For the fifth and final entry in the Coastal Flora of the Pacific Rim series, we travel away from the beach a little bit. We started with Nereocystis luetkeana in the subtidal zone, and then covered one intertidal and two beach species. Today’s photo of Pinus contorta var. contorta was taken a little less than a kilometer away from the beach, on the Shorepine Bog trail of Pacific Rim National Park, British Columbia, Canada. Daniel took this photograph, which shows Pinus contorta var. contorta growing with many other bog species. Thanks Daniel!
Even though Pinus contorta has been covered four times on Botany Photo of the Day, it is such a ubiquitous and interesting species that it is worth including in this series. There are three or four varieties of Pinus contorta, and together they range over western North America, from Baja California to Alaska. Pinus contorta var. contorta, or shore-pine, is found along the coast from southern Alaska to northern California. It is hard to believe that the gnarly, wind-swept shore-pine belongs to the same species as the tall straight Pinus contorta var. latifolia that is found inland. Some botanists argue that the varieties of Pinus contorta actually constitute subspecies. Despite huge variability in stature, all of the varieties of Pinus contorta have 2.5-5cm long paired needles that are often stiff and twisted. The small, hard cones are angled at the base so that they point toward the tree’s trunk.
What impresses me the most is Pinus contorta‘s ability to adapt to a wide variety of difficult terrain. A pioneer species, it will grow in places that other plant species cannot contend with. About 13,000 years ago, Pinus contorta was one of the first species to colonize the barren lands after the glaciers began to retreat in British Columbia (see Hebda 1983). Today, this species occupies habitat that is too wet, too acidic, too nutrient-poor, too elevated, too fire-prone, or too rocky for other tree species. Pinus contorta var. contorta is common in the bogs of Pacific Rim National Park. The low-nutrient and acidic conditions of these bogs yields shore pines whose stems twist and often grow sideways into botanical works of surrealist art. These pines grow incredibly slowly. Some are up to three hundred years old, yet will have reached a height of only a few meters (or less!).
Although Pinus contorta var. contorta has adapted to many growing conditions, it appears to be in decline at the northern edge of its range. Biologists in Alaska have noted a decrease in shore pine populations since the mid 1990s. This decline is attributable to fungi and pest infestations, but a 2014 study by Abby VanLeuven (pdf) points to a changing climate as the root cause of the problems affecting Pinus contorta var. contorta. The study takes place in the Gulf of Alaska, where the climate has become markedly warmer and wetter. In normal situations, shore pine growth is associated with precipitation. More recently, shore pine tree ring data does not match climate data, a phenomenon known as divergence. Van Leuven points out that while precipitation is generally beneficial to Pinus contorta var. contorta, too much precipitation in the wrong form favours insect pests and other pathogens over the growth of shore pine. Pinus contorta var. contorta was able to take advantage of a shifting climate following the end of the previous ice age, but this species may not be able to adapt quickly enough to the current climate change situation.