Pure Spruce Stands Research Articles

Do admixed conifers change soil nutrient conditions of European beech stands?

Context Establishing mixed forest stands is an option for improving soil nutrient conditions and for increasing the resilience of forest ecosystems. Aims Identify the effects on soil chemistry of spruce and Douglas fir admixed in European beech forest. Methods We analysed pure and mixed species stands in Germany. The pure stands were mature European beech (Fagus sylvatica), Douglas fir (Pseudotsuga menziesii), and Norway spruce (Picea abies). The mixtures were composed of beech with either Douglas fir or spruce. The stands were located in two regions with different soil conditions. Results Our results indicated that pure spruce stands, independent of site condition, had the lowest base saturation while beech showed the highest values. The impact of Douglas fir differed between site conditions. On sandy soils, there was higher pH and base saturation under Douglas fir than under spruce. On loamy soils, however, the pH under Douglas fir and beech was lower than under spruce. The cation stocks (Ca and Mg) on sandy soils were lower under spruce and spruce/beech stands than under Douglas fir and beech. In contrast, under loamy soil, exchangeable Ca and Mg stocks were less under beech than under spruce stands. Soil exchangeable K under mixed stands was among the highest compared to pure stands, independent of site condition. Conclusions Mixed species stands reduce soil base cation depletion compared to conifer stands. Implications Admixture of Douglas fir to European beech seems to be a more reasonable option for forest management than an admixture of spruce, since it does not negatively affect soil chemistry.

Which factors influence the density of birch (Betula pendula Roth) seeds in soil seed banks in temperate woodlands?

The natural regeneration of disturbed forest sites is becoming increasingly important due to climate change. Following disturbance events affecting large areas seed trees are often absent from the site, and regeneration solely by means of seed rain may not be successful. In these situations, soil seed banks are an important driver of the regeneration and reforestation of forest sites. The aim of the study was to determine the birch seed density in the soil of birch stands, spruce–birch stands and spruce stands dependent upon the number of seed trees (stands) and upon varying degrees of ground cover using the ‘seedling emergence method.’ The study revealed a significant link between the quantity of germinated birch seedlings in soil samples and the presence of seed sources. Seedling densities of birch in the different stand categories reached 2644–6414 seedlings per m2 [n m−2] in birch stands, 392–759 n m−2 in spruce–birch stands and 25–122 n m−2 in pure spruce stands. The density of germinated birch seedlings was also negatively affected by the soil layer. In all stand types, the factors humus thickness, litter cover, moss cover and herb cover had no significant influence on the amount of birch seedlings. Successful rapid regeneration of disturbed sites by means of the birch soil seed bank is guaranteed in cases where birch stands, or at least birch seed trees, were present before the event. The influence of ground cover on the regeneration potential of birch from the soil is negligible.

Potential relationships of selected abiotic variables, chemical elements and stand characteristics with soil organic carbon in spruce and beech stands

Increasing attention is given to carbon sequestration in forest soil with regard to climate change and the mitigation of its impacts; therefore, it is very important to know which parameters and variables could influence carbon sequestration and throw light on their relationships. The aim of this study is to assess the role of abiotic variables, chemical elements and stand parameters in soil carbon sequestration, and clarify which of these could affect soil organic carbon (SOC) content in the surface mineral horizon in Norway spruce and European beech stands in Czech Republic. We analyzed 81 monitoring plots within pure and mixed stands of spruce and beech with different degrees of forest naturalness. In each monitoring plot, SOC content, chemical elements (content of bound forms of oxides: tFe, tAl, tCa, tMg, tK, tMn, tP, tN) and related variables (BS, pH, C/N) were measured. The effect of these variables, including abiotic variables (elevation, temperature, precipitation, duration of growing season and soil group) on SOC content was tested, and differences between represented stands (natural vs. unnatural, pure vs. mixed, spruce vs. beech) were analyzed. The results showed that elevation has a positive relationship to SOC content. Of the studied chemical elements and related variables, only tN content was significantly related to SOC content. A positive relationship was also demonstrated between forest naturalness and SOC content. The highest SOC and tN contents were observed in pure natural Norway spruce stands, which likely play a very important role in SOC sequestration. In the context of the current issue of unnatural Norway spruce stands in the Czech Republic, a higher SOC content was found in mixed natural European beech stands than in either pure or mixed unnatural Norway spruce stands. Therefore, replacing the unnatural Norway spruce stands in the study area with mixed natural European beech stands could represent a viable alternative to current forest management in terms of soil carbon sequestration, especially in the context of global climate change and spruce dieback.

