以正射航照影像評估雪山亞高山林孔隙動態

Assessing the Gap Dynamics in a Subalpine Forest on Xue Mountain through Aerial Orthophotos

本研究以正射航照影像判釋冠層孔隙，探討臺灣亞高山林內的孔隙動態變化。研究區域位於雪山黑森林雪東線步道7.8-8.9 K處，海拔3,249-3,421 m，面積約38.59 ha，地被層以苔蘚類為優勢的臺灣冷杉（Abies kawakamii）純林。透過地理資訊系統判釋12年（2001-2013）間的航照影像，並劃為兩個年度區間（2001-2009, 2009-2013）進行比較。 The study area (approximately 38.59 ha) is a typical subalpine forest on the East Xue trail (7.8-8.9 K) on the north slope of Xue Mountain (3,249-3,421 m AMSL), which is dominated by endemic Kawakami fir (Abies kawakamii) and moss ground cover. Aerial photographs taken over 12 yrs. (2001- 2013) were analyzed using geographic information system technology and separated into two periods (2001-2009 and 2009-2013). The total gap areas of the 2001-2009 and 2009-2013 periods were 2.79% and 4.87%, respectively, and the mean gap area was 59.27-105.07 m2 . Small and medium gaps (closed, and only 1.10% remained opened. These results suggested that the spatial distribution of gaps varied according to geography. Of all the gaps observed, 51-57% appeared in the north aspect (windward), which was higher than the percentage of the study area occupied by the north aspect area (42.46%). In addition, the higher gap formation rate (0.33%) occurred during 2009-2013 when the average maximum wind speed, average maximum gust speed, and average cumulative rainfall during typhoons were stronger than they were during 2001-2009. Our research showed that typhoons were the most critical environmental factor infl uencing the gap dynamics of the canopy in the subalpine Kawakami fi r forest.