The Role of Wood Ants (Formica rufa group) in Carbon and Nutrient Dynamics of a Boreal Norway Spruce Forest Ecosystem

Wood ants (Formica rufa group) are regarded as keystone species in boreal and mountain forests of Europe and Asia by their effect on ecosystem carbon (C) and nutrient pools and fluxes. To quantify the impact of their activity on boreal forest ecosystems, C, nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca) pools and fluxes in wood ant nests (WAN), and soil were assessed along a 5-, 30-, 60-, and 100-year-old Norway spruce (Picea abies L. Karsten) dominated successional gradient in eastern Finland. Amounts of C and nutrients in WAN increased with stand age, but contained less than 1% of total C and nutrient pools in these stands. The CO₂-efflux from nests was also insignificant, as compared to CO₂-efflux from the forest floor. Annually, the amount of C brought by wood ants into their nests as honeydew, prey and nest-building materials ranged from 2.7 to 49.3 kg ha^?1 C, but this is only 0.1–0.7% of the combined net primary production of trees and understorey in boreal forests. The difference between wood ant nest C inputs and outputs was very small in the younger-aged stands, and increased in the older stands. Carbon accumulation rates in nests over a 100 year period are estimated to be less than 10 kg ha^?1 a^?1. In contrast to C, annual inputs of N, P, and K are larger compared to wood ant nest nutrient pool size, ranging from 3 to 6% of the annual tree stand and understorey uptake. This indicates a more rapid turnover and transport of N, P, and K out of WAN, and suggests that wood ants increase the cycling rate of these nutrients in boreal forests.     

Distribution of ant species and mounds (Formica) in different-aged managed spruce stands in eastern Finland

Mound‐building ants (Formica spp.), as key species, have large impacts on organisms and ecosystem functions in boreal Eurasian forests. The density, sizes and locations of ant mounds determine the magnitude and the spatial distribution of ant activities in forest ecosystems. Clear‐cutting can destroy wood ant colonies, and the species, abundance, dimensions and locations of ant mounds may change as forest stand structure changes with stand age. We compared ant species composition, ant mound numbers and dimensions, and the spatial distribution of mounds in Norway spruce [Picea abies (L.) Karst.] stands of different age (5, 30, 60 and 100 years) in eastern Finland. The mound density of Formica aquilonia Yarr. was greater in the two oldest stand age classes, while most mounds of Formica rufa L., Formica polyctena Först., Formica lugubris Zett., Formica exsecta Nyl. and Formica pressilabris Nyl. were found in the two youngest age classes. The mean volume, the volume per area and height/diameter ratio of F. aquilonia mounds increased with stand age. In the oldest stand age class, mounds were slightly smaller in well‐lit locations than in shade and near stand edges than further from the edges indicating that new mounds are established in well‐lit locations. Similarly, the longest slopes of the mounds faced south, indicating the importance of exposure to the sun. F. aquilonia mounds were concentrated near stand edges, and the spatial distribution of the mounds was aggregated in some stands. At the ecosystem level, the aggregation of ant mounds near stand edges may increase the edge productivity, as mounds concentrate resources to the edges and release nutrients after abandonment.     

Sources of variation in the incidence of ant–aphid mutualism in boreal forests

• 1 The mutualism between wood ants of the Formica rufa group and aphids living in the canopy of trees is a widespread phenomenon in boreal forests, and it can affect tree growth. However, not all trees in the forest are involved in this interaction.
• 2 To assess the incidence of host trees involved in this ant–aphid mutualism and its spatial distribution in boreal forests, we inventoried sample plots with a radius of 10–15 m around wood ant mounds in 12 forest stands of two age classes (5–12‐year‐old sapling stands and 30–45‐year‐old pole stands) and two dominant tree species (Scots pine and silver birch) in Eastern Finland from 2007 to 2009.
• 3 The proportion of trees visited by ants out of all trees on the individual study plots were in the range 4–62%, and 1.5–39% of the trees on the plots were consistently visited by ants during all 3 years. The percentage of host trees increased with the ant mound base area on the plots. Trees visited by ants were larger and closer to the mound than trees not visited by ants. Within the group of visited trees, more ants were found on bigger trees and on trees close to the ant mounds.
• 4 Extrapolated from plot to stand level, we estimated that 0.5–6.6% of the trees were host trees in at least one of the three study years, and that only 0.01–2.3% of all the trees were consistently visited by ants during all 3 years. It is concluded that ant–aphid mutualism is a minor occurrence at the stand level.

