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Vegetation Dynamics and Slope Management on the Mountains of the Hawaiian Islands
- Dieter Mueller-Dombois
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- Journal:
- Environmental Conservation / Volume 15 / Issue 3 / Autumn 1988
- Published online by Cambridge University Press:
- 24 August 2009, pp. 255-260
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Lyon's conclusion (cf. 1919) with regard to the stand reduction dieback on the lower wet slope of Haleakala Mountain led to a forest management policy that saw importation of alien tree species as necessary for protecting Hawaiian watersheds. Unfortunately, this also led to a further demise of native vegetation.
It is possible that the low-canopy species diversity in Hawaii may increase the rate of paludification and swamp (or bog) formation, under wet climatic conditions, over that in a similar environment with a broader spectrum of successional species. However, a boggy landscape can also be a good watershed. Historic evidence comes from the sugar-cane planters on Maui—the supposed beneficiaries of the exotic tree-planting programme—who had objected to it on empirical grounds (Holt, 1983). A more recent study of a canopy dieback in the Hilo watershed showed that extensive tree mortality had no effect on the rate and quality of the water yield from this area. The forest hydrologist, R.D. Doty (1983), who investigated this relationship, attribut ed the outcome to the vigorous undergrowth which remained intact during the dieback event.
Further landscape ageing in Hawaii's shield-shaped mountains involves a process of fluviomorphic dissecting of the gentle slopes lying inland. This results first in amphitheatre-headed valleys and eventually, on the windward sides, in steep residual escarpments with numerous secondary footslopes. Wirthmann & Hüser (1987) derived details of this process from the side-by-side comparison of younger with older Hawaiian mountains. When the waterlogged surfaces of the plateau-like lower wet slopes of shield volcanoes become laterally drained, closed Metrosideros forests can become re-established. That this natural re-establishment process works in the Hawaiian mountains can be seen by going from the shield-shaped slopes of the younger, to the more dissected slopes of the older, high islands. Vigorous Metrosidews forests occur also on the older islands, but they are typically of lower stature than those on the younger mountains.
Unfortunately, most of the secondary slopes formed at the base of the steeply-cut windward mountain slopes of the older high islands have been deforested to make way for crop agriculture. Many of these lower slopes have subsequently been abandoned for economic reasons; but instead of reverting to forests, they have become invaded in many areas by alien grasses and shrubs. Particularly damaging has been the introduced pyrophytic Broomsedge (Andropogon virginicus). This grass has retained a temperate-zone phenology, whereby it undergoes partial dormancy during the winter season when rainfall increases (Sorenson, 1980). As such it has contributed to accelerated erosion in two ways: (1) by preventing recirculation of soil water in areas where excessive runoff is a problem, and (2) by attracting repeated fires and preventing succession to a forest, which would provide much-improved protection against the accelerated soil erosion (Mueller-Dombois, 1973) that is such a common feature on the lower windward slopes of the older islands.
Litterfall and nutrient cycling in four Hawaiian montane rainforests
- Peter M. Vitousek, Grant Gerrish, Douglas R. Turner, Lawrence R. Walker, Dieter Mueller-Dombois
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- Journal:
- Journal of Tropical Ecology / Volume 11 / Issue 2 / May 1995
- Published online by Cambridge University Press:
- 10 July 2009, pp. 189-203
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The mass of fine litterfall and nutrient circulation through litterfall were determined in four Melrosideros polymorpha/Cibotium spp.-dominated rainforests that differed in substrate age, parent material texture and annual precipitation on Kilauea and Mauna Loa volcanoes on the island of Hawaii. Three of the sites had rates of litterfall of 5.2 Mg ha−1 y−1; the fourth, which was on the most fertile soil, produced 7.0 Mg ha−1 y−1 of litterfall with higher concentrations of nitrogen and phosphorus. Tree ferns of the genus Cibotium cycled relatively large amounts of nitrogen, phosphorus and potassium through litterfall; their contribution to nutrient circulation was disproportionate to their mass in the forest, or in litterfall. The forest on the youngest substrate, which also had the lowest concentrations of nitrogen in litterfall, was fertilized with complete factorial combinations of nitrogen, phosphorus and a treatment consisting of all other plant nutrients. Additions of nitrogen increased the quantity and nitrogen concentration in litterfall during the second year following the initiation of fertilization, while no other treatment had a significant effect. Additions of nitrogen had no effect on litterfall mass or nutrient concentrations in the most nutrient-rich site.
11 - Impoverishment in Pacific Island Forests
- Edited by George M. Woodwell, Woods Hole Oceanographic Institution, Massachusetts
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- Book:
- The Earth in Transition
- Published online:
- 24 November 2009
- Print publication:
- 25 January 1991, pp 199-210
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Summary
Editor's Note: Islands have provided some of the most fundamental of insights into evolution and ecology while bearing some of the greatest burdens of human depredation. What biologist can remain long innocent of the saga of Darwin's finches as spun out by Darwin himself and David Lack and others who have been puzzled by the diversity of life of the Galapagos? Whose curiosity is not piqued by the biotic anomalies of New Zealand, Australia, Madagascar, Easter Island, Surtsey? And yet, while scholars have found extraordinary insights in the biota of islands, the biota was often devastated early in the period of human expansion through the introduction of goats or other ungulates thought to benefit seamen on future visits.
Both the puzzles and the depredations grow more complicated as human influences spread. Dieter Mueller-Dombois addresses the current transitions in the forests of Pacific Islands. He describes the rain forests of the Hawaiian Islands as “originally impoverished and secondarily enriched.” They were impoverished by comparison with other large islands of the Pacific that are closer to continental areas of higher diversity; they have been enriched by high endemism, a product of their insularity and period of isolation. Mueller-Dombois introduces a concept new in this treatment, progressive development through a peak period of a thousand years or more followed by regression as soils deteriorate.