Spruce Canopy Research Articles

Modeling individual-tree growth in stands under forest conversion in East Germany

One major result of forest conversion in Saxony, East Germany, is the increasing importance of two-storied stands composed of a conifer canopy and a deciduous-tree understory. To enhance the applicability of the growth and yield simulator BWINPro under these conditions, three of its major sub-models were adapted to the regional growing conditions and to the relatively high level of diversity in spatial structure, mixture of species, and age variability typical for forests in conversion: (1) A new module for simulating single-tree juvenile growth was developed for European beech and Common oak under canopies of Norway spruce and Scots pine. Predictions in this sub-model are derived from individual height, diameter at breast height (dbh), and the influences of horizontal and vertical competition; (2) An alternative distance-dependent competition index was introduced to estimate individual basal area increment according to tree-specific growing conditions; (3) A modified logistic mortality model was parameterized for the most important Saxon species based on tree dimensions and basal area increment. Data came from permanent sample plots distributed throughout the region and from three chronosequence plot series established specifically for obtaining model input data. The new components were included into the existing structure of BWINPro. As a result of the adaption, the regional version BWINPro-S provides enhanced opportunities of planning and management for forest conversion and for multi-storied stands.

Vertical transmission of Nosema fumiferanae (Microsporidia: Nosematidae) and consequences for distribution, post-diapause emergence and dispersal of second-instar larvae of the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae)

We examined vertical transmission of Nosema fumiferanae in the eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), and how it affects overwintering distribution and survival and spring emergence and dispersal of second-instar larvae in outbreak populations. Females containing 5.0 × 10 5 spores or more consistently produced 100% infected progeny. Transmission efficiency was still 50% at burdens as low as 0.2 × 10 5 spores per moth. Infection intensity in offspring increased with maternal spore load but became highly variable above 25 × 10 5 spores per female. Nosema multiplied in second instars for at least 1 month after they entered dormancy, regardless of temperature (2 °C versus 21 °C). Infection did not affect the distribution of overwintering larvae in a white spruce canopy. Dormancy survival between late-summer and the following spring was lower in families from infected females and was negatively correlated with larval infection intensity. Infection delayed larval emergence from hibernacula in the spring and resulted in delayed dispersal of emerged larvae, at least when parasite prevalence and infection intensities were high. Infected larvae were less successful in establishing feeding sites after dispersal. Our results underscore the potential of Nosema infection to negatively affect processes early in the budworm life cycle.

Spectral composition of photosynthetically active radiation penetrating into a Norway spruce canopy: the opposite dynamics of the blue/red spectral ratio during clear and overcast days

The spectral composition of photosynthetically active radiation (PAR) during clear and overcast days was studied above the canopy (U) and at two layers of a dense Norway spruce stand [Picea abies (L.) Karst.] characterized with an average LAI = 7.3 ± 0.8 (middle layer: M) and 12.3 ± 0.7 (lower layer: L). Whereas the spectral composition of PAR incoming on the canopy surface during cloudy days (characterized by diffuse index DI > 0.7) was almost independent of the solar elevation angle, the proportion of the blue-green spectral region of PAR was significantly reduced at low elevation angles during days with prevailing direct radiation (DI < 0.3). The PAR spectrum at both M and L levels was only slightly enriched in the green spectral region (more pronounced for DI < 0.3). The penetration of diffuse radiation into the canopy resulted in a slight (approx. 5%) reduction of the blue region proportion that remained stable during the day. On the contrary, under clear sky conditions the penetration of blue and red radiation was dependent on the solar elevation in an opposite manner in comparison with the spectral composition of PAR incident on canopy, giving almost twofold proportion of the blue part of the spectrum at a low elevation angle at M layer. We suggest that the blue enhancement of the spectrum within the Norway spruce canopy during clear days is due to a specific spatial arrangement of the assimilatory apparatus of a coniferous stand. Further, the possible consequences of the observed dynamics of the PAR spectrum inside the canopy during clear days on the efficiency of PAR absorption of the needles located within the canopy are discussed.

