Claudia Catterall and Jo Green are undertaking research into the importance of small Big Scrub remnants. This is a transcript of Claudia’s presentation of her work so far given at the 2009 BSRD
The theme of Big Scrub Rainforest Day (BSRD) this year is All About the Big Scrub. I think that’s appropriate, because there is a lot that we still don’t know about the Big Scrub. My research aims to fill in a few of those gaps.
I live at Eltham, right in the middle of the Big Scrub, though there’s not much left in the area now. My house is built of Big Scrub – it dates to the early 1900s, and is made of teak, cudgerie, white beech and red cedar.
I moved to Eltham 1992, when my daughter was one year old, looking for a good environment in which to raise kids. Although I had little knowledge of the Big Scrub I started to really notice rainforest trees, and rainforest patches, on the drive from Eltham to Rosebank when taking my daughter to preschool. I started collecting seeds and identifying rainforest plants, slowly building up my recognition skills. I first focused on growing trees to ‘plant on’, and regenerate, our bare, ex-dairy farm, gradually becoming more aware of issues about remnant vegetation.
I’ve always wondered in particular about the very small remnants, paddock trees and roadside vegetation because these are often neglected and weed infested yet are potentially very important for the long-term future of the Big Scrub. The mission of BSL is to “help save the Big Scrub and its magnificent biodiversity”; I think we need more research into Big Scrub remnants to help achieve this aim.
I’m delighted to now have an opportunity to carry out some research into small rainforest remnants under the auspices of the School of Environmental Science and Management at the Southern Cross University, where I now teach. I’ve been working with, and been able to use the taxonomic expertise of, Jo Green, whom you might know from Brunswick Valley Landcare and the Mullum Creek Native Nursery.
This talk will outline the rationale and methodology of my research into small Big Scrub remnants of less than one hectare, and provide some preliminary results on the one remnant surveyed so far. BSRD is a community landcare event and as such is terrific in attracting people with a wide range of knowledge about the Big Scrub, so I will try to pitch the talk to suit all and I apologise if you have heard some of this before.
Before European settlement the Big Scrub Rainforest was the largest continuous expanse of lowland sub-tropical rainforest in Australia (see Fig. 1, Big Scrub Clearance). This area stretched from the Nightcap range in the North to Meerschaum Vale in the South and from Bangalow in the East to Lismore in the West. Originally 75,000 ha, now less than 700 ha which is less than 1%, with most remnant areas less than 5 ha. About half of the mapped areas occur in three relatively large patches in the extreme northern area – Big Scrub FR, Boomerang Falls and Minyon Falls; these are arguably not core ‘Big Scrub’areas.
Lowland subtropical rainforest has been extensively cleared for agriculture. In recognition of how little is left the NSW government has listed lowland rainforest on the New South Wales north coast and Sydney bioregions as an Endangered Ecological Community under the NSW Threatened Species Conservation Act. The Big Scrub is part of this vegetation formation.
It is also currently being considered for listing under federal legislation, the Environmental Protection and Biodiversity Conservation (EPBC) Act, as outlined in a recent email by Tony Parkes. (BSL’s nomination of Lowland Subtropical Rainforest on Basalt and Alluvium in NE NSW and SE Qld as a National Endangered Ecological Community has made it to the Final Priority Assessment List.)
The Threatened Species Conservation (TSC) Act (1995) defines ‘endangered’ as a species, population or ecological community that is likely to become extinct or is in immediate danger of extinction. The purpose of the TSC Act is to:
conserve biological diversity and promote ecologically sustainable development
prevent the extinction and promote the recovery of threatened species, špopulations and ecological communities
protect the critical habitat of those species, populations and ecological communities that are endangered
eliminate or manage certain processes that threaten the survival or evolutionary development of threatened species, populations and ecological communities
ensure that the impact of any action affecting threatened species, populations and ecological communities is properly assessed, and
encourage the conservation of threatened species, populations and ecological communities through co-operative management.
This is all very well, but what does it mean on the ground? They’re great aims, but how much is really being done to prevent extinction and promote recovery? It affects development proposals, and penalties can be applied for clearing etc, and funding has been provided for regeneration works (especially to BSL – which has done fantastic works), but an overall government management plan seems to be lacking.
In particular there has been a real lack of detailed research into the remnants; how can you manage a remnant if you don’t know what’s there?
An important report was prepared by Lott and Duggin in 1993 for the listing of Big Scrub remnants on the Register of the National Estate (see Register of the National Estate, right). The aim was to map all remnants, assess their conservation significance (in terms of plant diversity and habitat for fauna) and provide recommendations for management.
