Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5780781 | Geomorphology | 2017 | 14 Pages |
Abstract
This study examines biogeomorphic interactions between nurse rocks, slope processes, and 300 kÅ«paoa (Dubautia menziesii) shrubs in HaleakalÄ Crater (Maui, Hawai'i). Research objectives were to: assess the association of kÅ«paoa with substrates upslope and downslope of plants, and proximity to the closest rock uphill; contrast shrub/substrate relationships with site frequency of sediment types; measure surface soil shear-strength and compressibility on 50 paired locations near boulders; and investigate the aggregation characteristics and spatial patterns of kÅ«paoa in relation to rock and substrate variation. Data analyzed came from three 100-plant surveys at 3 sites: a plant census at 2720-2975 m altitude, and wandering-quarter transects (WQTs) across two areas (2610-2710 m); ground sediment cover was estimated along four phototransects on these sites. Data for the three 100-plant surveys included substrate type-outcrops, blocks, cobbles, pebbles, exposed soil, organic litter-upslope from each plant, and distance to the largest rock upslope. The two surveys examined along WQTs included substrate type found downslope from kÅ«paoa, plant height, plant diameters across and along the slope, and distance between successively censused plants. Most plants grew downslope of nurse rocks; > 74% were adjacent to blocks or outcrops, and > 17% near cobbles. Plants showed avoidance for finer substrates; only ~ 5.3% and 2.7% grew on/near bare soils and pebbles, respectively. About 92% of kÅ«paoa were â¤Â 10 cm downslope of rocks; > 89% grew â¤Â 2 cm away, and ~ 83% in direct contact with a rock. Some seedlings also grew on pukiawe (Leptecophylla tameiameiae) nurse plants. Several stable rock microsites protected plants from disturbance by slope processes causing debris shift. Site sediments were significantly finer than substrates near plants; shrubs grew preferentially adjacent to boulders > 20 cm wide, which were more common near plants than across sites. Soils downslope of 50 boulders-mean 41.3 cm-showed higher shear strength and compressibility than soils along rock sides. These boulder dams stop descending debris, steadily deflecting them toward rock sides, whereas protected soils downslope of blocks are infrequently disturbed and develop into downslope elongated, clast-free fine-earth flags. KÅ«paoa were uniformly dispersed across slopes, showing a single-phase mosaic arrangement, without apparent aggregation. Slopes where kÅ«paoa grows had a relatively uniform distribution of surface sediments; observed kÅ«paoa patterns may have resulted from the array of microsites generated by surface rocks and sediments, as shrubs simply responded to such spatial structure.
Keywords
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Earth-Surface Processes
Authors
Francisco L. Pérez,