Hawaii tropical moist forests are comprised of mixed mesic forests (about 750 to 1250 meters elevation), rainforests (found above mixed mesic forests up to 1,700 m), wet shrublands, and bogs in swampy areas. Moist to wet forests are commonly found on the windward lowland and montane areas of the larger islands and on mountain tops of some of the smaller islands. Koa (Acacia spp.) and Ohi’a lehua (Metrosideros spp.) are common dominant canopy tree species. Mesic forests are the richest for many taxa and have the highest proportion of endemic tree species. Many of the honeycreepers, an endemic group of birds that displays many specialized adaptations to different food and plant resources, were found in mesic and wet forests.
About 200 million years ago (during the Triassic and Jurassic periods), the landscape was dominated by conifers, which were the most diverse group of trees and constituted the greatest majority of large trees. When flowering plants emerged (in the following Cretaceous period), they quickly prevailed, causing most conifers to become extinct, and those that survived to adapt to harsh conditions. Perhaps the most significant difference in this change is that the primitive conifers invested their energy in the basic food supply for every seed, with no certainty of fertilization; by contrast, flowering plants create the food supply for a seed only after it is triggered by fertilization. The Pacific temperate rain forest now remains the only region on Earth of noteworthy size and significance where, due to unique climatic conditions, the conifers flourish as they did before being displaced by flowering plants.
Lowland and foothill moist forests have been largely eliminated. Some relatively large blocks of montane forest still exist on the larger islands, but even here there is much degradation from feral ungulates, introduced weed species, development, and recreational activities. Tropical moist forests of Hawai'i are comprised of mixed mesic forests (about 750-1,250 m elevation), rain forests (found above mixed mesic forests up to 1,700 m), wet shrublands, and bogs in swampy areas. Moist to wet forests are commonly found on the windward lowland and montane areas of the larger islands and on mountain tops of some of the smaller islands. Koa and ‘Ohi’a are common dominant canopy tree species.
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