Lott and Duggin’s report identified 41 remnants with a total area of 556 ha. They found that the long-term viability of the Nightcap Range sites (Big Scrub FR, Boomerang Falls and Minyon Falls), which was 50% of the total area, was good as it had a large size, was intact and formed a ‘closed’ forest habitat; and they found that Johnson’s Scrub near Federal was of high significance. Significantly, however, they thought that the long-term viability of small remnants was dubious, but that “their continued existence may be crucial in maintaining existing levels of fauna across the region”. They suggested that “major ecological functions of the Big Scrub rainforests are maintained by the existence of a network of remnants across the plateau”. Tree replacement and weed control were recommended as active management tools; BSL has been involved in working on many of the identified sites.
The point about a network of remnants is an important one. This scene (see Fig. 2 below) shows the Eltham valley with Dawes Bush (7 ha) in the foreground. Note the matrix of vegetation corridors and scattered trees – all important for birds to move across the landscape. Currently the landscape has greater tree coverage than 50 years ago, much of it camphor laurel, which provides habitat and food sources for rainforest birds and bats, forming mutually beneficial relationships.
The listing of remnants has provided a basis for sites given bush regeneration funding. However, not all remnants have been listed. There are lots of small remnants across the landscape, most less than one hectare, which have not been listed or surveyed at all.
According to Lott and Duggin the definition of a ‘remnant’ is a “specifically identified area which was never cleared”, or ‘original’ rainforest. There is an issue here, as some of the smaller patches may have been little more than a couple of trees originally, or maybe they were just missed, but when so little is left, and it is so valuable, then attention needs to be paid to all.
The suggestion has been made that small remnants are a case of the “living dead”: that they are essentially survivors from a past time, that are destined to die out and disappear over time. Ecological theory relates species diversity to the area of habitat available; rainforest patches in a landscape are like islands, and small islands are known to generally have a lower number of species than large islands. But rainforest islands differ from real islands – they are connected to one another and to other vegetation types by corridors of vegetation, and isolated ‘stepping-stone’ trees. This landscape matrix may be quite effective for some species, at least for those which have their seeds dispersed by flying animals, in being able to maintain themselves in the landscape.
So rather than big islands being better, maybe a lot of small islands can be just as good, or even better, in some ways. In any case, there are no more big islands available, so we need to look after the small ones; there is such a small proportion of the Big Scrub left, we need to save it all. Each small remnant is likely to be a genetic treasure chest. If there is to be long-term survival of the community (and rare species), genetic resilience is needed. The gene pool is already very depleted – we can’t afford to lose any more of it.
There is a lack of scientific study with the main published information on Big Scrub remnant vegetation taking the form of descriptive accounts with species lists. This is minimal information. We need to know a LOT more about these remnants.
The focus of government funding has been on restoration rather than research but we need both.
Some of the questions addressed by this research include:
Is species diversity in remnants being maintained?
Is species composition changing?
Do all remnants tend to have the same species mix?
Are remnants becoming more homogenous over time?
Is there evidence of species recruiting from outside remnants?
Where do rare and threatened species occur, and are they replacing themselves?
What is the overall condition of the remnants?
What is the level of weed invasion?
Are the trees healthy – especially with regard to termites?
The aim of the research is to document the diversity and size class composition of selected remnants, to be able to assess the effectiveness of community maintenance processes such as seed dispersal, plant recruitment and establishment within and between remnants across the landscape matrix.
My hope is that this research will provide information which can be used to push for better management of the Big Scrub remnants.
Methodology: Five small (less than 1 ha) remnants and 5 control sites in larger (greater than 5 ha) remnants will be surveyed. The entire remnant will be subdivided into 20 x 20 m sampling units to establish a relationship between area and species richness. All species (including groundcovers and epiphytes) will be identified, with shrubs, trees and vines assigned to one of four size classes based on stem diameter.
Five of the subplots will be intensively sampled with all individuals in each size class (11 size classes) counted. All study sites will be within the same subtropical rainforest community, the Castanospermum-Dysoxylum muelleri (black bean – red bean) Suballiance (Floyd 1990) on basalt soils on the Lismore-Alstonville plateau.
Tree size, percentage of canopy cover, abundance of dead trees and percentage of invasive exotic species will provide an index of community health; and the presence/abundance of canopy tree species in each size class will be used to assess within-remnant maintenance of species composition and community structure and dispersal of species between remnants.
Location: The studied Eltham remnant (see Fig. 3, right) is on private property, Glendower, belonging to Geoff Crawford. A second remnant of 2 ha on his property is included on the RNE and has work carried out on it by BSL. The studied remnant is about 1 km from Dawes Bush (7 ha), 3 km from Booyong FR (12 ha) and 8 km from the Boatharbour NR (13 ha).
