Technical Report No. 11

ESTIMATED NET AERIAL PRIMARY PRODUCTIVITY AND MONITORING OF SELECTED CHARACTERISTICS OF SPARTINA ALTERNIFLORA IN PADILLA BAY. WASHINGTON,
APRIL 1992 - MAY 1993

Sharon R. Riggs and Douglas A. Bulthuis

October 1994

 

Bibliographic Citation
Riggs, Sharon R. and Douglas A. Bulthuis. 1994. Estimated net aerial primary productivity and monitoring of selected characteristics of Spartina alterniflora in Padilla Bay, Washington, April 1992-May 1993. Washington State Department of Ecology (Publication No. 94-176) Padilla Bay National Estuarine Research Reserve Technical Report No. 11, Mount Vernon, Washington. 45 pp.

Abstract
The salt marsh plant, Spartina alterniflora, has been introduced to Washington state during the last century and is growing at latitudes north of the probable sites of origin. It has spread rapidly in some bays and has been designated a noxious weed by the Washington State Noxious Weed Board in some counties. The purpose of this study was to estimate the net aerial primary productivity (NAPP) of S. alterniflora in Padilla Bay, Washington (the most northerly known population of S. alterniflora on the west coast of North America), and to monitor selected characteristics of this plant for one year (April '92 - May '93). Data on growth form, stem density, mortality and the characteristics: culm elongation, leaf emergence, leaf senescence, and leaf abscission were obtained. Individual culms in twelve random 0.0625 m2 quadrats were tagged in a section of marsh approximately 45 m x 80 m and measured monthly except for Dec '92 and Jan '93. New plants > 10 cm tall were tagged each month and heights of plants <10 cm tall were recorded each month. NAPP was estimated using the nondestructive "summed biomass loss" method of Hardisky (1980). This method sums biomass losses resulting from leaf abscission from live culms and culm mortality within a population of tagged culms. Culms in a section of marsh adjacent to permanent quadrats were destructively harvested on a seasonal basis and regression equations of culm height vs. biomass were used to estimate biomass in the permanent quadrats. Dead leaves were harvested seasonally to estimate the biomass of abscissed leaves.

During the period of this study, culm elongation rates peaked in May '93 (0.59 cm/culm/day). Maximum culm heights ranged between 0.65 - 1.30 m and could be considered the tall growth form. Leaf emergence rates peaked from June '92 - Aug '92 (0.047, 0.045, 0.046 leaves/culm/day). Leaf senescence rates peaked in Jun - July '92 (0.037, 0.036 leaves/culm/day) and Nov '92 (0.040 leaves/culm/day) while leaf abscission rates were highest in Nov '92 (0.035 leaves/culm/day) and Mar '93 (0.038 leaves/culm/day). Culm densities (culms m-2) for the live component during this study ranged from 223 (±19 s.e.) to 519 (±55 s.e.). Percent mortality was highest in Mar '93 (46.9%). Basal diameters of live and dead culms were measured in Oct '92 and Nov '92. They ranged between 2 - 11 mm both months with respective overall means of x = 6.72 mm (± 0.095 s.e.) and 6.06 mm (±0.094 s.e.). NAPP was 1520 g/m2/year in this salt marsh. A total production of 73.112 kg/yr was estimated for S. alterniflora in Padilla Bay in 1991 (4.81 ha). The turnover rate was 1.14 crops/yr, that is, the peak standing crop turned over in 0.88 years.