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.

Are alpine ecosystems being transformed by climate change and fire?

I'll let you be the judge!

Below is a series of paired photos that I'm using to look for obvious changes in the 'woodiness' of alpine ecosystems in the Victorian Alps over the last few decades that might help us understand how alpine vegetation is responding to global change drivers such as climate change and fire.

Theory predicts that with climate warming - and there has already been a 0.8 deg C increase in Australian mountains over the last century - that alpine treelines should migrate upslope to higher elevations, while grassy communities might become shrubbier. Where low temperatures might have limited woody growth in the past, warming eases or relaxes those environmental filters.

First, I searched the Trove website to find historical photos that show mountain landscapes - this is the archive of the National Library of Australia. Mountains are good places to look for vegetation change over time using old photos because it is often easy to relocate the approximate location where the original photo was taken. You can match up ridgelines, rock outcrops, mountain summits etc and get a pretty good approximation of the original location. This is important if you want to re-photograph that same view from which to then make comparisons over time.

While it sounds easy, many of the original shots are too grainy to use, or there is a horse / cow / cattleman obscuring the really important bit of the landscape you want to see. Eventually, however, I found about 40 photos across eight mountain regions that looked promising for comparative purposes. I went up to the mountains last summer and tried my hardest to line up the old shot so I could take something as close as possible to the original. Surprisingly it is really difficult to get the exact same shot, although I think I succeeded some of the time!

While the interpretations are qualitative rather than quantitative at this stage, it is clear that there has been very little obvious change in the woody component of the landscape over a 60-100 year period. This was somewhat surprising given the substantial regional warming that has occurred over the last few decades. There have also been several fires in the alps over the last 80 years and these are generally expected to favour shrub establishment and hence, an increase in heathy vegetation in grasslands. My overriding impression is that treelines have not moved much. Total tree cover is higher in some photos, but this is mainly due to resprouting after fire rather new plants 'infilling' the landscape. Shrub cover is higher in some places but not others. Hence, structural transformation is not apparent.

I hope you enjoy these comparisons. If you think you have photos that might be useful to examine structural changes in alpine areas of Australia, I'd be really keen to hear from you (J.Morgan@latrobe.edu.au). Even better, how about you go up and take a shot of the same view and let me know whether you think the alpine is transforming!

Mt Hotham, looking towards Mt Loch (1929 and 2012).
Note substantial growth of trees in most recent photo (after 2003 fires).
These trees can be seen in the original photo - reshooting after
the 1926 fires.

Looking west towards The Bluff (in 1953 and 2012) from
Mt Eadley Stoney. Snow Gums appear more common now.
Low heathland still dominates much of the area. 

On the ridgeline towards Mt Loch (from Mt Hotham): 1946 and 2012
Note: trees seem more prominent in both the foreground and mid-ground where
grassy patches were previously more prominent



Mt Feathertop 1913 and 2013. Note very little difference in
position of upper treeline

Ngadju kala: fire management in woodlands

A new fire management report, lead by CSIRO scientist Dr Suzanne Prober, challenges common beliefs about Aboriginal burning practices in Australia.

Contrary to the common assumption that Aboriginal burning was widespread and frequent (e.g. Bill Gammage's book The Biggest Estate on Earth - see this YouTube video of Bill's view of the role of aboriginal burning), the report shows that the Ngadju community from south-western Australia were highly selective in where they burnt their country. Ngadju country covers a significant part of the region known as the Great Western Woodlands in south-western Australia. This region is nationally and internationally significant for its large, relatively intact expanses of eucalypt woodlands, shrublands, salt lake systems and mallee. When I was there a few years ago, I was blown away by the shear scale of the woodlands, and the beauty of the landscape. It's well-worth putting it on your itinerary when you're in Western Australia.

Ngadju used fire as a cultural tool for looking after rockholes and grassy areas, for protecting important cultural sites and special plants such as water trees, for access and hunting, and for encouraging grasses. The old growth woodlands were rarely burnt deliberately. Large-scale burning was not a common practice.

