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.

Friday, 22 May 2015

Do we need a moritorium on seed collection of rare plants in small remnants??

I've just visited one of my favourite temperate grassland remnants near Melbourne, Australia - Truganina Cemetery. It's long been a favourite of mine because I started my grassland journey there. It was at Truganina that I studied the seedling recruitment dynamics of a very threatened grassland daisy, the Button Wrinklewort (Rutidosis leptorrnhychoides), with the aim of enhancing conservation management for its persistence.

I've long since taken an interest in this remnant which is very species-rich and managed sympathetically by burning at 4-5 yr intervals. It's an excellent place to see the original plains grasslands that once covered 22,000 km2 of western Victoria. Indeed, as Neville Scarlett impressed upon me, if you want to save ecosystems like temperate grasslands, you need to save all the parts. And Truganina Cemetery is one of those places where we are trying to save the parts.

Truganina Cemetery is a 2 ha jewel in the crown of temperate grassland conservation near Melbourne. It was created in the 1850s and hence, avoided the plough and grazing by sheep. Currently the landscape matrix is one of cropping but urbanisation is rapidly encroaching. The graves are restricted to the eastern boundary. Trees are non-indigenous species planted decades ago in the native grassland. Curiously, their impacts have been positive: many Button Wrinkleworts survive in the halo of the trees where soils are drier and productivity low.

Saving the parts then means those parts get re-distributed elsewhere to reconstruct the ecosystem. Because Trugnina Cemetery contains such a high quality grassland remnant, it supports some very threatened plant species such as the Button Wrinklewort and Spiny Rice-flower (Pimelea spinescens). As a consequence, it is used heavily as a seed collection resource.

Seed collection might be by seed banking organisations, or indigenous nurseries, who follow guidelines for seed collection from remnant populations (e.g. taking no more than 10% of seed available at the time of collection from XX% of the population). To collect seed of indigenous species in the State of Victoria, a permit is required from the State agency responsible for public land, as well as permission from the land manager (in this case, a Cemetery Trust). My big concern is that over the last 10 yrs or so, when I've visited Truganina in summer as part of my ongoing ecological studies, it is clear that seed collection is having an impact on the Button Wrinklewort. Anecdotally I hear that many collectors come to this site to source seed of the Button Wrinklewort (one of only two populations in the Melbourne region, the other having on 20 plants or so).

It may be a coincidence, but in my population counts of this species over the last 20 years (currently sitting at 660 plants, down from 1100 a decade ago), there has been no effective seedling recruitment at this site in the last 5-6 yrs. Why? And might seed collection be contributing to this?

The Button Wrinklewort is a little prettier than the name would suggest!
(Photo: Jamie Pittock, Sterling Park, Canberra)
Climate clearly has a role to play here, so it is not suprising there was little recruitment during the decade long drought (2000-2009). My own research shows that recruitment is best when autumn rains come early in the season (April) as opposed to late in the season (June). Because Rutidosis has a transient seed bank, it requires annual seed input to ensure some probability of autumn germination. The plant itself lives for about 12-15 yrs in natural populations. Hence, seed production is critical to ensure population turnover at decadal timescales. Without seed, population decline in inevitable.

I think I'm starting to see the consequence of very rare plants in small remnants being over-harvested for their seed resource. I have no evidence for this. But I think it might be time we acknowledge this possibility, and over-harvesting as a threat to some populations of endangered plants. Such a threat is not intentional. No one seed collector is intending to imperil these populations. But my worry is that the cumulative effect of seed collection is effectively making populations like that of Rutidosis at Truganina unsustainable.

Perhaps we need a moratorium on seed collection of some species at some sites in some years to ensure that those populations continue to persist into the future. I don't know where most of the seed of Rutidosis is going - into revegetation projects, seed orchards? But what I do know is that the wild population seems to be struggling under current conditions. Certainly none of the seed is being used to propagate plants to be replanted into Truganina to bulk up the numbers.

A moratorium might be quite simple to enact. What about caging individual plants to ensure that some of the individuals in the population set lots of seed and we can then follow whether there is effective recruitment in the following year, and compare that to areas where ongoing seed collection occurs. This might give us some insight into just big a problem seed collection is. It might mean having an agreement with the land manager, who controls access to the site, to limit the number of collectors onto their site per year.

This is sort of radical but it points to the need for getting some control over seed collection, and the need to move entirely to seed production areas to supply the revegetation industry.

Seed production area at Organ Pipes NP,
first established in the early 1990s.
(Photo: John Morgan, January 2012)
Grassland managers in the Melbourne area have done this really well already. At Organ Pipes National Park, the site of Australia's first large-scale grassland restoration, it was recognised in the 1980s that to re-construct the community, seed production needed to be scaled up to supply propagules well in excess of what was available from wild populations. Seed production facilities were developed, learning how to do this through trial and error. Since, Greening Australia has effectively demonstrated how to grow grassland species in cultivation for seed production. They've had superb success. There are even commercial growers now that are being very successful at this endeavour.

This is a serious issue. I think I am witnessing the decline of Rutidosis at Truganina, one of a long-list of species that have declined without us even noticing, nor us understanding the mechanism(s) of decline. Whether seed collection has contributed to this process, I'm not sure. But I am certain that it can't be helping.