Saturday, 27 December 2008

Seasoned greetings


Photo: Sydney's Royal Botanic Gardens on Boxing Day 2008
One topic I'd like to return to regularly in this blog is an appropriate set of seasons for Sydney (and beyond?), and I'd welcome comments and feedback. I talked about this in early August, trying to convince Sydneysiders that spring had already started in the local bush and in our gardens. Unfortunately we had a particularly cold winter and not many people were convinced.

But as happens every year, the first flush of post-winter flowering began in late July and early August. Most of the wattles at our Mount Annan Botanic Garden blossom in August. It's the time of year when people start to wonder if it has been an early spring, again...

Of course there are plants in flower all year and you'll find plenty of local species flowering in July, August, September, as you will in your garden. Our spring walk at the Royal Botanic Gardens is usually at its peak in mid to late September. And you can plant your bulbs early for an early flush. Still, it's around early August when you get the sense that a change is taking place and there is a shift in the 'season', at least from a plants point of view.

Flowering will depend on recent rainfall, temperature and day-length. It will usually depend on what happened at the time of flower bud formation, rather than what is happening when the flower opens. It's a complex business and some species are more variable in there flowering time than others.

Now that the Hyacyinth Orchid season is with us, or just passing, we are about to head into 'high summer'. In past years that would have meant intense heat and dryness. This year, we seem to have a return to a wet steamy summer. For plants, what does it mean? Maybe we need an iconic and reliable plant event for each month of the year as starting point. The most significant of these could be used to define some Sydney Seasons, and a start to us moving away from the European-centric system.
As I've tentatively suggested in the past, moving Wattle Day from 1 September to 1 August could be one way to make a point - although this would draw intense historical and geographical argument. I'm inclined to side with correspondent Jim Nicol who thinks this change would not only help separate our celebration of the local flora (and local conditions) from the traditional start of spring in Australia, but also match the flowering season for wattles around Sydney. Now of course my interstate colleagues are not always as convinced, depending on their local conditions.

In any case, this is all very well if your life, like mine, centres around plants. But our sense of seasons is not just determined by flowers and autumn leaves. This was the problem with me announcing the start of spring in early August - it was very wintery weather. Do we have a separate plant season system (for gardeners or nature lovers) or do we try to combine all the signals into a single system that could replace our traditional summer-autumn-winter-spring?

I've mentioned already correspondent Rick Kemp (23 November 2008). He favours a system of five seasons, based on a range of climatic and biological cues, with 'spring' beginning (as I think it should) in August. Rick's additional season is a 'pre-summer', in October and November, but I won't give away his entire system here. It would be interesting to see what other ideas there are out there.

There is also some nice science to be done. One of the likely consequences of accelerated climate change is a change in seasonal patterns, part of what is also called 'phenology'. By coming up with a system of seasonal plant events we may be able to identify some good targets for monitoring and testing to see if they change.

I announced the start of a phenology project in the Friends of the Gardens magazine, The Gardens, mid way through 2008, but we've been a little slow off the mark getting it started. Behind the scenes we've been working with other botanic gardens and Earthwatch to devise a list of national target species, and early in 2009 I'll be getting back in contact with those who've expressed interest in assisting us. We might add to this list with some Sydney favourites and perhaps a few species to help us define our local seasons.

3 comments:

Catherine Stewart said...

Hi Tim,
I think Sydney has 5 seasons of uneven length, including 2 distinct springs. 1st spring Aug-Sep, 2nd spring Oct-Dec, summer Jan-Mar, autumn Apr-May and winter Jun-Jul.
This is based on looking at Bureau of Met data (especially for night time temps) as well as observing flowering and weather patterns. I think our relatively small temp range over the year (compared to northern hemisphere seasons) also requires a different approach to the one size fits all of 3 months of each.
As Sydney can have quite cold overnight temps until well into Dec (this most recent one being a great example), I don't think summer starts in earnest until Jan, and plant wood is not really hardening off until well into April. Autumn is scandalously short, winter mostly a non-event. As you say, our bush then explodes into blossom in Aug, the first of our springs!

Tim Entwisle said...

Hi Catherine. Yes there seems to be more resolution needed for the Sydney seasons (five seems to be popular) albeit at a finer scale than the big bold seasons of the Northern Hemisphere (or even somewhere like Melbourne). Rick Kemp has some interesting ideas about seasons for Sydney but in the end it depends whether you go with the climate or the biology.

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