Nov. 5, 2010 by Judy
Oh, I've Seen Fire And I've Seen Rain. Lots Of Rain.
If you’ve read the post before this one you now have a good idea of how water shapes the great bulk of these mid-ocean mountains.
So let’s go take a walk through the native rainforest, shall we? Since we’re in the neighborhood and all.
As you walk, say, downhill from the dry chill of the summit and into the top of the cloud deck, you may run across boglands, then descend to scrublands, then find yourself in the tall, dignified stands of ‘ohia lehua and koa.
Rainfall levels here are variable. November to May is when we are the rainiest, and this ranges from 60-100 inches at sea level to up to 300 inches at the upper limit of the wet slope. To get that upper measurement settled in your head, imagine it raining a little less than an inch a day, every day. Uh huh, soggy.
Haleakala, the mountain I know best, seems to heave up out of the sea. The eastern face has an especially dramatic, steepish slope and is quite visually arresting to travel across—as you can if you drive past Hana, past Kipahulu, and make your way across the skirt of Kaupo district. But I am getting distracted into the dry areas, excuse me. Let’s go back and up.
On the wetter N/E sides of Maui’s Haleakala volcano, the rain is falling across a long slope that stretches from sea level to generally around 8,000ft, and along this slope there are temperature gradients. Obviously the rain at the top of the slope falls through colder air than the rain at the bottom. When you have a mountain flank that sweeps 10,000 feet into the clean blue air of the mid-Pacific, you have a lot of canvas on which to sculpt--if you are a rain god or goddess—microclimates and microhabitats. Variety is good.
And it’s not all mud there, either, kiddo. Mud in some places, oh yes. But, each Hawaiian island is a different age, we are older and we are younger (going SE to NW), so some places have the hard black rock of newly cooled lava while others have the deep red soil of that same lava now oxidized. The thrum thrum thrum of the falling rain tends to keep the soil drained of any nutrients that dying plants and insects add to it, though. And the soils can be gravelly, or heavy with clays.
The many species of plants, so variable in their needs for sun and water, shift with the height of the slopes and the options offered by the afore-mentioned microclimates. Understory and overstory layers develop. Ferns start to claim ground at the higher elevations, and not just literal ground, either—they drape from trees as often as they rise from the soil. Mosses, sedges and grasses get their roots in and help stabilize the ground, catching the sometimes-pounding rain and allowing it seep, gently, into the soil so the other plants can make use of it.
Tree snails, each one giving birth to one exquisitely tiny, identical child, appear.
Insects are abundant at all levels. The world’s largest dragonfly is found here along with moths, beetles of an astonishing variety, dragonflies, picture wing flies, and butterflies. Spiders build webs that are daily hung with the diamonds of dew, or hunt on the bark of trees like wee solitary wolves.
Native insects are important pollinators of native plants; think of them as married to each other.
Birds, competing heavily with each other for forage and nest spaces, divide up the habitat to suit themselves and their diets. Some bird species like to be warmer and drier, some can do well with colder and wetter. They sift out, over the millennia, the diet options available to their kind—insects, seeds, fruit and nectar.
Kipahulu Valley, a deep and nearly inaccessible split-level valley contained within the boundaries of Haleakala National Park, shelters so many unique plants, insects and birds that it was recognized internationally as an asset to science in 1967. The upper, pristine section of the valley protects some 70 species of mosses, 80 species of ferns and at least 220 species of flowering plants, the majority of which are native. In the upper reaches of the valley, nearly 90% of the species are still native.
By the way: no mammals are native to the Hawaiian forests other than our one remaining species of bat. All introduced mammals to Hawaii—including but not limited to goats, deer, pigs, cattle—have been a disaster upon a disaster. Trampling, grazing, digging, predating on native species and causing erosion—these are but some of the ills brought by hoofed creatures into a world where they did not arise natively.
All that blessed water, forced into the great stone sponge of the porous mountain, wells up here and there as seeps and springs. Streams tumble to the sea, cutting great beds into the mountainside as they go. Some species of saltwater goby (a fish), have decided to make use of these streams by slowly and surely colonizing them, shifting over the ages from saltwater-dwelling to freshwater-dwelling. There are five species that spread themselves along overlapping territories of the streams, with the largest, heaviest species (about a foot long) patrolling the great pools at the bases of the braided cascades.
Now, get this: as larvae, these gobies (in Hawaiian: o’opu) flush out to the sea during great storms. This seems like it should kill them, but the part of them that remembers being a sea fish kicks in here, something magic in the genes activates, and they grow for a while in the ocean. When the internal timer goes off they aim for the land again, locate the outflow of streams, and use their belly fins to make their astonishing way back upstream to live out their lives—often climbing waterfalls like little suction cups with fishtails. Even up the undersides of overhangs.
And you thought fish were boring. Ha.
What are the gobies eating? Among other things: freshwater shrimp and snails. Were the snails and shrimp always freshwater? Nope. They did the same adjusting the gobies did, slowly shifting over the millennia from salt to fresh for whatever benefits that afforded them. Isn’t the planet awesome? Now, our streams tend to flashflood and then trickle, flashflood and then trickle. This is a hard way to live, if you live in water, and because of this there are no ‘typical’ fish like trout in Hawaiian streams.
For the new arrivals to the island, the ones that wafted down into the rainforest canopy on the wind over the long years, the options are near infinite for home-finding. Generally, new arrivals do not find here the same foods or enemies as they had in the places from which they ventured, fled or were blown. This means that they can, if they’re good at adapting, shift into living a new way. They can make fabulous new choices—moving higher up the tree, deeper into the soil, or closer to the fresh water than they possibly could ‘back home.’ New conditions might favor the random mutations of some of their offspring even better than it did the founding parents, conferring a better life on those offspring. Over time: speciation. New forms arise in response to new conditions. Those species are found only where they arise, they are our endemics: not replicable or replaceable.
This is how Hawaii became purely Hawaii, accepting sun and rain, receiving all migrants and letting them figure out where or if they will adapt and thrive and become, eventually, her children and hers alone. To do that required, in some cases and in the rainforests as much as the coast, summit, or drylands, very fundamental change.
There’s a lesson in there, I bet.