Huge country. Small population. High population density? How can that be? It all makes perfect sense once you realize we are measuring physiological population density and not arithmetic population density. The difference between the two makes a big difference!
Physiological Population Density Definition
If you are a country with lots of deserts, a single river, and a large population that is growing quickly, we're probably talking about you.
Physiological Population Density: The ratio of people to farmland (arable land), usually applied to countries or country subdivisions.
Physiological Population Density Formula
First, find the total population (P) of a unit of land (such as a county, state, or country).
Next, find the amount of arable land (A) within that unit of land. It will be either equal to or less in area than the unit of land.
Arable land is land that is farmed for crops, either actively or in rotation (i.e., is currently fallow but is part of a cropping system). Arable land does not include land that could theoretically be farmed but has not been converted to cropland, such as a forest. It also does not include pasture and grazing land unless part of a crop rotation system (in cases where animals are pastured on fallow cropland).
The physiological population density is P divided by A (P/A).
In the US, this is likely to be expressed as people per square mile, and in the rest of the world, as people per square kilometer or hectare.
Agriculture and farming, which include animal grazing, are often confused with cropland. Some measures of physiological population density may also consider population density in relationship to cropland AND grazing land. Meanwhile, agricultural population density considers the ratio of farms (and/or farms) to arable land.
Difference between Physiological and Arithmetic Density
Arithmetic density gives us the population density across an entire area, whether cropland or something else.
In a completely agricultural region made up only of arable land, physiological and arithmetic density are equal. In areas with no cropland whatsoever, there is no physiological population density.
Fig. 1 - Rice farmers in Bangladesh. Sixty percent of Bangladesh's land area is arable, the highest ratio in the world (Ukraine is 2nd, India is 5th)
The difference between the two types of density is important in regions with both arable land and non-arable land. In this case, it can be very misleading to assume that arithmetic population density is accurate and helpful if we are trying to determine the relationship between people and food consumption.
Country X has an arithmetic population density of over 3000 people per square mile. Over 50% of the land in the country is arable, so can country X feed itself? Some figures state that a single person can survive for a year on crops from about half an acre (a large garden), and there are 640 acres in a square mile, so it looks like only 1450 people per square mile could be fed. Country X might not be self-sufficient in food, then. However, we used the figures for Bangladesh, which is self-sufficient in rice (its staple crop, which is highly productive/acre), an amazing achievement for a country once hit by famines.
Country Y has the same arithmetic density as Country X, but its physiological density is around 10000 people per square mile. Can it feed itself? Not with its arable land, since ten thousand people have to rely on each square mile of cropland. Country Y is very likely a net food importer, at least of its fruits, grains, and vegetables.
Meanwhile, Country Z has a physiological density of 10 people per square mile. Country Z is likely a net food exporter.
Countries with High Physiological Density
Let's consider the top ten countries in the world in terms of their physiological population densities (PPD).
The Top Ten
This eclectic list is 1) Singapore, 2) Bahrain, 3) Seychelles, 4) Kuwait, 5) Djibouti, 6) United Arab Emirates, 7) Qatar, 8) Maldives, 9) Andorra, and 10) Brunei.
Singapore, a wealthy city-state, has a PPD of 386100 people/square mile compared to an arithmetic population density (APD) of 18654 people/square mi, a huge difference. This is because of Singapore's total land area of 263 square miles, only two square miles are arable land.
Indeed, most of the above are quite small in area (UAE is 32000 square mi., but mostly desert), and thus obviously can't rely on their own crops for food. Five are desert countries, four of these wealthy emirates in Southwest Asia, and one, Djibouti, is a state based around a port in the Horn of Africa. They have close to no cropland, people live almost entirely in urban areas or are nomadic herders or fishermen, and national income is used to buy crops on the international market.
The Pyrenean micronation of Andorra survives on tourism revenue, as do the Indian Ocean nations of Seychelles and Maldives. Brunei is an oil-rich rainforest nation that protects its forests rather than turning them into farms.
In other words, these, and others farther down the list, aren't highly relevant to the concept of physiological density.
AP Human Geography requires that you understand the differences between the two types of population density and in which cases each is informative for demographic studies.
Taiwan
Taiwan, at number 20 in the world, is the first country on the list for which the concept is quite useful. Taiwan's APD of 1849 people/square mile is a fifth of its PPD of almost 10000 people/square mile because much of Taiwan consists of high, steep mountains that are largely useless for crop cultivation. If you didn't know this, you might think Taiwan can feed itself. While its farming areas are critical to providing food for its population, Taiwan does not have nearly enough arable land to do so and relies heavily on food imports: it is equivalent to Country Y in the example above.
The US
The US, at number 173 on the list, has one of the world's lowest physiological population densities. It is also number two in total arable land area in the world (after India, which has three times the population of the US), so, not surprisingly, like County Z in the example above, the US is a net food exporter. Indeed, the US exports more food, in volume as well as value, than any other country.
