Autumn Colours
Have you ever wondered why leaves change colour in Autumn? Here’s a simple explanation: Leaves convert carbon dioxide, water and sunlight into energy in a process called photosynthesis. The special ingredient for this is the chemical pigment chlorophyll, which gives leaves their bright green colour. But leaves also contain other pigments - carotene and xanthophylls, which are yellow and orange based. These help absorb sunlight, which they transfer to chlorophyll for photosynthesis, but, as Summer comes to an end, leaves can’t continue photosynthesising because of the dry air and lack of sunlight. They stop producing chlorophyll, and the yellow and orange pigments get a chance to shine.
Red hues come from pigments called anthocyanins. Not all trees produce anthocyanins, and even those that do, need exactly the right conditions. Anthocyanins protect the leaves from excess sunlight and enable the trees to recover any last remaining nutrients before the leaves fall off. They give leaves bright red, purple and crimson colours. You’ll see more vibrant reds in years where there’s lots of sunlight and dry weather. You’ll also see more reds in near-freezing weather when low nutrient levels, and other plant stressors also seem to trigger increased levels of anthocyanins.
Arboretums are great places to view the best displays of fiery foliage. The future of Scotland’s
rich tree heritage is to be safeguarded with a series of registered collections across the country, effectively creating a gene bank of Scotland’s trees.
The National Tree Collections of Scotland (NTCS), overseen by the Royal Botanic Garden, Edinburgh and the Forestry Commission Scotland, will eventually serve as a national arboretum and could act as a buffer against the effects of climate change and habitat loss on tree collections throughout the British Isles.
Scotland has relatively few native tree species, but is home to some of the finest tree collections in Europe thanks to a rich history of introductions from overseas.
lairds’ led the fashion over 200 years ago for collecting specimens then considered exotic, and planted tens of millions of trees covering thousands of hectares of land.
They were helped by Scottish plant hunters such as Archibald Menzies, who introduced the Monkey-Puzzle tree, and David Douglas, who brought back over 240 new species including Sitka Spruce, Douglas Fir and the Giant Redwood.
Outside the UK, the world renowned places to see amazing Autumn colours such as Acadia National Park in Maine, USA. Fragrant Hill in Beijing. Kyoto in Japan, Alberta in Canada, the Loire Valley in France and Ahornboden in Austria. So whether you are in your back garden or half way across the world, enjoy nature’s magnificent Autumn colours.
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