Upper Columbia Basin Network aspen monitoring report 2008-2012: City of Rocks National Reserve (CIRO)

Strand, Eva; Bunting, Stephen; Nahorniak, Matthew; Stracervich, Leigh

The Upper Columbia Basin Network (UCBN) has identified 14 priority vital signs, indicators of ecosystem health. Quaking aspen is one particularly high priority vital sign for two UCBN parks, City of Rocks National Reserve (CIRO) and Craters of the Moon National Monument and Preserve (CRMO). Aspen is a focal resource at CIRO and CRMO because of its biological and aesthetic significance. Although aspen comprise only a small percentage of the land cover in the parks, the community type contributes significantly to species diversity and richness. In addition, current observations of aspen decline and die-off in the western states are of concern to natural resource managers and scientists. The sampling design for aspen is divided into three sampling panels. Panel 1 consists of aspen stands in CRMO while panel 2 and 3 consist of aspen stands in CIRO. Panel 1 was sampled in 2007 and the 21 stands with 102 plots were re-sampled in 2010. Panel 2, consisting of 77 plots in 15 stands in CIRO, was sampled in 2008 and re-sampled in 2011, while panel 3 consisting of 45 plots in 9 stands in CIRO was sampled in 2009 and re-sampled in 2012. Details regarding the sampling in CRMO 2007-2010 can be found in Strand et al. (2011) while sampling in CIRO in 2008, 2009 and 2011 is described in Strand and Bunting (2009, 2010, 2012). During the field seasons 2008-2009 and 2011-2012 in CIRO, 122 plots in 23 stands were common to both field seasons. One stand was added in 2012 (Stand #13). Only plots sampled in both sampling periods were included in the statistical analysis. The vital signs aspen monitoring protocol (Strand et al. 2009) was approved in September 2009. The methods presented in this report reflect version 1.0 of the protocol. The majority of the aspen stands sampled in CIRO in 2011-2012 are suckering, regenerating and contain a distribution of age classes. The regeneration in stand #24 is low (119 stems/ha), a few stands have a relatively low mature aspen stem density, and some stands contain conifer species of all size classes. Stand #6, #9, #37, #72, and #73 have mature aspen stem counts lower than 350 stems/ha. The suckering and regeneration in these stands is however above average, with regeneration higher than 1000 stems/ha, which has been recommended by Bartos and Campbell (1998) as a threshold for an aspen stand with adequate regeneration. A drastic change in suckering occurred in stand #33 with an increase in aspen size class I from 2,188 stems/ha in 2008 to 66,513 stems/ha in 2011. In stands #6, #37, #43, #56, and #57, conifer species are present in all live size classes. In stand #37 the mature aspen and conifer count are at the same level, 249 stems/ha. This change detection analysis of data from 2008-2009 and 2011-2012 examines a step trend change rather than a linear trend since data from only two time periods are currently available. As more monitoring data become available, more complex models will be applied. This step trend analysis tested for change in stem counts within tree size categories for aspen and conifers. A statistically significant increase in aspen regeneration, mature trees and dead trees from 2008-2009 to 2011-2012 was observed (P<0.05), and no difference was detected for suckers. A statistically significant increase in conifer seedlings (< 0.52 cm tall) was also detected (P<0.05), however no change was detected for the larger conifer size classes. While stands may be considered somewhat independent within the park, they are not independent in terms of time, thus any assessment of the long-term trend is based on only two points in time for each site, and four calendar years total for all data. Additional sampling data will help determine whether such temporal differences are indicative of long-term trends. The next sampling period is scheduled for 2015 in CRMO and 2016-2017 in CIRO.

Upper Columbia Basin Network aspen monitoring report 2008-2012: City of Rocks National Reserve (CIRO)

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