Some of the boulders, that were put in place to control erosion were displaced.
The morphology of the stream has been altered dramatically in several places. This area was once water, now it is dry land.
This was the same area three weeks ago:
Here is another area where the stream bed has changed. Notice the deposition in the middle:
Compared to two months ago:
How Effective are my Invasive Plant Removal Efforts?
Today, I began to evaluate the effectiveness of my project to restore Turkey Branch to a more natural state – without litter and invasive species. Since litter never stops, I decided to analyze the effectiveness of my invasive plant removal efforts. In order to do this, I selected 9 areas that I have weeded since May 2010. I measure a 3 feet by 3 feet square section with a tape measure.
I count all of the invasive plants [according to species] and remove [by pulling] them from the square. I then count the remaining native [and non-native non invasive plant species] which remain in the ground and checked my records to indicate when I weeded these areas:
The next step was to do the same measurements in an area that I have not cleared in the past. I took an 70 feet cross section of the stream, and sampled 3 feet by 3 feet squares, every 10 feet moving from the stream to the trail. I counted the invasive plants [and removed them] and counted the native plants which remained in the ground.
Before:
After:
Success in Removing Invasive Plants
Here are my data along with a calculation of the mean number of invasive plants per square yard:
Sadly, it is clear that some invasives, mostly notably Japanese Stilt Grass, return in areas that have previously been weeded. When these data are plotted graphically [invasive plants per square yard versus weeks since last weeded] a rather depressing observation emerges:
It is clear that, as time elapses after an area is first weeded, the invasive plants return. The next question: is the average number of invasive plants [per square yard] statically different for the areas that I previously weeded and the control areas which I did not weed? In other words, is the weeding of invasive plants an effective method to restore the natural ecosystem?
In order to test this, I will use the student t test:
Where:
X1 = the average number of invasive plants/square yard in areas I weeded
X2 = the average number of invasive plants/square yard in areas I have not weeded
s1 is that variance of weeded areas and s2 the variance of the untreated area and n1 and n2 are the number of samples.
Here are the calculations:
At the 90% confidence interval, with 14 degrees of freedom ((n1+n2) – 2) the table value is higher than -0.71 which indicates that the average number of invasive plants/ square yard are not different - statistically - in areas that were weeded than in the control area. A greater number of samples need to be taken because the variance is too high.
Success in Restoring Native Plants
Next, I did the same type of analysis for the native plants and found some encouraging results.
It appears that the number of native species in a sample area is directly related to how long ago the area was cleared of invasive plants. This can be seen graphically:
The Student t Test was also conducted to test whether the number of native plants/square yard are significantly different between areas that I weed and the control areas which I did not weed.
Here are the calculations:
There appears to be no statistically significant difference between the number of native plants per square yard between weeded and control areas.
More samples need to be taken over a longer period of time before I can make any conclusions. However, it appears that weeding invasive plants has some impact on controlling their future growth.
I know some time has passed since you published this, but I just found it now and it is fascinating to read. I live in Montgomery County, PA (a funny coincidence--also still a more-or-less similar eco-region) and we deal with a lot of the same plants here.
ReplyDeleteI've found that in order to sustainably remove plants from an area, you need to return regularly. Ideal is to do a little weeding every week. Over time, you'll need to do less work, but I think just going in once, or even just going in regularly for one year, isn't enough.
For example, one of my friends' yards has a lot of stilt grass. Just pulling it once isn't enough, but we try to pull a little bit of each week. I also planted Chasmanthium latifolium seeds where I removed it, figuring that plant grows taller and will eventually out-compete it, and we also planted or seeded in a number of other plants where we were removing the stiltgrass, including Cryptotaenia canadensis, Eurybia divaricata, Acalypha rhomboidea, and Ageratina altissima, to name a few. We also found the grass nimblewill (Muhlenbergia schreberi) growing amongst the stilt grass, and when we removed the stilt grass, the nimblewill really took off in growth. The community of plants has grown out to be lush and thick and the only remaining stilt grass that comes up seems to have trouble competing.
I'm curious to come back next year though. Stilt grass is an annual, so I think if we keep it out of the area manually for a couple of years, it will probably be gone for good except for a stray sprout here or there.
This is the second year I've been working on my friend's yard and it's starting to look really different, ecologically, but we're having better luck controlling some plants than others. We are still having trouble with the lesser celandine, which I don't see you mention here, if it's not in your region then be grateful as that's a tricky one to control!