Net Primary Production in Tropical Forests: An Evaluation and Synthesis of Existing Field Data

Abstract

Information on net primary production in tropical forests is needed for the development of realistic global carbon budgets, for projecting how these ecosystems will be affected by climatic and atmospheric changes, and for evaluating eddy covariance measurements of tropical forest carbon flux. However, a review of the database commonly used to address these issues shows that it has serious flaws. In this paper we synthesize the data in the primary literature on NPP in old-growth tropical forests to produce a consistent data set on NPP for these forests. Studies in this biome have addressed only a few NPP components, all aboveground. Given the limited scope of the direct field measurements, we sought relationships in the existing data that allow estimation of unmeasured aspects of production from those that are more easily assessed. We found a predictive relationship between annual litterfall and aboveground biomass increment. For 39 diverse tropical forest sites, we then developed consistent, documented estimates of the upper and lower bounds around total NPP to serve as benchmarks for calibrating and validating biogeochemical models with respect to this biome. We developed these estimates based on existing field measurements, current understanding of aboveground consumption and biogenic volatile organic carbon emissions, and our judgment that belowground production is bounded by the range 0.2-1.2 ϫ ANPP (aboveground NPP). Across this broad spectrum of tropical forests (dry to wet, lowland to montane, nutrient-rich to nutrient-poor soils), our estimates of lower and upper bounds on total NPP range from 1.7 to 11.8 Mg C·ha Ϫ1 ·yr Ϫ1 (lower bounds) and from 3.1 to 21.7 Mg C·ha Ϫ1 ·yr Ϫ1 (upper bounds). We also showed that two relationships that have been used for estimating NPP (the Bray-Gorham relationship based on leaf litterfall and the Miami model based on temperature or precipitation) are not valid for the tropical forest biome.

Assessing and Monitoring Forest Degradation in a Deciduous Tropical Forest in Mexico via Remote Sensing Indicators

“…NPP is a forest parameter that is difficult to estimate empirically and can be subject to high levels of uncertainty [43,69,70]. The average values of Net Primary Productivity estimated from the years 2007-2013 in this study are closely comparable to those reported for similar ecosystems elsewhere [71,72]. It is possible to observe from that lower values of NPP were located near urban settlements and agricultural fields.…”

Seasonal Dynamics of Litterfall in a Sub-Alpine Spruce-Fir Forest on the Eastern Tibetan Plateau: Allometric Scaling Relationships Based on One Year of Observations

“…Compared with deciduous angiosperms, evergreen gymnosperms amounted for more than 36.7% of total litterfall. On the one hand, evergreen species are dominant in the coniferous forest [37], and highly dominant species produce more litter per unit area [8,38]. On the other hand, more light energy can be fixed by evergreen species than by deciduous trees [39,40] due to the longer foliage retention time of evergreens under homogeneous climatic conditions [41]; evergreen forests are often considered to be more productive than deciduous forests [6].…”

Variations in Amazon forest productivity correlated with foliar nutrients and modelled rates of photosynthetic carbon supply

“…Underestimation of total net ecosystem exchange using bottom-up approaches for tropical forest can potentially be up to 20 per cent [50]. There are also difficulties in estimating G Ã P from eddy covariance fluxes.…”