Abstract from the Ecological Society of America's 85th Annual meeting, August 2000, Snowbird Utah.

Leaf area distribution and canopy clumping in an old-growth
mixed-species podocarp New Zealand rainforest.

Kim J. Brown LDEO-Columbia Univ., Palisades NY 10964-8000
William Schuster Black Rock Forest, Cornwall NY 12518
David Whitehead Landcare Research, Lincoln, New Zealand 8152
David Tissue Texas Tech.Univ., Lubbock TX 79409-3131
Matthew Turnbull Univ. of Canterbury, Christchurch, New Zealand
Kevin Griffin LDEO-Columbia Univ., Palisades NY 10964-8000

Keywords: LAI; clumping; LAI-2000; gap fraction; shoot silhouette area ratio; SPAR-bar; Dacrydium cupressinum; rimu; podocarp;

Estimation of the quantity and spatial distribution of leaf area is an essential task for scaling leaf-level processes from to the canopy and stand levels. Direct measurements of leaf area in old-growth forests are extremely difficult, and destructive sampling is sometimes not an option. Optically based methods of LAI estimation are non-destructive, but should be used carefully. Many canopies have been shown to possess 'clumped' foliage, possibly resulting in underestimates of LAI if such clumping is not explicitly accounted for. Non-destructive methods using radiation interception and gap fraction theory were chosen to measure LAI in an old-growth mixed-species podocarp New Zealand rainforest. The objectives of this research were: (1) to obtain estimates of LAI in the mixed-species podocarp stand near Okarito, Westland, NZ, using the Li-Cor LAI-2000, and (2) to estimate shoot-level and canopy-level clumping correction factors for shoots of rimu, <I>Dacrydium cupressinum</I>, the dominant tree at our study site. This study was part of a larger cooperative effort to characterize the forest structure, leaf-level gas exchange processes, and to model the stand net carbon flux at this site. LAI-2000 measurements were made at each point on a 5-m grid on a 50 x 50-m forest inventory plot, and corrected with above-canopy LAI-2000 data. Using a 23-m canopy access tower, shoots were then sampled from various canopy depths from three large trees. Shoots were immediately analyzed for their mean silhouette-to-projected area ratio (SPAR-bar) using a rotating frame and high-resolution digital camera on a mount that allowed for imaging at precise angles. Projected leaf area, rather than total area, was used for this analysis due to the extremely complex shoot structure of rimu. SPAR-bar was then used for the calculation of the canopy clumping factor. The rimu canopy was extremely heterogeneous. Shoots varied in 'clumpiness', displaying a large degree of within-canopy morphological adaptation. Within-shoot clumping was greater in upper canopy shoots than those from the lower canopy. Results will be presented which demonstrate the impact of clumping correction factors on LAI-2000 estimates of LAI in a multi-layered old-growth podocarp forest (where LAI was estimated to be 2.95).