REGIONAL-SCALE RELATIONSHIPS OF LEAF-AREA INDEX TO SPECIFIC LEAF-AREA AND LEAF NITROGEN-CONTENT

Specific leaf area (SLA) is an important link between vegetation water and carbon cycles because it describes the allocation of leaf biomass per unit of leaf area. Several studies in many vegetation types have shown that canopy SLA is closely related to canopy leaf nitrogen (N) content and photosynthetic capacity. SLA increases as light is attenuated by leaf area down through a plant canopy. It therefore follows that across an individual biome the spatial patterns in canopy-average SLA and leaf N content should be significantly correlated with the spatial patterns in leaf area index (LAI) and canopy transmittance. In this paper, we show that the LAI across the Oregon transect is closely related to canopy-average SLA (R2 = 0.82) and leaf N content on a mass basis (R2 = 0.80). Canopy-average leaf N per unit area is highly correlated to canopy transmittance (R2 = 0.94) across the transect. At any given site, canopy-average SLA and leaf N per unit area do not vary significantly, either seasonally or between different codominant species occupying the same site. The results of this study suggest that the spatial distribution of canopy-average SLA and leaf nitrogen content (and perhaps canopy photosynthetic capacity) can be predicted across biomes from satellite estimates of LAI.