Journal of Conference Abstracts

Estimate of State and Change in Tree Bioelements
in Small Catchments

Qinghong Liu (Qinghong.Liu@ma.slu.se) & Sven Bråkenhielm (Sven.Brakenhielm@ma.slu.se)

Department of Environmental Assessment, SLU, Box 7050, S-750 07 Uppsala, Sweden.

Trees contains a large and active pool of chemical elements in forested catchments. Changes in tree biomass, in which chemical elements are taken up, stored and released, greatly affect catchment biogeochemical processes.

Within the Swedish Integrated Monitoring tree populations in three catchments (Reivo, Tiveden, Berg) under different air pollution regimes were followed for 12 years on systematically distributed circular plots. At five year intervals diameter at breast height (dbh) of all trees was measured; tree height was estimated from dbh by height regression. Species-specific biomass of different tree compartments was calculated from dbh and height using equations from literature. The circular plots within each catchment were classified into different stand types based on tree species composition and abundance. Biomass density (kg ha^-1) was then obtained on the three levels, i.e. tree compartment, species and stand type. The total biomass element pool of each catchment was then calculated using species-specific element concentrations in tree compartments, obtained from the literature, extrapolating to whole trees of different species, and then to the stand. The area of each stand in a catchment was measured and the pools of elements from all stands summed. Tree biomass has increased in all three catchments during past 12 years. The uptake of N was estimated at 1.05, 2.14 and 14.6 kg ha^-1 yr^-1 at the three sites. Atmospheric deposition of N over the period was estimated as 2.36, 6.14 and 13.71 kg ha^-1 yr^-1 at these three sites, respectively. Nitrogen uptake plus runoff is more or less comparable to N inputs in wet deposition at each site (Fig. 1).

Fig. 1. Estimate of mean nitrogen deposition (wet) uptake in biomass (net) and output from drainage at three Swedish IM sites during 1986-1992.