The 7 Oaks of Mount Lemmon

Some Arizona Oaks after Vol. 27, J. of the Arizona-Nevada Academy of Science. Click on image to see more clearly

 As a biologist I have a a background in both botany and zoology. In the forest behind our house in Germany I could have named any flower or tree with both botanical and popular names. Here in Arizona I still often don't get past the family or if I'm lucky the genus of trees and herbs, while learning much more about bugs, herps, birds and mammals of the area. But the plant societies form the basis for most of the ecological niches that animals live in.
Understanding and often even identification of many insects in particular depends on knowledge of their host plants.
For the last couple of months I have been on a quest to collect and photograph local caterpillars. By June, most herbaceous food plants in the lower desert are drying up, but the oaks of high elevations are still a good place to look. There are so many species here! Arizona Flora by Thomas H. Keraney (University of California Press) gives a key to 12 Arizona species.

Yesterday botanist Bob Schmalzel took Charlie O'Brien and me on a tour of Mt Lemmon to teach us how to recognize and find 7 of the species along Catalina Highway. It was a beautiful day: Driving up the mountain, we enjoyed gorgeous views, steadily falling temperatures, deep forest greens (I miss those!), soft gopher churned soil under our feet, the sweet song of solitary thrushes, the aromatic smell (and loads of pollen) of pine and fir trees. I wanted to stay up there!

Mexican Blue Oak, Quercus oblongifolia

But back to learning about oaks:  Impressive Mexican Blue Oaks (Quercus oblongifolia) can be found quite low in Molino Basin where the little creek runs most of the year. The mature leaves are oval with a squared base, leathery and waxy. This gives the tree its typical blue-gray color. Mexican Blue Oaks keep their leaves during the winter. Like many wintergreen trees, their frost-hardiness is limited and during the cold spell of Jan. 2011 there was concern that we would lose this tree that reaches its northern most extension here in Arizona.

Q. oblongifolia with fresh leaves in April

When I hiked Brown Canyon in the Baboquivaries in early April, fresh leaves were just growing, giving the oaks a gold-bronze hue. In years of (even greater) drought,  the trees can delay leafing out and stand bare until the first heavy monsoon storms arrive. They are drought deciduous. Mexican Oaks bloom in April and the acorns ripen in December. Q. oblongifolia grows in the lower elevations, the foothills.

Emory Oak, Quercus emoryi with young acorns in June

Oaks with very dark trunks and glossy, spiky green leaves can be found around the Picnic tables at Molino Basin and genarally occupy sunnier, drier spots half way up the Catalina Mts. These are Emory Oaks. Many on the Catalina slopes were only brush sized, but old specimens can be big trees with weeping branches. Like the Mexican Blue Oaks, Emorys are marcescent, not dropping dead leaves until spring when they also bloom. Their acorn production is very quick: the acorns are ripe in July/August. Local Apache women still watch eagerly for the right time to collect the bounty of nutritious, low tannin fruit. Even though they are now falling out of favor like other traditional foods, Emory acorns used to be a very important staple for the Apache tribes.

Arizona Oak, Quercus arizonica/grisea

Higher up the mountain the road crosses the elevation where Arizona Cypress grows in shady canyons along boulder rich streams. Just above this area we stopped at  Middle Bear to see three more species of oaks: The Arizona Oak resembles Emory's somewhat but seems to like cooler, moister places in a forest setting among Alligator Juniper, Cherries, Walnuts and the first pines. Like Emory's Oak leaves Arizona Oak leaves are a little spiky, but not glossy, softer and greyish green. The best character to immediately tell them from Emory's is the light grey trunk. In Bob's notes it says Q. arizonica is subsumed now into Q. grisea.

Net-leaf Oak, Quercus rugosa/reticulata

Also at Middle Bear, the small bushy Net-leaf Oak, Quercus rugosa/reticulata has rounded irregular leaves, sculpted by a net of prominent veins and fuzzy with golden hairs on the underside. Young acorns were protruding from the branches on petioles that were several inches long. Bob pointed out that the leaf size is extremely variable and can reach hand-size. I imagine that this is an adaption to this oak's preference for shady, wet canyons and north facing slopes.

Silverleaf Oak, Quercus hypoleucoides

Silverleaf Oak with their narrow, willow-like leaves that are surprisingly thick and leathery, dominate the slopes from Middle Bear to just under 8000 feet. In cool, wet Madera Canyon in the Santa Ritas, their reign begins much lower. Silverleaf Oaks and Emory's Oak are the only Black Oaks of the Southwest. Malacosoma caterpillars seem to understand this relationship better than I do and freely wander from one species to the other.

Lophocampa mixta and a tentatively identified Punkie, Meganola sp. on Silverleaf Oak

 Since it got warm Silverleaf Oaks yield by far the most divers insect population: Weevils, Ants, Flea beetles, other Leaf Beetles, Jumping Spiders, Tree Hoppers, Mirids, Ladybugs, and in some years Clicking Cicadas tumble into the beating sheet when I tap the branches. This time there were also some very interesting hairy caterpillars.    .

Quercus chrysolepis

 A few specimens of a small bushy oak with tiny holly-shaped leaves grow in the slopes around San Pedro Vista. The leaves are covered on both sides with golden hairs. There are two closely related species that are both considered as very primitive oaks: Q. palmeri and Q. chrysolepis (no common name) the Catalina population seems to belong to Q. chrysolepis which develops acorns  whose cup are hugging the fruit as opposed to the flat saucer-like ones of Q. palmeri.

Gambel's Oak, Quercus gambelii

The only oak that really looks like a classic oak to European eyes, the Gambel's Oak, belongs to the White Oaks. It is the only winter-deciduous oak on Mt Lemmon, meaning it stands bare through the winter. Its large lobed leaves are more leathery than its Northern European relative's, but softer and thinner that those of the non-deciduous live oaks. Accordingly, it lives in elevations above 6000 feet, together with Black locust, Aspen, Maple and conifers, where the winters are cold, stormy and snow-rich  and the summers are cool and pleasant.

 

Poison Oak/Ivy, Rhus radicans

Poison Oak, or Ivy as it is called here, is of course no real oak at all, but it shares the habitat of the shade and moisture loving ones, so we ran into this nicely blooming plant while looking for caterpillars on Gambel's Oak. Poison Oak is in the Sumac or Cashew Family and contains oils that can cause skin eruptions. Its leaves are compounds of three leaflets.

 Abert's Squirrel, Sciurus aberti

This guy was waiting for all those acorns at Marshall Gulch. In German, squirrels are called Eichhoernchen because of their love for the fruits (Eicheln) of oaks (Eichen). He may be in luck, so far it looks like a year of rich crops in the highly variable annual production of the Mt Lemmon oaks.