We’ve seeded our last 150 tubes in preparation for planting in a few months time. When the rains come, we’ll have over 1000 plants ready to go. Most are destined for the regeneration areas we’ve fenced around the waterways, but a few others are non-indigenous livestock fodder plants, timber trees and food plants we’ve raised from seed and cuttings to begin developing other zones around the farm.
Late in 2013, along with a posy of other plant nerds, we attended a workshop with botanist Ann Prescott (author of It’s Blue with Five Petals) to explore ideas behind revegetation for habitat. We walked through remnant woodland in the hills above Yankalilla, and tried to imagine how our farm might have looked 180 years ago. Prescott can be a bit of a provocative figure, and her observations challenged many of our ideas for revegetation. As we walked through pastures that were once head high phalaris and are now native grasses sprinkled with self-sown eucalypts, she urged allowing regeneration at the pace of the ecosystem, rather than expending significant energy in growing and planting vast quantities trees that can often fail in the face of denuded soils, weeds or rampaging marsupials. Indeed, she suggested that planting one tree every 10 years could be enough to regenerate a landscape. Interestingly, Prescott also suggested that in the Southern Fleurieu region, optimum conditions for natural germination are achieved about every 2-5 years. Patience, with weed-control and managed grazing, can bring regeneration.
Humans tend to like trees. They’re easily visible. They give us shade and timber and fruit. An urge when regenerating a landscape then can be to plant as many different trees of as many different species as possible. But as we walked through the remnant woodland, we realised a few things. The species diversity of a woodland such as this can be imagined as a triangle. At the narrow top of the triangle are the trees. Perhaps five species in the hundred that the woodland might have are trees. Likewise, as the triangle thickens, perhaps five or so species in the total diversity of the woodland are shrubs. The real action happens at the wide base of the triangle, with the most substantial diversity of species amongst the forbs (flowering bulbs, lilies, etc.) and the grasses. The grasses grow in tussocks in the open space between trees, and the forbs emerge seasonally in the ‘inter-tussock space’, the space that also experiences the most intense colonisation by weeds.
When we paced them out, the trees in this woodland averaged about 20-25 metres apart, that is, they had about a 10 metre canopy, with about 10 metres of open ground between them. If looked at from the perspective of a black cockatoo, about half of the woodland is open ground, and consequently those species which compose the greatest diversity of the woodland, the forbs and grasses, thrive on sunlight. Density of trees produces forests and the growth form of trees changes to reflect that. In forests and woodlots, trees grow tall and narrow with minimal low branches as they compete for sunlight. In contrast, the growth form of trees in a woodland is low and broad. This allows for low and long lateral branching, essential for the creatures of the woodland to rest, nest and hunt from. Witness the behaviour of a woodland bird like the Scarlet Robin, which perches on low branches, dives to pick off insects, then returns to its observation post. Structurally, said Prescott, woodlands such as these are generally composed of broadly spaced eucalypts, interspersed with groves of sheoaks and wattles. Acacia pycnantha is particularly valued because of its propensity to keel over after a few years, providing more low, lateral habitat. In a woodland, said Prescott, you should be able to see through the trees for 100 metres in any direction.
Ann Prescott’s insight has been invaluable in shaping our thinking about how to proceed with our habitat zones. While restoring habitat is one of our key intentions for the property, we’re also committed to the role of trees in designed interventions in the landscape, such as erosion control, windbreaks, shelter, timber and food production. I’m also interested in considering how microclimates may need to be altered to support regeneration. In theory, we won’t be doing large-scale revegetation for too many more years. Rather, once a certain level of shelter and soil stability is returned, the habitat zones will become largely self-maintaining and we can, finally, enjoy a little shade and watch the robins hunt.
This article is based on my notes, and any factual errors are probably mine, not Ann Prescott’s!