Modeling of the long-term effect of tree species (Norway spruce and European beech) on soil acidification in the Ore Mountains

The MAGIC model was applied to estimate soil and soil water (−90 cm) chemistry between 1854 and 2094 at two experimental stands (Načetín, Ore Mountains), one covered by a Norway spruce monoculture and the other by a natural European beech forest. The primary aims were to evaluate the influence of tree species on long-term acidification and to predict future development under different forest management scenarios. Depletion of base cations from the soils, caused by high acidic deposition, resulted in low base saturations of 8.2% at the spruce stand and of 6.4% at the beech stand in 2003. The concentration of aluminum in soil water was 135 μmol l −1 and pH 4.32 at the spruce stand, and 70 μmol l −1 and pH 4.4 at the beech stand, respectively, in 2005. During the peak of acidification in the mid 1980s, modeled aluminum concentrations contributed 70% to neutralizing acidity at the spruce stand, and 55% at the beech stand. In addition, SO 4 concentration was significantly higher at the spruce stand (525 μequiv. l −1) compared to the beech stand (330 μequiv. l −1) as a result of higher dry deposition onto the spruce canopy. The enhanced leaching of base cations was comparable at both stands (191 μequiv. l −1 at the spruce stand and 215 μequiv. l −1 at the beech stand). The higher deposition of base cations onto the spruce canopy was able to partially mitigate the effect of high leaching. The model results suggest that future recovery of soil water will be significantly better at the beech stand (higher pH, ANC, Bc/Al ratio and lower SO 4 2− and Al concentrations). Interestingly, modeled soil base saturation for 2094 will be lower at the beech stand. Alternative scenarios such as clear-cutting and new re-forestation resulted in more favorable soil chemistry for the beech plantations compared to the spruce. The best regeneration of the soil environment is predicted for the scenario with an absence of forest. This suggests, that future soil recovery from acidification will be delayed by the removal of base cations through harvesting.

Flux contribution of coherent structures and its implications for the exchange of energy and matter in a tall spruce canopy

Thefluxcontributionofcoherentstructurestothetotalexchangeofenergy and matter is investigated in a spruce canopy of moderate density in heterogeneous, complex terrain. The study deploys two methods of analysis to estimate the coherent exchange: conditional averages in combination with wavelet analysis, and quadrant analysis. The data were obtained by high-frequency single-point measurements using sonic anemometers and gas analysers at five observation heights above and within the canopy and subcanopy, and represent a period of up to 2.5months. The study mainly addresses the momentum transfer and exchange of sensible heat throughout the roughness sublayer, while results are provided for the exchange of carbon dioxide and water vapour above the canopy. The magnitude of the flux contribution of coherent structures largely depends on the method of analysis, and it is demonstrated that these differences are attributed to differences in the sampling strategy between the two methods. Despite the differ- ences, relational properties such as sweep and ejection ratios and the variation of the flux contribution with height were in agreement for both methods. The sweep phase of coherentstructures is the dominantprocess close to and within the canopy, whereas the ejections gain importance with increasing distance to the canopy. The efficiency of the coherent exchange in transporting scalars exceeds that for momentum by a factor of two. The occurrence of coherent structures results in a flux error less than 4% for the eddy-covariance method. Based on the physical processes identified from the analysis of the ejection and sweep phases along the vertical profile in the rough- ness sublayer, a classification scheme for the identification of exchange regimes is developed. This scheme allows one to estimate the region of the canopy participat- ing in the exchange of energy and matter with the above-canopy air under varying environmental conditions.

Sensitivity of Lagrangian Stochastic footprints to turbulence statistics

This study tests the sensitivity of a Lagrangian Stochastic footprint model to the turbulence statistics describing the flow field, with a focus on the within canopy processes. Representative profiles of the input velocity statistics are taken from a long-term dataset of turbulence measurements within and above a tall spruce canopy. Based on a wavelet tool, which allows a detailed analysis of coherent structures along the vertical profile, we characterize several typical states of coupling and decoupling between surface, canopy and atmosphere. For each coupling regime, three flux footprints using different sources for turbulence statistics are compared: the first based on conditionally-averaged measurements, the second on a simple numerical solution and the third on measurements taken from literature. The effects of profile smoothing and connecting measured canopy data to parametrized atmospheric surface layer profiles are considered. Significant differences between footprints based on modelled and measured profiles were found for exchange regimes with the lower section of the profiles decoupled from the atmospheric surface layer. As such cases are likely to occur for tall canopies with moderate density, our results suggest that the accuracy of Lagrangian Stochastic footprint modelling could be improved by using better turbulence profiles for different exchange regimes.

