Calliandra eriophylla Survey in Smuggler Canyon 27 December 2013 and 2 January 2014
See Plant Species of the Borrego Desert: Fabaceae: Calliandra eriophylla, fairy duster for an introduction to this page.
This population was discovered by Florence Youngberg in 1936, and rediscovered by Franz Boschiero on 22 April 2005. This population was said to span 50 acres in 1936, with one plant to about every 200 square feet.
Our goal on 27 December 2013 was to see if the population still spanned 50 acres.
On 27 December 2013, Adrienne Ballwey, Tom Chester, Kate Harper and Frank Harris mapped the edges of the Calliandra distribution, so we could obtain the areal extent. We GPS'd individual plants along the boundary. We started with the first plant encountered on the southernmost edge of the population, and then surveyed counter-clockwise to find the edge of the distribution at every point. Binoculars were used by Kate and Adrienne to scout for more plants at the edges, and Frank climbed all over to look for more plants well outside of my path.
The only exception to this protocol was in climbing the main drainage here, where we stopped at an elevation of 3560 feet due to time constraints and the lack of a continuous population in this area. There were at least 20 plants in the drainage above this point, but they were mostly confined to the immediate vicinity of the drainage. If that continued, that location would not contribute much to the total area of the population.
No GPS points were taken inside the area defined by the edges. In most places, the interior of that area was densely covered by Calliandra.
We made a total of 164 GPS points to define the edges.
Fig. 1 gives the results of the survey.
Fig. 1. The GPS locations of the edges of the Calliandra distribution are shown as individual blue diamonds with red centers, superimposed on the topo map for this area. Red dashed lines indicate our survey routes on 27 and 20 December 2013 (20 December 2013 was the first time we saw this species). There are at least 20 plants higher up in the main drainage that were not GPS'd.
Fig. 1 shows that there is a quite well-defined area, shaped something like the country of Italy, which is mostly solid Calliandra until it suddenly ends at the edges. We spent a lot of time at the edges looking for more plants outside that area, which is how most of these points at the edge were taken.
To the north and west of that area the map shows scattered locations where the individual plants occur in clumps or lines.
The western boundary somewhat follows a contour line around the eastern side of a ridge. It is quite clear why the Calliandra population is not present in the flattish part of the ridge, which the population surrounds. That flattish part is made of big boulders, not suitable habitat for Calliandra.
The eastern edge of the population might be where the area gets too dry for the Calliandra. This population is centered on the main drainage in this area, which consists of several small drainages in its lower portion. It was noticeable in the field that the population would end before marching up to minor ridgelines to the east, with the edge of the distribution of these plants going to somewhat higher elevation in the current small drainage until the plants crossed the ridge and went into the neighboring drainage, where they were found most abundantly in the bottom of the new drainage.
Above the main population the drainage is single, and the plants were mostly, but not entirely, tightly confined to the bottom of that drainage.
Even if one considers the area as the smallest rectangle which covers all the points, and includes a few extra points to the north, that rectangle is just 0.13 miles east-west and 0.20 miles north-south, which is 17 acres, far smaller than the Youngberg / Gander estimate of 50 acres.
Possibilities for those discrepancies are:
- This population might keep going north in this drainage past where we stopped surveying, and greatly expand in area.
- There are additional populations in this area we have not yet surveyed. In particular, the drainage 0.3 to 0.4 miles to the east might harbor a second population.
- The population has significantly contracted in the 78 years since the Youngberg / Gander survey. The population is clearly sensitive to cold temperatures, and restricted to areas with more moisture here. A hard freeze and/or drought period might have killed off the plants in the most vulnerable habitat.
- Youngberg / Gander made a serious overestimate of the population areal extent at 50 acres.
We made no attempt at counting plants on 27 December 2013, but Kate Harper, Frank Harris and Tom Chester returned briefly on 2 January 2014 to count the main population. We counted three major portions of the entire distribution:
- Tom went up through the center of the main population (the area shaped a bit like Italy) from the bottom and counted all plants he could see.