Some of the report’s key findings include:

• The extensive old growth woodlands were rarely burnt deliberately, because they take hundreds of years to recover.
• The extensive sandplain shrublands were only occasionally burnt with planned fire. Mostly they burnt naturally by wildfires that were allowed to take their course.
• Rather, Ngadju used fire as a cultural tool for keeping the country clear around rockholes, for encouraging grasses in open grasslands and mallee, and to smoke out animals when hunting. These fires were often small, around 1 ha.
• They also used fire to protect important cultural sites and special plants such as water trees; and to maintain access along walking tracks and in coastal shrublands.
• Other activities such as firewood collecting around the edges of woodlands and rockholes, and sweeping and scraping up litter around individual trees, were undertaken to help control wildfire.
• Ultimately these activities would have led to a fine-scale fire mosaic over the top of the natural vegetation mosaic.

The report, written to document Ngadju knowledge about fire in Ngadju country, can be

downloaded at http://www.csiro.au/Outcomes/Environment/Biodiversity/Ngadju-kala.  As a land management tool, fire obviously has a more select role in Ngadju country than in other regions of Australia such as the tropical savannah and spinifex country where large parts of the landscape are frequently burnt. It highlights the importance of interpreting anecdotal historical information about fire and landscape structure (e.g. settler's diaries, paintings, etc) through the lens of local (rather than regional) scale ecological processes.

 

Geographic distribution ecology

The Austral Grass Tree - what happens to it with climate
change won't be just about climate space. Grasstrees
tend to be found on impoverished soils, so
predicting response is not just about projecting
future suitability of the climate.
(Photo: Michele Kohout)

I've just come back from the annual meeting of the Ecological Society of Australia (held jointly with the New Zealand Ecological Society this year). I saw lots of talks with climate change as their key focus. Many of the talks were excellent, and included projecting/forecasting future species distributions using modelling approaches (SDMs). However, I also saw a glaring absence of field experiments in the general area of 'climate change biology'. I want to raise this apparent research gap here (and perhaps start a discussion amongst the scientific community about how (or if) we can change this).

Field transplant experiments are the most important missing information for understanding species movements under climate change. There is lots of modelling suggesting species ranges will shift, i.e.  observed climate envelopes (realized niches in environmental space) are being projected into the future on a large scale using SDMs but the problem is, we don't know what stops species from establishing populations beyond their range boundaries, i.e.  is climate the direct or indirect driver of species distributions?  I'd argue that field transplant experiments across geographical range boundaries are urgent to test this basic question. They are the reality-test for what sets range boundaries, and especially for when it is climate directly versus when it is a competitive milieu mediated by climate.

Why didn't I see much on this?

Well, such field experiments are difficult and time-consuming. It is crucial that such experiments involve transplanting species beyond the range, with and without amelioration of suspected limiting factors, both physical and biotic. Hence, they can get pretty complicated and pretty quickly! 

But such field experiments are also the essential reality test in relation to SDMs. The general point here is that we need to know not how plants grow where they do occur (this is ecophysiology), nor how much two species compete with each other where both occur (this is experimental community ecology) but rather, what happens when species move into new areas where they experience new species compliments, soils and pathogens (this is geographical distribution ecology).

Unfortunately, the experiments conducted in the 1970s-90s were the era of field experiments on competition and predation, with the overwhelming majority directed at measuring intensity of interactions within a geographical range, with very few at determining why range boundaries are where they are. Hence, we've lost a couple of decades already in trying to understand this crucial question.

I suspect that if we rely on chance decisions by individual research groups to undertake geographical distribution experiments, it's likely that several more decades will pass before a useful number will accumulate to inform the general question: what sets range boundaries? We really need to arrive at a situation within a decade or two where we have a moderately well-founded overview so we can far better understand the response of biota to massive shifts in climate.  Suppose optimistically that, say, 30 experiments a decade could be achieved worldwide. Can the research community collaborate to target them in such a way as to obtain generalization across species and boundary-types as efficiently as possible?

One way might be to assemble a global network with standardised protocols - much like has been done in the Nutrient Network (which tests top-down versus bottom-up controls on diversity in herbaceous ecosystems) or the International Tundra Experiment  (which tests the effect of warming on tundra and alpine vegetation). Both networks have simple protocols and clear questions and they encourage collaborative research across a large range of field sites. Hence, the power of the experiments lies in their spatial distribution with uniform methods.

I think this approach is one that could work to test range boundaries (once it is clear what sort of factors would need to be manipulated), and am in the process of writing a review paper on this idea with (hopefully) a rallying call for such experiments. Stay tuned....