Last Sunday I was delighted to attend a field day organised by the Yass Landcare group. Our hosts for the day, Michael and Denise, have implemented some great restorative improvements on their property not far from Murrumbateman. I will write more on these and other aspects of the field day itself in a separate post, but first I wanted to share something that got me quite excited….
That was to finally see a demonstration of simple biologically-based incision repair. This restorative intervention was planted 18 months ago under the supervision of Cam Wilson and Peter Marshall. All planting material was provided by Peter, as cuttings from trees on his own farm. Check out the photo below and you’ll see what was once a bare and sunbaked incision, but is now a row of young trees growing very nicely.
In this post I’ll provide some background regarding the widespread phenomenon of incision in southeast Australia. Then I’ll describe what was done at Michael and Denise’s place to stabilise and begin to repair this incised flow-line. Finally, I’ll highlight why this excellent work is so novel and wonderful to see by illustrating some other, less-effective, approaches to incision repair observed during my recent research into this topic.
You can be the judge of what works, what makes sense, and what obviously doesn’t.
After reading this post, I’m hoping you’ll agree that officially-promoted “best practices” in land restoration are often perverse and even detrimental. Furthermore, I expect to reveal how nativist perspectives are dominating present work in land repair and to indicate why these approaches are mistaken and in desperate need of correction.
Introducing the swampy meadow and landscape incision
First up, a brief introduction to the valley-fill ‘swampy meadow’ and ‘chain of ponds’ landscapes common to southeast Australian flow-lines, then a bit about their widespread incision following European arrival.
The descriptive name ‘swampy meadow’ was first applied by Ian Prosser (1991) although previous authors had discussed the ‘chains of ponds’ that regularly occur within these features (Eyles 1979a, 1979b). A consistent focus for the above authors, and for most research concerning swampy meadows and chain of ponds systems, has been their widespread degradation by erosive incision following European arrival (see also: Mactaggart et al. 2008, Wasson et al. 1998). This incision process was first recognised as a problem during the early days of colonial expansion into southeast Australia (Scott 2001).
The following image shows an intact (non-incised) swampy meadow near Braidwood, NSW.
The low-lying meadow shown here presents as a moist and ‘grassy’ valley-fill flow-line zone, with no established channel, but with occasional discreet ponds (note the bright green patches in the mid-ground). Prosser (1991) confirms this situation as typical, stating that, prior to European arrival, catchments up to 100km2 contained no continuous channel or had only a shallow stream elevated above alluvial sediments.
Swampy meadows are formed by an ongoing process of interaction between vegetation and stream-energy as illustrated by the following diagram adapted from Gurnell et al. (2012).
Vegetation will naturally colonise flow-lines during low-flow periods. Having done so, it increases flow-line ‘roughness’ and dampens the erosive energy of subsequent elevated flows. This causes sediment deposition which allows further plant colonisation and enables new species to establish. A form of ‘ecogeomorphological’ succession may follow, eventually choking any pre-existing channel and forming a moist valley-fill zone. The key to the persistence of these zones is the dissipation of erosive stream-energy, and the aggradation of deposited sediment by continuous plant growth and colonisation.
Because they are created and maintained by plant growth, the arrival of European livestock (sheep and cattle) had dramatic consequences for swampy meadows and chains of ponds in many Australian catchments. The suppression and disturbance of vegetation via grazing and regular trampling by hoofed animals created exposed and pugged soils within valley-fill flow-lines, priming these areas for erosion. Hoofed animals also created soil compaction higher in the catchment which prevented infiltration and increased overland runoff, thereby further elevating erosive stream-energy lower down. As a natural result, many swampy meadows and chains of ponds rapidly began to incise. The image below shows a typical example of an incised valley-fill swampy meadow near Orange, NSW. This system was fully incised by 1911 and has remained so ever since.
The incision shown here snakes its way up through the floodplain to the low point in the background hills, it then continues into the upper catchment beyond. At the point where it reaches the hills it is 5 meters deep and has eroded to bedrock.
An elegant biological solution
The incision at Michael and Denise’s place was on a slightly steeper slope than that pictured above. At its upper end (toward the eucalyptus woodland in the background of the image shown below) the incision is 4 meters deep; in the foreground it is around 1.5 meters. 18 months ago, Michael and Denise, along with Peter Marshall, Cam Wilson and members of the Yass Landcare group used a crowbar to create holes at two meter spacings and planted cuttings of Yunnan poplars along the base of the incision.
