跨海拔生態系初級生產力與營養收支之比較(3/3)

We used hemispherical photography to measure understory light levels and leaf area index of Piluchi conifer forest, Wushiken hardwood forest and Leinhuachi hardwood forest located at high (2200 m), intermediate (1100 m) and low (750 m) elevations, respectively, in central Taiwan. The results indicate that the monthly mean understory photosynthesis photon flux density relative to the open (RPPFD) was lowest in September with 15% (LAI = 3.2) and highest (26%, LAI =2.3) in March and April with annual variation of 11% at Piluchi. The RPPFD of Wushiken reached 15% (LAI = 2.8) and 20% (LAI =2.5) at August and March with annual variation of 5%. At Leinhuachi RPPFD was lowest in July at 16% (LAI =2.8), and highest August reaching 26% (LAI =2.1) with annual variation of 10%. Patterns of light availability differed among the three forests. Although mature conifer forests are often considered of having low seasonal variation in canopy structure but our results indicate that the three forests all have relative higher understory light and similar seasonal variation. The seasonal pattern of understory light environments among the three forests mainly reflects their differences in response to typhoon disturbance and climate conditions. Light availability increased 10% after typhoon disturbance at Leinhuachi hardwood forest but less than 3% at Piluchi. In addition to forest types, the path and intensity of typhoons also played an important role on canopy dynamics and understory light environments. The recovery canopy after typhoon at Leinhuachi is consistent with patterns observed at Fushan forest in northeastern Taiwan. In contrast, the pattern of growth of forest and light availability at Piluchi was consistent with monthly mean temperature. The understory light (LAI) usually reached highest (lowest) during early spring before the start of growing season.