Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.

Tuesday, 11 February 2014

The earliest evidence for widespread declines in native grasslands in Australia??

Something a little different this week.

Native grasslands in southern Australia have undergone a massive transformation since European settlement. But the evidence for the speed of that transformation has been hard to come by. It's hard to guess whether people noticed the changes, or simply realised one day that grasslands were gone.

The following is an extract of an article from The Australasian, dated 18th October 1878. It shows that within 50-80 years of  settlement, an understanding of the impacts of agriculture on native grasses was already obvious. And, interestingly, there were already calls to develop a native grassland "seed industry". It's worth noting this type of information - perhaps the earliest record of grassland transformation in Australia - because we are still grappling with the same issues in 2014 in many respects.

It should make us reflect on what we now know, and yet how little has changed in some respects. We're still thinking about grazing regimes that promote native grasses & still grappling with how to best produce large quantities of seed. Enjoy.

"The deterioration of our native pastures as regards their fattening powers .... is due not only to the removal from the soil of certain proportions of the elements of fertility in the form of bone, flesh, and wool, but in some degree also to the loss of the best and most nutritious grasses, which inevitably occurs under the system of depasturing commonly practised in the whole of these colonies. Whether the grasses are only annuals or are those known as perennials, they must soon die out unless measures are taken to ensure a re-seeding of the ground at certain intervals.

Even the longest lived grasses must be renewed from seed occasionally; the old stools become enfeebled by continuous grazing, and the sorts that are most relished by sheep are actually eaten down into the soil, so that in the course of a few years they disappear altogether from the ground. Of this the common kangaroo grass is a familiar example; it will not bear the constant nibbling of stock, especially of sheep, and as it is often the only green feed, in hot dry weather, the plants are eaten completely out.  Within unstocked or lightly stocked enclosures, as between railway fences, native grasses of all kinds continue to thrive as formerly. They have the opportunity of renewing themselves from seed annually, and as they are rarely fed down they grow far more vigorously than grasses of the same species depastured in the ordinary way.

Here is a lesson of which graziers great and small may take note, if they have any desire to preserve the native grasses from extinction. The question whether it is desirable to preserve them at such cost and trouble as may be needed to effect that object is one upon which old and experienced graziers agree. They all affirm that no exotic grasses fatten so quickly as the native pasturage used to do, and there is an equally general agreement of opinion that the stock are far less healthy on " English grasses " than on the native pasturage of the country.
It is a principle in English husbandry, when laying down lands in permanent pasture, to employ as large a number as possible of species. In this they only imitate nature, for on examining a square yard of well-grassed ground it is found that the number of species thereon usually varies from 50 to over 200. In this country the number of species is not so great upon the plains, but there is a very considerable variety of pasture plants in districts having a name for fattening. In attempting to imitate nature, and replace the lost natural pasturage by sowing down, as in England, general mixtures of grasses, colonists have met with little success.
In the course of a few years the greater number of the grasses are found to have disappeared, leaving only the most robust, or those which by growing all the year round eventually extinguish the more delicate, which, are, usually, also the most desirable. Whilst, therefore, pastures of English grasses can be easily formed, they are found wanting in variety of food—an element of the greatest importance in maintaining the health of the stock. They supply a great abundance of rank and watery food, instead of the more moderate quantity of sweet and healthful food afforded by the native pasturage.

Seeing, then, the importance of maintaining the health, of our stock, the preservation of the native grasses becomes a matter of the first moment, especially to residents in the warmer districts, in which the so-called English grasses will not thrive. It has been remarked that when once the native grasses are gone a full sward can never again be established. Graziers, therefore, should conserve the pastures, and in order to succeed in doing this they will find it necessary to give some little attention to the habits of the several species as regards longevity and time of seeding. The winter grasses, for example, seed in spring; the summer ones later in the season, and at different periods of the summer and autumn. Unless these points are known and regarded, some important grasses will very soon become extinct, even in pastures which are allowed a season of rest from stock, with the object of permitting them to shed a crop of seed. It is obvious that unless the latter plan be adopted the alternative one of sowing native grass seeds must be pursued, and hitherto this has been out of the question, no such article having been upon the market.

The business of growing Australian grass seeds might surely afford profitable work for many farmers in different districts. Harvesting would, for the most part, take place before the grain harvest commenced; the late grasses would not be ready until after that work had been concluded. We can hardly imagine any line in which more could be made with certainty than in growing crops of native grasses specially for seed. Men of intelligence and good powers of observation would readily determine what species ripen simultaneously, and might, therefore, be grown together. The first matter is to collect sufficient seed by hand, and the present time is the season for commencing."

