Picea rubens growth at high versus low elevations in the Great Smoky Mountains National Park: evaluation by systems modeling

For half a century, red spruce ( Picea rubens Sarg.), a commercially and ecologically important boreal tree species, has experienced growth decline and high mortality in eastern North America. A tree growth systems model, ARIM (annual radial increment model), was developed to evaluate responsible factors for red spruce growth in the Great Smoky Mountains National Park. The dominant cause at higher elevations (1800–2000 m) was found to be air pollution involving high-frequency acidic rain and cloud immersion. The identified causes at lower elevations (1450–1700 m) were insufficient solar absorption due to photoinhibition, drought stress resulting from reduced precipitation and high evapotranspiration due to warmer temperatures, and minor effects of air pollution. The ARIM exemplifies a complex systems concept and methodology for evaluating multivariable factors in tree growth systems. ARIM provides a general model structure that incorporates complex direct and indirect interactions for tree system studies and quantitatively integrates knowledge and data from different disciplines by developing a new set of indices, the relative basis index values. The ARIM results implicate comprehensive habitat-dependent directions for long-term conservation policies and management of red spruce with environmental changes, climate change, and air pollution in the Great Smoky Mountains National Park.