Regeneration patterns and tree species coexistence in old-growth Abies-Picea forests in southwestern China

Abstract

We analyzed the population structure (size, age, spatial patterns) and radial growth patterns of Abies faxoniana Rehder & Wilson, Picea purpurea Mast., and Betula sp. to investigate the role of dwarf bamboo abundance, gap disturbance, and species life history on the coexistence of canopy dominants in old-growth forests in the Wang Lang Natural Reserve in southwestern China. Four stands were sampled with a single large plot (0.4-0.5 ha). There were fewer tree seedlings and saplings in the two plots with a dense bamboo understory, and A. faxoniana seedlings and saplings were much more abundant than those of P. purpurea. Picea purpurea and Betula sp. seedlings established more frequently on raised surfaces than those of A. faxoniana. Seedling density of A. faxoniana, and B. utilis was also higher beneath open than closed canopy conditions in the plots with little bamboo. Young A. faxoniana and Betula sp. trees were clumped at small to intermediate scales (25-900 m2), which are scales of clumping consistent with past regeneration in canopy gaps. Frequent peaks in radial growth releases in the canopy trees in the plots suggest a prevailing regime of small-scale gap disturbances. In each plot, A. faxoniana tree density and basal area was greater than that of P. purpurea. Picea purpurea trees were present in a wide range of age-classes in each plot indicating a pattern of intermittent regeneration in each stand for at least 500 years. In contrast, Abies faxoniana were abundant in age-classes <250 years, and few A. faxoniana were >350 years old. Betula sp. were mainly <120 years old. Betula sp. and P. purpurea preferred different seed-beds than A. faxoniana for establishment and regeneration of A. faxoniana, and especially Betula, is associated with gaps. Longevity and high survivorship are key life history traits of P. purpurea that prevent its replacement by A. faxoniana. In Wang Lang, stable coexistence is maintained by differences in species regeneration niche, species demographic characteristics, and species responses to the gap disturbance regime. © 2005 Elsevier B.V. All rights reserved.