FAIRBANKS — Weeds are a problem for gardeners, homeowners, farmers and the ecosystems in which they grow. Where do these weeds come from and how do they become established? Any time land is cleared, seeds from weeds can be transported or blown into this open land.
Take a look around the Tanana Valley. Imagine if we could watch a piece of land, let’s say one square meter, for the past 500 years or so, what would we see? Suppose that piece of land was just west of the box stores and south of the Johansen Expressway. Maybe 500 years ago it was in a black spruce forest. There might be one tree in the meter square, lots of moss and lichen, a bit of grass and maybe some blueberries.
At some point during a hot summer, a fire might have burned through and, if the organic matter was dry enough and the fire slow moving enough, all the vegetation and organic matter could have been burned off. Our piece of land would be bare ground with a layer of ash right after the fire. That autumn, seeds from surrounding areas would blow in and augment the seeds that were already in the soil.
The following year, our piece of land would have grasses growing on it in addition to fireweed. After a few more years, willows would be noticeable as well as birch, aspen and other woody plants. Our piece of land would go from having hundreds of grass plants and a lot of fireweed to a few clumps of grass and one bushy willow tree. Another 80 years go by and the piece of ground has a large birch tree, a small spruce seeding and a few small grass plants.
Another couple of hundred years go by and the birch tree is replaced by the spruce tree and it looks like the piece of ground is going to be returning to what it was 500 years ago. But then there is a discovery of gold, and people come and need wood for the mines, keeping warm and building homes. On our piece of ground, the spruce is cut down and the grasses and some berries flourish. Eventually, the willows, aspen and other woody plants follow.
But before these plants can really get going, the land is cleared with a bulldozer. There are stores going in and roads being built, and this piece of land is set aside for a commercial district. The bare ground that was left by the bulldozer has been compacted and the bulldozer brought in seeds of a plant that is not native to Alaska.
The normal grasses and windblown seeds that follow the clearing of a forest — whether by fire or logging — have a tough time growing in the hard ground. But this new plant does fine, putting down a taproot and storing energy for the following year. On our piece of ground there is one white sweetclover plant, some small grass plants and six small dandelions (another plant that is not from Alaska).
The next year the dandelions flower. The clover plant grows five feet tall and produces thousands of seeds. The following year on our piece of ground there are the same six dandelions, the same small grasses and hundreds of small white sweetclover plants. The year after that our meter square area is covered in seeds from the tall clover plants — seeds that can live up to 80 years in the soil. Our meter square of ground is a mix of six dandelions, thousands of white sweetclover plants and a few grasses, all covered in a thin blanket of snow.
If nothing is done, what will be on this piece of land 10 years from now? How about 20 years or 500 years? Could we make the land have a dense stand of fireweed? What are our choices? With just a little bit of work we could manage this land to grow something better than non-native plants. I am available to help with weed management decisions.
Steven Seefeldt is the Tanana District agriculture and horticulture agent for the Cooperative Extension Service, a part of the University of Alaska Fairbanks, working in cooperation with the U.S. Department of Agriculture. He can be reached at 474-2423 or firstname.lastname@example.org.