Short Communication |
Corresponding author: Tyler M. Dvorak ( tdvorak@catalinaconservancy.org ) Academic editor: Pavel Stoev
© 2016 Tyler M. Dvorak, Amy E. Catalano, C. Matt Guilliams.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Dvorak TM, Catalano AE, Guilliams CM (2016) Monitoring within non-native ungulate exclosures documents the inherent size of Crocanthemum greenei (Cistaceae). PhytoKeys 70: 11-16. https://doi.org/10.3897/phytokeys.70.9363
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Crocanthemum greenei (B.L.Rob.) Sorrie (Cistaceae), a perennial sub-shrub, was measured as part of a demographic monitoring effort on Santa Catalina Island, California, USA (hereafter, Catalina). Introduced ungulate browsers remain present on Catalina. Consequently, many palatable plant taxa on the island are subject to and putatively limited by top-down browsing forces. Historically, introduced ungulates have also been present on each island throughout the range of C. greenei. Habitat conservation work, resulting in the construction of ungulate exclosures on Catalina, has now allowed us to measure individuals in their mature, non-browsed form. The published value for C. greenei stem (height) is usually 15–30 cm. While the original description hints at a greater potential size, recent descriptions appear to be influenced by observations made during the decades when plants would have been impacted by introduced ungulate herbivores. Here we present stem measurements of 81 adult individuals, with a median of 49 cm and an interquartile range of 42–56 cm. These measurements suggest an expanded stem (height) range of 15–60 cm better describes the taxon and shed light on the historical impacts of invasive ungulates across the islands and those continuing on Catalina.
Cistaceae , Crocanthemum greenei , Helianthemum , Santa Catalina Island, stem measurement
Crocanthemum greenei (B.L.Rob.) Sorrie (Cistaceae) is a perennial sub-shrub endemic to the Channel Islands of southern California. It is currently known from Santa Catalina (hereafter, Catalina), Santa Cruz, and Santa Rosa islands. It was also documented on San Miguel Island, but is now considered extirpated from that locale (
A number of ungulate exclosures were constructed from 2008–2011 and have been maintained on Catalina for habitat recovery following wildfires and for focused conservation of select plant taxa. Crocanthemum greenei is present within six of these exclosures. We monitored 81 mature individuals within the exclosures as part of an overall island-wide demographic monitoring and study effort that is underway for the species. We measured the main stem of each plant as part of our monitoring protocol. All individuals were measured with a standardized method by the same researcher (A.E.C). A measuring tape was stretched from the base of the main stem to its tallest point, excluding the inflorescence. Photographs were taken of every individual with a standard ruler held or leaning next to the plant for scale (Fig.
Crocanthemum greenei stem height measurements within exclosures (n = 81) had a range of 29 cm to 68 cm (Fig.
Our measurement data show that C. greenei may grow substantially taller than previously reported in the absence of browsing by introduced ungulates. Furthermore, during our monitoring efforts we have consistently documented individuals outside of exclosures exhibiting severely browsed growth forms (Fig.
Crocanthemum greenei was first recognized as distinct from co-occurring Crocanthemum scoparium (Nutt.) Millsp. by Edward L. Greene in 1886. Greene named the new species from Santa Cruz Island Helianthemum occidentale Greene, but this name was already in use for a European plant (H. occidentale Nyman) and was therefore an illegitimate homonym. Regardless, Greene described the new species as suffrutescent, “a foot or more high”, and as having an inflorescence densely covered with glandular-viscid hairs; this latter feature distinguished it from H. scoparium, which is glabrous or with sparse short-glandular hairs. In his Flora of North America treatment of Helianthemum,
Since the original description of the species was made on the basis of plants collected on Santa Cruz Island, the primary ungulate impacts relative to those plants would have come from sheep. The first record of sheep introduction on Santa Cruz Island was in the mid-1850s and the first effects on the vegetation due to grazing were reported in 1875 (
Recent conservation and restoration efforts on the Channel Islands have eradicated ungulates from Santa Rosa and Santa Cruz islands, and resulted in actions on Catalina Island including the creation of exclosure habitats where our measurements of C. greenei were made. With browsing pressure removed in some portions of the historical range of C. greenei, individuals of the species can now grow to reach their full, inherent size. Beyond initiating a revision of the morphological description of C. greenei, we hope that these observations are suggestive of both the capacity for recovery of a rare, island-endemic plant and the continuing need to remove the remaining ungulates from its range, which would bring to completion a critical conservation action for the Channel Islands archipelago.
We thank all of those involved with exclosure construction and maintenance on Catalina over the years. Funding was provided by U.S. Fish and Wildlife Service (Grant # F10AC00790), Seaver Institute, and Marisla Foundation.