- Frank hiked up to the top of the population, and counted all the plants as he hiked down the main population until he and Tom met.
- Kate counted the plants in an area to the west of the main population, after she finished surveying that area for Hibiscus denudatus. This location is by far the highest-elevation population for that species in the Borrego Desert!
Tom estimated that he could reliably see all Calliandra plants within about 50 feet, which conveniently spanned the width of the main population in its main drainage. Plants to the east, in a separate drainage, were not visible, and were not counted.
Fig. 2 gives the results of the counts for various areas.
Fig. 2. Counts of the number of Calliandra plants are shown in each of the delineated areas. The densest patches are delineated by red lines, and each has 50 plants inside the individual areas. The paths walked by Tom and Frank are shown as red dotted lines with parallel lines 50 feet on either side of their path shown in green roughly indicating how far plants could be seen and counted. The points where Kate counted plants are shown as filled dark-red diamonds. The GPS locations of the edges of the Calliandra distribution are shown as individual blue diamonds with red centers.
The densest part of the Calliandra population is at bottom. In that area, the plants were continuously distributed, and whenever Tom counted 50 plants, a red GPS point was taken so that areas with 50 plants could be indicated on this map.
Outside of those five areas outlined in red, the Calliandra population was no longer continuously distributed, but was instead patchy. As a result, counts were made for individual patches to show the patchiness of the distribution and how the population density falls off.
Frank was able to climb much higher in this survey than on 27 December 2013, and reached an elevation of 3830 feet, where the ridge flattens out somewhat. He still was able to see plants of Calliandra above that point. And whereas he counted 20 plants that could be seen in the short distance above our turnaround point near 33.02° latitude on 27 December 2013, he counted 135 plants in the green area shown in Fig. 2 on 2 January 2014!
In an area that had just three GPS points taken on 27 December 2013, Kate counted a total of 40 plants on 2 January 2014.
The total plants counted on 2 January 2014 was 539.
To get the total number of plants in the entire population, we need to make an estimate of how many plants were in the uncounted areas.
There are a total of 92 GPS points taken on 27 December 2013 in the uncounted area. The absolute minimum number of plants in the uncounted areas is thus 92, which assumes that there are no other plants in the uncounted area than the GPS'd plants, and that there is only a single plant at each GPS location. This is clearly a severe underestimate of the number of plants in the uncounted area, but gives a very firm minimum number of Calliandra plants in the total population of 539 + 92 = 631.
An upper limit to the number of plants in the uncounted area would be to assume those areas have the maximum density observed in the areas marked in red. The uncounted area is roughly the size of four of those red areas, which would correspond to 200 plants in the uncounted area. The total population would then be 539 + 200 = 739.
Another way to estimate the number of plants in the uncounted area is to assume each of the GPS points in that area has n plants associated with each point, where n is an assumed multiplier. If n=2, there would be 2*92 = 184 plants in the uncounted areas, for a total of 723 plants. If n=3, there would be 3*92 = 276 plants in the uncounted area, for a total of 815 plants.
We conclude that there is an absolute minimum of 631 plants in this Calliandra distribution, with a likely total population of 700 to 800 plants.
This total number of plants is over a factor of ten smaller than the estimate the derived from the Youngberg / Gander estimate a population size of 50 acres with one plant to about every 200 square feet. That derived estimate would be 10,000 plants! We suspect that both the numbers reported by Youngberg / Gander were just quick ballpark estimates made in the field, and have significant uncertainties. The population extent was probably overestimated significantly, perhaps by assuming how far the population continued beyond where they could see it. The plant spacing was probably estimated in the densest patches, with no account made of the large areas which have no Calliandra plants inside the boundary of the Calliandra distribution.
However, as mentioned above, there may be other reasons for the discrepancy.