The Earth has existed for about four and a half billion years. Over this time, life came forth and populated the lands and seas. The life-forms, including us, do not live in isolation. We live in a rich web of inter-dependencies. We call this a complex ecological system or ecosystem.
Some characteristics of the land make for greater quantities of life and for richer varieties of life. For example, a tropical rain forest supports a tangled, expansive web of plants and animals. Other locations such as the Antarctic are almost barren of life. At least this was the Earth up to a few hundred years ago. Now, humans have made such an impact on the Earth’s ecosystem that they are creating a lasting effect. Future plans for civilization may have to consider whether the richness of life has value.
Biodiversity is a word that conveys the richness of the disparity of life. Land with many species and specimens has a high biodiversity. This occurs where energy is abundant and is readily mobile. For example, estuaries, tree tops and swamps have high biodiversity. Where there is little energy or little capacity to move energy about, there are few species and specimens. For example, as nothing much moves in the freezing cold of the Earth’s poles, they have a very low biodiversity.
What’s happened in the last few hundred years to change this? It’s us. Traditionally humans have usurped land with the richest supplies of immediate energy. Just consider the Babylonians and how the took over the Euphrates river for their own purposes. They removed the indigenous flora and fauna and built fields to cultivate crops. This removal, effectively the removal of the competition, was one of the first steps to re-image the land to solely benefit people.
The following map provides an indication of our re-imaging. It shows biodiversity hot spots; the richest and most threatened areas of the world.
In the above figure from Conservation International, the red areas on the map show where significant, threatening changes are ongoing.
What does this mean to us? It means that in planning for the future we should realize that humans were a part of somewhat balanced, sustaining ecosystem. But we are changing the balance. We change the land for our benefit. But this usually doesn’t benefit the local flora and fauna. Does our civilization’s future mean that we only allow species providing a direct, immediate benefit?
Take a look at the IUCN Redlist to get a feeling on the immediacy of this.
So when we consider biodiversity and the land, what do we mean? Well, through observation, we’ve learned to characterize land types. This characterization is usually a direct indicator of the land’s biodiversity. Plans for the future will use land characteristics to determine and enable energy flow. For example, is it better to place a new city on a lifeless desert (e.g. Las Vegas) or over a rich river delta (e.g. New York)? Associating ecosystems with land cover and with energy deposition can provide an indication of the amount of energy that is available and the amount that can be sustainably appropriated. The following map and table give an indication of our current knowledge.
This map defines land characteristics based upon satellite measurements made by the NOAA. The following table identifies the land types as defined by the NOAA.
There are many ways to characterize the land. As new, better satellites operate then classifications can be refined. Or, classifications can be more coarse as the FAO provides in the following table.
|Total area||13 432 420 000|
|Land area||13 013 475 400|
|Agricultural area||4 967 579 500|
|Arable and Permanent Crops||1 561 681 000|
|Permanent Pasture||3 405 897 000|
|Forest and Woodland||3 952 025 700|
|All other land||4 092 972 400|
|Inland Water||429 928 000|
In the above table, the values are in hectares for 2005. The database was accessed 2009 February.
For assessment purposes, this table of coarse values is very demonstrative. From it we see that humans use about 38% of the land’s surface for agriculture. That is, humans have appropriated 38% of the land from wildlife for their own purposes! True, we’ve left some behind; about 30% is forest and woodland, likely the Amazon forest and the northern taiga. And there’s about 31% as land that’s not able to sustain life; deserts, glaciers and such. For another comparison, the values tell us that humans have appropriated more land than what we’ve left for other species. Is this the future that our civilization path should continue?
In order to assess the global impacts of land use on the environment and help provide appropriate countermeasures, a group of researchers under the leadership of the Helmholtz Centre for Environmental Research (UFZ) has created a new world map of land use systems. Based on various indicators of land-use intensity, climate, environmental and socio-economic conditions, they identified twelve global patterns called land system archetypes.
Explore the UFZ site for more information.
In summary, with satellites we can now determine, with great fidelity, the land cover type. And the change in land cover type.
Why is the characterization of land so important? One reason is that with characterization we can measure what we’ve done to the Earth and we can consider futures or plans for the future of Earth. For instance, we’ve noted that it’s the mobility of energy that aligns with great biodiversity. Thus characterizing the land enables us to assess the potential of land for the future.
One thing to keep in mind is that before humanity’s great technological advance of the last few thousand years, we relied solely upon the biomass for our energy. To cook something we used a wood fire. To hunt something we made a spear from a sharpened rock and a wooden stick. Once we’ve exhausted the fossil fuels, we’ll need to find our energy from other sources. Know that the biomass, or vegetation, lies at the base of the trophic pyramid. At least it will as long as it still exists.
