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To get a better estimate of the actual number of trees on Earth, researchers combined data from multiple vegetation indexes, including the Enhanced Vegetation Index (EVI) from the Moderate Imaging Spectroradiometer (MODIS) onboard Terra, with actual tree counts for over 430,000 hectares from 14 different biomes on Earth (there is an estimated 4 million hectares of forested land on Earth). Thus, counting trees is a difficult process because they can vary in size and can hide beneath the canopy of larger trees, as well as be too small to be seen in satellite images. The Redwood example also points to another complication, the definition of a tree, which for most studies, including the one in Nature, is vegetation with woody stems 10 cm in diameter or larger at chest height. In addition, satellites are limited by their spatial resolution, not every tree is as obvious as a Redwood alone in a field. Satellites provide the best opportunity to achieve a global perspective, but their view of tree forest canopies from above tends to obscure individual trees and shorter trees, making it difficult to make accurate estimates. Scientists rely primarily on remotely-sensed to obtain estimates of global tree populations. The result is the BirdReturns program, a partnership between the Nature Conservancy and the California Rice Commission that compensates rice farmers to flood their rice fields at particular times to provide migratory habitat for shorebirds.Įfforts like this can help land managers better allocate valuable resources, such as water in California, where they are needed when competition for these resources are high.Ī recent study published in Nature now estimates that there are 3.04 trillion trees on Earth, a number that is almost 8 times higher than previous estimates To identify areas that would be beneficial “pop-up habitats,” satellite data on the location and timing of surface water was matched with migration patterns of shorebirds collected from the eBird program, a citizen science bird watching program that collects data on bird sightings. As water resources have decreased in the Central Valley of California due to development, agriculture and other land use changes, resting and feeding grounds for migratory birds has decreased.Ī team from Cornell Lab of Ornithology’s was able to use data from the Moderate Imaging Spectroradiometer (MODIS) on-board NASA’s Terra and Aqua satellites, along with data from Landsat to identify areas that could be turned into “pop-up habitats,” where rice fields could be flooded to provide temporary habitats for migrating birds for a couple weeks per year. Shorebird populations are struggling to find wetlands on their epic migrations down the Pacific Flyway, stemming from Alaska and Canada down to South America.
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