Ulf Söderberg

Land-Use and Land-Cover Dynamics in the Central Rift Valley of Ethiopia

Understanding the complexity of land-use and land-cover (LULC) changes and their driving forces and impacts on human and environmental security is important for the planning of natural resource management and associated decision making. This study combines and compares participatory field point sampling (pfps) and remote sensing to explore local LULC dynamics. The study was conducted in two peasant associations located in the central Ethiopian Rift Valley, which is a dry-land mixed farming area exposed to rapid deforestation. From 1973–2006, the area of cropland doubled at the expense of woodland and wooded-grassland in both of the study sites. Major deforestation and forest degradation took place from 1973–1986; woodland cover declined from 40% to 9% in one of the study sites, while the other lost all of its original 54% woodland cover. Our study concludes that assessing LULC dynamics using a combination of remote sensing and pfps is a valuable approach. The two methods revealed similar LULC trends, while the pfps provided additional details on how farmers view the changes. This study documents dramatic trends in LULC over time, associated with rapid population growth, recurrent drought, rainfall variability and declining crop productivity. The alarming nature of these trends is reflected in a decrease in the livelihood security of local communities and in environmental degradation. Given these dry-land conditions, there are few opportunities to improve livelihoods and environmental security without external support. If negative changes are to be halted, action must be taken, including building asset bases, instituting family planning services, and creating opportunities outside these marginal environments.

Diameter Increment in Picea abies Shelterwood Stands in Northern Sweden

In this study, the effect of shelterwood density on radial increment and stem form changes was evaluated after 9 yrs for a trial in a forest in northern Sweden dominated by Norway spruce [Picea abies (L.) Karst.]. Radial increment increased after the shelterwood cut, compared with control stands. The effect was of the same magnitude for sparse and dense shelterwoods. The response started in the third growing season and increased until the seventh season after release. The relative increment response was highest in the lower parts of the tree trunk, which indicates a reallocation of increment during the shelterwood period, causing a slight taper deterioration.

Does Soil Acidification Affect Spruce Needle Chemical Composition and Tree Growth

In 1994, a large survey of soil chemistry was undertaken in thecounty of Värmland in central Sweden (Lundström et al., 1998).The southern part of the county was affected by soilacidification whereas there were no such indications in thenorthern part. To investigate the influence of soil chemistryon the trees at the specific sites, the survey was continued byan analysis of needle chemistry (Norway spruce) which wasundertaken at 150 of the 180 sites, and of tree growth at 65 ofthe 180 sites. Growth was expressed as a ratio between expectedgrowth, estimated with a national, empirical growth model, andthe growth observed in the field. In statistical analyses,using rank correlation, PCA and PLS, there were only weakindications of an influence of soil chemistry on needlechemistry and on tree growth. A moderate correlation betweennitrogen and sulphur in needles was found, which wasinterpreted as an effect of deposition and of processes in thetree canopy. No obvious regional pattern of the growth ratiowas found, in contrast to the clear pattern of soilacidification. The statistical analysis could not with anycertainty point out any of the soil chemistry variables asespecially important for the tree growth ratio.

The choice of definition has a large effect on reported quantities of dead wood in boreal forest

A survey was conducted to assess the impact of the choice of definition on reported quantities of dead wood in Swedish forests, which to more than 90% are located in the boreal zone. The data collection was made on a subsample of the permanent plots of the Swedish national forest inventory. The objects included were standing dead trees and snags down to 5-cm diameter at breast height, dead lying stems and branches down to a threshold diameter of 1 cm and stumps down to a threshold diameter of 5-cm at normal stump height. Standing trees, snags and stumps were inventoried on 10-m radius circular plots while the downed objects were inventoried using both circular plots and line intersect sampling; thin objects (diameter 1–5 cm) were assessed only through line intersect sampling. The results showed that the estimated volume of dead wood was as high as 25 m3 ha−1 when all components were included. With the standard Swedish definition, the corresponding estimate was only 10.9 m3 ha−1, or 43% of the total value. Since definitions of dead wood vary greatly between countries we conclude that great caution must be exercised when figures are compared in connection with international reporting. For example, adding stumps to the Swedish definition would increase the amounts of dead wood from 10.9 to 15.7 m3 ha−1, i.e. with 44%.

Considering costs and revenues in long‐term forecasts of timber yields

In Sweden, long‐term forecasts of timber yields have traditionally dealt with the production of timber, without consideration of costs and revenues. A system for long‐term forecasting (HUGIN) has been further developed with incorporation of calculations of costs for logging and silviculture together with revenues from timber and pulp wood. The forecasts of HUGIN are based on sample plot data from the Swedish National Forest Inventory. After the specification of alternative silviculture and logging programs in HUGIN, the user can study costs, revenues and number of man‐days for each program. By using quality functions and price lists, the HUGIN system calculates the highest possible revenue for the individual tree by optimizing the division into assortments. The HUGIN system will be improved further in the future to include calculations of road transport costs, improved quality functions and revenues from other forest resources than timber.

Monitoring of Forest Biodiversity from Forest Resource Inventory Data

Forest biodiversity has become a new concern for society. It has introduced new regulations and new ways of thinking in areas of forest use and planning. In Sweden the Forestry Act of 1993 states that timber production and maintenance of biodiversity are objectives of equal dignity. This results in a need for monitoring the maintenance of biodiversity in order to know if the policy intentions are followed. The problem of maintenance of biodiversity can be looked at from different scales, such as species, ecosystem, landscape, regional and national.

A diameter growth index method for standardization of forest data inventoried at different dates

A model of tree diameter growth during the growth season was developed to standardize the forest data from different inventory dates. A diameter growth index is defined and its relation with the number of growing days is established. Parameters characterizing this relationship are estimated using accurate tree ring width measurements and other stand and tree related variables from the Swedish National Forest Inventory data for 1989. The residual analyses show that the model is an effective expression of the actual growth and the results are consistent with an earlier used tree growth model. Some climatic data are tested for model improvement, but no essential improvement is gained given the data available.