Floodwaters are gone, but storm may have left lasting damage to forests
With the loss of life, homes and personal property, and all of the economic and psychological suffering inflicted by Tropical Storm Irene last August 28 in Vermont, the focus was naturally on the human toll. The media also covered the story of the damage done (some $200 million) to roads and bridges around the state. There was even a fair amount of attention paid to the health of rivers and streams after the effects of the storm, as well as the impact of recovery efforts on water quality. Given all of this, it was understandable that little attention has been paid to the impact of Irene on the forests. However, some of this damage may prove more difficult to repair, and the results may be with us for a long time to come.
Windsor (Vt.) County Forester Jon Bouton took this photo on September 15 on the Upper White River showing a deep layer of silt covering the forest floor. "The deep soil deposits prevent the roots from functioning correctly. Upland trees need to exchange gasses and cannot if they are buried too deep," he explains. "These trees will be severely stressed and will probably die a slow death over the next 10 years or so."
Photo by Jon Bouton/Vermont Division of Forestry.
Jon Bouton, Windsor County forester with the Vermont Division of Forestry, begins the conversation by giving credit to Vermont's forests for helping to ensure that Irene wasn't even more of a disaster. "I really give the trees a lot of credit," he says. "I think that without the trees we have, the runoff and flooding would have been even more severe than it was, and I think we would have had more damage."
While Bouton isn't worried about the health of the state's forests in general after Irene, he is concerned about specific areas that may be vulnerable. Bouton says he has heard many accounts of forest access roads being washed out, and says that reports may continue to come in this spring as more woodlot owners can finally access their properties. "Many of the Class IV and Class III town roads that provide access to larger pieces of forestland were really wiped out, so in many cases forestland owners have been separated from their woodlots and haven't been able to get there yet," he explains. "It will take a fairly significant investment on somebody's part to put those roads back."
For woodlot owners who are able to access their woods when spring arrives, Bouton says it's more important than ever to check the status of water bars and the general condition of access roads. "Water bars might have been filled in by the storm so that erosion patterns have shifted and future storms may cause problems," he explains. "My recommendation to everyone is that, when the snow is gone, get out there and look at all of your roads. It might be that the next thunderstorm is the one that tips the scales. That makes sense any time, but particularly this year."
Some damage will impact not only woodlot owners, but everyone who enjoys recreation in the forest. "I think the damage that's going to prove to have a very big impact was the damage done to the edges of our streams and rivers," predicts Bouton. "Not only did the storm really change the course of a lot of rivers and streams, and make large deposits of sediment and gravel and boulders in places where we hadn't seen it before, but the cleanup and fixing of roads has also contributed to a lot of gravel being exposed. So we're really lacking a lot of the vegetation that we used to have on our stream banks, and in many cases there isn't a lot of soil there."
Efforts to revegetate stream banks may be required to help correct the situation, he adds. "Vegetation helps to maintain the stream banks; it helps to shade and cool the water, which is important for fish. And the woody debris that naturally falls from trees leaning over the water is organic matter which feeds the critters which feed the fish, and that's no longer there," Bouton explains.
Unfortunately, the tree damage from the storm wasn't contained just to stream banks, and some of it might take years to fully be realized. "I have walked through some of our lower-level riparian forests, places that don't flood every year, but maybe every 15 or 30 or 100 years, that now have a foot and a half of sediment on the forest floor," relates Bouton. "These places have sugar maples and ash trees - sort of the typical upland northern hardwood species. I do not believe those trees will survive with their root systems buried that deeply." He said there's no definite way to put a time frame on it, but predicts there will be slow decline seen in these trees, with significant mortality seen within 10 years. "These are big organisms, so it's going to take a while for them to run out of energy, but I think they will die."
In such cases, there's little, if anything, a woodlot owner can do to save the trees, says Bouton. The sediment should have been removed relatively quickly, and any equipment capable of doing the job likely would have severely damaged the root systems, which live very near the surface. "Now the trees have been buried for so long there's not much that can be done."
Perhaps worse news, says Bouton, is that the silt that came downstream and covered the forest floor also may have brought with it invasive plant species. He says that Oriental knotweed growing along many roadsides and stream banks that washed out was carried in the floodwater. "The flood tore those patches up, broke the plants up, and deposited the pieces when it dropped the silt. Knotweed sprouts aggressively from pieces; little tiny ground-up pieces of it can sprout," Bouton explains. "With the knotweed now spread throughout the floodplains, it has a competitive advantage. Sprouts were already a foot high last fall before frost killed them back to the ground surface! It grows fast, tall, spreads by sending out rhizomes and can completely shade the ground. It is also a poor stream bank stabilizer, and it is tough to control, let alone kill."
In most cases, when low-level forests are covered in silt from floods, seeds from established trees would sprout replacement seedlings. This would help to regenerate the forest after the existing trees died. However, with bare silt, the quick-establishing knotweed stands a good chance of covering the ground and outcompeting any tree seedlings, Bouton explains. "I am afraid that Irene was the perfect storm for knotweed. Trees die slowly; knotweed occupies the site; trees and other plants can't survive the shade of the knotweed; and diverse wooded floodplains develop into (worst case, but entirely possible scenario) knotweed monoculture floodplains."
He advises woodlot owners to get out in the spring to look for any signs of invasives that might have been brought in by floodwaters. "If you value your riverside or streamside forests, it's absolutely critical to be looking for invasives that have been spread around by this silt," says Bouton. "With invasives, you really need to find them when they are small populations. Once they get a foothold and the populations become larger, you usually need a lot of chemicals and persistence to control them."
Sam Schneski, county forester for Windham and Windsor counties, which were also hard-hit by Irene, agrees that the damage to woodlots was not as bad as it might have been. There were isolated incidents of damage that he says hold educational value for future storm events. "The worst thing I saw in the woods was probably a forest access road in the town of Plymouth," Schneski recalls. "This road was really built up; they must have brought in about 8 feet of fill to build it up. And uphill of it was just sheer bedrock."
The road was ditched properly, but the culverts were not installed properly and quickly plugged up. The result was a complete loss of the woods road and, with it, access to the woodlot. Because forest management activity was required on the property, it became necessary to restore access. "The contractor came in with an excavator and dozer and put the road back in as best he could with broad-based dips. You couldn't drive a car up there anymore, but it worked for skidding," explains Schneski. The lesson is, especially when steep, rocky terrain is involved, the design of any road must be done with extreme weather events in mind. This protects the investment in the road, as well as the surrounding ecosystem.
"Most of the other damage I saw was smaller in scale," says Schneski. "For the most part, with the vegetative cover we've got and the generally small size of the streams, the damage was confined to places where the water could build up and really get a good head behind it. For the average woodlot without a major river going through it, the damage seemed pretty minimal." Given all the bad news that Irene brought with it, this is a welcome bit of good news.
Patrick White is a freelance writer based in Middlesex, Vt. Over the past 10 years, he has covered a wide range of agricultural operations around the Northeast. He is always on the lookout for unusual stories.