Restoration Projects Support Nature’s Pollination Systems
By Michelle Boercker, Restoration Biologist
Historically, the Great Central Valley of California encompassed nearly one million acres of riparian habitat. Today, this riparian habitat is restricted to 5% of its original range and is highly fragmented. Despite these impairments, riparian habitat supports the most diverse wildlife of any habitat type in California. Many of these wildlife species pollinate plants, and thus play a critical role in plant reproduction. Pollinators include a vast array of extremely diverse animals, including insects (e.g. bees, butterflies and moths), mammals (e.g. bats) and birds (e.g. hummingbirds). Plants and their pollinators make up pollination systems.
By restoring riparian areas, River Partners creates habitat for pollination systems, which worldwide are declining due to habitat loss and fragmentation, climate change, and the introduction of exotic species. In response, restoration efforts are increasingly tailored to foster natural pollination systems (Kremen and Ricketts, 2000).
River Partners plants a diverse assortment of native riparian species, which in many cases flower at different times. As a result, nectar sources are more continuously available throughout the year to sustain pollinators. The chart at right depicts some of the woody species commonly planted by River Partners at our restoration sites. One can see that the wide variety of plants is accompanied by a wide range of flowering times.
While performing routine monitoring activities at the Del Rio Wildland Preserve on October 30, 2009, I was able to appreciate the differences in the timing of plant reproduction firsthand. Many of the plants onsite had flowered and subsequently produced fruit months prior to my visit and were now going dormant for the season. California rose (Rosa californica) shrubs possessed relatively few leaves and were bright with red berries (below).
Coyote brush (Baccharis pilularis) shrubs, on the other hand retained green foliage, displayed abundant and tiny, white flowers, and were literally buzzing with pollinator activity.
The flowers of gumplant (Grindelia camporum), an understory species frequently planted by River Partners, were also receiving a lot of attention from pollinators.
Although impressive, the abundance of bees at the Preserve came as no surprise. Recent work conducted by Dr. Neal Williams (2007) provides strong evidence that restored riparian areas in Northern California support bee communities as diverse as those in remnant riparian areas, and that this finding is consistent among seasons (Golet et al. 2009). Native bee communities can greatly contribute to crop production in Northern California (Kremen et al. 2004), and thereby provide society a supporting “ecosystem service.” Crop pollination by native species may become increasingly critical as the number of honey bee colonies continues to decline as a result of introduced pathogens and parasites.
Native Plant Flowering Times
Pollination in Riparian Ecosystems
One important, and direct, type of interaction between riparian species is the interaction between a riparian plant and its pollinators. Many plant species require, or benefit from, cross-pollination (rather than self-fertilization) which is facilitated by animals. To entice pollinators, plants present an impressive array of floral traits, including traits related to form, color, and scent. Some floral traits have evolved to facilitate pollination by single animal species (resulting in very specialized interactions), while others attract a more diverse set of pollinators. Most plant-pollinator interactions are mutually beneficial. The plant uses an animal to transport its pollen (containing the male gamete) to the stigma (the female receptacle) of another individual of the same species. In exchange the animal is typically rewarded with nectar.
Golet, G. H., T. Gardali, J. W. Hunt, D. A. Koenig and N. M. Williams. 2009. Temporal and taxonomic variability in response of fauna to riparian restoration. Restoration Ecology.
Kremen, C. and T. Ricketts. 2000. Global perspectives on pollination disruptions. Conservation Biology, 14 (5): 1226-1228.
Kremen, C., N. M. Williams, R. L. Bugg, J. P. Fay and R. W. Thorp. 2004. The area requirements of an ecosystem service: crop pollination by native bee communities in California. Ecology Letters, 7:1109-1119.
Williams, N. M. 2007. Restoration of native bee pollinators within the Sacramento River System (California). Ecological Restoration, 25 (1): 67-68.