Spruce Plantations Research Articles

Effects of Norway spruce shelter density and soil scarification method on mortality and height growth of underplanted European beech, European silver fir and Douglas fir

AbstractIn Europe, 6–7 million ha even-aged, pure stands of Norway spruce grown outside its natural range are prone to butt rot, windthrow, and bark beetle infestation. Climate change may well accelerate these problems and there is an urgent need to develop methods for converting Norway spruce plantations into more heterogeneous forest with larger resistance and resilience towards natural disturbances. Based on a field experiment located on former heathland on an outwash plain in western Denmark, we examined the mortality and height growth of European beech (Fagus sylvatica L.), European silver fir (Abies alba Mill.), and Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) planted under a shelterwood of 17–19 m tall Norway spruce (Picea abies (L.) Karst.) at shelter densities initially ranging by basal area from 10 to 36 m2 ha−1 (271–1099 stems ha−1). Underplanting included plots of beech (100 per cent) and silver fir (100 per cent) as well as plots with two-species mixtures of silver fir/beech (66 per cent/33 per cent and 33 per cent/66 per cent) and Douglas fir/beech (66 per cent/33 per cent). The experiment also included two soil scarification methods (patch and strip scarification). The experiment was laid out in an unbalanced factorial split-plot design, replicated in time and space, and totaling 144 plots in four blocks. The experiment was followed for 19 years during which a gradual reduction in shelter density took place although in some plots the shelterwood was removed abruptly by windthrow and bark beetle infestation. Shelter densities larger than 10 m2 ha−1 had only a minor effect on the mortality of beech and silver fir, while shelter densities larger than 20 m2 ha−1 resulted in increased mortality of Douglas fir. Subsequent abrupt reduction in shelter density resulted in increased mortality, especially of silver fir. Height growth decreased with increasing shelter density, more for Douglas fir than for beech, and marginally more for beech than for silver fir. For shelter densities <15 m2 ha−1, height growth of silver fir was unaffected. Beech grew faster when mixed with Douglas fir. The soil scarification method did not influence mortality, but strip scarification resulted in marginally larger height growth than patch scarification. We hypothesize that the shelter effect was related mainly to competition for light, while late frost and browsing were important factors in open shelters (<10 m2 ha−1). Based on these results, recommended initial shelter densities are at or <10 m2 ha−1 for the establishment of Douglas fir, at ~15–20 m2 ha−1 for silver fir, and around 15 m2 ha−1 for beech.

Корневое питание, фотосинтез и чистая первичная продукция у древостоев рода Picea на уровне организма в пределах российского ареала

A complex retrospective ecological and physiological analysis of the tabular data on the dry weight of stands of the genus Picea growing from the Northwest to the Russian Far East was carried out. Ecological and physiological indicators are calculated per an organism (conditional tree of average weight). Biological productivity (BP, times) was determined by the relative increase in the average dry weight of a tree in adjacent age periods. Quantitative data of mineral productivity (MP, mg/m2/per day) were found by the method of VM. Lebedev, and the net productivity of photosynthesis (NPPh, g/m2/per day) was calculated according to A.A. Nichiporovich at the organism level in stands of each age period in the range from 10–30 to 120–210 years. In all regions, there was a decrease in the element uptake by trees with age: nitrogen (N) by 14.9–93.7, phosphorus (P) by 18.7–119.9 and potassium (K) by 15.4–134.4 times. A sharp decrease in the element uptake continued until the age of 50–60 years, after which it stabilized at an extremely low level. The decline in the root uptake activity resulted in a 2.88–14.0 and 1.64–2.60-fold drop in NPPh and BP, respectively. The correlation between N, P and K uptake with NPPH and BP was highly positive in all zones. Within Russia in 30, 60, 90, and 120-year-old stands differences in the values of net primary production (NPP, g/m2 of nutrition area) reached 5.0, 4.7, 4.6, and 5.2 times, respectively, and net mineral productivity by nitrogen (NMP(N), g/m2 of nutrition area) reached 4.0, 4.3, 4.8, and 4.6 times, respectively. The correlation between these two indicators was described as highly positive. The correlation between the amount of nitrogen uptaken by spruce roots and the efficiency of its use in forming a unit of biomass was highly negative in all regions. The center of the Russian Plain and the Middle Volga region were the best regions for the growth of spruce plants, while the Krasnoyarsk and Khabarovsk (north) Krais were the worst.

