Clonal Stands: Using Space to Approximate Age Effects

Sand Island is one of the most intact wetlands we have been working in, with large expanses of native sedge meadow composed of Carex lasiocarpa, C. stricta, C. aquatalis, C. lacustris, and C. diandra. There are also several large stands of invasive cattail (Typha × glauca and T. angustifolia), and smaller “satellite” clones that have started growing more recently. Because cattails spread clonally by growing their rhizomes laterally, smaller clones are usually assumed to be younger individuals.

We are taking advantage of these younger clones of invasive cattail to answer several questions related to cattail management in high-quality wetlands. First of all, we want to know whether the effect our harvester has in older stands of cattail monoculture is different from the effect harvesting has on more recent invasions that still contain a significant native plant community. If harvesting young invasions negatively impacts the native plant species that are still present, then it shouldn’t be done. However, if harvesting were to push back invading cattail along the fringes of growing clones without having a negative impact on the native plant community, it could prove to be a useful management method for preventing the further invasion of high-quality wetlands.

In this study we divided five cattail clones into wedges, and assigned each wedge to one of three treatments: above water harvesting, below-water cutting, and un-manipulated controls. We established permanent transects from the center of each wedge extending outward past the edge of the clone, and took pre-treatment data on plant community composition, leaf litter accumulation, and cattail biomass and height metrics. We implemented the treatments in August 2015, and conducted a second harvest treatment in September 2016.

Plot layout at Sand Island, MI illustrating five isolated Typha stands, completely randomized block design, vegetation sampling transects and vegetation subplots, and the extent of Typha at three points in time (1998, 2008, and 2015).

Plot layout at Sand Island, MI illustrating five isolated Typha stands, completely randomized block design, vegetation sampling transects and vegetation subplots, and the extent of Typha at three points in time (1998, 2008, and 2015).

 

In August 2016, we revisited the permanent transects and collected the first year of post-treatment data. This on-the-ground data collection was paired with a drone flight that collected aerial imagery. By comparing the results of our traditionally collected field data with spectral data from the aerial photos, we are hoping to determine the feasibility of conducting large-scale restoration monitoring using drone imagery. This is important, because the majority of restoration work is not followed up with post-treatment monitoring. Drones are able cover a lot of ground in a short amount of time, and their use in monitoring could greatly advance our understanding of the effectiveness of large-scale restoration projects.

We  published the first round of results of this work in Frontiers in Plant Science. In summary, below-water cutting led to significant changes in vegetation structure that were detectable on the ground and from the air. The above water harvesting caused some changes, notably in the amount of leaf litter present in harvested wedges. Above-water harvesting did not appear to have a detrimental impact on the native sedge community, though we are going to continue to monitor this response over the next few years.

Vegetation responses to by treatment and subplot ± SE in 2016, one-year following treatment implementation. Capital letters denote significant treatment contrasts; lowercase letters denote within treatment subplot contrasts; asterisks denote no differences between subplots. Subplots approach the center of each stand with alphabetically increasing enumeration.

Vegetation responses to by treatment and subplot ± SE in 2016, one-year following treatment implementation. Capital letters denote significant treatment contrasts; lowercase letters denote within treatment subplot contrasts; asterisks denote no differences between subplots. Subplots approach the center of each stand with alphabetically increasing enumeration.

Comparison between UAV collected data and field collected data; UAV variable on left axes and comparable field collected data on right axes. Letter differences denote significant treatment contrasts, UAV data represented by capital letters, field data represented by lowercase letters. A) UAV green tissue cover (%) (area with NDVI value > 0.28 / total area); B) UAV brown tissue cover (%) (area with NDVI values between 0.0 and 0.28 / total area); C) UAV water cover (%) (area with NDVI value > 0.0 / total area); D) green tissue height (corrected using water average water elevation).

Comparison between UAV collected data and field collected data; UAV variable on left axes and comparable field collected data on right axes. Letter differences denote significant treatment contrasts, UAV data represented by capital letters, field data represented by lowercase letters. A) UAV green tissue cover (%) (area with NDVI value > 0.28 / total area); B) UAV brown tissue cover (%) (area with NDVI values between 0.0 and 0.28 / total area); C) UAV water cover (%) (area with NDVI value > 0.0 / total area); D) green tissue height (corrected using water average water elevation).