Biological Changes

The extensive hydrological (water) changes occurring in the Middle Rio Grande Valley during the last century have severely impacted its biological communities. Many wetlands dried up with the installation of drainage ditches, which rapidly lowered the water table. Overall, the Middle Rio Grande Valley lost over half of its wetlands between 1935 and 1989. Several rare plant species, found only in wetland areas, are severely threatened with loss of appropriate habitats. Although draining the valley initially benefited the reestablishment of the cottonwood bosque (which had been greatly reduced by heavy human use and waterlogged soils), the distribution of the forest is now largely limited to the area between the levees rather than throughout the wider floodplain. Further, the patchy mosaic of different habitat types has been lost and replaced with a more continuous, mature bosque within the new, narrow floodplain. This, combined with decreased overbank flooding, means that wildfires, which were probably not an important part of the bosque ecosystem historically, can now spread quickly along this continuous, dry corridor. The decrease in flooding has also led to an accumulation of leaf litter and woody debris within the forest, which provide fuels for the more catastrophic-level fires. In addition, manipulation of river flows and confinement of the river to a straightened and narrowed channel has decreased further cottonwood establishment, or limited it to areas within the active river channel. Now, as patches of the forest are cleared or die naturally, they are not replaced as rapidly as they are lost.

Follow this link to learn more about the impact of Biological Changes on Plants.

Follow this link to learn more about the impact of Biological Changes on Animals.