The Ravine Forest

The ravine forest (alternately ravine jungle) is an environment found across much of Pluvimundus' southern continent of Aenvarna, but which is most expansive throughout the northern half of the continent. It is a complex matrix of karst terrain - steep limestone ridges which over hundreds of millions of years have eroded into a maze of sheer cliffs, towering spires, and endless variety of arches and pedestals that rise up like islands over the surrounding landscape. Many of these free-standing stone monoliths can stand thousands of feet above the bedrock below them and support thick stands of vegetation in the form of hardy trees and creeping epiphytic vines that spread to form natural bridges between the cliffs. Though the roots of the plants collect detritus as they creep over their stone supports, such a dense cover of foliage on these exposed precipices is only made sustainable by intense, hydrating, nightly rainstorms that can drop almost two inches of precipitation daily, keeping the delicate roots so moist at all times that they can freely creep over the rocks and hang down into the air below in thick tangles like vines without withering.

This is an environment of incredible complexity, a multi-tiered and intricately interwoven vertical forest that extends from the high, mist-covered peaks of the limestone spires, down into a maze of wet, permanently shadowed pathways at the base of the spires, where only scant vegetation, mosses and mushrooms grow, and from there descending down even further until one reaches the lightless, seemingly limitless cave labyrinths beneath, all carved out by the constant force of erosion. It is an ideal recipe for the speciation of life, one biome comprised of countless smaller, connected habitats, and it is little wonder that the ravine jungle is the most biodiverse terrestrial environment on Pluvimundus.

The peaks of the ravine forest, exposed to sunlight more than any other part of the region, are where most of its trees and vegetation are able to survive, rooting into the rock with adventitious roots and collectively supporting one another upon the most delicate of these high perches. But it is a difficult environment to navigate if you are an animal, for the tops of the spires are frequently isolated by vast chasms without bridges or pathways between. It is so that, to survive here in the highlands, you would do very well to be able to jump very well, to fly, or the intermediate: to glide. Indeed, more clades of gliding animals have evolved just here, in this one region, than upon the entire Earth.

are above: life at the top of the ravine forest, its most productive level, requires great mobility and so all large vertebrate animals that survive here must either leap, glide, or fly. Among the most visible herbivores of the highest level are many varied species of jungelopes, fleet-footed ungulate-like mammals with exquisite color vision and an affinity for extravagant display in the form of bare colored skin and inflatable facial structures: these ones in particular are called blue-eyed black balloon boobers. Nearby a flock of sunsharks takes to the air. These warm-blooded but sprawling, gliding tetrapods share a common ancestor to both Pluvimundan 'birds' and 'mammals' but more closely resemble airborne rays, and with two pairs of wings can cross even the widest of chasms. Not capable of upward flight, by flapping their wings periodically they nonetheless prolong their descent, landing lightly on vertical walls and clinging to the rough rock surfaces with sharp claws on wrist and ankle.

below: a wide variety of wildlife thrives in the top levels of the ravine jungle, where fruiting plants abound. A pair of resplendent sunsharks nest, bird-like, in a tree cavity while psittacorillas, quadrupedal native 'birds', and a group of agile, active tetrapods which resemble both amphibians and primates and so aptly known as froglemurs pick succulent fruit. Agile and quick in swinging through the trees and very social too, they are related distantly to the world's 'birds' and 'mammals', though lack either's furry coats. Knowing they are more nimble, they boldly take food right out of the claws of the docile, herbivorous fum - a dog-sized, crab-like eight-limbed vertebrate belonging to an ancient lineage known as the arthrotheres - "jointed beasts" - which rarely leaves the treetops and moves so slowly moss and algae often grow over its thick epidermis. On the cliffs just beyond, two male red-nosed balloon boobers display in a lek for females yet to arrive.

Life upon the precipice requires animals find ways to cross the chasms between spires if a creature is to have any chance at being widespread. Animals unable to do so are effectively marooned upon their islands, as conditions change too drastically going downward for most to be able to descend and climb back up, and so each spire may host its own array of small, endemic species. All larger animals here, however, must find their own ways to move between these islands in order to maintain viable populations and enough food to support themselves. Lightly-built jungelopes leap the distances with strong legs, landing upon the narrowest ledges with feet equal parts cloven hoof and gripping primate hand; sunsharks glide for up to half a mile; and many Pluvimundan creatures long ago evolved powered flight before the ravine jungle ever existed, and so can now move with utmost freedom in this complicated three-dimensional world. But a major constraint for life at the top of this world is size; to make a living here requires you be small. Few animals at the peak of the jungle, barring a few large and wide-ranging flying animals, weigh more than forty pounds or eighteen kilograms; the delicately balanced environment simply demands a lighter-built frame. It is only at the next lower level where megafauna, animals as large or larger than humans, can survive. It is here, where the spires are somewhat less vertical and frequently bridged by both rock formation and horizontal vegetation, that both substantial herds of grazers, and large predators, both first appear.