     

Stand type is more important than red wood ant abundance for the structure of ground‐dwelling arthropod assemblages in managed boreal forests

• 1 The relationships between red wood ants (Formica rufa group) and other ground‐dwelling arthropods were studied in young managed forests stands in Eastern Finland. The main objectives were: (i) to test the influence of stand type (dominant tree species; age: sapling versus pole stage) and numbers of red wood ants on the occurrence of other ground‐dwelling arthropods and (ii) to study the occurrence of red wood ants versus other arthropods on a distance gradient from ant mounds. We used pitfall traps set in 5–14‐year‐old sapling stands and 30–45‐year‐old pole‐stage stands of Scots pine (Pinus sylvestris L.) and birch (Betula spp.) forests.
• 2 Pitfall trap catches of red wood ants did not vary significantly between the forest stand types, although some groups of other arthropods showed clear responses to stand type (e.g. catches of other Formicinae and Gnaphosidae were higher in sapling stands than in pole‐stage stands). The number of red wood ants clearly explained less of the variation in assemblages of other ground‐dwelling arthropods than the forest stand type.
• 3 Red wood ant numbers decreased significantly with distance from the mounds, but the other ground‐dwelling arthropods were insensitive to this gradient or even showed a preference for proximity to ant mounds and high ant activity.
• 4 The results obtained in the present study suggest that wood ants do not have strong effects on several other ground‐dwelling arthropod groups in young managed forests other than in the immediate vicinity of their mounds.

     

Impact of global warming on the tree species composition of boreal forests in Finland and effects on emissions of isoprenoids

This study aims to identify how climate change may influence total emissions of monoterpene and isoprene from boreal forest canopies. The whole of Finland is assumed to experience an annual mean temperature (T) increase of 4 °C and a precipitation increase of 10% by the year 2100. This will increase forest resources throughout the country. At the same time, the proportions of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) in southern Finland (60°≤ latitude < 65°N) will be reduced from the current 40–50% to less than 10–20%, with increased dominance of birches (Betula pendula and Betula pubescens). In northern Finland (65°≤ latitude < 70°N), the proportions of Norway spruce and Scots pine will be balanced at a level of about 40% as the result of an increase in Norway spruce from the current 21% to 37% and a concurrent reduction in Scots pine from 63% to 40%. The proportion of birches is predicted to increase from the current 17% to 23%, but these will become the dominant species only on the most fertile sites. Total mean emissions of monoterpene by Scots pine will be reduced by 80% in southern Finland, but will increase by 62% in the north. Emissions from Norway spruce canopies will increase by 4% in the south but by 428% in the north, while those from birch canopies will increase by about 300% and 113%, respectively. Overall emissions of monoterpene over the whole country amount to about 950 kg km^?2 y^?1 under current temperature conditions and will increase by 17% to 1100 kg km^?2 y^?1 with elevated temperature and precipitation, mainly because of an increase at northern latitudes. Under current conditions, emissions of isoprene follow the spatial distribution of spruce canopies (the only isoprene‐emitting tree species that forms forests in Finland) with four times higher emissions in the south than in the north. The elevated temperature and the changes in the areal distribution of Norway spruce will result in increases in isoprene emissions of about 37% in southern Finland and 435% in northern Finland. Annual mean isoprene emissions from Norway spruce canopies over the whole country will increase by about 60% up to the year 2100.     

