Seppo Kellomäki

Comparison of two models for predicting the critical wind speeds required to damage coniferous trees

Two independently developed mathematical models (GALES and HWIND) for predicting the critical wind speed and turning moment needed to uproot and break the stems of coniferous trees were compared and the results tested against field data on the forces experienced by forest trees and the wind speeds required to damage them. The GALES model calculates the aerodynamic roughness and zero-plane displacement of a forest stand. The aerodynamic roughness provides a measure of the stress (force/unit area) imposed on the canopy as a function of wind speed and the zero-plane displacement provides a measure of the average height on the tree at which the wind acts. Together they allow a calculation of the bending moment imposed on the tree for any wind speed. Data from almost 2000 trees uprooted during pulling experiments and destructive sampling of green wood then allow the model to make predictions of the wind speed at which the tree will be overturned and at which the tree will break for a number of coniferous species. The model assumes a linear relationship between tree stem weight and the maximum resistive moment that can be provided by the root system and it assumes that the stress in the outer fibres of the stem induced by the wind is constant with height. In the HWIND model the turning moment arising from the wind drag on the crown is calculated assuming a logarithmic upwind profile. Together with the contribution from the overhanging weight of the stem and branches caused by bending of the stem this provides the total bending moment. The angle of stem bend is explicitly calculated from the stiffness of the stem. The breaking strength of the stem and the support given by the root-soil plate are calculated from previous experiments on timber strength, and tree resistance to overturning by using root-soil plate mass to derive the resistive moment. This allows calculation of the wind speed required to break and overturn the tree. Model comparisons were performed for individual Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L.) with varying tree height and stem taper (dbh/height). Tree location was at the forest stand edge on a podzolic soil. Model comparisons gave good agreement for the critical wind speeds at the forest edge required to break and overturn trees with a maximum difference in prediction of 26%. Slightly better agreement was obtained for Norway spruce (mean difference of 10.8%) than Scots pine (mean difference of 12.3%) and the best agreement was for trees with a taper of 100. At higher taper the GALES model generally predicted higher critical wind speeds than the HWIND model whereas at lower taper the reverse applied.

Sensitivity of managed boreal forests in Finland to climate change, with implications for adaptive management

This study investigated the sensitivity of managed boreal forests to climate change, with consequent needs to adapt the management to climate change. Model simulations representing the Finnish territory between 60 and 70° N showed that climate change may substantially change the dynamics of managed boreal forests in northern Europe. This is especially probable at the northern and southern edges of this forest zone. In the north, forest growth may increase, but the special features of northern forests may be diminished. In the south, climate change may create a suboptimal environment for Norway spruce. Dominance of Scots pine may increase on less fertile sites currently occupied by Norway spruce. Birches may compete with Scots pine even in these sites and the dominance of birches may increase. These changes may reduce the total forest growth locally but, over the whole of Finland, total forest growth may increase by 44%, with an increase of 82% in the potential cutting drain. The choice of appropriate species and reduced rotation length may sustain the productivity of forest land under climate change.

Modelling the dynamics of the forest ecosystem for climate change studies in the boreal conditions

Abstract This paper summarizes a forest ecosystem model developed for assessing the effects of climate change on the functioning and structure of boreal coniferous forests under the assumption that temperature and precipitation are the basic dimensions of the niche occupied by any one tree species. Special attention is paid to specifying weather patterns to a level representing the time constant of different physiological and ecological processes relevant to the regeneration, growth and death of trees. The long-term dynamics of the forest ecosystem have been coupled with climatic factors at the level of mechanisms, e.g., photosynthesis and respiration, in terms of the energy flow through the ecosystem. Furthermore, hydrological and nutrient cycles couple the dynamics of the forest ecosystem with climate change through soil processes representing the thermal and hydraulic properties of the soil and the decomposition of litter and humus with the mineralization of nutrients. Simulations for southern Finland (62°N) and northern Finland (66°N) indicated that a transient increase in temperature by 4°C over a period of 100 years could substantially increase soil temperature and reduce soil moisture in forest ecosystems dominated by Scots pine. At the same time, the temperature increase could enhance photosynthetic production and consequent stemwood growth in southern Finland by about 8% and in northern Finland by about 19%. Given the current temperature but elevating CO2 concentration, the increase in photosynthesis in southern Finland could be about 23% and in northern Finland about 21%, but the concurrent elevation in temperature and CO2 concentration increased photosynthesis by about 32% in southern Finland and by about 40% in northern Finland. Transpiration decreased by as much as 10–20% under the changing climate with the consequence that water-use efficiency increased by as much as 25–45%, the higher values representing southern Finland.

