## 4 Aboveground Net Primary Production
Litterfall: [7; 53; 55; 56; 58; 60; 61; 65; 66; 67; 71; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 99; 100; 101; 102; 103; 104; 105; 106; 107; 108; 109; 111; 109; 112; 113; 114; 115; 116; 117; 118; 119; 120; 121; 122]. most of the other techniques. Gas exchange measurements are precise and rapid but are subject to the problem of extrapolation errors from a small area to an entire stand; relying solely on gas exchange measurements overestimates the ANPP as it does not account for most tree respiration [8]. Thus, arguably the most accurate method to measure the mangrove ANPP is to combine increments of stem increase with litterfall as it accounts for all, or most, aboveground tree parts. Based on these data, the ANPP averaged 14.3 Mg C ha\({}^{-1}\) y\({}^{-1}\), which is greater than the earlier estimates of 4.1, 5.8, and 8.7 Mg C ha\({}^{-1}\) y\({}^{-1}\) calculated by [PERSON] et al. [123], [PERSON] et al. [4], and [PERSON] et al. [124], respectively. An analysis of tropical forest NPP using the biomass increment/litterfall, radiation-based, and biogeochemical model-based methods shows that the three methods produced similar NPP estimates for undisturbed tropical forests [68]. However, the different methods produced very different patterns of NPP in space and time, which suggested a limited understanding of tropical forest NPP, especially in response to environmental change. Using all the data (see data repository), the rates of aboveground net primary production correlated positively with rainfall (P\({}_{\text{ANPPRainSal}}\) = 0.404, \(p\) < 0.001) after controlling for the positive relationship between rainfall and salinity (P\({}_{\text{RainSal}}\) = 0.326, \(p\) < 0.001). Conversely, ANPP correlated negatively with porewater salinity (P\({}_{\text{RainSal}}\) = \(-\)0.383, \(p\) < 0.001) after controlling for the relationship between rainfall and salinity. Other drivers may affect the mangrove ANPP as they affect GPP, including the forest age, light intensity, species composition, sediment pH and redox potential, nutrient availability, frequency of tidal inundation, disturbance, and geomorphological setting. Several studies have attempted to deduce large-scale and even global patterns in mangrove ANPP, including litterfall [52; 126; 127; 128; 129; 130]. In the neotropics, the mangrove litterfall rates are highest in riverine systems, especially in deltaic coastlines, and lowest in carbonate settings [126]. Unlike at the global level, the interaction between the minimum precipitation and minimum temperature in neotropical mangroves explained most of the variability (40%). Thus, low litterfall rates were predicted for areas with low rainfall, frosts, or no river input, whereas high litterfall rates were associated with higher temperatures and rainfall regimes, an increased tidal exchange, and a high riverine discharge, such as near the major tropical river deltas (e.g., the Amazon, Orinoco). A close positive relationship was observed [127; 128; 129; 130] between the litterfall production and forest age as well as with the basal area, stem density, and canopy height in mangrove plantations, which suggests that the mangrove ANPP increases faster with larger stand sizes. A comparison of the annual litterfall in mangroves and other forests [131] found that mangroves had the highest rates of litterfall (2.9 g C m\({}^{-2}\) d\({}^{-1}\)) and were also greater than found here (Table 1) but with identical bimodal seasonal patterns, with the first peak mainly in spring and the second peak in autumn or early winter; tropical evergreen broad-leaved and rainforests had average litterfall rates of 1.9 g C m\({}^{-2}\) d\({}^{-1}\). Drought and temperature were limiting factors for the mangrove litterfall as both affect porewater salinity and transpiration rates.