What happens to the willows once they are cut down/removed?
- Category: Questions about Willows
- Created: Monday, 17 February 2014 20:12
- Published: Monday, 17 February 2014 20:12
- Written by Jeff Cottrell
- Hits: 1659
There is not one answer to this question which is why the Willows Management Guide written by the National Willows Taskforce (A WONS committee) included the consideration of what happens to the dead willows before you consider any control program.
I should explain that i mainly do control work (as a volunteer) on willows that spread by seed (Black Willows and Grey Sallow) although i have treated crack willows in areas where they impact on endangered species like the Boorooralong Frog or they are invading into gorge country not used for agriculture and where the banks are mainly rock and so not subject to erosion. As we are a volunteer based group our control work is spread over a number of years. We are also kayakers and rafters and so are doing work in places where we like to go and so can go back and do followup weed control where we have removed the weeds.
I first became involved in Black Willow control programs in 2000 in the Wollemi National Park along the Colo River for this project we were told not to worry about removing the black willows as they would break down fairly quickly and re-enter the nutrient cycle. What we observed was that for the majority of the black willows that was the case. Borers attacked the dead or dying willows which allowed in water and fungi and also cockatoos, crows and various other birds went after the grubs and helped break down the willow trunks within 18 months but you would get the occasional trunk remain and harden and last for more than 5 years some times and then eventually get washed away. Once they fall and are on damp ground they do rot fairly quickly. These trees were in a remote area and away from public infrastructure and the general public. We started in 2000 and finished the primary treatment work in 2003 and moved into the monitoring and follow up. This was during a period of extended drought and there were very few major floods until about 2007 and so very little debris shifted along the river as most broke down . By 2006 you could not see where the old willow galleries were in the National park except for a dip in the height of the canopy along the river bank where the native veg replacing the willows was younger and so smaller
As we moved out of the park onto private land in 2004 there was more of an issue with public safety from falling dead trunks, dead stems moving in floods and damaging public and private infrastructure and also they are unsightly for the landowners until the fell over, but agency staff said it was still ok to leave them standing and again most broke down. We completed the primary treatment of the black willows in 2006 and although there was a low level wood bridge at Upper Colo which occasionally caught debris on the move it was never damaged and we were told if the black willows which had grown fairly large in exposed sand banks had been washed away alive they would probably have caused more damage to the bridge. Also no landowner reported any damage to their infrastructure due to the dead willows. There was an issue with a water skier hitting dead trees in the Hawkesbury after one of the first floods but they did not know if it was willows or some other tree. Also this was the one of the first floods after several years of low flows and there was no attempt to check the river for dead trees washed out of the tributaries. Water Skiers had become complacent after several years of low flows and so no floods brining new debris into the water ski area. But after the incident in 2008 we went along the river with a local landowner and cut down and blocked the remaining dead black willows and dropped the piles of timber in a local camping ground to be used as fire wood. It burns quickly and so the pile only lasted two weekends. I should also make it clear that generally we do not remove all types of willows just those likely to spread into National Parks or areas impacting on an endangered species or an endangered Ecological Community.
After the Willows out of Wollemi project in the Colo Catchment we then took the skills and equipment acquired during the project to other rivers in NSW mainly focusing on doing follow up monitor of previous black willows programs and during one of these trips we were asked by a local crown land manager is we could remove some small crack willows on a travelling stock reserve. This developed into a bigger program with several private landowners to remove Crack willows along 4km of the Goobarragandra river near Tumut to protect two endangers species along the river. All of the work was on private land, or crown land next to private land, and so with this project we obtained funding to cut down the dead trees so we left very little debris. This became difficult to manage so we stopped remove the larger trees and just removed smaller trees and so our goal there is to let the larger trees die of old age (which they are) over time and continue to remove the smaller crack willows and all black willows. There was a 1 in 100 year flood event on the river in 2012 which pretty well removed all riparian vegetation plus banks, fences, roads, bridges etc. There area where we remove willows from was about 4km of river bank about 1/3 of the way down the 32km of river between the national park border and the junction with the Tumut River and the full length of the river was changed by the flood even in some of the rock gorges large boulders were moved along the river bed.
During the time we worked on the Goobarragandra we also rafted about 20 rivers in south east NSW mapping the willows by type and treating them in national parks and where we had landowner consent. Most of our activities involve treating or hand pulling small black, grey sallow or crack willows or seedlings that are growing amongst good native vegetation and so the dead plants are can be left to break done over twelve months or less. This will become increasingly so in the future as we maintain sections of river where we have previously removed the invasive willow species.
In 2008 we started a project to remove large crack willows from along the Wingecarribee river between Berrima and Goodmans Ford where we had landowner consent. This project was started several years before by the local historical society trying to reclaim historical sites along the river at Berrima and also to recover views of their river. We came on board to help the council with this project and using out whitewater rafting skills treated the crack willows growing in rapids and the canyons downstream of Berrima and the council contractors treated the larger numbers of crack willows near town. We expanded the project area from 4 km around town to 80 kilometers of river also linking in with the previous work done by a Oxley college near Burradoo and moss vale. We found the willow trunks were slower at breaking done outside of the Sydney area. I think this is because the cooler locations do not suit the borers that did the work in the Hawkesbury region. So after we completed the treatment program we started cutting up the willow trunks into 2 to 3 meter long pieces to allow the fungi to get in and break down the trunks. We had completed about half the work in our area before the floods in 2102 and so now we have a large log jam in the canyon to cut up when we have time to get in and work on it. I should add that there are about 30 to 40 large crack willows left in the 80km because the land owners did not give consent and also they were on alluvial banks that needed replacement planting before the trees could be removed. So my conclusion is that in Cooler climates you should always cut up the dead willows or if you can get equipment to them remove them during the treatment process.