Trees are integral parts of most permaculture designs. They are also an incredibly important part of the global ecosystem. One of the reasons that designs make trees a central component is that they perform so many different functions.
Perhaps the most immediately obvious function of a tree is to provide a harvest. Many of the trees in a permaculture design will be fruit trees for this reason. With judicious design, even a small plot can support a number of different fruit trees, providing succession harvesting so that you have a fruit crop at different points throughout the year, and offering variety to your harvest and, hence, diet.
When leaves fall from the branches of trees, they are just starting the next stage of the cycling of nutrients through an ecosystem. Fallen leaves are one of nature’s great mulches. Leaving the foliage on the ground allows it to rot and all the nutrients contained within it to return to the soil where they can be used by the tree and other plants to create more growth. A good covering of fallen leaves also acts to help prevent excess evaporation of moisture from the soil and keep weeds in check. Alternatively, you can add fallen leaves to your compost pile where the same process will take place, as bacteria and other microorganisms break down the leaves.
When trees need to be pruned, perhaps to thin out the branches and allow wind or rain to move through them, or to allow more sunlight to penetrate to the ground cover underneath, the removed branches are valuable additions to the compost pile. Cut the branches into small pieces so that they break down quickly.
A tree also offers shade from the sun. This can provide relief for livestock, but also enable the permaculture gardener to plant suitable species in the shaded niche that the tree creates. Trees help gardeners to influence and expand the range of microclimates on a permaculture site. Trees can also be used to shade houses, reducing the need to use energy-hungry air-conditioning devices in the summer months.
Simply by performing their natural processes, trees improve air quality. By giving off oxygen, they benefit not only the organisms in their vicinity, but help, in their small way, the overall quality of the atmosphere. The removal of trees across the planet is one of the reasons why climate change is accelerating – there are not enough trees to help convert excess carbon dioxide into oxygen, meaning that excess enters the atmosphere. The trees can also help to filter the air that flows through them, removing dust and bacteria before the air reaches other plants, and the gardener!
One of the functions that trees are best suited to providing on a permaculture plot is as a windbreak. Sited correctly, having done an analysis of wind direction and speeds, trees can help divert wind from more vulnerable plants. This windbreak effect is also beneficial to animals, from chickens to insects. If you are considering instituting a beehive on your plot, a position on the leeside of a tree line windbreak is ideal. Trees can also be used to divert cooling winds away from houses, so helping them maintain their warmth during the winter months.
Trees add to the aesthetic appeal of a permaculture plot. Majestic and vital, they offer many pleasures to the permaculture gardener, from the sound of the wind through their leaves, to the colour of their blossoms in the spring. Added to this is the sight and sound of the wildlife the trees attract, as well as the opportunity to sit in the shade of a tree on a summer’s day and appreciate the beauty of the permaculture garden. Being around trees is also thought to reduce stress. In Japan there is a recognised therapeutic notion called ‘forest bathing’ whereby taking a walk among trees allows stress levels to fall and mood improve.
Trees put down strong, deep roots. This enables them to draw up nutrients from lower down in the soil, making them available for plants around them with shallower roots. These strong roots also help to improve the soil structure, creating more passages through which aeration of the soil can occur, as well as the percolation of moisture, and the movement of organisms living in the soil. The roots of a tree also help to maintain the integrity of the soil, providing an anchor that helps prevent erosion by rain and wind. This is one of the main problems when forests are cleared for the planting of monocultures – the soil is no longer bound together and is easily eroded.
A tree provides a habitat for animals. Insects are attracted to its blossoms and fruit, while birds are attracted by the fruit, the availability of insects to eat, and the coverage the tree’s branches offer both for protection from the elements and predators, and a place to nest. Trees also offer benefits to the permaculturist’s livestock. A fruit tree offers foraging opportunities for chickens, ducks and pigs, and as they eat fallen fruit they help to prevent potentially damaging pest insects, which use the fallen fruit to lay their eggs, from breeding.
Trees help to irrigate the land more effectively. The canopy of leaves of a tree means that rain is dissipated over a larger area, dripping down through the leaves and being diverted to the tree line. This helps to make moisture available to a greater number of plants underneath the tree. And by dispersing the rain over a larger area, the tree also helps to prevent soil erosion.
These plants that are underneath and planted around the tree can, in a permaculture design, provide an effective guild with each species contributing certain functions that benefit the whole group of plants. For instance, the tree might provide shade that helps a nitrogen-fixing leguminous plant thrive which in turn benefits another species that attracts insects that are beneficial to the pollination of the tree’s blossoms.