SURVIVAL RATES AND PERFORMANCE OF MULTI-TRUNKED TREES IN EVEN-AGED STANDS OF SITKA SPRUCE IN WESTERN SCOTLAND

Survival and performance of ail trees in 26 stands of Sitka spruce (Pi cea sitchensis (Bong.) Carr) were monitored for periods of 4-15 years in Glenbranter Forest, Argyll Initial stand ages ranged between 8 and 35 years, and in the younger stands many trees were multi-trunked. Som e multi-trunked trees became single-trunked and a smaller number died. The trees becoming single-trunked were distributed fairly evenly amon g classes and quartiles based on initial girth; the trees dying belong ed chiefly to the lowest quartiles. Declines in the incidence of multi -trunking occurred mostly in stands aged between 18 and 45 years. Decl ines were caused principally by trees becoming single-trunked, mortali ty being no greater in multi-trunked trees than in single-trunked tree s. Multi-trunked trees grew more slowly than single-trunked trees, jud ged from the girth increment of the bigger or biggest trunk. Growth wa s most reduced in the top-quartile girth classes, but in the lowest qu artiles multi-trunked trees tended to have slightly greater increment than single-trunked trees. Nearness to top-quartile trees reduced girt h increment in both single and multi-trunked trees. Individual multi-t runked trees showed a widening in the ratio of the girths of their fir st- and second-ranked trunks during the study period. But the trees be coming single-trunked were usually more disparate in trunk girth than the trees remaining multi-trunked. So the mean girth ratios calculated for all multi-trunked trees in stands of three ages changed little du ring the study period, widening only slightly in the younger stands an d narrowing in the older stands.