Beyond the 'extinction debt'

The best examples of temperate grasslands of SE Australia, like tallgrass prairies in the USA, now largely exist in small, isolated pockets, and are of variable quality due to a century of more of land use. They're the last bastions of these once great ecosystems.

Basic conservation biology theory tells us that long-term conservation of the ecosystem will be challenging - populations are small and isolated, habitats have been degraded by weed invasion to varying degrees, and interactions (such as plant : pollinator mutualisms) may have already been disrupted.

High quality native grassland on three-chain wide roadside at
Derrinallum. Mt Elephant looms large in the background.
(Photo: John Morgan)

Hence, conservation of the biota will be a challenge.

To illustrate the scale of the problem, thanks to generous funding from the The Myer Foundation, our research team has just recently completed a floristic survey of Melbourne's Urban Grasslands. Our fabulous botanist Ben Zeeman (and team) recently surveyed the floristic composition, structure and population size of selected plant species. In total, we surveyed 79 public grasslands for composition (totalling 1393 ha), did 904 transects defining structure, and made 45,200 species observations. Wow! What an effort. Of the 250 native species we observed, 80% were confined to 20% or fewer sites. Hence, while there is still lots of native plant biodiversity in urban Melbourne, much of it is perhaps on the brink of extinction.

Extinction debt is a concept in ecology that may have great relevance to Melbourne's grasslands.

Extinction debt occurs because of time delays between impacts on a species, such as destruction of habitat, and the species' ultimate disappearance. For instance, long-lived trees may survive for many years even after reproduction of new trees has become impossible, and thus they may be committed to extinction. Extinction debt is most likely to be found in long-lived species and species with very specific habitat requirements (specialists).

Extinction debt has important implications for conservation, as it implies that species may go extinct due to past habitat destruction, even if continued impacts cease, and that current reserves may not be sufficient to maintain the species that occupy them.

So what can be done to reverse the extinction debt in Melbourne grasslands? This is a conversation we need to have. Biologists are telling us there will be a continuing crisis (and they have been very good at documenting declines) but is there a way to slow / reverse the extinction debt?

There are probably several answers here. Using a basic understanding of the threats to remnant vegetation that apply anywhere where land use has transformed the native landscape, I can think of four key things we should be doing.

1) Supplement / enhance small populations: we know one of the main reasons that populations go extinct is that they become small and hence, vulnerable to loss of genetic diversity, environmental stochasicity, and regeneration failure due to the fact so few propagules being produced. Hence, having identified which species are in this category in Melbourne's grasslands, perhaps we should look at bulking up population numbers. This might be done with transplanting plants and sowing seeds. Importantly, such activities should not be restricted to just rare species. Our data tells us lots of species might be in trouble.

2) Promote population turnover: one of the reasons populations become small is because recruitment ceases to replace mature plants. If deaths > births, then it is inevitable that populations decline to local extinction. Hence, rather than just maintaining adults (the thing that we see in grasslands), it is imperative that the mechanisms that allow seedling recruitment are well-understood and, more importantly, the conditions for regeneration are maximised. A focus on seedling recruitment needs to occur. My own work suggests that seedlings of many species require lots of light to survive, and that recruitment is episodic and probably related to years of above-average rainfall. Maybe we can enhance recruitment success by removing canopy (by fire or slashing) and watering plots to see if seedling recruitment improves.

3) Maintain important ecosystem processes: one of the critical processes in grasslands is the effect that dominant grasses have on smaller intertussock species. Strong, asymetrical competition means that Kangaroo Grass tends to win the battle when left undisturbed. Hence, frequent implementation of fire (or some other mechanism such as slashing) needs to occur if you want to maintain intertussock species of the majority of the flora. This is well known, but needs to be implemented.

4) Empower people to care: if we are to avoid a massive loss of Melbourne's grassland biodiversity, we have to make people care about this. Many people already do. There are dozens of terrific Friends Groups, individuals and agency staff who are working tirelessly to improve grassland condition and recognition. This energy needs to be harnessed, and a broader audience cultivated. Those people who live near grasslands have to care about them, otherwise conservation of local diversity will always be a challenge.

Recently I saw some excellent signs that advertise the values of grasslands and their habitats. This was on one of the best rural roadsides for native grasslands there is, so the values are already well-known. But I applaud the local Shire for emphasizing the values of remnant grasslands, and why we should care. This needs to happen in Melbourne, least we lose lots of our grassland flora and no-one notices.

The fabulous signs on the Cressy-Shelford Rd promoting the values of the native grassland
as habitat for endangered species. The signs measures approx. 7 m x 2.5 m and are produced in high quality materials.
(Photo: John Morgan)

Publications from the Lab - 2013

Here's a list of papers that were published in 2013 from my Lab. If you want a copy of any of these papers, feel free to email me at J.Morgan@latrobe.edu.au and I can supply a PDF.

1. Farmilo, B.J., Nimmo, D.G. and J.W. Morgan (2013) Pine plantations modify local conditions in forest fragments in southeastern Australia: insights from a fragmentation experiment. Forest Ecology and Management 305: 264-272.

