Dynamics of annual falling debris decomposition and forest floor accumulation

Abstract

The level of forest ecosystems’ productivity and functioning character may be to a great extent explained by its soil cover properties and carbon cycling peculiarity. The fabric and properties of forest ecosystems’ topsoil (designated in Estonia as “humus cover type”, but by Humusica as “humus form”) depends on the dynamics of annual falling debris (AFD) accumulation-decomposition in the forest floor (FF). For characterization of AFD dynamics or its flow throughout the FF into soil or atmosphere, the mean perennial graphical models were used. The comparative analysis of AFD flow and FF formation dynamics was carried out in four forest ecosystems of the temperate zone of the Atlantic-continental region. The studied forest stands were by their layers structure and interrelationships of the system “plant-soil” in stabilized stage. The used data originated from our previous researches on the dynamics of AFD by different fractions and of fractional composition of the FF. The flow of mean aboveground AFD throughout the FF depends on the quantity and dynamics of the AFD, on fractional composition of AFD and on pedo-ecological conditions of decomposition. The lowest decomposition rate was obtained in fresh moder humus cover (by Humusica Hemi- and/or Eumoder) on Glossic Retisols, but the highest, in fresh forest-mull humus cover (by Humusica Eu- and/or Mesomull) formed on Calcaric Cambisols. Due to the low decomposition rate in ecosystems formed on Glossic Retisols, only readily decomposable parts (herbs, leaves) disappear quickly from the newly formed FF. The more resistant parts of AFD accumulate for many years in a half-decomposed state on the surface of mineral soils (or on A-horizon), forming a multi-layered FF. The superficial density of phytogenic origin FF dry mass on Glossic Retisols is in limits of 21.5–24.5Mg ha−1, whereas the mean accumulation coefficient of FF formation varies from 3.35 to 3.44. The mean amount of phytogenic FF on Calcaric Cambisols with mixed spruce forest was 7.6Mg ha−1 and in the oak forest 3.2 Mg ha-1. The accumulation coefficient of FF formation in conditions of fresh forest-mull type humus cover was in the mixed spruce forest 1.50 and in the pure oak forest 0.66. The most important factors of AFD decomposition-mineralization are biological activity and agrochemical status of soil.