Some types of leaves rot much faster on the forest floor than
others. Analyzing why this happens reveals a great deal about how to
make compost piles decompose more effectively.
Leaves from leguminous (in the same botanical family as beans and
peas) trees such as acacia, carob, and alder usually become humus
within a year. So do some others like ash, cherry, and elm. More
resistant types take two years; these include oak, birch, beech, and
maple. Poplar leaves, and pine, Douglas fir, and larch needles are
very slow to decompose and may take three years or longer. Some of
these differences are due to variations in lignin content which is
highly resistant to decomposition, but speed of decomposition is
mainly influenced by the amount of protein and mineral nutrients
contained in the leaf.
Plants are composed mainly of carbohydrates like cellulose, sugar,
and lignin. The element carbon is by far the greater part of
carbohydrates [carbo(n)hydr(ogen)ates] by weight. Plants can readily
manufacture carbohydrates in large quantities because carbon and
hydrogen are derived from air (C02) and water (H2O), both substances
being available to plants in almost unlimited quantities.
Sugar, manufactured by photosynthesis, is the simplest and most
vital carbohydrate. Sugar is "burned" in all plant cells as the
primary fuel powering all living activities. Extra sugar can be more
compactly stored after being converted into starches, which are long
strings of sugar molecules linked together. Plants often have
starch-filled stems, roots, or tubers; they also make enzymes
capable of quickly converting this starch back into sugar upon
demand. We homebrewers and bakers make practical use of a similar
enzyme process to change starches stored in grains back to sugar
that yeasts can change into alcohol.