Effects of Thinning on Dynamics and Drought Resistance of Aspen-White Spruce Mixtures: Results From Two Study Sites in Saskatchewan

Drought stress associated with warm temperatures is causing increased mortality and reduced growth of trees in drier portions of the boreal forests of western Canada with both warming and drought expected to increase over the coming decades. While thinning is often shown to reduce drought stress, there is little information on its effects in stands comprised of mixtures of trembling aspen and white spruce that are common in the forests of this region. This study examined effects of pre-commercial thinning on aspen and spruce growth, response to drought stress, and stand dynamics for two study sites located in Saskatchewan, Canada. In unthinned plots aspen densities declined from initial densities of 40,000 to 200,000 trees ha−1 to 2,639 trees ha−1 at age 26. Twenty-one years after thinning (i.e., at age 26) diameter of aspen and spruce had increased, with largest trees being found at the lowest aspen densities (200 aspen ha−1 for aspen and 0 aspen ha−1 for spruce). Aspen density affected average height but not height of aspen top height trees. Spruce height decreased significantly with increasing aspen density. Crown width and live crown ratio of both aspen and spruce declined with increasing aspen density. Data from cores collected from aspen and spruce indicate significant positive effects of tree size (basal area at beginning of the year), and CMI (Climate Moisture Index) on basal area increment of both aspen and spruce while increasing aspen basal area (m2ha−1) had negative effects on aspen and spruce growth. Increasing tree size (basal area) and aspen competition (basal area ha−1) both had negative effects on drought resistance and resilience for both aspen and spruce. Yield projections provided by the Mixedwood Growth Model (MGM) suggest that the mixture of 1,500 aspen ha−1 and 1,000 spruce ha−1 has the potential to provide a 23% increase in total mean annual increment (MAI) with a single harvest at age 100, compared to unthinned aspen stands, but with a 44% reduction in spruce MAI compared to pure spruce stands. Thinning of aspen to densities below 4,000 trees ha−1 at age 5 resulted in reduced aspen yields but increased spruce yields.

Contrasting Root System Structure and Belowground Interactions between Black Spruce (Picea mariana (Mill.) B.S.P) and Trembling Aspen (Populus tremuloides Michx) in Boreal Mixedwoods of Eastern Canada

This study explored the underground interactions between black spruce and trembling aspen in pure and mixed stands to understand how their soil resource use help these species coexist in the boreal mixedwoods of Western Quebec. We analyzed species-specific fine root foraging strategies (root biomass and root tissue density) along three soil layers (organic, top 0–15 cm, and bottom 15–30 cm mineral soil), using 180 soil cores. We collected cores in three sites, each containing three 20 × 50 m2 plots of pure spruce, pure aspen, and mixed spruce and aspen stands. Spruce had a shallow rooting, whereas aspen had a deep rooting in both types of stands. Compared to pure spruce stands, spruce had a lower fine root biomass (FRB) and a higher root tissue density (RTD) in the organic layer of mixed stands. Both patterns were indicative of spruce’s more intensive resource use strategy and competitive advantage over aspen in that layer. Aspen FRB in the organic soil did not differ significantly between pure and mixed stands, but increased in the mineral soil of mixed stands. Since we did not observe a significant difference in the nutrient content of the mineral soil layer between pure aspen and mixed stands, we concluded that aspen may experience competitive exclusion in the organic layer by spruce. Aspen exhibited an extensive nutrient uptake strategy in the organic layer of mixed stands: higher FRB and lower RTD than spruce. In mixed stands, the differences in aspen rooting patterns between the organic and mineral layers suggested the use of contrasting nutrient uptake strategies along the soil profile. We speculate that the stronger spatial separation of the roots of spruce and aspen in mixed stands likely contribute to a higher partitioning of their nutrient uptake along the soil profile. These results indicate the competitive exclusion of aspen by spruce in boreal mixedwoods, which likely occurs in the soil organic layer.

