle and western parts of the basin were not suitable for plantation of the trees. The findings of this study may help land-use planners to rehabilitate the watershed by expanding forest plantation which ecologically tolerates extreme conditions of the region.

川西亚高山不同林龄粗枝云杉人工林土壤微生物生物量及酶活性

林分结构随林龄增加发生变化，致使土壤微环境变化，进而对土壤微生物生物量和酶活性产生直接或间接影响。以川西亚高山米亚罗林区25、40、50、60年生粗枝云杉（Picea asperata）人工林表层（0-20 cm）土壤为研究对象，分析不同林龄表层土壤微生物生物量碳（MBC）、氮（MBN）和酶活性的变化以及驱动土壤酶活性变化的主要环境因子，为人工林生态系统恢复效果评价及经营管理提供科学依据。结果表明：随着林龄的增加，MBC和MBN先上升后下降，在40年生达到最大；β-葡萄糖苷酶（βG）、β-N-乙酰氨基葡萄糖苷酶（NAG）和多酚氧化酶（PHO）活性与微生物生物量碳氮变化趋势相似，其中βG、NAG活性在50年生人工林达到最大，PHO活性于40年生人工林达到最大；50年生人工林过氧化物酶（PEO）活性显著低于其他林龄人工林；纤维素水解酶（CBH）活性随林龄增加而显著增加。冗余分析显示，碱解氮（AN）、pH和可溶性有机碳（DOC）是影响土壤酶活性变化的主导因子，分别解释了土壤酶活性变异的65.4%、9.7%和7.6%。综上可知，林龄对粗枝云杉人工林表层土壤微生物生物量和酶活性变化产生了显著影响，60年粗枝云杉林地力呈现衰退态势。为此，可对近60年的粗枝云杉人工林增加碳氮元素（尤其是氮素）的输入，以提升土壤质量和酶活性。;Stand structure changes with forest age caused the variation of soil microenvironment, which can directly or indirectly affect soil microbial biomass carbon and nitrogen, and soil enzyme activities. To better understand the change characteristics of soil microbial biomass contents and enzyme activities along an age sequence of spruce plantations, this study was conducted to evaluate the theoretical basis for restoration and effective management of subalpine plantations. In this study, Picea asperata plantations of various ages (25, 40, 50, and 60 years old) were selected in Miyaluo forest area of western Sichuan, China. The soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), available nitrogen (AN) and pH, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and light fraction organic carbon (LFOC), soil enzyme activity index(β-glucosidase, βG; Cellulose hydrolysis, CBH; β-N-acetylglucosaminidase, NAG; Phenol oxidase, PHO and Peroxidase, PEO) in 0-20 cm soil was measured,respectively. The results showed that the MBC and MBN increased up to 40 years, and then decreased with the increase of age. There was a similar trend in changes of the activities of βG, NAG and PHO, while βG and NAG were highest at 50 years, and PHO was highest at 40 years. PEO activity of 50 years was significantly lower than other plantations. The activity of CBH increased with the increasing age of Picea asperata plantation stands. Redundancy analysis (RDA) indicated that AN, pH and DOC were main influence factors of soil enzyme activities in the top-layer soil, accounted for 65.4%, 9.7% and 7.6% of total variation of soil enzyme activities, respectively. Overall, our results suggested that the growth of Picea asperata had a significant effect on soil microbial biomass and enzyme activities. The soil fertility in 60 years of Picea asperata plantation was the lowest in all Picea asperata plantations. Therefore, we can increase carbon and nitrogen elements (especially nitrogen) devotion to improve soil quality and enzyme activities in Picea asperata plantations nearly 60 years.