Fine root foraging strategies in Norway spruce forests across a European climate gradient

Fine root acclimation to different environmental conditions is crucial for growth and sustainability of forest trees. Relatively small changes in fine root standing biomass (FRB), morphology or mycorrhizal symbiosis may result in a large change in forest carbon, nutrient and water cycles. We elucidated the changes in fine root traits and associated ectomycorrhizal (EcM) fungi in 12 Norway spruce stands across a climatic and N deposition gradient from subarctic‐boreal to temperate regions in Europe (68°N–48°N). We analysed the standing FRB and the ectomycorrhizal root tip biomass (EcMB, g m^?2) simultaneously with measurements of the EcM root morphological traits (e.g. mean root length, root tissue density (RTD), N% in EcM roots) and frequency of dominating EcM fungi in different stands in relation to climate, soil and site characteristics. Latitude and N deposition explained the greatest proportion of variation in fine root traits. EcMB per stand basal area (BA) increased exponentially with latitude: by about 12.7 kg m^?2 with an increase of 10° latitude from southern Germany to Estonia and southern Finland and by about 44.7 kg m^?2 with next latitudinal 10° from southern to northern Finland. Boreal Norway spruce forests had 4.5 to 11 times more EcM root tips per stand BA, and the tips were 2.1 times longer, with 1.5 times higher RTD and about 1/3 lower N concentration. There was 19% higher proportion of root tips colonized by long‐distance exploration type forming EcM fungi in the southern forests indicating importance of EcM symbiont foraging strategy in fine root nutrient acquisition. In the boreal zone, we predict ca. 50% decrease in EcMB per stand BA with an increase of 2 °C annual mean temperature. Different fine root foraging strategies in boreal and temperate forests highlight the importance of complex studies on respective regulatory mechanisms in changing climate.     

Organic mound-building ants: their impact on soil properties in temperate and boreal forests

Ants are important components of most soil invertebrate communities, and can affect the flow of energy, nutrients and water through many terrestrial ecosystems. The vast majority of ant species build nests in the mineral soil, but a small group of ants in temperate and boreal forests of Eurasia and North America build large parts of their nests above‐ground using organic materials collected from the surrounding soil. Many studies have shown that ants nesting in mineral soil can affect water infiltration rates, soil organic matter (OM) content, and nutrient cycling, but much less is known on how mound‐building ants influence soil physical and chemical properties. In this paper we summarize what is known on the soil impacts of organic mound‐building ants in temperate and boreal forests, and how these ants could be affected by ecosystem disturbance and future climate change. Much of this information comes from studies on Formica rufa group ants in Europe, which showed that CO₂ emissions and concentrations of C, N, and P are usually higher in ant mounds than in the surrounding forest soil. However, ant mounds are a minor component of total soil C and nutrient pools, but they do increase spatial heterogeneity of soil water and available nutrients. Mound‐building ants can also impact tree growth, which could change the quantity and quality of OM added to soil. Forest management, fire, and projected climate change, especially in boreal forests, could affect mound‐building ant population dynamics, and indirectly, soil properties.     

Abundance and distribution of organic mound-building ants of the Formica rufa group in Yellowstone National Park

Red wood ants (Formica rufa group) are ubiquitous in many conifer and mixed‐conifer forests of northern Europe and Asia. In contrast, relatively little is known about the abundance and distribution of the 24 North American F. rufa group species. As ants are important components of most soil invertebrate communities and are considered ecosystem engineers that alter the flow of energy and nutrients through terrestrial systems, it is important to gain information on their distribution and abundance. We conducted a survey for red wood ant mounds in Yellowstone National Park (YNP), Wyoming/Montana, USA, where human disturbance has been kept to a minimum for over 130 years. We found a total of 85 red wood ant mounds (0.11 to 0.17 mounds/ha) on 327 km of roads and 180 km of the hiking trails we surveyed. The occurrence of ant mounds was higher then expected by random distribution at elevations between 1600 and 2400 m, annual precipitation of 250 to 760 mm, middle and late successional lodgepole pine, late successional Douglas fir forest and non‐forested grassland/sagebrush prairie vegetation. Additionally, mounds were clustered in gently sloped not north‐exposed locations and in areas that had not recently burned. Most of the mounds detected were inhabited by Formica obscuripes Forel, which occupied 94% of the mounds sampled. Based on a multi‐criteria binary Geographic Information System model that we developed, we found that ant mounds were to be expected with a high probability in less then 1% of the YNP area. These results together with the detected low density and small size of the red wood ant mounds within the study area suggest that these insects have a much lower impact on invertebrate biodiversity and ecosystem processes, such as forest productivity and carbon and nutrient cycling on the ecosystem scale compared with their counterparts in European or Asian systems.     