Silvicultural and ecological assessment of renewal cuttings

The objects of research were forest plantations, passed through renovation rubles in the Arkhangelsk forestry of the Arkhangelsk region. Trial plots were established in spruce plantations (bilberry spruce forest and sphagnum spruce forest), on fresh haulage, in apiary, and on old haulage after felling more than 30 years ago. Based on the results of the research, a model was built, with the help of which it is consistently assessed during the course of the research what happens to the forest stand after cutting (on a fresh trail, 4-5 years after cutting) and after more than 30 years on an old trail. In the blueberry spruce forest, 4-5 years after felling, the amount of undergrowth increased slightly (by 1500 pieces/ha) compared to the forest stand and mainly due to self-sowing, the species composition was preserved - spruce, birch, aspen. After more than 30 years, there was a massive increase in undergrowth by 8 times. In the sphagnum spruce forest in the apiary, birch prevailed; immediately after felling, due to littering and the impact of machinery, undergrowth settlement was not observed. After more than 30 years, the number of undergrowth increased due to birch (69%). Thus, by evaluating the undergrowth and undergrowth in the blueberry type of forest, the felling strategy is updated. In the sphagnum type, reforestation processes continue and reforestation processes are still observed.

МОДЕЛЬНЫЙ АНАЛИЗ ПРОДУКТИВНОСТИ ЕЛОВЫХ НАСАЖДЕНИЙ В ЗАВИСИМОСТИ ОТ СХЕМЫ ПОСАДКИ И ИНТЕНСИВНОСТИ ВОЗДЕЙСТВИЯ СЛУЧАЙНЫХ ВНЕШНИХ ФАКТОРОВ

With rational forestry management, it is created special artificial forest plantations of high productivity for technically valuable species allowing the largest supply of grown wood. One of the ways to increase the supply of wood per unit of forest area is to regulate the initial density and planting pattern of trees. Using simulation methods, it is shown that in the absence of external influences, a checkerboard planting pattern is an optimal one providing a larger supply of wood as compared to a rectangular pattern. In real conditions, there are risks of dying off for individual trees due to random external factors like gusts of wind and phytophages. Therefore, in real life the supply of wood grown under such optimal planting schemes would be significantly lower as compared to the calculated values obtained. In this regard, there arise problems aimed at studying the plantings productivity dependent on the planting pattern and the intensity of tree death during the forest stand growth as a result of the random external factors influence. To solve these problems, we used a simulation model of tree communities dynamics, which takes into account the spatial location of each tree, in this way making it easy to simulate various forest planting schemes and remove some trees at any step of modeling. As a result of the computational experiments, the optimal values of spruce plantations initial density have been defined for different planting schemes, dependent on the intensity of the external factors influence. It is shown that at a certain intensity of the external factors impact, the maximum timber stock does not depend on the planting scheme, but is determined by the initial density of the forest stand.When the impact intensity increases,, the planting density also needs to be increased, in order to obtain the maximum reserve.

Uprooting as a pre-commercial thinning operation in young Norway spruce stands

Uprooting, as a mechanical pre-commercial thinning operation (PCT), removes competitive, undesired trees with roots to prevent or reduce the need for a second PCT. The state of 66 young Norway spruce (Picea abies (L.) H. Karst.) stands was explored 3–5 years after uprooting to assess the quality of uprooting in terms of the number of competing birches (Betula spp.) and the probability of freely growing crop tree spruce (no competing trees taller than 2/3 of the crop tree’s height). In the uprooted spruce stands, the number of birches was, on average, about 3800 stems ha−1, and in every fifth stand, it was less than 2000 stems ha−1. The number of birches increased with increasing site wetness (TWI), site fertility and thickness of the humus layer. In 80% of the stands, there were at least 1000 freely growing spruces ha−1, which is approximately the stem number to be left growing after first thinning in a spruce stand. If the height of crop tree spruces was 125 cm at uprooting, the probability of freely growing stems varied from 0.6 to 0.8 in typical cases. According to simulations at the first thinning stage, in most stands, birch was less than 10% taller than spruce, and the volume of birches was low enough that, in the future, spruce and birch would grow in the same crown layer as a mixed spruce–birch stand. The results showed that uprooting can serve as the only PCT operation in a planted spruce stand. The quality obtained by uprooting can be improved with careful selection of timing and conditions for uprooting; the optimal uprooting time is when crop tree spruces have reached about breast height.

