The early growth of P. roxburghii pine is slow. During its first year it makes little height growth but sends out a number of shoots from the base of the stem. This slow height growth, during which the tree develops a dense, very bushy, almost spherical form and reaches about 1 m in height, continues to the fourth or fifth year after planting. There follows a period of rapid height growth.
Best height growth recorded so far is from the experiments at Lumle Agricultural Centre, referred to above, where at 1460 m altitude the mean height of the Sanno provenance, at five years old, was 8.2 m. Near Chautara. Sindhupalchok District (1500 m) Applegate et al. (1988a; 1988b) recorded a predominant height of 8.7 m and dbh of 11.4 cm at the age of nine years, in what they regard as a high quality stand, found to correspond to Site Quality I of the Indian yield tables for P. roxburghii. Their low quality site at the same age had a mean height of 4.7 m and a mean dbh of 4.8 cm. The current annual increment was the mean for the three years before the measurements were made. Wood includes stem and branchwood, 56 per cent and 44 per cent respectively. The mean annual increment of stem wood is equivalent, very approximately, to about 4 m3 ha-1, though this may be expected to increases the trees grow larger. In India, according to Howard (1941), the mean annual increment of Quality I natural P. roxburghii culminates at slightly under 13 m3 ha-1, at about 50 years of age, including the yields from thinnings. The only trial from which figures have been seen in which the growth rates exceed the high-quality site at Chautara is the one at Lumle, described above. On the other hand a number of trials have produced results worse than the low-quality site.
At this stage no obvious correlations with altitude or other site factors can be seen, though there may be a tendency for plantations at low altitude, in the Bhabar Terai, to grow faster than those in the hills. Pinus roxburghii has failed in some trials at high altitudes, but at others reasonable growth has been obtained. For instance in a trial 82 months old at Tistung (about 1900 m) there were 94 per cent survivors, with a mean height of 4.0 metres and a dbh of 5.6 cm. In Baitadi in the Far Western Development Region plantations at 1760 m on a southeast-facing slope were successful, but at 1580 m on a northwest-facing slope results were poor (Margolis, 1982). In Solukhumbu District the most common cause for failure in P. roxburghii plantations has been planting it on sites that are too cold; however 75 per cent survival and good growth was obtained in a plantation at 2200 m on an east-facing slope in this district (J. Stewart, 1984). In the Far Western Development Region winters are colder than in the Solukhumbu area.
Some of the poor results in trials may be due to such factors as poor maintenance and the effects of brown needle disease, rather than the conditions at the particular site.