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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Water Management and Systems Research » Research » Publications at this Location » Publication #423066
Research Project: Improving Resiliency of Semi-Arid Agroecosystems and Watersheds to Change and Disturbance through Data-Driven Research, AI, and Integrated Models

Location: Water Management and Systems Research

Title: Forest restoration treatments increase native plant diversity but open the door to invasion in the Colorado Front Range

Author
item Mahood, Adam
item STEVENS-RUMANN, CAMILLE - Colorado State University
item RHEA, ALLISON - Colorado State University
item RITTER, SCOTT - Us Forest Service (FS)
item BARRETT, KEVIN - Colorado State University
item FORNWALT, PAULA - Forest Service (FS)
item Barnard, David

Submitted to: Forest Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2025
Publication Date: 6/7/2025
Citation: Mahood, A.L., Stevens-Rumann, C., Rhea, A., Ritter, S., Barrett, K., Fornwalt, P.J., Barnard, D.M. 2025. Forest restoration treatments increase native plant diversity but open the door to invasion in the Colorado Front Range. Forest Ecology and Management. 593. Article e122881. https://doi.org/10.1016/j.foreco.2025.122881.
DOI: https://doi.org/10.1016/j.foreco.2025.122881

Interpretive Summary: Thinning treatments are being conducted in forests across the western US. These are intended to reduce the chances of high severity fire, make forests more resilient after fires, and make firefighting safer. We found that treatments remained effective for ten years after treatment. There were increases in native plant diversity at treated sites. There were also increases in non-native plants. Surveys and treatments for management of non-native species are recommended. They should ideally be conducted 5 to 10 years after treatment. This may give managers the best chance of controlling non-native species while populations are small.

Technical Abstract: In the Colorado Front Range, thinning treatments are being implemented in an attempt to re-establish historical forest structure and increase the system's resilience against future wildfires. But there is relatively little research on the long-term efficacy of these treatments, and their long-term effects of these treatments on understory plant composition. We used a before/after control/impact study design to assess the effects of thinning treatments on understory plant composition ten years after treatment. We found that stand structure remained mostly unchanged ten years after treatment, except for an increase in seedling density in year ten. Impacts of treatment were minimal one year after treatment, but significant increases in relative cover and richness of non-natives, P(invasion) plateaued after 5 years. Native cover also increased at the 5 year mark and reached a plateau, but species accumulation curves showed region-wide increases in native richness continued 10 years out, indicating an increase in beta diversity not captured by per-plot averages in species richness. Basal area was positively associated with non-native invasion and relative cover, and negatively associated with native cover, while tree density was negatively associated with non native invasion, non-native relative cover and native richness. Thinning treatments increase native alpha and beta diversity in the understory, but early detection/rapid response management for non-native plants is recommended after 5 years.