above: a manguar - a large, native carnivore of the xenopard tribe of native 'mammals', rests with her young cub on a high ledge in the ravine forest as a bronkjird - a common theropodal ‘rodent’, one of numerous species like it which grazes the steep slopes of the lower spires in herds, passes unaware on the rocks below. Manguar are the apex predator of the mid-levels of the ravine jungle, primarily nocturnal hunters as large as a tiger but well-adapted to climb the cliff walls like a panther in search of their equally-nimble prey. Fiercely solitary carnivores, their only enduring social bonds are between mother and her single cub.

below: some bronkjirds have evolved flight to better navigate the ravine jungle. Not only able to cross chasms with powerful leaps, these species known as farkles use membranous wings to flutter upwards. They are unlike most bronkjirds and eat small animals instead of vegetation, and have evolved forward-projected tusk-like upper incisors used as chisels to dig them out of tree bark. Some species, such as the rightusk at right, have only one emergent tusk - almost always on the same side. Others have two, sometimes asymmetrical, teeth, all for the same role. Most species are small and weigh just a few pounds. One, however - the secondarily flightless glubchuck, can weigh up to thirty pounds. Having abandoned gliding, now finding its food on the forest floor, its wings are uselessly small and totally absent in the female. The male, however, has retained them and now uses them as brightly marked display structures - and he will pursue her even up a tree in order to win her favor. This lack of flight, however, limits their range to the lower levels of the forest.

To the untrained observer, the ravine jungle looks like a mountain range, but this is actually a matter of skewed perspective. The peaks of the forest's cliffs and spires are in fact closer to the level of the original ground, and are near or below sea level. The daily torrential rainfall, slightly acidic from a high concentration of carbon dioxide gas that keeps the planet's atmosphere so warm, has totally washed away the limestone bedrock around them to reveal the striking shapes that remain today. This layer of highly soluble rock covers more than 70% of the planet's crust, laid down hundreds of millions of years ago by calcium-producing reef organisms that dominated the planet's seas before the evolution of free-swimming vertebrate animals, and most of what is now land was underwater before 600 million years ago when these coral-like creatures were building their stone shells. It is so that even just the second tier of the ravine jungle is, relative to the sea at least, underground. Nonetheless the midlands are sunlit and productive, and support the highest number of megafaunal animals in the entire environment including herds of plant-eaters and a variety of specialist carnivores. As this realm of the forest combines the rigors of both jungle canopies and rocky mountainsides, its endemic animals too often show traits of both alpine and arboreal lifeforms.

above: apex predator of the ravine jungle, a manguar ambushes a prismatic jungelope while a pair of dizzers - more arthrotheres, many-legged vertebrates of only a very distant relation to either of them with an insect-like bodyplan, fly by. A large relative of the boobers of higher forest levels too heavy to live on the steeper precipices, the prismatic jungelope must stick to more level ground and prefer more open spaces, but this does not leave them invulnerable to surprise attack. The manguar is a skilled ambush hunter, preferring to drop down onto unsuspecting prey from a higher ledge. Cat-like and heavily muscular, with long hooked claws for climbing up the steepest cliffs, it also sports a long, prehensile tail that can act like a third limb for support in the trees. It is a xenopard, a group of primitive carnivorous 'mammals', and though it is not the largest, it is the most widespread of them, ranging across all of the southern continent.

The manguar is a predator of almost any creature, big or small, that shares its range. It kills by grabbing on the back of its prey with its talons, and slashing prey to death with its jaws. Unlike a cat which delivers a killing bite and holds onto the neck, the manguar's teeth are recumbent and project forward like serrated blades. It pulls back its long pursed lips to reveal a wicked set of teeth and swipes its open jaws side to side, slicing up the neck and throat of the prey animal devastatingly, often severing either the spinal cord or the jugular. Manguars are patient hunters, lying in wait on high ledges above choice grazing patches, and can drop down as far as forty feet from their ambush site and land on the back of a large jungelope, staying atop the bucking bronco and slashing it until it collapses from blood loss. As black as night, the manguar slinks in its prey's peripheral vision, disappearing seamlessly into shadows and especially the dark night, though in bright sun it can be seen to retain faint stripes in its short sleek coat, indicative of its ancestral markings.