Holocene environmental history on the eastern slope of the Polar Ural Mountains, Russia

The Holocene environmental history of the eastern slope of the Polar Ural Mountains has been reconstructed using pollen, spores, algae and other microfossils from the Chernaya Gorka palsa section (67°05'N, 65°21'E, 170 m a.s.l.). An initial oligotrophic lake was formed at the study site c. 9800–9500 14C yr BP Although tundra communities dominated the vegetation in the area, birch and larch trees might have grown at lower elevations. Dry and disturbed soil habitats also occurred around the lake. Algae (mostly Pediastrum and Botryococcus) started to expand in the lake as climate gradually improved after c. 9500 14C yr BP. However, the role of mosses (mostly Calliergon and Drepanocladus) was most important for the infilling of the lake basin. Increased temperatures and subsequent improvement of hydrological conditions resulted in vegetation changes: stands of willows developed rapidly and the role of tree birch in the local vegetation increased. The lake was completely filled at c. 8600 14C yr BP. Peat accumulation started with Bryales mosses and, later, Sphagnum became dominant. Stands ofLarix, Picea and Betula became well developed during the Boreal climate optimum. Tree birch began to spread into the tundra. Different Bryales mosses formed peat c. 8000–6500 14C yr BP. Cyperaceae later became the main peat‐forming element. Dense spruce canopies with Larix sibirica and Betula pubescens surrounded the study site during the Atlantic period, pointing to the warmest climate during the Holocene. Summer temperatures might have been up to 3–4°C higher than today. However, a decline of spruce and an increase of birch around 6700–6300 14C yr BP may reflect some climate deterioration. There are no dated deposits younger than 6000 14C yr BP. It is assumed that Subboreal climate deterioration resulted in the development of permafrost and formation of the palsa at the site. The deposits, now protruding above the surrounding terrain, were eroded by wind, water and cryogenic processes.

Spinnen aus Baumkronen-Klopfproben (Arachnida: Araneae), mit Anmerkungen zuCinetata gradata(Linyphiidae) undTheridion boesenbergi(Theridiidae).

Spiders from branch-beating samples in tree crowns (Arachnida: Araneae), with remarks on Cinetata gradata (Linyphiidae) and Theridion boesenbergi (Theridiidae). In winter 2000/01 and in June 2001 branch-beating methods were used for sampling spiders in canopies of spruce (Picea abies) and Douglas-fir (Pseudotsuga menziesii) in SW-Bavaria (Germany). Differences in spider assemblages between the two tree spe- cies are discussed with particular emphasis on the dominant species and taxa. For the rare species Theridion boesenbergi Strand, 1904 remarks on their occurrence in Bavaria, Germany and Europe are given. For Cinetata gradata (Simon, 1881) we present an update to the entire known distribution including a new map. For both species new records are specified and discussed concerning habitat preference, phenology and distribution. Both species seem to be obligate tree colonisers, C. gradata primarily in the canopy stratum. Adults of C. gradata are to be found during all months of the year; T. boesenbergi exhibits an abundance peak in June, males are known to occur from May to August and females the whole year round. The distribution of both species is restricted to Europe, excluding the northern and western parts (Arctic and Atlantic climate) and the Mediter- ranean zone.

