I have been commissioned by my local City Council to create some Urban Monoliths.

I’m not sure the title is correct; a monolith is a large single upright block of stone serving as a pillar or monument. My monoliths will be wooden, they will be discretely hidden away and they will not be monuments in the traditional sense. I’m creating Habitat Trees.

Actually, ‘creating’ sounds a bit grand for what I am doing. I’m turning some existing dead and nearly dead trees into vertical habitat. The trees are currently standing so they are already vertical, and they are already habitat… so maybe saying ‘I’m turning them into vertical habitat’ is a bit of an exaggeration.

What I am actually going to do is allow the city to keep what is theirs and I’m not going to cut down some of their dead trees – but I am going to charge them for doing, or not doing that, as a case may be… I’m sure it didn’t sound quite like that when I wrote the proposal, but I am genuinely excited to be involved in the project.

In their own weird way my monoliths will be monuments – all be they bio-degradable monuments. My trees will stand to mark a momentous occasion, a turning point; a subtle but important shift in Local Body thinking. By keeping these dead trees, the Council has decided that the benefits for keeping urban habitat are greater than the cost to the community to remove it. The Council is investing in the ecological wellbeing of its current and future community. It’s a brave move and a first for these parts.

So what are habitat trees all about and how does one ‘make’ one?

As the name suggests, a habitat tree is a tree that is retained for habitat. The three main reasons that we plant urban trees are aesthetical, functional and memorial, those reasons can then be further split and divided to fit anything you can imagine. Habitat trees would fall into the functional category, but not in the traditional sense (we are not planting them to create habitat, we are leaving them to retain habitat).

The obvious question, which I’m sure you would ask – if you could, is; doesn’t every tree provide habitat? And the answer to that is, Yes and No. Dead trees offer a different type of habitat to living trees. Habitat is a spectrum of interconnected ecological niches that range in scale, distribution and complexity. What we consider to be ‘good urban tree management’, involves removing dead branches and limbs from living trees, and once a tree is dead the tree is removed altogether. So good tree management results in the removal of an entire ecological niche from the urban environment – if there is no aerial dead-wood then there is no potential for organisms to exist in that deadwood, and therefore no potential for organisms that consume those organisms to exist either, and so on and so forth (the organic reaction).

Good urban tree management practices have so much to answer for…

The next question, which I’m sure you would ask – if you could, but you can’t, is; what organisms are we talking about? This is where we start to enter the sublime to the ridiculous zone. We are not just talking about charismatic megafauna [sorry – I’ve waited years for write that. Charismatic megafauna is just a term for cute likeable animals – the sort of thing environmental campaigners lead with.] Most of the time we are talking about fungus and insects. With the establishment of fungus and insects come the larger fauna (if we are lucky) and some of that maybe charismatic; birds, bats, squirrels and possums etc. (depending on where you live are and what is considered cute and likeable).

So how do you make a habitat tree? You can make a habitat tree by killing a live tree, or repositioning a dead tree, but the easiest thing to do is, do nothing – don’t remove naturally occurring deadwood and don’t cut down dead trees. But alas, that is not a reality for some places and a very bad idea for others. Habitat trees also fall into the ‘right-tree-for-the-right-place’ mantra. Habitat trees require management – you can manage the size, location and amount of deadwood in the tree relatively easily – but first, you have to manage the risk (the risk to people and property). Not every dead tree or dead branch in the urban environment can or should be retained.

For my habitat trees, we have selected a number of potential candidates based on location. We are going to reduce them in size to make them more stable and we are going to make some bad pruning cuts and/or dice-up the cut branch ends to create a ‘natural’ look. The ‘natural’ look is just for show – the fauna and flora that we are hoping to attract don’t really need natural looking dead branches – any dead branch will do. We are going to place signs near the trees to explain what they are and why they are there. Then we are going to monitor them – once they become unstable and/or the risk they pose to people and property becomes too great, we will recycle them into horizontal habitat. If all goes well, we should get six or eight years out of them – I have just come back from Australia where I was shown some dead standing trees that had been there for at least 40 years, so maybe mine could last for longer than we think.

So, I’m going to create some bio-degradable monuments that will mark a shift in thinking – if all goes well the mind-set will remain and no one will think twice about seeing a standing dead tree. If this goes well, future generations won’t know to care – a new normal will exist.

• Written for Tree Matters Magazine (NZ)