Fine-scale environmental variation and structure of understory plant communities in two old-growth pine forests

1 Although it is well established that nitrogen and light play major roles in structuring plant communities across the landscape, it is not as clear how they structure communities within forest stands. Virtually nothing is known about within-stand structure of understorey communities of herbs and small shrubs in near-boreal forests. 2 We tested the hypothesis that fine-scale (5–20 m) variability in N and light structure forest-floor plant communities in two old-growth mixed Pinus resinosa and Pinus strobus forests in north-eastern Minnesota, USA. 3 In each forest, all trees > 1.4 m tall were mapped on a 0.75–1.0 ha area. A grid of subplots 5–10 m apart was established (total n = 147), and N mineralization ( μ g g − 1