Signs of Spring 4: Natural History of the White Pine

Longfellow Trail (Cook Forest, PA). Photo by daveynin, Flickr

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A couple of years ago I was standing in Cook Forest in front of the “Longfellow Pine.” There was no marker or sign that told me that this was the Longfellow, but I inferred that it was from its astonishing height. It was really quite uncomfortable bending my neck so far back to look up the trunk of this tree!

The Longfellow Pine is over 180 feet tall and is estimated to be 300 years old. Nearby is the “Seneca Pine” which is “only” 172 feet tall but its incredible trunk diameter of four feet makes it easily the largest tree by volume in Pennsylvania. There are a number of other massively girthed white pines scattered about in the protected space of Cook Forest. One hundred and twenty of these pines are over 150 feet tall, and a few have been estimated to be over 500 years old! All of these trees, named or not, are spectacular examples of what a white pine can be and, also, what the white pines of our state once were.

The white pine is the tallest tree in the eastern North American forest.  It grows in a variety of conditions but was once an important component of the untouched forests of Western Pennsylvania especially along rivers and streams and in the soils that formed from sand and gravel out-washes generated by the last glaciers that touched the northern parts of our state. These locations reflect the preference of the species for moist yet well drained soils in which to grow.

White pine tree. Photo by J.S.Conn, Flickr

White pines regularly reach 100 feet in height but there have been a few especially vigorous individual trees that soared up and even over 200 feet. Trees that were 150 feet tall and 40 inches in trunk diameter were common in the virgin forests of America. White pines live for 200 to 450 or more years and can become because of their great heights and longevity dominant emergent trees in a canopy of hemlocks and hardwoods.

White pines typically grow in cool, moist climates and are most often found in forests intermixed with many other species of trees including red pine, northern red oak, red maple, eastern hemlock, chestnut oak, white oak and more. Pure stands of white pine (“pineries”) were never common even in the pre-settlement forests.  A potential pinery site needed to be “excessively well drained” in order to both provide the periods of time of high moisture needed for the growth of the white pine and also periods of extremely dry conditions that curtailed competition from other, less drought resistant tree species. Periodic fires in these seasonally very dry sites also help to remove potentially competing tree species that are less fire resistant than white pines.

White pine needles. Photo by S. Rae, Flickr

The pineries contained a relative small number of “dominant” trees (i.e. very old, very large individuals). They primarily consisted of large numbers of medium-large, 200 year old trees.  Individual variations in vigor and fitness and external, sculpting forces like wind and fire kept these pure stands of white pine in a dynamic equilibrium of stress and re-growth and, thus, sustained the pure white pine “climax” forest ecosystem.

The white pine was the most valuable timber tree in the virgin forests of America. Its great height and straight growth form was in great demand for ship masts. Large specimens of white pines were labeled in the colonial forests as property of the king and his Royal British Navy. The wood of the white pine is light but very long grained and strong.  It is both easily transported (the cut trees float very well!) and easily worked. It was the ideal wood for construction and served as the structural material for houses, factories, and other buildings of growing cities and towns of America. It was, in fact, called the “tree that built America.”

The white pine was never as abundant in Western Pennsylvania as the local myths and land sale advertisements claimed. It made up at most 15% of the forest cover and was especially concentrated in the moist soils along the rivers and streams and in the well-drained, gravely, glacial soils in the far north of the state. These were the trees that settlers clearing their land cut and sold first. Sufficient numbers of white pines on a property could go a long way to pay back land purchasing costs and could help to support a settler’s family during the difficult initial years of farming.

White pine seedlings grow best in full sunlight and, so, require breaks in the forest canopy in order to thrive. Its seedlings grow very slowly for their first two or three years but are then capable, after they have established an extensive root system, of rapid growth (up to three feet per year for 10 or 15 years!).  They then settle into a slower growth rate (a foot of height gain each year) for the remainder of their lives.

White pine grove. Photo by J.Mayer. Wikimedia Commons

White pine is both an early “pioneer” species in a forest succession sequence and, for those specimens that survive and reach their mature heights and girths, members of the “climax” forest at the end of the successional sequence.  Excessive shading by highly competitive hardwood species (like aspens, oaks, and maples) can eliminate the relative shade intolerant white pine from a site. Less intense shading by an over-story of birches or pitch pine, though, can allow some white pine individuals to grow sufficiently tall to reach high into the canopy.

White pine trees have both male and female flowers. The female flowers may form when a tree is as young as 5 or 10 years of age. Flowering is full, though, when a tree reaches twenty feet of height. The female flowers are found primarily in the upper crown of the tree on the ends of the branches. Male flowers are not formed until the tree is older and larger (12 to 24 inches in diameter!). The male flowers are very small (0.3 to 0.4 inches long) and are concentrated on the bases of new shoots in the lower crown of the tree. A white pine does not produce male flowers every year. Pollen production, then, is only an occasional occurrence for any give tree. Possibly, this, along with the relative locations of a tree’s male and female flowers and the asynchrony of a tree’s formation of its flowers (a tree forms its male flowers a week or more before its female flowers), is another mechanism to reduce the probability of self fertilization, and, thus, increase the genetic variability of the subsequent generation.

Pollen is released in May or June and is dispersed by the wind. Pollen grains that find a female flower slowly develop and do not accomplish fertilization until some thirteen months later! The female cones, then, with their seeds, develop and mature up through the August or September of this second year. Mature cones drop their seeds within the month of their maturation. Seeds may be dispersed 200 feet from the parental tree. Gray squirrels are a major cone/seed dispersing agent and are also responsible for extensive burying of white pine seeds. Good seed production occurs every 3 to 5 years. Insect infestations (like the white pine cone beetle) can drastically impair seed production.

