I live in North America. A couple of weeks ago I was at a botanical garden which featured some flora from Oceania. There was a tree there that was native to New Zealand, and although there were many leaves still left on the tree, a great number of the leaves had fallen, and many others were turning brown. I asked aloud ‘Why are the leaves falling? It’s not autumn.’ Then it struck me: It’s autumn in New Zealand!
So to my question: do tree species that are native to the Southern Hemisphere still respond cyclically to the seasons in the Southern Hemisphere, even if they are planted in the Northern? Or am I totally bonkers? Is there a tree in New Zealand that sheds its leaves in the Spring?
Help me, botanists and/or Kiwis, you’re my only hope!
Trees shed their leaves in response to day length and in some cases temperature as well. They don’t respond to the conditions in the hemisphere where they germinated any more than nightflowerng plant germinated in Germany will flower in the day if moved to the US.
As calm kiwi has pointed out a great many plants from Oceania are broadleaf evergreens or semi-deciduous. The trees shed their leaves wither continuously or else more in one season but never defoliate. Still other trees drop their leaves in response to water stress to avoid drought.
The other possibility is that the tree is exposed to an electric light which has recentl changed prompting it to respond as though the days were shortening.
What you saw could be due to either of those reasons or several others but unless the tree was recently moved from NZ it had nothing to do with conditions ‘back home’.
calm kiwi beat me to it. The medal-winning Kiwi entry at Chelsea was populated with plants (particularly ferns) native to New Zealand. These would typically flower in New Zealand’s spring (September), but they were in bloom at this year’s Chelsea show, held in May. To achieve this, the garden design team began sending plants from New Zealand to the United Kingdom up to a year in advance of the show. This appears to have given the plants enough time to adjust to northern hemisphere seasons.
It is not at all unusual for Chelsea exhibitors to manipulate the growing cycle of their plants by refrigerating them or forcing them in a heated, illuminated greenhouse.
But aside from these measures, a plant moved to the wrong hemisphere will either die or adjust to the local seasons. Many of the garden plants we grow in the northern hemisphere originated in the southern.
It’s not about different hemispheres, but it’s probably relevant –
At the Boston Museum of Science there’s an automatic presentation on the natural history of an urban neighborhood, and it points out that one of the trees is of a variety that’s “still adjusting to the northern Boston climate” – it sheds its leaves too late, or something. In a case like that, it wouldn’t matter when you planted the seeds, the length of the growing season doesn’t match the physical season, and evidently there’s a pre-programmed internal “clock” that helps regulate the plants rhythms, in addition to external cues.
This is true; some plants are sensitive to day length and moving them to a different latitude confuses them terribly, but moving them to an opposite latitude should be OK, except that the climate (which is not solely dependent on latitude) needs also to be reasonably suitable
Nothing of the sort is evident. Although circadian cycles are primarily enedogenous even there external cues ensure that the cycle is synchronised to local time. In the case of leaf fall, dormancy etc. there is no evidence whatsover of “a pre-programmed internal “clock” that helps regulate the plants rhythms”. Such annual cycles are entirely dependent on photoperiodism and temperature response.
Those plants “still adjusting to the northern Boston climate” are experiencing difficulties because they have been moved to different latitude or a regon with a different climate as Mangetout has said. In this case presumably Bostoin temperatures fall too rapidly in Autumn for the plants to cope, or to put it another way Bostoin has colder Autumns than the area these plants are native to. Day length no longer corresponds to temperature for those plants, it’s as simple as that. There is no evidence of a pre-programmed internal clock.
We have some Northern hemisphere plants that grow to huge proportions, much larger than in their native areas because the climate is much milder. We have big problem with some that love the conditions so much they become a problem, eg gorse, bracken and ginger.
That’s not just the climate Mel.
Plants, unsurprisingly, adapt to climatic conditions so there’s no reason those plants wouldn’t have adapted to their natural habitat in the past billion years or so. The reason plants introduced to new areas grow so large is a lack of predators, pathogens etc that they evolved alongside in the past billion years or so.
Bracken is a native plant in New Zealand. In fact it is native to just about and is the single most widely naturally distributed vascular plant in the planet.
