Effects of forest gap size on initial decomposition of twig litter in the subalpine forest of western Sichuan, China

doi:10.17521/cjpe.2017.0186

Abstract

Abstract:

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.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201801004

Key words: forest gap, twig, mass loss, subalpine forest

GUO Cai-Hong, YANG Wan-Qin, WU Fu-Zhong, XU Zhen-Feng, YUE Kai, NI Xiang-Yin, YUAN Ji, YANG Fan, TAN Bo. Effects of forest gap size on initial decomposition of twig litter in the subalpine forest of western Sichuan, China[J]. Chin J Plant Ecol, 2018, 42(1): 28-37.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2017.0186

https://www.plant-ecology.com/EN/Y2018/V42/I1/28

Figures/Tables 9

Table 1 Basic characteristics of forest gaps in the subalpine forest of western Sichuan

林窗类型 Gap type	林窗面积(m²) Area of gap	林窗形成木 Species of gap maker	林窗边界木 Species of gap border	林窗形成方式 Causes of gap
FG1	255-290	岷江冷杉, 高度以20-30 m为主, 胸径以40-70 cm居多 Abies faxoniana with height and diameter at breast height ranging between 20 and 30 m and between 40 and 70 cm, respectively	岷江冷杉、红桦, 高度以20-30 m为主, 胸径以40-60 cm居多 Abies faxoniana and Betula albo-sinensis with height and diameter at breast height ranging between 20 and 30 m and between 40 and 60 cm, respectively	折干, 枯立 Breakage at trunk, standing death
FG2	153-176
FG3	38-46

Table 2 Initial quality in twig litter of Abies faxoniana (mean ± SE, n = 5)

有机碳(g·kg^-1) Organic carbon (C)	总氮(g·kg^-1) Total nitrogen (N)	总磷(g·kg^-1) Total phosphorus (P)	木质素(%) Lignin	纤维素(%) Cellulose	碳:氮 C:N	碳:磷 C:P	氮:磷 N:P	木质素:氮 Lignin:N
441.8 ± 10.7	8.11 ± 0.20	0.7 ± 0.1	32.4 ± 1.7	23.8 ± 1.2	54.4 ± 0.9	657.4 ± 21.4	12.1 ± 0.4	41.7 ± 0.8

Fig. 1 Snow depths associated with the forest gaps and the closed canopy in the subalpine forest of Western Sichuan (mean ± SE). Different lowercase letters indicate significant differences among the three forest gaps and the closed canopy. FG1, 255-290 m2; FG2, 153-176 m2; FG3, 38-46 m2; CC, closed canopy.

Fig. 2 Mean surface temperature and frequency of freeze-thaw cycles in the litterbag associated with the forest gaps and the closed canopy in the subalpine forest of Western Sichuan (mean ± SE). Different lowercase letters indicate significant differences among the three forest gaps and the closed canopy. FG1, 255-290 m2; FG2, 153-176 m2; FG3, 38-46 m2; CC, closed canopy. 1W, the first winter; 1GS, the first growing season; 2W, the second winter; 2GS, the second growing season; 3W, the third winter; 3GS, the third growing season; 4W, the fourth winter; 4GS, the fourth growing season.

Fig. 3 Water holding capacity of twig litter associated with the forest gaps and the closed canopy in the subalpine forest of Western Sichuan (mean ± SE). Different lowercase letters indicate significant differences among the three forest gaps and the closed canopy. FG1, 255-290 m2; FG2, 153-176 m2; FG3, 38-46 m2; CC, closed canopy. 1W, the first winter; 1GS, the first growing season; 2W, the second winter; 2GS, the second growing season; 3W, the third winter; 3GS, the third growing season; 4W, the fourth winter; 4GS, the fourth growing season.

Fig. 4 Mass remaining of twig litter associated with the forest gaps and the closed canopy in the subalpine forest of Western Sichuan. Different lowercase letters indicate significant differences among the three forest gaps and the closed canopy. FG1, 255-290 m2; FG2, 153-176 m2; FG3, 38-46 m2; CC, closed canopy. R2adj, adjusted coefficient of determination.

Table 3 Decomposition constant, adjusted correlation coefficient, and time of 50% and 95% decomposition of twig litter in different forest gaps and the closed canopy

林窗类型 Gap type	回归方程 Regression equation	分解系数k Decomposition constant k	调整决定系数 Adjusted coefficient of determination	半分解时间 Time of half decomposition (a)	95%分解时间 Time of 95% decomposition (a)	显著性 Significance
FG1	y = 91.53e^-0.127^t	0.127	0.773	5.458	23.588	p < 0.001
FG2	y = 95.55e^-0.131^t	0.131	0.786	5.291	22.868	p < 0.001
FG3	y = 95.55e^-0.120^t	0.120	0.764	5.776	24.964	p < 0.001
CC	y = 95.55e^-0.135^t	0.135	0.758	5.134	22.191	p < 0.001

Fig. 5 Mass loss rate per 30 days of twig litter associated with the forest gaps and the closed canopy in the subalpine forest of Western Sichuan (mean ± SE). FG1, 255-290 m2; FG2, 153-176 m2; FG3, 38-46 m2; CC, closed canopy. 1W, the first winter; 1GS, the first growing season; 2W, the second winter; 2GS, the second growing season; 3W, the third winter; 3GS, the third growing season; 4W, the fourth winter; 4GS, the fourth growing season.

Fig. 6 Percentage of mass loss at different sampling stages associated with different forest gaps and the closed canopy in the subalpine forest of Western Sichuan. FG1, 255-290 m2; FG2, 153-176 m2; FG3, 38-46 m2; CC, closed canopy. 1W, the first winter; 1GS, the first growing season; 2W, the second winter; 2GS, the second growing season; 3W, the third winter; 3GS, the third growing season; 4W, the fourth winter; 4GS, the fourth growing season.

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