The remnant has camphor laurel forest on its SW flank. It is unfenced so cattle have access, although they don’t go in most of it – a possible benefit of asparagus vine?
There were several difficulties in doing the survey. Climbing asparagus vine and lawyer vine made movement through the remnant very difficult. Did I say “the entire remnant will be subdivided into 20 x 20 m quadrats” – it sounds so easy! Not till you get in amongst the asparagus (exotic) and the lawyer vine (native) do you realise the difficulties. Unless you’re Jo Green…
I said earlier that I would present preliminary results for one remnant. In fact we managed about 7/8 of one remnant: we had spent 14 days in the field and only completed 18 quadrats! It can take a whole day to record an area 20 x 20 m. Just laying out the transect tapes can take an hour. Asparagus is the worst – secateurs are a must!
Another challenge, apart from the ticks, was craning the neck looking upwards to identify trees.
The preliminary results are quite impressive: our small remnant recorded 152 species of trees, shrubs, vines, herbs, ferns or epiphyte of which 139 were natives and 13 exotic (see Species Richness, next page). There were 97 native trees and shrubs.
These results can be compared to the species diversity recorded by Lott and Duggin for the 41 larger remnants registered on the National Estate. You will see that this small Eltham remnant of just 0.7 ha came out third in species richness (just trees and shrubs), when compared to the National Estate registered remnants of 2 ha or less (again, see Species Richness, next page). Eltham is substantially higher in tree and shrub diversity than the larger Glendower, only 400 m away. In fact, for the 20 remnants listed by Lott and Duggin which are below than 10 ha in size, Eltham ranks equal 9th (with Morton’s Scrub at 4.5 ha).
Of the 79 native tree species recorded 22 species had individuals with a trunk diameter at breast-height or ‘DBH’ (see DBH on page 16 and What’s Your Biggest Tree?, below) greater than 50 cm (see Tree Regeneration, bellow). This is all very well but it is the sapling numbers that indicate tree regeneration and we note here that there were 19 (86.4%) species which had saplings present (ie less than 10 cm DBH).
When we looked at the 22 species with a DBH of greater than 50 cm (see Tree Regeneration, below) we found that 68% had saplings present smaller than 1 m in height, 86% had saplings less than 10 cm DBH and 68.2% had representative individuals between 10 and 50 cm DBH. This shows that the large trees are regenerating.
There were three species, giant stinging tree, yellow kamala and yellow carrabeen, that had no saplings present, although yellow kamala comes up regularly at my place, so no problem there, and so we would need to study more remnants to see if there was a problem with the other two species; it is difficult to draw broad conclusions from just one remnant.
Looking more closely at seedling regeneration, defined for our purposes as trees of less than 1 m in height (see Seedlings < 1 m High, right), we found 36 of the 79 tree species present as seedlings (two of these, veiny laceflower and red lilly pilly are listed as rare). Four species, underlined, were only present as seedlings.
We were surprised to find that nine of the species with trunk diameter over 50 cm exceed the recorded DBH listed by the rainforest guru, Alex Floyd, in Australian Rainforests in NSW (1990) in his appendix listing “outstanding trees of NSW rainforests”. There is a good chance that this is to do with the different growing conditions in a small remnant, where light levels are probably higher and the canopy may be less closed, causing the trees to grow “short and fat” rather than “tall and thin”.
It’s possible that tree health may not be as good in small remnants as in more extensive tracts of rainforest, and this is a question we hope to be able to answer with the research. Many trees in the Eltham remnant showed signs of termite infestation: for instance 11 of the 53 trees bigger than 50 cm DBH had obvious termite damage.
Four species listed as rare or endangered under the TSC Act (1995) were found in the remnant: Clematis fawcetti, Desmodium acanthocladum, Syzygium hodgkinsoniae and Tinospora .
Of the 13 weed species present climbing asparagus was by far the worst, and in many places it was causing damage to the mid-stratum by clambering over small trees and causing them to bend and break. The major tree weed was broad-leaved privet, with many young trees coming up in some parts of the remnant. Most other weeds were of minor importance. Camphor laurel was common on the remnant edges, but did not appear to be able to germinate and grow under the shaded conditions within the remnant.
Conclusion: This talk provided a snapshot of a single, small, unknown and uncared for remnant. Our survey showed that it was high in species diversity and possessed surprisingly good levels of regeneration. More small remnant surveys are needed to answer the questions I posed earlier, but there is no doubt, given the tiny amount of lowland rainforest left, that every remnant is precious.