Water and Fertilizer Effects on the Germination and Survival of Direct-Seeded Golden Paintbrush (Castilleja levisecta)

Golden paintbrush (Castilleja levisecta), a hemiparasitic member of the Orobanchaceae, was historically found in lowland prairies in the Pacific Northwest. Reduced to only about a dozen sites in western Washington and British Columbia (extinct in Oregon), golden paintbrush was listed as a threatened species by the U.S. Fish and Wildlife Service in 1997. Since development of a species recovery plan in 2000 (USFWS 2000), restoration efforts have specifically focused on increasing the number, size, and geographic distribution of golden paintbrush populations by augmenting existing populations, establishing the species in new sites, and enhancing the suitability of habitats for sustaining viable populations.

Initially, restoration efforts relied primarily on outplanting of nursery-grown plugs, as seed was extremely scarce and establishment of field-sown seed was typically only 1-2%. Production beds greatly increased seed supplies in recent years, and many restoration efforts are now shifting towards sowing paintbrush seed directly into potential sites. With this transition, we have sought to increase seedling survival rates, which are much higher when grown in the greenhouse (40-70%). Here, we describe the results of an experiment where we manipulated two variables in the field—water and fertilizer—to determine how they affect paintbrush germination and survival.

This experiment was carried out by a dedicated group of volunteers—the Friends of Puget Prairies—in the Glacial Heritage Preserve, a native prairie owned by Thurston County, Washington. The site is one of the largest protected prairie and oak woodlands systems in the South Puget Sound region. Although there are no historical records of golden paintbrush occurring at the site, one robust wild population remains in a prairie remnant 15 km away. During the past century, most of the region's prairies were lost or severely degraded due to urban development, agricultural conversion, conifer tree invasion due to fire suppression, and invasion and proliferation of non-native species, all factors that also contributed to the decline of golden paintbrush.

Our experiment employed a randomized block design with each block consisting of four 1 m² plots separated by 1m buffers. The four treatments in each block included water, fertilizer, water+fertilizer, and an untreated control. Blocks were replicated in six locations that met several criteria, including: 1) presence of Roemer's fescue (Festuca roemeri) and woolly sunflower (Eriophyllum lanatum), both known hosts for golden paintbrush; 2) a history of at least one prescribed burn; and 3) previous treatment with a grass-selective herbicide to reduce competition from non-native grasses. Three blocks were located in the central portion of the prairie, and three were in groups ca. 600 m north. Prior to seeding, we installed GB-1 Gypsum Sensor Blocks (Delmhorst Instrument Co., Towaco, NJ) at a depth of ca. 12 cm to measure soil moisture. We collected readings weekly from April through September 2010.

In January 2010 we sowed 1,000 paintbrush seeds, collected the previous fall from the nearby wild population, in each of the 24 plots. We applied approximately 70 cm³ of Osmocote Smart-Release Plant Food (19-6-12) (Scotts Miracle-Gro Company, Marysville, OH) to the fertilizer and water+fertilizer plots in late April, when daily high temperatures reached about 21°C. We began watering in the water-only and water+fertilizer plots in mid-July, when the moisture readings from the gypsum blocks had begun to descend. We added 8 L of water weekly to each plot for 10 weeks. No additional treatments were applied in 2011.

We monitored plots three times in 2010 and twice in 2011. At each visit, we located all golden paintbrush plants and marked them with a plastic toothpick. At each visit, we marked new germinants with a different color so mortality of groups could be tracked separately. Some unmarked plants noted in 2011 may have germinated the previous year but lost their toothpicks over the winter. In 2011, we also estimated percent cover for all species in each plot to understand how associated species in the plots may have responded to the...