Purshia Research

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PVA Model Details for Purshia subintegra (Arizona cliffrose):

The PVA was derived from demographic data gathered in both drought and non-drought years between 1996-2003 in central Arizona upper Sonoran desert for the federally endangered Arizona cliffrose (Purshia subintegra). The species is known from four disjunct populations in central Arizona, where it usually occurs on lacustrine outcrops, which have a distinct chalky white appearance (U.S. Fish & Wildlife Service 1984).  The largest population of Purshia subintegra occurs in the Verde Valley, Arizona.

Usually less than 2 m tall, P. subintegra is a long-lived xeric rosaceaeous non-clonal evergreen shrub with pale yellow flowers and entire leaves that lack glands.   Adult P. subintegra plants bloom from late March through early June (Fitts et al. 1993; Baggs & Maschinski 2000).  Seeds disperse from July through August and seed germination occurs the following spring from March through June depending upon temperature and rainfall.   In dry years, plants may not produce any viable seed and there may be no seedling recruitment (Baggs & Maschinski 2000). 

To determine the demographic patterns of P. subintegra growing in the Verde Valley, AZ, in 1996 we established 30- 4 m x 10 m plots.  We randomly selected six plots in each of four areas that span the species 5 km range within the valley and systematically selected six plots where we observed high densities of relatively young P. subintegra. Each year we classified individuals into five non-overlapping stages based on size, presence of cotyledons, and/or reproductive status (Fig. 1).  Because seeds can persist in the seed bank and germinate up to 3.5 yrs following release from reproductive adults, we included a persistent seed bank stage in the model and used mean values from the studies of Maschinski et al. (2004) to estimate seed bank parameters.

Details of model construction, matrices and elasticities are given in Tables 1-7.  Our trajectories for models derived from historic climatic conditions and scenarios of increased aridity are under consideration for publication: Joyce Maschinski, Joanne E. Baggs, Pedro F. Quintana-Ascencio, and Eric S. Menges. In Review. Using PVA to Predict the Effects of Climate Change on the Extinction Risk of an Endangered Limestone Endemic. Submitted to Conservation Biology. Correspondence related to these models should be addressed to: 
 
Joyce Maschinski
Fairchild Tropical Botanic Garden
11935 Old Cutler Rd.
Miami, FL  33156 
jmaschinski@fairchildgarden.org.
 
Fig 1 Diagram of P. subintegra life cycle and transition elements
Table 1 Details of calculations for fecundity matrix elements.
Table 2 Matrix probabilities assigned to stochastic models for precipitation patterns in the last 8 and 100 years, and scenarios of increasing aridity by 20% and 40%. 
Table 3 Life Table for Known Cohort of 1600 Seeds in Field Germination Experiment.
Table 4 Group Means for Significant Environmental and Demographic Factors.
Table 5 Total Individuals in Stage Classes in Each Year.
Table 6 Transition Matrices for 1996-1998 for Dry and Moist Sites.
Table 7 Elasticities and Lambda Values for Moist and Dry Sites for transition years 1996-2003.
 
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Last modified: Monday May 12, 2008