Manipulating Internal System Feedbacks to Accelerate Reed Canarygrass (Phalaris arundinacea) Control: From Theory to Practice

Reed canarygrass (Phalaris arundinacea) displaces indigenous species and creates extensive monocultures that frustrate restoration efforts. Restoration gains are typically short-lived at sites heavily impacted by this species, but suppression may be feasible at sites in the early stages of invasion (Annen et al. 2008). However, even under these conditions, reversal of invasion and replacement of reed canarygrass by desired endpoint species may require 5 to 6 consecutive growing seasons of effort (pers. obs.).

State and transition models predict that internal feedbacks maintain vegetation in one state (reed canarygrass monoculture) rather than an alternate state (remnant sedge meadow). Local and landscape-scale disturbances make sites vulnerable to reed canarygrass invasion, while feedbacks maintain the invaded state and resist restoration to a pre-invasion state. In other words, invaded states are internally reinforced by indirect feedbacks involving interactions among disturbances and species characteristics (Zedler 2009). Litter accumulation is one example of a feedback mechanism that maintains reed canarygrass dominance. Senescent reed canarygrass litter has a suppressing effect on competing species. As reed canarygrass increases in abundance and comprises a greater proportion of a site’s standing crop, more litter accumulates each subsequent growing season, which further hinders emergence of competing species. This feedback cycle helps maintain reed canarygrass dominance and must be broken for restoration to be successful. Using fire to disrupt litter feedbacks is relatively easy compared to uncoupling other feedbacks that maintain a reed canarygrass-dominated state (e.g., hydrological disturbance). Nevertheless, Herr-Turoff (2005) documented that sethoxydim herbicide applications were more effective when disturbances were addressed prior to initiating chemical control efforts. Consequently, successful reversal and restoration of a reed canarygrass-dominated state requires not only properly implementing effective control techniques, but also disrupting feedbacks that maintain the invaded state. Regrettably, control efforts for reed canarygrass are rarely applied in conjunction with removal of disturbances and manipulation of the feedbacks indirectly responsible for maintaining a system in a degraded condition.

The 186-ha Swamplovers Nature Preserve, located in southwestern Wisconsin, USA, includes a 10.5-ha sedge meadow remnant. When the property was acquired as a nature preserve, this sedge meadow remnant was on a trajectory toward reed canarygrass dominance. Ten hectares immediately north of the sedge meadow had been planted to row crops for several decades. To make the area more suitable for agricultural production, a drainage ditch and drain tiling system had been installed in the sedge meadow, disconnecting it from its original hydrology. Nitrogen levels were low (10.7 ppm NH₄-N and 9.2 ppm NO₃-N), but available phosphorus was high (57 ppm) when measured in 2007. Long-term absence of fire encouraged successional progression to shrub-carr/lowland forest dominated by fire-intolerant shrub and tree species. This change in vegetation composition exacerbated hydrological losses, as these species have high evapotranspiration rates. Three and one-half hectares of the sedge meadow remnant were dominated by reed canarygrass, with additional outliers of reed canarygrass expanding into canopy gaps in relic populations of sedge meadow species. An additional 2.8 ha existed in the wet meadow condition, dominated by a matrix of reed canarygrass intermixed with aggressive perennial forbs such as Canada goldenrod (Solidago canadensis) and sawtooth sunflower (Helianthus grosseserratus).

Restoration began in 1998, when a wet-mesic prairie buffer was planted into the former cropland bordering the remnant (50 species were planted). The drain tile system was destroyed with a backhoe in 1999 to partially restore the site’s hydrology. Hydrological restoration was completed in 2007 when the agricultural drainage ditch was filled and 4 small scrape ponds were created. Recontouring and scrape pond construction created 0.6 ha of bare ground, a condition that facilitates subsequent reed canarygrass invasion unless a closed vegetation canopy is established. Bareground space was seeded with 60 native species at a rate of 11.9 kg/ha following recommendations of Wisconsin’s Reed Canarygrass Working Group (2009). Contractors also planted plugs or bare root tubers of an additional 15 sedge meadow and aquatic vascular plant species. The next phase of the restoration was to...