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  • Caloric Values of Selected Wetland and Coastal Sage Scrub Vascular Plant Seeds
  • Peter A. Bowler (bio), Jenny Liou, independent scholar (bio), and Jocelyn Moon

Seeds of vascular plants differ greatly in their caloric content, and there is significant variation within families and genera, as is also the case with seed carbohydrates and oils (Earle and Jones 1962, Jones and Earle 1966, Barclay and Earle 1974, Levin 1974, Ensminger et al. 1995). In both wetland and upland habitats, seeds sustain the food chain for many granivores. In this study, we examined the caloric values of seeds from eight species of the upland coastal sage scrub community and seven species from an adjacent wetland community at the University of California Natural Reserve System's (UCNRS) San Joaquin Marsh Reserve in Irvine, California (see Bowler and Elvin 2003 for the site's vascular plant species list).

Caloric values of seeds are well known for grains and other seeds important for human uses but are not as well understood in groups that lack direct economic significance. The caloric value of seeds has been estimated for desert granivores (Reichman 1976, Gordon 1980) but wetland seed caloric values have not been well surveyed, even though they are staples in the diets of many waterfowl species (Martin et al. 1951) and were extensively used by Native Americans. Large and abundant wetland plants such as Schoenoplectus californicus (California bulrush) were a food source, and were used for the construction of tule boats and houses, for basket weaving, and for making rope and cord (Harrington 1972, Clarke 1977, Timbrook 1997). Jones and Earle (1966) demonstrated that the protein and average oil contents of seeds are positively correlated, and that families with lower values of protein and oils are more likely to include species with starchy seeds than families high in oils and proteins (Gordon 1977). Understanding the caloric contribution of a restoration site is important in interpreting an overlooked ecological service of a successful ecological restoration.


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Table 1.

Above ground biomass, individual stems, and total seed heads from representative dense stands of Bolboschoenus maritimus, Schoenoplectus americanus, from the UCNRS San Joaquin Marsh Reserve.

We sampled above-ground plant material from 2-m2 randomly selected plots for two species of bulrushes, Bolboschoenus maritimus (alkali bulrush) and Schoenoplectus americanus (chairmaker's bulrush), in the UCNRS San Joaquin Marsh Reserve (Table 1). These were located in dense monotypic stands. Other wetland taxa were sampled individually in mixed stands or as isolated plants. We determined the caloric values of seeds from seven wetland and eight upland vascular plant species using bomb calorimetry (Table 2).

We found that the seeds of Schoenoplectus and Bolboschoenus species would have been nutritious for Native Americans, as well as wildlife granivores and omnivores. For B. maritimus, we estimated that a granivore eating 100 grams of seed would have access to 547 calories. For S. californicus, another abundant species with prolific seed generation, 100 grams would yield only 262 calories. It is difficult to generalize about seed availability in wild stands because of the differences in stem densities, phenotypic expression, interspecific hybridization, periodicity of inundation, herbivory, and other factors. However, if managers or restorationists desire to estimate seeds per square meter and their caloric values, they could be calculated on a site-specific basis using a determination of seed density per square meter and applying the caloric values presented here. [End Page 142]


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Table 2.

The caloric values of seeds from selected wetland and upland vascular plant species in adjacent habitats.

Using this approach and establishing site-specific baselines for seed production, wetland restorations could be monitored for the seasonal increase in seed caloric availability as a wetland restoration site matures and wetland habitat expands in extent, stem and panicle densities, and seed production. These kinds of interpretations provide a data-driven approach to quantifying an important ecological service, in this case to granivores, which a restoration can contribute for onsite and colonizing consumers. Monitoring seed production throughout a restoration site's history and development would be a useful documentation of an amenity provided by wetland or upland restorations. This strategy is an important...

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