Estimating leaf area index and photosynthetic production in canopies of the mangrove Rhizophora apiculata

Abstract

Comparative estimates of the leat area lndex (LAI) of a mangrove folest canopy in Peninsular Malaysia were obtained by 3 independent methods (1) from direct measuremc,nt of canopy leaf area above a prescnbed ground area, (L) trom simple measurements of llght flux den5ity above and beneath the cilnopy (3) from ineasulements of dilect beam transmlttance through the canopy Measurements \ \ L I ~ also made of the rate of net photosynthesis at dlffcront levels In the canopy LAIs obtained by dlrect measurement rangcd from 2 2 to 7 4 over 4 rephcdte O 25 m' quddlats wlth a mean of 4 9 This hiclh deglee of vanabil~ty was attribut1.d pdrtly to the s ~n a l l quadrat size and partly to the spatial h e t e r o q ~~~~c ~~t y of the canopy In contrast est~iilates of LA1 obtained from log averaged measurements of light transmission over a larger area of forest vaned by less than 5% between replicates, with an average of 5 1 Measurements of dilect beam transmlttance y ~e l d e d an average canopy LA1 of 4 4 Average rates of net photosynthesis ranged from 4 pmol CO, m -5 ' at the bottom of the cdnopy to about 10 pmol CO2 m s ' at the top of the canopy The LA1 weighted average rate of net photosynt h e m integrated over the entire canopy was 9 pm01 CO, m-' leaf S ' Assuming an etfcctive daylength of 8 h total dally net photosynthetic carbon f~xation was estimated to be 155 kg C ha I d ' giving a n annual net photosynthetic production of 56 t C he ' yr.' This 1s substantially higher than prev~ously reported for mangrove forests K E Y WORDS. Mangrove. C a n o p y . Leaf area index Photosynthesis