When dead doesn’t mean dead!
I have written about the various log piles that are dotted around the wildlife plot and found a great graphic that shows who and what lives on dead wood so in this post I would like to look at the stages of decay in the log piles and what they look like.
There are several stages of decomposition in trees which this diagram clearly shows
Stage 1 and 2 are living trees but stage 2 has a tree that is slowly declining with patches that are dead or severely damaged. Branches and twigs may break off but the tree is left intact and standing.
Stage 3 is a dead tree which is still standing but starting to sag and its texture is starting to soften. This is represented on the plot by the dead trees I have planted in the Thugs Bed.
Stage 4 is where the tree starts to lose its bark, sags to the ground and breaks into large pieces. Plant roots invade the sapwood. An example of this is the standing dead tree on the wildlife plot which is losing its bark through peeling and creating a heap on the floor which plants (weeds!) are starting to colonise.
This is not a planted dead tree but a dead tree that remained where it stood when alive, by far and away the best place for them to stay.
In stage 5 most of the tree is on the ground, in contact with the soil and decomposing by breaking into smaller, softer pieces. Roots of plants invade the heartwood. There isn’t any of this at present on the plot.
Stage 6 is the final stage where the tree is soft, powdery and basically a decomposed mound. We don’t have any of this either.
My understanding is that for a healthy forest you need trees at each stage of the decomposition process and whilst the plot is not a forest, each stage of decomposition has different fungi, lichens, invertebrates etc living on it and so it provides for the greatest diversity.
Fungi are the main agents of decay in wood, breaking it down with secretions of enzymes.
After the wood is softened, saproxylic beetles – those that feed on dead wood – and their grubs feed on the tree and on the fungal bodies on the tree. There are around 650 beetle species that are thought to need dead wood at some point in their life cycle. The tunnels and holes they make allow water to get into the wood and this softens it more and this is an invitation to the invertebrates such as woodlice and millipedes to feed on the wood. Predators and parasites such as robber flies and ichneumon wasps arrive to feed on the beetles and other invertebrates.
There are three main types of decay in dead trees; white rot, brown rot and soft rot. White rot breaks down the chemical components of wood into carbon and water, releasing nutrients such as nitrogen and phosphorus that were locked in the material. As the rot proceeds the wood takes on a bleached appearance, becoming fibrous and springy. The silver birch branches at edging the beds have rotted down like this and there is some at the top of the standing dead tree.
Brown rot only breaks down the simple sugars such as cellulose and the wood becomes brown, cracked into cubes and crumbly. Soft rot happens in environments where moisture content fluctuates such as wood lying on the ground. Lignin is broken down and the wood is white in colour.
The first picture shows cracking in the wood where the different fungi are working. The middle is holes in dead wood caused by beetles and their grubs and the third is an example of white rot in the standing dead tree.
See a short video about this process on post no.4
Have you got any decaying trees? What wildlife have you seen on them?