Vegetation is also refereed to as biomass production or net primary production or NPP. The following maps give an idea of the impact that we have had on the land surfaces of Earth. Obviously any appropriation that is greater than the rate of replenishment is not sustainable. If we use 100% or more of the net primary production, then the vegetation can not replenish and it will perish. Thus, it cannot collect any more energy from the Sun for us to use. The sustainable level of appropriation is likely much less than 100%. Yet, from the first map, we see that huge swathes of the most productive land are having their energy stores directed to human usage.
The map above was created by NASA, 2006.
We can also consider the HANPP as a value rather than a percentage. This allows us to visualize where human’s are consuming the most as seen in the following map.
The news is no better for the ocean resources. We will discuss this later.
In summary, today, humans draw their energy mainly from fossil fuels. However, once we’ve exhausted their supply then we will need get our energy from elsewhere. We can’t return to using biomass as our energy needs are too great and the amount of available biomass is too little. What do you think humans should use for energy?
The Trophic Pyramid
Energy is essential for life on Earth. Energy enables plants to grow and animals to move. We’ve defined levels of life or a pyramid of life to illustrate the transfer of energy. At the base level are autotrophs. The autotrophs, or plants, typically absorb the energy from the Sun and store it within their structure of barks or leaves. The herbivore is an animal that eats plants. Herbivores traditionally are grazers like cattle, gazelle or bees. At the next level of the pyramid is the carnivores. These hunters eat the herbivores. They include tigers, wolves and sharks. This level of the pyramid also includes the omnivores. These creatures can get their energy from almost anything. The omnivores include humans, bears and swallows. At the very top of the pyramid are the saprotrophs. The saprotrophs eat the dead and allow the energy and material for others to use. When considering the needs for biological energy, keep the trophic pyramid in mind.
While there is energy transfer through the levels of the ecosystem, the transfer is not very efficient. Even after hundreds of millions of years of genetic improvements, there’s still only about a 10% transfer of energy from one level of the pyramid to the next level. The shape, the pyramid, is to highlight this poor transfer rate. The shape also highlights the dependence of one level to its supporting level underneath. The trophic pyramid, as shown below, illustrates a fundamental need of life and we will use its concept extensively in our analysis.
Let’s look at people again. Some people are pure vegetarians. Because of this, they live at the herbivore level of the trophic pyramid. Thus they are much more efficient in transferring energy than the carnivores and omnivores. Even so, their efficiency leads to only about 10% of the plants energy stores getting transferred. But they are more efficient which is why many people vouchsafe a future civilization where vegetarians predominate.
The carnivores eat other animals, usually herbivores but sometimes other carnivores. Because of the inefficiencies of energy transfer, these meat eaters get only about 10% of the energy stores in the herbivores. And this is only 1% of the original energy in the plants. Given this poor energy transfer efficiency, it is no wonder that carnivores on Earth are greatly outnumbered by herbivores who themselves are greatly outnumber by plants.
The tertiary consumer is at the top of the pyramid. It is something to beholden. You may think these would be like the majestic lion, proudly surveying their domain on the Serengeti. Not so. The tertiary consumers are tiny. Almost insignificant. But what they lack in size, they make up in numbers. They are called saprotrophs and they eat the dead! These little critters eat the energy that remains in the rotting corpse of the tree, the cow or the whale. As well, these creatures release the chemicals of the corpse. On being released, the chemicals become available for entry into another body. This is the role of the saprotroph. But remember, considering efficiencies, only 10% of the dead creature or about 0.1% of the originating plant’s energy gets captured by the saprotrophs. As displayed on the trophic pyramid.
Now think on how to plan for the future. We know the amount of energy in the Sun. We know the efficiency of energy transfer between the trophic levels. Thus we should be able to plan. We should be able to plan on the types and quantities of each creature at each level. As we can do this then let’s do it! Let’s plan our civilization so that the energy flow is sustainable and that we continue to share this Earth with other creatures.
We’re going to add fertilizers to this page on the ecosystem and energy transfer as it is crucial to our civilization. This relates to how we changed our lifestyle from being mobile hunter/gatherers to being sedentary agriculturalists. Agriculturalists learned to grow particular plants (autotrophs) in particular places for their own needs. However, as the plants were harvested, that is removed, then the saprotrophs could not return chemicals and energy into the ground. To re-mediate this, the agriculturalists used fertilizer to put chemicals and energy back into the ground for the next generation of plants.
