Pawpaw (Asimina triloba L.) ramet leaf-area scaling and patch foliar estimation in a midwestern upland forest 1

Abstract

Forest understory shrub and small tree taxa vary in their shoot architectures in response to their physical and biotic environments and in turn alter the conditions around them, particularly patterns of light. Clonal shrubs establish patches that expand three dimensionally over time as new ramets are produced and the ramet population responds to environmental heterogeneity, competition, and disturbance. Ramet leaf-area scaling and patch foliar structure were examined for the shade-tolerant clonal species Asimina triloba L. Dunal (pawpaw) on upland sites in a mixed-deciduous, old-growth forest preserve in west-central Indiana, USA to address three questions: (a) How strong are predictive relationships for ramet foliar organization across individual leaves, leaf clusters, and whole ramets of differing size? (b) Is it possible to estimate patch foliar area nondestructively and accurately using scaling factors derived from the analysis of ramet foliar organization? (c) How does foliar structure differ within and across patches, including total leaf area estimated with scaling factors? A sample of 48 ramets spanning a wide size range of 0.25 to 2.5 m in height was extracted from the field and analyzed for whole-ramet relationships between main-stem length and several foliar variables. Forty-one long and short leaf clusters from these ramets were used to quantify relationships among cluster size, individual leaf area, and total leaf area and to estimate total ramet leaf area. Eight patches varying in areal size, stature, and ramet density were measured for numerous structural variables and a single cluster-based scaling factor was used to estimate total leaf area, leaf-area index (LAI), and leaf-area density in 2 3 2 m quadrats along continuous transects through patches. The results showed strong curve fits among foliar variables for both the ramet-level and cluster-level relationships and suggest that leaf clusters may be an important focus of foliar organization and dynamic adjustment for A. triloba. The eight patches showed substantial within-patch structural variation and their means differed significantly for all structural variables including LAI, which ranged from 0.42 to 1.28 m 2 m À2 . The results also suggest that total leaf area for A. triloba patches in undisturbed, mature upland forests like those in this study may be estimated nondestructively by counting the number of clusters projected over a sample plot base and multiplying by a weighted mean total cluster leaf area derived from the cluster-scaling relationships. This promising method should be tested across other physiographic conditions and forest types and where nontrivial canopy disturbance has affected A. triloba patch history.