In Praise of Trees

Autumn is a time to look at trees even if we can’t compete with the seemingly endless blazing colour of countries like Canada. A friend from Te Popo Garden, inland from Stratford, commented in passing that it didn’t get much better than last weekend with the sun streaming through the autumn leaves on the trees. We have had remarkably little wind recently and a sharp drop in temperatures from the Indian summer straight into winter chill, so it is shaping up to be a splendid display.

It should not be necessary to point out that you only get spectacular autumn colour on deciduous trees which shed all their leaves each year. I thought everybody knew that, just as I thought that everybody knew that our native flora is pretty well all evergreen. Ergo, we do not get autumn colour from our native plants. This did not stop an enquiry a couple of months ago about whether we have places noted for autumn colour in Taranaki and (wait for it) were any of these native trees, for example a grove of kauris. I could accept that the enquirer did not know that kauris do not occur naturally this far south, but I did wonder what had happened to general knowledge that nobody in the chain of this particular organisation had picked up on the fact that our native plants do not colour up in the way that some deciduous plants do. There are subtle seasonal colour changes at best in our native flora but for the golden leaves or the fiery reds and oranges of autumn, you must look to imported deciduous trees and shrubs such as maples, poplars, parrotias, gleditsias and cornus.

It is the sharp drop in temperatures which triggers the plant to stop feeding its leaves and let them die and drop. Inland areas are colder at night so they get significantly more impressive autumn colour than those of us closer to the coast who just gradually drift from one season into another. And coastal points northwards (Auckland and Northland) get even less autumn colour. Travellers in the tropics will know that you don’t get autumn colour at all in hot climates.

That said, Prunus Awanui has been a vision of golden leaf this past week. The wisterias and rugosa roses always surprise me with their autumn colour and the grape vine which covers the large verandah out from my office is a delight every year. It looks as if the sun is shining on even the greyest of autumn days.

But while admiring the trees in autumn, gardeners may also like to do some critical analysis on the merits of the different trees in their garden. We have been talking recently about the failure to differentiate between short term nurse trees and long term trees.

In our windy country, we need nurse trees. They are a quick and cheap option to grow in order to provide some protection so that longer term, quality trees (which by their very nature tend to be slow growing) can get established. And because nurse trees grow quickly, they can give height and impact in a garden in a surprisingly short space of time. But few nurse trees in our climate age gracefully and there comes a time when decisions need to made about which are worth keeping and which have frankly passed their use-by date. Not all trees are equal and not all trees improve with age.

Many gardeners make one of two mistakes. They either overplant badly and then fail to discriminate a few years down the track as to which are the good long term trees worth looking after, even if it means cutting out the filler trees. Or they plant specimen trees out in exposed areas in solitary confinement.
In using nurse trees, you are learning from nature. When bush regenerates, the nurse plants are the first to get established and to create some cover. In that protected environment, the longer term trees come through and are forced up in search of light. In due course they supersede those nurse plants. Without the protection and microclimate of nurse trees, they can be too exposed, stunted and often multi trunked because they do not need to shoot up in search of light.

Trees are going to become a great deal more important in the immediate future. The talk about carbon footprints, climate change and sustainability is not just a fad which will fade away in a few months. We are in a time of radical change and long term trees will be part of our future and quite possibly part of the survival of our planet. The day may not be far away when we are shamed by our outdoor furniture made from Indonesian hardwoods.

While tiny town sections are not going to accommodate forest giants, neither is an espaliered apple tree going to save the planet (though it might help feed the family and taste better than cool store apples). But gardeners with a bit of space (or non gardeners for that matter) could and should be thinking about planting long term trees and treasuring existing trees which have the potential to outlive most of us. By long term trees, I mean those with a lifespan which will be fifty years at least, maybe a hundred and some have the potential to live many hundreds of years if they are planted in the right position. In New Zealand we have a tendency to think in terms of ten or twenty years and far too few trees are allowed to ever reach maturity.

So by all means plant pretty flowering cherries, albizzias (though I think I have seen those on a banned list somewhere), gleditsias, paulownias and birches. But see these for what they are, which are short term trees and look to using them as cover to get some good trees of potential longevity established. It doesn’t have to be a mighty kauri, rimu or totara though goodness knows, we plant too few of our majestic native trees. There are some magnificent members of the conifer family which are not native – the sciadopitys or Japanese umbrella pine is a gem and the somewhat maligned Norfolk Island pine is a great statement of form on the landscape. Magnolias can live a very long time and are unparalleled for splendour in flower. Liriodendrons give brilliant autumn colour, as do scarlet oaks, ginkgo biloba and even plane trees. All get more impressive with age.

If you are unsure what you are doing, seek out advice and never plant any tree anywhere near power lines. It will come off second best in a tangle with the lines companies. The challenge is to make sure that you plant some good, long term trees in your lifetime. What better legacy to leave?