Responding to further enquiries from Andrew Robinson about effects of spacing on tree height growth in very young stands: I was allowed to use data from several Nelders during my PhD studies, courtesy of Bob Tennent, from the Forest Research Institute in Rotorua. The only semi-published reference I have covering this effect is my thesis, from which which I should publish more 8-). The analysis of initial growth in the Nelders was a prelude to modelling of growth in plantations between ages 0 and 5. I detected a hint of the same stocking-related effect on height in my wider (non-Nelder) dataset, but it wasn't a large enough effect to warrant inclusion in my model. Height has been observed to be correlated with stocking in older stands, but since I'm answering this from home I can't immediately place my hands on any references. The unique thing about the Nelder results was that the height differences showed up a couple of years before the diameters differed between stockings in some cases. I have visually observed very young Nelders which appear to have taller trees in their centres, as well. A few possible explanations include: 1) The Nelders may have been established with spot weed control, and weed site occupancy in their centres would have been lower. Assuming that site resources were used to a greater extent by the weeds than by the young trees, the overall effect may have been to create a more favourable microsite for young trees at higher stockings. The soil, at least would have been warmer, and radiata is very sensitive to temperature. The data came from Nelders which were established many years ago, and, as far as I am aware there are no records of what sort of weed control was used during their establishment. 2) There may be some root contact long before there is any canopy contact between trees. However, in this case one might have expected that diameters would also have been affected. 3) There may be something else we are missing which enables trees to detect their neighbours before the onset of competition for site resources. A further question, of course, is when neighbours are detected, how and why is height growth increased? Regards, Euan ================================================================== Dr Euan G. Mason Silviculture, Modelling and Lecturer in Silviculture Decision-support systems School of Forestry University of Canterbury New Zealand's professional Christchurch, New Zealand Forestry School ==================================================================
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