Characterization of glutathione S-transferases in needles of Norway spruce trees from a forest decline stand

Glutathione S-transferases (GST) detoxify many electrophilic xenobiotics, including several volatile organic compounds and pesticides. The GST activity for the conjugation of several xenobiotic substances was isolated from needles of Norway spruce (Picea abies L. Karst.) trees from a forest decline stand in the northern alps. Trees that exhibited different degrees of damage were selected from several stands in an altitude profile. The GST activity toward 1-chloro-2,4-dinitrobenzene (CDNB) in crude protein extracts of needles showed a seasonal pattern with highest activity during summer. The GST activity exhibited a strong dependence on the altitude of the stand showing highest activities in trees growing in the valley and lowest activities in trees growing in the summit regions of the mountain. When cytosolic GST from needles of healthy and damaged trees was purified, trees of healthy appearance exhibited three distinct GST isozymes with activities for the conjugation of CDNB and 1,2-dichloro-4-nitrobenzene (DCNB), whereas severely defoliated trees exhibited four GSTs with additional activity for the conjugation of ethacrynic acid. The main GST isozymes catalyzing the conjugation of CDNB differed in molecular weight, isoelectric point and catalytic properties between damaged and healthy trees.     

The influence of magnesium deficiency on carbohydrate concentrations in Norway spruce (Picea abies) needles

Both short- and long-term effects of Mg deficiency on carbohydrate metabolism were investigated in 6-year-old clonal Norway spruce (Picea abies (L.) Karst.) trees cultivated in sand culture with an optimal supply of nutrients, except for Mg which was supplied at 0.203, 0.041 and 0.005 mM to provide optimal, moderately deficient and severely deficient Mg supply, respectively. Annual changes in carbohydrate concentrations (starch, sucrose, glucose and fructose) were analyzed and diurnal changes were investigated on a single day during the summer. Older needles of trees in the moderate Mg-deficiency treatment developed tip-yellowing symptoms, whereas current-year needles remained green. The severe Mg-deficiency treatment led to pronounced yellowing symptoms in needles of all ages. Increased carbohydrate concentrations were observed before needle yellowing occurred. Diurnal and annual changes in carbohydrates were similar in all treatments; however, carbohydrate concentrations were influenced by Mg supply. In both Mg-deficiency treatments, starch concentrations increased in needles, especially during summer and autumn. Starch accumulation was more pronounced at the beginning of the Mg-deficiency treatments than at the end of the treatments. Sucrose, and to a minor extent, glucose and fructose concentrations tended to increase in response to Mg deficiency. The consequences of Mg deficiency on carbohydrate metabolism are discussed with respect to reduced plant growth and decreased transport rates of carbohydrates to sink organs.     

Ceratocysts polonica inoculated in Norway spruce: Blue-staining in relation to inoculum density,resinosis and tree growth

When Norway spruce trees were inoculated with Ceratocystis polonica, a dose-dependent response was recorded. Local resinosis near the inoculation sites decreased with increasing inoculum density; parallelled by an increasing degree of sapwood staining, and tree mortality. Suppressed trees, and trees showing growth decline appeared more susceptible than trees suffering less competition.     

Fluxes of Ca(2+), K(+) and Cl(-) across the surfaces of detached needles from Sitka spruce trees: pathways and compartmentation

Uptake and efflux of (36)Cl(-), (45)Ca(2+) and (42)K(+) were measured in water-infiltrated detached needles from Sitka spruce (Picea sitchensis (Bong.) Carr.) trees incubated in 1 mol m(-3) KCl or CaCl(2) or 2 mol m(-3) NaCl solutions or in artificial rain water containing mmol m(-3) amounts of these ions. Surface efflux was measured separately from leakage from the cut ends of the needles. Needles loaded with (36)Cl(-) and killed in liquid N(2) before elution displayed a rapid and extensive loss of radioisotope, indicating that mesophyll cell membranes were the limiting factor for (36)Cl(-) exchange. Data for live needles revealed a novel phase of (36)Cl(-) efflux, with an exchange halftime of about 20 min, which was faster than that for either the vacuole or the cytoplasm, but much slower than that for the free space. The novel phase was interpreted as representing diffusion of Cl(-) through the predominantly negatively charged cuticle. Killing needles loaded with (45)Ca(2+) or (42)K(+) also increased efflux relative to that from live needles, but only to a limited degree, indicating that the main factor limiting cation efflux was the cuticle. During the first hours of (45)Ca(2+) uptake, the isotherms displayed a shoulder, indicating that there was a significant Donnan free space phase in the cuticle for Ca(2+). A shoulder was absent from (42)K(+) uptake isotherms because of the preferential adsorption of divalent cations on the exchange sites.     