Systematische Erfassung der Moosflora als Grundlage für ein Monitoring in der Naturwaldzelle Zweibach und in bewirtschafteten Referenzflächen im Erzgebirge (Sachsen)

Baumann, M. 2022. Systematic investigation of the bryophyte flora as a basis for monitoring in the strict nature reserve Naturwaldzelle Zweibach and in managed reference sites in the Ore Mountains (Saxony). – Herzogia 35: 395 – 419. The results of the first systematic bryophyte species survey in the strict forest reserve Naturwaldzelle Zweibach (Ore Mountains, Saxony federal state, Germany) are presented. Species inventories were done in the unmanaged strict forest reserve (30.5 ha) and managed reference sites in the immediate vicinity (70.8 ha). The study included a survey of ground-dwelling bryophytes (humus/mineral soil) in systematically distributed permanent sample plots as well as an overall mapping of the area, including all substrates. With a total of 180 species, a very rich bryophyte flora was encountered, including numerous endangered species. This is due to the heterogeneity of the area with occurrences of different types of forest communities (near-natural beech forest, spruce plantation), rock outcrops, large boulders, springs and forest brooks. While the bryophyte layer on the forest floor was only sparsely developed in the beech stands, it had a higher cover and number of species below spruce. In the substrates deadwood and especially tree bark, however, the ratios were reversed, where species diversity was significantly higher in beech stands. Both in the strict forest reserve and in the managed reference area, mainly typical forest bryophytes were found, the proportion of species preferring open land conditions was low. With regard to the two management categories, there was a tendency to different indicator values, particularly for lower light conditions in the strict forest reserve.

Growth Dynamics of Young Mixed Norway Spruce and Birch Stands in Finland

Mixed-species forests in Fennoscandia are of increasing interest because they may improve resilience, biodiversity, and productivity. Currently there is scarce knowledge available of the early growth dynamics of mixed spruce–birch stands in even-aged managed production forests with artificial regeneration of spruce. The main objective of our study was to examine the present state and the past growth dynamics of current single-storied, young spruce–birch (Picea abies (L.) Karst., Betula pendula Roth, Betula pubescens Ehrh.) stands (age 17–29 years), where spruce was planted and birch naturally regenerated, and juvenile management practices (early cleaning and precommercial thinning) were carried out. We inventoried ten such stands in Southern Finland, for a total of twenty plots. For 160 spruces and 160 birch trees, we reconstructed the past diameter and height growth through stem analysis. We analyzed mean stand characteristics by tree species, and we modelled the individual tree height and diameter growth using the mixed effects Chapman–Richards model. Spruces had slower initial height growth, but by the age of about 20 years their height growth rate eventually approached and exceeded that of birches regenerated naturally at the time of spruce planting. The diameter growth of planted spruce exceeded that of birches even sooner (at the age of about 10 years). Thus, spruces are not suppressed by birches, and they may coexist in the same canopy layer in managed stands. Contrary to earlier guidelines, due to the fast growth of planted spruces, birch mixture needs to be maintained already in the first juvenile stand management (i.e., early cleaning). The growth dynamics of young, planted spruce, and naturally regenerated birch allow the establishment and management of such mixtures and also maintenance of the mixture in the future until the end of the rotation, thus improving biodiversity in boreal, planted spruce forests.

Invertebrate predators in Sitka spruce plantations managed by clear-cutting or continuous-cover silvicultural systems

Invertebrate predators of aphids were sampled at ground level and in the canopy in 13 even-aged Sitka spruce Picea sitchensis forest stands managed by clear-cutting and replanting, and in 11 Sitka spruce stands managed as continuous cover forestry using either shelterwood or group selection silvicultural systems. The expectation was that stands managed using shelterwood or group selection systems would support a greater abundance and diversity of invertebrate predators, because of their more complex internal structure, but results were mixed. Hoverflies (Syrphidae), predatory bugs (Hemiptera), ladybird beetles (Coccinellidae) and spiders (Araneae) were more abundant in shelterwood and group selection stands, but soldier beetles (Cantharidae), lacewings (Neuroptera) and harvestmen (Opiliones) were more abundant in mid-rotation and mature even-aged stands, and vespid wasps (Vespidae) showed a similar abundance across all stand types. In contrast, species richness and diversity of the insect predator groups were higher in shelterwood and group selection stands, even for groups that were less abundant in those stands. It was not clear, however, whether the greater species richness of insect predators in shelterwood and group selection was the result of these stands supporting breeding populations of a wider range of species, including less common species, or was because the more open structure of these stands allowed introgression of species from other habitats within the forest.