Competition and climate influence growth of black spruce in western boreal forests

The effects of competition and climate on the growth of black spruce (Picea mariana (Mill.) BSP.) were examined using long term measurement data collected across the western Canadian boreal forest. Non-linear mixed effect models were developed and used to examine tree growth responses to competition and climate across the range of upland forest types where black spruce is found in this region including: spruce/fir, deciduous and pine forest types. Basal area of competitor trees larger than the subject tree, and at least one of the following climate variables: frost free period, mean annual precipitation and mean annual temperature, were selected as predictors of diameter and height growth. Spruce/fir competition had a stronger negative effect on the growth of black spruce than pine competition. However, deciduous competition had a positive effect on diameter and height growth of black spruce. Growth was generally sensitive to changes in climate across the three forest types. Increases in temperature (except in pine forest stand) and reductions in precipitation (except in deciduous forest stand) lead to increases in diameter and height growth; however, our model also predicted that increasing temperature when pine stand densities are high will lead to a reduction in growth. These results indicated that forest types and competition will determine the impact of climate on the growth of black spruce trees. Climate sensitive growth functions developed for black spruce in this study will be useful in modeling and managing pure and mixed stands of black spruce across the western boreal forest.

Вплив лісових насаджень плантаційного типу на показники родючості лісових ґрунтів в умовах Західного Лісостепу України

Між насадженнями різного складу та родючістю ґрунту існує тісна взаємодія, яку можна корегувати, змінюючи участь порід у складі деревостану. Питання особливо актуальне з погляду запровадження плантаційних лісових насаджень на місці низькопродуктивних деревостанів. Тому вивчення змін показників родючості ґрунту у системі – плантаційні насадження → ґрунт → корінний деревостан, є надзвичайно важливим чинником забезпечення високої продуктивності та біотичної стійкості лісових фітоценозів. 
 Досліджені темно-сірі опідзолені ґрунти на лесоподібному суглинку характеризуються високим лісорослинним потенціалом, результатом якого є формування чистих і мішаних насаджень модрини та ялини за високими класами бонітету – від І до Іс. Водночас значення показників родючості ґрунтів (вміст гумусу та рухомих сполук NPK) під цими насадженнями відрізняються.
 Вміст гумусу у ґрунтах під насадженнями за участю ялини коливається в межах від 0,32 до 4,52 % та в середньому становить 1,80 %, що нижче, ніж під насадженнями модрини – 0,32-9,32 % та 2,17 % відповідно.
 Склад насаджень впливає на вміст у ґрунті усіх досліджених елементів живлення. Середній вміст легкогідролізованого азоту у ґрунтах під насадженнями за участю ялини є нижчим (5,68 мг/100 г ґрунту), ніж за участю модрини (7,10) та більш амплітудно знижується вниз по профілю. Так, його середній вміст у Не-горизонті становить 9,63 мг/100 г ґрунту, в НІ – 4.87, в І – 2,52, а під насадженнями за участю модрини – 10,41, 6,51 та 4,24 мг/100 г ґрунту відповідно. 
 Середній вміст рухомих сполук фосфору в обох групах насаджень є доволі подібним –5,93 мг/100 г ґрунту за участю ялини та 5,80 – модрини. Водночас в І-горизонті у культурах з модриною він значно вищий, ніж у культурах з ялиною – 7,70 проти 2,64 мг/100 г ґрунту, що сприяє росту модрини за Іb-Iс класами бонітету. Характер розподілу обмінного калію за профілем ґрунту принципово відрізняється. Так, якщо під насадженнями за участю модрини його найвищий вміст (9,50 мг/100 г ґрунту) зафіксовано в Не-горизонті, то за участю ялини – у І-горизонті (11,85), що свідчить про інтенсивний прояв процесу кислотного гідролізу у ґрунтах під впливом опаду ялини. Проте середньопрофільний вміст обмінного калію у ґрунтах під обома групами насаджень є доволі подібним – 8,90 мг/100 г ґрунту у культурах з модриною та 9,17 – з ялиною.
 Загалом чисті ялинові та модринові культури в умовах свіжого і вологого груду Західного Лісостепу України не виявляють негативного впливу на показники родючості темно-сірого опідзоленого ґрунту. Водночас сприятливіші поживні властивості формуються у ґрунтах під насадженнями за участю модрини, які, своєю чергою, забезпечують найвищий рівень їх продуктивності, що необхідно брати до уваги під час проектування складу лісових культур плантаційного типу.

Recent climatic drying leads to age-independent growth reductions of white spruce stands in western Canada.