Photosynthesis,nutrient, growth and soil investigations of a declining Norway spruce (Picea abies) stand in the coastal region of Northern Germany

The research site, Wingst Compartment 123B, is a 68-year-old Norway spruce (Picea abies (Karst.)) stand located in the coastal area of northern Germany. This area receives high atmospheric inputs of ammonium and also has relatively high ozone concentrations (0.061 mg m⁻³).Ten trees were categorized as healthy to slightly damaged (3–29% needle loss) or severely damaged (49–71% needle loss). Apparent net photosynthetic rates were measured on detached branches at light saturation (1000 μE m⁻² s⁻¹). Needles were analyzed for chlorophyll, N, C, Ca, Mg, K, Zn, Mn and Fe.When compared to the healthy-to-slightly-damaged trees, the severely damaged trees tended to have higher rates of net apparent photosynthesis in the 1 and 2-year-old needles and similar rates in the current-year needles. All three needle ages from the severely damaged trees had higher average stomatal conductances to water vapor (g_s. Although the damaged trees had significantly less total chlorophyll in all needle ages sampled, there was no statistically significant difference in the chlorophyll a:b ratio between the healthy and severely damaged trees.Nitrogen contents of the current-year needles were slightly lower in the severely damaged trees. Carbon and calcium levels did not significantly differ between the damage classes, although the average Ca content of all younger needles was generally under the recommended sufficiency levels. The current-year needles of the severely damaged trees had significantly less magnesium (0.42–0.46 mg Mg g⁻¹) than those of the healthy trees, and all trees had Mg values in the deficiency range (< 0.7 mg g⁻¹). The severely damaged trees also had lower average potassium levels in the older needles.The annual volume increment per unit crown surface area declined with increasing crown damage. Trees with a 50% needle loss showed a 62% loss of volume increment.Soil investigations revealed conditions of high soil acidity and poor nutrient capacity. The low pH values (pH < 3.8) in 64% of all samples indicated a high risk of acid toxicity for plant roots in the investigated area.The significance of these results relative to the current ideas concerning forest decline is discussed.     

Irradiance in thinned Norway spruce (Picea abies) stands and the possibilities to prevent suckers of broadleaved trees

Both incoming shortwave radiation (R_g) and photosynthetically active radiation (PAR) in percentage of full daylight were measured at the same time by point and strip sampling in four plots (0.1 ha) of Picea abies (L.) Karst. The standard deviations (%) of R_g and PAR were, respectively, 11.1 and 9.8 at 64 points, 15.7 and 13.9 at 32 points, and 24.7 and 23.8 at 16 points per plot.

A period of at least 40 s per strip (30 m min⁻¹) gives a CV (coefficient of variation) of 30%. There is no significant difference between relative irradiance (RI) estimated by the point method (64 points) and by the strip method (8 strips). Curves of RI (R_g and PAR) and basal area (m² ha⁻¹), diameter sum (m ha⁻¹) and density (stems ha⁻¹) of fifteen trials with different thinning programmes are presented. Irradiance (R_g) in heavily thinned stands was 3–14% of irradiance on an open place. The irradiance, R_g, in extra-heavily thinned stands is 12–27%, and in unthinned stands, 1–3% that of an open place. The R_g curve lies above the PAR curve in all cases. Some practical implications of the study are presented. Heavy thinning of Norway spruce stands gives RI (R_g) values 10% at basal area of 25m² ha⁻¹ which is necessary to minimize development of suckers of broadleaved trees.     

Size, shape and surface morphology of starch granules from Norway spruce needles revealed by transmission electron microscopy and atomic force microscopy: effects of elevated CO(2) concentration

We compared the effects of ambient (350 ppm) and elevated CO(2) concentration (700 ppm) on the size and shape of starch granules in Norway spruce (Picea abies (L.) Karst.) needles during one growing season. Starch granules were isolated from needles by alkaline digestion and analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Measurements made with a particle size analyzer indicated that starch granules ranged between 0.5 and 10 microm. Granule size and shape varied according to needle developmental stage and CO(2) concentration. Generally, elevated CO(2) concentration increased the size of the starch granules. Fine surface structures (< 10 nm in size) studied by AFM were characterized by the presence of protrusions, furrows and pores.     

