Aims Existence of forest gaps affects soil moisture, temperature, and decomposer community structure in forest ecosystem; however, it remains largely unknown how the size of gaps affect litter decomposition. The objective of this study was to determine the rate of mass loss of twigs associated with the closed canopy and forest gaps of different sizes in a subalpine forest of western Sichuan, China.
Methods Three forest gaps (FG1: 255-290 m 2, FG2: 153-176 m 2; FG3: 38-46 m 2) and three plots under a closed canopy in an alpine fir (Abies faxoniana) forest of western Sichuan, China were selected to conduct a litter decomposition experiment. The air-dried samples of A. faxoniana twigs were placed in nylon litterbags (size 20 cm × 20 cm, pore size 1.0 mm), and those litterbags were placed on the forest floor of experimental plots. The experiment was carried out for a period of four years from November 2012 to October 2016. Mass loss rates associated with different forest gaps and closed canopy were estimated every six months.
Important findings Our results showed that there were significant differences in the depth of snow cover, the temperature and the frequency of freezing and thawing cycles on the forest floor associated with the three gaps and a closed canopy. The snow depth and the temperature were highest in the FG1 and lowest under the closed canopy. After four years, the remaining mass percentages of twig were 59.9%, 59.5%, 62.1% and 55.3% for the FG1, FG2, FG3 and the closed canopy, respectively. Correspondingly, the decomposition constant (k) was 0.127, 0.131, 0.120 and 0.135, and the time for 95% decomposition was 23.6, 22.7, 25.0 and 22.2 a for the FG1, FG2, FG3 and the closed canopy, respectively. Compared with the closed canopy, the mass loss rates in the forest gaps increased in the growing season for the first year and the second year, but reduced in the winter for the first year and fourth year. The effects of gap sizes on the mass loss rates varied with the decomposing periods. The mass loss rates increased with the increase of the gap size in the winter during the first year and the third year decomposing, and reduced with the increase of gap size in the growing season in the third year. Also, the percentage of mass loss was the highest in the first year and increased with the gap size. The percentage of mass loss in the winter was higher than that in the growing season. In conclusion, the formation of forest gaps profoundly affects the litter decomposition in the subalpine forest of western Sichuan.