San Juan Island Oak a Climatic and Edaphic Summary

The conservation of Quercus garryana in San Juan County, Washington is advanced by the consideration of the ecological components of the species distribution. The project analysis is from the iNaturalist observations in the Quercus garryana Range Project and on the San Juan Islands, Washington. The Quercus garryana Range Project is a collection of over 4,700 location specific observations. This dataset is an effort to estimate the climatic boundary of Q. garryana by the climatic values of Annual Mean Temperature (AMT) and Annual Mean Precipitation (AMP). The project compiles the AMT and AMT, the geocoordinates, soil map units, and elevation. This enables mapping of Q. garryana by soil extent, elevation, and climate. These provide a foundation for ecological understanding and to assist in the conservation and recovery.

The known spatial range of Q. garryana extends from southern California at 34.553603 -118.2388 to Campbell River on Vancouver Island at 49.978311 -125.221938. Across this range the elevation of occurrence decreases to the north. The southern California maximum occurrence is 6,734 feet is limited by the height of at the mountain range elevation. In the area of the Salish Sea the elevation range is from sea level to just over 1,700 feet with the highest observation in the San Juan group at905 feet. The San Juan Island observations may be reviewed on iNaturalist. The San Juan Islands are an EPA Level 4 Ecoregion an identifiable and unique subset of the EPA Level 3 Puget Lowlands. This considered ecological habitat area provides a rational area in which to study the ecological forces that define the Q. garryana range in the Salish basin. The San Juan Island study consist of 132 observations. These observations are biased, therefor can not be used to make statistical quantitate inference. The last observed endpoints are less then the species climatic boundaries and the current best estimated limits to guide management activities.

The dataset consists of point geocoordinates provided to iNaturalist. Elevation is estimated by the Google Earth digital terrain model. The climatic variables are the primary determinates of the species range. For the first analysis the AMT and AMP are used to estimate the climatic range by ClimateNA a streaming scale-free point climate values from the PRISM 800-meter grids. The soil data is from the SoilWeb interface to the USDA-NCSS SSURGO and SATSGO Soil Survey Products. The soil map unit is an association of the floristic community and thus it provides a spatial area of the local occurrence of the oak and a predictive area for the identification of addational or potential habitat. The primary edaphic control below the climatic control is the available soil water. This is the critical resource for summer dry season survival and the point of competition with the conifers Spittlehouse (2003). The values from Soilweb are cm of water per the top 100 cm soil profile. For the analysis this is considered an ecological index number. The product of the soil water capacity and growing season precipitation are believed to provide a higher acracy model value but are not at this time analyzed. Aspect is currently not included in the dataset. This is a needed modifying parameter as the quantity of solar input has a direct impact on the plant respiration and the water budget.

The occurrence of Q. garryana is thought to be normal relative to the climatic temperature and precipitation with a mean and variance. Across the spatial range the climatic range is truncated by the mountain height in the south and sea level in the north. The competition by conifers skew distribution in the cool wet realm. Habitat islands occur within the area of ecological exclusion. The identification of these isolated populations within the conifer competition zone are needed to confirmation an extend boundary.

San Juan Oak
Three different Q. garryana habitats are identified, marine shoreline, upland, and mesic or wetlands. This broad range of habitats is a function of genetic diversity within the taxa. The marine shoreline population is evident throughout the Salish Sea and may be a function of a saline soil and a non completive solar exposure of the water side. Examples are;
the image of observation 67730282, in the Cady-Rock Outcrop complex, 5 to 30 percent slopes, Water Index 10.09, AMT AMP Coordinate 9.9, 780
and image from observation 69461554 in Cady-Rock Outcrop complex, 5 to 30 percent slopes, Water Index 10.09m, AMT AMP Coordinate 9.9, 782.
These are among the warmest, high precipitation and mid range water index oak sites with the same values with the upland sites. The median values support the assumption of a high sodium soil.