Long-term photosynthetic acclimation to increased atmospheric CO(2) concentration in young birch (Betula pendula) trees

To study the long-term response of photosynthesis to elevated atmospheric CO(2) concentration in silver birch (Betula pendula Roth.), 18 trees were grown in the field in open-top chambers supplied with 350 or 700 &mgr;mol mol(-1) CO(2) for four consecutive growing seasons. Maximum photosynthetic rates, stomatal conductance and CO(2) response curves were measured over the fourth growing season with a portable photosynthesis system. The photosynthesis model developed by Farquhar et al. (1980) was fitted to the CO(2) response curves. Chlorophyll, soluble proteins, total nonstructural carbohydrates, nitrogen and Rubisco activity were determined monthly. Elevated CO(2) concentration stimulated photosynthesis by 33% on average over the fourth growing season. However, comparison of maximum photosynthetic rates at the same CO(2) concentration (350 or 700 &mgr;mol mol(-1)) revealed that the photosynthetic capacity of trees grown in an elevated CO(2) concentration was reduced. Analysis of the response curves showed that acclimation to elevated CO(2) concentration involved decreases in carboxylation efficiency and RuBP regeneration capacity. No clear evidence for a redistribution of nitrogen within the leaf was observed. Down-regulation of photosynthesis increased as the growing season progressed and appeared to be related to the source-sink balance of the trees. Analysis of the main leaf components revealed that the reduction in photosynthetic capacity was accompanied by an accumulation of starch in leaves (100%), which was probably responsible for the reduction in Rubisco activity (27%) and to a lesser extent for reductions in other photosynthetic components: chlorophyll (10%), soluble protein (9%), and N concentrations (12%) expressed on an area basis. Despite a 21% reduction in stomatal conductance in response to the elevated CO(2) treatment, stomatal limitation was significantly less in the elevated, than in the ambient, CO(2) treatment. Thus, after four growing seasons exposed to an elevated CO(2) concentration in the field, the trees maintained increased photosynthetic rates, although their photosynthetic capacity was reduced compared with trees grown in ambient CO(2).     

Influence of a high Mn supply on Norway spruce (Picea abies (L.) Karst.) seedlings in relation to the nitrogen source

Effects of 3, 25, 100, 200 and 800 microM Mn on biomass and pigment, starch and nitrate concentrations were studied in Norway spruce (Picea abies (L.) Karst.) seedlings grown with either NO(3) (-) or NH(4) (+) as the sole nitrogen source. After 77 days of exposure to 800 microM Mn, shoot growth had ceased in about 50% of the seedlings independently of the N source. Despite high Mn concentrations in roots and shoots of the Mn-treated seedlings, no visible symptoms of Mn toxicity were evident. The rate of root elongation was decreased by treatment with >/= 200 microM Mn when N was supplied as NO(3) (-), but not when it was supplied as NH(4) (+). This difference could be attributed to the higher Mn concentrations in root tips of the NO(3) (-)-grown seedlings compared with the NH(4) (+)-grown seedlings. In Mn-treated seedlings, the concentration of Mg, and to a lesser extent that of Ca, decreased. Depletion of these elements might account for the observed growth depression. Potassium concentrations were similar in the control and Mn-treated seedlings. Treatment of seedlings with 800 microM Mn for 50 days led to several physiological changes: starch accumulated, the concentrations of nitrate and phenolic compounds increased, pigment concentrations decreased, and in vivo nitrate reductase activity in roots was reduced.     

Growth, shoot phenology and physiology of diverse seed sources of black spruce: I. Seedling responses to varied atmospheric CO(2) concentrations and photoperiods

