Biodiversity: More Is Not Always Better

Happy Biodiversity Day! Most of us have heard the word biodiversity being tossed around as an important subject that requires our attention, but why is biodiversity so important? This topic is much more difficult to address than you might think. Biodiversity refers to the level of variation of life within an ecosystem. Plants and animals have everything they need to live sustainably together in an ecosystem that has healthy biodiversity. Although biodiversity is a crucial subject in restoration science, there can be a misunderstanding that more biodiversity is always better. Researchers are finding that the types of species in an ecosystem are just as important as the number of species and more isn’t always better. Save The Bay confronts this issue of biodiversity every time we design a habitat restoration plan for tidal wetland transition zones within the San Francisco Bay.

biodiversity
Biodiverse restored transition zone habitat at Eden Landing with invasive monoculture of mustard on the other side of the fence.

To better understand this idea that more biodiversity isn’t always better when designing habitat restoration plans, let’s first consider what habitat restoration means and what’s being restored. Effective environmental restoration will restore ecosystem function. Ecosystem function involves biological, geochemical, and physical processes that vary between systems, but maintain a specific balance within each ecosystem, and that balance is delicate. Plants, animals, water, and earth all contribute to how ecosystems function, and when one of those contributions change, so do the others. Those changes not only displace the effectiveness and sustainability of food webs (Zedler and Kercher, 2004) but they also affect ecosystem services that humans rely on, such as food, water, medicine, transportation, employment, inspiration, shelter, and protection… to name a few. For example, an important ecosystem service that wetlands offer humans is their role as breeding and nursery grounds for economically important fish species, including the Pacific anchovy, California halibut, rainbow trout, and Chinook salmon. Tidal wetlands also provide important feeding and stopping grounds for migrating birds, which not only contribute to maintaining healthy populations of those economically important fish species, but also help to maintain healthy native insect and rodent populations.

Once researchers learned the importance of biodiversity and discovered it was diminishing, so began the mission to determine the cause for this great loss. Many factors have contributed to our worldwide decrease in biodiversity, and tidal wetlands are among the greatest victims. 90% of the San Francisco Bay wetlands have been destroyed due to bayfill, contamination, industrial use, and fragmentation. This hardship makes life difficult (if not impossible) for the San Francisco native species that depend on a healthy wetland habitat, and therefore, the wetlands have developed a decreased immunity to invasions by non-native species. Invasive non-native species thrive when conditions are difficult for the natives and they often completely take over entire ecosystems if left unchecked. Not all non-native species are invasive, just the ones that demolish the native diversity. And San Francisco Bay has the greatest number of invasive species anywhere in the western hemisphere.

As environmental scientists learned more about the intricacies of biodiversity, it became apparent that diversity should reflect the needs of the resident flora and fauna, since both are so interconnected. This observation may indicate that, while biodiversity offers the benefit of ecosystem stability, restoring an ecosystem to a sustainable functioning state should be the ultimate goal. So, rather than focusing on the blanket idea of increasing biodiversity across the board, researchers and practitioners have begun to implement the idea of restoring the biodiversity that has been lost in a particular area. That means that if a particular ecosystem historically was home to only a few species, practitioners are better off trying to restore the functions that those few species provided to that area, which is the entire point of restoration. Save The Bay works hard to understand and recognize the specific ecosystem functions at each of our sites and the specific native plant species that are capable of supporting those functions. Join us on one of our community-based restoration programs to ensure that the flowers have bees for pollination, the birds have a place to perch and nest, and the salt marsh harvest mouse has sufficient refugia during high tide.

Reference:
Zedler, JB and Kercher S. (2004). Causes and consequences of invasive plants in wetlands: Opportunities,
opportunists, and outcomes. Critical Reviews in Plant Sciences. 23(5):431-452.