Connectivity of green and blue infrastructures: living veins for biodiverse and healthy cities

Think like a large disturbance-making omnivore

A recent paper in Science summarizes archaeological knowledge about the history of agriculture change and human environmental impacts.

This paper has gotten a lot of press in the past couple of days. The ArchaeoGLOBE project is a group of archaeologists who have gotten together to collate their knowledge of local and regional trajectories of human land use and food production. The result was published in the most recent issue of Science (https://science.sciencemag.org/content/365/6456/897/tab-pdf). While the paper is called “Archaeological assessment reveals Earth’s early transformation through land use” they do not actually show any data on land use or environmental condition per se. What they do show is the rise and decline of different livelihoods and the geographical areas over which they were practiced: hunter-gatherer practices, pastoralism, low-intensity shifting agriculture such as swidden, and higher-intensity continuously-cropping agriculture (the dataset ends at 1850 so they leave out so-called “conventional agriculture” which is much more intensive than most of what existed before 1850). They also have some data on the rise of cities around the world.

ArchaeoGLOBE finds that increasingly intensive forms of agriculture replaced hunting and gathering in waves in different geographical areas since 10,000 years ago. Compared to estimates based on modeling of ecological data, they also find that humans had a wider-spread influence on the environment in the form of hunting and gathering practices, at an earlier date, than previously thought. This has been widely reported as a surprise, with an undercurrent of dismay: humans were never innocent, we have been disturbing the balance of Nature right from the beginning.

What I find confusing about this is that algae, trees, beavers, elephants, ants, bison, prairie dogs, wolves, wild boar, corals, earthworms, soil mesofauna, and a whole bunch of other widely distributed taxa have been modifying habitats and biogeomorphological processes for way longer than 10,000 years and no one finds this disturbing or surprising. In fact, ecological systems as we know them depend on the long-term and large impacts of these species. This is called niche construction (evolutionary-scale) and ecosystem engineering (ecosystem-scale). In my own work, we have found that if you compare human ecosystem engineering to the same behaviours found in other animals—we looked at path-making—the mean impact on the ecosystem is comparable (Root-Bernstein & Svenning 2018). In a forthcoming paper (Root-Bernstein & Ladle in press) we ask what happened to all the ecosystem processes carried out by hunter-gatherer humans when these were replaced by other livelihoods, as the ArchaeoGLOBE paper demonstrates has occurred around the world. What have ecosystems lost with the loss of human hunter-gatherer ecosystem engineering/ niche construction?

In the Science paper livelihoods are treated as the same as land-use change. Thus there is an assumption of correspondence between what state or condition the land/ environment is in, and what category of livelihood practice is taking place there. This assumption is tricky and often problematic. Within any livelihood category or land-use category, different impacts may be had depending on the intensity with which it is carried out, and the habitat context. A “green” urban area and a polluted city are both cities, but can be expected to have different ecological impacts (that’s the point!).

The authors do point out (in a rather ambiguous and noncommittal way in my opinion), “Our data seem to support a unilineal trajectory toward increasingly intensive land use and the replacement of foraging with pastoralism and agriculture, a process that appears largely irreversible over the long term. Such trends also mask more complex pathways, as well as reversals at the local scale in numerous regions. In some parts of the world, agriculture did not simply replace foraging but merged with it and ran in parallel for some time…” In other words, to put it more forcefully and perhaps clearly, although the big-picture story makes it look like humans have no choice except to modify the environment for agriculture in ways more and more intense, there is nothing inevitable about this. Complex stories of politics, technology, culture and violence lie behind these short-term (10,000 year) ecological macro-trends. Nothing in politics, technology, culture or violence is preordained. As many particular cases of hunter-gatherer and agricultural coexistence or mixing have shown, different kinds of livelihoods have many possible stable points.

I’m not suggesting that we all leave the cities and become itinerant hunter-gatherers tomorrow. Socio-ecological systems can’t just be reversed or set back to a previous time point. But socio-ecological variation in the past should inspire us to create socio-ecological variation in the present and future. Humans are not inherently bad and doomed to destroy the world, any more than are worms or trees.

The real story here is not that human hunter-gatherer impacts are more widespread than we thought, but that all of this niche construction and ecosystem engineering, and their contributions to ecosystem dynamics, have not only been lost, but also replaced by something qualitatively different. Perhaps human destruction of the environment today can be explained (at some level) when we think of humans as a large omnivorous disturbance-making foraging animal, like bears or pigs (as we do in Root-Bernstein & Ladle in press). When you are that kind of animal, you make a small or medium sized disturbance—you destroy a rotting log to find larvae in it, or you turn over the leaf litter over several hectares. Then you turn your back on it, go away, do other things elsewhere for a season or a year or two, and then when you come back, something new, interesting and useful has grown up in the place where you made a mess before—oak seedlings that will eventually feed you, some mushrooms, a pond. This doesn’t happen anymore with the kinds of disturbances most of us are now contributing to. We now make not small or medium scale disturbances, but big ones that simply destroy things and take a long time to recover from (this is predicted by the Intermediate Disturbance Hypothesis). Our disturbances are now not only large but huge, and of many evolutionarily novel varieties—such as all our industrial wastes—meaning sometimes there is no existing natural process to convert them into anything else. Perhaps it is no wonder we externalize all these costs and ship our waste to wastelands—turning your back and expecting the world to revert to a useful state again in short time span all by itself seems to be the behaviour and psychology of the kind of animal we are. Notoriously we are not particularly good at caring about the distant future, worrying about things we can’t see, or cleaning up after ourselves*. So we should not play to our weaknesses by creating socio-ecological problems that fall into those black holes. We could play to our strengths by designing systems that are reusable, recyclable, or have circular economies. Reinvesting urban ruins with new uses is an example of the human talent for thriving on short-term cyclical regeneration. We need economic and technological systems that operate like ancient swidden farming.

*I am not trying to justify the social and technological systems that thrive on these forms of “irrationality,” nor lend support to the elaborate anti-empathetic cultural justifications that in turn justify those systems, I am just looking for what kind of world our intelligence works well in. While there is considerable work on psychological biases (perhaps because we seem to be creating a world that is escaping our ability to be smart in it), there is less emphasis put on what we are cognitively/ emotionally good at.

References:

Root-Bernstein, M., & Svenning, J.-C. 2018. Human paths have positive impacts on plant
richness and diversity: A meta-analysis. Ecology and Evolution 8(22), 11111-11121.
Root-Bernstein, M., & Ladle, R. In press. Ecology of a Widespread Large Omnivore, Homo sapiens, and its Impacts on Ecosystem Processes. Ecology and Evolution
Stephens, L., Fuller, D., Boivin, N., Rick, T., Gauthier, N., Kay, A., ... & Denham, T. (2019). Archaeological assessment reveals Earth’s early transformation through land use. Science, 365(6456), 897-902.

--Meredith Root-Bernstein 2-9-2019

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