We conducted a greenhouse experiment to determine: (1) if diverse provenances of black spruce (Picea mariana (Mill.) B.S.P.) respond similarly in growth, phenology and physiology to an approximately 300 ppm increase in atmospheric CO(2) concentration, and (2) the influence of photoperiod on both provenance and provenance x CO(2) interaction effects. Seedlings from provenances that originated from the Yukon (63 degrees 34' N, 135 degrees 55' W), British Columbia (58 degrees 47' N, 123 degrees 38' W), Alberta (52 degrees 22' N, 115 degrees 15' W), Newfoundland (50 degrees 54' N, 56 degrees 06' W) and Ontario (48 degrees 59' N, 80 degrees 38' W and 45 degrees 10' N, 77 degrees 10' W) were subjected to growth analysis in greenhouse growth chambers supplied with 712 +/- 93 (SD) ppm CO(2) (elevated) or 394 +/- 59 ppm CO(2) (ambient). Seedlings from Provenances 7000 and 6901 were also subjected to an extended photoperiod treatment and periodically measured for shoot and root gas exchange. In response to a natural photoperiod, southern provenances grew more, broke and set bud later, and partitioned more biomass to shoot versus root than northern provenances. These differences among provenances were influenced by the extended photoperiod treatment but not by the elevated CO(2) treatment. Averaged across all provenances, elevated CO(2) increased seedling final weights by 55%; however, the elevated CO(2) treatment had no effect on the provenance differences in any measured trait. We conclude that the large differences in physiology, phenology and growth among these diverse provenances of black spruce were expressed similarly in both ambient and elevated atmospheric CO(2) concentrations.     

Age effects on Norway spruce (Picea abies) susceptibility to ozone uptake: a novel approach relating stress avoidance to defense

Cumulative ozone (O3) uptake and O3 flux were related to physiological, morphological and biochemical characteristics of Norway spruce (Picea abies (L.) Karst.) trees of different ages. Under ambient CO2 conditions, photosynthetic capacity (Amax) declined in mature trees when cumulative O3 uptake into needles, which provides a measure of effective O3 dose, exceeded 21 mmol m-2 of total needle surface area. A comparable decline in Amax of seedlings occurred when cumulative O(3) uptake was only 4.5 mmol m-2. The threshold O3 flux causing a significant decline in Amax ranged between 2.14 and 2.45 nmol m-2 s-1 in mature trees and seedlings subjected to exposure periods of > or = 70 and > or = 23 days, respectively. The greater O3 sensitivity of young trees compared with mature trees was associated with needle morphology. Biomass of a 100-needle sample increased significantly with tree age, whereas a negative correlation was found for specific leaf area, these changes parallel those observed during differentiation from shade-type to sun-type needles with tree ontogeny. Age-dependent changes in leaf morphology were related to changes in detoxification capacity, with area-based concentrations of ascorbate increasing during tree ontogeny. These findings indicate that the extent of O3-induced injury is related to the ratio of potentially available antioxidants to O3 influx. Because this ratio, when calculated for ascorbate, increased with tree age, we conclude that the ratio may serve as an empirical basis for characterizing age-related differences in tree responses to O3.     

The prospects of silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) Karst) in mixed mountain forests under various management strategies,climate change and high browsing pressure

European Journal of Forest Research - In the Dinaric Mountains, the future of silver fir and Norway spruce appears to be uncertain, especially given the threat of climate change to both species and...     

Responses of foliar gas exchange to long-term elevated CO(2) concentrations in mature loblolly pine trees

Branches of field-grown mature loblolly pine (Pinus taeda L.) trees were exposed for 2 years (1992 and 1993) to ambient or elevated CO(2) concentrations (ambient + 165 micro mol mol(-1) or ambient + 330 micro mol mol(-1) CO(2)). Exposure to elevated CO(2) concentrations enhanced rates of net photosynthesis (P(n)) by 53-111% compared to P(n) of foliage exposed to ambient CO(2). At the same CO(2) measurement concentration, the ratio of intercellular to atmospheric CO(2) concentration (C(i)/C(a)) and stomatal conductance to water vapor did not differ among foliage grown in an ambient or enriched CO(2) concentration. Analysis of the relationship between P(n) and C(i) indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase during growth in elevated CO(2) concentrations. Based on estimates derived from P(n)/C(i) curves, there were no apparent treatment differences in dark respiration, CO(2) compensation point or P(n) at the mean C(i). In 1992, foliage in the three CO(2) treatments yielded similar estimates of CO(2)-saturated P(n) (P(max)), whereas in 1993, estimates of P(max) were higher for branches grown in elevated CO(2) than in ambient CO(2). We conclude that field-grown loblolly pine trees do not exhibit downward acclimation of leaf-level photosynthesis in their long-term response to elevated CO(2) concentrations.     

