by Abby Yancy
Leaf litter is the dead plant material that has fallen from trees, shrubs, and other plants. It hangs around on the ground surface until it decomposes, with some plant species producing leaf litter that takes longer to decompose than others. You may have read about stopping the practice of raking your leaves in the fall because of the important nutrients and habitat for beloved wildlife the fallen material provides in your own backyard. The same goes for our forests, an environment where scientists have studied this critical component for many decades.
The leaf litter in forests acts as a protective layer for soil conditions. It creates a physical barrier between the soil surface and atmosphere that reduces soil drying, responds to atmospheric temperature fluctuations, and reduces erosion from precipitation events. Through decomposition, nutrients stored in the dead material re-enter the system and act as a natural fertilizer for plants throughout the year. The controls and nutrient cycling are especially important for forest wildflowers.
Many forest wildflowers begin their aboveground life cycles in early spring before the trees have developed their leaves. During this time, light at the forest floor is highest, allowing wildflowers to gain high amounts of energy. However, before they emerge from below ground storage organs or germinate from seeds, the flowers are thought to rely on environmental cues to know when to begin this growth without the risk of frost damage. These environmental cues include soil temperature, which is regulated by the leaf litter layer. Despite many decades of research on the leaf litter component of forests, little is known about the influence of it on the timing of these lifecycle events (or phenology) for wildflowers. Past and ongoing research in the CMNH Section of Botany explores the changing phenology of many plants. One ongoing project is looking at the impact of early tree leaf out and the extended phenology of non-native shrubs on forest wildflower phenology and biological success.
The question of the leaf litter’s role in wildflower phenology arose after some simple, but fascinating, natural history observations early last spring—noted variations in phenology within our research site. We struggled to find some tagged individual plants, despite many of the same species being not only present in surrounding areas, but in full bloom. After moving the layer of leaf litter, we found the “missing” plants nearly a week behind in growth compared to their neighbors. These observations were more common than initially thought, and strongly related to the decomposition rate of each leaf litter species. Tree species that produced slower-decaying leaf litter delayed the phenology of plants more than those that produced faster decomposing litter. This underexplored relationship inspired one of the research projects I’m working on this year.
My project is aimed at understanding how different amounts of leaf litter control the cues for wildflower phenology. Specifically, I want to know how leaf litter regulates the soil temperature and moisture within relatively small areas of our site and how the wildflowers respond. To test this, I have several leaf litter manipulation plots where I removed all leaf litter in some subplots and added it to another of the same size. To measure the changes related to leaf litter, I record soil temperature and moisture and wildflower phenology.
I began collecting this data in early March and have already noticed many differences. Before many of the flowers have started their aboveground lifecycles, they were already present in plots without leaf litter, but still hiding under the leaves in both the litter addition and the control plots. On a few of our random freezing days, the top layer of soil and plants were frozen in litter removal plots, while the same layer of soil was moist and visibly warmer in the litter addition plots. Additionally, one wildflower, trout lily, frequently grew around stray Sycamore leaves, which happen to be one of the slower decomposing species.
The findings from this project will not only allow us to gain a better understanding of relationships among species but will also provide a basis for understanding variations in phenology within a site.
Stay tuned for final results from this project!
Abby Yancy is a researcher in the Section of Botany. Museum employees blog about their unique experiences and knowledge gained from working at the museum.
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Carnegie Museum of Natural History Blog Citation InformationBlog author: Yancy, Abby
Publication date: May 4, 2022