The MIXED MESIC FOREST vegetation zone ranges from 750 to 1250 meters altitude and possesses the greatest variety of plant species of all of Maui’s vegetation zones. Although this zone does not receive as much annual rainfall as thee Rain Forest Vegetation Zone, its precipitation is more reliable and constant, so it does not go for long periods without rainfall. This zone once existed on all but the smallest islands of the chain but is now highly disturbed or entirely absent in mary areas. Despite the fact that many tracts of land within this zone retain much the same species diversity and abundance as they did before humans arrived in the islands, the mixed mesic forests have been badly degraded in the last 100 years. Large areas of what was once forest have been converted to pastures; this is especially true on the lower slopes of Haleakala, where elimination of the forest ecosystem has enabled many aggressive invasive species of trees, shrubs, and grasses to edge out less aggressive endemic species. The photograph below (taken on the higher slopes of Haleakala on Ulupalakua Ranch) is a good example of the result of conversion of a large tract of land once part of the mixed mesic forest to open glens of naturalized introduced tree species and grassy pasture.
The RAIN FOREST VEGETATION ZONE, along with the Mixed Mesic Forest zone, contain the largest number of unique endemic plant species. Annual precipitation averages 150 to 300 inches; in several locales on Maui it is higher. During the Winter, the rain forests are obscured by low clouds and heavy mist. During the rest of the year, mornings in the rain forests are clear, but in the late afternoon and after nightfall are given over to thick clouds and intense rain showers. Maui’s rain forests range in altitude from about 1300 to more than 5000 feet; they always occur above mixed mesic forests. Hawaiian rain forests may not be as extensively altered as other native ecosystems, but they being adversely impacted, especially by the introduction of feral pigs that destroy the root systems of native plants such as ferns and lobelias. Weeds such as blackberry and guava are colonizing those areas denuded by the pigs. The following photographs show good examples of rain forest habitat on Maui. The first photograph is of a small clearing in the rain forest on the Keanae Peninsula, north Maui.
This second photograph gives one a good sense of the thickness of the rain forest canopy (note the pickup truck for scale); is was taken along the Lower Nahiku Road, near Nahiku, north Maui.
The plant life of the SUBALPINE WOODLAND, SHRUBLAND, AND ALPINE DESERT vegetation zone resides at elevations above 6000 feet. The climate in this zone is characteristically more temperate than tropical: diurnal and nocturnal temperatures are lower, rainfall is considerably less, and on Maui and Hawai’i (the Big Island), it often snows on the highest peaks. The terrain is typically steep, consisting of open woodland and schrubland, and alpine grassland. There are parts of the highest slopes of Haleakala on Maui that are referred to as alpine deserts. The picture below is of Haleakala Crater. At the left-center portion of the image are some thin patches of hardy alpine grasses. This is a classic example of alpine desert!
The next photo is of an immature Silversword (Argyroxiphium sandwicense) growing along the hiker’s trail into Haleakala Crater. Silverswords are well-adapted alpine plants that grow at the highest places on Haleakala.
At the next posting, I’ll begin to concentrate on some of the more interesting groups and individual species of plant that I’ve met on Maui. Aloha… malama pono, malama aina!
Tags: mesic forests, plant ecology, rain forests, vegetation zones
