IMPORTANCE OF SURVIVAL IN SHORT-ROTATION TREE BREEDING PROGRAMS

An empirical growth function was used, relating individual tree growth and spacing, to predict the economic importance of improving early su rvival. Selection index theory was used to examine the importance of i ncluding survival as a selection criterion, providing survival ability against a specific environmental effect can be identified, with the a im of maximizing the productivity per hectare in a short-rotation bree ding program. The results clearly showed that survival is a highly imp ortant selection trait. The importance of including survival increased with increasing mortality within a stand, and with adverse genetic co rrelations between volume per tree and survival. In all cases, surviva l was shown to be, in relative terms, of greater importance than volum e per tree, unless initial plantation survival was very high (>90%). I ndex selections combining volume per tree and survival resulted in 10% to 90% greater gains in volume per hectare than selection based on an index including only volume per tree alone. The opportunity cost of i ncluding survival in a selection program, in terms of gains foregone i n volume per tree, was shown to only become an issue in the unlikely c ase where selection pressure on survival in breeding programs is maint ained even though mortality in plantations is zero. In this case, the desired gain in survival may be set as high as 15% before any substant ial gains in volume per tree are foregone.