Selection in a provenance trial of Norway spruce (Picea abies L. Karst) produced a land race with desirable properties

Selections were made within East European Norway spruce provenances in a provenance trial in northern Sweden and the selected clones were grafted in a Norwegian seed orchard mixed with plus trees of local origin. Full-sib families were generated by controlled crosses, producing sets of both inter- and intraprovenance families, which were planted in two short-term and in long-term trials. Measurements were made of frost damage, tree height, annual shoot growth rhythm and lammas shoots, and genetic parameters were estimated. The intraprovenance families from selected trees of East European origin showed the least variation in all traits and had the lowest heritability values. The variation among the intraprovenance families of local origin was large and with the highest estimates of heritability. The means of the provenance hybrid families were intermediate between those of the intraprovenance families. Strong genetic correlations were present between the growth rhythm traits measured, and in the family group of local origin also between these traits and frost damage, as well as for lammas shoots and height. The progenies of the selected parents of East European origin seem to be a desirable land race with less damage, lower percentage of lammas shoots and less variability in growth capacity.     

Assessing the impacts of climate change and nitrogen deposition on Norway spruce (Picea abies L. Karst) growth in Austria with BIOME-BGC

The aim of this paper is to determine whether a detectable impact of climate change is apparent in Austrian forests. In regions of complex terrain such as most of Austria, climatic trends over the past 50 years show marked geographic variability. As climate is one of the key drivers of forest growth, a comparison of growth characteristics between regions with different trends in temperature and precipitation can give insights into the impact of climatic change on forests. This study uses data from several hundred climate recording stations, interpolated to measurement sites of the Austrian National Forest Inventory (NFI). Austria as a whole shows a warming trend over the past 50 years and little overall change in precipitation. The warming trends, however, vary considerably across certain regions and regional precipitation trends vary widely in both directions, which cancel out on the national scale These differences allow the delineation of 'climatic change zones' with internally consistent climatic trends that differ from other zones. This study applies the species-specific adaptation of the biogeochemical model BIOME-BGC to Norway spruce (Picea abies (L.) Karst) across a range of Austrian climatic change zones, using input data from a number of national databases. The relative influence of extant climate change on forest growth is quantified, and compared with the far greater impact of non-climatic factors. At the national scale, climate change is found to have negligible effect on Norway spruce productivity, due in part to opposing effects at the regional level. The magnitudes of the modeled non-climatic influences on aboveground woody biomass increment increases are consistent with previously reported values of 20-40 kg of added stem carbon sequestration per kilogram of additional nitrogen deposition, while climate responses are of a magnitude difficult to detect in NFI data.     

Factors enabling Epinotia granitalis (Lepidoptera: Tortricidae) overwintered larvae to escape from oleoresin mortality in Cryptomeria japonica trees in comparison with Semanotus japonicus (Coleoptera: Cerambycidae)

The factors involved in the successful escape of overwintered larvae of Epinotia granitalis from host oleoresin in the phloem of Cryptomeria japonica were studied. The mortality, period, and body weight of E. granitalis overwintered larvae while feeding on the phloem of C. japonica were compared with the same parameters for Semanotus japonicus larvae. The seasonal fluctuation in the ability of C. japonica to form traumatic resin canals in the phloem was also assessed. The oleoresin mortality of E. granitalis was low compared with that of S. japonicus. Although both species started feeding on approximately the same date in spring, the feeding period of E. granitalis was only about 24 days, showing that E. granitalis faced the danger of host oleoresin for a shorter period than S. japonicus. The larval weight of E. granitalis was consistently greater than that of S. japonicus through the phloem-feeding period of E. granitalis, and the growth rate was also higher in E. granitalis, suggesting that E. granitalis had a better ability to avoid host oleoresin. These results demonstrated that not only the feeding habits, that is, the tendency of a single larva to feed at several sites, but also the shorter feeding period and larger body size were probably the important factors facilitating escape of E. granitalis from host oleoresin mortality. Furthermore, the ability of C. japonica to form traumatic resin canals increased after the starting date of larval feeding in spring. Because E. granitalis finished feeding before the culmination of the ability of C. japonica to form traumatic resin canals, it was likely that the shorter feeding period was the most important factor in enabling E. granitalis to escape from mortality by host oleoresin.     