Modelling the short-term effects of climate change on the productivity of selected tree species in Nordic countries

A boreal version of the process-based simulation model, BIOMASS, was used to quantify the effect of increased temperature and CO2-concentrations on net primary production (NPP). Simulations were performed for both coniferous (Pinus sylvestris, Picea abies) and deciduous broad-leaves stands (Fagus sylvatica, Populus trichocarpa), growing in different Nordic countries (Denmark, Finland, Iceland, Norway and Sweden), representing a climatic gradient from a continental climate in Finland and Sweden to a maritime in Denmark, Norway and Iceland. Simulations with elevated temperature increased NPP by ca. 5–27% for the coniferous stands, being less for a Scots pine stand growing in a maritime climate (Norway) compared with a continental (central Sweden, eastern Finland). The increase in NPP could largely be ascribed to the earlier start of the growing season and more rapid recovery of the winter-damaged photosynthetic apparatus, but temperature-driven increases in respiration reduced carbon gain. The effect of elevated temperature on NPP was similar in the P. trichocarpa stand on Iceland, mainly caused by an earlier budbreak and a more rapid leaf development in spring. Increased temperature reduced, however, NPP for the F. sylvatica stand in Denmark, since elevated temperature had no effect on budbreak but increased the water deficit and water demand during the summer and lowered photosynthesis. Increased CO2-concentrations had an additional effect on NPP by 25–40% for the conifers and beech, which originated from increased photosynthesis, through enhanced carboxylation efficiency in summer and improved water use efficiency (beech). The effect of elevated CO2 on NPP was somewhat less for the P. trichocarpa by 13%. # 2003 Elsevier Science B.V. All rights reserved.

Effect of grouping of foliage on the within-stand and within-crown light regime: Comparison of random and grouping canopy models

Abstract The effect of grouping of foliage of Scots pine (Pinus sylvestris L.) was studied theoretically and the following results were obtained: 1. (1) grouping of needles and shoots at any level of the canopy compared with the canopy representing horizontal homogeneity decreased the light absorption in the canopy substantially, but; 2. (2) the average light conditions for the lowest part of the canopy were improved by the grouping effect since it enabled more light to pass through the upper layers down to a lower canopy, and; 3. (3) the within-plant shading was in most cases considerably greater than the between-plant shading and, consequently, the light conditions affecting an individual tree were to a high degree determined by the structure of the tree itself, which seemed to be true especially in sparse and/or young tree stands. The silvicultural interpretation of the results regarding the spacing of tree stands is also discussed.

Comparison of a physiological model and a statistical model for prediction of growth and yield in boreal forests

The structural and functional properties of a physiological model (FinnFor) and a statistical model (Motti), developed independently, were analysed in order to assess whether the former would provide the same prediction capacity as the latter, which is based on a huge body of long-term inventory data. The predictions were compared in terms of (i) stand-level variables, (ii) analysis of volume growth graphs, and (iii) stand structure variables (diameter and height distributions). Both unmanaged and managed (thinned) stands of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and silver birch (Betula pendula) growing on medium-fertility sites in central Finland were used for the comparison. In general, the outputs of the models agreed well in terms of relative growth rates regardless of tree species, with the implication that both predict competition within a stand and the effect of position on tree growth in a similar way. The statistical model was stable in its predictions, but not as sensitive to initial stand conditions and management as that based on physiological processes, but the two models agreed well in their dynamics and predictions. The process-based model may therefore be applied to practical management situations, in order to achieve more precise predictions under changing environmental conditions, as in the case of climate warming. On the other hand, some elements of process-model thinking could be incorporated into statistical models in order to make these responsive to changing conditions.

Acclimation of photosynthetic parameters in Scots pine after three years exposure to elevated temperature and CO2

