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In southern California more and more restoration projects involve control of non-native species, because most mitigation lands are degraded from their original condition, and invaders are good at taking advantage of disturbed habitat. |
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Carla D'Antonio
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The overarching goal of restoration activities is to guide the composition, structure and functioning of a degraded site along a trajectory towards a more desirable state. That state is either what was there before or a chosen reference ecosystem that appears reasonable for the site. Ecological restoration challenges our understanding of fundamental ecological processes and what it takes to put a community of organisms and the processes that sustain them back together into a functional landscape.
An activity that has become extremely familiar to restoration practitioners is that of removing or controlling unwanted non-native species. These species are variously referred to as “weeds” or “invasive” species. I prefer to call them invasive non-native species since the term “invasive” really says nothing about where a species came from.
Invasive non-native species get here as a result of accidental or purposeful human transport and then spread away from the areas where they were introduced.
Many of them are essentially harmless and have become a part of our landscape without raising many eyebrows.
Indeed on the scale of the entire state, successfully established, self-replacing populations of introduced plant species have added at least 1200 species to the California flora. About 10% of them, however, interfere with the values we gain from ecological or agricultural systems, including interfering with restoration goals.
These are the ones referred to as harmful, invasive species (= invaders with an impact we care about). Notorious examples in southern California include saltcedar (Tamarix-- two species, mostly from Asia) which can transpire large amounts of water from western streams and reservoirs, the aggressive giant reed grass (Arundo donax, from Europe and Asia) which can promote the spread of fire up river channels, clog culverts and create large debris deposits during flood events, a variety of very aggressive streamside vines including English ivy (Hedera helix) and Cape ivy (Delairea odorata, from South Africa) and fire-promoting annual grasses, such as red brome (Bromus madretensis var. rubens from the Mediterranean basin), that are contributing to increased fire frequency and the local decline of native species in the Mojave desert.
For a complete list of harmful, invasive plant species in California wild lands, see www.cal-ipc.org.
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After heavy rains in 2005, Arundo debris washed up along miles of shoreline.
Some of it rooted, forming new infestations. Photo by C. D'Antonio. |
Control of non-native species as a “restorative activity” can be as simple as removing populations of invaders as they establish in a site that is under long-term management. More often, however, it involves intensive efforts to shift community composition from dominance by unwanted species to dominance by desired target species. Challenges can include both immediate and long-term control and dealing with possible legacies that these species might leave behind after control, such as changes in soil structure or chemistry. In southern California more and more restoration projects involve control of non-native species, because most mitigation lands are degraded from their original condition, and invaders are good at taking advantage of disturbed habitat. Many of our projects at CCBER involve such lands.
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