Breeding to minimise the effects of collapse in Eucalyptus nitens sawn timber

Checking and collapse have been identified as major causes of degrade for appearance grade boards produced from Eucalyptus nitens pruned logs. The normal methods for managing these problems are through selection of sawing and drying techniques. This paper evaluates tree breeding as a means of managing this problem. Genetic parameters were estimated for tangential collapse measured on 12 mm wood cores taken at 0.9 m height. Data were collected from 12 year old E. nitens progeny trials in Tasmania. Collapse was under moderate to strong genetic control. Heritabilities across sites varied from 0.23 to 0.61 and for a combined site analysis the heritability was 0.38. Genetic correlations between collapse and basic density were strongly favourable (rg = -0.75) but correlations between collapse and diameter, and collapse and cellulose content were strongly adverse (rg = 0.75 and 0.54 respectively). There was no genotype by environment interaction for collapse. A hypothetical model for predicting checking from collapse was used to predict product out turn of appearance board grades and some different selection strategies are discussed. Selecting for diameter alone is predicted to cause a large increase in checking resulting in very few boards being acceptable for the joinery market. Selecting on a diameter and basic density index is expected to cause no change in checking and therefore this is a reasonable option if current wood quality is acceptable for the appearance grade market. Selecting on an index of diameter and collapse measured on increment cores is predicted to lower the incidence of checking to a point where most boards will be suitable for the joinery market.