The mesic wetland populations are a surprising physiological attribute of Q. garryana. In the Willamette Valley, in the winter Q. garryana may be observed standing in flooded or hydric soil. The wet soil likely prevents healthy mycorrhizal biosymbionts with the conifers and weakens the soil foundations making them susceptible to windthrow. Q. garryana is known on San Juan Island that are on a soil complex containing a hydric soil. These oak are generally large trees with full canopies and without conifer competition. Pseudotsuga menziesii the primary conifer competitor is considered to be intolerant of flooding. Examples are the;
image of 89937587 in the Mitchellbay-Sholander-Bazal complex, 0 to 8 percent slopes, Water Index 12.75, AMT AMP Coordinate 9.7, 773,
the image of observation 89978473 in the Mitchellbay gravelly sandy loam, 5 to 15 percent slopes, Water Index 15.25, AMT AMP Coordinate 9.7, 784,
the image of observation 132106814 in the Roche-Killebrew complex, 2 to 10 percent slopes, Water Index 15.95, AMT AMP Coordinate 9.6, 748,
and the image of observation 17148083 in the Coveland-Mitchellbay complex, 2 to 15 percent slopes, Water Index 16.14, AMT AMP Coordinate 9.8, 836,
the image of observation observation in the Cady-Rock Outcrop complex, 5 to 30 percent slopes, Water Index 10.09, AMT AMP Coordinate 9.7, 776

The upland population is in a range of soil moisture capacities from to moist. The driest soil habitat restricts the establishment of conifers. At the moist end conifer competition occurs. In the San Juan Islands this is mostly Pseudotsuga menziesii, a drought tolerant taxa. In soils with a low water index Q. garryana is a dominate canopy taxa. On the wet end the conifers are able to overtop and suppress Q. garryana and prevent reproduction.
Examples are the image of observation 73906103 in the Rock Outcrop-Haro complex, 25 to 75 percent slopes, Water Index 4.01 AMT AMP Coordinate 8.1, 780,
the image of observation 84612194 in the Haro-Hiddenridge-Rock Outcrop complex, 5 to 30 percent, Water Index 4.58 AMT AMP Coordinate 9.5, 779,
the image of observation 122191671 in the Cady-Doebay-Rock Outcrop complex, 25 to 75 percent slopes, Water Index 9.85, AMT AMP Coordinate 8.1, 783,
the image of observation 129864134 in the Whidbey gravelly loam, 3 to 15 percent slopes, Water Index 8.31, AMT AMP Coordinate 9.7, 773,
the image of observation 86668737 in the Doebay-Cady-Rock Outcrop complex, 10 to 30 percent slopes, Water Index 10.91, AMT AMP Coordinate 9.4, 778,
the image of observation 109601732 in the Doebay-Morancreek complex, 5 to 25 percent slopes, Water Index 13.4, AMT AMP Coordinate 9.4, 778.

As noted seasonal precipitation and soil moisture capacity requires addational analysis. The soil water capacity is producing a range of ecological dominances, a dominate oak, a subdominant oak, and a serial oak habitats. In soil that lacks moisture to support conifers Q. garryana is a stable dominate. In soil complexes of mixed moisture capacities a mosaic of Q. garryana and P. menziesii may exist with a dynamic changes in composition with climatic cycles but with separation of the two taxa.

Soil Map Unit----------------------------------------------------------------------- Water Capacity----Hydric Soil

Beaches-Endoaquents, tidal-Xerorthents association, 0 to 5 percent slopes---2.25----------------Complex
Rock Outcrop-Haro complex, 25 to 75 percent slopes---------------------------4.01
Haro-Hiddenridge-Rock Outcrop complex, 5 to 30 percent slopes-------------4.58
Haro-Hiddenridge-Rock Outcrop complex, 25 to 75 percent slopes------------4.58
San Juan sandy loam, 5 to 20 percent slopes-------------------------------------6.91
Whidbey gravelly loam, 3 to 15 percent slopes-----------------------------------8.31
Sucia-Sholander complex, 5 to 20 percent slopes--------------------------------8.73
Cady-Doebay-Rock Outcrop complex, 25 to 75 percent slopes-----------------9.58
Cady-Rock Outcrop complex, 5 to 30 percent slopes---------------------------10.09
Doebay-Cady-Rock Outcrop complex, 10 to 30 percent slopes----------------10.91
Doebay, moist-Cady-Rock Outcrop complex, 10 to 30 percent slopes --------10.91
Doebay, moist-Cady-Doebay complex, 25 to 75 percent slopes---------------11.26
Pilepoint loam, 2 to 8 percent slopes---------------------------------------------11.35
Mitchellbay-Sholander-Bazal complex, 0 to 8 percent slopes------------------12.75---------------Complex
Doebay-Morancreek complex, 5 to 25 percent slopes--------------------------13.4
Roche-Killebrew-Rock Outcrop complex, 5 to 35 percent slopes--------------14.59
Mitchellbay-Rock Outcrop-Killebrew complex, 3 to 15 percent slopes--------14.84
Roche-Killebrew complex, 2 to 10 percent slopes-------------------------------15.95---------------Complex
Mitchellbay gravelly sandy loam, 0 to 5 percent slopes------------------------16.05---------------Complex
Coveland-Mitchellbay complex, 2 to 15 percent slopes-------------------------16.14---------------Complex

