Do plants respond to multi-year disturbance rhythms and are we missing the beat?

Authors: Vermeire, Lance; Reinhart, Kurt; OTT, JACQUELINE - Forest Service (FS)

Submitted to: Oikos
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Seasonal timing and regularity of disturbances can create complex interactions of effects on species and ecosystems. Fire is a key grassland disturbance, yet long-term research examining seasonality and return intervals is limited. A 15-yr experiment testing combinations of fire seasonality (summer, fall, spring) and return interval (2, 3, 6-yr) plus non-burned controls was conducted in northern mixed prairie to evaluate effects on the plant community. Needle-and-thread is a native cool-season bunchgrass that is among the dominant species in this and adjoining systems and previously observed to be fire-sensitive. Current-year aboveground biomass results were generally counter to expectations based on short-term research. Fire increased needle-and-thread biomass with a strong, rhythmic response pattern to a specific fire seasonality-return-interval combination (fall fire at 3-yr return intervals) that periodically increased biomass to more than 3 times that with no fire. Through the first 4 post-fire growing seasons, biomass with summer, fall and spring fire was 41, 89 and 93% of that with no fire. Afterward, no fire combination produced less biomass than no fire and recurring patterns emerged with large increases in biomass, particularly with fall fire at 3-yr intervals. Peak biomass years were regularly 2 growing seasons after 3-yr fall fire and occurred across wet, near-average and dry conditions. We hypothesize that productivity responses were driven by the combination of demographic processes of seedling recruitment and synchronization of multiple tiller age classes. Because short-term negative effects were reversed and regular patterns only emerged 5 years after study initiation, more long-term research evaluating fire regimes is recommended to expand upon tests of individual factors over short periods. This suggestion is based on fire research, but likely applies to multiple forms of disturbance and demonstrates how demographic processes can inform responses for individual species and larger ecosystem functions, such as productivity.

Technical Abstract: Disturbance seasonality and return interval can create complex interactions of direct and indirect effects on species and ecosystems. Fire is a key grassland disturbance, yet long-term research examining seasonality and return intervals is limited. A 15-yr experiment testing combinations of fire seasonality (summer, fall, spring) and return interval (2, 3, 6-yr) plus non-burned controls was conducted in northern mixed prairie to evaluate effects on the plant community. Hesperostipa comata is a native C3 bunchgrass that is among the dominant species in this and adjoining systems and previously observed to be fire-sensitive. Current-year aboveground biomass results were generally counter to expectations based on short-term research. Fire increased Hesperostipa comata biomass with a strong, rhythmic response pattern to a specific fire seasonality-return-interval combination (fall fire at 3-yr return intervals) that periodically increased biomass to more than 3 times that with no fire. Through the first 4 post-fire growing seasons, biomass with summer, fall and spring fire was 41, 89 and 93% of that with no fire. Afterward, no fire combination produced less biomass than no fire and recurring patterns emerged with large increases in biomass, particularly with fall fire at 3-yr intervals. Peak biomass years were regularly 2 growing seasons after 3-yr fall fire and occurred across wet, near-average and dry conditions. We hypothesize that productivity responses were driven by the combination of demographic processes of seedling recruitment and synchronization of multiple tiller age classes. Because short-term negative effects were reversed and regular patterns only emerged 5 years after study initiation, more long-term research evaluating fire regimes is recommended to expand upon tests of individual factors over short periods. This suggestion is based on fire research, but likely applies to multiple forms of disturbance and demonstrates how demographic processes can inform responses for individual species and larger ecosystem functions, such as productivity.