Leaf-litter - a mysterious realm that is vital to woodland function. Plant
tissues contain many tough materials like cellulose, lignin and suberin.
These polymers form the main structure of the plant body and few
animals have enzymes that can digest them. (After all, cellulose is made
from glucose, if animals could easily digest it then plants would
effectively be made of sugar and would soon be eaten!). Some animals
harbour bacteria that can digest cellulose - some earthworms will take
leaves back to their burrows to nibble on and woodlice feed on decaying
plant matter.

It is estimated that every cubic metre of leaf litter contains 100 000
springtails. These tiny wingless insects are seen by few and have paired
spring-loaded tail appendages (furcula) which they can snap-out straight
in order to leap through the air to escape potential predators. Their
seaside relatives, the sandhoppers, are much better known. These
ancient creatures evolved at least 400 million years ago and feed upon
plant remains and fungi.
The best way to observe leaf-litter creatures is to set-up a Tullgren funnel - collect a few scoops of leaf litter and place them in a
large funnel above a beaker of alcohol. Shine a desk-lamp onto the leaf litter for a few days. As the leaves dry out, the creatures
inside will move deeper down to escape desiccation and will eventually fall into the alcohol, die and become preserved. They can
then be examined with a magnifying glass or microscope. If you prefer a less destructive method, then sieve leaf litter onto a white
sheet. Other common inhabitants of leaf litter may include hordes of brightly coloured mites, and other strange wingless and pale
or colourless tiny insects like diplurans (two-pronged bristletails), thysanura (3-pronged bristletails), venomous pseudoscorpions,
centipedes and millipedes, venomous hunting wolf spiders, several different types of worm, and the very strange proturans
(coneheads). These are ancient and prehistoric creatures, the wingless bristle-tails and proturans are ancient hexapods (they
have six legs, though they also have three extra pairs of vestigial legs called styli) that evolved before insects were able to fly.
Proturans lack pigmentation (they are white or pale brown) and have conical heads with no obvious eyes (just two light-sensitive
pseudo-eyes) and no antennae - they use their front pair of legs like antennae, walking on the other two pairs and their bodies are
segmented and worm-like, but less than 2 mm long. Proturans are so different to other insects that they are often placed in a
separate class. Their numbers in leaf-litter are possibly much greater than even that of the springtails. Bristletails and probably
proturans too feed on fungi, including lichens. Very little is still known about strange hexapods like proturans. It appears that
proturans evolved from centipede-like creatures (which in turn evolved from worm-like marine creatures that colonised the land).
Thysanura are probably the most familiar to most people, for they include the silverfish that inhabits buildings, but again these are
strange prehistoric insects.

Many of these leaf-litter creatures will also be found amongst moss and beneath the bark of trees. Microorganisms are also a vital
component in these ecosystem. Bacteria and fungi digest the plant materials, including the lignin. Some bacteria can feed off wood
fragments for many years, slowly eating away this tough material with special enzymes. Current culture methods only detect a
fraction of the bacteria present in any natural sample and so I wager that most of the bacteria present in this leaf-litter are
unknown to science! This rotting underworld is truly a dark and mysterious place! How many of those bacteria and fungi produce
valuable antibiotics unknown to science?

Leaf-litter is thus hard to decompose, but in the end it has to rot so that the plants and trees can recycle the nutrients locked-up in
it. Trees will put-up many tiny feeder-roots into the leaf-litter layer to absorb these nutrients as they become available. The
leaf-litter of coniferous woodland is especially hard to decompose as it contains resins, acids and other chemicals that inhibit many
decomposers. Conifers and walnut trees shed toxins into the soil with their litter which inhibits rival plants that may compete for
resources - there is little undergrowth beneath these types of tree. The roots, leaves and walnuts of the walnut tree (
Juglans)
contain juglone - a chemical toxic to most plants which has been used as a herbicide. This way the walnut tree gets more of the
soil nutrients and light for itself!

Place leaf-litter in a jar of water and within a few days it will be teaming with strange microscopic creatures - ciliates like Vorticella
and Paramecium, heliozoans (spherical single-celled organisms with sunlike radiating spikes), amoebae, nematode roundworms,
small oligochaetes (related to the more familiar earthworms, but quite different) and perhaps a hydra (a relative of the jellyfish) or
two, and many other things besides! These creatures are abundant in woodland ponds and when the ponds dry-out they form
desiccated dormant states that blow about on the wind or get carried about by birds and animals.
Click here to see some of these
strange creatures!
External links:

Proturans:
 
http://en.wikipedia.org/wiki/Proturan
Springtails (Collembola):
 
Lander University - Collembola lab
Pseudoscorpions
 
Lander University - Pseudoscorpion lab
vorticellid
Click to see some of the strange
microscopic animals that you might find
in woodland leaf-litter, ponds and wet
tree-holes.
Leaf-Litter
More on leaf decay.
Proturan, By David R. Maddison [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Left: a proturan.
By David R. Maddison [CC BY-SA 3.0
(http://creativecommons.org/licenses/by-sa/3.0)], via
Wikimedia Commons