Forests face an unprecedented range of disturbances from climate change, introduced pests and pathogens, and novel species, which frequently interact causing severe consequences to forest communities and ecosystem function. Understanding the mechanisms by which forests recover from disturbance and maintain stability of function is not only an issue of ecological interest, but one of pressing human need, as forest functioning is involved in maintaining a suite of ecosystem services that provide for humanity, including the global carbon and water cycles.
Using an experimental manipulation of tree species diversity within an oak-dominated temperate northeastern deciduous forest, this dissertation broadly asks: how do forest community biomass and diversity influence stability and magnitude of forest community growth and water use? All three chapters are based on data from the same forest, where four treatments had previously been established by trunk girdling, which kills a tree by severing the cambium and sapwood, but leaves it standing, similar to the effect of many pathogens on trees. The treatments represent a range of species richness (2-10 species), biomass (5.5 × 104 kg/ha to 7.1 × 105 kg/ha), and level of disturbance, with experimental plots losing anywhere from zero to 94% of their living biomass.
Chapter 1 focuses on competitive release after the loss of a dominant species using an annual census of trees over the last 10 years. Community level growth rates showed that diversity positively influenced biomass recovery rate. Chapter 2 addresses the role of the tree community’s biomass and diversity on soil water content using soil moisture sensors, which have recorded data hourly for two years, as well as the trees’ water stress, by using foliar stable carbon isotope ratios. Here, diverse communities have higher and more stable levels of soil water as well as trees that are less water stressed. Using the same long term data as Chapter 1, Chapter 3 assesses whether growth in the tree communities has been more stable over the past 10 years, and investigates whether this can be explained by shorter term fluctuations in tree growth measured by automated point dendrometers.
While more diverse communities are more stable in their growth rates over time, this was strongly dependent on how much of the original community had been mechanically girdled. Species showed complementarity in phenology of tree growth at the seasonal scale, but our models could not directly link this intra-annual complementarity in more diverse communities to the stability seen over 10 years. Taken together, results from these three chapters suggest that diversity plays a role in mediating recovery of function from disturbance, which has implications for both the global carbon and water cycles.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/qasc-ns87 |
| Date | January 2024 |
| Creators | Bruner, Sarah |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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