Entomophages of spruce bud scales (Hemiptera: Coccidae) in the Ukrainian eastern forest-steppe

The population number of spruce bud scales within localities can be regulated by a complex of predators and parasitoids, of the predatory species, the most massive is Antribus nebulosus Forster – Anthribus nebulosus. Apart from Antribus nebulosus Forster, numerous representatives of incheumonids from the Encertidae family develop, among which representatives of the Microterys genus are most commonly spread on spruce bud scales. In the course of our research, we have found that in spruce plantations inhabited by spruce bud scales entomophages populate females. Beyond the city limits, spruce plantations are more populated by entomophages than within the city limits. Both species of entomophages populated females in the dendrological park of Kharkiv National Agrarian University named after V.V. Dokuchaiev (49°90'N, 36°45'E) and Feldman Ecopark (50°66'N, 36°16'E). The highest inhabiting percentage of phytophages by entomophages was observed in the dendrological park of KhAU – 65 % of the examined females, of which 65 % were inhabited by Anthribus nebulosus and 45 % by Microterys lunatus. On the territory of Feldman Ecopark, 50% of the examined females were inhabited by entomophages, of which 25% were inhabited by Anthribus nebulosus and 75% by Microterys lunatus. In the nursery garden of ornamental plants (75 Siverska St.) (49°99'N, 36°36'E), only beetles of Anthribus nebulosus were found in 55 % of the studied female specimens. In the village of Vysoke (49°53'N, 36°07'E), Kharkiv district, in 80% of the studied females of spruce bud scales we have found only Microterys lunatus incheumonids. The lowest inhabiting percentage of phytophages by entomophages was observed in areas with severe man-caused air pollution. In the street plantations of Kharkiv Tractor Plant neighborhood (49°95'N, 36°40'E), 15 % of the studied females of spruce bud scales were inhabited by incheumonids of Microterys lunatus. Near the plant “Turboatom” (3 Energetychna St.) (49°97'N, 36°30'E) – 10 % of entomophages. Entomophages are collected in different places of the city and region, and in laboratory conditions we have once again convinced that the number of useful insects depends on the location of spruce plantations. The more spruce trees are negatively affected by cities and people, the fewer entomophages were recorded. Our research has shown that of the two entomophage species that are most sensitive to air pollution, beetles of Anhtribus nebulosus species, their number within the city limits is minimal or completely absent.

Resilience of natural forests can jeopardize or enhance plantation productivity

The demand for wood products continues to increase globally. Productivity of forest plantations can be greater than that of naturally regenerated forests. Plantation forestry could thus be employed to meet up to 75% of global wood supply by 2050. The resilience of natural forests could jeopardize plantation productivity. If the plantation scenario is not oriented in the same direction as the natural successional trajectories that are driven by resilience, then naturally regenerating tree species could recover to the detriment of planted species. Unproductive plantations will likely generate sustainability issues, as they must provide ecosystem services (e.g., wood fiber production) while being economically viable for forest management to be sustainable. Our general objective of our study was to assess whether resilience of natural forests can jeopardized plantation productivity. We studied successional trajectories in recent, young and old black spruce plantations that are located within the balsam fir ecological region on balsam fir ecological site types. To compare with a plantation scenario that was more susceptible to aiming in the same direction as resilience-driven successional trajectories, we also studied successional trajectories in recent, young and old black spruce plantations that are not only located within the balsam fir ecological region, but on black spruce ecological site types. Successional trajectories on balsam fir ecological site types pointed towards recovery of balsam fir and white birch, to the detriment of black spruce. Successional trajectories on black spruce ecological site types pointed towards the recovery of black spruce. Thus, we showed that resilience of natural forests could jeopardize plantation productivity when the plantation scenario is not oriented in the same direction as resilience-driven successional trajectories. It also can enhance plantation productivity when the regime is oriented in the same direction as resilience-driven successional trajectories. To ensure that plantations are economically viable and promote sustainability, forest managers should thus favor plantation scenarios that point in the same direction as resilience-driven successional trajectories. Finally, we suggest adopting such scenarios, and stress that it would also be necessary to develop regimes that would promote sustainability in the context of alternative successional trajectories that will undoubtedly arise because of global changes.

