Bamboo Mangroves

On Earth, the mangrove biome is one of the most unusual of natural environments. Consisting of a varied tapestry of largely unrelated types of plants that have adapted a high tolerance for saltwater, it's a habitat of constant change, on the edge of land and sea. The rise and fall of the tides submerge large tracts of it every day only to leave them high and dry again a few hours later in an endless cycle. The roots of the trees in the mangrove catch soil and sediment washed in by the waves, trapping it, and over time extending the beach outwards into the water so that over many areas the shore extends out further and further, creating new land that other plants can eventually colonize. Mangroves are builders, living a life of extreme, literally caught between two worlds.

Earth's mangroves are based on a variety of plants, but most notably trees of the genus Rhizophora, the true mangroves. In the thin belt of subtropical climate Serina retains by the start of the Cryocene, an analogous biome has formed from an entirely different branch of the plant family tree: the bangroove bamboo.

Bangrooves are a hardy, salt-tolerant bamboo variation found only along the subtropical coastlines of Serina's equator, initially sprouting on the beach but eventually spreading a considerable distance out into the ocean. They are a distinct variety of "type-D" bamboo, immediately recognizable by the plant's large, elevated rhizomes, which in mature colonies stretch above and out of the ground as thick, woody trunks, regularly dipping back into the soil and coming out again almost like a sea serpent moving through water. The strange appearance is of course a result of the plant's novel tendency to expand from the roots up until in places the plant's root system literally pushes itself out of the ground, sometimes to heights of twenty feet. Unlike most other bamboo which has developed this mutant growth habit however, bangrooves don't produce large canes out of these "trunks: Their shoots are stunted and never become hardened but rather grow from the tops of the highest rhizomes as small clumps of thin, leafy reeds that flex, rather than break, in the face of wind or water. Bangrooves are thus the only representative of this growth habit that can survive and even thrive on their own, without requiring the support of neighboring plants.

Unlike Earth mangroves, bangrooves are not singular trees but rather large colonies that spread underground and through the water. Though a seedling must initially take root on a beach, once it reaches a few years old it begins to send out runners that take root some distance from it, including out into the water. Colonies can spread as far as three miles from the actual shoreline, formed by floating rhizomes that have sent long anchoring roots through the water - sometimes as far as one hundred feet - and buried themselves in the sand to hold the colonies of floating trunks and shoots in place. Once established far from shore, over the years the connecting tethers of rhizome that originally connected the land-rooted section of the colony with the floating one may degrade, producing large floating "forests" far off from shore that eventually accumulate enough sediment around their free-floating roots to produce a new island.

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A bangroove's life begins as a large seed suspended from its parents' upper shoots, in a clump of three or four similar seeds each encased in long green pods. Whereas both bamboo die back after seeding, the bangroove continues to grow, nourishing the seed with enough food and water that it begins to sprout before even falling off the parent plant. A long taproot extends from the bottom of the seed pod, breaking through it and reaching down to the water. The seed pods will only be released once it is several feet long and sufficiently well-grown that the pod will now float upright, weighed down by the root but kept floating by a pocket of air stored in its upper section. Well-endowed with food, a seed can survive while floating in the water for as long as six months, during which time it will likely have been carried far away from its parent colony by the tides. Eventually it is likely to be washed onto the beach, where its root can catch into the sand; once this happens, it begins to anchor itself at a remarkable rate, its tap root growing as much as five inches a day for several days until it is securely held in place. By now its food reserves will have run low, having just enough sugar left to allow the seedling to put out its first leaf - a long, unbranched blade about three feet long. From here on it its growth is slow for the first year or so, as it concentrates more on establishing deep anchor roots to prevent it being washed back out to sea than on upward growth. Once this is done however it begins to put out numerous shoots and to spread along the beach. A young bangroove resembles more a bed of rushes than a young forest, but within a few more years, as the rhizomes grow above the ground and lift the shoots off the sand, the forest begins to take shape. As it spreads outwards through traditional underground rhizomes, the leading edges of the colony stay small, never extending far enough down the beach that they are totally covered by the sea, for though their roots can handle this their stems would drown. Only the runners produced from the older, woody rhizomes above the ground can grow out away from shore, keeping their shoots above the high tide line. These old woody rhizomes grow higher and higher upwards, their rhizomes contorting and twisting, developing a hard protective bark, and arc out over and into the water. Eventually they stop producing underground stems all together, spreading by sending down long woody roots to anchor the branches of the rhizomes that stand above the water. On Serina's coasts, the strange growth habit of type-D bamboo has found an environment where its mutation is very advantageous over those bamboo that only spread underground; it's only when the rhizomes have become large, woody, and above the sediment that a colony can survive actually in the ocean, as the roots can only grow in the thick sea mud if oxygenated by the portions that arc above the water, and the shoots could not survive being buried underwater for any length of time. The canes of any traditionally-growing bamboo, lacking any rhizomes inclined to grow taller and out of the mud and seawater, would quickly drown in the environment that the bangroove thrives in, and their roots would suffocate in the mud. It is also only here that the bangroove's ancestor was able to evolve the smaller and less vigorous canes from which its leaves sprout, for in this extreme habitat there was no traditionally taller and more aggressive bamboo to compete with it for light.

