Restoring Packera layneae on the Plumas N.F. using prescribed burning Kyle Merriam, Sierra Cascade Ecology Program 27 Jan 2012 INTRODUCTION Packera layneae (Layne’s butterweed) is a federally listed as threatened plant species found primarily on gabbro or serpentine soils in fire adapted chaparral and coniferous forest vegetation types. P. layneae is considered an early successional species, occurring in openings with exposed bare ground and low canopy cover, and thriving on disturbed sites (Figure 1). Figure 1.Typical Packera layneae habitat on serpentine soils, Plumas National Forest. Alteration of natural fire regimes is thought to have contributed to the decline of P. layneae (U.S. Fish and Wildlife Service 1996). In 2006, the Plumas National Forest (PNF) proposed a project to conduct a small prescribed burn within a portion of a P. layneae population to determine if a low intensity underburn might benefit this rare species. After several years of pre‐treatment data collection, the PNF treated a portion of a P. layneae occurrence by prescribed burning in 2008. The remainder of the occurrence was not treated and used as a control. This report describes the effects of the prescribed burn on P. layneae after three years of post‐treatment data collection. METHODS Study Site Packera layneae is known from western El Dorado, Tuolumne, and Yuba counties. The PNF population occurs on serpentine soils in Yuba County, within a ponderosa pine (Pinus ponderosa) and Douglas fir (Pseudotsuga menziesii) dominated plant community at 800‐950 meters in elevation. Experimental Design and Data Collection In 2006, we located and permanently marked five circular plots in an area of the P. layneae occurrence to be burned. We also established five plots in a nearby control area. Plots were located randomly, with the only requirement being that they each contained at least 15 individual P. layneae plants. Five 1 individual P. layneae plants were permanently marked within each plot, for a total of 25 permanently marked plants in the treatment area and 25 permanently marked plants in the control area. At each sampling time the size (height and width), stem number, flowering stem number, and flower number of each permanently marked plant were recorded. Within the circular plots, all P. layneae plants were tallied according to four size classes: < 1 centimeters (cm) tall, 1‐5 cm tall, > 5 cm tall and non‐flowering, and > 5 cm tall and flowering. Environmental data was also collected, including percent cover of herbaceous understory vegetation, moss, bare ground, litter, coarse woody debris, and rock. Canopy closure was measured using a spherical densiometer, and litter and duff depth were measured. Timing Pre‐treatment data was collected in July of 2006 and 2007, and post‐treatment data was collected in July of 2009, 2010 and 2011. Data will be collected again in 2013, five years after project implementation. Data Analysis Data were analyzed using the statistical software program SAS 9.3 (SAS Institute 2010). Treatment effects on P. layneae and environmental variables were evaluated with ANOVA, and linear regression analyses were used to identify relationships between environmental variables and P. layneae. RESULTS and DISCUSSION Most P. layneae plants in both the control and treatment area were in two size classes; 1‐5 cm in height, or >5 cm in height and not flowering. We found very few P. layneae plants in the flowering stage or smaller than 1 cm in height (Figure 2). 60
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Figure 2. P. layneae density by size class in control and treatment plots both before and after the prescribed burn. 2 We found that total P. layneae density was not affected by the prescribed burn in 2008 (Figure 3). Plant numbers in individual size classes also did not change after the 2008 prescribed burn treatment. 120
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Figure 3. There was no statistically significant change in average P. layneae density in either control or treatment plots over the five year monitoring period. 9
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The number of flowering P. layneae plants in the treatment plots did not change after the prescribed burn in 2008, but the number of flowering plants in the control plots significantly increased during this time period between 2007 and 2009 (Figure 4). 2009
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Figure 4. The average number of flowering P. layneae plants did not significantly change in treatment plots over the five year monitoring period, while flowering plant numbers increased between 2007 and 2009 in the control plots (p‐value for year*treatment interaction term = 0.007) . The prescribed burn had no significant effects on the environmental variables measured, including the cover of bare ground, litter, coarse woody debris, rock, canopy closure and duff and litter depth. These results suggest that the prescribed burn treatment may have been too low in intensity to have significant effects on the environmental conditions of the P. layneae habitat (Figure 5). 3 Figure 5. Prescribed fire effects in P. layneae habitat. The cover of herbaceous plant species did not change in the treatment plots after the burn, but there was a significant increase in herbaceous cover in control plots over the same time period (Figure 6). 30
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Figure 6. The percent cover of understory vegetation was similar in control and treatment plots prior to the burn, but was significantly lower in treatment plots after the burn (p‐value for year*treatment interaction term = 0.04). We found that P. layneae density was positively associated with the amount of bareground exposed, particularly for plants between 1‐5 cm tall (Figure 7). 4 140
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Figure 7. Both the total number of P. layneae plants (a) , and the number of 1‐5 cm tall P. layneae plants (b) were positively associated with the cover of bare ground. The number of plants in the 1‐5 cm tall size class was also higher in plots with less overstory canopy closure (Figure 8). 90
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Figure 8. The number of P. layneae plants in the 1‐5 cm‐tall size class was negatively associated with the amount of overstory canopy closure. Other P. layneae characteristics, including flower and flowering stem number and plant size were not significantly associated with any of the environmental characteristics we measured. CONCLUSIONS There were no significant changes in P. layneae density, size or reproductive potential after the prescribed burn, suggesting this treatment had a neutral effect on P. layneae. However, increases in the number of flowering P. layneae plants observed in the control unit did not occur in the treatment unit. This suggests that there may have been some negative effects of the treatment on P. layneae such that it could not benefit from environmental conditions that promoted flowering in the control unit. Total herbaceous cover similarly remained unchanged in the treatment unit but increased in control plots 5 over the monitoring period. It is possible that the prescribed fire could have negatively affected P. layneae and other herbaceous species through direct effects of heat and flame contact. Many plants require the conditions created by fire, but can still be killed or injured by fire. P. layneae density was positively associated with the bare ground and negatively associated with canopy closure. These results suggest that a prescribed burn which can reduce surface fuels and reduce overstory canopy closure may benefit P. layneae by creating the kind of habitat conditions this species prefers. The prescribed burn treatment we evaluated had no significant effect on these or any other environmental variables measured. Although we still have another monitoring period to complete in 2013 five years after the treatment, a few general recommendations can be made based on these data to improve habitat restoration efforts for P. layneae using prescribed fire. A successful prescribed burning treatment should:  Have sufficient intensity to create the kind of environmental conditions preferred by P. layneae, including: o reducing surface fuels and exposing bare ground; and o reducing overstory canopy closure, which might also be achieved through thinning treatments.  Consider creating control areas to protect existing P. layneae plants from the direct effects of burning. 6