The soil beneath a white pine is full of seeds and potential pine seedlings.  The seeds require a period of cold stratification before they can germinate. The characteristics of the seedbed for the germinating seed and the developing seedlings are quite important. Under shading over-stories, seeds will readily germinate and seedlings will grow and develop on both disturbed and undisturbed litter layers. In full sun, though, moist mineral soil, moist mosses, and/or a protective short grass cover are needed both for germination and seedling development. If the shading is too dense, though, seedlings will grow so slowly that they will be unable to out-compete other tree species.

White pine cone. Photo by Famartin, Wikimedia Commons

The cones and seeds of the white pine are food for many birds (including chickadees, nuthatches, pine warblers, pine grosbeaks, red crossbills, and yellow bellied sapsuckers) and mammals (including gray and red squirrels, and  many species of mice). Beaver and porcupines consume the bark of white pines, and white-tailed deer, snowshoe hares, and cotton-tailed rabbits eat its seedlings and saplings.

The white pine is affected by several hundred insects and over a hundred diseases. Most serious of these are the white pine weevil that kills an affected tree’s terminal growth shoot, and the introduced pine shoot beetle which affects many pine species including the white pine. Also, white pines can be severely damaged by the introduced, exotic fungus that causes white pine blister rust .

White pine blister rust is a fungus native to Asia that had become established in European pines by the nineteenth century. When, as Gifford Pinchot so succinctly put it, the “orgy of forest destruction” was finally ebbing here in North America in the early Twentieth Century, the clear cut  forests required extensive rehabilitation and replanting.  Seedlings of North American white pines that had been exported to Europe many decades before were re-imported from German nurseries as one part of this rehabilitation effort. These seedlings, though, were contaminated with the fungus that causes white pine blister rust. The rust then became established throughout the east and represents to this day a major threat to the overall health and potential survival of the white pine throughout its native range.

White pine seedlings under thinned red pines. Photo by E. Sagor. Flickr

In Cook Forest around the Longfellow Pine, there are very few white pine seedlings growing. The disrupted, fragmented forest around this iconic tree is full of a variety of hardwood species, but there are very few young white pine trees anywhere to be seen. The dense canopy cover has prevented substantial growth of the shade-intolerant pine seedlings and encouraged the survival of a broad array of white competitors.

Here is what I wrote about the trail that climbs up around the Longfellow Pine back in 2010 when Deborah and I hiked the Baker Trail from Freeport to the Allegheny Forest (the Longfellow Trail in Cook Forest is a very short part of the 140 mile Baker Trail):

The forest around us is dense, shady, and old. Many great hemlocks and white pines covered the hillside. Clusters of American beech and many young hemlocks grow under and around them. Occasionally, one or two hemlock or white pine trunks stand out from the crowd of trees. These trunks, often four or five feet in diameter just radiate age and an ecological gravitas even in the continuous tapestry of all of the other magnificent trees. Looking up the trunks of these giants we frequently couldn’t even see the upper branches through the canopy. These tall, straight trees seem to disappear up into the tangle of the upper branches and feel like they are going “up” forever. One white pine whose full trunk could be visualized was five feet in diameter and approximately 140 feet tall. There are other trees that are even more massive.

I remember hiking in this forest with my family when I was a very little boy 50  years ago. This area had been hit by a large windstorm in 1956 (there is a plaque that commemorates this storm up along the Forest Cathedral trail). These past 50 years have been a period of significant re-growth in these forests. One of the impressions that I retain from our 1960 hikes across this hillside was how open, and sunny many of the trails were.  These trails today are tree covered and shady. Many of them are lined with young hemlocks growing up under a standing cover of tall birches and red maples. Most if not all of these trees are components of the vigorous  forest re-growth and succession that was triggered by these severe 1956 storms.

The lack of white pine seedlings on the Longfellow Trail is important. The forest floor is dominated by ferns and mosses, and there are quite a few young hemlocks and beeches. The large, older trees are surrounded by these species and are sometimes hard to pick out in the dense under-story. The large trees along the trail are reaching or have surpassed their expected, natural life spans. A 400 year old white pine is quite old and is nearing its natural end, but the 500 year old white pines in this forest are really living on borrowed time!

It is possible that the attempt to keep this forest unchanged and unchanging so that the large trees could be seen and enjoyed by passing generations of nature lovers may have put this ecosystem on an unsustainable, and fatal trajectory. Even the wind event of 1956 didn’t open the forest for white pine seedlings. Maybe even then there were too few seeds or an inhospitable seed bed in which they might grow.

White pine. Photo by PumpkinSky. Wikimedia Commons

If we think about white pines in the wild here in the East we have to add up the pressures of insects and diseases (especially those exotic species for which the white pines have no evolutionary experience or protections) along with the huge population of browsing white-tailed deer and the loss of suitable seedbeds and seed germination sites through habitat disruption and soil and litter erosion. All of these factors may have synergistically come together to doom the wild existence of this once great tree species. White pines now mostly exist as domesticated trees throughout their once broad, natural range. They are grown on Christmas tree plantations and are frequently used as an ornamental trees in urban and suburban parks and lawns. The white pine has lost its wildness and, in this reduced condition, has much less a capacity for wonder or for generating ecological awe.

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