Net Primary Productivity Data (NPP)
Purpose:
To evaluate the role of topography at the hillslope scale on grassland productivity in the southern California grasslands.
Where this data was collected:
Our study site is in the University of California Sedgwick Natural Reserve located in Santa Ynez Valley and San Rafael Mountains, 45-km north of Santa Barbara. The Reserve is 2064 ha ranging in elevation from 320 - 732m (Figure a). The climate is Mediterranean with cool, wet winters and hot, dry summers. Average annual precipitation is 38 cm, but is highly variable. Summer temperatures often top 38 degrees C and exhibit diurnal fluctuations of up to 30 degrees C. There is coastal fog intermittently throughout the year. A catena study was established on the southwest aspect of a 2ha zero-order hillslope (i.e. does not include an incised drainage channel) in grassland with occasional oaks (Image 7 , Figure b). The area was fenced with electric wire in 1996 to exclude cattle grazing. The slope faces southwest and drains to Lisque Creek, a tributary to Figueroa Creek that ultimately flows into the Santa Ynez River below the Bradbury Dam. The underlying geology is the Paso Robles formation and the soils are mapped as Chamise series (fine, mixed, active, thermic Typic and Pachic Argixerolls; USDA-SCS, 1972). Hillslope elevation ranges from 332 to 365m (33m of relief) with slopes ranging from 0-66% and an average slope of 22%. The study area contains several blue oaks on steep terrain, and two coast live oak in the colluvial hollow. The grassland vegetation is dominated by annual Mediterranean grasses such as rip-gut brome (Bromus diandrus Roth), soft chess brome (B. hordeaceus L.), wild oats (Avena barbata Link and A. sativa L.), and rat-tail fescue [Vulpia myuros (L.) C. Gmelin]. Several patches of a perennial bunchgrass called purple needlegrass [Nassella pulchra (A. Hitchc.) Barkworth] are scattered on the hillslope. Herbaceous annuals are primarily exotic species that include filaree [Erodium cicutarium (L.) L'Her.], black mustard [Brassica nigra (L.) Koch], tocolote (Centauria melitensis L.), and a biennial mustard [Hirschfeldia incana (L.) Lagr.-Fossat]. Extremely well-drained xeric sites contain the native shrub saw-toothed goldenbush [Hazardia squarrosa (Hook. & Arn.) E. Greene]. Other native herbs include vinegar weed (Trichostema lanceolatum Benth.) and chia sage (Salvia columbariae Benth.).
How this data was collected:
Net primary productivity was measured during the first week of May for four years from 1997 to 2000. Plastic quadrats (20 cm x 50 cm) were placed in duplicate, one meter above each of 21 soil pit faces sampled for soil attributes (Figure b). All grasses and forbs rooted in the plot were clipped to 1 cm above the soil surface. Grasses and forbs were identified, separated and dried at 65oC for a minimum of 48 hours before weighing. Tree biomass was not sampled because of its sparse areal extent on the study site. NPP was determined as grams of biomass per square meter at each sample location.
How to get more information on this data:
To request this data and get more information on this project please contact Lynne Dee Althouse: (althouse@tcsn.net).
