A secret reservoir of bees in the forest

Because I live adjacent to a 91,650-acre state forest, I’m always interested in bees that might dwell in the woods. On hikes through the trees, I seldom see any bees except for an occasional bumble-sounding bee that circles me as I walk. Around it goes, getting louder and then receding, over and over. Its behavior is so predictable, I could swear it’s the same individual every year.

The Capitol State Forest is managed for timber production, and the money made from sales goes primarily to education within the state. Like many managed forestlands, the area is divided into segments. Each year, some segments are logged while the rest are allowed to grow. In newly logged areas the slash is piled into great mounds, Douglas-fir seedlings are planted, and other growth is sprayed with herbicide until the seedlings are large enough to compete on their own.

In 25 years, I’ve seen a number of sections harvested and replanted. Regrowth seems slow in the beginning, but once the seedlings get started, they shoot up like moon rockets. In this rainy climate, conifers do indeed grow like weeds.

So how does all this forest disturbance affect bees? After listening to a number of presentations at the PNW Pollinator Summit last week, I learned that woodland bee populations generally behave exactly as I have observed, and the cycle is completely predictable.

No sun, no bees

Not many bees live in dense coniferous forest for two reasons. First, conifer trees do not produce flowers themselves and, second, the forest floor is too dark to support flowering plants. In my area, a thick canopy of trees passes enough light to grow of variety of ferns, mosses, lichens, and mushrooms on the forest floor, but not many bee-attractive plants.

However, as soon as a section is logged, the light comes flooding in. Seeds that have remained dormant for years suddenly have a reason to live, and the logged area bursts into flower with forbs, shrubs, and small flowering trees. Bees quickly arrive from neighboring areas, and you can find them the very first year after a cut.

Soon after logging operations end, I find aggregations of sweat bees in the ground, longhorn bees plying the thistles, and honey bees in the fireweed. I find bumble bees in the salal and Oregon grape, while leafcutters and tiny Ceratina work some of the smaller blooms. Butterflies arrive, too, as well as an assortment of moths, beetles, and pollinating hover flies.

Early seral communities

The first stage of forest regrowth is called the early seral stage. Early seral is simply the very first plant community that establishes itself after a disturbance. The disturbance could be caused by forest fire, volcano, flood, wind, ice, or—in this case—logging. The landscape of an early seral stage is characterized by herbaceous plants including weeds, broadleaf shrubs, and various grasses. And along with these plants comes a host of animal life, including bees, birds, butterflies, and plant-consuming animals.

Unfortunately, the widespread use of herbicides to kill these plants delays the sunshine feast. Forest managers are expected to grow trees—not wildlife—so they battle the competition with spray. But without forage, there can be no brood rearing. Basically, re-establishment of animal populations is restricted until the trees reach a certain maturity that the foresters call “free to grow.” Basically, a free-to-grow stand of trees is one that is large enough and healthy enough to grow on its own and outcompete other plants.

Once the replanted stand is mature enough to outcompete other woodland plants, the herbicide treatments stop, and the plants that characterize first seral growth are allowed to proliferate. Once this happens, the bees, birds and other animals return and populate the area.

Trees get a head start

As you can imagine, allowing the planted seedlings to have a head start shortens the length of time before a shaded canopy returns. As soon as a canopy begins to form, the shade-intolerant species die off. Then, in a few more years, you are back to dense shade, conifer trees, mosses, and ferns.

Early seral growth is extremely important to animal populations. Some biologists refer to these areas as animal reservoirs, a place where bees, birds, and other species can flourish. Even managed honey bees find them extremely attractive. With any luck, many of the species will move on to the next logged location as the shade sets in, and in this way, perpetuate their populations.

Time for change

Due to better understanding of the role of pollinators in a healthy planet, some forest managers are investigating ways to extend the early seral stage of regrowth to accommodate the insects while still turning a profit from trees. Others are trying to figure out how and why certain forestry laws interfere with pollinator recovery.

For example, is it best to pile the slash (twigs, branches, root balls, etc.) or leave it strewn across the landscape? Should native plants be seeded in the recovering areas, or should it be left alone? Should the soil be turned? Must herbicides be used on invasive plants?

What is best for forest bees?

At this point, the answers to many of these questions are not clear. We do know that ground-nesting native bees love bare soil. After logging operations, nests are found on skid roads and in places where slash has been removed. Equally attractive are places were the slash has been piled and then burned, leaving mineral-rich deposits.

On the other hand, cavity nesting bees often reside in the slash itself, especially in wood containing beetle holes. In addition, slash piles are famous for providing cover for all kinds of wildlife that is suddenly left without a protective forest. The piles become homes for mammals, reptiles, birds, and other invertebrates including beneficial insects.

And while invasive plants are generally considered bad, some need careful evaluation. Some bees, such as the tiny masked bees, Hylaeus, prefer invasive Himalayan blackberry vines for nest building, and dozens of other species use it as a bountiful source of pollen and nectar. Once the forest canopy closes, the blackberry will disappear, so how much management—and how much herbicide—does it really require?

New bee frontiers

For me, it is exciting to see so many different groups of people becoming interested in bee conservation. Until I attended the PNW Pollinator Summit, I never really thought about bees in the forest. Although I often hunted through newly logged areas looking for bees to photograph, I never really thought of those areas as a conservation resource. Now I’m thinking, dah! Of course it’s a resource—and one that deserves a closer look.

Rusty
Honey Bee Suite