Influence of the wood ant, Formica polyctena, on soil nutrient and the spruce tree growth

The effect of Formica polyctena ant nests on the distribution of soil nutrients, soil pH and the growth of Norway spruce trees was studied in the southern part of the Czech Republic. Soil nutrient content (exchangeable P, N, K and pH) and growth of mature spruce trees were measured at four distances from the nearest ant hill (0–1, 3–5, 10–50 and >200 m). Trees at all distances were visited by ants, except for those >200 m from the nearest nest. Soil pH and of P, K and NO₃ concentrations were higher near ant nests (<1 m), and pH and K at distances of 3–5 m, when compared with distances of 10–50 and >200 m from the nests, where no significant differences in these variables were detected. In contrast, tree ring analyses (1974–2004) showed that trees >200 m from the ant nests grew significantly faster than trees at other distances, followed by trees within 1 m of the nests. No growth differences were found between the growth of trees at 3–5 and 10–50 m from ant nests. We postulate that nutrient and carbohydrate removal of honeydew collected by ant‐tended aphids are slowing growth of tree. However, trees may partly compensate for this depletion by having access to a larger supply of soil nutrients near ant nests.     

Stand characteristics and biodiversity indicators along the productivity gradient in boreal forests: Defining a critical set of indicators for the monitoring of habitat nature quality

Abstract

We quantified the effects of anthropogenic disturbances on the structure and biodiversity of boreal forests on acidic soils and created a statistically supported rational set of indicators to monitor the stand “naturalness”. For that, we surveyed various traits of tree layer, understory, herb layer, forest floor and several widely accepted biodiversity epiphytic indicators in 252 old‐aged boreal stands in Estonia, mostly dominated by Scots pine or Norway spruce. Multifactorial general linear model analyses showed that many forest characteristics and potential indicators were confounded by the gradient of soil productivity (reflected by the forest site type), local biogeographic gradients and also by stand age. Considering confounding effects, boreal forests in a near‐natural state have more large‐diameter trees (diameter at breast height >40 cm) and larger variety of diameter classes, higher proportion of spruce or deciduous trees, a larger amount of coarse woody debris in various stages, a more closed tree canopy and denser understory than managed mature forests. By increasing light availability above the field layer, forest management indirectly increases the coverage of herbs and lichens on the forest floor but reduces the alpha‐ and beta‐diversity of herbs and the proportion of graminoids. Human disturbances reduce the relative incidence of many commonly accepted biodiversity indicators such as indicator lichens, woodpeckers, wood‐dwelling insects or fungi on trees. The test for the predictive power of characteristics reacting on disturbance revealed that only a fraction of them appeared to be included in a diagnostic easy‐to‐apply set of indicators to assess the nature quality of boreal forest: the amount of dead wood, the proportion of deciduous trees, the presence of specially shaped trees and woodpeckers and, as an indicator of disturbances, the forest herb Melampyrum pratensis. Many of these indicators have already been implemented in practice.     

