Relationships between net primary productivity and forest stand age in U.S. forests

Abstract

[1] Net primary productivity (NPP) is a key flux in the terrestrial ecosystem carbon balance, as it summarizes the autotrophic input into the system. Forest NPP varies predictably with stand age, and quantitative information on the NPP-age relationship for different regions and forest types is therefore fundamentally important for forest carbon cycle modeling. We used four terms to calculate NPP: annual accumulation of live biomass, annual mortality of aboveground and belowground biomass, foliage turnover to soil, and fine root turnover in soil. For U.S. forests the first two terms can be reliably estimated from the Forest Inventory and Analysis (FIA) data. Although the last two terms make up more than 50% of total NPP, direct estimates of these fluxes are highly uncertain due to limited availability of empirical relationships between aboveground biomass and foliage or fine root biomass. To resolve this problem, we developed a new approach using maps of leaf area index (LAI) and forest age at 1 km resolution to derive LAI-age relationships for 18 major forest type groups in the USA. These relationships were then used to derive foliage turnover estimates using species-specific trait data for leaf specific area and longevity. These turnover estimates were also used to derive the fine root turnover based on reliable relationships between fine root and foliage turnover. This combination of FIA data, remote sensing, and plant trait information allows for the first empirical and reliable NPP-age relationships for different forest types in the USA. The relationships show a general temporal pattern of rapid increase in NPP in the young ages of forest type groups, peak growth in the middle ages, and slow decline in the mature ages. The predicted patterns are influenced by climate conditions and can be affected by forest management. These relationships were further generalized to three major forest biomes for use by continentalscale carbon cycle models in conjunction with remotely sensed land cover types.

Creating a Regional MODIS Satellite-Driven Net Primary Production Dataset for European Forests

“…Although the specific climate input differs (periodic average climate used in Equations (4) and (5) for NFI NPP versus daily maximum, minimum temperature and precipitation used in MOD17), it cannot be ruled out yet that the climate source explains the better match of MODIS EURO and NFI NPP. Thus, the performance of the currently used approach and alternative options for instance by using Foliage mass and Leaf longevity [43] needs to be tested using European litter fall data.…”

Moderate forest disturbance as a stringent test for gap and big-leaf models

“…For example, NEP in the ∼ 100 yr old Harvard Forest has more than doubled in the last 18 years (Keenan et al, 2012). More broadly, recent syntheses of North America's mixed temperate forests found no evidence for a substantial decline in NEP or net primary production (NPP) with age (He et al, 2012;Amiro et al, 2010).…”

Comparing MODIS Net Primary Production Estimates with Terrestrial National Forest Inventory Data in Austria

“…Turnover of foliage, including mortality of other plant components, is represented by a climate-sensitive litterfall model [19]. The advantage of this model is the requirement of little input data and assumptions compared to calculating litterfall using biomass and turnover rates [18]. We lack a reliable model for fine root turnover in Austria and we assume that carbon uptake of fine roots is already incorporated in litterfall and coarse root increment.…”

“…NPP can be calculated as the sum of biomass increment, mortality, and turnover of foliage and fine roots [18]. We employ volume and biomass functions along with repeated observations to get increment and mortality.…”