Plant Species of San Jacinto Mountain:
Distribution of Jeffrey pine, Pinus jeffreyi and ponderosa pine, P. ponderosa
Distribution of Jeffrey pine, Pinus jeffreyi and ponderosa pine, P. ponderosa
Fig. 1. Distribution of ponderosa pine (green diamonds) and Jeffrey pine (blue diamonds) in the Dark Canyon (north fork San Jacinto River) area, from a Google Earth view of San Jacinto Mountain from the west (the viewing direction is toward the east). Note that in Dark Canyon itself, in the center of the picture, the two species separate cleanly on elevation. But in the Stone Creek Campground / lower Sawmill Road area, on the right of the picture, some Jeffreys occur at lower elevation, within the ponderosa population. See elevation vs. longitude plot below.
Click on the picture for a larger version with labels.
This page discusses and shows maps of the distribution at San Jacinto Mountain for these species.
See Plants of Southern California: Pinus jeffreyi and P. ponderosa var. pacifica for much more information about these two species, and a discussion of how to identify them, and a map of their distribution on the Ernie Maxwell and Devils Slide Trails.
We have found ponderosa pine only on the west side of San Jacinto Mountain, from a bit south of Idyllwild on the south to the James Reserve on the north. The distribution we have found is consistent with the much-lower resolution map shown in Minnich and Everett, Conifer Tree Distributions in Southern California, published in Madroño 48: 177-197, 2001.
In fact, surprisingly, despite the small areal coverage of our surveys at elevations below 6500 feet, the Minnich and Everett map does not seem to show any additional areas containing ponderosa pine. (We can't place their locations precisely on our map since the entire area shown in our map is only 2-3 mm long in their printed map, which shows all of southern California.) Of course, there are more ponderosa pines surrounding each of the areas shown in our map; our map is incomplete in the extent of ponderosa pine distribution in each of the plotted areas.
That our map nearly shows all the major areas containing ponderosa pine is almost too hard to believe, due to our low sampling of the lower-elevation areas where it lives. However, since the Minnich and Everett map was made from aerial photography of the entire area, their map should show the complete distribution of these pines.
The following maps shown every location where we have found ponderosa pine and digitized its location, with an identically-sized map giving locations for Jeffrey pine:
| Jeffrey pine | ponderosa pine | |
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Fig. 2. Map of distribution of Jeffrey pine (left) and ponderosa pine (right)
Click on the maps to show a larger area with all of our digitized P. jeffreyi locations, or to place the P. ponderosa locations in context of a larger area.
Most areas without a location for either species have not been mapped, although some of them in fact do not contain either species. In particular, we have surveyed along SR74 from Garner Valley to SR243, and all of SR243.
In general, locations are GPS points made for specific plants of each species, but some points were derived from observations, without specific locations, made for the plant guides for those trails. These points are generally simply regularly spaced along those trails in locations where each of those species was found; such points are easily picked out on the map.
The following plots show the locations of the two species on the same map, but without the topography and landmarks, on the left; a plot of elevation versus longitude is on the right:
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Fig. 3. Distribution of ponderosa pine (filled pink squares)) and Jeffrey pine (filled blue diamonds) plotted in map view (left) and as elevation vs. longitude (right).
For GPS points, the elevations are from GPS measurements in the field and could be off by up to 100 feet. The elevations of points placed from field observations without GPS points were derived automatically from National Geographic Topo Software, and could also be off by up to 100 feet.
The distribution of these two species is not a simple pattern in geographic area nor in elevation, except for the following:
- only Jeffreys are found above ~6800 feet.
- only Jeffreys are found in the Mountain Center / Garner Valley area on the south side of San Jacinto Mountain below 5000 feet.
- only ponderosas are found in the Dark Canyon / North Fork of the San Jacinto River drainage below about 6800 feet.
- essentially only ponderosas are found below 5800 feet on the west side of San Jacinto Mountain north of Idyllwild.
The two species are both found at mid-elevations of 5000 to 6800 feet, although they often separate by habitat. Only Jeffreys have been found on sharp ridges so far. Ponderosas are found in flatter areas, drainages and on east-facing slopes, sometimes with Jeffreys and often without Jeffreys in the same area. The area where the two species are found in close proximity is small.
Jeffreys are much more widespread than Ponderosa pine, covering much of the high country above 6800 feet, and are found below 5000 feet continuously from Mountain Center down to Garner Valley, throughout Garner Valley along SR74, to the eastern limit of my survey just east of SR371.
It seems contradictory that only Jeffreys are found above 6800 feet and below 5000 feet. The explanation for the presence of Jeffreys below 5000 feet appears to be that they are confined to moist places. We speculate that normally Jeffreys can't live at lower elevation due to a combination of the hotter climate and less rainfall. But in moist places, it can overcome the hotter climate.
Note that this is completely at odds with the conventional wisdom that wetter areas favor ponderosas! We had previously found that the conventional wisdom about the distribution of ponderosas was also incorrect in the San Gabriel Mountains; see our article in The Paintbrush, CNPS San Gabriel Mountains Chapter, Winter 2015, 32:1 (download PDF).
The Jeffrey locations at 4500 feet elevation are in Garner Valley, with its famous inverted tree distribution, with trees growing on the valley floor, but not at higher elevations above it on either the north-facing or south-facing slopes until much higher elevations. (They are found in the drainage along SR74 northwest of Garner Valley above Lake Hemet, a moist area.)
These observations seem to imply that the Jeffrey pines in Garner Valley do not appear preferentially in Garner Valley for any reason other than there is enough water to support their growth. I.e., they do not just appear in the coldest parts of Garner Valley, so low temperatures do not appear to be the major factor in their distribution.
It is a mystery to us why there are no ponderosa pines in Garner Valley.
The best areas to see the two species in close proximity are:
- The Stone Creek Trail / Upper Sawmill Road, which has the two species interspersed throughout. This is probably the best place to study them, since both species are seen repeatedly along the route.
- The area immediately west of the northernmost parking lot in Idyllwild Park, just south of SR243. In this area, only ponderosas are found south of the parking lot, and only Jeffries are found to the north. Both species occur together in the immediate vicinity of the parking lot.
- Along the access road to the South Ridge Trail.
We thank Keir Morse, Mike Crouse, Frank Harris, Bob Smith and Elize Van Zandt for help with the field surveys, and Keir Morse for making a suggestion that resulted in the Google Earth Map in Fig. 1.