One of the key principles that underpin all permaculture design is the effort to increase the biodiversity of a site. Biodiversity essentially refers to the number and variability of species of plants and animals within an ecosystem. These range from bacteria, algae and fungi up to birds, mammals and trees. An ecosystem with a rich biodiversity has many plants and animals at many different levels, creating a system that is balanced and self-sustaining.
In a permaculture garden, we seek to replicate these natural systems, increasing the numbers of different plants on the site which will in turn attract a range of insect species that will support a variety of larger animals (as well as providing produce for the gardener).
Not only is biodiversity important on the level of the permaculture plot, it is crucial to the health of the planet as a whole. Biodiverse systems not only provide us with resources and food, they preserve climate stability, provide oxygen, help keep water sources clean, prevent overpopulation of pest species, and provide us with enjoyment and pleasure.
Unfortunately, the biodiversity of the planet is under threat as never before. This is due to the pressures put upon the natural world by the human population – a population that is now over 7 billion strong and still growing rapidly.
The destruction of natural habitats to service the needs and desires of humans is arguably the biggest threat to global biodiversity. The clearance of native ecosystems for the production of agricultural crops, timber for construction, as well as to create space for urbanization and industry destroys all the native species in the area, from the smallest to the largest, and creates many more problems, from degradation of soil to increased threats of flooding. As well as destroying individual animal and plant species, habitat loss also threatens the long-term survival of species not directly targeted, by fragmenting habitats. Smaller areas of native land can only support smaller populations of animals, and are more vulnerable to environmental fluctuations and disease. Fragmentation can also prevent animals reaching other individuals for mating purposes.
Pollution from human activity is poisoning the land, water and animals. A knock-on effect of habitat clearance for agriculture is the increased use of chemical fertilizers and pesticides, which leach into the land and water sources. The runoff of these agricultural chemicals is having a significant impact upon the ocean, by turns causing population explosions of algae which crowds out other forms of life, as well as killing coral reefs, which are among the most diverse ecosystems on the planet. We also pollute the land with our refuse, much of which also ends up in the sea. Chemicals in the oceans become part of the food chain, as larger organisms (including humans) eat smaller ones that have ingested the chemicals. This can have serious health impacts.
A more direct threat to animal and plant numbers is the overexploitation of the natural world by humans. Not only does this impact upon population of targeted species, the removal of certain animals or plants can unbalance ecosystems, leading to further problems. An example would be the over hunting of seas turtles for their meat and shells. Not only are sea turtle numbers very small, hunting them has removed the primary predator of jellyfish from ocean ecosystems. The jellyfish population explodes causing populations of other fish species to decline as they out-compete with them for nutrients in the water. Exploitation of the earth includes everything from cutting down trees for timber, and catching fish for food to hunting animals for their skins or to sell as pets. In general these activities are not done in a sustainable manner (meaning levels of harvest are low enough ensure a viable ecosystem that can regenerate itself), with short-term gain emphasized over long-term sustainability.
In many ways the globalization of the planet, with communication, travel and trade possible to every corner, has had some significant benefits, such as allowing people to experience other cultures and way of life. But it has also meant it has been much easier for alien, or invasive, species of plant and animals to move to a new area, which often results in the diminishment of native species. These species can be introduced deliberately or accidentally, but always affect how a native ecosystem functions. Three examples show the effect of alien species on native ones. In the United Kingdom, American Signal Crayfish that had been imported for farming escaped and entered native river systems. Being bigger than the native crayfish, they invariably won in the competition for food, and now the native species are virtually extinct. A type of tree snake was inadvertently transported from Australia to Guam in the 1950s. With no predators, the snake population expanded and caused populations of native birds to plummet. While on the Galapagos Islands, goats introduced for farming decimated native vegetation that the biologically unique species of the island, such as the giant tortoise depended upon. To prevent the tortoises and other animals going extinct, the government had to cull all goats on the islands.
Climate change is one of the biggest threats to biodiversity on a long-term scale. Carbon emissions caused by human activity are causing temperature changes that affect ecosystems and so impact upon animal and plant species. It is causing some animal populations to migrate to areas they would not normally inhabit, with the potential to upset those systems, while also directly causing numbers to decline. Consider the polar bear. Rising temperatures mean that the pack ice on which they hunt has begun to break up much earlier in the year than previously. This means they do not have enough time to build up the fat reserves that will see them through the winter. Polar bears are now an endangered species.
Climate change is also causing more unpredictable extreme weather events, such as tsunamis and droughts, which affect biodiversity and the ability of ecosystems to regenerate. It is also affecting where humans are able to grow crops, which will also have an impact on native plants and animals, with the attendant problems due to habitat loss, pollution and over exploitation.