Taneli Kolström

A spatial yield model for optimizing the thinning regime of mixed stands of Pinus sylvestris and Picea abies

This paper presents a distance‐dependent yield model for a mixed stand of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) that accounts for the possible mixture effects...

Modelling the structural growth of Scots pine with implications for wood quality

Abstract A model for simulating the growth and development of individual Scots pines ( Pinus sylvestris L.) is presented in terms of three-dimensional structure of the tree as determined by the influence of local light conditions on branch growth, with implications for the properties of the wood. The basic computational unit for structural growth is the shoot. Each shoot produces new shoots with dimensions related to the amount of direct and diffuse radiation intercepted in the parent shoot and supplied by other shoots in the crown. The calculation procedure utilises the spatial distribution of shoots produced by the growth process (location, azimuth, inclination), and the structure of the shoots determined in terms of the density, angle and length of the needles. The allocation of tree biomass amongst the needles, branches and stem is basically related to the allocation of the growth of forming shoots between the shoot axis and the needles under the control of the hierarchical position of the parent shoot, branch age and the height of the tree. The growth, death and pruning-off of shoots and branches are modelled over the life span of the tree using time step of 1 year, taking special care to identify the location of green and dead knots in the wood. The properties of the stem are further described in terms of the stem form, wood density and heartwood, which are modelled in the context of the overall growth of the tree. The computation produces the three-dimensional distribution of ring widths, density and heartwood in the stem, i.e. from the pith to stem surface and from the stem base to tree top. The model produces quite a realistic crown and stem structure for simulated Scots pines regardless of the life span of the tree. Furthermore, the model is capable of calculating quite accurately, e.g. average wood density values for any section of wood within a tree.

Forest fire history in Viena Karelia, Russia.

The history of forest fires was studied in north-west Russia near the Finnish-Russian border on a total of 22 transects within a 3 x 4 km area, 100 m long and 20 m wide, bydendrochronological methods. In total, 25 fires were identified as having occurred in the area between 1400 and 1998. On average, a fire occurred somewhere within the area once every 23 yrs, and once every 13 yrs between 1650 and 1950. The fire frequency (proportion of the area burnt per time unit) broadly followed the changes in the number of fires, but there were also differences. The fire frequency was 1.87% from 1679 to 1872 and 0.40% from 1873 onwards. The mean fire interval was 62 yrs and the median interval 56 yrs. According to the tree-ring width chronology tree growth was significantly lower in the dated fire years than in other years. Forest fire history in north-west Russia is broadly similar to that in many parts of Scandinavia.

Productivity of mixed stands of Pinus sylvestris and Picea abies

Growth comparisons of different mixtures of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) were based on spatial individual‐tree growth models in which the competition by pines and spruces was accounted for by separate competition indices. The study material represented growing sites of medium fertility. The models indicated that a spruce competitor decreases the growth rate of another spruce clearly more than a pine competitor. The diameter growth of a pine was affected slightly more by another pine than by a spruce of the same size and at the same proximity. According to growth and thinning simulations conducted, a conifer mixture may have a volume increment 10–15% higher than a pure pine or spruce stand with the same stand age and basal area.

Modelling the development of an uneven‐aged stand of Picea abies

A transition matrix model of an uneven‐aged Norway spruce (Picea abies (L.) Karst.) stand is presented. The transition probabilities are based on material from 48 study plots in eastern Finland. The ingrowth of the transition matrix is based on material from 8 study plots and on previous studies. In the model runs the sustainable harvest proportion for 5 years varied between 7 and 20% of the stocking depending on the stand basal area. The shape of the stand diameter distribution had no notable effect on the sustainable harvest proportion. The extension of the thinning interval from 5 to 10 years slightly reduced the total removal during the simulation time.

Clear-cut Detection in Boreal Forest Aided by Remote Sensing

The study compares the applicability of different remote sensing data and digital change detection methods in detecting clear-cut areas in boreal forest. The methods selected for comparisons are simple and straightforward and thus applicable in practical forestry. The data tested were from Landsat satellite imagery and high-altitude panchromatic aerial orthophotographs. The change detection was based on image differencing. Three different approaches were tested: (1) pixel-by-pixel differencing and segmentation; (2) pixel block-level differencing and thresholding; and (3) presegmentation and unsupervised classification. The study shows that the methods and data sources used are accurate enough for operational detection of clear-cut areas. The study suggests that predelineated segments or pixel blocks should be used for image differencing to decrease the number of misinterpreted small areas. For the same reason the use of a digital forest mask is crucial in operational applications.

