Simulating effects of fire disturbance and climate change on boreal forest productivity and evapotranspiration Sinkyu Kang a,b, ⁎ , John S. Kimball b,c , Steven W. Running b a Department of Environmental Science, Kangwon National University, Chunchon, Kangwon-do 200-701, South Korea b Numerical Terradynamic Simulation Group, Department of Ecosystem and Conservation Sciences, The University of Montana, Missoula, MT 59812, USA c Flathead Lake Biological Station, The University of Montana, 311 Bio Station Lane, Polson, MT 59860-9659, USA Received 31 March 2005; received in revised form 28 October 2005; accepted 1 November 2005 Abstract We used a terrestrial ecosystem process model, BIOME-BGC, to investigate historical climate change and fire disturbance effects on regional carbon and water budgets within a 357,500 km 2 portion of the Canadian boreal forest. Historical patterns of increasing atmospheric CO 2 , climate change, and regional fire activity were used as model drivers to evaluate the relative effects of these impacts to spatial patterns and temporal trends in forest net primary production (NPP) and evapotranspiration (ET). Historical trends of increasing atmospheric CO 2 resulted in overall 13% and 5% increases in annual NPP and ET from 1994 to 1996, respectively. NPP was found to be relatively sensitive to changes in air temperature (T a ), while ET was more sensitive to precipitation (P) change within the ranges of observed climate variability (e.g., ± 2 °C for T a and ±20% for P). In addition, the potential effect of climate change related warming on NPP is exacerbated or offset depending on whether these changes are accompanied by respective decreases or increases in precipitation. Historical fire activity generally resulted in reductions of both NPP and ET, which consumed an average of approximately 6% of annual NPP from 1959 to 1996. Areas currently occupied by dry conifer forests were found to be subject to more frequent fire activity, which consumed approximately 8% of annual NPP. The results of this study show that the North American boreal ecosystem is sensitive to historical patterns of increasing atmospheric CO 2 , climate change and regional fire activity. The relative impacts of these disturbances on NPP and ET interact in complex ways and are spatially variable depending on regional land cover and climate gradients. © 2005 Elsevier B.V. All rights reserved. Keywords: BOREAS; Boreal forest; Spatial modeling; NPP; ET; CO 2 ; Fire; Climate change; Simulation 1. Introduction Terrestrial carbon cycles exhibit spatial and temporal vari- ability in response to natural climatic fluctuations and environ- mental gradients, as well as anthropogenic and natural disturbances. The boreal forest biome is of special concern for global carbon cycle research because it contains roughly 14% of the world's vegetation cover, and 27% and 28% of the world's vegetation and soil carbon inventories, respectively (McGuire et al., 1995, 1997). The boreal forest is also experi- encing unprecedented changes in regional climate (Barber et al., 2000; Serreze et al., 2000). Over the past 30 years annual surface air temperatures have increased by approximately 5 °C in Alaskan boreal and arctic regions (Lachebruch and Marshall, 1986), Canadian boreal forest (Beltrami and Mareschal, 1994), and North America in general (Oechel and Vourlitis, 1994). Consequent summer drought has reduced growth of Alaskan white spruce in the 20th century (Barber et al., 2000) with potential increases in regional fire occurrence (Wotton and Flannigan, 1993). The annual area burned has increased by an approximate factor of 3 in boreal North America from 1.2 × 10 6 ha in the 1960s to 3.2×10 6 ha in the 1990s (Zimov et al., 1999). Wildfires in boreal forests show tremendous interannual variation in both severity and area burned (Harden et al., 2000). In the 1980s in Canada, 10 times more land area was burned than in any previous decade on record (Murphy et al., 1999). Wildfires affect atmospheric CO 2 concentrations through direct Science of the Total Environment xx (2005) xxx – xxx + MODEL STOTEN-09207; No of Pages 15 www.elsevier.com/locate/scitotenv ⁎ Corresponding author. Department of Environmental Science, Kangwon National University, Chunchon, Kangwon-do 200-701, South Korea. Tel.: +82 33 250 8578; fax: +82 33 251 3991. E-mail address: kangsk@kangwon.ac.kr (S. Kang). 0048-9697/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2005.11.014 ARTICLE IN PRESS