In our species-area plots that have been done in a variety of Native Plant Communities and covertypes, we generally see an increase in species richness following any disturbance. Of course, that level would be expected to be lower after herbicide application or some forms of mechanical site prep (shearing). As the canopy and subcanopies develop, species richness tends to decrease as shade intolerant species are diminished or eliminated. This being a retroactive case study, we don't know what the species richness was prior to disturbance.
On FDc23 plots, we found an average of 69 species for herbicide sites, 71 species for mechanical site prep sites, 66 for the wildfire origin jack pine site, and 61 for the natural origin aspen site. Compared to the FDc23 Species Frequency and Cover table, on herbicide treatment sites, we found 97% of the high affinity species (species present in >50% of FDc23 sites). We found 89% of the high affinity species on mechanically prepped sites, 82% on the wildfire origin site, and 63% on the aspen dominant site. Non-native and invasive species were most abundant on the mechanically prepped sites (6-11 species). Herbicide sites held 2-3 non-native species. The wildfire origin jack pine site had three and the aspen site had one.
On FDc24 plots, we found an average of 78 species for herbicide sites, and average of 85 species on mechanically prepped sites, 64 species on the aspen dominated natural regeneration site, and 65 species on the jack pine dominated natural regeneration site. Compared to the FDc24 Species Frequency and Cover table, we found 96% of the high affinity species on the herbicide treatment and mechanically treated sites, 86% of them in the aspen dominated stand, and 90% in the natural origin jack pine stand. We found up to 16 non-native and invasive species on the herbicide treatment sites, 10 on the mechanically treated sites, two in the natural origin jack pine, and one in the natural origin aspen stand.
Some differences in species composition can be explained with synecological coordinates. On a scale of 1 to 5, they rate species on their demand or tolerance of Moisture, Nutrients, Heat, and Light. The coordinates for the various treatment on FDc23 sites are fairly close. The herbicide treated sites were neither highest nor lowest for all four measurements. The FDc23 mechanical treatment sites ranked highest for Heat and Light and tied with the aspen site for the highest rank in moisture. The wildfire origin jack pine stand ranked neither highest nor lowest for every measurement. The aspen site ranked highest for Nutrients, tied with mechanical site prep for highest in Moisture, tied with natural jack pine for lowest in Heat, and ranked lowest for Light.
In FDc24, the aspen site ranked highest for Moisture and Heat, tied the natural jack pine site for highest in Nutrients, and was neither highest nor lowest for Light. The natural jack pine site tied wtih herbicide and mechanical treatments for lowest Moisture rank, tied with aspen for the highest in Nutrients, had the highest score for Light, and was in the middle for Heat. The scores for herbicide and mechanical treatments were identical, ranking low for Moisture, Nutrients, Heat, and Light.
It's interesting to consider the environmental context for these species. Although FDc24 can experience periods of high soil moisture, these sites are generally very dry. Soil descriptions classify drainage as somewhat excessive to excessive. They are also low in nutrients, partly due to soil parent material being a well-sorted glacial outwash sand, and partly due to jack pine's influence in lowering pH levels below the tolerance level for many species. Sites tend to get poorer and drier as time goes on. FDc24 sites tend to have a dark rich topsoil, reflecting their recent history as prairie (500 years before present). FDc23 sites converted from prairie to woodland earlier (~1500 years ago), and have a correspondingly poorer and drier character. With the virtual elimination of wildfire from the ecosystem, we see more deciduous trees and shrubs on these sites, which gradually alter the soil through nutrient cycling. As a deciduous component increases, jack pine's influence on soil pH is somewhat diminished.
Overall, from our limited examination of species richness after disturbance, it appears that one of the worst things land managers can do to these communities is allowing them to become aspen dominated. Such sites will experience a slow mesification process, and fire adapted species will gradually be eliminated. Using herbicides or mechanical site prep may seem preferable if it means maintaining pine dominance. These are disturbance-dependent ecosystems, so denying them disturbance (either natural or anthropogenic) is also destructive to the community.