Effects of altitude on aphid-mediated processes in the canopy of Norway spruce

Abstract 1 The abundance of aphids and their honeydew are important in shaping the ecology of food web interactions and nutrient cycling in forests of Norway spruce. Here, the effects of the different environmental conditions at two study sites located at different altitudes (500 m, 765 m a.s.l.), in the Fichtelgebirge, north‐eastern Bavaria, Germany, on the abundance of Cinara pilicornis and their influence on epiphytic microorganisms on shoots of Picea abies were compared. Subsequent changes in throughfall fluxes were measured over a period of 12 weeks beneath infested and reference trees. In a laboratory experiment, the effects of ultraviolet (UV) radiation on microbial mortality and C and N concentrations in leachates were determined. 2 The warmer and drier conditions at the low altitude site favoured an early onset to aphid multiplication in spring compared with the high altitude site, where aphid numbers peaked 3 weeks later. 3 The presence of honeydew was associated with a significant increase in the total number of cultured epiphytic filamentous fungi, yeasts and bacteria in 12 of the 18 sample units, indicating better culturability or growth, whereas altitude had no significant effect on cultured cell numbers. By contrast to the reference trees, the high dissolved organic carbon (DOC) and hexose‐C fluxes beneath infested trees at the peak in aphid abundance, in June and July, resulted in a concomitant decrease in the fluxes of total inorganic nitrogen beneath infested trees (low altitude: ?19.7%; high altitude: ?52.3%). Fluxes of organic nitrogen were significantly higher beneath infested trees at the time of infestation. Similarly, potassium fluxes in throughfall increased 1.6–2.0‐fold in response to aphid infestation. 4 The exposure of infested and uninfested shoots of Norway spruce to UV‐A and UV‐B radiation only weakly affected epiphytic microbial mortality and did not affect the concentrations of the different nitrogen compound in leachates. However, bacteria, tended to be more active in the leachates collected from infested shoots, which resulted in the higher concentrations of aminosugar‐N. The aphids had a more pronounced effect on the concentrations of DOC in leachates, with average DOC concentrations being 4.2‐fold higher than in leachates from uninfested shoots. 5 It is suggested that, even at very low densities, aphids exert a strong influence via honeydew on the performance of microorganisms, and nutrient and energy flow, in spruce forests.     

Honeydew amino acids in relation to sugars and their role in the establishment of ant-attendance hierarchy in eight species of aphids feeding on tansy (Tanacetum vulgare)

Abstract. The ratio of the concentration of honeydew total amino acids to total sugars in the honeydew of eight species of aphids, all feeding on tansy, Tanacetum vulgare (L.), was determined and correlated with honeydew production and ant‐attendance. The honeydew of the five ant‐attended aphid species [Metopeurum fuscoviride (Stroyan), Trama troglodytes (v. Hayd), Aphis vandergooti (Börner), Brachycardus cardui (L.), Aphis fabae (Scopoli)] was rich in total amino acids, ranging from 12.9 to 20.8 nmol µL^?1 compared with the unattended aphid Macrosiphoniella tanacetaria (Kalt.) with only 3 nmol µL^?1. Asparagine, glutamine, glutamic acid and serine (all nonessential amino acids) were the predominant amino acids in the honeydew of all species. The total concentration of amino acids in the phloem sap of tansy was much higher (78.7 nmol µL^?1) then in the honeydew samples, and the predominant amino acids were glutamate (34.3%) and threonine (17.7%). A somewhat unexpected result was the finding that those aphid species with the highest total amino acid concentration in the honeydew always had the highest concentration of sugars. The lowest amino acid–sugar combined value was 104–28.8 nmol µL^?1 in the non ant‐attended species M. tanacetaria, and the highest value was an average of 270–89.9 nmol µL^?1 for the three most intensely attended aphid species M. fuscoviride, A. vandergooti and T. troglodytes. There is no evidence that any single amino acid or group of amino acids in the honeydew acted as an attractant for ant‐attendance in these eight aphid species. The richness of the honeydew (rate of secretion × total concentration of sugars), along with the presence of the attractant sugar melezitose, comprised the critical factors determining the extent of ant‐attendance of the aphids feeding on T. vulgare. The high total amino acid concentration in sugar‐rich honeydews can be explained by the high flow‐through of nutrients in aphids that are particularly well attended by ants.     

