One thing most observers of the forest does not acknowledge during excursions in the wood is the importance of leaves. I am not talking about the time they are on the trees but the fall, winter and spring times. My impression of the woods while walking thru the fall leaves in that it is a time for growth and living in the woods to slow down prepare to winter. Howeveer the truth is that the preparations for winter for the invertebrates and those animals who immediately feed off that population have an explosion of activity in the fall.
As fall advances fallen leaves that have accumulated in our ponds, streams, and river start a process that is critical for the nourishment of the whole forest. From caddisflies to up the food chain to eagles and other birds of prey, the food supply, especially those immediately feeding off the waterbodies, originates in the form of fallen leaves.
Upon falling into streams leaves proceed through a process of leeching the natural chemicals that discourages insects from eating green leaves as they grow on the tree also is a repellent to creatures that scavenge freshly fallen leaves under water. The cold water must first leech out the nasty chemicals n a process similar to soaking and resoaking a tea bag. During this time the leaves are also being colonized by microscopic organisms. For the hungry invertebrate, the cleansed, layered leaves, covered with fungi, bacteria and algae is a feast.
Because trees lose their leaves at different times their leaves also decompose at different times and attract different predators throughout the fall, winter, and spring. Some leaves are tough, leathery and laden with toxins. Certain laurels can release so much cyanide that entomologists have used them to directly kill specimens they want to study. Other species such as linden, are comparatively soft and become an early underwater food source. Oaks and Beech trees hold onto their tough leaves into the season, and when those leaves finally fall they are slow to convert into edible condition.
Edible eaves are also available during winter. In this season much aquatic invertebrate growth occurs. A caddisfly species called Pycnopsyche gentilis acts like a chronicler of the leaf supply. In fall and early winter its larvae cut disks from the leaves and use that to make silk to make and line pencil-diameter casings in which they live. Early spring, as leaves become scarce and the larvae continue to grow they add large sand grains to their cases. These cases are easy to find in the spring.
Although fish are not leaf eaters, the cranefly, caddisfly, and stone fly larvae fatten up on leaves and are protein packed for trout, salmon, and bass. Without invertebrates fish would go hungry and fisher men would have to use something else besides lures, that look like live invertebrates, to catch them.
The cleanest streams host the most invertebrates. A clean stream will have as many as 20 different species, while a cloudy stream passing thru a human inhabited area will have a few as 10. Cleaner streams include giant stoneflies, an assortment of mayflies, midges, and craneflies.
Change in climate is starting to make a difference in the leaf litter. The increase of CO2 is creating leaves having lower nutritional value which may very well affect the entire ecosystem adversely and ultimately people. How that will happen is under speculation.
A view of the world of submerged invertebrates is just a bunch of leaves away. You can easily lift an inverted chunk of wet habitat from a streambed for your study; place into a basin and lift each leaf individually. The major objective to a study is to count the number of different species to indicate the health of the forest you are in. Your study of leaves can create a new appreciation of the outdoors!
Reference: Declan McCabe “The Conservationist”
