On this beautiful, 40° day in late December, twenty curious conifer-seekers passed around my samples of cones and needles in the Arboretum Visitor Center. I shared red and white pine, white spruce, douglas fir, and tamarack cones, and red and white pine, white spruce, and balsam fir needles. With this brief introduction to the world of conifers, we headed out to Longenecker Horticultural Gardens to see what species we might find in the Pinetum.
Are all conifers ever-green? Are all evergreens cone-bearing? We made for the pine section to begin answering these questions. After some searching, we stopped at a towering white pine (Pinus strobus) and recalled that it has clumps of five feathery needles—which matches the five letters in the word “white”—along with long, narrow, silvery cones. While most of the tree’s needles were green, we also noticed many clumps of brown needles on the branches and fallen needles around the trunk.
Conifer needles are modified leaves built to thrive in nutrient-poor soils, drought conditions, and/or extreme cold. With less surface area than a large maple leaf, a white pine needle holds moisture far better during dry stretches and winter. Designed to last multiple years, conifer needles also hold onto minerals throughout the year and are able to photosynthesize down to 20° F. That means all of the conifers we saw today were most definitely producing sugar!
All needles degrade over time of course, and so the average lifespan of a needle is about three years. Most conifers replenish their entire leaf stock slowly over the years as needed. However, as we saw in the larches section of the Pineum, there is one Wisconsin evergreen that loses all of its needles. The tamarack (Larix laricina) is a deciduous conifer, believe it or not, that drops its needles after they turn golden yellow in late fall. Tamaracks, however, are one of our hardiest conifers, ranging far north into the artic circle and surviving in temperatures much colder than many of our common southern Wisconsin conifers can.
We then looked into the spruces, admiring the blue-green needles of Colorado blue spruce (Picea pungens), which is a non-native tree commonly planted in urban areas. We saw the large drooping needles and cones dangling at the ends of Norway spruce (Picea abies) branches. We compared its large football-shaped cones to the tiny bright cones of our native white spruce (Picea glauca). White spruce can be identified by its small cones; light green, very short and spiky needles; and its broad shape with thin branches.
A look at the native balsam fir (Abies balsamea), our only fir species in Wisconsin, showed us how evergreens are adapted for winter. Growing tall and narrow like a spire, the balsam’s flexible branches angle downward and bend under heavy snow, shedding it harmlessly. Spruce and fir both have another amazing adaptation to survive in the arctic as well. Called extracellular freezing, at temperatures below -40° F, these trees will move water out of their cells to spaces between, where ice crystals do no damage. While white spruce needles are spiky and round (you can roll them between your fingers), balsam fir needles are flat and soft, with two white stripes underneath.
Finally, we stopped by the junipers to answer our second question. We saw that many junipers reproduce by small blue berries instead of cones. Our most common juniper in Wisconsin is the eastern white cedar (Thuja occidentalis), which is not a cedar at all but a member of the Cypress family. We also noticed their variation of the leaf, which is a scale-like set of needles that look like tiny green branches of their own. As we walked back towards the Visitor Center, the feel of spring rains filled the air and a fog thickened in the gardens. A strange feeling for late December, but becoming more normal during El Nino winters.
—Tom Pearce