Since 2001, climatic conditions have been notably drier than normal across large areas of the western Canadian interior, leading to widespread impacts on the forests of this region. This poses a major concern for the future, given climate change projections for continued warming and drying. We conducted tree-ring analysis in 75 pure stands of white spruce (Picea glauca) across Alberta and west-central Saskatchewan to examine the effects of recent climatic drying on the growth of this important boreal tree species. Allometric equations were used to calculate annual growth in aboveground tree biomass (GBM ) from ring width measurements. Results showed an increasing trend in GBM from the 1960s to the 1990s, followed by a sharp decline during the severe drought of 2001-2002. Of the 75 stands, only 18 recovered sufficiently to cause an increase in mean GBM from the predrought decade of 1991-2000 to the subsequent decade of 2001-2010. The remaining 57 stands exhibited a decline in mean GBM between these decades. Climatic drying was a major cause of the growth decline, as shown by the significant stand-level relationship between percentage change in decadal mean GBM and the change in decadal mean values of a climate moisture index from 1991-2000 to 2001-2010. Subsequent analyses of boreal stands sampled across Alberta during 2015 revealed that white spruce growth had declined even further as drought conditions intensified during 2014-2015. Overall, there was a 38% decrease in mean GBM between 1997 and 2015, but surprisingly, the percentage decrease was not significantly different for young, productive stands compared with older, less productive stands. Thus, stand ageing cannot explain the observed decline in white spruce growth during the past quarter century, suggesting that these forests are at risk if the trend towards more frequent, severe drought continues in the region.

Specific leaf area and leaf area index in developing stands of Fagus sylvatica L. and Picea abies Karst.

European beech (Fagus sylvatica L.) and Norway spruce (Picea abies Karst.) are two of the most ecologically and economically important forest tree species in Europe. These two species co-occur in many locations in Europe, leading to direct competition for canopy space. Foliage characteristics of two naturally regenerated pure stands of beech and spruce with fully closed canopies were contrasted to assess the dynamic relationship between foliage adaptability to shading, stand LAI and tree growth. We found that individual leaf size is far more conservative in spruce than in beech. Individual leaf and needle area was larger at the top than at the bottom of the canopy in both species. Inverse relationship was found for specific leaf area (SLA), highest SLA values were found at lowest light availability under the canopy. There was no difference in leaf area index (LAI) between the two stands, however LAI increased from 10.8 to 14.6m2m−2 between 2009 and 2011. Dominant trees of both species were more efficient in converting foliage mass or area to produce stem biomass, although this relationship changed with age and was species-specific. Overall, we found larger foliage plasticity in beech than in spruce in relation to light conditions, indicating larger capacity to exploit niche openings.

Влияние структуры древостоя на плотность древесины сосны и ели в черничном типе леса

Mixed stands of spruce and pine of myrtillus y forest types occupy large areas of the forest
 fund of the Leningrad region. For the theory and practice of forestry it is important to know the impact
 of plantations on the density of wood in bunk mixed spruce-pine stands. In mixed stands of
 pine and spruce disks and cores of wood species were selected from the model tree to determine the
 basic density by the method of maximum water capacity. The study of basic wood density of pine
 and spruce in the coniferous bunk stands revealed that its rates are higher for both species in the
 mixed forest stand than in pure coniferous plantations in the region of the study. With the predominance
 of pines in the stand composition, its wood density is higher than in stands dominated by
 spruce. Density of pinewood increases from smaller to larger classes of stand diameters. Variability
 of wood density by diameter of trunk is higher in spruce than in pine in mixed stands. In stands, after
 cutting dilutes the density of pinewood is lower than in the plantation, which is not passed with
 felling. In the bunk spruce-pine the stand, to the age of maturity, larger mass of stem wood of coniferous
 species is formed than in the pure one-tier stands of pine or spruce. Developed regression
 equations depending on the density of the wood at a height of 1.3 m to the average density of trunk
 allow for a more accurate assessment of this parameter in mixed stands than previously published
 equations for pure stands of myrtillus forest types for the study area.