2. Seabloom, E., Borer, E.T., Buckley, Y., Cleland, W.E., Davies, K., Firn, J., Harpole, W.S., Hautier, Y., Lind, E, MacDougall, A, Orrock, J.L., Prober, S.M., Adler, P., Alberti, J., Anderson, T.M., Bakker, J.D., Biederman, L.A., Blumenthal, D., Brown, C.S., Brudvig, L.A., Caldeira, M., Chu, C., Crawley, M.J., Daleo, P., Damschen, E.I., D’Antionio, C.M., DeCrappeo, N.M., Dickman, C.R., Du, G., Fay, P.A., Frater, P., Gruner, D.S., Hagenah, N., Hector, A., Helm, A., Hillebrand, H., Hofmockel, K.S., Humphries, H.C., Iribarne, O., Jin, V.L., Kay, A., Kirkman, K.P., Klein, J.A., Knops, J.M.H., La Pierre, K.J., Ladwig, L.M., Lambrinos, J.G., Leakey, A.D.B., Li, Q., Li, W., McCulley, R., Melbourne, B., Mitchell, C.E., Moore, J.L., Morgan, J., Mortensen, B., O’Halloran, L.R., Partel, M., Pascul, J., Pyke, D.A., Risch, A.C., Sankaran, R.S-G.M., Schuetz, M., Simonsen, A., Smith, M., Stevens, C., Sullinav, L., Wardle, G.M., Wolkovich, E.M., Wragg, P.M., Wright, J. and Yang, L. (2013) Predicting invasion in grassland ecosystems: is exotic dominance the real embarrashment of richness. Global Change Biology doi: 10.1111/gcb.12370.

3. Mayfield, M,. Chalmandrier, L., Wells, J., Dwyer, J., Bonser, S., Catterall, C., DeClerck, F., Ding, Y., Fraterrigo, J., Metcalfe, D., Vesk, P. and J.W. Morgan.2013. Differences in forest plant functional trait distributions across land-use and productivity gradients. American Journal of Botany 100: 1356-1368.

4. Morgan, J.W., Kviecinskas, P.A. and M. Maron 2013. Effect of proximity of buloke (Allocasuarina luehmannii) trees on buloke early sapling survival in a semiarid environment. Australian Journal of Botany 61: 302-308.

5. Morgan, J.W., Meyer, M. and Young, A.G. 2013. Habitat fragmentation leads to interrelated genetic and ecological processes that likely imperil persistence of small populations of a once-common Australian grassland daisy. International Journal of Plant Sciences 174: 1209-1218.

6. O’Halloran, L.R., Borer, E.T., Seabloom, E.W., MacDougall, A.S., Cleland, E.E., McCulley, R.L., Hobbie, S., Harpole, W.S., DeCrappeo, N.M., Chu, C., Bakker, J.D., Davies, K.F., Du, G., Firn, J., Hagenh, N., Hofmockel, K.S., Knops, J.M.H., Li, W., Melbourne, B.A., Morgan, J.W., Orrock, J.L., Prober, S.M. and Stevens, C.J.2013. Regional contingencies in the relationship between aboveground biomass and litter in the world’s grasslands. PLOS ONE  8(2): e54988. doi:10.1371/journal.pone.0054988.

7. Camac, J.S., Williams, R.J., Wahren, C-H., Morris, W.K. and Morgan, J.W. 2013. Post-fire regeneration in alpine heathland. Does fire severity matter? Austral Ecology 38: 199-207.

8. Venn, S.E., Morgan, J.W. and J.M. Lord 2013. Foliar freezing resistance of Australian alpine plants over the growing season. Austral Ecology 38: 152-161. 

9. McCartney, V.A., Silvester, E., Morgan, J.W. and P.J. Suter. 2013. Physical and chemical drivers of vegetation in groundwater source pools on the Bogong High Plains, Victoria. Australian Journal of Botany 61: 566–573.

 

 

 

 

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.


SUMMER MANAGEMENT OF NATIVE PASTURES

"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

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
http://theconversation.com/genetics-to-the-rescue-hybrid-mountain-pygmy-possums-born-on-mt-buller-6134

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.

New analyses (thankfully) confirm a long-held notion in grassland ecology

Kangaroo Grass grassland at Evans St
in Sunbury, Victoria,  with lots of
native forbs. This type of grassland
has always been thought to be associated
with areas that have a long history of
frequent burning and little stock grazing.

One of the most important papers on the ecology and management of temperate native grasslands in southern Australia was published by John Stuwe and Bob Parsons in 1977. It's a great paper for two main reasons.

First, it has a very simple objective. To answer the question: how do long-term management regimes affect the floristics of grasslands. This was a paper way ahead of its times in some respects because it recognised that grassland 'condition' (or 'state' to used the modern jargon) was likely a function of its disturbance regime. In this case, frequently burned areas versus grazed versus 'unmanaged'.




