Decomposition of cellulose strips in relation to climate, litterfall nitrogen, phosphorus and C/N ratio in natural boreal forests.

Abstract

The decomposition of cellulose strips in relation to climatic variables was studied in a wide range of forested sites with minimal anthropogenic influence. The 22 study sites located in four catchments (61°–69°N in Finland) had stands composed of varying proportions of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karst.) and deciduous species (mainly Betula spp.). The cellulose strips were placed both on and buried in the forest floor of upland and peatland sites for two 1-year periods and the weight loss measured. The decomposition data from all plots had the highest correlations with evaporation of canopy intercepted water, actual transpiration and actual evapotranspiration out of the 17 climatic variables studied. These variables (calculated using SOIL-model) incorporate the effects of climate and vegetation. The decomposition in the Scots pine dominated upland plots was additionally well related to the temperature variables of the frost-free period (May–September mean temperature, temperature sum, soil temperature and July mean temperature) and the number of frost days. Some of the correlations between decomposition and climatic variables are among the highest reported for boreal forests (up to r = 0.98, p <0.001). The nutrients of litterfall were also measured. The weight loss of the cellulose strips, the evaporation of canopy intercepted water and the actual transpiration correlated positively to litterfall amounts of N and P. The same parameters correlated negatively to the litterfall C/N ratio. The results emphasize the need to consider vegetation when effects of climatic factors on decomposition are being studied in boreal forests.