Climate Variation and Disturbance Regime Affect Stand Composition and Structure of the Boreal Forests in Southwest Yukon of Canada

The cold and dry boreal forests of the Southwest Yukon are dominated by white spruce (Picea glauca), trembling aspen (Populus tremuloides) and balsam poplar (Populus balsamifera), and the variability in structure and composition of stands depends on the favourability of disturbance, climate and site conditions for stimulating regeneration. In this study, we investigated relationships between stand structure and ecological, climatic and disturbance factors in the southwest Yukon. We found that white spruce dominates mature forests across the landscape, but it is regenerating proportionately less than trembling aspen. Nevertheless, regeneration of all the three species was abundant following any type or severity of disturbance. Height and diameter of both species varied with several environmental variables, particularly site physiography. Mixed stands of aspen and white spruce were more productive than pure stands of aspen or spruce. However, overall productivity in mixed stand decreased when density of aspen was more than 1000 stems/ ha. These results suggested that mixed stands of deciduous and coniferous species where appropriate should be promoted maintaining aspen density below 1000 stems/ha as the productivity declined beyond this threshold. Similarly, we suggest carrying out selection harvesting of co-dominant trees and regular thinning of intermediate trees to promote the height and diameter growth of the remaining trees.

Association of Geosmithia fungi (Ascomycota: Hypocreales) with pine- and spruce-infesting bark beetles in Poland

Abstract Bark beetles (Coleoptera, Scolytinae) are known to be associated with fungi, particularly species of the orders Ophiostomatales and Microascales. However, very little is known about other ectosymbionts of phloeophagous bark beetles on Pinaceae. In this study, we examined the Geosmithia species associated with eight bark beetle species infesting Picea abies and Pinus sylvestris branches in Poland. Fungi were isolated from 1 731 samples collected from 14 study sites. We identified a total of 653 isolates that were sorted into nine taxa based on their phenotypic similarity and phylogeny of their ITS-LSU regions of rDNA, β-tubulin, elongation factor 1α and the second-largest subunit of the RNA polymerase II gene. They represented nine species without formal names. There were large quantitative and qualitative differences in the composition of Geosmithia communities between P. sylvestris and P. abies trees. The proportion of samples infested with Geosmithia species suggests that this association is more widespread among bark beetles infesting branches of P. sylvestris . In addition, these beetles were vectors of different Geosmithia species compared with than the beetles that colonize P. abies . In mixed-conifer forests, the Geosmithia communities were more diverse and richer than in pure spruce or pine stands, where the insects Pityogenes chalcographus and Pityophthorus pityographus with low host-specificity play a distributing role for various Geosmithia species. Among eight bark beetle species examined, only P. bidentatus , P. pityographus , P. chalcographus and Polygraphus poligraphus acted as effective vectors for Geosmithia species. The following hypothesis emerges from these studies: changes in the composition of ectosymbionts of pine- and spruce-infesting bark beetles in Central Europe run along a gradient of thickness of the wood substrata preferred by insects.

Mixed Norway spruce (Picea abies [L.] Karst) and European beech (Fagus sylvatica [L.]) stands under drought: from reaction pattern to mechanism

We review causes of synergies in mixed-species stands, develop guiding hypotheses for revealing their mechanisms and present a rainfall exclusion experiment along with a transect (KROOF) for exploring drought effects. While monocultures have dominated forest research and practice in the past, in face of growing resource scarcity and climate change, mixed-species stands are on the advance. Long-term observations show that mixed-species stands frequently over-yield monocultures, and they further suggest that the over-yielding is often higher on poor than on fertile sites and in low-growth than in high-growth years. However, the underlying causes have not yet been clarified. We start with a review of, among others, hydraulic redistribution, complementary eco-physiological traits, and ectomycorrhizal networks as possible causes behind the observed productivity gains in mixed-species stands. Then, we develop guiding hypotheses for further exploration of synergies in mixed-species stands. Finally, we introduce into the concept and model approach of the rainfall exclusion experiment for examining the role of water supply in mixed versus pure forest stands of spruce and beech. At the Kranzberg site, six plots are equipped with water retention roofs, which only close during rain events. The remaining six plots serve as non-roofed control. Together with the rainfall exclusion experiment, an ecological gradient with five sites extending through SE-Germany forms the “Kranzberg Roof Experiment” (in short KROOF). Kranzberg Forest is a part of this gradient from moist to dry conditions, with each site providing mixed and pure associations each of spruce and beech. The ecophysiological approach will be complemented by tree ring analysis and modelling of productivity of the tree associations under intense drought.

