Minor Trees Part I: Riparian

I’ve been dealing with many of our more notable trees singly and in what some might call excessive depth (did I really need to discuss French fables, Classical Greek sculpture, and Japanese animation to express my deep interest in the valley oak? Well, yes, of course I did). But we have some trees that on account of their limited local presence or modest proportions just don’t seem to demand so many words of me right now. Today, I’ll cover the riparian, or streamside, trees of Novato and Northeast Marin – a group of species that have a relatively light presence in our area due to our scarcity of watercourses that both run year-round and survive in undisturbed natural form. In an follow-up Minor Trees Part II, I cover a few smaller tree species that are just too little to get the full-scale treatment, as well as other notable native shrubs.

Minor Riparian Trees

The following trees belong to a habitat known as riparian (ripa = Latin for riverbank), a habitat with which we are not overly blessed due to the combined forces of climate and topography (we have relatively few watercourses with year-round waterflow) and urbanization (we have built or paved over a good chunk of Novato Creek, as well as our more minor streams, and private property limits easy access to much of the remainder). Many of the smaller creeks running through our public lands are bordered by our generalists who can survive our dry summers: bays, buckeyes, and live oaks. Sunny but damp areas including creeksides, edges of freshwater ponds, and roadside ditches often host willows, who will get a full length treatment someday. But first, let’s take a look at the four trees below that have only a limited local presence and are always found near water.

Bigleaf Maple, Acer macrophyllum

This species, our only real maple tree, is unmistakable, with classic maple-shaped leaves that are deeply and geometrically lobed in a palmate pattern and seeds that are borne in two-winged, helicoptering samaras. This is a truly fine tree – both the biggest-leafed and tallest maple in North America – that richly deserves a lengthy encomium, which I will pen sometime in September or so when their lovely leaves turn to gold and drift down in the cool breeze of autumnal twilight. Marin County as a whole has plenty of fine maples along creeks at Point Reyes or Mount Tam, where the water is reliable and the shade is significant.

Here in Novato, however, it’s mostly too hot and our waterways too dry to support a robust maple population. Our best public patch of big-leafs is found at Ignacio Valley Open Space Preserve, on the short Buck Gulch Waterfall Trail at the end of Fairway Dr. They line an early section of the creek, and even if you visit in the leafless midwinter waterfall season, you can still recognize them by their opposite twig pattern, thinly striated gray bark, lingering two-winged samaras, and by the classic maple leaves littering the ground.

There are also several more scattered fine trees in the lower portions of Indian Tree Open Space Preserve as you ascend from the shady creekside redwood grove on the Deer Camp Trail. And as far as I have ascertained at this point, there is a single good-sized tree in Indian Valley Open Space on the Witzel Trail, though you’d think that tree might have some cousins or nephews somewhere in the vicinity. I expect that some of the other deeper, shadier canyons held privately and off limits to the walking public on the north side of Big Rock Ridge also host some maples and redwoods.

Box Elder, Acer negundo

This is a relative of the maple, though the leaves are quite different, comprised of three or five lobed leaflets. If you see the seeds, also borne in winged pairs called samaras, show the maple relation more clearly. Around here, box elders are mostly a smaller and less conspicuous tree than the mighty maple, and locally less common.

The Marin Flora assures me they are somewhere in Ignacio, but I haven’t found them yet. They are easily overlooked and I haven’t made a concerted effort to locate them, though now that I’m writing this I think I shall have to do so. They’re probably here somewhere. I have seen them just over the ridge to the south, along Miller Creek in Terra Linda, where they join in with the next-listed Oregon Ash under the tall and stately next-next-listed White Alders. (I consider Miller Creek part of my valid home territory, on account of it fitting within the 10-mile bike journey radius of my Thoreauvian Big Year and on account of my being born, ignoring the pedantic detail of the hospital, within a 1-mile stroller journey of these trees.)

Oregon Ash, Fraxinus latifolia

The noble ashes comprise one of the fine old families of the northern hemisphere arboreal tradition. When Little John had that scuffle with Robin Hood on that skinny bridge, for instance, I imagine him doing so with a staff of ash. I have some basis for this statement (not actually evidence, but something to take it out of the realm of pure wishful thinking) in this random phrase from some obscure book called Plaine Percevall quoted by the OED to give context to the word “quarterstaff”:

Plodding through Aldersgate, all armed as I was, with a quarter Ashe staffe on my shoulder

Here, we have a minor member of the family, the Oregon Ash. They may often be fairly small here, but they still illustrate the basic pattern of the ash family, which you can then practice on a few more commonly seen ornamentals. Most immediately obvious is the fact that ashes have pinnately compound leaves, a rare pattern in these parts, with many pointed leaflets arranged along a central axis like a feather (pinna in Latin). You can see a few in that same place along Miller Creek (walk on Old Lucas Valley Road, now an Open Space fire road), along the scattered bits and pieces of upper Novato Creek which are kind of intact and accessible (Stafford Lake Park above the lake, the bit of O’Hair Park where the bike path to Stafford Lake goes inland from the road and borders the creek, the tiny Lee Garner Park by the library), and according to the Flora, on the privately owned lands around San Antonio Creek on the northern Marin border.

White Alder, Alnus rhombifolia

Like the maple, the white alder is another fine and stately tree with which the county is quite well provided along our more sizeable watercourses to the south and west (we also have red alders close to the coast). Some of the most numerous and accessible can be seen around Samuel P. Taylor State Park (along with maples) and the Cross Marin Trail along Lagunitas Creek. Here again, I must confess that I have yet to find any in Novato proper, and I am forced to refer you once more to Miller Creek and the Old Lucas Valley Road.

But why not go there? I am not so provincial that I will deny you the pleasures of a nice January bike circuit to Las Gallinas to look at ducks and then a quick pop a mile up Lucas Valley Road to see the flourishing golden drapery of alders in bloom. Their flowers and fruiting bodies provide useful clues to identification: males flowers emerge in dropping catkins before the trees produce their simple, double-toothed leaves, while low-key female flowers develop woody cones that then persist on the tree after dispersing their seeds. If you see those little cones, it’s an alder!