Growth rates of Eucalyptus and other Australian native tree species derived from seven decades of growth monitoring

Abstract

There is widespread interest in estimating and forecasting individual tree and forest growth rates for restoration and carbon sequestration objectives. Outside intensively managed forests, past attempts have been limited by the lack of accurate long-term monitoring in multi-age mixed native forests to provide estimates of both expected mean diameter increments and the statistical variation in those estimates. A dataset from Eucalyptus-dominated native forests in subtropical Queensland, Australia offers an opportunity to provide accurate estimates of tree and forest growth rates. Over 86,400 trees from 155 native species were identified and remeasured between 1936 and 2011 in 641 permanent sample plots across a 500–2000 mm mean annual rainfall gradient. Individual tree diameter at breast height (DBH) increments observed for all species ranged mainly from 0.01 to 0.5 cm yr−1 (94 % of values), with consistent differences between rainfall zones (mean of 500–2000 mm yr−1), and varying differences between species (155) and stem diameter class (10–100 cm). For some species, diameter increment increased progressively with rainfall (e.g. Eucalyptus siderophloia, Eucalyptus propinqua, and Lophostemon confertus), but in others (e.g. Corymbia citriodora subsp. variegata, Corymbia intermedia, and Eucalyptus biturbinata) the greatest diameter increments were recorded between 1200 and 1600 mm yr−1. Where there were sufficient data, most species exhibited a quadratic relationship between DBH increment and DBH class, but two species (Callitris glaucophylla and Eucalyptus crebra) native to the 500–800 mm annual rainfall zone showed linear increases in DBH increment with increasing DBH. Continued monitoring of these plots would add to their already great value.