Could alfalfa replace Missoula’s poplar grove? Wastewater, sequestration in play

The future of Missoula's poplar plantation remains unclear, and city officials this week said they're still exploring a number of options that consider the benefits of keeping the grove or replacing it with a different crop.

The poplar plantation was established around 2013 to help Missoula meet federal regulations regarding wastewater. The city is permitted to discharge wastewater into the Clark Fork River, though it’s required to monitor for various nutrients.

If the city fails to meet those guidelines, it could be on the hook for wastewater improvements topping $50 million and more. To avoid that, it currently directs more than 1 million gallons of effluent from the treatment plant to the poplar plantation to water the hybrid forest.

But now the forest is mature and thoughts of harvesting the trees for their wood have changed with the national economy. The future of the forest and the ground on which it grows is uncertain.

“While we haven't measured the carbon sequestration benefits of it (the forest), there's a huge benefit of keeping nutrients out of the river,” said city CAO Dale Bickell. “While the market has dried up for this type of wood, Plan A is now our compositing operation, where they do have a continued need for woody materials.”

The city’s poplar plantation and its ties to the wastewater treatment facility could see the material used more as compost and stream-bank stabilization than lumber, as first envisioned when the facility was established nearly a decade ago.

Those trees have grown tall, thick and green over the years, absorbing nutrients in a closed system while sequestering carbon. But the future use of those trees is shifting.

“They're looking at the option of cutting down the trees and growing a different crop that would be more successful,” said Leigh Ratterman, the city's climate specialist. “Everyone recognizes the trees do have a benefit. It's a matter of quantifying that benefit to see if it's enough to justify keeping the trees.”

Along with the plantation's ability to sequester carbon, it also absorbs nutrients from the treatment facility that cannot be released into the river. Bickell said the plantation remains an effective way of keeping nutrients from the water – and it's less expensive than a multi-million dollar facility upgrade.

But Bickell also suggested other crops could be just as valuable.

“The most viable option for us moving forward on a more usable crop is alfalfa. It has a very similar nutrient uptake as our poplar trees,” Bickell said. “We're making plans to expand even further our ability to apply some of this. Nutrient standards are going to get more stringent over time, and we can be proactive on our land application.”

City leaders said discussions around the future of the plantation remain ongoing, and no decisions have been made. But not everyone is sold on the idea of growing alfalfa as a replacement crop, especially when considering the city's goals around carbon mitigation and climate change.

“You grow alfalfa, cut it and bail and feed it cows, and they produce methane,” said council member Julie Merritt. “I'd like us to think about these things to the very end of the process. If we're not doing that, we're gaining short term but not long term.”