Invasive Ecology and Biodiversity Conservation

What an extraordinary winter! Looking in any direction here in our coastal refuge, emerald slopes capture the eye and lift the spirit. Even in urban backyards, well above average rainfall this ‘water year’ (October 2022 to September 2023) has boosted life beyond our usual spring unfurling in unexpected ways. Here in California, and especially on the south coast, our Mediterranean climate (warm, dry summers and cool, wet winters) drives an exceptional array of species diversity and ecological processes. We marvel as the tawny blur of dry season dormant vegetation on our hillsides transforms after winter rains into a vibrant wonderland of color, texture, and fragrance.

Globally, areas with a Mediterranean climate encompass only 2% of the world’s terrestrial area but almost 20% of earth’s botanical diversity. Our native species have evolved over millennia to develop specialized adaptations to endure often eight months of the year with no precipitation, and sometimes only a fraction of average rainfall for several consecutive years. Dropping leaves in the summer and through exceptionally dry periods to preserve resources, called drought deciduousness, is a common strategy employed by many of our coastal sage scrub shrub species, as is taking advantage of variable conditions like slope aspect, soil composition, and soil depth. This beautiful cadence of seasonal growth, species diversity, and community composition is made more dynamic by natural disturbances like intermittent fires that prompt a successive wave of species complexity and interactions.

Native species aren’t the only organisms benefiting from this abundant rainfall. Significant disturbances like livestock grazing, high frequency fires, agriculture, and urban development have created unique conditions for introducing, distributing, and encouraging the dominance of introduced plants that are often from other parts of the world with a Mediterranean climate—highly adapted to our unique resource conditions but without natural population checks. Several species of non-native mustards, thistles, and annual grasses are some of our most prolific invasive species, often able to grow faster, earlier, and denser than native species and thereby excluding native populations (Figure 1). When this happens, it isn’t just native plants that are affected. As the foundation for the ecological system, plants provide the scaffold for all the other interacting webs of life. When their populations are impacted, native wildlife are affected too. Successful life cycles of invertebrates, the basis of the food chain and pivotal conductors in ecology’s orchestra, are often very closely associated with specific native plant species, and invasive dominated areas provide poor habitat to sustain their populations. Relatedly, reptiles, amphibians, birds, and mammals are also negatively impacted by the rippling affects from invasive dominated landscapes. Although invasive ecology isn’t generally a kitchen table issue, it should be. Fire frequency and intensity is magnified in invasive dominated landscapes, affects from heavy precipitation are amplified when shallowly rooted invasive plants cannot hold soil on steep slopes or embankments in riverine floodwaters, and while non-native honey bees are utilized as a managed commercial pollination resource in our food systems, native pollinators including bees, butterflies, flies, bats, and birds provide crucial pollination services for crops worldwide, with an estimated $3 billion of US agriculture reliant on native bees alone. Without intact native plant communities to support these vital pollinators, our very food system is at risk.

So while we are all in awe at the extraordinary processes at play in our wildlands this abundant winter, let’s take special notice of the amazing diversity, beauty, and ecological services native plants provide, and support them by building our awareness of and active engagement with invasive species. Correctly identified invasive plants in your neck of the shrublands can be managed, and every effort contributes to stemming the tide of their impacts (check out the excellent online resources of the California Invasive Plant Council). And support your local land trusts that are working towards effective conservation management of wildland preserves, stewarding a future for our diverse and complex native systems to flourish in abundant times and endure through scarce ones. Together we can ensure a diverse and productive future for the extraordinary wildlands in our backyard.