Effects of Gap-Size Classes on Long-Term Litter Decomposition Rates of Beech, Oak and Chestnut Species at High Elevations in Northeast Turkey

Effects of gap-size classes on litter decomposition rates were investigated in a high-elevation forest for 4 years by placing leaf litter of beech (Fagus orientalis Lipsky.), oak (Quercus robur L.), and chestnut (Castanea sativa Mill.) in (1) a closed canopy, (2) small gaps with a diameter of less than 15 m, (3) intermediate gaps with a diameter of 15-30 m, and (4) large gaps with a diameter of more than 30 m. The leaf litter placed under the closed canopy or within the small gaps decayed more rapidly than those in the intermediate or the large gaps for all three deciduous species. Among the microclimatic and soil factors, soil temperature was most strongly positively correlated with litter decomposition rates, and among the three species, initial lignin concentration was the best predictor of litter decomposition rates. Differences in litter decomposition rates among the four gap-size classes were generally significant, but varied among the three species. Litter with low lignin concentrations tended to be more responsive to canopy openings. Large forest gaps significantly reduced litter decomposition rates in this study by changing environmental conditions, especially by decreasing soil temperature and soil pH which reduced soil respiration rates. These changes may result in reduced nutrient cycling, carbon cycling, and organic matter turnover rates in these forest ecosystems.