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 4Average 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 INTRODUCTIONReliable estimates of mangrove forest primary production are essential for many ecological studies, and for assessing management options for these in~portant coastal ecosystems. The most reliable estimates of pnmary production come from measurement of biomass accumulation over a suitable period of time This usually involves measurement of the increase in DBH (stem diameter at breast height, ca 1.5 m) of all trees in a plot over a period of 1 to 5 yr. DBH measurements are then converted to biomass using allometric relationships (Ong et al. 1984, Putz & Chan 1986, Clough & Scott 1989. Such measurements are laborious and time consuming, and are generally not well suited to broad scale survey and comparative studies. There is thus a need for simple, survey type methods that can provide con~parative data on a broader scale.A relatively simple survey technique for estimating net photosynthetic production by mangrove forests was described by Bunt et al. (1979). Estimates of net photosynthetic production derived from this technique range from 18 to 34 kg C ha-' d-' (equivalent to 6.6 to 11.3 t C ha-' yr-' or 13 to 25 t dry matter ha-' yr-') for a wide range of mangrove forests in Papua New Guinea and northern Australia (Bunt et al. 1979, Boto et al. 1984

Gas Exchange Analysis for Estimating Net CO2Fixation Capacity of Mangrove (Rhizophora stylosa) Forest in the Mouth of River Fukido, Ishigaki Island, Japan

“…1.3 m) and the single stand biomass (Ong et al, 1984(Ong et al, , 1995Putz and Chan, 1986;Clough and Scott, 1989;Ong, 1993;Matsui, 1998;Komiyama et al, 2005). This measurement is painstakingly hard and time-consuming (Clough et al, 1997), taking up to 1 to 5 years to establish the relationship between the trunk diameter and plant biomass. Thus, this method is not suitable for a large-scale survey and comparative studies involving different species in different areas and climates.…”

“…This is obtained by measuring leaf photosynthetic rates, leaf area index (LAI), and light extinctions in the canopy (Bunt et al, 1979;Boto et al, 1984;Ong et al, 1995;Clough et al, 1997;Clough, 1998). Net canopy productivity can be estimated as the difference between the photosynthetic absorption and the respiratory emission of CO 2 , although canopy respiration has scarcely been estimated.…”

Estimating Mangrove Biophysical Variables Using WorldView-2 Satellite Data: Rapid Creek, Northern Territory, Australia

“…For instance, Clough et al [17] A remote sensing study on LAI in the British West Indies showed a range from 0.8-7.0 with 3.96 as the mean. Statistics from the predicted LAI map of this study with a 5-m spatial resolution (4.2) was as close as previous mangrove studies.…”

“…Clough et al [17], Green and Clark [18] and Green et al [14] established a relationship between vegetation indices derived from remotely-sensed data and in situ LAI samples for mangroves. Kamal et al [15] studied the spatial resolution of satellite images, spectral vegetation indices and different mapping approaches for LAI estimation at Moreton Bay, Australia, and Karimunjawa Island, Indonesia.…”

Assessment of vegetative Phenology with respect to leaf elongation pattern of Avicennia marina and Rhizophora mucronata in Hajambro creek, Indus delta, Pakistan

“…In Australia, the phenology of at least 35 mangrove species has been documented [5,10]. This study is also helpful in understanding the population dynamics of mangroves [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. However, many countries of the world including Pakistan have lost their original mangroves covered area [15,25] mainly due to the deforestation.…”