title: Canopy structure of tropical and sub-tropical rain forests in relation to conifer dominance analysed with a portable LIDAR system.
abstract: OBJECTIVE
  Globally, conifer dominance is restricted to nutient-poor habitats in colder, drier or waterlogged environments, probably due to competition with angiosperms. Analysis of canopy structure is important for understanding the mechanism of plant coexistence in relation to competition for light. Most conifers are shade intolerant, and often have narrow, deep, conical crowns. In this study it is predicted that conifer-admixed forests have less distinct upper canopies and more undulating canopy surfaces than angiosperm-dominated forests.
  
  
  METHODS
  By using a ground-based, portable light detection and ranging (LIDAR) system, canopy structure was quantified for old-growth evergreen rainforests with varying dominance of conifers along altitudinal gradients (200-3100 m a.s.l.) on tropical and sub-tropical mountains (Mount Kinabalu, Malaysian Borneo and Yakushima Island, Japan) that have different conifer floras.
  
  
  RESULTS
  Conifers dominated at higher elevations on both mountains (Podocarpaceae and Araucariaceae on Kinabalu and Cupressaceae and Pinaceae on Yakushima), but conifer dominance also varied with soil/substrate conditions on Kinabalu. Conifer dominance was associated with the existence of large-diameter conifers. Forests with higher conifer dominance showed a canopy height profile (CHP) more skewed towards the understorey on both Kinabalu and Yakushima. In contrast, angiosperm-dominated forests had a CHP skewed towards upper canopy, except for lowland dipterocarp forests and a sub-alpine scrub dominated by small-leaved Leptospermum recurvum (Myrtaceae) on Kinabalu. Forests with a less dense upper canopy had more undulating outer canopy surfaces. Mixed conifer-angiosperm forests on Yakushima and dipterocarp forests on Kinabalu showed similar canopy structures.
  
  
  CONCLUSIONS
  The results generally supported the prediction, suggesting that lower growth of angiosperm trees (except L. recurvum on Kinabalu) in cold and nutrient-poor environments results in a sparser upper canopy, which allows shade-intolerant conifers to co-occur with angiosperm trees either as emergents or as codominants in the open canopy.
authors.affiliation: Graduate School of Science and Engineering, Kagoshima University, Kagoshima 890-0065, Japan.
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Aiba
authors.forename: Kosuke
authors.initials: K
authors.lastname: Akutsu
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Onoda
mesh_terms: D000531:Altitude; D017753:Ecosystem; D007564:Japan; D008027:Light; D064028:Tracheophyta; D014197:Trees; D014329:Tropical Climate
keywords: Additive basal area; Mount Kinabalu; Yakushima Island; altitudinal gradient; canopy structure; conifer–angiosperm coexistence; forest stratification; portable LIDAR system