You can see the original article at http://trove.nla.gov.au/ndp/del/article/2982085

Saturday, 1 February 2014

Learning a little about ecological restoration from Pygmy Possums

The restoration industry in Australia of the last 30 yrs has been dominated by the 'local is best' philosophy when it comes to thinking about what to replant at a revegetation site. Here, the use of local-collected seed has been promoted because of the belief that local provenance equates to offspring that are likely to be better-adapted to the site and hence, will outperform non-local ecotypes. It also has the added benefit of conserving local genes that might otherwise be lost as species diminish in the local landscape. This may be true, although there is conflicting scientific evidence on this topic. Locally collected seed for example, if derived from small populations, might have low genetic diversity and fitness may be compromised because of inbreeding depression.

But even if inbreeding depression is not a problem, is this philosophy going to deliver us the restored ecosystems of the future?

The prospect of rapid climate change should, I believe, make us consider shifting the local provenance paradigm in restoration ecology, particularly in highly fragmented landscapes where there is probably zero chance of natural gene flow and species migrations. While plants grown from locally collected seed are often better adapted to local abiotic conditions, uncertainty lingers over their suitability for restoration under climate change. It may be better to source seeds from climates that more closely match the predicted future climate of the restoration project, e.g. to source seeds from drier, warmer climates if the local climate is predicted to dry and warm. To do this will entail a massive shift in thinking, one that is likely to take some time.

One of the biggest perceived problems about introducing non-local propagules to restoration sites is the idea that it will lead to outbreeding depression. In short, outbreeding depression is when offspring from crosses between individuals from different populations (i.e. the 'local' and 'new' populations) have lower fitness than progeny from crosses between individuals from the same population. Hence, there has been a reluctance to mix genotypes because of unknown effects of such mixed matings.  Some people also think that the mixing of genotypes in this way reduces the distinct characteristics of the populations involved, and should therefore be avoided. Outbreeding depression won't be a problem if you are bringing seeds of species to new areas where the species currently doesn't exist. It only applies if you bring new genotypes (perhaps dry adapted ones) in contact with local genotypes.

But this may not always be a problem.

Dr Dean Heinze and a Mountain Pygmy Possum
at Mt Buller
An outstanding example of introducing new / novel genes into a gene pool has undoubtedly been responsible for saving the Mountain Pygmy Possum at Mt Buller. Ian Mansergh and co-workers recently reported on this incredible story of population recovery that is strongly underpinned by conservation genetics.

The Mountain Pygmy Possum (Burramys parvus) population at Mt Buller was about 300 in 1996 but dropped to 30 by 2009. It was on the path to local extinction.  The population had extremely low genetic diversity, offspring fitness was low (babies were small and had high rates of mortality) and there were few males in the population.

The solution was simple. Introduce new animals (with a different suite of genes from the local population) to improve the genetic basis of the species at Mt Buller, even if that meant "mixing" two genotypes that have been separated in space for thousands of years. The introduction of new genetic material to Mt Buller from a population more than 100 km away (the world's biggest Pygmy Possum population at Mt Hotham) has rescued this population from almost certain extinction. Half of the Mt Buller population now contains genes from the Mt Hotham population; the genetic variation has doubled. In addition, because of this genetic shift, the population size has more than tripled since 2009 and male survival has dramatically increased.

So why do we fear outbreeding depression so much?

We have long recognised that populations differ genetically, and often those differences provide adaptations to local conditions. The best scenario is usually seen as preserving genetic diversity between populations. But the evidence is that outbreeding depression is rare. In conservation genetics, it is understood that outbreeding depression can be temporary. When co-adapted gene complexes are disrupted, fitness declines are inevitable but short-lived. Natural selection soon acts on the new genetic opportunities and populations bounce back. With new genetic material, the population may be able to face the new challenges of climate uncertainty.

The recovery of the Mountain Pygmy Possum population at Mt. Buller is a good news story and one that should be celebrated. And it possibly has implications for thinking about restoration of systems elsewhere. Given the dramatic loss of native vegetation in southern Australia, the creation of small and isolated remnants, and the rapid warming and drying of much of the landscape, restoration that thinks about "future proofing" our native species and ecosystems might consider more than the local proximity as the sole rationale for seed collection. One might be drawn to ask: is local species extinction preferable than the introduction of novel genes that enable regional species survival?

Further Reading
Mansergh, Heinze, Weeks and Perrin  (2013)  Gene-pool mixing: Lessons from the high country.  Wildlife Australia 50, No. 4, Dec 2013: 32-35.