Wa’ahila Ridge is a great hike to discover the dry habitats of Hawaii. Its located just to the Koko Head side of the University of Manoa and winds its way up the ridge to St. Louis Heights Recreation area. If you plan to hike the trail, its often easier to start at the top and walk down. That is of course if you plan on catching a ride back up. The description of the trail is from the top down.
The beginning of this hike is in a cook pine forest. Cook pines (Araucaria columnaris) come from the Cook Islands. The name is misleading, as they are not pines at all but in the family Araucariaceae, a genus of 18 or 19 species found from New Guinea to New Zealand and Brazil to Chile. Interestingly its one of the few plants only natively found in the southern hemisphere.
Begin by heading down the trail so that you’re overlooking manoa valley to your left. Your elevation at first is about 1242 feet. Quickly you leave the cook pines behind and enter eucalyptus and ironwood pine growth where there is some fiddlewood mixed in. The trail is obviously heavily used by mountain bikers so stay alert. There are several y intersections in the trail. Make sure to always stay on the right-hand side going down so that you see the best part of the hike at the bottom.
If you are having any problems at this point, I would not procede. Instead, turn around and head back to the car. It just gets steeper and steeper. It is worth the hike though as the senery and vegetation at the bottom is amazing.
The ridge descriptions listed here are based primarily on work done for Ecology 265. Most ridge pictures are of individual sample plots.
At about 850 feet elevation, you run into the first plot that was set up by the University of Hawaii Ecology classes. These consist of orange flags along the sides of the trail. Please do not disturb these areas as they are part of important class studies on how the elevation, rainfall and soil depth effect the diversity of plants and animals. This study has been going on for several years and what has been found is that there is a significant decrease in rainfall as one heads down slope. The lower you go in elevation from plot 10 the more species you get as well.
Around plot 8 at 688 feet elevation you reach an interesting cactoid plant. Its actually not a cactoid at all, but a euphob (Euphorbia lacteaa) or mottled candlestick. Its native to India but is often cultivated because it looks so much like a cactus.
Around plot 5.5 at 570 feet you will see the first agavaes. These large agavae-like plants are actually Fucraea foetida. There are also some small Agavae’s mixed in as well. They are smaller and have spines. In this area, be on the lookout for the dead carion plant (Stapelia gigantea). Its large, five parted flowers smell like rotten meat and attract flies. Its stems are succulent and often resemble cactus. They are however, actually in the milkweed family.
Farther down the trail around plots 2 through 3, the soil depth is much smaller. About 7 species of grasses can be found here interspersed around the hale koa (Leucaena leucocephala), thorny bastards (logwood – Haematoxylum campechianum), and Senna surattensis. Be sure to look on the ground for the famous Kalanchoe pinnata and K. tubiflora, both of which can create baby plants on the tips of their leaves. Finally at the bottom of the trail you weave through a hobo camp. Try to stay to the left as you walk down this section to stay out of their homes.
