|English ivy taking over|
On my walk back home from the coffee shop in the mornings, I pass by this bench and pretty green area, which is now covered with English ivy (Hedera helix). Although it's pretty, it is invasive. See how it's climbing up the bench? And the entire ground cover is now ivy. This is one of several areas of ivy I see on my walks. It reminds me of kudzu, which I am familiar with from seeing it take over huge swaths of trees in southern states. (That article tells of how the kudzu invasive species, Japanese arrowroot, came into the country.)
But for now, I'll concentrate on English ivy and how it got here. This article on invasive species tells the tale.
English ivy is an aggressive invader that threatens all vegetation levels of forested and open areas, growing along the ground as well as into the forest canopy. Vines climbing up tree trunks spread out and envelop branches and twigs, blocking sunlight from reaching the host tree’s foliage, thereby impeding photosynthesis. An infested tree will exhibit decline for several to many years before it dies.
So, even though it's pretty, and came here as early as the 1700s, it's not native, and it's something we should cultivate. My friend Peggy long ago showed it to me in the forest and we pulled some out while we were walking. I also learned that it can cause skin irritation in sensitive individuals, but if ingested it's pretty awful. (Don't worry, I won't try it!)
Another invasive species around here is the Himalayan blackberry. I remember when we first moved here and I discovered the sweet, heavy fruit on these plants, I was enchanted. Then I found out that it is not quite the innocent fruit it appears to be.
Contrary to its common name, Himalayan blackberry (HBB) is a native of Western Europe. HBB was probably first introduced to North America in 1885 as a cultivated crop. By 1945 it had naturalized along the West Coast. HBB occurs on both acidic and alkaline soils, mainly in areas with an average annual rainfall greater than 76 cm (29 inches) at altitudes up to 1800 meters (6000 feet).
This information comes from a PDF document entitled, "Controlling Himalayan Blackberry," and I learned that it too is very difficult to eradicate. We certainly have enough rainfall around here to entice it to grow. Learning all this doesn't mean I'll stop gathering and eating these blackberries when hiking, but I now have a healthy respect for their ability to take over other species. If only they weren't so delicious!