Tree planting into alien environments

By Angus Deans

As people become more aware of the need to modify their environment, so that it may become more hospitable or even more productive, the talk often moves to planting of trees. Trees for shelter, trees for shade and cooling, and trees for sequestering carbon. Easy? (except for the work of course!) Or not?

Helping farmers question the limits to productivity in their landscapes the issue of shelter to reduce the harmful effects of wind on both plant and animal production often arises. In Australia earlier government policies required settlers to clear their land in order to keep title to it. This trained farmers to believe that removing trees was essential for production. So thinking of planting trees to increase production and profit is a huge shift in mindset.

The value in planting trees is often not easy for producers to grasp.   It is common to see massive amounts of money and effort expended in tree planting programmes that often fail to either establish or persist. So what could change this?

First we need to realise that the environment in which we are planting the trees is frequently an alien environment for the health and wellbeing of them! We often plant trees either into a grassland/cropland, or a landscape devoid of meaningful herbage as a rule.  These soil environments are typically massively bacterial which favours grasses, weeds, and sometimes even lower order plants such as moss and lichen. And these conditions massively disadvantage trees!

And then some of the mandated cultural requirements – if government funded, are often designed inadvertently to have the planting fail! When we are required to deep rip (so that water drains beneath the root zone of seedlings) and herbicide before and after planting we are actively seeking to create an alien landscape for tree growth – a dry bacterial wasteland.

So what can we do?

First we need to understand that most trees have mycorrhizal associations that are vital to their health and wellbeing.  We then need to recreate conditions that are conducive both to the creation and formation of these mycorrhizal associations. We need to create a soil environment that is fungal dominated rather than bacterial in order that trees might thrive.

So where to start?

Ideally tree seedlings we are intending to plant could be inoculated with species appropriate fungal varieties whilst in the nursery in order to simplify this, but typically they are grown in sterile media. So we can achieve the same by creating an extract from leaf litter collected from the soil surface under more mature trees/plantings of the same family of trees. We can either water this onto seedlings before planting or as we water them in after planting. It is beneficial to add extract of a fungal dominated compost or vermicompost (or both!) at this time also.

We can also mulch around seedlings with woodchip in order to promote fungal formation and dominance in the soil, being mindful to keep the trunks of seedlings clear of contact with mulch in order to prevent collar rot. This same mulch also serves as our weed control. If any grassy weeds should inadvertently grow in this scenario they are easily removed, as their root growth is typically much impaired even though growth may look very vigorous. This mulch could also have been put in place months prior to planting in order to start the ‘fungalisation’ process earlier.

So I guess the real question is whether we really wish to see the work and money we invest in planting trees actually give a return on investment by having it work, or whether we are merely indulging in an experiment to see whether trees can actually grow in an alien environment? As in all things agricultural success comes from asking “How would Mother Nature do this? What conditions do these trees require to thrive in Nature?”