When the manguar targets a victim, it rarely misses, and if it does there is always another opportunity. It is a highly efficient hunter with a well-developed brain, and is able to exploit the unique geography of the ravine jungle to its full advantage. Thanks to its hooked claws, grasping tail and powerful hind limbs that let it leap as much as forty feet across a chasm, the manguar is one of only a few animals which ranges quite comfortably across the entirety of the vertical jungle, from the tallest pinnacles of the canopy to the lowest, darkest recesses of the shadowlands.

The ravine forest is a highly dynamic, three-dimensional layered environment, like a traditional rainforest on an enormous scale where towers of solid rock function like jungle trees, and in some places can extend almost six miles down. Eventually, if you descend deep enough through the mist and shadows, you will come to the floor level of the forest. Dimly-lit, musty and eternally wet, but at last horizontal, few large plants are present save for the roots of taller forest trees that have snaked their way down here seeking nourishment over hundreds of years. In a world of low light, wet, heavy air, and a permanent odor of decay, plant growth otherwise is sparse and limited to rock-clinging mosses, algae, and the most shade tolerant nettles and foul-tasting vines, many of which defend themselves with venomous spines or toxic alkaloids. There is no fruit and few available seeds at these levels. There are, however, mushrooms - and these fungi, which feed upon all of the organic detritus that tumbles into these dark holes and alleyways from above - leaf litter, droppings and carcasses - nourish what little can survive here.

These are the shadowlands, the gutters of the jungle, a matrix of alleys between tall cliffs formed by streams of water descending toward the lowest elevations down from the peeks where they fell as rain. Most life, both plant and animal, which survives in the gutter do so by consuming detritus that has fallen with the rain from higher, more productive levels. Large animals are present but widely dispersed, eking out what they can in the bottom of the forest. The gutter is dimly lit like twilight even at midday, with only enough sunlight cutting through the shadows and the mist to support simple plants, but enough light remains for vision to remain useful. Down here, both plants and animals are known to make their own light, and terrestrial bioluminescence is common.

above: a group of wary gutter mumps pass briefly underneath a skylight in the shadowlands - a sunlit clearing between the narrow, dark alleyways in the rocks. A flock of blue glasswings, arthrotheres closely related to the dizzers, flit in the light; their shimmering beauty, fluttering flight and semi-transparent wings seem to be in conflict with their habits; they are detritivores and feed on smelly, rotting matter including droppings, and have descended to the bottom of the jungle to feed on the decaying matter found there. The mumps, tetrapods whose closest living relatives include the froglemurs, pass through the clearing quickly and uneasily. Long ago, the mumps ancestors would have feared the dark, but having long ago fallen by accident to its depths from the sunlit world above, have now grown to seek its protective cover. After nightfall, the canyon comes alive with bioluminescence, used by plants to attract pollinators in the dark.

But even the shadowlands are not the lowest level in the jungle. Even further down we find the ravine forest's basement. At the shadowlands' lowest points, where all water travels, in some places the ground has fallen away entirely, revealing enormous caves below. Access points to this hidden underworld are not a facet of the shadowlands alone, but can occur even at high levels in the forest where erosion has so worn away the bedrock that massive collapses have formed sinkholes, ometimes with sheer drop-offs of thousands of feet into total darkness, whereas in other places many square miles have collapsed and the land is relatively flat. As all water eventually makes its way down by the force of gravity, the daily rainfall high above builds into streams and eventually into an enormous maze of caves and underground rivers beneath Aenvarna. When the stone roof of these caves becomes too thin to support itself, the result is a localized collapse of the bedrock which opens up a skylight into the depths of the cave systems beneath. Such sinkholes sometimes allow mingling of life forms from very different habitats, otherwise separated by miles of altitude in the layered forest environment.

above: an emperor skystrider, a giant native 'bird' and one of Pluvimundus' largest flying animals, soars over a collapsed section of ravine jungle. Few spires here remain, and sunlight streams down into the caves below alongside a torrent of flood waters. Here, where two very different regions of the forest meet, bronkjirds and sunsharks can survive just a few hundred meters above the subterranean caves.

below: two worlds meet in a fleeting contact as two more bronkjirds - diurnal herbivores from the higher levels of the ravine forest - peer into the dark abyss of a ravine forest sinkhole, as sinister-looking sewerstriders - eerie, troglodyte creatures that appear equal parts insect and reptile - slink along an underground stream. This cave, formed by an ancient sinkhole, will be illuminated for just a few minutes each morning, when the sun's rays are angled just right to peer inside. But sunlight is useless to the sewerstrider, a species so long lost in the deepest caves that it has no longer any eyes at all. On the cave's high ledges, flocks of opportunistic fauks - parrot-like 'birds' with heavyset beaks - rear their young. Though dwellers of the sunlit world, they seek safe shelter for their young and have found it here. Adults begin to leave the cave for forage in the canopy forest outside and will return later in the day with food for their young.

