Seija Kaakinen

Effects of growth differences due to geographic location and N-fertilisation on wood chemistry of Norway spruce

We studied the effect of long-term nitrogen fertilisation on wood chemistry at two boreal sites in Finland: the northern site (Kemijärvi) and the southern site (Heinola). N-fertilisation was repeated in five-year intervals from the 1960s. Norway spruce (Picea abies L. Karst.) trees that had been planted in 1938 and 1954, in the northern and the southern site, respectively, were harvested in October 2002. Altogether 20 trees, in five different size classes, either unfertilised or fertilised, were felled. Wood sections at breast height, consisting of five consecutive annual rings, from six (Kemijärvi) or five (Heinola) points with different distances from the pith were examined. Differences in growth between the northern and southern sites were marked in favour of the southern site. In the northern site fertilisation had clearly increased the diameter growth, while in the southern site fertilisation had no effect. Nitrogen fertilisation resulted in slight changes in wood chemistry that included increased nitrogen concentrations in the northern site and extractives in the southern site. Stem wood had higher concentrations of extractives, starch, and uronic acids, and lower concentration of cellulose, in the northern than in the southern site. Changes in the stem wood chemistry along radial axis were marked. The changes in wood chemistry are discussed in relation to the physiological function and also how the changes can influence the suitability of wood for different end-use purposes.

Rising Atmospheric CO2 Concentration Partially Masks the Negative Effects of Elevated O3 in Silver Birch (Betula pendula Roth)

Abstract This review summarizes the main results from a 3-year open top chamber experiment, with two silver birch (Betula pendula Roth) clones (4 and 80) where impacts of 2× ambient [CO2] (EC) and [O3] (EO) and their combination (EC + EO) were examined. Growth, physiology of the foliage and root systems, crown structure, wood properties, and biological interactions were assessed to understand the effects of a future climate on the biology of silver birch. The clones displayed great differences in their reaction to EC and EO. Growth in clone 80 increased by 40% in EC and this clone also appeared O3-tolerant, showing no growth reduction. In contrast, growth in clone 4 was not enhanced by EC, and EO reduced growth with root growth being most affected. The physiological responses of the clones to EO were smaller than expected. We found no O3 effect on net photosynthesis in either of the clones, and many parameters indicated no change compared with chamber controls, suggesting active detoxification and defense in foliage. In EO, increased rhizospheric respiration over time and accelerated leaf senescence was common in both clones. We assumed that elevated O3 offsets the positive effects of elevated CO2 when plants were exposed to combined EC + EO treatment. In contrast, the responses to EC + EO mostly resembled the ones in EC, at least partly due to stomatal closure, which thus reduced O3 flux to the leaves. However, clear cellular level symptoms of oxidative stress were observed also in EC + EO treatment. Thus, we conclude that EC masked most of the negative O3 effects during long exposure of birch to EC + EO treatment. Biotic interactions were not heavily affected. Only some early season defoliators may suffer from faster maturation of leaves due to EO.

Resistance of Scots pine wood to Brown-rot fungi after long-term forest fertilization

The susceptibility of Scots pine (Pinus sylvestris L.) sap- and heartwood against the wood decaying brown-rot fungus (Coniophora puteana) was investigated after long-term forest fertilization at three different sites in central Finland. Different wood properties: wood extractives, wood chemistry, and wood anatomy were used to explain sap- and heartwood decay. Scots pine sapwood was more susceptible to decay than its heartwood. In one site, sapwood seemed to be more resistant to wood decay after forest fertilization whereas the susceptibility of heartwood increased. Significant changes in the sapwood chemistry were found between treatment and sites, however, no relationship between wood chemistry and wood decay was observed in the factor analysis. The results of this study show that there was an inconsistent relationship between decay susceptibility and fertilization and the measured physical and chemical attributes of the wood were not consistently correlated with the decay rate.

Effects of timing and intensity of thinning on wood structure and chemistry in Norway spruce.

Abstract The effects of thinning intensity on wood structure and chemistry of Norway spruce [Picea abies (L.) Karst.] have been studied in a long-term thinning experiment established in the 1960s in south-western Sweden. The experiment comprised datasets of unthinned control trees and trees of four thinning treatments, in which thinning operations of different intensities were carried out. These thinning operations were applied either once, three, or five times over the course of the stand rotation. Thinning intensities varied from 0% to 60% based on the stand basal area (BA) before thinning: (A) 5×20% (i.e., 20% of the BA removed five times); (B) 3×40% (i.e., 40% of the BA removed three times); (C) 1×60% (i.e., 60% of the BA removed once); and (D) 5×40% (i.e., 40% of the BA removed five times). Altogether 60 trees that were 67 years old were sampled 38 years after the treatment onset. Radial growth rate, wood density, tracheid properties, and the chemical composition of wood were studied in detail. All four thinning treatments increased growth rate and decreased wood density; however, treatment D showed the greatest change. Single, heavy thinning in treatment C resulted in unfavourable intra-stem variation in ring width and wood density. No significant differences in tracheid properties and wood chemistry were found between the treatments. We conclude that only a remarkable increase in growth rate would induce detrimental changes in tracheid properties and wood chemistry in the context of thinning.