Emergent Vegetation at Malheur Lake: An Update!


Emergent Vegetation at Malheur Lake: An Update!

By Beth Boos, LSU Master’s Student

In September, I finished the last of my fieldwork for my master’s project on Malheur Lake. It has been an exciting growing season out on the lake this year, and we have seen a boom in vegetative growth— including annuals, perennials, and vegetatively-producing perennials (plants with rhizomes). As cooler weather rolled in, some areas of the lake that have been lacking vegetation historically are seeing quick growth of cattail. The southern portion of the lake has been filled with coyote willow, which is a plant that does not have a recorded history in the last several decades. Observing the lake as it changes every day, week, and month has given me an insight to the influencing factors of vegetation growth and establishment.

Exiting the Donnner und Blitzen River into Malheur Lake (primarily cattail)
New growth at the center of the lake near Tern Island
Coyote willow growth in Briggs Bay, SE Malheur Lake
Hardstem bullrush exclosure

The establishment and growth of vegetation is incredibly important for the future of Malheur Lake. If vegetation can become established, we should see a reduction in turbidity, which will further encourage submergent vegetation such as pondweeds to grow. This will grant us more habitat, coverage, and food available for birds: especially waterfowl. Vegetatively-reproducing perennials, which are plants that produce rhizomes and can expand and create dense mats of vegetation, are key to this success. Specifically, cattail and hardstem bulrush are examples of species that we see expanding on the lake. Throughout my research project, I have been examining the possible limitations to vegetation expansion, including seed production & viability, seed dispersal, germination, and establishment & survival. We completed a greenhouse experiment in both 2021 and 2022 to test for seedbank viability, presence, and dispersal. It proved to be conclusive that the seedbank throughout Malheur Lake is present with perennial emergents, although further out into the central reaches of the lake there was less cattail seeds detected. Wetland seedbank presence is a vital confirmation because it eliminates specific restoration techniques that would introduce species through seeding or transplantation.

Hardstem bulrush germinants from our greenhouse experiment.
Broadleaf cattail (right) germinants from our greenhouse experiment.

Next, we wanted to confirm that germination conditions are present on the lake itself. The exclosures that we set up last year were maintained throughout the rest of the experiment, and we saw interesting patterns of germination. In the first growing season (2021), we saw germination occur when water levels receded. These ‘drawdowns’ are often necessary for certain wetland species to germinate, especially on Malheur Lake where the water levels often reduce sunlight availability. There are many conditions that must be met for germination to occur, including sunlight availability, oxygen, soil moisture, standing water depth, and nutrient levels. It becomes difficult to determine where the limiting factor lies, so we work to eliminate each as we go. Through drawdowns, seeds are exposed to sunlight and oxygen. Once germination occurs, there must be a certain amount of soil moisture and nutrients to continue growing. Because of the droughts experienced in the last two years, the lake saw drawdowns that encouraged germination of cattail and bulrush. However, to some extent, we saw less survival of germinants into the next growing season due to some other factor. We currently suspect it is tied to soil moisture, but it could also be attributed to herbivory, wind, erosion, nutrient levels, etc.

Germination plot where we monitored seedling survival over the growing season

The last portion of my project tested potential restoration tools for vegetation survival and expansion. We used plastic sheet panels to reduce wind, hardware cloth panels to exclude herbivory, and attempted transplantation of hardstem bulrush. We could not eliminate or regulate other naturally occurring variables such as soil moisture & salinity, but our results showed no significant difference between exclosure types (hardware cloth, hog panel, hog panel with sheet panels, and controls). This leads us to believe that although herbivory and wind may contribute to vegetation survival, during our study they were less influential than some other variable. Based on our available data and observations, we believe that soil moisture is likely to be the key to the survival and expansion of existing hardstem bulrush. 

Additionally, we found the transplants to be largely unsuccessful, and it seems there is an unpredictable nature to their success in the future. Water levels and soil moisture on the lake are nearly impossible to predict as they depend on inflows, groundwater, and wind action across the lake. With these factors, it would be difficult to select a site where a transplant could receive adequate moisture while also be given the opportunity to stabilize and root itself in the sediment, especially when conditions must be suitable for 2-3 years for establishment and expansion.

Although research often leaves us with unanswered questions, it is important as a guide to the next step in restoration processes. We have seen things on the lake these past two years that have not been documented or observed in the last decade. We have eliminated seedbank presence and viability as a limiting factor to restoration. This project has been the first research and documentation of vegetation growth and expansion since before the flooding in the early 1980s. We still have hope in the restoration of the lake, especially considering the promising bulrush and cattail growth in areas of the lake that have not seen vegetation since the 1970s. Hopefully, all the root systems of the new growth will help stabilize the lakebed and reduce the turbidity enough for more vegetation to establish. This study did not evaluate long term climactic trends, but it will be an important factor for future restoration targets. Although drought and water level variation play an important role in vegetation dynamics and succession, it is also a concern as we have observed high levels of competition between wetland vegetation and prairie vegetation. If conditions remain suitable for dry-land species, they will out-compete wetland vegetation. For now, we are merely excited to have made progress towards the restoration of Malheur Lake. I am honored to have been a part of this work, and I am grateful to Friends of Malheur NWR for their constant support and interest throughout the project.



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