Measuring Net Primary Production in Forests: Concepts and Field Methods

Abstract

There are pressing reasons for developing a better understanding of net primary production (NPP) in the world's forests. These ecosystems play a large role in the world's carbon budget, and their dynamics, which are likely to be responding to global changes in climate and atmospheric composition, have major economic implications and impacts on global biodiversity. Although there is a long history of forest NPP studies in the ecological literature, current understanding of ecosystem‐level production remains limited. Forest NPP cannot be directly measured; it must be approached by indirect methods. To date, field measurements have been largely restricted to a few aspects of NPP; methods are still lacking for field assessment of others, and past studies have involved confusion about the types of measurements needed. As a result, existing field‐based estimates of forest NPP are likely to be significant underestimates. In this paper we provide a conceptual framework to guide efforts toward improved estimates of forest NPP. We define the quantity NPP* as the summed classes of organic material that should be measured or estimated in field studies for an estimate of total NPP. We discuss the above‐ and belowground components of NPP* and the available methods for measuring them in the field. We then assess the implications of the limitations of past studies for current understanding of NPP in forest ecosystems, discuss how field NPP* measurements can be used to complement tower‐based studies of forest carbon flux, and recommend design criteria for future field studies of forest NPP.

Implications of differing input data sources and approaches upon forest carbon stock estimation

“…Various approaches have been developed to assess forest ecosystem C exchange, from the measurement of temporal changes in biomass (Clark et al 2001) and soil C (Lal et al 2001) to the measurement of C exchanges themselves using eddy covariance flux towers (Baldocchi 2003). Although these approaches have been used to assess C exchange for a large number of forest sites around the world, these measurements are not necessarily representative of entire landscapes (Running et al 1999); hence, the description of regional or biome-level ecosystem C dynamics remains difficult (Aalde et al 2006).…”

Scaling Gross Primary Production (GPP) over boreal and deciduous forest landscapes in support of MODIS GPP product validation

“…In principal NPP is simply the measurement of biomass production over the course of a year, but in practice there are myriad difficulties and great cumulative uncertainties (Clark et al, 2001;Gower et al, 2001). As noted, the uncertainty for belowground production was much greater than that for aboveground production since only the latter was measured.…”

Assessment of Aboveground Woody Biomass Dynamics Using Terrestrial Laser Scanner and L-Band ALOS PALSAR Data in South African Savanna

“…Hence, most allometric equations do not take into consideration the differences in tree species associated with variations in ecological regions. Allometric models are developed based on relationships between biomass and tree characteristics such as height and basal diameter [7]. Such relationships are therefore prone to errors associated with models used in their development [5,8].…”