The garden habitat is what we are really trying to manage

The garden habitat is what supports the growth of all your plants and is managed through and understanding of the basic principles of garden ecology. The garden habitat begins in the soil and this is an ecosystem in its own right, so I will be dealing with soil biology separately , however, all the basic concepts will apply in soil just the same. Also, the condition of the soil has a big impact on the habitat, so it is worth the effort to improve your garden soil.

Ecological succession

One of the most important concepts to become familiar with is that of ecological succession. If you have heard people talking about "Old-growth forest", this is what you get at the end of a succession (in a forest). At the other end of the process is a 'disturbance'.

Lets say there is a bush fire. This disturbance can be regarded as nature re-booting an ecosystem. Some trees may survive, but essentially the forest must start again from scratch. New trees, shrubs and herbs sprouting from seed.

Of course, this is not a random process. Short-lived herbs grow profusely first. These are called 'Pioneer species' and they cover the ground, creating a micro-climate suitable to the germination of under-story shrub seeds.

These taller species grow and shade out the herbs, which allows the upper-story trees to grow, These eventually shade out many of the under-story shrubs to make room for a range of other species. At the end of the succession you have a climax community.

In the garden habitat, herbs and vegetables are mostly pioneer species, fruit trees and vines are under-story species and things like Walnuts and Ginseng are examples of climax species.

Disturbance

In the garden habitat this is the most important concept to understand, since virtually all gardens are managed in a state of perpetual disturbance.

Although the previous example of a bush fare was rather extreme, disturbances can be quite subtle. They don't even need to be 'bad'. Put simply, a disturbance is anything that interrupts the 'status quo' of a community. It could be a frost, drought, cultivation, irrigation or even just the application of fertilizer. What is important is understanding the consequences of each disturbance so you can manage things properly.

For example, in your garden habitat, digging in the vegetable garden interrupts the status quo that had existed before and create an opportunity for pest and weeds. Mulching around your new seedlings with straw will serve to minimize the disturbance and reduce the opportunity for pests and weeds.

Biodiversity

I bet you think that when it comes to biodiversity, more is better. Sorry, not quite that simple. Every ecosystem has just so many available niches that one or more species can occupy.

The species that form the community can be of two broad types - generalists and specialists. Put simply, a specialist can occupy only one niche, while a generalist can adapt to more than one.

Adding extra species to increase the biodiversity will do one of two things. Either it is a specialist and there is no niche available, so it dies out; or it is a generalist and populates like a weed, eliminating those species already there.

In a garden habitat, we manage this problem by keeping the potential combatants apart - each to its own space and no more. Although, if you believe that really works then you have never grown gooseberries, forget-me-not, mint, Chilean Balsam, and son, and so on.

Niches

So what is a niche? In basic terms it is a combination of space, interactions and micro-climate that presents an opportunity for something to live. For example, horses are adapted to situations where they can access new growth that follows after other herbivores have grazed an area, with space to run when confronted by the predators with which they interact. That is their niche.

In the garden habitat, many herbs and vegetables are pioneer species that are adapted to disturbed areas of high fertility soil, low population densities and few interactions with other species (except the gardener of course, when harvest time comes around!).

Micro-climate

OK, this sounds straightforward - like climate, only smaller? Yes, well sort of. Climate is a particular combination of seasonal temperatures (day and night), day-lengths, rainfall, humidity and sunlight hours (also called heat accumulation). Many people think of these things as averages, such as average annual rainfall, etc. While these measures are important, the seasonal distribution of rainfall is often more important.

For example, the climate where I live is a one with varying day length from one equinox to the next and day temperatures varying between about 10°C or less in winter and 30°C or more in summer, with a moderate (about 800mm), winter dominant rainfall pattern and generally high humidity and low frost risk. In short, a warm temperate, winter rainfall, maritime climate.

A micro-climate would be a localized variation on the overall climate, such as a local rain-shadow area, a riverbank that remains damp and relatively humid year round, and so on.

In the garden habitat, you can make use of various micro-climates by learning about the plants you grow and using combinations and placements to give them the best conditions. For instance, Ginseng is a shade loving plant, so you either build a shade house or wait until some trees have grown the you can plant them under.

Air Movement in the garden

One aspect of micro-climate that is of special relevance to the garden habitat is air movement. This is not simply wind, but the way air moves through the garden. Like the flow of a river, there can be still ponds, rapids and turbulence.

Still air is conducive to the development of fungal diseases in plants and so we try to minimize these. This can sometimes be difficult in gardens surrounded by solid fences. We can also use windbreaks to slow down air flow and prevent wind damage. However, the risk in both these cases is the creation of drafts. These are directed and relatively continuous air flows that most plants cannot tolerate. Interestingly, one of the few plants that can tolerate drafts is Aloe vera

Competition and Rivalry

Like most people, I used to think of competition as a good thing. The driver of evolution! Textbooks define it as a situation where two or more species need to access a limited resource and their populations are constrained according to how well or how poorly they compete for that resource.

Then I saw an interesting experiment with Pea Weevils that was inspired by the work of some entomologists working in the Amazon.

Peas grown in a greenhouse were deliberately infested with weevils. Later, the peas were harvested and grouped according to the number of 'stings' on the outside (ie. the number of marks left where a weevil had laid an egg).

Those with no stings had no grubs inside - no surprise there. Likewise, those with one sting had one nice plump little weevil grub inside, but the rest...

No matter how many additional stings, whether 2, 3, 4, or more - there were no additional grubs. In fact there were no grubs at all! Not even a sign that any of the peas had been chewed on.

The bottom line is that a pod of peas cannot provide enough food for more than one grub to reach maturity, so it would make no difference if one was a better competitor or had a head start or anything - the moment more than one egg was laid, all the grubs in the pod died.

The classical idea of competition is actually just rivalry, but where the resource goes from limiting to limited, it becomes competition and as such is "Equally Lethal to all Competitors".

In the garden habitat, there is probably not much you can do with this, but it is good to know as you watch things grow and develop.

Allelopathy

Many plants control the level of competition (or rivalry) they must tolerate, but producing toxic compounds in the soil to keep others away. This is called 'allelopathy' and can involve compounds secreted directly from the roots, or that some that are produced by decomposition of dead leaves, bark or roots.

Although a common strategy, this can be a double-edged sword. For instance, Peach trees produce a toxin from their roots, but it is not just toxic to other plants - it kills Peach roots too. This is why Peaches need very well drained soil - even 24 hours of wet conditions will result in roots dying from their own toxin!

Not many herbs or vegetables do this, but one notable example is asparagus, which produces allelochemicals from dead, decaying roots.

Further reading and Useful Links

We will be adding more to this page from time to time, but below there are some useful links to help get you going in the meantime.

Of course another good way to stay in touch with this rapidly developing topic is to subscribe to our Free newsletter - The Food Gardener