Weed Trees – Nature Finds a Way!
Our gardens are our own private haven. Invasive plants, however, do not distinguish from formal garden or bushland type settings. They can take advantage of any available opportunity to take up residence.
There are several ways that invasive plants can inhabit your garden. Seed dispersal through bird droppings, transported by birds and animals, and wind movement. Some seeds lay dormant in the soil and are encouraged to develop when the area, or soils, are disturbed.
In addition, there can be sapling and tree development from the roots of established feature trees, on you or your neighbours’ property. Species examples where this has been seen to occur include varieties of Liquidambar, Elms, Poplars, Ash, and Sheoak.
While your local tree-work mulch is a wonderful resource, and provides many benefits to your garden, keep an eye out for any seedlings that develop from seed or tree parts in the mulch. You may not be so grateful for your ‘free’ tree when it turns out to be too large or in the wrong spot years later.
Three very common examples (pictured above)
Arguably, number one in these three examples, found in many areas throughout Greater Melbourne, is Pittosporum undulatum (Sweet Pittosporum).
Medium sized tree. It has glossy dark green leaves. Flowering is in Spring, which can provide an attractive perfume in the air. Fruiting follows in clusters of orange grape sized berries ripening in autumn through to winter.
A contributing factor in successful seed dispersal is the splitting open of the fruit with sticky seeds inside. The Latin translation of the genus provides an indication of this. Pitt (to pitch), Sporum (seed). A clever way for birds and animals to help with the spread.
While unplanned or excessive colonisation of an area can be a concern, weed trees can provide some positive amenity. These can include habitat, visual amenity and shading. This species is reasonably tolerant of heavy pruning and makes an effective hardy hedge if managed properly.
Consider the following for management to reduce or inhibit further plant development
be vigilant in identifying new developing saplings and remove them
as much as practical, remove fruit before ripening – consider canopy reduction on taller trees to help with this
regarding habitat (small native bird species love dense weed specimens) - weed small patches at a time to minimise impact and replace with indigenous species to supplement habitat
always carefully dispose of the material. Be aware that the species has the ability to develop re-growth from tree stumps. Left unchecked, eventual full re-establishment can occur.
There has been some debate over the ‘amenity value’ of established mature ‘weed’ trees. There are some Victorian councils that consider certain weed species as a very serious impact to the indigenous growth in their regions. They encourage efforts to minimise retention of these trees.
Some other Councils may have tree-removal permit requirements triggered. As such, it is prudent to make a general enquiry with your local council when removing any established tree.
Other native trees can establish in numbers, in areas outside their normal range, such as some species of Acacia, as an example. However, this Pittosporum species has become highly established in many areas of Melbourne. It is a Victorian native, indigenous to East Gippsland. But is now widely spread, and considered a high threat environmental weed. The dominant area of concern is out competing, and making it difficult, for indigenous species in the area, to establish or develop. Particularly with its dense canopy and shading.
Cotoneaster sp (different varieties. Pronounced ko-tone-e-aster). Shrub or multi-stemmed small tree. Small white October to January, and produces masses of small red berries (birds love them) late summer to Autumn. Seeds are long-lived in soil. Thjis species is native species to China.
Coprosma repens (New Zealand Mirror Bush). Shrub to small tree. Flowering - spring/ summer. Fruit/seeds – summer/autumn. Clusters of orange/red berries. Fleshy, glossy leaves.