Epsilon Archive for Student Projects

Abstract

The occurrence of epiphytic vegetation in temperate and boreal forest is a fairly recent phenomenon. Epiphytic algae have increased especially on Norway spruce (Picea abies L.Karst.) needles in the southern part of Scandinavia and in Central Europe. The algae present on spruce needles are mainly green algae and take their nutrients directly from rainwater and air. Thick layers of algae may accumulate over several years. The colonisation of the needles by the algae may cause different problems for the vitality of the tree. The most probable repercussion is the reduction of photosynthetic active irradiation available to the needles.

In this report the correlation between the algae and the main site factors, such as climate, atmospheric deposition of nutrients and acidifying compounds, soil properties, site hydrology and indices for vegetation productivity, were evaluated. In addition, the description of the individual tree and its vitality were considered. The algae variables used were the youngest needle colonized and coverage of needle in percent. The data used were obtained from the Swedish National Survey of Forest Soils and Vegetation, the National Forest Inventory and the Swedish Hydrological and Meteorological Institute and collected between 1993 and 2000. The total number of plots was 4055, covering the whole forested area in Sweden. The correlation was evaluated using multivariate statistical analysis, in particular principal component analysis and the analyses were made on three datasets. Each dataset was further divided into four groups, according to the geographic position and to the presence of algae, to study different rapports between the variables. The results showed that the most important factors for algae growth are climatic conditions and atmospheric deposition. Temperature is the most important climatic factor. The growth of algae seems to be inhibited up to a certain temperature sum threshold of between approximately 1100 – 1300 day degrees. Under Swedish climatic conditions, humidity does not seem to be a limiting factor for algae. Many plots with algae were found in areas with low humidity. However, it may act as a contributing factor. In favourable climatic conditions, atmospheric deposition could play the principal role for algae colonisation, acting as a limiting factor and as an accelerator. The correlation with the other variables is quite weak. The local variability of different factors, such as vicinity to nutrient sources or structure of the stand, could also play an important role for the algal colonisation. The algae show a clear geographic distribution that coincides well with climatic and deposition gradients in the country. The northward sharp decline of algae corresponds approximately to Limes norrlandicus. In addition to the correlation evaluation between variables, a partial least square regression model was calculated to try to predict the algae growth using measured values of the variables describing site factors. The prediction ability of the model was not very high. This is probably a result of local factors not covered in the present investigation The investigation of the temporal variation of algae showed a slight tendency to decrease over the period 1995 to 2000.