Subtropical forests occur in the U.S. only in the southern border states, with roughly 2.7 million acres primarily in south Texas and the southern tip of Florida. About 40% of U.S. subtropical forest is protected on public land, mostly in Florida, with more than 200,000 acres of hardwood hammocks in Everglades National Park and Big Cypress National Preserve. Important public lands in south Texas include the South Texas Refuge Complex (120,000 acres) and the Bentsen-Rio Grande Valley, Resaca de la Palma, and Falcon state parks along the lower Rio Grande Valley.

Percentage of the U.S. distribution of 17 subtropical forest-breeding bird species on public vs. nonpublic lands (left). Breakdown of bird distribution on public lands shown for each public agency (right).

Subtropical Forest Birds on Public Lands

Public lands support only 8% of the geographic distribution of the 17 bird species restricted to subtropical forests in the United States. Gray Hawk and Short-tailed Hawk have the largest percentage of their small U.S. distributions on public lands. Species with very small ranges in the lower Rio Grande Valley, including Red-billed Pigeon and Altamira Oriole, have only 2–3% of their distributions on public lands, primarily on National Wildlife Refuges and state parks.

Unlike most other forest types, nearly half of the public lands supporting subtropical forests are managed to maintain natural habitats, providing greater protection for bird populations. Because most subtropical forest birds have large portions of their distributions within Mexico and the Caribbean, international cooperation is essential for their long-term conservation.

Conservation Successes

The Rio Grande Joint Venture is working on the South Texas Refuge Complex implementation plan, including expanding the National Wildlife Refuges to their full acquisition potential and conserving forest corridors within Mexico, connecting the
lower Rio Grande Valley with coastal thorn forests near the Laguna Madre inland to the Sierra Picachos.

In South Florida, large-scale efforts by the NPS, USFWS, and other federal and state partners to eradicate invasive trees such as melaleuca, Australian pine, and Brazilian pepper on public lands are essential for improving the populations of both breeding and wintering-migrant birds.

Conservation Challenges

Maintaining the distinctive birdlife in subtropical forests requires increased acquisition of public land, as well as public-private partnerships to protect and restore forests in south Texas, including the lower Rio Grande Valley. The greatest threats are rapidly expanding urbanization and continued clearing for agriculture in the U.S. and adjacent areas of Mexico. Increased support for cross-border initiatives that include the Mexican government and other Mexican partners is essential for meeting these regional challenges.

In south Florida, a rapidly expanding urban interface, continued spread of invasive plant and animal species, and proliferation of feral cat colonies in public parks present significant management challenges. Hardwood hammocks within the Everglades ecosystem are sensitive to fluctuating water levels and especially to long-term drought conditions. Restoration of natural hydrology in this system will benefit forest and wetland birds.

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