Height increment of understorey Norway spruces under different tree canopies

Abstract Background Stands having advance regeneration of spruce are logical places to start continuous cover forestry (CCF) in fertile and mesic boreal forests. However, the development of advance regeneration is poorly known. Methods This study used regression analysis to model the height increment of spruce understorey as a function of seedling height, site characteristics and canopy structure. Results An admixture of pine and birch in the main canopy improves the height increment of understorey. When the stand basal area is 20 m2ha-1 height increment is twice as fast under pine and birch canopies, as compared to spruce. Height increment of understorey spruce increases with increasing seedling height. Between-stand and within-stand residual variation in the height increment of understorey spruces is high. The increment of 1/6 fastest-growing seedlings is at least 50% greater than the average. Conclusions The results of this study help forest managers to regulate the density and species composition of the stand, so as to obtain a sufficient height development of the understorey. In pure and almost pure spruce stands, the stand basal area should be low for a good height increment of the understorey.

Does mixing of beech (Fagus sylvatica) and spruce (Picea abies) litter hasten decomposition?

Background and aimsIt is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling, since the formation of thick organic layers is commonly ascribed to the recalcitrance of spruce needles. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.MethodsLitter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on a nutrient-rich site and a nutrient-poor site over a 2-year period using litterbags which were filled with five different mixtures of beech and spruce litter.ResultsMass loss of beech litter was not higher than mass loss of spruce litter. Decay was primarily affected by tree species composition of the incubation stand and was faster in (mixed) beech forests stands than in spruce forests, while the influence of litter species and their mixtures on decay rates was small. Net transfers of nutrients between the two litter species (direct effects) in the mixed bags were minimal, since initial beech and spruce litter did not have different litter quality. However, in a few cases indirect effects (e.g., changing decomposer abundance and activity) caused non-additive patterns for the totals within the mixed bags, hastening decomposition within the first year.ConclusionsGreater accumulation of litter in spruce compared to beech stands is not a consequence of the inherent recalcitrance of needles. Adverse environmental conditions in spruce stands retard decomposition. Indirect effects on decomposition caused by stand mixture are not mimicked by litter mixtures within mesh bags.

Changing of the Site Index and Soil Characteristics in Conjunction with the Environmental Factors in the Pure Oriental Spruce (Picea orientalis) Forests

The study was conducted in forested areas of pure Oriental Spruce (Picea orientalis) that were grown naturally, have the same age, and not treated in the normal canopy. The 40 sample areas (162 soil samples total) in Ormanustu, Macka, Trabzon were selected within the scope of this research and the sample areas were selected from the same aspect (northern aspect group), at two altitude levels (1550-1850 m and 18502050 m), and two different parent materials (andesite and granite). The soil samples obtained from the field were analyzed in the laboratory. The relationship between the stand age and maximum height were used for the determination of the site index for the sample areas. The pure Oriental Spruce stands, in connection with, the altitude climate zones and parent materials, were evaluated. According to the results, it can be stated that the values belonging to the site index, sand (%), clay (%), fine particle, loss on ignition, Ca++, and CEC (cation-exchange capacity) do show differences in regards to the parent materials (p<0.001). The Site index values of the Oriental Spruce indexes also differ in relation to the altitude climate levels (p<0.001). The results of the variance analysis indicated that the altitude of the climate levels affected the values belonging to the sand, clay, available water capacity, loss on ignition, Ca++, CEC, and available P2O5 among the soil characteristics (p<0.001 and p<0.05). Moreover, the correlation between altitude and site index was found to be meaningful and significant (p<0.01).

Distribution of white spruce lateral fine roots as affected by the presence of trembling aspen: root mapping using simple sequence repeat DNA profiling

Mixedwood forests of white spruce ( Picea glauca (Moench) Voss) and trembling aspen ( Populus tremuloides Michx.) may possess ecological advantages over monospecific white spruce stands. Belowground competition may be reduced through vertically stratified roots; facilitation of growth may occur in upper soil layers through nutrient-rich trembling aspen litterfall. These effects may incentivize white spruce to preferentially exploit upper soil layers in mixedwood stands, resulting in wider root systems. This research contrasted white spruce fine root (diameter &lt;2 mm) distributions in organic layers of white spruce and mixedwood stands. Research occurred at the Fallingsnow Ecosystem Project site in northwestern Ontario. Eighteen plots represented mixedwood and pure white spruce stands. Trees were mapped; foliage and root samples were collected. Roots were separated by species and scanned to determine length. Simple sequence repeat DNA profiles were determined for all white spruce trees and for 45 white spruce root fragments per plot. Root and tree DNA profiles were matched; corresponding distances were calculated. Most (80%) root fragments were within 3.2 m of tree stems. Root prevalence decreased rapidly with distance. Organic layer pH was significantly less acidic in mixedwood plots, but only in one block. A subtle significant trend towards wider root distributions occurred in mixedwood stands.

