Quantitative analyses of shade-shoot architecture of conifers native to New Zealand

Shoot architecture was quantified by measuring the "maximum silhouette area ratio" (R-max). R-max was calculated from the maximum silhouette area (or projected area) of the intact shoot, divided by the silhouette area of the leaves or phylloclades (leaf-like flattened stems) when they are removed fr om the shoot and laid out flat. Like conifers of the Northern Hemisphere (N H) with non-appressed foliage, the R-max of shade-adapted shoots ranged fro m 0.5 to 1.0 in New Zealand (NZ) conifers with non-appressed foliage. Defin ing a "leaf" to mean either a true leaf or a phylloclade, the following was found: leaf area/leaf dry weight, leaf area/shoot dry weight, and leaf dry weight/shoot dry weight, were all similar in the shade-shoots of NZ and NH conifers. None of these variables were significantly correlated with R-max in the NZ conifers, unless species with leaves averaging less than 4 mm(2) in size were excluded from the analyses. Foliage dry weight/shoot projecte d area was strongly correlated with R-max. NZ conifers had both smaller and larger mean leaf sizes in comparison to NH conifers. The mean projected ar ea per shade-adapted leaf of NZ conifers varied from 2.7 to 436 mm(2). In N H conifers, the mean projected area per shade leaf varied from 12 to 83 mm( 2). Except for the strikingly larger range in leaf size in NZ conifers, the data support a hypothesis of strong convergent evolution of shade-shoot ar chitecture in NZ and NH conifers. The results are discussed in relation to photosynthesis, stand production, and the ecological distribution of conife rs.