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This is one of a series of questions centered around how an isolated group of people would survive. Each question focuses on a single aspect of survival. Details about the peoples' situation are below:

In a novel I am developing, an undefined number of people is living on a peninsula. The isthmus connecting the peninsula to the mainland is very narrow, and spanned by a wall, which prevents the people from leaving (there are deterrents preventing them from climbing the wall or otherwise circumventing it). They also cannot swim around the wall. This also means that no land-based animals can cross onto the peninsual from the mainland. The inhabitants have to live with what they have. For the sake of details, assume the peninusla is roughly the size, shape, and location of Mahia Peninsula.

My question is about the population. I want to know how many people I can have on the peninsula (all living together in one village) and still maintain the ecosystem.

I want to avoid such things as deforestation and hunting animals to extinction (remember that the animals are stuck there too), as well as depleting the peninsula's natural resources. Taking into account the size of Mahia Peninsula, how small does my population need to be to avoid these things?

A very important detail is that there are novel-related events which keep the population at the same number. Overpopulation through reproduction is not an issue.

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According to this blog, a pure hunter gathering society would need around 10 square miles per person, although this number can vary depending on the exact environment. Your peninsula is around 100 square miles, which means it might be able to only support around 10 people sustainably. But Mahia is a tropical area with a lot of wildlife, so maybe you can bump that down to 5 or even fewer sq. miles per person, for a small village of 20-30 people.

On the opposite end of the spectrum is agriculture, which is very efficient at feeding people. Going off the top post in this thread, 1.2 acres per person is a reasonable amount. But this also includes land needed to raise animals for meat, which might not be realistic here. At 1.2 acres, if you converted the entire island to agriculture, you'd have enough food for around 50,000 people. If you skipped the animals and had perfectly efficient farmers with no soil degradation and such, you can even lower that down from 1.2 acres to a mere 0.2 acres, or 5 people per acre. At that rate, your population could boom to a massive 320,000 people. Although this doesn't take into account space needed for housing and other requirements.

With these numbers, even accounting for less than optimal farming practices, you could easily set aside a tiny portion of the peninsula for agriculture, say around 10%, and keep a modest population of around 3,000, leaving the rest of the area in its more or less natural state.

At this point, the last factor to consider is deforestation. It takes a lot of trees to build a home, around 22 per. If we suppose there are an optimal 700 trees per acre, then one acre can build around 30 homes, or enough to house 150 people. With our population of 3000, then you'd need a mere 20 acres to house everyone, which isn't many compared to the total size of the peninsula. This number would likely be higher in your circumstance (your forests won't be pure lumber trees), but even then I think your forests would still be sustainable.

Obviously, there's a lot of spitballing here. A lot of my numbers depend on North American data, for one. You'll definitely need to tweak things around, but the main takeaway is that you can have a sizable population without too much harm to the environment.

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  • $\begingroup$ It looks like those 22 trees are for modern-day houses. How many trees would it take to build a fairly robust Polynesian-type house? $\endgroup$ – Thomas Myron Nov 27 '16 at 1:31
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The limiting factor for enviornmental degredation is firewood. And not just for home fires and home cooking, though that is important; the limiting factor is firewood for industry. Do your people smelt copper and bronze? Iron? Make glass? Then they need charcoal in immense quantities.

Here is a paper on someone imitating a bloomery technique. They used 90 kg of charcoal to turn 40 kg of ore into 4 kg of iron. And according to FAO, firewood turns to charcoal at a 7:1 ratio, so you need about 600kg of lumber (over a half a ton) to make one axe or sledgehammer.

The FAO link also states that the 'least developed' countries in the world, which get 86% of their energy from firewood, use an average of 1.18 m$^3$ of firewood per person, per year. Wood density is variable, so lets say 1.18 * 700 kg/m$^3$ (about oak or maple density) = 825 kg per year.

Lets put the above together to figure out hoe much wood we need. You can do your own math based on technology level, but lets say that per-capita consumption of iron, bronze and/or glass totalls 20kg per person, for 20 * 600 / 4 = 3000 kg of firewood, plus 825 for domestic use is 3825 kg of fire wood per person per year.

From a New York State handbook,

A well-managed and well-stocked hardwood forest on a good site in the Northeast can grow approximately 250 board-feet of lumber per acre over a 90-year rotation from seedling to mature tree.

A board-foot is 144 cubic inches, so 250 board feet = 36000 cubic inches = 0.59 cubic meters. This only counts lumber, so you would get more burnable mass, but then it is for a good site, and not all sites would be good sites. We'll call those two factors even.

Using the density factors from above 0.59 cubic meters = 413 kg of wood, so the average person would need about 9.25 acres or 3.7 hectares of forest land; if all forest land was being actively used for wood production.

Lets add in arable land to bring the total to an even 5 hectares requried per person. If Mahia peninsula is 200 km$^2$, or 20000 hectares, then you can have a max of 4000 people in your village. And that is riding the very edge of ecological sustainability. You probably want less than that, more like 2000 or even 1000 people.

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  • $\begingroup$ Thank you for your details and research. It looks like there's some good info in here. However, I'm planning on my people having no metalworking abilities. The most advanced tools they have are wood and stone. I'm assuming this would greatly reduce the amount of wood they need? $\endgroup$ – Thomas Myron Nov 27 '16 at 2:33
  • $\begingroup$ @ThomasMyron Well then drop the 3825 kg to 825 kg per person (I assume they still need firewood) and re-calculate. I get 0.8 hectares of forest per person; rounding up to 2 with arable land that leaves a max of 10,000 people, but again more like 3 or 4 thousand is probably better. $\endgroup$ – kingledion Nov 27 '16 at 3:22

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