The 2016 Bruce Watts Census of Boechera johnstonii, Johnston's rock cress
Bruce Watts and Tom Chester
Table of Contents
Introduction
Bruce began studying the flora of Garner Valley intensely in 2015, visiting it for at least a few hours on most days. He encountered his first plant of Boechera johnstonii in bloom on 1 April 2015, and immediately started counting the number of plants he saw, since this is one of our rarest species at San Jacinto Mountain. He counted 46 plants in bloom that day, and exactly 99 plants in bloom the next day, all on the northwest-facing slope of the "plateau" just east of Quinn Flat except for five plants in a little pen across the street from the entrance to the Kenworthy Forest Service entrance road.
In May 2015, he found his first Penstemon californicus in bloom, and began surveying for it in Garner Valley. He encountered what he thought was probably Boechera johnstonii a number of times during that survey, and became curious about its exact distribution. Accordingly, he planned on doing a full survey for B. johnstonii in 2016, and decided to count every plant he saw in bloom to give a reliable count for the entire population of this species.
Plants of Boechera johnstonii and Penstemon californicus are difficult to distinguish when not in bloom or fruit, and young plants of Eriogonum wrightii are also similar. In contrast, plants in bloom of these species are easy to distinguish at a glance from a standing position. Hence surveying for plants in bloom is by far the most reliable way to census the population. Fortunately, it appears that essentially all plants of Boechera johnstonii bloomed in 2016, so his 2016 census is also highly complete.
Bruce asked Tom to come near the end of his surveys to GPS the populations he found so that we could create a good map of the entire population.
In 2016, Bruce encountered the first plant of Boechera johnstonii in bloom on 15 February, and began intensive surveys for it a month later, on 13 March. B. johnstonii is one of the very first plant species to bloom, with a distinctive purple color that made it easy to spot in the first month of his surveys.
Bruce censused the Garner Valley population on 13, 18, 20, 21, 23, 26, 27 and 30 March, and 2, 4, and 9 April, counting 3,339 plants in bloom. He visited some patches multiple times to catch them at peak bloom, but never counted any plant twice in the multiple surveys. On each visit, Bruce was very methodical in counting each patch, dividing each patch into smaller patches delineated by his hiking sticks, logs or other reference points, to make sure no plant was counted twice.
He also surveyed all areas near the Valley Floor "in between" the patches he found, finding no B. johnstonii plants there, which is just as important a result as the areas where he found them.
On 4 April 2016, Tom accompanied Bruce in visiting each patch of Boechera johnstonii he found, taking GPS points at Bruce's direction. The GPS points are mostly the vertices of a polygon enclosing each patch. Bruce was intimately familiar with each patch, and so directed us around the perimeter of each patch, where Tom recorded GPS points at the location of the plants that were on the perimeter. I.e., every GPS point corresponds to at least one B. johnstonii plant, but plants inside the perimeters were not individually GPS'd, just counted previously by Bruce.
Some small patches only have a single GPS point at the location of the plants.
Bruce's summary of his field notes are given below, with the GPS point numbers attached to each patch. Some patches that Bruce divided into smaller patches were combined into a large patch; this is noted below when it occurred.
Census Maps
Fig. 1 shows the entire population extent of B. johnstonii in Garner Valley, including at the top of Old Morris Ranch Road. Fig. 2 shows a portion of the "Plateau" population just east of Quinn Flat.
Fig. 1. The entire population extent of B. johnstonii in Garner Valley overlain on a Google Earth image. The pink filled circles each represent a GPS point corresponding to at least one plant of B. johnstonii. Click on the picture for a larger version.
Fig. 2. A portion of the "Plateau" population of B. johnstonii in Garner Valley overlain on a Google Earth image, as viewed from the west, looking to the east. The population is almost entirely confined to the northwest facing slope of the Plateau, which is made of the remnant Bautista Formation. Click on the picture for a larger version.
Fig. 3 shows two different views of the population in the area of the PCT in the Little Desert Peak area, which is just east of the top of the Cedar Spring Trail junction with the PCT.
|
|
| Fig. 3. Top: View looking north at the Boechera johnstonii population in the Little Desert Peak area. The pink filled circles represent a GPS point corresponding to at least one plant of B. johnstonii. The blue tracks show our survey routes in this area; tracks with no pink filled circles had no B. johnstonii observed. Bottom: View looking to the west of just the points on Little Desert Peak. Click on the pictures for larger versions. |