Journal of the Royal Society of New Zealand abstracts
Agricultural and forest productivity for modelling policy
scenarios: evaluating approaches for New Zealand greenhouse gas
mitigation
W. Troy Baisden
Landcare Research, Private Bag 11 052, Palmerston North, New Zealand.
Abstract The New Zealand Government is currently
reviewing policies for the Kyoto Protocol’s first commitment
period, and entering international negotiations that will define the
rules for the second commitment period. Policy makers and stakeholders
require robust tools to evaluate national scale policy scenarios.
Models for robust scenario analysis must combine the best available
biophysical and economic information, and include understanding of
uncertainties. I evaluate three different datasets as candidates for
estimating the biological net primary production (NPP) of pastoral and
forest land, as well as C sequestration potential under exotic or
indigenous forest. For scenario analysis of land-use change, estimating
NPP is critical to represent the flow of agricultural and forest
production into the economy, while estimating C sequestration potential
in forests is required to estimate the quantity of C available for
credits and liabilities. First, a 4-year average of NASA’s
1 km annual NPP product from the MODIS satellite sensor was
verified using published New Zealand data, and used to test and
calibrate the following indices. The MODIS NPP data were compared to
average stocking indices for pasture and site indices for Pinus radiata forests
derived from 10- to 30-year-old mapping in the Land Resources Inventory
(LRI). Third, a “Storie Index” approach was developed using
factors representing climate and soil properties that co-limit
potential productivity, and calibrated to MODIS NPP. Each approach
represents the apparent variation in NPP at the national scale, but may
risk serious errors at a more local scale. The calibrated Storie Index
approach offers the best predictions for pastoral and tussock land (R2 = 0.71) and indigenous forest (R2 = 0.38), while the LRI-derived site index is most predictive for exotic forests (R2
= 0.16). While both the LRI-derived indices and the “Storie
Index” are recommended for modelling policy scenarios, the
“Storie Index” approach shows the greatest versatility
because it does not depend on current or past land use for estimation,
provides the highest level of spatial detail, and can easily be
improved.
Keywords net primary productivity (NPP); forest; pasture; MODIS; Storie Index; Kyoto Protocol
R04022 Received 22 November 2004; accepted 7 February 2006; Online publication date 17 March 2006
Journal of the Royal Society of New Zealand
Volume 36, Number 1, March, 2006, pp 1–15
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