The se­crets be­hind fall­ing au­tumn leaves, the munt­jac deer and meet the gar­dener’s best friend

Sussex Life - - Inside -

As sum­mer drifts into au­tumn, we’re treated to a spec­tac­u­lar show of colour as the nat­u­ral pal­ette shifts from myr­iad shades of leaf green to a golden blaze of red and yel­low.

This dra­matic dis­play is in­cred­i­bly beau­ti­ful but it also serves an im­por­tant eco­log­i­cal func­tion as de­cid­u­ous trees pre­pare for the per­ils of win­ter. By shed­ding their leaves they can con­serve pre­cious wa­ter, which can be in short sup­ply when the ground is frozen, and also re­duce the risk of be­ing blown down or dam­aged by win­ter storms. Growth is halted and the trees en­ter a dor­mant state to ‘sleep’ through the worst of the win­try weather.

The rea­son the leaves change colour be­fore they fall is linked to the pro­duc­tion of chloro­phyll, the green pig­ment that is vi­tal for pho­to­syn­the­sis. Each leaf is like a minia­ture so­lar panel, us­ing the en­ergy from sun­light to pro­duce the sug­ars that fuel new growth, and chloro­phyll lev­els are reg­u­larly topped up through­out the spring and sum­mer to make the most of the grow­ing sea­son. But as the days shorten and there is less so­lar en­ergy avail­able, chloro­phyll pro­duc­tion slows down and will even­tu­ally stop al­to­gether. The green fades and the leaf pig­ments that were pre­vi­ously masked by chloro­phyll are grad­u­ally re­vealed. The yel­lows and oranges are pro­duced by carotene pig­ments, while reds, pinks and pur­ples are cre­ated by an­tho­cyanins.

Mean­while, within each leaf, a wall of cells starts to form across the base of the stem. This process is trig­gered by a drop in tem­per­a­ture and a sub­se­quent change in the tree’s hor­mone lev­els, and will even­tu­ally sever the leaf to send it drift­ing to the ground. But be­fore this hap­pens, the usual flow of sug­ars out of the leaf to­wards the trunk is blocked. With nowhere to go, the ex­cess sugar is con­verted into more an­tho­cyanin pig­ments, pro­duc­ing an even deeper red blush.

The au­tum­nal colours are most im­pres­sive when there is a com­bi­na­tion of low (but above freez­ing) tem­per­a­tures, dry weather and plenty of sun­shine. These con­di­tions all serve to re­duce chloro­phyll lev­els and en­hance the con­ver­sion of leftover sug­ars, pro­duc­ing more in­tense shades of red and a truly mag­nif­i­cent wildlife spec­ta­cle.

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