Proportions of a pine nurse influences overyielding in planted spruce forests of Atlantic Europe

The wider use of mixtures in planted forests is desirable to increase their resilience against the impacts of climate change and the potential damage caused by abiotic and biotic disturbances. However, there is limited evidence about the long-term effects of mixtures upon productivity in planted forests. In western regions of the British Isles ‘nursing mixtures’ of pines (Pinus spp.) and Sitka spruce (Picea sitchensis) have been used since the 1930s to establish spruce forests on nutrient poor soils without expensive chemical inputs (herbicides, fertilisers). Despite this history, there are few reports either of the effect of these mixtures on long-term stand productivity or of any interaction between productivity and proportion of mixture.We explored these aspects using data from an experiment which compared a nursing mixture of Sitka spruce and Scots pine (Pinus sylvestris) arranged in five different mixture proportions ranging from 25:75 to 75:25 spruce:pine. There were also pure plots of Scots pine and Sitka spruce (the latter grown with and without nitrogen fertiliser) so allowing estimation of overyielding (i.e. where the mixture is more productive than expected from the performance of the component species in pure plots). After 30 years, all treatments had closed canopy and Sitka spruce formed the major component of all mixtures. All the nursing mixtures showed significant overyielding (calculated on the basis of measurements of basal area) when the pure Sitka spruce without nitrogen was used to predict performance. The highest overyielding was found in the mixture with 33 per cent Sitka spruce. By contrast, if the pure Sitka spruce with nitrogen was used to predict mixture performance, significant overyielding was only found in mixtures with a low proportion of spruce (25 and 33 per cent), while those with a higher proportion (66 and 75 per cent) showed significant underyielding. Examination of growth in earlier years, supported by foliage analysis of the spruce, suggests that the mixture performance reflects pine facilitation of the spruce in the stand initiation phase when nitrogen was limiting growth. Once canopy closure had occurred, competition between the species in these unthinned stands favoured the more vigorous spruce. The advantage of using a lower proportion of the spruce in mixture was that it limited intraspecies competition and allowed the development of larger diameter spruce trees which could be more resistant to windthrow. The results demonstrate that nursing mixtures can overyield pure stands on nutrient poor soils and that proportion of mixture can materially affect overall productivity.

Release of retained oaks in Norway spruce plantations. A 10-year perspective on oak vitality, spruce wood production and ground vegetation

This study explores the decade-long effects of release cutting around old retained oaks (Quercus robur L.) in a Norway spruce (Picea abies L. Karst) stand that was 33 year old when thinned. The impacts on both nature conservation values and spruce wood production were evaluated in a randomized block design. To release oaks from competition, stems of Norway spruce were cut around 33 oaks, in three different treatments: high release (HR), medium release (MR) and no release (NR). Trees within a circular sample plot (15 m radius from the oak) were measured at time of treatment and 10 years after. The treatment effects on stand development, oak vitality and understory vegetation were evaluated after ten years, using tree diameter, height measurements, oak crown and tree structure estimates as well as ground vegetation surveys. Release cutting did not impact spruce production within the sample plot, and given that there were no other obvious sources of spruce suppression in the stand, we speculate that release cutting has little to no impact at the stand scale. Oak crowns in the control plots (NR) became smaller after ten years, while the crowns expanded and colonized the gap in the release treatments. Simultaneously, the amount of dead wood in the crown increased among oaks in the control treatment, indicating dieback. Cover and species richness of vascular plants in the understory were significantly higher in the HR and MR treatments compared to NR. These results suggest that the creation of relatively wide gaps (greater than 2 m) around retained oak crowns is one efficient approach to maintain their conservation values in a spruce-dominated stand on a longer time frame. This will allow oaks to expand their crowns, increase their vitality and increase species richness and diversity of plants under the canopy. The economic loss of creating large gaps instead of no gaps may be negligible since the overall spruce production was not affected within 15 m of each oak.