In order to assess if the harvest impacted plant diversity, specifically richness, we installed two species-area curve plots. One was placed in the unharvested site and the other in the nearby harvested site, about 225 feet apart (see image below). The plots were done by starting at 1 square meter and noting the presence of all plant species within that area and then doubling the plot size ten times until 1024 square meters is reached. As the area was expanded we noted all newly observed plant species.
The harvested plot had a greater number of native species at 91 than the unharvested plot with native 73 species (Figure 1 and Table 1, attached).
Additionally, Table 1 shows that the harvested plot has the same number of species that are considered MHs38 indicator species and more MHs39 indicator species than the unharvested plot. MHs38 and MHs39 indicator species for both plots are shown in Table 2 (attached) listed by the plot size in which they were first observed. The individual plot reports that highlight indicator species are in the supplemental content section.
This increase in species could be caused by an increase in sunlight due to the gap openings created from harvesting.
The harvested site also had more introduced and invasive species than the unharvested site (6 and 2, respectively; Table 1). The introduction of invasive and introduced species during logging is another potential threat to rare plant species. At the time of the harvest, the sale regulations required all logging equipment to arrive visually clean of soil, seeds and vegetative manner. Five years later only the harvested plot had invasive Canada thistle and reed canary grass, and introduced giant chickweed and dandelion present, although not in high numbers. In this forested setting, these species are not overly worrisome, because once the trees become established they will likely be shaded out. Common buckthorn and common burdock which were present in both plots and likely introduced by birds and animals, pose a more serious threat to the stand’s biodiversity.
In addition to observing changes to plant diversity, we wanted to know the current composition of trees to see we were achieving our goal of establishing oak in the next stand. We measured basal area in fixed area plots in both the unharvested and harvested areas as well. Basal area per acre in the unharvested site is 113 square feet per acre. Basal area per acre in the harvested site is 59 square feet per acre. Due to northern red oak being the major timber sale component, it had the largest change in basal area from 46.7 sq. ft. per acre in the unharvested site to 7.0 sq. ft. per acre in the harvested site (Table 3). Sugar maple’s BA didn’t change much since it was a large component of the remaining pole sized trees.
The harvest created a growing environment that favored the planted oak and walnut regeneration. In the harvested site there were 300 oak seedlings per acre and 400 walnut seedlings per acre (Table 4, attached). Conversely, there was no oak or walnut regeneration in the understory of the unharvested site.
Table 3: Basal area by species for each site
Species
|
Unharvested site
|
Harvested site
|
Northern red oak
|
46.7
|
7.0
|
Sugar maple
|
40.0
|
35.0
|
Basswood
|
11.7
|
11.0
|
Ironwood
|
8.3
|
--
|
White oak
|
5.0
|
3.0
|
Ash
|
1.7
|
--
|
Black walnut
|
--
|
1.0
|
Bitternut hickory
|
--
|
1.0
|
Big-tooth aspen
|
--
|
1.0
|
Total Basal Area (ft2/ac)
|
113.3
|
59.0
|