Trees are not just passive elements of the landscape, but active hosts of diverse communities of insects and fungi.
These communities depend on the genetic variation of the trees, which influences their traits and interactions.
A new study by a researcher at the University of Georgia has revealed how tree genetics can affect biodiversity patterns at a continental scale, offering insights for reforestation efforts and conservation strategies.
The influence of tree genetics on insect and fungal communities
The study, led by Helen Bothwell, an assistant professor at the UGA Warnell School of Forestry and Natural Resources, focused on cottonwood trees, a foundation species of riparian ecosystems in the North American southwest, as Per Phys.org.
These ecosystems are biodiversity hotspots that provide habitat and resources for many animals and plants, but they are also among the most threatened in the United States due to human activities and climate change.
Bothwell and her collaborators collected hundreds of samples from trees across more than 50 sites from California, Nevada, Utah, Arizona, and northern Mexico.
They analyzed the genetic variation of the trees and the composition of the insect and fungal communities associated with them.
They found that different tree genotypes supported different communities and that this relationship was consistent across the large geographic area.
The researchers suggest that tree genetics influence the traits of the trees, such as leaf chemistry, shape, size, and phenology, which in turn affect the preferences and performance of the insects and fungi.
For example, some tree genotypes may produce more defensive compounds that deter herbivores, while others may have larger or more nutritious leaves that attract them.
The researchers also found that tree genetics influenced the carbon isotope composition of methane produced by microbial communities in both tree stems and river sediments.
Methane is a potent greenhouse gas that contributes to global warming, and understanding its sources and sinks is important for climate change mitigation.
The researchers showed that different metabolic pathways were involved in methane production in different environments, and that tree genetics could affect the availability and quality of organic matter for methanogens.
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The Implications for Reforestation and Conservation
The study is the first to link tree genetic variation to community biodiversity at the continental scale. It shows that tree genetics can have a cascading effect on the diversity and functioning of the whole ecosystem.
It also has important implications for reforestation and conservation efforts, as it suggests that planting diverse reforestation stock can enhance the resilience and sustainability of riparian ecosystems.
Bothwell said that understanding the relationship between tree genotypes and the organisms they support offers a more comprehensive roadmap for reforestation efforts that also support healthy ecosystems.
She said that diversity begets diversity and that planting diverse reforestation stock is critically important for conserving the wealth of pollinators and predators that in turn contribute valuable services to agricultural systems and serve as a food source for bird and wildlife populations.
The researchers hope that their findings can inspire more studies on other tree species and regions, and help inform management practices that promote biodiversity conservation and ecosystem services.
Riparian cottonwood forests are vital for maintaining aquatic habitats in streams, lakes, and wetlands.
They provide shade, organic matter, nutrients, erosion control, flood attenuation, and carbon sequestration. They also support many wildlife species, such as birds, mammals, reptiles, amphibians, and fish.
However, these forests are threatened by hydrologic alteration caused by dams, water diversions, groundwater pumping, and climate change.
These factors can reduce river flows, lower groundwater levels, alter flood regimes, and increase drought stress.
To restore riparian cottonwood forests, it is essential to consider their hydrologic requirements as well as their genetic diversity.
Cottonwood trees depend on periodic flooding for seedling establishment and survival5. They also need access to alluvial groundwater for growth and reproduction.
Planting diverse reforestation stock can help increase genetic variation within populations, which can enhance their adaptability to changing environmental conditions. It can also increase their resistance to pests and diseases, which can reduce mortality rates.
By restoring riparian cottonwood forests with diverse genetic stock, we can not only improve their health and productivity but also support the biodiversity and ecosystem services they provide.
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