Differential bacterial ammonia oxidation patterns in soil particles from two contrasting forests: The importance of interfacial interactions

Soil inorganic nitrogen (N) deficiency limits forest productivity in subalpine regions. The traditional view holds that subalpine coniferous forests are characterized by lower soil inorganic N availability, and such differences are greatly affected by the diversity and abundance of ammonia-oxidizing bacteria. It is known that interfacial interactions between bacteria and solid particles in agricultural and aquatic ecosystems can alter bacterial metabolic activity and biogeochemical processes. However, whether bacteria-soil interfacial interactions induce different ammonia oxidation processes in distinct soil particles remain unknown. Herein, we collected soil particles of different sizes from two contrasting forest sites (a spruce-dominated natural forest and spruce plantation) and examined the effect of soil-Nitrosomonas europaea (a model ammonia-oxidizing bacteria) interfacial interactions on the oxidation of ammonium (NH4+-N) using batch adsorption and semipermeable membrane experiments. The metabolic activity of bacteria was also examined using an isothermal microcalorimetric method. Upon adsorption on soil particles, the ammonia oxidation rate and bacterial metabolism activity were slower than those of free bacteria. The inhibition effect ceased when the bacteria were physically isolated from the soil particles by a membrane, indicating the importance of interfacial interactions in the ammonia oxidation process. Additionally, clay particles were more effective than silts and sands in binding cells and greatly reduced the ammonia oxidation reaction. Across the two forests, natural forest soils exhibited a higher bacterial adsorption capacity but lower bacterial metabolic activity, resulting in a fewer loss of NH4+-N. Our results suggested that stronger bacteria-soil interfacial interactions (especially for clay fractions) were responsible for maintaining high soil inorganic N availability in forests, highlighting the need to incorporate interfacial interactions into biogeochemical models of N cycling in forest ecosystems.

Structural and functional organisation of the phytopathogenic fungi Phoma sp.1 mitochondrial genome

The article presents the results of the mitochondrial DNA (30 837 n. r.) sequencing of the phytopathogenic fungi Phoma sp.1 – causative agent of Phoma blight of the pine and spruce plants cultivated in the forest nurseries. Annotation of the Phoma sp.1 mitochondrion showed 43 coding loci. Potential open reading frames (orf89, orf87, orf76 and orf108) and gene introns (cox3, nad1) are described. A comparative single genes analysis in the NCBI GenBank database showed, that Phoma sp.1 belongs to the Didymella spp., which can have Phoma anamorph. It has been shown that mitohondrial genes can be used as DNA markers for the diagnosis of Phoma and phoma-like fungi. Analysis of the mitochondrial synthenia of Phoma sp.1 and a related species (including phoma-like fungi), revealed significant structural rearrangements in mtDNA during phylogenesis.

Analisis Golongan Metabolit Sekunder Ekstrak Etanol Kulit Batang Cemara Laut (Casuarina equisetifolia L.) dan Cemara Gunung (Casuarina junghuhniana Mig.)

The use of medicinal plants as natural medicine is increasingly trend and developing rapidly to prevent and treat disease, also maintain human health. Spruce plants belong to Casuarinaceae family and Magnoliophyta, generally contain of secondary metabolite compounds such as: alkaloid, saponin, polyphenol, flavonoid, and tannin that can be efficacious to cure diseases in human. The purpose of this study was to analyze the secondary metabolites compound of Casuarina equisetifolia L. and Casuarina junghuhniana Mig. using the Fransworth phytochemical screening method of bark ethanol extracts. The analysis of phytochemical screening of spruce bark shows flavonoid, saponin and tannin activity, while the montain spruce shows alkaloid, steroid, saponin and tannin activity. Further research is needed to investigate the ethnopharmaceutical information on the use of the spruce plants as a traditional medicine.Key words: Spruce plants; screening; extract; analysis; phytochemical; secondary metaboliteÂ

Оценка структуры и состояния молодняков с использованием беспилотных летательных аппаратов и наземным методом

