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

曾勝華(Sheng-Hua Tseng) ； 曾喜育(Hsy-Yu Tzeng)

《林業研究季刊》 38卷4期 (2016/12) Pp. 227-240

摘要

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。雪山黑森林觀測期內的平均孔隙面積介於59.27-105.07 m^2，孔隙面積覆蓋率介於2.79-4.87%，中小型孔隙（＜150 m^2）約佔90%，為典型以小尺度干擾為主體的森林。孔隙動態指數中，2001-2013年的孔隙形成率為0.11%，孔隙鬱閉率0.28%，孔隙有逐漸轉為鬱閉的現象，冠層轉換時間為258年；變遷分析中，2001-2013年間93.24%的冠層保持鬱閉，僅1.10%維持孔隙狀態。研究區內51-57%的孔隙位於北向坡（迎風坡），高於北向坡於研究區域所佔的比例（42.46%），孔隙的空間分布受地理位置所影響。2009-2013年颱風的平均最大風速、平均最大陣風風速、平均累積雨量均高於2001-2013年，並造成較高的孔隙形成率（0.33%），本研究證實颱風造成的孔隙干擾影響著臺灣亞高山冷杉林內的冠層動態變化。

關鍵字

正射航照影像 ； 雪山 ； 臺灣冷杉 ； 亞高山林 ； 孔隙動態 ； 空間分布 ； 颱風

並列摘要

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 m^2. Small and medium gaps (＜150 m^2) were the dominant gap disturbances (90%) in the Kawakami fir forest. The gap dynamic indices were determined that the gap formation rate was 0.11%, gap closure rate was 0.28%, and canopy gaps were closed gradually. Canopy-turnover time was 258 yrs., and transition analysis indicated that 93.24% of the study area remained 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 influencing the gap dynamics of the canopy in the subalpine Kawakami fir forest.

並列關鍵字

aerial orthophoto ； Xue Mountain ； Abies kawakamii ； subalpine forest ； gap dynamic ； spatial distribution ； typhoon