Tuesday, 10 February 2009

Natural Regeneration of Yellow Box Trees

Since taking over management of our place on 1st February 2007 we applied ‘rest’ for most of the time and have witnessed the re-growth of eucalypts and regeneration of acacias. What we’d like to see is regeneration of especially the Yellow Box eucalypts in the paddocks as the existing trees are very old. I read somewhere a long time ago that some eucalypts need chemical reaction from smoke on seeds to trigger germination. It occurred to me that all the smoke currently in the atmosphere from the Victorian fires coupled with showers we are experiencing today might get some regeneration activity going.

I posed the above question to a contact I have in the native vegetation science field (RR). Below is an edited version of his response.

“You are right about smoke-induced germination. This was discovered by botanists at WA many years ago. Apparently you can buy “smoke water” that you can apply to seeds to get them to break their dormancy. I have spoken to a colleague who has spent time over in WA. His understanding is that smoke will induce germination in certain species. We cannot tell whether that applies to Yellow Box. It may very well do so, but it could also be that this species (like others) requires a certain combination of events for successful recruitment. For example, a good flowering, followed by a big seed crop, coinciding with good soil moisture conditions and a suitable seed bed (i.e. not too much competition from grasses). On the other had, I do know that recruitment of Yellow Box can follow an interesting pattern whereby repressed seedlings that may be very old (i.e. 10 or twenty years) sit under or nearby the crown of existing trees, growing each year from lignotubers but not achieving more than a few feet in height and being constantly eaten by stock or insects. If the adult tree, however should fall over (from old age or strong winds), then the repressed seedlings are suddenly released from the competition of the adult trees and a large grove of young saplings apparently suddenly emerges. This grove of trees eventually thins out to one or two adult trees to repeat the process, over a long time period.

I have recently seen healthy crops of recruiting Yellow Box trees coming up in a paddock dominated by African Lovegrass which has been rested from grazing for over ten years. I suspect this is a result of the first described phenomenon, rather that the second.”

Input from another contact (JF) who has been looking into tree regeneration on farms was as follows.

"It's important to differentiate between long-term drivers, and short-term events. It often seems that the short-term events get a lot of attention when people think about regeneration -- e.g. presence of bare ground, fire, or perhaps smoke. In many ways, we can't really control those short-term conditions very easily, other than through pretty intensive and active local-scale management. However, it is possible to control the overall long-term conditions to a fairly large extent, so that when the right short-term events come around, regeneration has a chance."