Stand and landscape level effects of a major outbreak of spruce beetles on forest vegetation in the Copper River Basin, Alaska

From 1989 to 2003, a widespread outbreak of spruce beetles ( Dendroctonus rufipennis) in the Copper River Basin, Alaska, infested over 275,000 ha of forests in the region. During 1997 and 1998, we measured forest vegetation structure and composition on one hundred and thirty-six 20-m × 20-m plots to assess both the immediate stand and landscape level effects of the spruce beetle infestation. A photo-interpreted vegetation and infestation map was produced using color-infrared aerial photography at a scale of 1:40,000. We used linear regression to quantify the effects of the outbreak on forest structure and composition. White spruce ( Picea glauca) canopy cover and basal area of medium-to-large trees [≥15 cm diameter-at-breast height (1.3 m, dbh)] were reduced linearly as the number of trees attacked by spruce beetles increased. Black spruce ( Picea mariana) and small diameter white spruce (<15 cm dbh) were infrequently attacked and killed by spruce beetles. This selective attack of mature white spruce reduced structural complexity of stands to earlier stages of succession and caused mixed tree species stands to lose their white spruce and become more homogeneous in overstory composition. Using the resulting regressions, we developed a transition matrix to describe changes in vegetation types under varying levels of spruce beetle infestations, and applied the model to the vegetation map. Prior to the outbreak, our study area was composed primarily of stands of mixed white and black spruce (29% of area) and pure white spruce (25%). However, the selective attack on white spruce caused many of these stands to transition to black spruce dominated stands (73% increase in area) or shrublands (26% increase in area). The post-infestation landscape was thereby composed of more even distributions of shrubland and white, black, and mixed spruce communities (17–22% of study area). Changes in the cover and composition of understory vegetation were less evident in this study. However, stands with the highest mortality due to spruce beetles had the lowest densities of white spruce seedlings suggesting a longer forest regeneration time without an increase in seedling germination, growth, or survival.

Seasonal changes in the distribution of green spruce aphid Elatobium abietinum (Walker) (Homoptera: Aphididae) in the canopy of Sitka spruce

Abstract1 Seasonal changes in the distribution of green spruce aphid Elatobium abietinum (Walker) within the canopy of 20–25‐year‐old Sitka spruce are described based on data from two low‐altitude sites (310–420 m above sea‐level), two mid‐altitude sites (500–550 m a.s.l) and one high‐altitude site (610 m a.s.l).2 Aphids were counted throughout the canopy on shoots representative of all needle age‐classes present at each whorl of branches. Counts were made during the middle week of each month from September to July for 4 years (1999–2003), and mean E. abietinum densities at each canopy position were calculated separately for each month and for the low‐, mid‐ and high‐altitude sites.3 During September to November, the highest densities of E. abietinum occurred on 3–4‐year‐old needles on branches low in the canopy. Over the winter and spring, the centre of the aphid’s distribution shifted outward and upward, so that by June of the next year the highest aphid densities occurred on current and 1‐year‐old needles on branches near the top of the tree.4 The aphid distribution was re‐set each year during July, at the time when the nutrient quality of the host was in decline and E. abietinum populations were decreasing. Aphid densities decreased less on 3–4‐year‐old needles than on current and 1‐year‐old needles, suggesting that older needles were a superior food resource at this time of year and in the autumn. However, other factors, such as higher temperatures in the upper canopy during the summer or differential mortality caused by natural enemies, could also have contributed to the change in distribution.5 The outward and upward shift in the aphid distribution over the winter period provided no evidence that aphids at positions lower and deeper in the canopy were better insulated from freezing temperatures and had higher over‐winter survival rates. Mean air temperatures at the top and bottom of the canopy during the winter were also found to differ by only 0.1–0.2 °C.6 The percentage of the total aphids per tree that occurred on current or 1‐year‐old needles varied widely between seasons and between sites. Consequently, sampling programmes designed to estimate total population numbers of E. abietinum have little option but to sample needles throughout the canopy, and at regular intervals during the period when the aphid is abundant.

Biases in LI-COR Plant Canopy Analyzer estimates of seasonal light interception by black spruce and trembling aspen canopies

This article examines four sources of bias in the estimation of seasonal light interception by black spruce (Picea mariana (Mill.) BSP) and trembling aspen (Populus tremuloides Michx.) canopies using the LI-COR LAI-2000 Plant Canopy Analyzer: (i) geometric averaging of gap fractions, (ii) unrepresentative elevation angle intervals for radiation detectors, (iii) assumption of isotropic radiance distribution, and (iv) inclusion of light intercepted by stems in the estimate of canopy light interception. Bias source i caused overestimates of canopy light interception, source ii caused underestimates, source iii caused little bias, and source iv caused overestimates. The magnitude of bias from sources i, ii, and iv increased as fractional light interception by canopies decreased. The average bias in seasonal light interception for all sources combined was 5% for black spruce canopies and 17% for trembling aspen canopies. It is recommended that canopy light interception and understorey light level estimates be calculated in a way to reduce bias from sources i and ii. For estimates of canopy interception alone, bias from source iv should also be reduced.