In addition to fertilizer, we’re also going to consider water. The reason for this is quite simple, plants need both fertilizer and water in order to grow. This is appropriate for two reasons. One, without dead plants for the saprotrophs then the dirt losses the chemicals and energy needed for future generations of plants. Two, with people growing plants deeper and deeper into marginal ground then plants needs water and fertilizer to grow. That’s why water is important.
The last thing to keep in mind is that plants beget plants. Agriculturalists plant a seed and calmly, reasonably expect the plant to provide nurture. Wise farmers eat some of the plants and save the seeds of the best plants to use in the following year. Thus every year their crop improves…as long as they get sufficient water, nutrients and sunshine.
How much fertilizer do we use? The International Fertilizer Industry Association (IFA) tabulated a usage of 140 megatonnes (Mt) in the year 2002 as apportioned in the following table.
There is no doubt that adding these fertilizer components increases an agriculturalist’s yield. But, there’s a maximum benefit (see ) after which more fertilizer is a hindrance. And remember that there’s an energy cost to fertilizers; to making or gathering the fertilizer and depositing it on the land.
The European Fertilizer Manufacturers Association (EFMA) paints a rosy picture. They indicate an energy production cost in gigajoules per tonne for the fabrication of Nitrogen as in the following (see).
|1910||Birkeland-Eyde Electric Arc||400|
|1975||Steam Reforming Natural Gas||50|
By experimentation, they determined an optimum application of 170 kg Nitrogen fertilizer per hectare. This yielded 8.2 tonnes per hectare, with the plant having absorbed 126 GJ of solar energy. Without Nitrogen, the yield was 3.5 tonnes per hectare, with 71 GJ of solar energy captured.
Now imagine if all 16.8 million hectares of land now used for growing wheat used this optimum application of Nitrogen. They believe that the result is a yield of 252 gigajoules (GJ) worth of biomass with 126 GJ of grain (ie seed) and 126 GJ of straw. That’s a lot of energy that the humans could garner from the autotrophs.
Also, by the estimate of FEMA, the energy cost for the production, transportation and spreading of Nitrogen is 40, 1, and, 3 GJ per tonne respectively. If 8.2 tonnes are applied to one hectare, the total cost is 360.8 GJ/ha. This results in an increase of 55 GJ of solar energy or an energy benefit of 0.15. Presumably this doesn’t take into account the cost to harvest the wheat, deliver the wheat to manufacturers, mill the wheat into flour and make the flour into food. But, it is a good indicator.
Again,let’s keep these numbers in minds when we assess futures for our civilization.
 Yara, Agricultural Energy Balance
 EFMA, ‘Harvesting Energy with Fertilizers’, accessed 2009 Feb.
Let’s run an example on the flow of energy. We’ll consider mushrooms; they being saprophytes.
People, in addition to hobbits, seek out mushrooms for their wonderful tastes. Coming in many exotic shapes and colours, these culinary treats can bring excitement to many a dinner plate. Caution must always be practised as so many mushrooms are toxic and can kill whether from touch or from ingestion. But getting a bit of education so as to learn which are safe is a small price to pay so as to savour these treats.
Typical mushrooms have a paltry 18 kcal of energy per 70 grams or 1.1e6 Joules per kilogram according to the USDA. Frying these wonders on the stovetop for 20 minutes at medium temperature (about 1000 Watts) consumes 1.2e6 Joules of electrical energy. Hence, frying mushrooms takes more energy than what they provide to us. They’re a net energy loss. And, this doesn’t account for hiking in the woods to pick the mushrooms, effort to clean the mushrooms, building the stove and generating the electrical power to heat the stovetop element.
According to the law of entropy, every activity results in a net energy loss. This is a vivid example of people promoting energy loss. While the flavour of mushrooms may be wonderful, their Energy Returned on Energy Invested (EROEI) is very low. We’ll see more of this term. For now though, consider, when energy supplies become limited then how will we decide which activities are worth the energy expenditure and which aren’t?
Since our solar system began about 4.5 billion years ago, the energy from the Sun has shined upon the Earth. The Earth became covered in living organisms, both plants and animals. In the last few thousand years, humans have created a civilization that uses huge amounts of energy. Humans are also using vast tracts of land for growing their specialized plants and animals (e.g. crops and cattle). As measured by the ecological footprint, this is not sustainable. If we want our civilization to continue into the future then we must find a sustainable path.
Sometimes when planning for the future, it is useful to look at the past. Take a look at our synopsis next.