Leaf area index measurements at the middle reaches of Heihe River forest sites

Leaf area index (LAI) is one of the most important parameters of canopy structure as it related to many biophysical and physiological processes, including photosynthesis, respiration, transpiration, carbon cycling, rain intercepting, net primary productivity, energy exchanging etc. Rapid, accurate and reliable estimations of LAI are required in these studies above. There are two main categories of procedures to estimate LAI: direct and indirect methods. The objective of this study is to evaluate LAI estimations obtained by different methods in HeiHe River forest sites. These methods include the LAI-2000 plant canopy analyzer, HemiView, fifty-seven degree photography method, fisheye photography method, the tracing radiation and architecture of canopies (TRAC), and Multi-Purpose Canopy Observation System (MCOS). HemiView shows a large variation on gap fraction measurements compared to LAI-2000, fifty-seven degree photography method is the superior choice to provide initial LAI values compared to other methods. To determine the non-photosynthesis elements and foliage clumping effects for optical methods, a new device named MCOS (Multi- Purpose Canopy Observation System) and TRAC were used. Finally, the results show that with the combination of MCOS or TRAC and LAI-2000 or hemispherical photography can provide accurate and efficient LAI values.