Ants accelerate succession from mountain grassland towards spruce forest

Question: What is the role of mound‐building ants (Lasius flavus) in successional changes of a grassland ecosystem towards a spruce forest? Location: Slovenské Rudohorie Mountains, Slovakia; ca. 950 m a.s.l. near the Obrubovanec point (1020 m a.s.l.; 48°41′N, 19°39′E). Methods: Both chronosequence data along a successional gradient and temporal data from long‐term permanent plots were collected on ants, spruce establishment, and vegetation structure, together with additional data on spruce growth. Results: There are more spruce seedlings on ant mounds (4.72 m^?2) than in the surrounding vegetation (0.81 m^?2). Spruce seedlings grow faster on these mounds compared to surrounding areas. The first colonization wave of seedlings was rapid and probably occurred when grazing prevailed over mowing. Ant colony presence, mound volume, and plant species composition change along the successional gradient. Mounds become bigger when partly shaded but shrink in closed forest, when ant colonies disappear. Shade‐tolerant acidophylic species replace grassland plants both on the mounds and in surrounding areas. Conclusions: The massive occurrence of Lasius flavus anthills contributes to a runaway feedback process that accelerates succession towards forest. The effect of ants as ecosystem engineers is scale‐dependent: although they stabilize the system at the scale of an individual mound, they may destabilize the whole grassland system over a longer time scale if combined with changes in mowing regime.     

Forest microsite effects on community composition of ectomycorrhizal fungi on seedlings of Picea abies and Betula pendula

Niche differentiation in soil horizons, host species and natural nutrient gradients contribute to the high diversity of ectomycorrhizal fungi in boreal forests. This study aims at documenting the diversity and community composition of ectomycorrhizal fungi of Norway spruce ( Picea abies ) and silver birch ( Betula pendula ) seedlings in five most abundant microsites in three Estonian old-growth forests. Undisturbed forest floor, windthrow mounds and pits harboured more species than brown- and white-rotted wood. Several species of ectomycorrhizal fungi were differentially represented on either hosts, microsites and sites. Generally, the most frequent species in dead wood were also common in forest floor soil. Ordination analyses suggested that decay type determined the composition of EcM fungal community in dead wood. Root connections with in-growing mature tree roots from below affected the occurrence of certain fungal species on seedling roots systems in dead wood. This study demonstrates that ectomycorrhizal fungi differentially establish in certain forest microsites that is attributable to their dispersal and competitive abilities. Elevated microsites, especially decayed wood, act as seed beds for both ectomycorrhizal forest trees and fungi, thus affecting the succession of boreal forest ecosystems.     

Stability in the patterns of long‐term development and growth of the Canadian spruce–moss forest

Aim The spruce–moss forest is the main forest ecosystem of the North American boreal forest. We used stand structure and fire data to examine the long‐term development and growth of the spruce–moss ecosystem. We evaluate the stability of the forest with time and the conditions needed for the continuing regeneration, growth and re‐establishment of black spruce (Picea mariana) trees. Location The study area occurs in Québec, Canada, and extends from 70°00′ to 72°00′ W and 47°30′ to 56°00′ N. Methods A spatial inventory of spruce–moss forest stands was performed along 34 transects. Nineteen spruce–moss forests were selected. A 500 m² quadrat at each site was used for radiocarbon and tree‐ring dating of time since last fire (TSLF). Size structure and tree regeneration in each stand were described based on diameter distribution of the dominant and co‐dominant tree species [black spruce and balsam fir (Abies balsamea)]. Results The TSLF of the studied forests ranges from 118 to 4870 cal. yr bp . Forests < 325 cal. yr bp are dominated by trees of the first post‐fire cohort and are not yet at equilibrium, whereas older forests show a reverse‐J diameter distribution typical of mature, old‐growth stands. The younger forests display faster height and radial growth‐rate patterns than the older forests, due to factors associated with long‐term forest development. Each of the stands examined established after severe fires that consumed all the soil organic material. Main conclusions Spruce–moss forests are able to self‐regenerate after fires that consume the organic layer, thus allowing seed regeneration at the soil surface. In the absence of fire the forests can remain in an equilibrium state. Once the forests mature, tree productivity eventually levels off and becomes stable. Further proof of the enduring stability of these forests, in between fire periods, lies in the ages of the stands. Stands with a TSLF of 325–4870 cal. yr bp all exhibited the same stand structure, tree growth rates and species characteristics. In the absence of fire, the spruce–moss forests are able to maintain themselves for thousands of years with no apparent degradation or change in forest type.     