Tree species ( Picea abies and Fagus sylvatica) effects on soil water acidification and aluminium chemistry at sites subjected to long-term acidification in the Ore Mts., Czech Republic

The effect of European beech ( Fagus sylvatica) and Norway spruce ( Picea abies) on acid deposition and soil water chemistry was studied at a site in the Ore Mts., Czech Republic, that has been subjected to decades of elevated acidic deposition. Dry deposition onto the spruce canopy significantly increased acid input to the soil in comparison to the beech canopy. As a result soil waters were more acidic; Al, SO 4 2 - , and NO 3 - concentrations were significantly higher; and Ca and K concentrations were lower in the spruce stand than in the beech stand. The concentrations of potentially toxic inorganic aluminium (Al in) were, on average, three times higher in the spruce stand than in the beech stand. Thus, Al played a major role in neutralizing acid inputs to mineral soils in the spruce stand. Despite the higher dissolved organic carbon (DOC) concentrations in spruce organic soil solutions, organic Al (Al org) accounted for only 30% of total Al (Al tot), whereas in beech organic soil solutions Al org was 60% of Al tot. Soil waters in the beech stand exhibited Al in concentrations close to solubility with jurbanite (Al(SO 4)OH · 5H 2O). The more acidic soil waters in the spruce stand were oversaturated with respect to jurbanite. The Bc/Al in ratio (Bc = Ca + Mg + K) in O horizon leachate was 4.6 and 70 in spruce and beech stands, respectively. In beech mineral soil solutions, the Bc/Al in ratio declined significantly to about 2. In the spruce stand, mineral soil solutions had Bc/Al in values below the critical value of 1. The observed Bc/Al in value of 0.4 at 30 cm depth in the spruce stand suggests significant stress for spruce rooting systems. A more favourable value of 31 was observed for the same depth in the beech stand. The efficiency of the spruce canopy in capturing acidic aerosols, particulates, and cloud water has resulted in the long-term degradation of underlying soils as a medium for sustainable forest growth.

Long-term effect of elevated CO&lt;sub&gt;2&lt;/sub&gt; on spatial differentiation of ribulose-1,5-bisphosphate carboxylase/oxygenase activity in Norway spruce canopy

Total in vitro activity of RuBPCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) enzyme was assayed spectrophotometrically by the continuous measurement of 3-phosphoglycerate-dependent NADH oxidation in a coupled enzyme system. RuBPCO activities were found in the ranges 1.01–2.76 and 1.23–3.10 µmol(CO2) m−2 s− 1 in current Norway spruce needles growing in ambient (AC) and elevated (EC) CO2 concentration, respectively. RuBPCO activity in AC needles from the upper layer (U) was 11–15 % higher compared to those from the middle (M) layer, and even 44–56 % higher compared to the lower (L) layer of spruce crown. Over the vegetation season, we observed a highly significant decrease of RuBPCO activity in the EC-U needles from 3.10 (July) to 1.60 (October) µmol(CO2) m−2 s−1 as a consequence of downward feedback regulation. Moreover, this down-regulation was not caused by a non-specific decrease in total leaf nitrogen content.

Forests as protection against airborne immissions

The effect of a spruce forest in the Solling-hills (Germany) on the concentration of airborne trace compounds in the atmospheric boundary layer is discussed. The discussion is based on field measurements of vertical concentration profiles and vertical fluxes of reactive trace gases and particles in and above a spruce forest and on numerical modelling. Measured SO 2 -, O 3 - and PAN-concentrations are 10 % to 20 % lower near the forest floor than just above the canopy. NO 2 is emitted from the forest into the atmospheric boundary-layer and NO is transported both from the atmosphere and from the forest floor into the spruce canopy air space. The net NO x -flux between the atmosphere and this spruce forest can be neglected compared quantitatively to other N-fluxes. Numerical experiments using two models show that a 1000 m long spruce forest reduces the near surface concentration of an airborne trace substance with a deposition velocity of about 0.7 cm/s by up to 6 % as compared to the upwind SO 2 -concentration. If a forest is replaced by a meadow the SO 2 -concentration at the former downwind side of a forest increases by about 10 %.