Kinetics of nitrogen uptake by Populus tremuloides in relation to atmospheric CO(2) and soil nitrogen availability

Sustained increases in plant production in response to elevated atmospheric carbon dioxide (CO(2)) concentration may be constrained by the availability of soil nitrogen (N). However, it is possible that plants will respond to N limitation at elevated CO(2) concentration by increasing the specific N uptake capacity of their roots. To explore this possibility, we examined the kinetics of (15)NH(4) (+) and (15)NO(3) (-) uptake by excised roots of Populus tremuloides Michx. grown in ambient and twice-ambient CO(2) concentrations, and in soils of low- and high-N availability. Elevated CO(2) concentration had no effect on either NH(4) (+) or NO(3) (-) uptake, whereas high-N availability decreased the capacity of roots to take up both NH(4) (+) and NO(3) (-). The maximal rate of NH(4) (+) uptake decreased from 12 to 8 &mgr;mol g(-1) h(-1), and K(m) increased from 49 to 162 &mgr;mol l(-1), from low to high soil N availability.Because NO(3) (-) uptake exhibited mixedkinetics over the concentration range we used (10-500 &mgr;mol l( -1)), it was not possible to calculate V(max) and K(m). Instead, we used an uptake rate of 100 &mgr;mol g(-1) h(-1) as our metric of NO(3) (-) uptake capacity, which averaged 0.45 and 0.23 &mgr;mol g(-1) h(-1) at low- and high-N availability, respectively. The proximal mechanisms for decreased N uptake capacity at high-N availability appeared to be an increase in fine-root carbohydrate status and a decrease in fine-root N concentration. Both NH(4) (+) and NO(3) (-) uptake were inversely related to fine-root N concentration, and positively related to fine-root total nonstructural carbohydrate concentration. We conclude that soil N availability, through its effects on fine-root N and carbohydrate status, has a much greater influence on the specific uptake capacity of P. tremuloides fine roots than elevated atmospheric CO(2). In elevated atmospheric CO(2), changes in N acquisition by P. tremuloides appeared to be driven by changes in root architecture and biomass, rather than by changes in the amount or activity of N-uptake enzymes.     

Effects of climate on radial growth of Norway spruce and interactions with attacks by the bark beetle Dendroctonus micans (Kug., Coleoptera: Scolytidae): a dendroecological study in the French Massif Central

Samples of Norway spruce (Picea abies [L.] Karst) were dendrochronologically investigated in order to detect infestations by Dendroctonus micans (Kug.), the great spruce bark beetle (Col. Scolytidae), a relatively recent introduction to France. Uninfested natural forests located in the north-eastern French Alps and heavily infested plantations in the Ardèche region (Massif Central) were compared. The penetration holes bored in trunks by the bark beetle induced visible marks on wood, such as extreme ring width reductions, locally missing rings and crescent-shaped resin patches between consecutive rings that make possible a post-infestation dating.The outbreak began in 1979, 5 years prior to first insect visual detection by foresters. In the infested forest, tree basal area growth was not as sustained as in uninfested natural stands, but showed an inflection point at an unusually young tree age (from 30 to 40 years). Ring widths showing extreme synchronous radial growth reductions were caused either by excessively cold periods (e.g. in 1948, 1980, 1984, 1992) or by summer drought (as in 1986). Most of these weak growth years were shared with uninfested sites. In healthy forests, the consequences of extremely cold years were usually recorded only in high elevation stands, especially near the timberline, whereas summer drought effects were mostly visible in low altitude forests. By contrast, both phenomena were recorded in the infected Ardèche plantation. An analysis of tree-rings and monthly climate confirmed that Norway spruce growth in Ardèche plantations was reduced by excessively low minimum temperature during most parts of the year prior to ring formation, by higher than average maximum temperature during current spring and summer, and by drought in winter, spring and summer. Thus, the regional Ardèche climate with both cold winters and dry summers (especially in July) seems to weaken spruce trees planted there. Moreover, tree sensitivity to climate was found to be greatly enhanced by insect infestation. Such interactions between climatic stress and insect outbreak led to forest dieback in a 15–20-year period, when trees were still young (less than 70 years), and without any tree recovery. Therefore, in that region spruce plantations should be replaced by non-host species of Dendroctonus micans, especially where soil conditions may exacerbate drought effects.     

Impacts of changing climate on the productivity of Norway spruce dominant stands with a mixture of Scots pine and birch in relation to water availability in southern and northern Finland

A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000-99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (P(nc)) and total stem wood growth (V(s)) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (E(T)) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (W(d)) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce.