Fall in New York City – Otoño en Nueva York. 2011 (Photos).

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Fotos del Otoño en Nueva York – Fall pictures in New York City. 2011.

Las hojas rojas, amarillas anuncian que el Otoño esta aquí. El Invierno viene pronto.

How Leaves Change Color

Seasonal conditions and the resultant chemical changes in the leaves are the key factors in the timing and coloration of the leaves. Generally, clear, sunny days and cool nights with temperatures in the 40’s bring about the most striking autumn colors.

Three chemicals within the leaves – chlorophyll, carotenoids and anthocyanins – are involved in the annual color change process. As temperatures cool and the days shorten, cells at the base of the leaves disintegrate, blocking passages from the leaves to the branches and causing chlorophyll to decompose.

Chlorophyll is what gives most plants their green color. As the chlorophyll fades, colors in the other pigments – the carotenoids and anthocyanins – come to the surface. Trees with leaves having a preponderance of carotenoids – like beech, birch and willow – turn varying shades of yellow. When anthocyanins predominate – as in the case of many maples, dogwoods and sumac – reds and purples appear.

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