The article presents the data on the composition and condition of mixed young forests, obtained using unmanned aerial vehicles and the classical land technique. The plotting of the forest area was carried out by quadcopters. The land technique was used to assess the composition and condition of young stands, undergrowth and live ground cover on10 m2 circular plots. At each object, 48 discount areas were laid. The objects of study are young stands of natural and artificial origin. It was established that young growths of natural origin were formed in the 7 hectares cutover plots in 2006. They include pine, spruce, birch, aspen and alder. Spruce plantations were created in 2012 on an area of 12 hectares. It is shown that the understories and small undergrowth are not visible from a quadcopter, while the classical method gives the detailed characteristics. Additional characteristics of young forests obtained with the help of unmanned aerial vehicles are given. It is shown that the results obtained by the two methods are consistent, the error in the main characteristics does not exceed 10%. The combination of the two methods gives more complete information on the forest area. However, each of the methods used has its own advantages and disadvantages.

Pre-Commercial Thinning Increases the Profitability of Norway Spruce Monoculture and Supports Norway Spruce–Birch Mixture over Full Rotations

Pre-commercial thinning (PCT) is a common measure in Norway spruce (Picea abies L. Karst.) stands but the profitability of doing PCT and timing of PCT has not been fully investigated over a full rotation. Further, limited knowledge is available for mixed forest management compared to monocultures. In this study, different PCT strategies were tested to investigate the effect of PCT and timing of PCT on the production and profitability of Norway spruce monocultures and mixed Norway spruce–birch stands. A forest decision support system was used to simulate stand development during the whole rotation. Our study findings show that there is a positive effect of PCT on Norway spruce plantations’ long-term profitability but that the timing of PCT has little effect on profitability. However, site variation might influence the effect of PCT timing on the profitability of Norway spruce stands. Moreover, we also found that retaining 1000 Norway spruce ha−1 and 1000 birch ha−1 after PCT supports a mixture of Norway spruce and birch over a full rotation, with little or no economic loss compared to pure Norway spruce stands. Therefore, such a mixture can lead to profitable production while still providing other ecosystem services.

Tree Maladaptation Under Mid-Latitude Early Spring Warming and Late Cold Spell: Implications for Assisted Migration.

Global warming is predicted to extend the growing season of trees and plants, and advance spring phenology. However, intensification of extreme climate events in mid-latitude forests, from weakening of the jet stream and atmospheric blockings, may expose trees to increased risk associated with more frequent late-spring frosts. Still, little is known regarding the intraspecific variation in frost tolerance and how it may be shaped by local adaptation to the climate of seed origin. As part of an assisted migration trial located in different bioclimatic zones in the province of Quebec, Canada, and following an extensive late-spring frost that occurred at the end of May 2021, we evaluated the frost damages on various white spruce (Picea glauca) seed sources tested on three sites (south, central, and north). The severity of frost damages was assessed on 5,376 trees after the cold spell and an early spring warming which advanced bud flush by approximately 10 days on average. The frost damage rate was similar among sites and seed sources and averaged 99.8%. Frost damage severity was unrelated to the latitude of seed origin but was variable among sites. The proportion of severely damaged trees was higher in the northern site, followed by central and southern sites. The proportion of severely damaged trees was linearly and inversely related to tree height before the frost event. Apical growth cancelation was not significantly different among seed sources including local ones, and averaged 74, 46, and 22%, respectively, in central, northern, and southern plantation sites. This study provides recommendations to limit the loss of plantation productivity associated with such a succession of spring climate anomalies. Implications for seed transfer models in the context of climate change and productivity of spruce plantations are discussed in the light of lack of local adaptation to such pronounced climate instability and ensuing large-scale maladaptation.

Spruce (Picea abies L.) planting leads post-clearcut bird assemblages to a novel successional pathway\u2014a comparative study in hemiboreal mixed forests

