Undetected but Widespread: the Cryptic Invasion of Non-Native Cattail (Typha) in a Pacific Northwest Estuary

Abstract

Early detection of invasive species is an important predictor of management success. Non-native narrowleaved cattail (Typha angustifolia) has been detected in the Fraser River Estuary (FRE) in recent decades, but questions around their degree of establishment, and the potential emergence of hybrid cattail (Typha x glauca), remain unanswered. This study models the current and potential future distribution of nonnative cattails in the FRE using a unique combination of spectral imagery analysis and species distribution modelling. Contrary to our expectation, we nd that non-native cattails are already widespread, currently occupying approximately 4% of FRE tidal marshes. Though never formally recorded in the FRE, hybrid cattail is the more abundant of the two taxa, suggesting that heterosis may be facilitating this invasion. In our species distribution model, we distinguish between site suitability (ability to establish and persist) and site susceptibility (risk of being colonized when suitable). Our model predicts that 28% of the estuary has > 50% probability of suitability, and 21% has > 50% probability of susceptibility to non-native Typha, indicating the scale of this invasion may increase over time. Restoration projects had proportionally more cattail, susceptible habitat, and suitable habitat than the overall estuary, casting doubt on their effectiveness at mitigating wetland destruction. Due to their resemblance to native Typha latifolia, these cattails qualify as cryptic invaders, which explains how they were able to establish and remain undetected for decades. Regional eradication is unlikely given the extent of invasion, therefore management should prioritize areas of high conservation and cultural values.

Managing invasive hybrids with pond hydroperiod manipulation in an endangered salamander system

“…Similar to the CTS system, non‐native hybridization in cattails is cryptic and fairly widespread, with hybrids apparently exhibiting greater fitness than either parental species on the landscape (Stewart et al., 2023). Hydroperiod management was introduced as a method to reduce the success of these destructive hybrids because longer duration wetlands are more susceptible to hybrid invasion compared with more natural, short‐duration wetlands (Boers et al., 2007).…”

Plant Community Stability over 40 Years in a Fraser River Estuary Tidal Freshwater Marsh

“…We suggest that the plant community changes described here should alert land managers not only to what species diversity might be targeted in conservation practice, but also to how reference sites may have changed with respect to non-native, invasive encroachment during the span of 20-40 years. We strongly advocate for the development of long-term vegetation monitoring to inform non-native invasive species management occurring in this and similar WMAs (see alsoStewart, Hood, and Martin, 2023).…”