I'd really like to say something about a possible political strategy for the Ecology Movement, and the Green Party as its political wing. But first I'd like to talk about an aspect of the breadth of the green (as opposed to ecology) movement and the relationship between its various parts - its internal ecology if you like.

Back in the beginning the founders of PEOPLE and Movement for Survival (MS) which became the Ecology Party were quite clearly driven by an ecology, or ecosystem agenda.

This was expressed in concerns about the consequences of over-population, resource depletion and rising pollution. The stuff of the Limits to Growth models. Underneath it all, the roots if you like, was a (sometimes implicit) recognition that a sustainable society or civilization must exist within its ecological niche and respect its ecosystem limits.

From these roots a trunk of fundamentally ecological concerns grew. And from this trunk sprouted branches as the work was done to develop a plan for dealing with or withdrawing from ecological overshoot.

Thus the 1974 election manifesto was essentially a rewrite of ideas from the original Ecologist Blueprint for Survival issue published in Jan'72. During 1975 this was rewritten and extended largely by Paul Allen and by 1978 had become a 112 page document (albeit in approx A5 size so only 55 sides of A4). In some ways this represented an attempt to integrate ideas and principles from other movements - civil rights, the labour movement, socialism, feminism and the peace movement - rather than deriving ideas and policies in these areas from ecological principles.

In 1979/80 the German Greens (Die Grünen) got going and introduced the idea of green politics being based on four pillars - ecology, social justice, grassroots democracy and peace & non-violence . ("ökologisch", "Sozial", "Basisdemokratisch" and "Gewaltfrei" were the original German labels).

It is interesting that there is a fundamental difference in the real world between the structure of a tree and a building. Where a tree has roots that anchor it to the earth, a building has foundations which impose it on the earth. Where a tree has a trunk which supports the whole superstructure and connects all of the branches to all of the roots, a building has pillars (or columns or walls) which support the rooms above and the roof. A building presses down on the earth where a tree springs up from it. A building is a fundamentally human structure, whereas a tree is an organic whole which may have humans and other life forms living in it.

The four pillars model of green politics has subtly shifted the focus from the ecological basis of early green thought. It has introduced anthropocentric elements. Ecology can lead you to the same practical implications, but allowing equal weight to all four pillars encourages the argument that you can't have a sustainable future without, say, social justice.

An ecologically sustainable tree of green politics could certainly exist without the branch carrying social justice. It might appear as a poor unbalanced specimen, but it could live and we might want to encourage a social justice branch to sprout from the ecological trunk.

In a similar way the rooms of a green house standing on the four pillars can be seen as independent, and we might choose to decorate and furnish the room called "gender politics"  first because we can and recognition of, say, gay marriage is achievable with a little effort in a place where it has not previously been so. Or introducing trams and bannishing cars from cities, or banning single use plastic bags, or whatever takes our fancy to deal with first.

On the other hand with the tree model we see immediately that it is nonsensical to expect the leaf of gay marriage to open on the twig of gay rights on the branch of gender equality on the limb of social justice if the trunk of ecology is not yet capable of supporting the load.

Thus in the building with four pillars the room labelled "population and carrying capacity"  can be locked shut and the door plastered with "hazardous, do not enter" notices.

A pertinant point since over-population (of humans just like any other species) was seen as a real and present danger by our founding fathers - but once the four pillars came to be the dominant model it became difficult and then impossible to talk about, as it conflicted with some aspects of social justice and democracy.

Yet it remains a core aspect of our worsening ecological situation. If the human population was still "only" 1 billion then it would be much easier to eradicate poverty and hunger, create a socially just society, and deal with resource conflicts whilst respecting our ecological niche.

It is only by finding our way back to embrace the trunk of the tree that can support our movement that we can begin to make real progress. There is only one viable political strategy and that is to pursue ecological sustainability as single-mindedly and doggedly as UKIP pursued leaving the European Union.

Green candidates should agree a single SMART goal achievable within a single parliament and not stand against any candidate from any major party (Lab or Tory) who agreed (in a binding way) to support the measure. Force it onto the agenda.

Needless to say such a goal should be fundamentally ecological - perhaps something eye-catching to do with fossil fuels, not too technically complex, not too disruptive to ordinary voters but not soft.

A very simple message and one that puts ecology and ecosystem thinking front and centre. That would do for a start.

We must become tree-huggers again.