Physiological Population Density Example
Wealthy desert countries such as Qatar and Bahrain have barely any cropland, but they can also afford to import what they need. Egypt, another desert country, is another story.
Egypt
Egypt, with around 110 million people and growing rapidly, has a moderate arithmetic population density of 289 people per square mile, around that of France or Turkey, countries with little problem feeding themselves. However, Egypt's physiological population density is around 3500 per square mile, one of the highest in the world for non-city states. This isn't much higher than Bangladesh, but Bangladesh is a wet, tropical country with plenty of fresh water and no need for irrigation. Most of Egypt's population and crops can only exist along a narrow ribbon of land and water, the Nile Valley and Nile Delta.
Egypt depends on every square inch of available cropland and, outside a few oases, irrigation from the Nile.
Fig. 2 - Population density of Egypt's governorates (subdivisions) shows the contrast between the high concentration of population along the Nile, increasing to the north where more cities are located, and the extremely low densities of the desert
Before Egypt went through the demographic transition, farmers had large families, but populations grew quite slowly. Now, people still have large families, the population is growing rapidly, and little new farmland is available (though see below). Thus, people who stay in Egypt must find other trades, and their numbers tend to swell the cities. As urban areas grow larger and larger, buildings, roads, and other infrastructure overwhelm agricultural land, driving physiological population density even higher. Water becomes scarcer and scarcer. More and more people depend on the same amount of cropland. is there any way out of this debacle?
Modifying Physiological Density
Physiological population density can be changed if non-arable land can be made arable. If you have ever flown over the US, you may have seen this in action. The semi-deserts of Nebraska's High Plains, underlain by the Ogallala Aquifer, pump fossil water from the last Ice Age to the surface to make land arable that otherwise would only be suitable for grazing.
Making the Desert Bloom, but at What Cost?
Egypt can theoretically make the Sahara arable. This is not far-fetched: the Sahara, after all, was once a grassland in wetter times of the Earth's history. All that is needed now is water. But there is a catch (several, actually) to altering your physiological density by increasing your amount of arable land.
Irrigation needs water from somewhere. In Egypt, this could mean turning Red Sea or Mediterranean saltwater into freshwater, using water piped from the Nile, buying freshwater from another country, tapping into aquifers, or some combination. Here are the catches:
Aquifers are problematic because, if they aren't recharged fast enough, often the case in deserts, they will run dry.
Without rainwater to flush out mineral salts, avoiding salinization of irrigated soil can be difficult. Once salinization happens, agriculture is no longer an option.
Desalinization of seawater only works for wealthy countries because it is an extremely expensive technology.
Pipes from the Nile? This threatens the ever-growing need for freshwater in urban areas as well as existing agriculture along the Nile.
As for neighbor countries, they are either in the same situation (e.g., Libya, Israel, Jordan, Saudi Arabia) or they are not on friendly terms (e.g., Sudan).
Changing the Farm
What if we farmed desert plants or at least plants that don't need much water?
The farming of cacti, particularly the nopal or prickly pear (Opuntia), provides nutritious food as well as a cash crop.
Fig. 3 - The prickly pear or nopal is one of many species of cacti that grow as weeds in Mexico and elsewhere but are also farmed for their delicious fruit
Farming the City
Traditionally, arable land has meant rural land where plants grow in soil. But what if we changed the definition of crops? What if they could grow on a wall, a road, or a vacant lot? Stacked up in layers...underground? Without soil? Welcome to the world of hydroponics, aeroponics, and other urban agriculture solutions.
The idea here is that cities can and should provide much of their own food. And why not? The majority of humanity lives in cities, and the proportion is steadily increasing. Yet cities are filled with spaces where food could be grown (and boy, would it cut down on transport costs!). French intensive gardening has existed in France's urban areas for over 500 years, after all. And in China, it is common to see vegetable gardens filling every available niche in cities.
Physiological Population Density - Key takeaways
- Physiological population density is the ratio of people to arable land.
- Physiological population density expresses the demand of people on cropland and gives a measure of whether a country is likely to be self-sufficient in food, a food importer, or a food exporter.
- Physiological population density is more useful than arithmetic population density wherever the relationship of people to cropland is being studied.
- Physiological population density can be altered if more non-arable land is brought into cultivation, or crops with higher yields, such as rice, are planted.
References
- Fig. 1: Bangladesh (https://commons.wikimedia.org/wiki/File:Farmer_of_bangladesh.jpg) by Ashef Emran is licensed by CC-BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)
- Fig. 2: Egypt density (https://commons.wikimedia.org/wiki/File:Population_density_of_Egypt_governorates.png) by Austiger is licensed by CC-BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)
- Fig. 3: prickly pear (https://commons.wikimedia.org/wiki/File:Purp_F,_Prickly_Pear_1833.jpg) by Chris Light (https://commons.wikimedia.org/wiki/User:Chris_Light) is licensed by CC-BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)
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