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.

Direct measurements of CO 2 flux below a spruce forest canopy

We applied the eddy covariance technique below the canopy of a mature Norway spruce ( Picea abies) forest in SE Germany, with a dense ground cover of the grasses Calamagrostis villosa and Deschampsia flexuosa. Measurements were carried out during three field campaigns between May and November 1999. Data quality analysis led to the exclusion of around 61% of flux measurements. Chamber measurements of soil CO 2 efflux at the same site showed that the micro-meteorological measurements systematically under-estimate the night-time CO 2 efflux on average by about 41%. By correcting the eddy covariance flux on the basis of chamber measurements, flux measurements over a larger area could be obtained, and so it was possible to calculate the day-time gross assimilation flux for the ground vegetation averaged for each of four 4-week periods. Separation of fluxes according to grass species (by wind sectors) showed no detectable difference in CO 2 flux, but scarcity of data following quality tests meant that comparisons were limited to selected periods only. Light response curves of the corrected flux values indicate different saturation values for the gross assimilation rates in each period, which reflect the phenological development of the grasses, as well as differences in environmental conditions. On the basis of mean day-time assimilation by ground vegetation, the contribution to the total gross assimilation of the stand was estimated as between 3 and 12% at different times of the year. About 30% of the carbon emitted annually as CO 2 from the soil is estimated to be assimilated by the ground vegetation (ca. 170 g C m −2 year −1).

Indirect effects of black spruce (Picea mariana) cover on community structure and function in sheep laurel (Kalmia angustifolia) dominated heath of eastern Canada

Recent studies on phenotypic plasticity of plant traits indicate that within-species variation in litter quality may be a significant factor that feeds back on litter decomposition and nutrient cycling rates at the stand level. These findings may be especially significant for understanding biodiversity-stability relationships in species-poor ecosystems that have little functional redundancy among primary producers. We tested the null hypothesis that black spruce and Kalmia were functional equivalents with respect to their structuring roles of subordinate vegetation and their influence on site biogeochemistry. The purpose of the study was to determine the degree to which forest cover exerts top-down control on community structure and function of Kalmia-black spruce communities. This community type dominates much of the forest understory and unforested heathlands in Atlantic Canada. We intensively studied a representative stand of Kalmia heath in Terra Nova National Park in eastern Newfoundland. Thirty-two 0.5 m × 0.5 m sample plots were randomly distributed among five transects bisecting gradients in dominance of black spruce and Kalmia. Light levels, species composition, vascular plant cover and soil respiration rate were determined for each plot. Tissue samples of litter, mature and current year leaves of Kalmia were collected and analyzed for nutrient status. Herbaceous species richness and cover peaked at intermediate light levels. Kalmia foliar N concentration and above-ground biomass increased with increasing shade. Soil respiration rates were strongly related to the light gradient and increased with increasing quality of Kalmia litter inputs. Our data indicate that Kalmia’s vigour and foliar nitrogen concentrations are greater under black spruce canopy as opposed to heath condition and that the shaded phenotype has relatively benign feedbacks on soil productivity compared to the open-habitat phenotype. In the absence of functional diversity at the species level in these species-poor habitats, phenotypic plasticity in Kalmia appears to be an important dimension of the biodiversity-stability relationship in these communities since our data suggest that this species has the potential either to inhibit or facilitate carbon cycling and the pathway is strongly linked to the presence or absence of overstory cover. The role of forest regeneration as an indirect control of forest soil processes such as carbon and nitrogen cycling in this ecosystem is discussed.

