The role of local differences in pollutant deposition on spruce growth dynamics at selected mountain ridges in Poland

Introduction

The main goal of this study is to reveal that existing spatial differences in spruce growth dynamics are controlled in considerable extent by atmospheric pollutant deposition, which by itself shows large spatial and temporal variations. Some results of experiments conducted in mountainous regions in the Central Europe indicate that such dependence really exists and the largest spatial variations of forest degradation stem from direct deposition of fog/cloud droplets called also ‘fog drip' or ‘horizontal precipitation'. In places where pollutant deposition via fog is considerable and locally even larger than that via precipitation i.e. in the belt of subalpine spruce forest, this dependence is especially strict. On the other hand the spatial variations of precipitation related deposition have surprisingly little influence on the observed spruce growth dynamics. According to some experiments the width of annual increments at spruce trees in lower subalpine zone is related mainly to a given tree age rather than to pollutant deposition field. Another substantial task is to demonstrate the influence of changing pollutant deposition rates over the last 60 years on spruce growth dynamics.

Methodology

One of the most important research methods, which enable trees condition inventory and reconstruction of the growth dynamics in the past, is dendrochronology. This method allows the analysis of present and past tree health condition, which is extremely important in the context of strongly changing pollutant deposition structure and efficiency. The study area will contain selected Central European mid-mountain ranges located on Polish territory: Karkonosze Mts., Izera Mts., Orlickie and Bystrzyckie Mts., Table Mts., Śnieżnik Massif, Beskid Śląski i Żywiecki, Gorce Mts. and the Tatra Mts. (as a representation of the high mountains). These areas are currently covered in large extent by coniferous mountain forests with diverse degree of damage and unequal defoliation rate, preasumably related to spatial differences in pollutant deposition.

Questions

The research allow to recognize the scale, structure and mechanisms of atmospheric pollutant deposition and then to understand the relationships between deposition field and detrimental changes in subalpine spruce ecosystems. In the context of changes in pollutants emission and deposition observed during last decades, it is particularly important to examine: how the dynamics of spruce have changed; have these ecosystems come back to equilibrium after ecological disaster; in which extent still observed local outreaching of critical loads - particularly in case of total nitrogen at sites with the enhanced fog deposition – consists a limiting factor for spruce forest growth. The identification of a strong signal at forest stands exposed to intense fog deposition will contribute to better understanding of this interaction as well as its temporal variations. The most intense forest destruction was observed at the sites with effective fog deposition: upper parts of western to north-western slopes (windward to prevailing airflow) and at forested mountain summits. Further deforestation was stopped in the mid-1990s, after substantial reduction of anthropogenic emission, mainly from neighboring large power plants.

Results

The health status of the drilled trees is closely correlated with the spatial variability of fog deposition, showing only slight growth reductions at foothill reference sites where fog deposition is negligible. The ratio of annual growth in 1980s to 1950 is as low as 0.2-0.3 at the windward subalpine sites. In the subalpine spruce forests at leeward, eastern slopes growth reduction is significantly smaller, reaching 0.5-0.6 of the 1950s value. It is also interesting that for the last two decades a significant regeneration of conifers has been observed. Concluding, dendrochronological methods appear to be decisive for testing the hypothetical role of fog deposition for the health status of montane Norway spruce stands.