Cementrees
On the uplands and the margins of the soglands, a strange sight has begun to appear. Tall, pillar-like trees growing in isolated stands on high ground, that have seemingly found a way to avoid the thorngrazer's hunger: they are the cementrees.
A fascinating, specialized descendant of the hiddenwood, these sunflower ant trees have escaped the boulders that other plants must take root on to avoid grazing by making their own rock-like armor. The symbiotic ant colonies that live in association with these trees, after a young queen disperses and plants a seedling after her maiden flight, construct a protective cement-like spire around it as it grows to provide protection from thorngrazers. The ants raise the spire as the host plant grows until it reaches about 40 feet and is considered mature.
These ants no longer live in their host tree, and may not seem to need it. Their immediate ancestors fed on animal droppings, and only used the plant for shelter; now, however, they get much of their energy from the plant itself, which shares sugars in the form of sap that drips out of specialized pores in its green tissues and protein-rich sacrificial buds which grow continuously along the trunk of the tree, in exchange for protection. The two species are now obligate symbiotes and linked together as one; the ants protect the tree and the tree feeds the ants, like organs in a single large organism. Food produced by the host tree greatly reduces their need of the ants to forage outside the safety of the spire, and this allows colonies to grow very large. The remainder of their diet is comprised of animal droppings and small pest insects of their host tree.
The spire of the cementree begins as a simple wet-clay mound made by a single ant queen, but once the colony is established the building material is replaced with a much stronger composite made of cellulose from dead plant matter nearby, clay, grains of sand, and their own feces. This material has a similar strength and lightness to hempcrete, and allows the mound to hold its shape and withstand wind and weather for many years.
Inside the spire, a cementree does not need to support its own weight, as the tower replaces its own trunk for the purpose. The trunk it does grow stays just a few inches across, and with much less growth needed to hold up its height, it can grow extraordinarily quickly, especially in its first few seasons. 6-8 feet in one year, 12-16 in two, reaching adult height of up to sixty feet in six to eight years, at which time it may extend 20 feet higher than its spire and be safely out of reach of all plant-eaters... for now.
All along its trunk within the mound, the cementree grows aerial roots; some of these grasp the inside of the spire and so stabilize it, while others snake along the hollow interior, find the ground, and become secondary trunks to root into the earth. This system means that even in the event the tower is damaged by a large animal and the trunk is damaged or even severed completely, the tree is not doomed. As the climate is humid and the tree already has abundant extra roots along its height, as long as the entire spire is not toppled, the hole will be repaired by the insects and the tree will send down new roots to connect its canopy back to the soil, with the severed top surviving as an epiphyte attached to the mound in the interim.
Growing within protective earthen shelters allows cementrees to grow tall despite heavy thorngrazer pressure that severely limits the extent of forest in the northern hemisphere. Yet as they can only grow on upland ground that rarely floods, their range is inherently limited within the soglands to small, isolated islands of high ground. In a few places such as the upland plain and the arctic plateau, however, drier soil conditions suit them well enough that they will soon begin to form denser stands.
