Timber milling

We have recently updated our chainsaw milling rigs to enable us to make use of any worthwhile timber that we come across as a by-product of our tree surgery works. This has a number of advantages, both for us and for you:

• We can mill timber on site anywhere – sometimes it can be quicker and less messy to plank timber up and carry it out in lengths rather than having to ring up the timber and carry it out piece by piece;

• We can convert appropriate timber into useful planks or beams, either for the client’s use or our purposes;

• Low value timber, particularly softwoods that have little use as firewood (the ultimate destination of most of our timber arisings), can be converted into an added value product.

Not all timber is appropriate for milling and with log prices at an all time high converting timber into firewood is almost certainly a worthwhile consideration if you have a use for it. In addition, the milling of timber is only the first step towards producing a useful product. In almost all cases the converted timber will need to be seasoned and stored correctly and, if the wood’s final destination is indoors, the timber will require kiln drying.

Putting the financial calculations to one side though, I know that many people would relish the opportunity to utilize part of that felled tree rather than loading it all into the log-burner and I would be happy to advise on the practicality of this.

Woodchips

Whilst on the subject of by-products, this is a good time to talk about the benefits of recycling woodchip. Almost all the smaller material (ie less than 6” diameter) that we process will go through one of our woodchippers and will end up looking like the picture on the left. This is whole tree woodchip, so it will include smaller diameter wood, leaves or needles (if there are any), twigs, bark and buds. This is quite a complex mix and is very different in terms of its chemical and mineral content than chipped pallets or sawdust from timber mills. Conifer timber in particular will contain a variety of phenolic compounds which can increase the durability of the chip. Generally the branches are chipped onto the back of one of our chip trucks or left on site, if it goes back to the yard it will be piled in one heap together with all the other woodchip previously stacked there. The material is regularly moved, which assists in the natural break down of the woodchip.

Most of the chipped material is wood, so is relatively cellulose/lignin rich and relatively nitrogen poor. As soon as it is chipped, micro-organisms go to work breaking down the material, exactly as happens in a normal compost heap. These micro-organisms are nitrogen hungry, so woodchip will generally take a long time to fully break down. This is good news if you want to mulch around your plants with woodchip, as it is likely to last for quite a long time compared to some carbon rich mulches.

Some species provide longer lasting woodchip than others, though in practice I suspect that most woodchip piles are like ours, a mixture of many species. But, for connoisseurs of such things, if all you want to achieve is a layer of organic matter that will remain on the soil surface to suppress weeds, then fresh spruce woodchip would probably be very good. The richness of phenolic compounds contained within conifer tissue and its relatively high ratio of lignin and cellulose to nitrogen mean that it is slower than mulches of many other tree species to break down.

If you plan to apply the mulch to increase soil nutrient levels, you may be better off using a fresh mulch derived from species that break down quicker, such as Ash and Sycamore, that contain lower levels of phenolic compounds. Alternatively some of the older, well rotted mulch from the back of our woodchip pile that has a lower ratio of lignin/cellulose to nitrogen, may be of greater benefit. Well composted mulch is likely to be relatively nutrient high, whatever the constituent species.

The effect that the mulch may have on soil pH can sometimes be of concern. Spruce, for instance, does have a slightly lower pH compared with other tree species (circa. 4.66 compared with Leyland cypress c. 4.98, sycamore c. 5.47 and ash c.5.31). However, I understand that it is unlikely to cause a reduction in soil pH in the longer term (depending on the existing soil texture and organic content). Concern can sometimes also be expressed regarding the fact that a nitrogen poor mulch may lead to the depletion of fertility in the upper soil layer, as the nitrogen hungry micro-organisms rob the soil of nitrogen. This is only likely to be of any significance when using very fresh woodchip with a particularly low nitrogen content (ie Spruce) around nitrogen needy plants, such as newly planted material. Even then, studies have demonstrated little observable growth retardation as a result of applying fresh woodchip mulch as opposed to well rotted material.

So, to summarise:

• Mulching to increase soil fertility – use well rotted woodchip mulch;

• Mulching to keep weeds down on beds – use fresher woodchip mulch;

• Using chip on paths, to keep weeds down – use the freshest woodchip, ideally conifer.

The above has only looked at the benefits of woodchip mulch as a weed suppressant or nutrient provider. Woodchip mulch can also have many other benefits it can be especially useful for aiding moisture retention on dry sites. Also, as woodchip breaks down fungal activity can increase. These fungi are purely beneficial; pathogenic fungi such as Honey Fungus cannot grow on a woodchip layer. In fact there is some evidence to show that increasing the fungal diversity within the upper soil layers can help to keep the more pathogenic fungi at bay. It is notable that Honey Fungus for instance is rarely a problem in natural woodlands, where a rich fungal flora is present.

By Graham Joyce | January 31st, 2014