The Road to Plant Diversity
Nearly nineteen years ago our orchard was close to a monoculture in terms of plants. Four varieties of apples with just a few species of grass in the mown strip between the rows of trees.
We now have about 90 varieties of apples (about 4000 trees), eight varieties of peaches (about 200 trees), three varieties of nectarines, plus apricots, quinces, olives, plums, cherries, kiwifruit, figs, grapes, pomegranates, almonds, a bay tree, a Juniper tree and we still need to plant some walnuts, chestnuts and various other bits and pieces.
From these 90 varieties of apples we have selected about 30, purely on the basis of taste and disease resistance which we grow in commercial quantities. A totally brown russeted (but delicious) apple like Egremont Russet made the final cut, whereas the modern Red Delicious did not (because we don't think it lives up to its name).
Other than apples, everything is only in quantities that we can easily sell in our local area or of course eat ourselves. And it is advantageous when selling at a Farmers Market to have a wider range of products.
This diversity helps minimize risk, both agronomically and economically. For example a particular variety of apple may be delicious but very susceptible to fungal problems in a wet year. But that cool wet year may be perfect for some of the old English apple varieties. With the climate warming we saw the potential for peaches and about 8 years ago planted a few hundred which have produced beautifully this year.
What grows beneath the fruit trees is quite significant and understorey management of plants is quite a tricky task.
A diverse range of small woody herbs would be ideal. Vigorous perennial grasses are really not good, but around Kalangadoo it can be quite a challenge to prevent Phalaris and Cocksfoot from dominating the understorey.
Grasses compete with the trees for nutrients and this is a problem especially in spring when the grass grows vigorously just when the tree's demand for nutrients is greatest.
Small woody herbs help to encourage a fungally dominated soil which helps the trees better access the available nutrients in the soil. Their root system is not so big as to provide major competition (as do the grasses) and they are often edible plants in themselves.
If grasses dominate between the rows of trees where the tractor drives it is not quite so bad as this area can be slashed to keep the grasses from becoming too vigorous. However maintaining mulch and herbs within the line of trees (as seen in the picture at the top) is enormously beneficial to the health of the trees.(see weed control)
Diversity in plant species has another really important role which is so neatly illustrated in the following story:
Light Brown Apple Moth (LBAM) is a native insect found throughout our district. As it's name suggests, it is a pest in apple orchards, but it is also a major pest of wine grapes in the nearby Coonawarra vineyards. Some years ago, a survey was done to see what native parasitic wasps might be able to assist in the control of LBAM. In the middle of the Coonawarra vineyards (an area of monoculture 5km wide by 15km long), only one or two species of native predators could be found. In those vineyards on the edge of this area and close to areas of native bush, five or six different species of native predators were present. In the nearby Penola Conservation Park (a relatively intact area of native vegetation with a huge diversity of plant species), over twenty different species of LBAM predators were found, and LBAM itself was present but in extremely low numbers due to the high pressure from the diverse range of predators (that were dependent on the diverse ecosystem for their survival). Which of course means that if local orchards and vineyards more closely resembled native bush (rather than monoculture) , "pest" species such as LBAM would not be a pest at all, and control measures would be unnecessary.