Root development and whole-tree allometry of juvenile trees of five seed lots of Pinus radiata D.Don: implications for forest establishment on erosion-prone terrain, East Coast region, North Island, New Zealand

Background Establishment of exotic forest on erosion-prone pastoral hill country in the East Coast region of New Zealand escalated following a major cyclonic storm in 1988. Pinus radiata D.Don is the predominant species used for erosion control. It has been suggested that planting densities could be reduced if faster growing P. radiata seedlings and cuttings from genetically improved seed lots were used. Methods A field-based trial was established to measure and compare annual growth rates between P. radiata seed lots (GF 16 and GF 19 seedlings and cuttings grown from GF 23 seed) used during the period of early forest establishment (1960s onwards) in this region and genetically improved seed lots (GF 27 seedlings and GF 28 cuttings) developed at a later date. Over a 4-year period, the above-ground parameters (diameter at breast height, root collar diameter, tree height and canopy diameter) were measured before whole trees (canopy and root systems) were destructively sampled. Results Root collar diameter (over bark) was most highly correlated with tree height, with r 2 ranging between 0.95 and 0.98 for all the seed lots, and all regressions were highly significant ( P