Key messageBird assemblages in planted spruce (Picea abies L.) forests were compositionally distinct from those in naturally regenerated mixed stands. Despite rapid stand development on productive soils, even-aged silviculture cannot host most old-forest species. However, their habitat quality could be supported in landscape mosaics with retention forestry and set-asides.ContextThe most productive forest lands have naturally the richest bird assemblages but tend to be also most intensively managed. Sustainable solutions to this conflict are unclear.AimTo assess bird assemblages and their successional dynamics in planted Norway spruce (Picea abies L.) stands compared to naturally developing stands.MethodsWe mapped breeding bird assemblages in forty 5-ha plots on highly productive soils in Estonia. The plots included sets of naturally regenerated and planted stands, and (as successional endpoints) clear-cuts and old stands.ResultsPlanted stands had fewer bird species and pairs than naturally regenerated stands; the latter having a species composition resembling late-successional deciduous-dominated stands. Importantly, the species composition in mature spruce plantations converged toward the composition observed in late-successional conifer-dominated stands. Downed dead wood, stand age, deciduous trees, and stock density were the most significant stand characteristics shaping bird assemblages.ConclusionThe habitat value of established spruce plantations can be primarily improved by allowing for some deciduous trees and gaps with deciduous undergrowth. At the landscape scale, the bird diversity of even-aged systems would be enhanced by multi-scale applications of retention forestry—from retention trees to old-growth set-asides.

Post-Fire Habitat Heterogeneity Leads to Black Spruce–Kalmia L. Shrub Savannah Alternate State

Many nutrient-poor coarse-textured Kalmia L.–black spruce forest sites in eastern Canada turn to ericaceous heath dominated by Kalmia angustifolia L. after clearcutting and fire. While the mechanisms of post-fire forest and heath formation have been well documented, the origin of shrub savanna vegetation has received limited attention. This study demonstrates the significance of post-fire island regeneration of black spruce in Kalmia heath to the origin of shrub savannah alternate state. The study was conducted in Three Brooks, 10 km west of Grand Falls-Windsor, Newfoundland (48°51′ N; 55°37′ E). Black spruce forest in the site was clearcut, then a wildfire burned the area, and the site was subsequently planted with black spruce. Plant species cover, black spruce growth (stem density, stem height, basal diameter, and yearly volume increment), and foliar nutrients of planted spruce and soil properties (pH, humus and Ae horizon depth, and nutrients) in tree islands were compared with adjacent Kalmia heath. Black spruce islands had significantly lower cover of Kalmia and higher stem density of black spruce compared to Kalmia heath (7100 stems/ha in islands vs. 1920 stems/ha in heath). Height, basal diameter, and yearly volume increment of black spruce were more than three times higher in spruce islands than in Kalmia heath. Foliar nutrients of black spruce growing in Kalmia heath had significantly lower N and Mg (33 and 38%, respectively) but had significantly higher Mn and Zn (46 and 33%, respectively) than in black spruce islands. Black spruce growth inhibition in Kalmia heath is attributed to soil nutrient imbalance due to Kalmia evidenced by reduced concentrations of N and Mg and increased concentrations of Al, Fe, and other inorganic ions in the foliage. These results suggest that post-fire black spruce islands in severely burned patches provide “safe sites” for spruce regeneration, whereas Kalmia heath developing in non-severe burn area inhibits spruce regeneration and creates shrub savannah community as an alternate vegetation state.

Environmental Factors Indirectly Impact the Nematode Carbon Budget of Subalpine Spruce Forests

Nematodes play a significant role in soil biogeochemical cycling. However, our understanding of their community carbon budget response for a shift in the environmental conditions of natural and planted forests is limited. Therefore, we investigated the nematode community composition, daily carbon used in production and daily carbon budget, environmental variables, and the interaction among trophic groups in the moss, litter and 0–5 cm soil layers of natural subalpine spruce forest and plantations in western Sichuan, China. The result revealed that plantations increased the total nematode daily carbon budget by approximately 52% through the herbivore channel in the 0–5 cm soil layer. The herbivorous nematodes’ daily carbon budget and production in the moss layer of plantations decreased by approximately 60% compared to natural forests. Nematode daily carbon used in production and carbon budget had a strong negative correlation with genus richness. The water content and total carbon was the most important environmental factor that affected the nematode carbon budget and production, respectively. However, the environmental factors indirectly affect the daily carbon budget of herbivore nematodes through omnivore top-down control in subalpine forest ecosystems. Our findings highlight that the planted ecosystems have a certain capacity to maintain abundance, richness, and carbon budget of soil nematode but increase the risk of herbivorous pests.