Importance of mineral nutrition for photosynthesis and growth of Quercus petraea, Fagus sylvatica and Acer pseudoplatanus planted under Norway spruce canopy

The aim of this study was to combine data on photosynthetic performance, growth and mineral nutrition of Quercus petraea, Fagus sylvatica and Acer pseudoplatanus growing six years under a Norway spruce canopy. Three years old saplings were planted on several adjoining plots from the forest edge up to 35 m inside the spruce forest on nutrient poor dystric cambisols. Growth parameters, photosynthetic capacity and leaf nutrition were repeatedly measured on 11 to 13 selected plants for each species every year from 1996 to 2001. The general performance of the plants growing along the light gradient from forest edge into the closed canopy decreased in the order F. sylvatica, Q. petraea and A. pseudoplatanus. The photosynthetic performance of Acer declined from the second year onwards as consequence of low nutrient supply. The plants had in most cases higher leaf nitrogen concentration in shade. This increase going along with declining light input was the best in Quercus and was found in Acer leaves only in the second year after the planting. The growth parameters of all investigated plants were not correlated to the light environment within the range of canopy gap fraction between 0.05 and 0.62. However, the total leaf area as well as nutrient amounts in the foliage were good predictors for total plant height and plant diameter at root collar of Fagus and Quercus, but failed in most cases for Acer. These results emphasise the important role of nutrient acquisition for young broadleaves introduced in Norway spruce stands and underline the different requirements for nutrient supply at the species level.

A functional relationship between species richness of spiders and lichens in spruce

Modern forestry has created stands with even age distribution of trees and fragmentation of the habitat. In boreal forests, the effects on biodiversity within many taxa need to be examined. We tested the hypothesis that species richness of foliose and fruticose lichens and spiders is positively related in the lower canopy of spruce (Picea abies) in forests with, or without, management in central Sweden. High species richness of lichens may increase the structural complexity of the microhabitat on spruce branches, and bring a higher species richness also in the spider community. In six areas, spruce branches were sampled in old-growth and managed boreal forest stands, respectively. Forest management did not affect the species richness of spiders or lichens, but an effect due to sampling area was found in the latter taxon. There was a significant covariation between species richness of lichens and spiders, and the hypothesised positive correlation was confirmed by separate analyses for each area and combining the probabilities. Moreover, regression analysis on mean values from each site revealed a positive relationship. We conclude that species richness of lichens and spiders covary on spruce branches for functional reasons, i.e. more lichen species promotes a more diverse spider community by increasing the structural heterogeneity. Our results might provide a ‘shortcut’ for assessing biodiversity in boreal forests.

Five-year measurements of ozone fluxes to a Danish Norway spruce canopy

Abstract Ozone concentrations and fluxes have been measured continuously during 5 years (1996–2000) by the gradient method in a Norway spruce dominated forest stand in West Jutland, Denmark, planted in 1965. The method has been validated against other methodologies and a relatively good relationship was found. The data are analysed to quantify diurnal, seasonal and yearly fluxes, and non-stomatal and stomatal removal are estimated. Monthly means of climatic data are shown, and day and night values of the aerodynamic resistance, ra, viscous sub-layer resistance, rb, and the surface or canopy resistance, rc, are presented. The yearly ozone deposition is approximately 126 kg ha−1. The canopy ozone uptake is highest during the day and during the summer. This is interpreted as increased stomatal uptake and physical and chemical reactions. The daily means of ozone concentration and fluxes averaged over 5 years correlate, but the correlation is primarily based on two different uncoupled processes outside and inside the stomates: (1) The ozone destruction in the canopy occurring outside the stomates is much influenced by temperature, light and humidity, e.g. surface reactions, NO- and VOC-emissions. (2) The same factors have a strong influence on the stomatal opening, e.g. midday and night closure. Thus, looking at diurnal variations, the diurnal ozone concentration and ozone flux do not correlate at all during the growing season. The maximum diurnal difference for the ozone concentration is a factor 1.3 and the maximum diurnal difference for the ozone flux is a factor 3. From dawn to ca. 8:00 the ozone deposition increases and the ozone concentration decreases. The yearly stomatal uptake of ozone is estimated to minimum 21% of the total deposition, being highest in May–August (30–33%) and lowest in November–February (4–9%). The physiological ozone uptake per leaf area is estimated to 0.33 g ozone m−2 y−1.