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Feedbacks between canopy composition and seedling regeneration in mixed conifer broad-leaved forests


  • S. Catovsky,

  • F. A. Bazzaz

S. Catovsky and F. A. Bazzaz, Dept of Organismic and Evolutionary Biology, Harvard Univ., 16 Divinity Avenue, Cambridge, MA 02138, USA (present address of SC: NERC Centre for Population Biology, Imperial College at Silwood Park, Ascot, Berks SL5 7PY, UK []).


To address the role of canopy-seedling feedbacks in the structure and dynamics of mixed conifer broad-leaved forests in the eastern US, we monitored seedling regeneration patterns and environmental conditions in the understorey of stands dominated by either hemlock (Tsuga canadensis) or red oak (Quercus rubra) for three years. Hemlock seedlings were favoured over other species’ seedlings in hemlock stands (a true positive feedback), due to a combination of high seed inputs, high seedling emergence and relatively high seedling survival during the growing season, which allowed hemlock to remain dominant under its own canopy. Red oak stands favoured a suite of mid-successional broad-leaved species over hemlock. A more even age structure of broad-leaved species in red oak stands revealed that high seedling survival in such stands were driving this feedback. Canopy-mediated variations in both understorey light availability (1.5% for hemlock vs 3.5% for red oak) and soil pH (3.9 for hemlock vs 4.4 for red oak) were found to be the primary correlates of stand-level differences in seedling regeneration dynamics. In mixed temperate forests in the eastern US, canopy-seedling feedbacks could act to slow successional trajectories and contribute to the maintenance of a stable landscape structure over many generations.