Despite the good season in areas to the east, there has been little rainfall over this sub-catchment of the Yass River in the last year and a half. Nonetheless, most of the trees have established and will continue to grow in years to come. As they grow they’ll create more shade over the exposed soils of the incision and will drop twigs and leaves, creating viable living soil and enabling more plants to establish along the base of the incision.
According to Peter Marshall, some of the trees already have enough bulk to begin to cut and bundle their branches into fascines. These will be laid in the base of the incision upstream of their pollarded stumps. They create a trap for sediments and organics and slow pulses of water. As the base of the incision begins to build more soil and hold more moisture, the trees will grow even better; shedding more organic matter each year; producing more branches to be used as structural material for fascines; and providing new cuttings for further planting. Over time it becomes an increasingly productive and restorative system. Positive feedbacks emerge between plant growth, moisture retention and soil-fertility improvement. With occasional management, biological production and incision repair will tend to accelerate over time.
This method of planting within the incision mirrors the natural processes of repair observed by Zierholtz et al. (2001) at a site near Jugiong, NSW. At that location, volunteer colonisation of the channel by phragmites and typha was observed to cause sediment deposition and natural stabilisation along the base of the incision. These observations effectively confirm the modelling of Gurnell et al. (2012, presented above). This process of channel colonisation by vegetation is what created Australia’s swampy meadows in the first place, and has naturally repaired previous incisions in some areas (Zierholtz et al. 2001).
Detrimental nativist perspectives in landscape repair
To put what I saw at Michael and Denise’s property in context, the following photographs give an indication of the approach to incision ‘repair’ work that currently holds sway among many ‘experts’ working in NRM and conventional land repair in Australia. It is my contention that these interventions are, in fact, guided more by nativist ideology than by any useful understanding of hydrology, geomorphology or landscape function. The overwhelming attitude seems to be that simply planting eucalypts near an incision will magically fix everything! Below is an example from Orange, NSW (higher up the incision shown previously). Here, nothing has been done to stabilise the incision itself other than to exclude grazing livestock for a few seasons (they’re now back in), but alongside the incision a row of eucalypts have been planted.
It seems a common misconception that planting eucalypts alongside an incision like this, somehow helps, in some way. But I’ll admit, it’s completely beyond me….I just can’t understand what these trees are supposed to achieve with regard to incision repair. Seriously, is this some kind of magic?
In reality, the introduced grasses are doing more to stabilise this erosion than the trees planted by well-intentioned nativists. Below is another example of the same approach, this time from near Bungendore, NSW. The vegetation in the gully floor is the only thing in this picture that is helping to stabilise this dramatic erosion.
Time and again, this is the approach taken by nativist-inspired “restoration” projects: they simply plant eucalypts 5 to 10 meters away from the incision. Recent Honours research by Will Higgisson from the University of Canberra re-examined 123 different Greening Australia erosion-prevention projects conducted over a ten year period in the ACT. Whilst Will found varying degrees of plant regeneration and biodiversity at these sites, he confirmed that not one of the projects included planting within the incision, all of them simply excluded cattle and introduced eucalypts beside the incised flow-line (Will Higgisson, pers. comm., 2014).
It is clearly apparent to any observant person visiting these project sites that the eucalypts achieve very little of practical value in terms of soil stabilisation. It will be decades–perhaps centuries–before they begin to provide functional woody debris to the floor of the channel. They are planted to boost habitat and diversity, so cannot be cut or coppiced for use as structural material within the incision. Even when mature, they provide only scattered shade to nearby soils. They often actively suppress the growth of grasses and other groundcover species through allelopathy and moisture competition. Tree feeder roots growing from beside the incision do little to stabilise exposed banks because soil surface conditions are too hot and desiccated for roots to colonise. The trees are deliberately planted away from the eroding wall of the channel because the soil is unstable at the edge and the trees may be disturbed as it continues to erode!
What’s more, if the incision is ever actually repaired, the swampy meadow hydrology will return to its previous state and soil moisture conditions will change dramatically in these locations. Periodic inundation and persistent soil saturation can be extremely detrimental to some eucalypt species, creating root-rot and eventual dieback. It seems reasonable to expect that any species which grows well in the relatively-dehydrated soil beside an incision will not enjoy the saturated conditions that occur within an intact swampy meadow. These zones were once dominated by low-growing water-loving plants–typha, phragmites and eleocharis, along with other reeds, grasses and sedges–but this historical fact is completely ignored by many naive would-be “restorers”.
