Disturbance Type and Timing Affect Growth and Tolerance Strategies in Grassland Plant Leaves

Abstract

As human activities alter winter climates and disturbance regimes in grassland and rangeland ecosystems, the temperatures that plants experience during spring are changing. Litter can help buffer overwintering herbaceous plants from temperature fluctuations, and management practices dictate whether litter is present during the winter. Here, we investigate how disturbance type (burning, mowing) and timing (spring, fall) affect leaf characteristics related to growth and stress tolerance and how these traits change over time for five common tallgrass prairie species including four forb (Monarda fistulosa, Ratibida pinnata, Silphium integrifolium, Symphiotrichum laeve) and one grass species (Bromus inermis). To do this, we established a field experiment in Wisconsin, where plots were annually burned in the fall, mowed in the fall, burned in the spring, or left undisturbed (control) for 3 yr. We sampled leaves of target species seven times from spring emergence through early summer to measure specific leaf area (SLA) and leaf cold tolerance in each treatment. Leaves from fall-burned plots had lower SLAs, while leaves in spring-burned plots had higher SLAs early in the growing season. Leaf cold tolerance was similar across most treatments except in spring-burn plots, where leaves became more cold-hardy through time. We found weak evidence of a tradeoff between leaf growth and both cold tolerance and SLA. These results suggest that management decisions like litter removal before winter (e.g., fall burn or mow) prompted different plant responses compared with plots where litter was present during winter (e.g., spring burn). As species respond to winter climate change, management decisions have implications for mitigating climate change impacts and maintaining diversity in grasslands by affecting early-season plant growth strategies. For example, removing litter in the fall by burning promotes stress-tolerant responses, which may better equip plants to tolerate changing spring conditions.