Fuel Loads and Plant Traits as Community‐Level Predictors of Emergent Properties of Vulnerability and Resilience to a Changing Fire Regime in Black Spruce Forests of Boreal Alaska

AbstractBlack spruce forest communities in boreal Alaska have undergone self‐replacement succession following low‐to‐moderate severity fires for thousands of years. However, recent intensification of interior Alaska's fire regime, particularly deeper burning of the soil organic layer, is leading to shifts to deciduous‐dominated successional pathways, resulting in many socioecological consequences. Both fuel load quantity and quality (or “burnability”) influence black spruce plant communities' potential to burn. Even relatively low fuel loads, such as those seen in black spruce forest understory, can be highly influential drivers of fire behavior due to their high flammability. Additionally, black spruce community self‐replacement following fire can be largely attributed to the suite of functional and life history traits possessed by the species dominating these communities. We used fuel load (quantity and quality) and amount of within‐population plant trait variation (coefficient of variation; CV) as community‐level emergent properties to investigate black spruce forest vulnerability and resilience to a changing fire regime across the landscape. Our burn severity potential index (BSPI), calculated from fuel load quantity and quality measurements, indicates that drier, higher elevation stands with thicker active layers were the most vulnerable to fire‐induced vegetation shifts under a changing fire regime. Forest resilience to fire‐induced vegetation shift, represented by higher CV, was negatively associated with BSPI and greatest in ecoregions dominated by lowland black spruce forests. Together, these analyses provide critical information for determining the likelihood of stand‐replacing shifts in dominant vegetation following fire and for implementing appropriate ecosystem management practices.

Climate sensitivity of the complex dynamics of the green spruce aphid-Spruce plantation interactions: Insight from a new mechanistic model.

Aphids can have a significant impact on the growth and commercial yield of spruce plantations. Here we develop a mechanistic deterministic mathematical model for the dynamics of the green spruce aphid (Elatobium abietum Walker) growing on Sitka spruce (Picea sitchensis (Bong.) Carr.). These grow in a northern British climate in managed plantations, with planting, thinning and a 60-year rotation. Aphid infestation rarely kills the tree but can reduce growth by up to 55%. We used the Edinburgh Forest Model (efm) to simulate spruce tree growth. The aphid sub-model is described in detail in an appendix. The only environmental variable which impacts immediately on aphid dynamics is air temperature which varies diurnally and seasonally. The efm variables that are directly significant for the aphid are leaf area and phloem nitrogen and carbon. Aphid population predictions include dying out, annual, biennual and other complex patterns, including chaos. Predicted impacts on plantation yield of managed forests can be large and variable, as has been observed; they are also much affected by temperature, CO2 concentration and other climate variables. However, in this system, increased CO2 concentration appears to ameliorate the severity of the effects of increasing temperatures coupled to worsening aphid infestations on plantation yield.

Forest canopy nitrogen uptake can supply entire foliar demand

Abstract Plant canopies intercept, process and potentially assimilate atmospheric nitrogen (N) additions, but the forest‐scale effects of canopy processes on N cycling and plant nutrition are not clear. Substantial method artefacts and scaling issues exist in previous experimental studies which measure relevant N fluxes either at (a) natural abundance, (b) via a 15N tracer or (c) by incorporation of additional 15N into measured biomass, meaning these processes are often overlooked or discounted. Here, working in a mature Sitka spruce plantation and under ambient conditions, we used all three of these methods independently at stand, tree and branch scale to assess the effects of canopy interception on capture, assimilation and incorporation of inorganic N deposition by canopy biomass. We consistently found that above 70% of N deposition was unaccounted for (i.e. assimilated, processed beyond detectability, volatilised or retained) when passing through the canopy, independent of the assessment method. Using short‐term 15N tracers, we found that this unaccounted N was retained in canopy tissues. Apparent uptake from monitoring of ecohydrological fluxes was sustained and consistent, suggesting that the tree canopies were a sink for N deposition. Seasonal variation in recovery also suggested biological activities influenced fluxes and transformations of this ion within the canopy. The total amount of this canopy N uptake was greater than the mean annual N in litterfall, implying that this flux was supporting the turnover of the canopy. When we used 15N to directly assess uptake into branch biomass we also did not find evidence for immediate relocation to other parts of the tree. Our findings suggest that at our N‐limited site, canopy uptake of N deposition is likely to be as important as root uptake of N but may be limited to supplying N to the canopy rather than the whole tree. Further research in this area is crucial to better understand the interactions of future changes in N deposition on primary production and carbon storage in forests. A free Plain Language Summary can be found within the Supporting Information of this article.