Nature Watch: Life at the Top

Author: Steve Ellis | 10/31/24
       

About the author: Steve Ellis is a naturalist and Land Trust member who enjoys sharing his love of the natural world. His blog series, “Nature Watch,” will appear each month in “Habitchat,” chronicling native plants and wildlife you can expect to see during that particular time of year. We thank Steve for sharing his passion, illustrating the importance of island conservation.

What lives at the top of the forests? Photo by Martha Ellis.

Overview

There’s a habitat on our islands that is as mysterious as the ocean floor. Few of us have explored life at the top of the forests.

Local forests consist of four general levels: ground cover, understory, canopy, and emergent layer.

The canopy is the wealth of foliage found on the upper portions of the forest. Above the canopy is the emergent layer, consisting of those trees that are outgrowing their neighbors. This patchwork of layers allows for spores, seeds, and aerial plankton to drift through the forest to land and grow in new areas.

No soil is available at the top, yet lichens, moss, fungi, and ferns become established in the forest’s penthouse. These organisms are epiphytes, drawing nutrients from the air and precipitation, and are not parasites of the trees.

Eventually, abraded pieces of the moss and lichens along with falling conifer needles accumulate on lower branches, creating “perched soil” that supports other plant life.

Lichens are very important for the health of forests. They take nitrogen out of the air, which is eventually leached to the forest floor. Trees and the understory flora cannot access this nitrogen without the help of lichens.

Many other life forms thrive in the two top layers. Flying and creeping residents include beetles, moths, ants, spiders, mites, and millipedes. Even snails make their home in the canopy.

Birds are highly mobile and often visit the canopy and emergent layer. Chickadees, finches, kinglets, nuthatches, and others forage for invertebrates and seeds found high in the trees. Red Crossbills, a species of finch, may spend their whole lives feeding on cones located in the canopy.

Townsend’s Warblers and Olive-sided Flycatchers are two species that spend the summer high in our forests. The former glean caterpillars from the twigs while the latter perch on treetops in order to ambush flying insects. Both species return to Mexico and Central America in the fall.

Bald Eagles have favorite emergent layer sites for perches. From these positions they can scan for feeding opportunities and keep a watchful eye out for other eagles intruding into their territories.

Few mammals make it to the canopy in our forests. Bats may find daytime roosts there, and both Humboldt’s Flying Squirrels and Douglas Squirrels search for conifer seeds high up in the trees.

Only the most intrepid human tree climbers have an opportunity to experience this exciting habitat. We can, however, find bits and pieces of it following fall and winter storms. November’s high winds bring down patches of lichens, moss, and fungi. Walk a forest trail after strong gales and you’ll be given a glimpse of life at the top.

 

Look for licorice ferns on bigleaf maples and alders. Photo by Martha Ellis.

Flora:  Licorice Ferm (Polypodium glycyrrhiza)

The easiest epiphyte to identify is licorice fern. While not restricted to the forest canopy, it does occur there and also at lower levels in our wetter forests.

Licorice ferns by Martha Ellis.

Licorice ferns grow as single fronds from rhizomes snaking under moss attached to limbs and trunks of trees. The fronds grow to a foot in length and are roughly triangular with pointed leaflets. Round-shaped spore sacs called sori form on the underside of the fronds, lined up in rows from the main rib.

The life cycle of this species is so unusual it can almost be described as the “anti-fern.” Its spores are released in the cool, wet weather of late fall through spring. Most fern species release their spores in summer. Licorice fern spores are dispersed by wind, rain and possibly by animals brushing against the sori.

Licorice ferns go dormant and turn brown during periods of hot, dry weather. Their rhizomes store water to keep the plant alive until the refreshing rains of fall. Other ferns add growth in summer.

Deer occasionally browse licorice ferns that are within reach. A few insects eat the leaflets, while moths and other invertebrates find shelter beneath the fronds. Some small bird species such as Red-breasted Nuthatches cache food items under licorice ferns. The common name comes from sweet-tasting compounds found in the rhizomes.

November is the perfect time to search for licorice fern. They’ve greened up after summer’s dormancy. Look for them on bigleaf maples and alders. They do occur on conifers, but maples are the preferred location for the “anti-fern.”

Northern Flying Squirrel, a close cousin of Humboldt’s Flying Squirrel. Photo by Dana Visalli.

 

Fauna: Humboldt’s Flying Squirrel  (Glaucomys oregonensis)

One of the most intriguing local mammals ventures high into the forest canopy.

This species was named for Alexander von Humboldt, a naturalist and explorer. It was recently discovered to be distinct from the widespread Northern Flying Squirrel.

Humboldt’s Flying Squirrels have a body length of 6.7 inches with a tail measuring 5.7 inches. The body color can be varied but is usually grayish-brown with paler belly fur. A featherlike tail and large black eyes round out the visible field marks. The fur glows pinkish under ultraviolet light. Many theories have been proposed for this trait but nothing has been proven yet.

No flying squirrel actually “flies.” Instead they have a large membrane called a patagium that stretches from the wrists of the forelegs and the ankles of the hind limbs. This structure allows them to make epic glides of up to 150 feet. The tail aids in steering.

Admiralty Inlet Preserve by Martha Ellis.

Conifer and deciduous seeds compose a large part of the flying squirrel diet. Tree sap, insects and fungi are also eaten, with the latter especially prominent in fall. Fungi hunting can bring a squirrel down to the forest floor in November.

Nests of these rodents are located high in a tree cavity or in the dense foliage of the canopy. Females give birth to 2 to 4 kits in spring or summer. Being solitary animals, the females raise their young without help  from males.

Dense fur keeps flying squirrels warm, allowing them to be active most of the winter. They do store foods such as cones and buds in tree cavities for consumption during the worst weather.

Humboldt’s Flying Squirrels thrive in old growth conifer forests but also inhabit mixed forests.

Almost totally nocturnal, flying squirrels can be difficult to find. Try arriving in a forest at dusk and sit quietly in a small opening. A flashlight – always carry a spare! – may illuminate a flying squirrel in mid-glide, snuffling for fungi on the forest floor, or as a lump on a tree trunk.

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