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.

A Quasi-brief History of Mustard, the “Triangle of U,” and Your Favorite Veggies

Weeding
Invasive species removal is an important part of the restoration cycle.

Spring is right around the corner, which means that weeds are sprouting at many of our newest restoration sites. Not to worry, we were expecting this to happen! Invasive species management is an important part of the restoration cycle. Most project sites will require at least 2-3 years of intensive invasive removal before our native plantings grow large and dense enough to overtake the annual invaders such as mustard, radish, fennel, and iceplant.

Of all the invasive species removed by Save The Bay’s dedicated volunteers and wetland restoration staff, black mustard, Brassica nigra, is perhaps our most targeted invader. Our relationship with this plant is conflicted; though we love to see it removed from wetland areas, Save The Bay staff have also brought it into their homes to process into homemade yellow mustard for consumption as a condiment. Perhaps this behavior is a restoration practitioner’s fulfillment of Sun Tzu’s famous axiom from The Art of War:

If you know your enemy and know yourself, you need not fear the result of a hundred battles.

Because we all interact with mustard either in our kitchens, backyards, or local wetlands, it makes sense to learn a little more about it. Hold on to your pocket protectors, it’s time to get a little geeky.

More than an invasive species

History of mustard
Black mustard even made its way into scripture.

Black mustard is native to the Mediterranean region of Europe, where it has been grown as a food crop for thousands of years. The shoots and stems can be cooked and consumed, while the seeds can be ground for use as a spice, cough suppressant, and treatment for respiratory infection. In addition to its culinary and pharmaceutical utility, mustard also found its way into scripture:

The Kingdom of Heaven is like a grain of mustard seed, which a man took, and sowed in his field; which indeed is smaller than all seeds. But when it is grown, it is greater than the herbs, and becomes a tree, so that the birds of the air come and lodge in its branches.
-Matthew 13:31-32

Besides being culturally influential, the Brassica genus has also contributed to our understanding of genetics. In 1935, Korean-Japanese botanist Woo Jang-choon (the Japanese translation of this name is “Nagahara U”) crossed the three “traditional” Brassicas—B. nigra (black mustard), B. rapa (turnip, Chinese cabbage), and B. oleracea (kale, cabbage, broccoli, cauliflower, Brussels sprouts)–to create three new hybrid species–B. juncea (Indian mustard), B. napus (rapeseed, rutabaga), and B. carinata (Ethiopian mustard). The artificial interbreeding of three separate, yet closely related, diploid species (each with two set of chromosomes), to create three new tetraploid species (each with four sets of chromosomes) is referred to as the “Triangle of U,” in reference to Nagahara U.

Triangle of U
Overview of species relationships in the genus ‘Brassica’. Original work by Mike Jones

Though the Triangle of U was only a theory in 1935, it has now been confirmed by DNA mapping. The Triangle is significant in that it explains the creation (by both natural and artificial means) of many of our most important food crop species, and provides the genetic understanding necessary to prevent undesired hybridization of these species.

Next time you pull a mustard plant out of the ground or buy mustard seed in the grocery store, take a second to appreciate the scientific and cultural significance of this pesky weed, without which we would not have some of our favorite condiments and vegetable oils.