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For the region St-Martin-de-Londres (southern France), information on vegetation formations is available for 5 different years between 1946 and 1979. Isoprenoid emission factors are assigned according to dominant plant species that were related to the vegetation formations. Potential isoprenoid emissions are simulated with the help of the Solar Radiation Model (SORAM) considering spatial effects of the complex terrain as well as temporal effects of photosynthetically active radiation and surface temperature, the main controlling parameters for biogenic volatile organic compound (BVOC) emission. The SORAM is embedded in a geographic information system environment and considers a digital elevation model of the modeling domain. Results illustrate long-term changes of emission fluxes due to plant succession between 1946 and today. By comparing the daily amount of isoprenoid emissions over a time period of 34 years, today's totals have increased by a factor of 4.4 as compared to the 1946 modeling results. The results presented give an example of possible impact of increasing natural plant cover on isoprenoid emissions for the Mediterranean region. These scenarios at the landscape level further emphasize the need for detailed information concerning vegetation (species, distribution, coverage, biomass) as well as the need for reliable emission factors in order to improve inputs of potential BVOC emissions to tropospheric chemistry models.

[1] Sensitivity studies for simulations of yearly cycles and terrain effects are presented for the St.-Martin-de-Londres region (southern France). Potential isoprenoid emissions are simulated using the Solar Radiation Model (SORAM), spatial effects of complex terrain, photosynthetically active radiation, and surface temperature. SORAM is embedded in a geographic information system (GIS) environment and considers a digital elevation model (DEM) of the model domain. Compared to the maximum case (i.e., no variation in emission factors and leaf area index (LAI)), seasonality in LAI for that Mediterranean-type landscape mainly covered by evergreen plant species resulted in an annual amount of 3.5% less for total isoprenoids. By including the intra-annual change in emission factors an additional 12.5% reduction was derived for the area. When the SORAM module that accounts for light extinction within the canopy was switched off, modeled yearly amount in emission increased by 48%. Complex terrain effects showed only a weak influence for the rather moderate terrain of the modeling domain (mean difference of approximately −2.5% in daily sums). However, sensitivity studies based on the DEM exaggerated by a factor of 2 (resulting in differences of −11.7% for the light- and temperature-dependent isoprenoids) revealed that in the case of pronounced relief or if highly resolved results are necessary, the orography should be considered when modeling the driving parameters of light and temperature.