Model Computations on the Effects of Elevating Temperature and Atmospheric CO2 on the Regeneration of Scots Pine at the Timber Line in Finland

Based on model computations, the regeneration of Scots pine (Pinus sylvestris L.) was studied at the northern timber line in Finland (70°N) in relation to elevating temperature and atmospheric CO2. If a transient increase of 4°C was assumed during the next 100 years, the length of growing season increased from the current 110–120 days to 150–160 days. This was associated with ca. 5°C increase in the soil temperature over June–August with larger variability in temperature and deeper freezing of the soil due to the reduced depth and duration of the snow cover. At the same time, the moisture content of the surface soil decreased ca. 10% and was more variable, due to less infiltration of water into the soil as a consequence of the enhanced evapotranspiration and deeper freezing of the soil. The temperature elevation alone, or combined with elevating CO2, increased flowering and the subsequent seed crop of Scots pine with a decrease in the frequency of zero crops. In both cases, temperature elevation substantially increased the success of regeneration in terms of the number of seedlings produced after each seed crop. The increasing number of mature seeds was mainly responsible for the enhanced regeneration, but increasing soil temperature also increased the success of regeneration. The soil moisture was seldom limited for seed germination. In terms of the density of seedling stands, and the height and diameter growth of the seedlings, the establishment of a seedling stand was substantially improved under the combined elevation of temperature and CO2 in such a way that the temperature increased the number of mature seeds and enhanced germination of seeds and CO2 increased seedling growth. Even under the changing climatic conditions, however, the growth of the seedling stands was slow, which indicated that the northward advance of the timber line would probably be very slow, even though regeneration was no longer a limiting factor.

A palaeotemperature record for the Finnish Lakeland based on microdensitometric variations in tree rings

X-ray based tree-ring data of maximum latewood densities (MXD) was combined for south-eastern Finland. This data originated from subfossil and modern pine (Pinus sylvestris L.) materials comprising a continuous dendroclimatic record over the past millennium. Calibrating and verifying the MXD chronologies against the instrumental temperature data showed a promising opportunity to reconstruct warm-season (May through September) temperature variability. A new palaeotemperature record correlated statistically significantly with the long instrumental temperature records in the region and adjacent areas since the 1740s. Comparisons with tree-ring based (MXD and tree-ring width) reconstructions from northern Fennoscandia and northern Finland exhibited consistent summer temperature variations through the Medieval Climate Anomaly, Little Ice Age, and the 20th century warmth. A culmination of the LIA cooling during the early 18th century appeared consistently with the Maunder Minimum, when the solar activity was drastically reduced. A number of coolest reconstructed events between AD 1407 and 1902 were coeval to years of crop failure and famine as documented in the agro-historical chronicles. Results indicate an encouraging possibility of warm-season temperature reconstructions using middle/south boreal tree-ring archives to detail and enhance the understanding of past interactions between humans, ecosystems and the earth.

A stochastic spatial regeneration model for Pinus sylvestris

A simulation model of pine regeneration is presented, based on earlier models and research for natural regeneration of Scots pine in Finland. The model is stochastic, reflecting the unpredictable variation in regeneration results observed in nature. Geographic area, site and stand characteristics and soil preparation affect the simulated regeneration result. The model predicts the amount and quality of seed crop, germination and predation of seeds, and survival and growth of seedlings. The effect of parent trees on seed dispersal, and growth and survival of seedlings is accounted for. At the stand level, the model gives results similar to empirical measurements. The simulation example provided illustrates the effect of density and spatial distribution of the parent tree stand on the regeneration result.

Simulation of the development of Norway spruce stands using a transition matrix

Abstract The transition-matrix model was applied to a Norway spruce selection forest grown under Finish conditions. The transition probabilities depended on stand density according to a model which was estimated by using empirical single-tree growth models. The dynamics of small seedlings was modelled by adding a separate size class for them to the matrix model. A computer program with comprehensive output was prepared for making simulations. According to the simulations, the selection forest is insensitive to small changes in management and the model is insensitive to small errors in parameters. The volume production of a selection forest is inferior to that of an even-aged stand.