Vegetation asymmetry in Hawaii under the trade wind regime

Abstract

Abstract. Interpretation of aerial photographs (1962–1965) revealed vegetation asymmetry on opposite valley slopes in the semi‐arid to semi‐humid zones of the island of Oahu. Field studies after 5 and 10 yr showed that this asymmetry is a transitional feature during recovery from disturbance (fire). The types of asymmetry ranged from difference in vigour of shrub canopies to total difference in floristic composition. Slopes exposed to the trade winds are typically characterized by grassy vegetation and landslides, whereas on the protected part of the upper west‐facing slope immediately behind a ridge, vigorous shrubs and trees grow without any mechanical damage or deformation of crowns. This part of the slope is richer in species, including rare ones, than other parts. It is also characterized by the invasion of grasses from more exposed sites and the elongation of shrub canopies above the crest line. Different levels of exposure to exceptionally strong trade winds and salt spray at different parts of slopes seem to allow different speeds of recovery and thus contrasting vegetation structure and species composition. The existence of many shrub seedlings on the exposed upper slope suggests that succession is taking place and the vegetation asymmetry seems at least structurally to be a transitional feature.

Trees and Wind: Wind Scales and Speeds

“…Other studies of tree deformation by chronic wind include those by Cordero (1999), Musselman et al (1990), and Noguchi (1979Noguchi ( , 1992. These indices and studies may be useful in assessing wind exposure of trees and biomechanical effects of winds of varying speeds.…”

Hydrometeorological differences between opposite valley slopes and vegetation asymmetry in Hawaii

“…Hydrometeorological observations were carried out at 10 stations across a small tributary of the Punaluu Valley, northeastern Oahu, exposed to tradewinds [see Noguchi (1992) for details of topography and site selection]. All stations were located at sites where vegetation is mostly herbaceous and the shelter effects by plants and micro-scale topography are negligible.…”

“…The interpretation of aerial photographs taken between 1962 and 1965 on the island of Oahu indicates widely distributed asymmetric vegetative patterns in the semi-arid zone (Noguchi 1992). The short-lived nature of the vegetation asymmetry at some places on the island (e.g.…”

Landscape Representation by a Permanent Forest Plot and Alternative Plot Designs in a Typhoon Hotspot, Fushan, Taiwan

“…For example, cyclone-induced tree damage often varies with elevation, resulting in change of biomass and tree height along the altitudinal gradient [24,25], depending on cyclone strength (see [26]). In addition, wind exposure, which is heavily influenced by topographic position, also explains some of the spatial heterogeneity in cyclone tree damage [27,28] and vegetation structure [29] across the landscape. In general, valley and ridge vegetation are more damaged than slope vegetation [30,31], but ridgetops can be less susceptible than slopes to landslides caused by heavy rainfall [24].…”