Bangrooves have a longer lifespan than other primitive colony-producing bamboo, for they don't die after flowering. Rather, they bloom modestly every few years, after which individual canes die but the rhizome survives, sprouting new canes to replace those which degrade. Because they spread indefinitely outwards away from the spot where they initially sprout and the newer parts of the colony regularly become detached from the old, bangrooves could be considered biologically immortal; portions growing on any given coastline could easily be 500,000 years old or even more, and may have originally germinated hundreds of miles from their current locations. Sometimes a remnant of the same genetically-identical colony might remain there - a single organism split into two over the eons. Bangrooves are thus sometimes referred to by an alternate name, migrating mangroves.

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Life of the Bangroove Forest

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Bangrooves are a hub for life, both terrestrial and aquatic. Bangrooves are considered a foundation organism, their presence stabilizing the sediment, building land, and over time providing an environment for the colonization of thousands of other species. The islands that gradually form around their roots eventually rise far enough out of the waves for less salt-tolerant land plants and animals - like the red reed canary-thrush pictured at top right, which feeds on insects near water and is abundant both in the bangrooves and in freshwater environments - to survive, while the trunk- and branch-like rhizomes themselves form a foundation for epiphytic plants to gain a foothold in the sun while keeping their roots safely out of the dangerous waters below.

Countless birds nest in the bangrooves, both those that fly out to sea to feed on fish - like the little gull-like violet ternsprite, a piscivorous descendant of early Serinan insectivores that now comes to land only to nest - and those which make a living directly within the forest itself, probing for small invertebrates in the mud, like the pair of plover-like ruddy groovecocks above, shown picking earthworms from the mud with their long bills. A descendant of the stiltskins of the Tempuscenic, it shares an ancestry with a variety of larger heron- and stork-like waders that hunt for fish in the forests' shallow pools for a variety of prey including whiskered catfish-like eelsnakes, burrowing crayfish, and caecillian-like species that raise their young in underwater nests dug into the shore - but one of the waders doesn't share a close relation. With a long, sickle-shaped bill curved upwards at its tip, the lower bill longer than the upper, this filter-feeding, flighted basal pelicanary shares a method of filter-feeding with the bloon and the blorca with a tongue edged in hair-like cillia , but is unrelated; it has a common ancestor harking back to the stiltskins. A very colorful rail-like bird descended from the galliwalt meanwhile has evolved a large bill suited to cracking clam shells, picking the molluscs from the roots of the bangroove during low tide but not actually swimming itself. From the galliwalt line have also emerged the duck-like serinan waterfowl, a widely diverse group of semi-aquatic birds with webbed feet that still retain a powerful ability of flight; a pair of some small dimorphic species, the duller hen pictured with three young chicks resting on her back, can be seen swimming away from the bangroove forest to feed.

The bangrooves even have an endemic lineage of symbiote ant, one which takes advantage of its host plant without contributing as much as its ancestors did. The mangrove ants still nest in hollow bolls that form on the emerged rhizomes of mature bangrooves, but as there are few other insects near the sea that would try to harm their host, they don't actively protect it - nor do they eat the bitter, salty bangroove plant themselves. Instead they simply use the plants for shelter, emerging from their nests at the daily low tide mark to scour the newly-turned sediment for any little pieces of organic refuse that they gather and take home to the nest to eat, from scraps of algae and plankton to pieces of dead fish or birds. When the tide comes back in the ants scurry back to the safety of their nests, which have only one entrance at their lowest point. As the waters rise they cover the nest completely, but the colonies remain full of air like a diving bell, giving the ants refuge until the waters recede again. Because the bangroove is no longer directly benefiting from the ants' presence, the small hollow bulbs along its roots are no longer ideal ready-made lodging for ant colonies to move into - in order to make them livable, the ants must chew their tunnels into the spongy tissue, causing the root to grow a larger boll as it heals from the damage. The mangrove ant's relationship with its host is slowly transitioning into one of parasitism.

The ants, one of only a few insects to thrive near the sea, are preyed upon by mudwickets and small tweezer-billed songbirds called ditzes, named for their seemingly drunken tendencies to turn upside down while scurrying along the branches in search of ants to eat, often spontaneously dropping from a perch, doing a somersault in the air, and landing on a lower perch to catch an insect.