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Equiangular elliptic sector method, an improved approach to estimate forest gap size

HU Li-le1,2; ZHU Jiao-jun1; TAN Hui1,2; YU Li-zhong1; HU Zhi-bin1,2; ZHANG Jin-xin1   

  1. 1Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;
    2Graduate University of Chinese Academy of Sciences, Beijing 100039, China
  • Received:2006-10-09 Revised:1900-01-01 Online:2007-03-15 Published:2007-03-15

Abstract: Gap size is one of the important characteristics of forest gaps, and an important index for characterizing the light penetration and resource availability within forest gap. Therefore, it is of significance to measure gap size conveniently and accurately. One kind of the most commonly used methods in measuring gap size is to measure the distance from gap center to its edge along eight or sixteen compass directions, and then, estimate gap size approximately as a siogon. In this paper, this kind of method is called siogon methods (SMs), including equiangular octagon method (EOM), equiangular sixteen-gon method (ESM), and equiangular quadrangle method (EQM). Although EOM has less precision, it has been used more universally than ESM, because of its less time-consuming. Previous studies indicated that both EOM and ESM underestimated gap size, and thus, an improved approach was proposed in the present paper, i.e., using the same data sets to calculate the gap size approximating forest gap as 8 or 16 equiangular elliptic sectors. This improved method was named as equiangular elliptic sectors method (EES), which involved 8-equiangular elliptic sector (8-EES) and 16-equiangular elliptic sector (16-EES). Paired t-test indicated that the gap size estimated by ESM was significantly larger than that estimated by EOM and EQM, with an average of 10.96% and 61.66% increment respectively. The gap size estimated by 16-EES was significantly larger than that estimated by ESM, with an average of 1016% increment, while 8-EES had no significant difference with 16-EES, but had significant difference with EOM. Moreover, there was a significant difference between the gap size estimated by EOM with two data sets (the octagons were formed with eight different compass directions), but not for 8-EES. Therefore, it is recommended that gap size could be better estimated by 8-EES.

Key words: Gossypium hirsutum, Physiological development time, Simulation model