Schweingruber, F. H., & Wirth, C. (2009). Old trees and the meaning of 'old'. In C. Wirth, G. Gleixner, & M. Heimann (Eds.), Ecological studies: Vol. 207. Old-growth forests. Function, fate and value (pp. 35-54). https://doi.org/10.1007/978-3-540-92706-8_3