How much birch (Betula papyrifera) is too much for maximizing spruce (Picea glauca) growth: a case study in boreal spruce plantation forests

Interest in conifer-broadleaf mixedwood forests has greatly increased due to continuous demand for hardwood products and a shift towards more biological or ecosystem-based management. In British Columbia, more than 30% of the productive forest land is a conifer&amp;ndash;broadleaf mixture and current forest regulations are more conifer biased rather than maintaining a mixed-species condition. The aim of this study was to examine the impact of paper birch on white spruce growth. Spruce growth data from 10 to 18 years old complex stands indicate that radial, height, and stem volume was not impacted by retaining up to 3,000 stems&amp;middot;ha&lt;sup&gt;&amp;ndash;1&lt;/sup&gt; of birch. Similarly, growth and yield model projections suggest spruce-birch stands would be more productive up to a threshold birch density (3,000 stems&amp;middot;ha&lt;sup&gt;&amp;ndash;1&lt;/sup&gt;) than pure spruce stands. At a 4% real interest rate, the removal of birch from these stands does not appear to be warranted as an investment. The results suggest that instead of encouraging uniform broadleaf removal across conifer plantations, mixed species management strategies could enhance the forest productivity, stand diversity and resilience. &amp;nbsp;

Greater accumulation of litter in spruce (Picea abies) compared to beech (Fagus sylvatica) stands is not a consequence of the inherent recalcitrance of needles.

Background and aimsReplacement of beech by spruce is associated with changes in soil acidity, soil structure and humus form, which are commonly ascribed to the recalcitrance of spruce needles. It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.MethodsLitter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on three nutrient-rich sites and three nutrient-poor sites over a three-year period using the litterbag method (single species and mixed species bags).ResultsMass loss of beech litter was not higher than mass loss of spruce litter. Mass loss and nutrient release were not affected by litter mixing. Litter decay indicated non-additive patterns, since similar remaining masses under pure beech (47%) and mixed beech-spruce (48%) were significantly lower than under pure spruce stands (67%). Release of the main components of the organic substance (Corg, Ntot, P, S, lignin) and associated K were related to mass loss, while release of other nutrients was not related to mass loss.ConclusionsIn contradiction to the widely held assumption of slow decomposition of spruce needles, we conclude that accumulation of litter in spruce stands is not caused by recalcitrance of spruce needles to decay; rather adverse environmental conditions in spruce stands retard decomposition. Mixed beech-spruce stands appear to be as effective as pure beech stands in counteracting these adverse conditions.

The development of a simple basal area increment model

AbstractIn most cases forest practice in Austria use yield tables to predict the growth of their forests. Common yield tables show the increment of pure even-aged stands which are treated in a way the table developer recommends. The usage of these tables in stands which are either uneven-aged, mixed or treated in another way, may lead to inaccurate predictions. To avoid these problems, forest growth models have been developed. Until now they are not widely used in Austria. One reason may be, that most of the models need some input parameters which are usually not gathered by companies. In this work a basal area increment per hectare model has been developed which is based on the input parameters: diameter at breast height, height to diameter ratio, top height at age 100 years and a selection out of several simple competition indices (growing space, basal area of larger trees, competing basal area, crown cross sectional area, crown competition factor, d/dg, d-dg, basal area and stand density index) which are distance independent. The model parametrization was done with seven different statistical methods (linear regression, linear mixed effect model, resistant linear regression, local polynomial regression, lazy learning model, random forest model and neural network model). By using only few input-parameters it should be possible to parametrize this model for many local areas by using inventory data sets of the specific region. The model works in pure and mixed stands of spruce and beech at the Rosaliengebirge. The observed average diameter increment per 5 years is 18.1 mm for spruce and 21.1 mm for beech. The average difference of the predicted and observed diameter-increment on a validation data-set is 0.3 mm for spruce and -0.3 mm for beech within 5 years and the estimated additional spread caused by the model is +-4.5 mm/5 years for spruce and +-4.0 mm/5 years for beech.