Restoring arthropod communities in coastal sage scrub
Published source details
Burger J.C., Redak R.A., Allen E.B., Rotenberry J.T. & Allen M.F. (2003) Restoring arthropod communities in coastal sage scrub. Conservation Biology, 17, 460-467.
Published source details Burger J.C., Redak R.A., Allen E.B., Rotenberry J.T. & Allen M.F. (2003) Restoring arthropod communities in coastal sage scrub. Conservation Biology, 17, 460-467.
Coastal sage scrub (CSS) is a threatened plant community of southwestern USA. In California and northern Baja California much has been lost or degraded due to urban expansion. Efforts to restore CSS, including seeding and planting mixtures typically of only five or six species at one site, have met with varied success. The species are often selected because of their ease of establishment rather than their restoration value. Restorations are also susceptible to weed invasion, thus can result in a community of low diversity very different from the original natural vegetation.
This study looked at arthropod abundance and diversity on the native shrub California sage Artemisia californica (Asteraceae), a common, often dominant shrub species in CSS, to evaluate whether arthropod communities had become reestablished after a restoration attempt. Arthropods were collected from shrubs on planted and undisturbed sites 6 years after a restoration attempt for comparison.
Study plots: Plot 1 (126 m²) had been planted with A.californica seedlings and seeded with the native perennial, purple needlegrass Nassella pulchra in 1993. At the time of this present study (1997), 10 shrubs remained and nine were large enough to sample. Plot 2 (121 m²), 100 m away, had been planted with A.californica seedlings in 1993 and seeded in 1994; 18 shrubs remained and 15 were large enough to sample. Each shrub was paired with a similarly sized one that had established naturally on the adjacent undisturbed habitat; thus 24 planted and 24 naturally established A.californica were sampled.
Arthropod sampling: Arthropods were sampled on 2–3 June 1997, coinciding with the peak seasonal abundance of arthropods and maximal annual shrub expansion. Arthropods were collected by vacuuming each shrub for 1 min and sorted and identified in the laboratory.
Identification and analysis: Most arthropods were identified to morphospecies within family, in many cases, to genus or species. A morphospecies (a relatively robust indicator of true species identity, defined as a morphologically distinct and recognizable organism that represented an assumed species). Springtails (Collembola), booklice (Psocoptera) and thrips (Thysanoptera) were not identified beyond order. Acarina and Aphididae (Homoptera) were identified to family. Each family was assigned to a foraging guild (detritivore, herbivore, predator or ant).
The species richness of orders, families, species diversity, adult morphospecies, total arthropod abundance and the proportions of each major foraging guild were compared between naturally established and planted shrubs.
Vegetation: Some features of vegetation in and around shrubs that might influence arthropod communities were measured: shrub structure and character (size, volume, density and health); other shrubs, brome grass Bromus spp., wild oats Avena spp., yellow star-thistle Centaurea solstitialis and perennial grass occurring within or around shrubs.
A total of 882 arthropods of 57 families and 169 morphospecies (of which 146 were adult) were collected; 51% of morphospecies (adults and imms.) were represented by one individual. The most abundant species was a leafhopper, Empoasca decora (Homoptera); its abundance was unrelated to shrub type (i.e. natural established vs. planted). More families and morphospecies were collected, and abundance also tended to be higher, on planted shrubs.
However, arthropod diversity was greater on naturally established plants; common arthropods occurred at similar densities regardless of shrub type but the proportion of single occurrences of a species was significantly greater on naturally established shrubs; planted shrubs tended to support more predators relative to herbivores. Even after 6 years, planted shrubs were still distinguishable from naturally established ones in that they were both more isolated from nearby shrubs and surrounded by more invasive weeds.
The authors suggest that small-scale CCS restoration attempts can be successful at restoring basic elements of arthropod biodiversity, but creating a less diverse community with, and at least initially, less able to support rare species.
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