Ants protect conifer seedlings from feeding damage by the pine weevil Hylobius abietis

• 1 Ants that protect food resources on plants may prey on (or deter) herbivores and thereby reduce damage. Red wood ants (of the Formica rufa group) are dominant ants in boreal forests of Eurasia and affect the local abundance of several herbivorous species.
• 2 The pine weevil Hylobius abietis (L.) is a herbivore that causes severe damage by feeding on the bark of coniferous seedlings within areas of forest regeneration.
• 3 We investigated whether ants can protect conifer seedlings from pine weevil feeding. In a manipulative experiment, ants were attracted to sugar baits attached to spruce seedlings and the damage caused by pine weevils was compared with control seedlings without ant‐baits.
• 4 The feeding‐scar area was approximately one‐third lower on the seedlings with ant‐baits compared with the controls. Besides red wood ants, Myrmica ants were also attracted in high numbers to the ant baits and the relative effects of these species are discussed.
• 5 The results obtained in the present study support the trophic cascade hypothesis (i.e. damage to herbivores is suppressed in the presence of predators). The decreased pine weevil feeding on the baited seedlings was probably a result of nonconsumptive interactions [i.e. the presence of (or harassment by) ants distracting pine weevils from feeding].
• 6 Understanding the role of ants may have important implications for future strategies aiming to control pine weevil damage. For example, maintaining suitable conditions for ants after harvesting stands may be an environmentally friendly but currently unexploited method of for decreasing weevil damage.

     

Carbon flux from decomposing wood and its dependency on temperature,wood N2 fixation rate,moisture and fungal composition in a Norway spruce forest

Globally 40–70 Pg of carbon (C) are stored in coarse woody debris on the forest floor. Climate change may reduce the function of this stock as a C sink in the future due to increasing temperature. However, current knowledge on the drivers of wood decomposition is inadequate for detailed predictions. To define the factors that control wood respiration rate of Norway spruce and to produce a model that adequately describes the decomposition process of this species as a function of time, we used an unprecedentedly diverse analytical approach, which included measurements of respiration, fungal community sequencing, N₂ fixation rate, nifH copy number, ¹⁴C‐dating as well as N%, δ¹³C and C% values of wood. Our results suggest that climate change will accelerate C flux from deadwood in boreal conditions, due to the observed strong temperature dependency of deadwood respiration. At the research site, the annual C flux from deadwood would increase by 27% from the current 117 g C/kg wood with the projected climate warming (RCP4.5). The second most important control on respiration rate was the stage of wood decomposition; at early stages of decomposition low nitrogen content and low wood moisture limited fungal activity while reduced wood resource quality decreased the respiration rate at the final stages of decomposition. Wood decomposition process was best described by a Sigmoidal model, where after 116 years of wood decomposition mass loss of 95% was reached. Our results on deadwood decomposition are important for C budget calculations in ecosystem and climate change models. We observed for the first time that the temperature dependency of N₂ fixation, which has a major role at providing N for wood‐inhabiting fungi, was not constant but varied between wood density classes due to source supply and wood quality. This has significant consequences on projecting N₂ fixation rates for deadwood in changing climate.     

Not just for the birds: Spiders as natural enemies of spruce budworm (Choristoneura fumiferana,Clem.)

