Back to the Future......

Vegetation changes!

This might seem like an obvious statement to anyone who has more than a passing interest in natural ecosystems. Climate variation (such as the annual timing and amount of rainfall, and extreme events like frost), as well as disturbance (such as fire, landslips, animal activity and flooding) continually shape vegetation from small- to large spatial scales.

But to find good, long-term evidence of such changes is remarkably hard for ecosystems in southern Australia. The slow nature of long-term change requires monitoring techniques to capture this, but also requires ecologists to cast their observations with questions in mind. Otherwise, why would we bother to document changes?

There are many ways to document change in natural ecosystems but I'll present just two examples here to illustrate their utility. These methods are a way of 'looking back to inform the future'. Corny, but not far off the mark.

Aerial photos were first flown for the whole of Australia in the 1940s. Many of these are readily available (e.g. DSE has burnt to CD aerial photo mosaics of the whole state of Victoria from original photo runs in the 1930s and 40s) and hence, they provide an excellent baseline from which to assess multi-decade changes in vegetation cover. In the image below, you can see how tree cover in the Barmah forest has changed between 1945 and 1985. Indeed, with Google Earth and NearMap, it's now relatively easy to collect up-to-date imagery and compare this to the historical photos. We've used aerial photographs to great effect to detect changes in shrub cover in landscapes after agricultural abandonment (Geddes et al) and in woodlands during their first few decades of conservation reservation (Price & Morgan).

While aerial photos can give broad, landscape-scale perspectives on vegetation change, they lack the resolution to detect local changes. Here, permanent photo-points, where the investigator takes a photo of local vegetation condition from a fixed point repeatedly through time, can provide great insights. It's pretty obvious, though, that photos need to be archived in way that makes them valuable resources into the future.

Photo-points have been used to superb effect at Koonamore in South Australia  (see Recalling the past - there are a heap of photo-point videos worth looking at) to show how semi-arid vegetation responds to climate variation and grazing by stock/rabbits. Unbelieveably, these photo points have been regularly taken since 1926 and they now provide insights the original scientists could only have dreamed of. You can see the dramatic effects of low rainfall on productivity, when individual shrubs established and their growth rates, as well as the devastating effect that rabbits can have.

So when thinking about long-term vegetation dynamics, you really should explore the historical datasets that already exist. They may give you an insight into multi-decade changes that have already been occurring. What better way to place future changes into context.