Quercus garryana Climatic Range

AMT Range 17.4 - 6.1 Celsius --------------63.3 - 42.9 Fahrenheit
AMP Range 4130 - 264 mm---------------162.6 - 10.4 inch

San Juan Island Climatic Range

AMT Range 10.52 - 9.6 Celsius------------50.93 - 49.28 Fahrenheit
AMP Range 781 - 593 mm-------------------30.7 - 23.3 inch

The known MAT endpoints of Q. garryana is 16.4 C and 6.1 C, a range of 10.3 dC (61.5 dF to 43.0 dF.) Q. garryana is able to occupy any habitat between the hot and cold temperature boundaries. The MAP difference likewise is significant. Annual precipitation endpoints are 4,130 and 264 millimeters. This is an astounding 12.7 feet to 10.4 inches of annual precipitation. The high precipitation value is not an outlier as other high precipitation observations are similar but lower. This high value is a condition of high elevation winter precipitation and fast runoff on steep slopes. The growing season water that is mostly the soil water. The trees at the lower precipitation boundary are likely limited by heat stress and limited precipitation.

The lower value of AMP may require the removal of the obvious ground water hydration. For this reason future analysis requires a classification of Q. garryana as trees that supported by the climatic precipitation and those that are supported by groundwater. A clear example of groundwater supported oak is observation. This oak is riparian on the bank of the Deschutes River at a 10.9 C and 279 mm AMT AMP coordinate, terrain a vegetative community of sagebrush and grass. The San Juan Islands are completely within the zone of climatic precipitation.
Q. garryana occupies a precipitation niche on the east Cascade slope with and below Pinus ponderosa. The generally excepted limit for P. ponderosa is 16 inches MAP. This identifies the Q. garryana limit as less than Ps. menziesii's the 23 inch San Juan MAP but more then the P. ponderosa limit. Riparian Q. garryana in the east Cascades lower canyons are able to thrive at the MATs but observations suggest the MAP is above 280mm. It is suspected that a climatic decrease in the local summer precipitation or an increase in the MAT may have a negative impact on P. menziesii by increasing the mortality and fire vulnerability.

The San Juan Island Q. garryana are at the cooler end of the AMT range. It is unknown where the cold endpoint is within the islands. It is higher then 1000 feet but not known if it extents to the height of Mt. Constitution. The highest known local elevation of Q. garryana is on Mt. Tuam on Saltspring Island at 1727 feet. The high point of Mount Constitution is 2400 feet. This is an elevation that suggests the topographic range is adequate for a endpoint to be expressed. The known cold end point MAT is at high 5785 foot elevation in the Oregon Cascades. This Oregon Cascade Q. garryana occurrence is restricted to an isolated narrow rock habitats with southern exposure. This indicates that Q. garryana could be found at higher elevations in the islands but observations are lacking for establishing an end point. The wetter higher island locations may not provide competitive niches for Q. garryana.

Also of importance to the management of Q. garryana habitat and a second result of the climatic and edaphic variables is the associated vegetative associations. These are partly visible in the examples of the upland and mesic habitat. Future work should be undertaken to access the association structures as defined by Chappell 2004 and Buechling 2008. Chappell's work was conducted in the Puget Basin and is the first resource for the San Juan Islands. Buechling's work was conducted in the Willamette Valley and is complimentary to the San Juan environment. The upland and mesic observations demonstrate vegetative changes with the soil water capacity.

Posted by carexobnupta carexobnupta, September 29, 2022 05:40 PM