A COMPARISON OF RED SPRUCE AND BALSAM FIR SHOOT STRUCTURES

I compared the shoot structures of high-elevation red spruce (Picea ru bens Sarg.) and balsam fir (Abies balsamea (L.) Mill.). Needle widths, thicknesses and perimeters were measured to estimate total leaf areas from measured projected leaf areas. Measured needle perimeter/needle width ratios differed significantly from estimated ratios that assumed needles were either rhomboidal or elliptical in cross section. The ve rtical and horizontal silhouette shoot area to total leaf area ratios (STAR(v) and STAR(h)) Of the two species were negatively correlated wi th needle packing and canopy height. Red spruce had higher values of S TAR(v) than balsam fir at each canopy height, but STAR(v) declined wit h canopy height at a similar rate in the two species. The STAR(h) valu es of the two species did not differ significantly at a given canopy h eight. Needle packing increased with canopy height at the same rate in the two species. Needle weight increased in red spruce and decreased in balsam fir with increased needle packing, but showed no significant dependence on canopy height. Red spruce had higher values of STAR(h) than balsam fir at low values of needle packing, but STAR(h) Values co nverged at high values of needle packing. The generally comparable val ues of STAR, along with similar needle diameters, may imply that red s pruce and balsam fir have similar collection efficiencies of wet and d ry particles. Measurements of STAR may be used to estimate leaf area i ndices (LAI) more accurately when using indirect techniques.