When you walk through a forest, do you hear a symphony of sound from a multitude of bird species, or only a small chorus of a few different voices?
Bird biodiversity is an important indicator of overall ecosystem health. Understanding differences between forests with a lot of different birds and those with only a handful could help us make better decisions in maintaining ecosystem diversity and health. Using airborne remote sensing and ground-based bird and bird breeding counts, a recent study explored the idea that the structure of forest vegetation is a key driver of bird biodiversity.
Researchers from the University of Tennessee-Knoxville and the National Institute for Mathematical and Biological Synthesis used data from NEON to explore this idea. The principal investigator of the study, Dr. Luis Carrasco, and his co-investigators wanted to find out if and how forest structure relates to bird biodiversity. Vegetation structure is only one of many factors that impact bird species diversity in a given area, but it is an important one. Forested areas have a mix of vegetation types including the tall trees that make up the forest canopy and layers of shrubs, mosses, ferns and other plants that make up the understory. These plants provide food sources, breeding and nesting habitats, and protection from predators. Different birds have different habitat preferences. Some prefer more open habitats; others thrive in dense underbrush.
Carrasco and his team wanted to determine how forest structure and bird biodiversity were related. They used two kinds of data that came from forested NEON field sites across the United States.
LiDAR is generated from airborne remote sensing instruments carried by light aircraft flown over NEON sites. The data can be used to create a 3D model of the forest, showing how dense the vegetation is at different vertical layers, from the ground to the top of the canopy.
Breeding land bird countswere collected by painstaking and intensive fieldwork at NEON sites through direct observation.
The scientists found that forests with greater variation in 3D structure, in other words, with a mix of dense understory and more open areas, supported the most bird biodiversity. Using these results, other researchers can predict the level of bird biodiversity in a forest by using LiDAR images, something that can be quickly and easily collected over large areas. This enables faster and more effective modeling of how forests are changing over time and how bird populations may be impacted.
The results of the study also suggest that protecting species diversity requires more than simply setting aside land for conservation. When it comes to bird biodiversity, what matters is not just the number of acres of forest preserved, but also the types and density of plants and the overall structure of the vegetation. For maximum species diversity, a forest needs a variety of habitats within the canopy and the understory, including areas with dense underbrush and many young plants and more open areas with mature trees and less groundcover.
"This has important implications for conservation," said Carrasco. "If we know that environmental heterogeneity is a key driver for biodiversity, we can focus our conservation and land management efforts towards maintaining these heterogeneous landscapes."