Bob Parsons

Second, despite 35 yrs of research since then, the overarching premise of the paper still stands. There hasn't been a magic new understanding of grasslands, just better resolution of the mechanisms that underpin the reponses observed by Stuwe & Parsons (S&P). For example, my own research has shown that grassland canopy gap size positively affects recruitment success  and survival of many grassland herbs because it allows high light penetration to the soil surface. Gaps can be maintained by frequent burning, hence maintaining species coexistence through ramet survival and maximising infrequent (but potentially very successful) recruitment opportunities.

Much of the important insight that was gained from the S&P paper was based on collecting floristic data from areas with different management history (lists of species and their abundance using 4 x 5 m quadrats) and then using a technique called 'hand sorting' to create a Two-Way Table. From this, they identified 'character species' that typify each management area, as well as community metrics such as species richness. They found that frequently burned areas contained more native species than unmanaged areas, and that daisies were more common in burned areas compared to grazed areas. But, when you eyeball the data, there appears to be a lot of overlap in the species composition of grasslands with different management (both in native and exotic species). When I gave the dataset to my Honours student to look at, they were not convinced that S&P had such clear-cut outcomes as appear in their paper. Could S&P have 'over-emphasised' their data, rendering one of the great papers in Australian grassland ecology misleading????

With modern analytical methods like classification and ordination, there is an opportunity to check whether the basic results of the original study were correctly manipulated and interpreted. We can add rigour to the data analysis rather than relying on subjective sorting as was originally done.

With this in mind, I transcribed the original data (which is both found in the original thesis and in the published paper, and shows the value of archiving ecological data in accessible locations that can be retrieved despite changes in technology). I then used a common data analysis package to examine floristic data (Primer) and undertook both a non-metric multidimensional scaling ordination (NMDS) and a cluster analysis. If S&P were correct - that management history affects the floristic composition of grasslands - then we should see "groupings/clusters" in the resultant outputs that are reflective of the a priori identified management regimes. And, using analyses such as ANOSIM and SIMPER (I won't go into the details), we can see if management causes significant differences in composition, and which species are responsible for the differences.



Lightly grazed grasslands have fewer
native daisies than frequently burned
grasslands 

With a little trepidation, I ran the analysis. Either way, the outcome was always going to be interesting. But I didn't really want to 'prove' S&P got it wrong.

Much to my relief, the ordination and cluster analysis confirm that management history in native grasslands DOES affect grassland composition, and that the differences are due to those identified by S&P - more daisies in frequently burned grasslands, and more weeds in unmanaged and grazed grasslands. Phew! That was somewhat of a relief given the importance this paper has had for a generation of grassland ecologists, many of whom have trained under Bob Parsons.


Here is the main figure I generated showing the outcomes of this analysis.

In this ordination, based on abundance data (so species are weighted according to how much cover they project), we can see that RA (frequently burned railway remnants) are floristically distinct from both RO (unmanaged roadside remnants) and PG (remnants partially grazed by stock). RO and PG remnants do not differ significantly from one another in composition (indicating there is a lot of overlap in the species that occur in these remnant types). The way to read the figure is such: coloured symbols indicate quadrats that were sampled in areas with different management histories. How far apart each symbol is from other symbols indicates how similar the composition of any two quadrats is. Hence, if two symbols are near each other, they are similar in composition while the most dissimilar quadrats will be further apart from each other.

Clearly the analysis lends support to the idea that the composition of grasslands (both species present, and the abundance of those species) is affected by management history.

You can see also which species mostly give rise to these stark differences. The lines you see on the ordination that radiate from the centre of the image, with species names at their end, tell us which species have a high contribution in quadrats. We can see that most of the lines point towards the green symbols (the frequently burned railway remnants); this can be equally read as they are pointing away from the RO and PG remnants. These species are mostly native forbs (including the daisies Leptorhynchos and Helichrysum (now Chrysocephalum)) and we interpret this as suggesting that RA sites are characterised by a suite of native (and some exotic) species that tend not to be found as much in PG and RO sites (i.e. they contribute little there). By contrast, the unmanaged RO sites tend to be characterised more by exotic species such as Holcus and Hypochoeris.

Hence, S&P seem to have got it right; frequently burned roadsides have a composition that is different from other native grasslands, and this is due to management history promoting some species over others. In essence, daisies are promoted in frequently burned areas, but tend to disappear in grazed and unmanaged areas. The concept of 'habitat segregation', first coined by S&P, has been at the heart of conservation management of native grasslands for 35 years and continues to resonate even today. I wonder what other ecological and conservation ideas will stand the test of time.

Here's to S&P.


Further Reading

Stuwe, J. & Parsons, R.F. (1977) Themeda australis grasslands on the Basalt Plains, Victoria: floristics and management effects. Australian Journal of Ecology 2, 467-476.

Morgan, J.W. (1998) Importance of canopy gaps for recruitment of some forbs in Themeda triandra-dominated grasslands in south-eastern Australia. Australian Journal of Botany 46, 609-627.