Metadata

Description
The count of leaf losses and gains of R. mangle trees (i.e., leaf count) was monitored using a modified leaf tagging technique (Ross et al., 2001; Ewe et al., 2006) in TS/Ph6b and TS/Ph7b from 2012 to 2021. Foliar Net Primary Productivity (NPPF) was assessed based on observations of leaf losses and gains at ca 6-month intervals (dry and rainy seasons) within the two permanent plots (20 x 20 m, 20 m apart) established in each study site. We sampled leaf count of 5-6 randomly selected branches of individual trees within tree islands located on the corners of the 20 x 20 m plots. A minimum of five trees in each plot were monitored for a total of 20 branches per plot (40 per site). During the first sampling (May 2012), a small plastic cable tie (hereafter referred to as a “ring”) was placed between the distal and a second-to-distal leaf pair on all shoot tips. All leaves, including the distal one, were counted on each branch. At subsequent samplings, leaves of previously marked cohorts were counted, and a new cohort was marked similarly. Senescent leaves in each branch were recorded during each sampling. New branches were incorporated over the study period due to mortality in a few cases.
Beginning in December 2012, the total number of leaves (Tleaves), the rings still caught by the leaves (Rcaught), and the rings that accumulated at the base of the tagged branches (Rloose) were counted separately; after counting, a new ring was placed around each pair of new apical leaves. All leaves lost between samplings were assumed to fall to the ground, given the visible accumulation of senescent leaves under the tree canopy and the lack of leaf damage due to herbivory. Therefore, two methods were used to calculate the number of leaves fell (Fell) to the ground:
Direct count method: DFell = TLeaves (t1) - TLeaves (t0) (1)
Ring count method: RFell = 2 x [ Rloose (t1) - Rloose (t0) ] (2)
where t1 and t0 indicate “current” and “last” sampling, respectively; the multiplicator (2) in equation 2 (ring count method) represents R. mangle opposite leaf arrangement; thus, each ring represents two opposite leaves.
In addition, the number of branches per unit area (m2) in the tree island canopy at each plot (TS/Ph6b Plot 1: 8.05 branches m-2, Plot 2: 8.28 branches m-2; TS/Ph7b Plot 1: 9.38 branches m-2, Plot 2: 8.27 branches m-2) was estimated by randomly harvested four canopy within a 0.6 m x 0.6 m plot in 2017. From each canopy plot, 30 individual R. mangle leaves were randomly collected, oven-dried at 60°C to a constant weight, and weighed to obtain a mean individual leaf dry weight per site (TS/Ph-6: 0.58±0.019 g; TS/Ph-7: 0.58±0.022 g). The annual NPPF was calculated by adding the values obtained in the December (~6 months) and May (~6 months) seasons; the actual sampling period was determined by the duration (days) between two sequential sampling trips and the number of days in a calendar year. A factor of 0.46 was used to convert the annual dry weight of leaves that fell to the ground to NPPF based on the average carbon content determined in the laboratory and previous studies. Mean annual values were obtained by each method in MgC ha-1 yr-1 to account for the uncertainty in measuring NPPF using the leaf count method.
Reference
Ewe, S.M.L., Gaiser, E.E., Childers, D.L. et al. Spatial and temporal patterns of aboveground net primary productivity (ANPP) along two freshwater-estuarine transects in the Florida Coastal Everglades. Hydrobiologia 569, 459–474 (2006). https://doi.org/10.1007/s10750-006-0149-5
Ross, M.S., Ruiz, P.L., Telesnicki, G.J. et al. Estimating above-ground biomass and production in mangrove communities of Biscayne National Park, Florida (U.S.A.). Wetlands Ecology and Management 9, 27–37 (2001). https://doi.org/10.1023/A:1008411103288