Ecosystem engineers and keystone species

In large areas of Australia there are probably several hundred tons of termites in every square kilometre.

From *The Desert, Lands of Lost Borders,*Chapter 6:

The most ubiquitous (and irritating) vegetation in the Australian outback is spinifex, strictly *Triodia.*This coarse, tough grass grows in landscape-smothering tussocks, and its spiky leaf tips contain small shards of silica that have a habit of embedding themselves in the skin of passing animals, including humans.
Spinifex performs an important function in terms of dune stabilization and is a key participant in the fire ecology of the desert, but it is essentially inedible for animals and would smother the land and clog the ecosystem if left unchecked. In other climates, plant debris is cleared by wood-decaying fungi, but the desert is too dry for them. However, crucially, termites eat spinifex and there are a lot of them. Spinifex may be an archetypal feature of the landscapes of the outback, but so are termite mounds. They come in a bewildering array of shapes and sizes, each one extending far below the surface for water supply and providing a complex climate-controlled home to a community of hundreds of thousands of individuals. The termites consume the spinifex (along with a vast variety of other organic matter) and keep it under control, but they cannot digestit. For that, through a remarkable example of symbiosis, they require the specialized microbes in their gut that convert the cellulose to acetate, a kind of vinegar that then feeds the termites. Termite mounds provide safe havens for a variety of other creatures (some lizards lay their eggs in them) and the process of their construction moderates the desert soils, influencing water infiltration and evaporation, changing the structure and permeability. This, in turn, promotes plant growth and diversity, the entire vertebrate and invertebrate burrowing ecology and the food chain as a whole. Termite mounds in the Sahara and the Sahel are referred to as ‘houses of the devil’, but without this ‘keystone species’ arid lands would be very different — it has been estimated that most or all of the biomass produced in the Chihuahuan Desert is consumed by termites.

As a recent press release from Princeton University observed, “Termites might not top the list of humanity’s favorite insects”, but it went on to highlight our on-going and emerging understanding of the critical role that they play in the arid ecosystems of the world’s arid lands:

new research suggests that their large dirt mounds are crucial to stopping the spread of deserts into semi-arid ecosystems and agricultural lands. The results not only suggest that termite mounds could make these areas more resilient to climate change than previously thought, but could also inspire a change in how scientists determine the possible effects of climate change on ecosystems.
In the parched grasslands and savannas, or drylands, of Africa, South America and Asia, termite mounds store nutrients and moisture, and — via internal tunnels — allow water to better penetrate the soil. As a result, vegetation flourishes on and near termite mounds in ecosystems that are otherwise highly vulnerable to “desertification,” or the environment’s collapse into desert.
Princeton University researchers report in the journal Science that termites slow the spread of deserts into drylands by providing a moist refuge for vegetation on and around their mounds. They report that drylands with termite mounds can survive on significantly less rain than those without termite mounds. The research was inspired by fungus-growing termites of the genus Odontotermes, but the theoretical results apply to all types of termites that increase resource availability on and/or around their nests.

This research is fascinating, but it would not be entirely surprising to farmers in the Sahel who are resurrecting – very successfully – the traditional methods of water management for new trees and for new crops. Digging a planting pit through the hardened surface and adding organic matter creates not only a water-conserving environment for plant growth, but attracts termites that process the organic material for use by the plants and aerate the soil through their tunnelling. And those tunnels are extraordinary. The internal structure of a termite mound (a complex ecosystem in its own right) has been dramatically demonstrated by the work of Scott Turner at The State University of New York College of Environmental Science and Forestry. Through taking plaster casts, he reveals the architectural skills of the ecosystem engineers as strange and compelling sculpture:

The tunnelling continues far below the surface (termite mound materials that bring minerals from the subsurface have been used for gold prospecting in Australia) and for many metres beyond the mound. The scale of this landscape management activity is staggering: look carefully at this photo of just a small area of the Australian desert, and you will see hundreds of termite mounds.

No, termites may not be our favourite insects, but our planet would be a different – and, arguably, worse – place without them.

[Image, “Crater termites of the worker and soldier castes attending to damage of their nest, Schanskop, Pretoria”, GNU Free Documentation License, Author JMK] SIGNATURE

Comments

Richard Bready (2015-04-06):

“Slow-motion soil fountains,” Scott Turner calls the termite mounds. Thanks for the link to his work - the pictures and discussion are fascinating. I’d love to see a similar cast of a tree’s circulatory system, but I suppose that will have to wait. Pevsner likened Sagrada Familia to anthills; had he but known.

Originally published at: https://throughthesandglass.typepad.com/through_the_sandglass/2015/03/ecosystem-engineers-and-keystone-species.html