Lastly, there are a few places in northern Aenvarna where erosion has so badly broken down the limestone bedrock that entire tracts of the ravine forest have collapsed into the hollow caverns beneath, forming immense, totally flat basins with a basement of ancient igneous rock, primarily granite, which is resistant to further erosion. These marshy environments, where regular flooding limits the extent of forests and favors grassy plants, are known as rain plains. They are lush and rich in standing water and can be more than a hundred miles across, forming oasis within the harsh terrain of surrounding jungle. The largest and most distinctive is the Great Basin, which is easily seen from space and consists of a four hundred mile wide fluvial plain, rich with sediment washed down from the surrounding forests and home to some of the world's largest land-living animals, gardenbacks, immense herbivorous arthrotheres notable for the growth of epiphytic vegetation that colonizes the stone-like carapace of mature adults as if they were built from stone itself. Gardenbacks are frequently utilized as nest sites by large birds, and in turn shelter smaller herding animals in their shade from predators.

Descended from a form of arthrothere very much like the small, clambering (and closely related) fum, gardenback ancestors reached a much younger great basin fifteen to twenty million years ago when it was considerably smaller, and there adapted to feed on the ground as grass was abundant and predators scarce. When carnivores gradually reached the isolated refuge, the gardenbacks grew larger to avoid predation, adapting to bear their weight upright on sturdy pillar-erect limbs. Today they are veritable giants virtually immune to predation as adults, and have become a keystone species in the great basin - their only habitat, by preventing the growth of tall vegetation through their feeding and maintaining the marshes and grasslands for the benefit of countless other species that rely upon them. Striding slowly on four primary weight-bearing limbs, they also bear weight on their largest claws, used to tear out trees and move enormous boulders to access food, while a much more delicate pair of manipulatory appendages picks up food and brings it to the mouth.

Adult gardenbacks may grow to fifty feet tall and weigh many tons; this protects from all threats, but poses its own problems. They are trapped in the basin by their size, and so can disperse to other rain plains only when very young - but this is exceedingly dangerous. Their hatchlings, which receive no parental care and emerge from eggs buried in the substrate, must trek into the ravine forest and its many threats, alone. While juveniles retain arboreal adaptations from their distant ancestor and so can climb the limestone spires, they are vulnerable to a wide range of predators, and though huge numbers are born semi-annually and in synchronicity in an effort to flood predators as they flee by night into the surrounding forest, certainly very few ever manage to meander their way to another basin and reach adult size and sexual maturity. Those which do manage, however, may live upwards of three hundred years, with a slow metabolism and a body so remarkably resistant to the effects of aging that it is much more likely to be an unfortunate accident, such as a fall, which kills them in the very end.

above: a gardenback strides across the rain plain of the Great Basin, accompanied by an entourage of grazers which seek safety in its shadow from their flying enemies, the emperor skystriders, which stalk the basin and nest on the outlying cliffs. Behind, semi-aquatic blunderbeasts - large flightless 'birds' - swim in the shallow rivers and feed on the abundant low-lying vegetation allowed to prosper because of the gardenback's selective foraging.

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The ravine forest's entire existence, from its highest peaks down to the caves and the sunlit basins, is owed to the rain. But the rain is not always kind to its inhabitants.

The sky of the ravine forest is almost always overcast, with breaks in the clouds fleeting and brief. Sunlight reaching even the canopy of the forest is thus often filtered, leaving the lower reaches especially dark except during brief spells where the sun's direct rays trickle down into the canyons. Rain falls off and on nearly constantly, rarely ceasing for more than an hour or two at a time, keeping the forest and its inhabitants almost constantly damp. A layer of algae and moss covers most exposed rock, these simple plants in turn providing a foundation for the germination of higher plants, and even the hair of animals can be quickly tinted green by opportunistic algal spores that can take root almost anywhere in this world of rain. The rain is the bringer of all life in this extreme environment; with little soil to hold onto moisture, without the nearly daily showers upon these high clifftop gardens, these fragile ecosystems would soon wither away. Yet as readily as it makes life possible here, the rain can take everything away in an instant. When the sun sets every day, this vital bringer of life experiences a drastic role reversal. Under cover of darkness, the rain becomes a fierce antagonist.