Single Scots pine (Pinus sylvestris L.) was subjected to elevated temperature (year-round elevation), elevated CO2 (elevation from April 15 to September 15) and a combination of elevated temperature and CO2 for three years in open-topped chambers. Using the data obtained from field measurements of gas exchange, Farquhar and von Caemmerers basic equations for photosynthesis of C3 plants were parameterized. The values of the estimated parameters at five ranges of leaf-temperature for trees growing in four different environments are presented and discussed. The estimates of the parameters show that Scots pine grown at elevated CO2 or elevated temperature, compared to those grown in the ambient conditions, did not show significant decreases in the maximum RuP2 (ribulose-1,5-bisphosphate) saturated rate of carboxylation, Vcmax, the maximum rate of electron transport, Jmax, and the ‘day respiration rate’, Rd, within a given range of measuring temperatures (5–25°C). But at high measuring temperature (> 30°C), the elevated CO2 treatment significantly decreased Vcmax and Jmax, whereas the elevated temperature or the combination of CO2 and temperature significantly increased Vcmax and Jmax. Furthermore, elevated CO2 led to a slight leftward drift of the whole temperature-response curves for Vcmax and Jmax; while elevated temperature or the combination of CO2 and temperature led a slight rightward drift of the curves. The model computations show that given a constant intercellular CO2 concentration, Ci (230 or 540 μmol mol−1), there are no significant differences in the maximum rates of assimilation among treatments; when Ci was doubled, the maximum rate of assimilation increased by 28%–34% with no significant differences among treatments.

The scenic value of the forest landscape as assessed in the field and the laboratory

Abstract Kellomaki, S. and Savolainen, R., 1984. The scenic value of the forest landscape as assessed in the field and the laboratory. Landscape Plann. , 11: 97–107. The scenic value of selected forest stands was studied with the help of a questionnaire concerning the actual stands and photographs of the same stands studied in the laboratory. The field and laboratory measurements yielded similar results, suggesting that black-and-white photographs may represent a reliable tool for estimating the scenic value of forest landscapes. The results showed that mature stands of moderate density had the greatest scenic value. This was especially true of coniferous stands with intermixed birches.

Effects of long-term CO2 and temperature elevation on crown nitrogen distribution and daily photosynthetic performance of Scots pine

Abstract Single Scots pines (Pinus sylvestris L.), aged 20–25 years, were grown in open-top chambers and exposed to elevated temperature (Elev. T), elevated CO2 (Elev. C) and a combination of elevated CO2 and temperature (Elev. C + T) for 4 years. The vertical distribution of needle nitrogen concentration was measured simultaneously with gas exchange of attached shoots. Based on the measurements, the dependencies on needle nitrogen concentrations of four photosynthetic parameters, i.e., RuP2 (ribulose 1,5-bisphosphate)-saturated rate of carboxylation (Vcmax), maximum potential electron transport (Jmax), the rate of respiration in the light (Rd) and light-use-efficiency factor (δ), were determined. Using a crown multilayer model, the performance of daily crown photosynthesis in Scots pine was predicted. Compared to the control treatment, the mean concentration of nitrogen in the foliage decreased by 20% and by 17% for trees grown under Elev. C and under Elev. C + T, respectively, but increased by 4% for trees grown under Elev. T. However, the total content of foliage nitrogen per unit ground area increased by 25% for trees grown under Elev. C, by 19% for trees grown under Elev. C + T and by 6% for trees grown under Elev. T; these were due to the increase in the total needle area index. Regressions showed that the foliage grown under Elev. C and Elev. C + T had steeper slopes representing the responses of Vcmax, Rd and δ to leaf nitrogen concentrations, while Elev. C + T and Elev. T had steeper slopes representing the response of Jmax to needle nitrogen concentrations. Predictions showed that, on a typical sunny day, the daily total of crown photosynthesis increased 22% and 27%, separately for Elev. C and Elev. C + T, and by only 9% for Elev. T alone. Furthermore, the increased daily crown photosynthesis, resulting from treatments involving elevated CO2, can be attributed mainly to an increase in the ambient CO2 concentration and the needle area index, while modification of the intrinsic photosynthetic capacity had only a marginal effect. Based on the current pattern of crown nitrogen allocation, the prediction showed also that the relationship between daily crown photosynthesis and crown nitrogen content was strongly dependent on the daily incident PAR and air temperature. The CO2-elevated treatments led to an increase in the sensitivity of daily crown photosynthesis to changes in crown nitrogen content, daily incident PAR and temperature, while the temperature-elevated treatment had the opposite effect on the sensitivity.

Prediction of the amenity of a tree stand

Slides and computer drawings of 100 managed stands were evaluated for scenic beauty and recreational value by 121 people. The size and age of trees increased the beauty and recreation scores as well as a big share of pines and birches. A great number of stems per hectare indicated low amenity. Characteristics describing the tree population explained 70 % of the variation in slide ratings. Ratings of computer illustrations of stands accounted for about the same proportion of the variation in slide ratings indicating that they can be used as successfully as the regression models for estimating the amenity of a tree stand. The ratings of forestry students did not differ from those of biology students nor the ratings of foresters from those of urban citizens.