(1) The eastern spruce budworm (Choristoneura fumiferana, Clem.) is a native irruptive forest pest that defoliates spruce-fir forests throughout North America's boreal zone. (2) Past studies suggest that successful spruce budworm population control requires high natural mortality from a variety of sources, including predators, especially from parasitoids and birds. While well represented in many different ecosystems, the role of generalist predatory spiders in these boreal systems remains largely unstudied. (3) To determine the identity and percentage of spiders preying upon spruce budworm, we hand-collected spiders from balsam fir (Abies balsamea) in stands with relatively high spruce budworm densities from forests in insular Newfoundland and Labrador, Canada. (4) Using a spruce budworm-specific TaqMan real-time PCR assay, we successfully amplified spruce budworm DNA in 32% of collected spiders. After spider molecular barcoding, we found the web builders Grammonota angusta Dondale, Pityohyphantes (aff. subarcticus), Dictyna brevitarsa Emerton and Estrandia grandaeva (Keyserling) represented 58% of the spiders feeding on spruce budworm, and the wandering hunter Philodromus rufus Dondale represented 11.8%. (5) Our molecular approach was an effective means with which to identify recently consumed prey and natural enemies in this boreal system.     

Dead Wood is Buried and Preserved in a Labrador Boreal Forest

Large amounts (36.4 Mg ha⁻¹ or 179 m³ ha⁻¹) of buried dead wood were found in overmature (146–204-year-old) black spruce (Picea mariana (Mill.) B.S.P.) forests in the high boreal region of eastern Canada. Amounts of this size indicate that burial reduces rates of wood decay producing an important component of long-term carbon (C) storage. Radiocarbon-derived ages of black spruce stems buried near the bottom of the organic soil horizon at three old-growth sites were up to 515 years old. Together with information on current stand age, this suggests that the stems have been dead for more than 250 years. Most aboveground dead wood decays or becomes fragmented within about 70 years of tree death in these forests. The presence of old yet well-preserved buried wood suggests that decay rates are greatly reduced when downed dead wood is quickly overgrown by moss. Thus, the nature and type of ground-layer vegetation influences the accumulation of organic matter in these forests. This process of dead wood burial and the resultant addition to a large and long-enduring belowground C pool should be considered when estimating dead wood abundance for habitat or forest C accounting and cycling.     

The influence of fire on carbon distribution and net primary production of boreal Larix gmelinii forests in north-eastern China

The boreal larch forest of Eurasia is a widespread forest ecosystem and plays an important role in the carbon budget of boreal forests. However, few carbon budgets exist for these forests, and the effects of wildfire, the dominant natural disturbance in this region, on carbon budgets are poorly understood. The objective of this study was to quantify the effects of wildfire on carbon distribution and net primary production (NPP) for three major Dahurian larch (Larix gmelinii Rupr.) forest ecosystems in Tahe, Daxing'anling, north‐eastern China: Larix gmelinii–Ledum palustre, Larix gmelinii–grass and Larix gmelinii–Rhododendron dahurica forests. The experimental design included mature forests (unburned), and lightly and heavily burned forests from the 1.3‐million‐ha 1987 wildfire. We measured carbon distribution and above‐ground NPP, and estimated fine root production from literature values. Total ecosystem carbon content for the mature forests was greatest for Larix–Ledum forests (251.4 t C ha^?1) and smallest for Larix–grass forests (123.8 t C ha^?1). Larix–Ledum forests contained the smallest vegetation carbon (13.5%), while Larix–Rhododendron contained the largest vegetation carbon (63.1%). Fires tended to transfer carbon from vegetation to detritus and soil. Total NPP did not differ significantly between the lightly burned and unburned stands, and averaged 1.58, 1.29 and 1.01 t C ha^?1 year^?1 for Larix–grass, Larix–Rhododendron and Larix–Ledum lightly burned stands, respectively. Above‐ground net primary production (ANPP) of heavily burned stands was 92–95% less than unburned and lightly burned stands. The estimated carbon loss during the 1987 fire showed substantial variability among forest types and fire severity levels. Depending upon the assumptions made about the fraction of the landscape occupied by the three larch forest types, the 1987 conflagration in north‐east China released 2.5 × 10⁷?4.9 × 10⁷ t C to the atmosphere. This study illustrates the need to distinguish between the different larch forests for developing general carbon budgets.