Though rain can and does fall at any time of day in the ravine jungle, the most intense precipitation occurs after dark, when the heavy air begins to cool without the warming rays of the sun overhead and much of the water vapor therein contained is suddenly released. While daytime rain in the jungle is frequently a steady but gentle shower of light rain drops, the night rains are usually more substantial and originate from a thick cover of low-altitude storms that form quickly as the air cools in the late hours of the evening and dump as much precipitation as occurred over the course of a whole day in as little as an hour. Life of the jungle has therefore had to adapt to endure these relatively brief but intense nightly deluges of hard rain, frequently accompanied by flashes of lightning and strong winds. Torrential downpours attack the cliffs themselves, eroding away their surfaces bit by bit over time and sculpting them into their unique forms, while the dangers are much more immediate to the animals that make their homes upon them.

The canopy of the forest, where the majority of its food is produced and where so many creatures spend the daylight hours feeding, is at night the most vulnerable level of the ecosystem, racked by this pounding rain and wind, with few places to hide. Animals which spend their days high on the rocky crags and feeding in the uppermost branches must partake in a daily migration hundreds of feet down to seek shelter from the evening's severe weather. The weather can change in an instant as darkness falls, and so the land-bound animals must begin their careful descent down the cliffs in the late afternoon, before the daylight dims, so that they can find a safe refuge in the lower cliffs before the rains begin in earnest.

above: a bahmu, a carnivorous native 'bird' that hunts small prey on the sheer vertical slopes of the high precipices, takes notice of the first misting rain of the evening and begins its descent to safety at lower levels in the forest.

The smaller and more maneuverable flyers which spend the daylight hours feeding in the trees and socializing on the highest cliffs retire shortly before night to safe dens in tree holes or rocky crags, while the emperor skystrider, able to soar almost effortlessly on the storm's updrafts, simply avoids the storms altogether and spends the first few hours of the night on the wing, rising above the level of the storm and there riding it out before returning to the peaks to roost when the worst of the weather has passed. Even the otherwise indomitable manguar flees from the evening's storms, spending the worst of the weather in sheltered crevasses in the rocks - and yet in seeking shelter, it may in fact find opportunity. The herbivores of the high peaks seek out the same secure hiding places, which are limited in number. In following the herds down into protected caves it may be able to corner them, rendering them unable to escape an ambush. If they do startle and bolt from their hides, it is likely some will miss their mark and catapult over the edge of the mountain in the chaos of the storm and if so, the predator's job is even more simplified; as soon as the storms begin to subside, it simply follows the scent of death down to where the prey lies crippled or killed.

Though the lower levels of the ravine jungle are less exposed to the direct brunt of the nightly storms, they are not immune from their devastation. Strong winds can send monuments of ancient limestone tumbling down, taking with them any plant or animal life that clings to its surface, and from this the manguar is just as vulnerable as its prey. Collapsed pillars can produce landslides as they strike other structures in their descent, trapping animals that have taken shelter in low crannies beneath inescapable depths of rock.

The deepest depths of the shadowlands are as dangerous as the peaks; here the nightly rainstorms produce flash floods that sweep through the low-lying gutters and wash them clean of almost everything except the most tenacious beds of moss and fungus which cling to the bedrock beneath. Any creature unable to scurry above the water level is swept to its death into the subterranean rivers far beneath, and so just as the life of the canopy must descend to seek shelter in the night so must the lowland-dwellers do the reverse. Mumps and other creatures of the eternal gloom seek shelter for the night on ledges as high as they can manage, where the torrents will not sweep them into the underworld. Even so, many - the young and the old, the sick or the infirm - surely loose their footing and drown in the chaos. Unable to see in the darkest of darkness thousands of feet below the open sky, with the cliffs all around them roaring with the sound of rushing water, it is all too easy to stumble off a ledge and into the surge below.

The nightly storm is intense and punishing, but short-lived. Within an hour or two the worst has passed. The cooling atmosphere dumps the water it cannot hold and the storms break apart. Rain slows to a drizzle and may cease entirely for the rest of the night. Some of the animals, particularly the hunters, cautiously begin to emerge from their hide-outs at this time and will stalk through the night, seeking out their vulnerable victims, many of which remain holed up in cracks and caves until dawn. Of all the forest's nocturnal predators, one stands out as a specialist at this particular manner of hunting. Like sharks and eels which roam an underwater reef at night in search of fishes hiding in the crannies so too does the bahmu slink along the cliffs of the ravine jungle, stalking small animals seeking shelter in the matrix of the cliffs and spearing them out with its sharp talons. Even in challenging conditions, some species can exploit difficult circumstance to their favor.

above: a bahmu feeds upon a sunshark it has captured from its shelter in a ravine crevice following the night's deluge of rain.