The descriptor “tropical forests” usually conjures images of lush green forests with high canopies brimming with life—or at least for me it did. But as I look across the lands of the Sierra de Alamos-Rio Cuchujaqui Protected Area in Sonora, Mexico, I see large, columnar cacti peeking out from the fading green and pale brown of surrounding trees. Yet this, too, is considered a tropical forest—a tropical deciduous forest. Here the lush green foliage bursts forth with the summer monsoons and extends through mid-fall and hurricane season. As winter approaches, the trees drop their leaves, though not because of the cold temperatures, as with temperate forests, but due to the dry climate. By March, there is nary a leaf in sight, and the hillsides have taken on a red-brown-gray referred to locally as mojino. Many of the adaptations we associate with desert plants developed here to survive the harsh, dry season. The green that remains is found along the arroyos and in the stems of the tall cacti. That’s not to say there is no color, for during the dry season there is always something flowering. Blooming amapas Tabebuia impetiginosa add a splash of color to the fading greens and brown as we drive to the protected area.
But the image of a forest brimming with life still fits, even if the first view doesn’t confirm it. Thousands of plant species live here, many are found only here. The Sierra’s tropical deciduous forest supports a rich array of fauna as well. With over 450 resident and migratory bird species, and many recognized as threatened or endangered, Birdlife International has designated the Sierra de Alamos as an Important Bird Area. The area also provides essential habitat and corridors for charismatic megafauna such as jaguars, ocelots, and margays. Many tropical amphibian and reptile species reach their northern range limits here, while desert species, such as the Gila monster, also extend into the region.
The protected area where we are working represents the northernmost stretch of tropical deciduous forest in the Americas, and possibly the most intact. Once extending from here in southern Sonora to Panama, and usually with only a width of around 30 miles, only 15 percent of the tropical deciduous forest in North America remains. And only about 1 percent of that is in protected areas. Though rather unusual for a protected area, the majority of lands in the Sierra de Alamos-Rio Cuchujaqui Protected Area remain in private hands; the reserve limits activities such as mining and land clearing, but cattle ranching still dominates the land, and overgrazing prevents a large risk. As part of the Applied Plant Ecology Division of the San Diego Zoo Institute for Conservation Research, I’m here as part of a research team focusing on a threatened palm, Brahea aculeata, and how various management practices (i.e. cattle grazing) affect the palm population.
Nature and Culture International (NCI), a nongovernmental organization partnering with San Diego Zoo Global in several locations in Latin America, represents an important resource for our project. They own land, have staff who serve as excellent field assistants and guides, and have strong relationships with ranchers in the area. Seeing the importance in conserving this little-known corner of the tropics, NCI has taken on the task of adding more stringent protection by purchasing the ranches along the main watershed. With just a few years’ break from cattle, it is easy to distinguish NCI lands from neighboring ranches; willows and other riparian vegetation really do flourish without the constant munch of cows. Hoping to widen its impact beyond the landholdings, NCI is working with us on some land-management issues in the area. We hope to base management practices in science and share them with the neighboring ranches. Building on this partnership, we hope to conserve this special part of Mexico, the tropical deciduous forest and the wonderful wildlife it contains.
Christa Horn is a senior research technician in the Applied Plant Ecology Division of the San Diego Zoo Institute for Conservation Research. Read her previous post, Observing Nature as a Child.