December 2012 Number 1 - Utah Native Plant Society

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Utah Native Plant Society Long-term Responses of Penstemon clutei (Sunset Crater Beardtongue) to Root Trenching and Prescribed Fire: Clues for Population Persistence Judith D. Springer 1 , Peter Z. Fulé 2 , and David W. Huffman 1 1 Ecological Restoration Institute, Northern Arizona University, Flagstaff, AZ, and 2 School of Forestry, Northern Arizona University, Flagstaff, AZ Abstract. Penstemon clutei A. Nelson (Sunset Crater beardtongue) is narrowly endemic to the cinder hills and volcanic fields northeast of Flagstaff, Arizona. Disturbances such as wildfire, tornadoes, logging activity, and tree mortality from bark beetle outbreaks appear to stimulate regeneration of this species, but the manner in which populations persist between events is still largely unknown. From 1994-2000, we examined P. clutei responses to prescribed burning and root trenching treatments that were experimentally implemented as proxies for surface fire and reduced tree densities that might be observed following natural disturbance. We revisited this experiment in 2008 to assess long-term effects of the treatments. We also collected soil samples at this time to evaluate the importance of a persistent seed bank in population dynamics. In 2008, the mean number of P. clutei plants on trenched plots had declined with time, but was still significantly higher than on the control plots (mean density of 7.4 plants in trenched plots vs. 0.6 plants in control plots). There was no significant difference in density between burned and unburned plots. Only 21 P. clutei seedlings emerged from 176 soil seed bank samples, and we found no correlation between the number of P. clutei plants aboveground and the number of emergents from the samples. A targeted study to obtain samples near the base of reproductively mature plants produced 9 emergents from 30 samples. Results from this work suggest that disturbances that reduce competition for soil resources may be associated with long-term population persistence. Latent seed banks appear to be of only minor importance in recovery after disturbance; however, additional research with larger sample sizes would allow for greater confidence in this conclusion. We also recommend that additional long-term research be conducted on the response of this species to specific disturbances and stressors such as wildfire, tree mortality from bark beetle outbreaks, and water limitations. Penstemon clutei (Sunset Crater beardtongue) is a narrow endemic that occurs on volcanic soils to the northeast of Flagstaff in northern Arizona. The species is primarily restricted to tephra deposits from the Sunset Crater eruption (estimated dates of eruption vary from approximately 1040-1100 AD) at an elevation of approximately 2135 m (7000 ft), but a disjunct population is also present on older cinder cones about 20 km to the northwest of Sunset Crater (Figure 1). P. clutei is typically found in open ponderosa pine forests and pinyonjuniper woodlands in areas containing a sparse understory, commonly on fairly coarse and dry, cindery soils that lie over a series of finer textured sandy or silty bands, which may alternate with coarse layers of cinders (Abella and Covington 2006, Phillips et al. 1992). The type specimen was collected by Willard Clute in July 1923 north of the San Francisco Peaks in “lava sand,” and was described and named by Aven Nelson from the University of Wyoming (Nelson 1927). Growing to about 50-75 cm (20-30 in) in height, P. clutei has bluish-green glaucous leaves with serrated margins and gradually inflated, deep pink corollas. It is a very showy and attractive specimen plant and is readily available to gardeners through the horticultural trade. Flowering times vary by year, but it has been observed to flower from April through early September. It is ranked G2 (imperiled) by NatureServe (2009) and is on the U.S. Forest Service sensitive species list for Region 3 (Southwestern Region) (Arizona Game and Fish Department 2003; D. C. Crisp, personal communication, 2009). There is speculation that P. clutei is descended from P. pseudospectabilis (desert penstemon) and that geographic isolation occurred following the Sunset Crater eruption (Bateman 1980), or it may be intermediate between P. pseudospectabilis and P. palmeri (Palmer’s penstemon) (Clokey and Keck 1939). Phylogeny reconstruction of the genus Penstemon using nuclear and chloroplast sequence data and parsimony analysis produced incongruent results (Wolfe et al. 2006). Strict consensus trees generated from ITS (Internal Transcribed Spacers) placed P. clutei in a polytomy with P. bicolor (pinto beardtongue), P. floridus (Panamint beardtongue), P. palmeri, and P. rubicundus (Wassuk Range beardtongue). In contrast, strict consensus trees generated from chloroplast sequence data placed P. clutei as sister to P. centranthifolius (scarlet bugler) (Wolfe et al. 2006). With both methods (ITS and chloroplast sequence), the genera within the tribe Cheloneae had high bootstrap values. However, few terminal line- 164
Calochortiana December 2012 Number 1 Figure 1. Range of Penstemon clutei (Sunset Crater beardtongue) in northern Arizona. ages of sister taxa within the Penstemon clade had bootstrap values above 70%, which is the generally accepted value for moderate to strong support. The contradictory results are likely due to hybridization and/or rapid speciation among penstemons. Wolfe and her co-authors (1998) have documented hybridization among some Penstemon species and have also demonstrated that pollen-mediated gene flow occurs via hummingbird vectors. Many narrow endemics are found in extreme edaphic conditions, including recent volcanic soils (Lesica et al. 2006). Characteristic of many of these species are high population growth rates but poor dispersal rates. Their restricted ranges may in some cases be due more to recent evolution than to ecological tolerance: it may simply be the case that some species have not yet had time to spread across the landscape and may therefore be relatively young (neoendemics) (Lesica et al. 2006). Neoendemism is common in intermountain regions of western North America, and P. clutei is likely a fairly recently evolved species. Little is currently known about the ecology of P. clutei, and information in the scientific literature is sparse. It is believed to be a short-lived perennial like many other taxa in the genus Penstemon, perhaps living five to seven years on average. No long-term population studies following individual plants have been conducted to date in its natural habitat, so estimates of its longevity are purely speculative at this time. Observations in the field have suggested a link to disturbances. Prolific growth was observed following the Burnt Fire in 1973 (Goodwin 1979) and the Hochderffer Fire in 1996 (Fulé et al. 2001). It has also been observed growing in large numbers in the path left by a tornado (Crisp 1996) as well as surrounding Pinus edulis (pinyon pine) trees that were killed by drought and bark beetles in 2002-2003 (J.D. Springer, personal observations, 2008 and 2009). Phillips and others (1992) noted vigorous plants and high seedling numbers in areas of past disturbance, especially from logging operations. Plants were particularly prevalent near decaying logs and stumps. Large numbers of reproductively mature plants are also sometimes found in a ring surrounding recent Pinus ponderosa (ponderosa pine) snags (Fulé et al. 2001). Because plants had been noted to emerge in abundance following wildfire, two prescribed burning studies 165
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December 2012 Number 1 - Utah Native Plant Society

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