Perhaps the worst aspect of this one-size-fits-all ‘silver-eucalyptus-bullet’ approach is that for some illogical reason it has been used to justify the removal of existing vegetation from within eroded flow-lines. The image below shows a typical incised swampy meadow floodplain that has been stabilised by introduced willow trees. As pointed out in a previous post, these trees are well-adapted to conditions within agricultural floodplains like this one. Many of these trees were deliberately planted by intelligent land-holders wanting to stop the incision process. They have not spread beyond the incision and they clearly mark its location.
The nativist “solution” to incisions where riparian willows are established, is to remove these non-native trees and then plant eucalyptus 5 to 10 meters away from the eroded channel as per usual. The next photo, from an incised valley-fill near Lucknow, NSW, shows this nativist “repair” technique (cough, cough) in action. You can see the line of the incision because the removed willows are re-sprouting from stumps and suckers. Note well the eucalypts planted back from the eroded channel using their magic powers to prevent further erosion occurring! (I still don’t get it).
Rest assured, within a month or so of me taking this image, the willow regrowth that you can see had been re-sprayed and killed. So, not only have some essentially-useless eucalypts been planted 5-10 meters away from the incision, but some extremely effective riparian species that were growing within the eroded channel (where the erosion actually is!) have been destroyed.
Can you imagine the crunching gears, the whirring cogs and the very, very lonely brain cells that would trundle out this bizarre response to landscape incision.
It could only be a nativist “solution”.
It’s not that there is anything terribly wrong with planting eucalyptus trees 5-10 meters away from an eroded channel, it’s just that this is not a solution to landscape incision! And if wanting to plant pointless eucalypts leads to the removal of other, more effective, riparian stabilisers from incised flow-lines, then this ideologically-motivated approach becomes a serious impediment to landscape health and function.
We desperately need to re-examine what is going on.
Throughout my recent research into erosion stabilisation, I could see there was something illogical about the conventional ‘magic eucalyptus’ approach illustrated above. My focus was on the way that natural repair was occurring within these incisions, so it was pretty obvious that pulling vegetation out of the channel and then planting trees 5-10 meters away from it made no sense at all. Surely it’s obvious to anyone who’s actually had a look?
That’s why it was such a pleasure to finally see a clear-headed, simple, and beautiful demonstration of an effective repair technique growing within the incision at Michael and Denise’s property. It’s a credit to them both and an excellent example for other landholders to consider; a real-world biological solution that will actually work.
EYLES, R. (1977). Birchams Creek: the transition from a chain of ponds to a gully Australian Geographical Studies, 15 (2), 146-157 DOI: 10.1111/j.1467-8470.1977.tb00094.x
Eyles, R. (2007). Changes in drainage networks since 1820, Southern Tablelands, N.S.W. Australian Geographer, 13 (6), 377-386 DOI: 10.1080/00049187708702716
Gurnell, A., Bertoldi, W., & Corenblit, D. (2012). Changing river channels: The roles of hydrological processes, plants and pioneer fluvial landforms in humid temperate, mixed load, gravel bed rivers Earth-Science Reviews, 111 (1-2), 129-141 DOI: 10.1016/j.earscirev.2011.11.005
Mactaggart, Barbara; Bauer, J; Goldney, D and Rawson, A. (2006). The Restoration and Protection of the Swampy Meadow Within an Agricultural Landscape Australian Farm Business Management Journal, 3 (2), 68-75 Other: http://search.informit.com.au/documentSummary;dn=201032108518740;res=IELBUS
Prosser, I. (1991). A Comparison of Past and Present Episodes of Gully Erosion at Wangrah Creek, Southern Tablelands, New South Wales Australian Geographical Studies, 29 (1), 139-154 DOI: 10.1111/j.1467-8470.1991.tb00711.x
Scott, A. (2001). Water erosion in the Murray-Darling Basin: learning from the past CSIRO Land and Water Technical Report No 43/01 Other: https://publications.csiro.au/rpr/pub?list=BRO&pid=procite:30c606fa-5a68-419e-afd4-6ed495fe0f73
Wasson, R., Mazari, R., Starr, B., & Clifton, G. (1998). The recent history of erosion and sedimentation on the Southern Tablelands of southeastern Australia: sediment flux dominated by channel incision Geomorphology, 24 (4), 291-308 DOI: 10.1016/s0169-555x(98)00019-1
Zierholz, C., Prosser, I., Fogarty, P., & Rustomji, P. (2001). In-stream wetlands and their significance for channel filling and the catchment sediment budget, Jugiong Creek, New South Wales Geomorphology, 38 (3-4), 221-235 DOI: 10.1016/s0169-555x(00)00092-1