California’s riparian forests are at risk of decline – Courthouse News Service
The state’s vital forest ecosystems have become dependent on water supplied by humans and may no longer be able to survive when the tap is turned off, putting the future of a number of animals at risk. endangered that inhabit these forests.
(CN) – Riparian forests, those wooded areas that border rivers and streams, are home to important wildlife, but water management practices focused on meeting the needs of growing communities and agriculture can undermine their future in danger.
These forests serve to protect water quality and stream integrity, shelter wildlife, and control flooding along streams, but the ecosystems they support are at risk of collapse over time. decades to come. While water management practices have provided a short-term boon to these ecosystems by providing “subsidies” to water, reliance on these artificial supplies could undermine their long-term viability.
At first glance, the older trees in these ecosystems appear to be thriving, but the forest soils have become devoid of new growth, which means that when these older trees inevitably die, there will be nothing to replace them. Researchers describe this predicament in a new study published Monday in the journal PNAS.
“We need to be more intentional in integrating the water needs of ecosystems when we manage water, both for aquatic organisms and terrestrial species,” said lead author Melissa Rohde, PhD . candidate for State University of New York College of Environmental and Forestry Sciences, in a related statement. “These forest ecosystems are in a precarious state because we have disrupted the natural hydrological processes on which these plant species depend to support and maintain key life processes. “
Researchers employed NDVI (Normalized Difference Vegetation Index) satellite data to assess the growth health of riparian forests. NDVI data measures the health of plants based on how they reflect light; Healthy plants contain higher levels of chlorophyll, which in turn absorbs greater amounts of visible light than diseased plants. Technology allows scientists and farmers to assess the health of vast expanses of flora without ever setting foot on the ground.
Based on five years of NDVI measurements taken between 2015 and 2020, along with data on groundwater elevation and stream flow, the authors found that California’s riparian forests exhibit a response to the problem. stress to deeper groundwater supplies and decrease in reflectivity, indicating that their health is declining.
These areas depend on seasonal flooding and variable groundwater and river flows throughout the year to propagate and thrive. By artificially subsidizing and normalizing their water flow, trees in these regions are prevented from reproducing naturally, and just like their human counterparts in recent times, there are fewer and fewer saplings on the verge of replacing elderberries. as they die.
Rohde called these forests “living dead”. Because these older trees have become accustomed to the regular water supplies provided by humans, they now have a reduced ability to tap into groundwater sources during dry periods, such as droughts that are becoming all too common in California.
“Altered flow regimes, which stabilize the flow of streams throughout the year and artificially improve the water supply to riparian vegetation during the dry season, disrupt the seasonal cycles of the abiotic engines to which these Mediterranean forests are suitable, ”the authors explained in their study. “Therefore, our analysis suggests that many riparian ecosystems have become dependent on human-altered flow regimes, making them more vulnerable and less resilient to rapid hydrological changes, potentially resulting in future loss of riparian forests in areas. increasingly stressed arid regions. “
A number of endangered aquatic and terrestrial species have made their home in these biodiversity hotspots and depend on their continued health to survive. By modifying these ecosystems to become dependent on artificial water management practices, many are no longer able to support themselves when these water sources stop flowing. These trees may appear momentarily healthier in NDVI data, but this may mask their underlying vulnerability to changes in water management, the authors say.
Rohde and his colleagues will use the lessons learned from their research to advise California natural resource agencies on how best to sustainably manage groundwater-dependent ecosystems in the state in the future.
“California is one of the most biodiverse regions in the world, containing more species than the rest of the United States and Canada combined,” Rohde said in a related statement. “In the midst of the Sixth Mass Extinction, the long-term sustainability of California’s river ecosystems and the preservation of the rare and endemic species that inhabit them now depend on the deliberate and coordinated management of resources and government agencies.”