Grassland production under global change scenarios for New Zealand pastoral agriculture

Abstract

Abstract. We adapt and integrate the Biome-BGC and Land Use in Rural New Zealand models to simulate pastoral agriculture and to make land-use change, intensification of agricultural activity and climate change scenario projections of New Zealand's pasture production at time slices centred on 2020, 2050 and 2100, with comparison to a present-day baseline. Biome-BGC model parameters are optimised for pasture production in both dairy and sheep/beef farm systems, representing a new application of the Biome-BGC model. Results show up to a 10 % increase in New Zealand's national pasture production in 2020 under intensification and a 1-2 % increase by 2050 from economic factors driving land-use change. Climate change scenarios using statistically downscaled global climate models (GCMs) from the IPCC Fourth Assessment Report also show national increases of 1-2 % in 2050, with significant regional variations. Projected out to 2100, however, these scenarios are more sensitive to the type of pasture system and the severity of warming: dairy systems show an increase in production of 4 % under mild change but a decline of 1 % under a more extreme case, whereas sheep/beef production declines in both cases by 3 and 13 %, respectively. Our results suggest that high-fertility systems such as dairying could be more resilient under future change, with dairy production increasing or only slightly declining in all of our scenarios. These are the first nationalscale estimates using a model to evaluate the joint effects of climate change, CO 2 fertilisation and N-cycle feedbacks on New Zealand's unique pastoral production systems that dominate the nation's agriculture and economy. Model results emphasise that CO 2 fertilisation and N-cycle feedback effects are responsible for meaningful differences in agricultural systems. More broadly, we demonstrate that our model output enables analysis of decoupled land-use change scenarios: the Biome-BGC data products at a national or regional level can be re-sampled quickly and cost-effectively for specific land-use change scenarios and future projections.

Atmospheric CO<sub>2</sub> observations and models suggest strong carbon uptake by forests in New Zealand

“…Biome-BGC (v4.2 final release) is an ecosystem process model that estimates the storage and flux of carbon, nitrogen, and water (Thornton et al, 2002). The model has been extensively tested and validated for North American and European ecosystems and in addition was recently extended and applied to New Zealand managed pasture systems (Keller et al, 2014). The adaptation of the Biome-BGC model to New Zealand by Keller et al (2014) is used in this study to estimate net ecosystem pro- duction (NEP) for five biomes across New Zealand: dairy pasture, sheep and beef pasture, shrub, evergreen broadleaf forest (EBF), and evergreen needleleaf forest (ENF).…”

“…The model has been extensively tested and validated for North American and European ecosystems and in addition was recently extended and applied to New Zealand managed pasture systems (Keller et al, 2014). The adaptation of the Biome-BGC model to New Zealand by Keller et al (2014) is used in this study to estimate net ecosystem pro- duction (NEP) for five biomes across New Zealand: dairy pasture, sheep and beef pasture, shrub, evergreen broadleaf forest (EBF), and evergreen needleleaf forest (ENF). The model is driven by daily weather data from the NIWA virtual climate station network (VCSN).…”

“…Weekly first-guess CO 2 flux maps are obtained by simple interpolation of the monthly estimates throughout 2011-2013. An uncertainty estimate is computed for the a priori CO 2 flux from each grid cell. Based on Keller et al (2014) and personal communication with the authors, we assign 10 % of the flux as uncertainty for pasture land. For forests, we assign 10 % everywhere except in the Canterbury and Otago regions in the South Island, where 56 and 36 % are used, respectively.…”

The effects of changes in water and nitrogen availability on alien plant invasion into a stand of a native grassland species

“…Global environmental change has a strong effect on plant growth and community structure in grasslands (Shaw et al 2002;Zavaleta et al 2003;Keller et al 2014). Temperate grasslands are widely distributed across the Eurasian continent and known as "the Eurasian steppes" (Bredenkamp et al 2002).…”

Land-Use Modelling in New Zealand: Current Practice and Future Needs

“…It can produce results from the local to the national level. Model parameters were calibrated using observed pasture growth data and historical climate data, and validated for both dairy and sheep systems (Keller et al, 2014 For recent publications see Table 14.…”