Process based inventory of isoprenoid emissions from European forests: model comparisons, current knowledge and uncertainties

Abstract

Abstract. Large uncertainties exist in our knowledge of regional emissions of non-methane biogenic volatile organic compounds (BVOC). We address these uncertainties through a two-pronged approach by compiling a state of the art database of the emissions potentials for 80 European forest species, and by a model assessment and inter-comparison, both at the local and regional scale, under present and projected future climatic conditions. We coupled three contrasting isoprenoid models with the ecophysiological forest model GOTILWA+ to explore the interactive effects of climate, vegetation distribution, and productivity, on leaf and ecosystem isoprenoid emissions, and to consider model behaviour in present climate and under projected future climate change conditions. Hourly, daily and annual isoprene emissions as simulated by the models were evaluated against flux measurements. The validation highlighted a general model capacity to capture gross fluxes but inefficiencies in capturing short term variability. A regional inventory of isoprenoid emissions for European forests was created using each of the three modelling approaches. The models agreed on an average European emissions budget of 1.03 TgC a−1 for isoprene and 0.97 TgC a−1 for monoterpenes for the period 1960–1990, which was dominated by a few species with largest aerial coverage. Species contribution to total emissions depended both on species emission potential and geographical distribution. For projected future climate conditions, however, emissions budgets proved highly model dependent, illustrating the current uncertainty associated with isoprenoid emissions responses to potential future conditions. These results suggest that current model estimates of isoprenoid emissions concur well, but future estimates are highly uncertain. We conclude that development of reliable models is highly urgent, but for the time being, future BVOC emission scenario estimates should consider results from an ensemble of available emission models.

Emissions of isoprenoids and oxygenated biogenic volatile organic compounds from a New England mixed forest

“…Among emission models, those for isoprene and monoterpenes are the most robust and well characterized, though shortcomings do exist (Guenther et al, 1993Grote and Niinemets, 2008;Keenan et al, 2009). This is in part due to the fact that the mechanisms governing the emissions of these compounds are relatively straightforward.…”

“…This could be due in part to the use of air rather than leaf temperature and the assumption of 100 % sunlit leaves rather than use of a canopy environment model. Keenan et al (2009) also compared the MEGAN algorithm to measured isoprene fluxes. Their results indicate that, while the MEGAN algorithm performed well on average, there were discrepancies between the model and measured values on short time scales.…”

“…Uncertainties in the existing data on emissions of BVOCs and their dependence on environmental factors make predictions of future emission trends and the response to changing climate difficult (Grote and Niinemets, 2008;Keenan et al, 2009). Canopy-scale studies, which can bridge the divide between leaf-level experiments and global models and be used to test the accuracy of model parameterizations, are a critical component in improving model formulations.…”

Predicting the future of forests in the Mediterranean under climate change, with niche- and process-based models: CO2 matters!

“…Phenology is temperature-dependent and accounted for in an updated version of the Pelkonen & Hari (1980) approach for calculating the seasonal variations in photosynthetic potential. GOTILWA 1 has been validated and widely applied both in the Mediterranean region and the rest of Europe (see Kramer et al, 2002;Morales et al, 2005;Keenan et al, 2009a for validation exercises and Keenan et al, 2009bKeenan et al, , c, 2010 for example applications).…”

Simulating precipitation decline under a Mediterranean deciduous Oak forest: effects on isoprene seasonal emissions and predictions under climatic scenarios

“…Since Quercus pubescens Willd. is the second isoprene emitter in Europe and the main one in the Mediterranean zone (Keenan et al 2009), Biogeosciences Discuss., doi:10.5194/bg-2017-17, 2017 Manuscript under review for journal Biogeosciences Discussion started: 9 February 2017 c Author(s) 2017. CC-BY 3.0 License.…”