The Life of a Forest Stand
The different forest types in the Acadian Forest have very different life cycles. Some trees live up to 400 years, while some others do not live to 100 years. Trees that are “tolerant” of shade make up the mature climax forest, as they can grow in grow with under a canopy of trees. Certain combinations of soils, topography, aspect, and climate make up a “site”. Hardwood, softwood, and mixed hardwood-softwood stands are often associated with certain site conditions, but stand history also contributes to current composition.
In addition to old age, trees can also be killed by diseases, insect infestations (ex. spruce budworm), wildlife damage (ex. porcupine, beaver), and fire.
A “yield curve" is a projection of what wood volume is expected from a particular stand type at a certain age. Yield curves are used in computer forest simulation models, in combination with clear objectives, to develop forest management plans.
Following are several graphics showing yield curves with associated sketches depicting the life of the forest type. Note the relationships between the graphs and the sketches. The yield curves presented for the softwoods are essentially for an even-aged pure species condition.
Please note that all yield curves presented are simplified versions for illustration purposes.
The life of a short-lived Softwood Stand - Balsam Fir
The following graphic shows the life cycle and wood yield of a short-lived Balsam Fir stand over a 200 year period. Young trees grow to maturity, over-maturity, death, and natural regeneration; starting the cycle of life over again. Fir is a short-lived tree which commonly grows in pure even-aged stands. Fir is a staple in the diet of Moose, and is also a preferred winter habitat of White-tailed deer.
Once fir dominated stands reach 40 years of age, they become too unstable for partial harvest unless there is a significant hardwood component in the stand. After 40, partial harvests should only be conducted in fir stands to establish natural regeneration, for subsequent harvest of the overstory trees (called overstory removal) 5-10 years later.
The life of a White or Black Spruce Stand
White or black spruce have a lifespan of between 120 and 150 years and both spruces have excellent wood properties. White Spruce are more stable than Balsam Fir, withstanding harvests in stands up to 60 years of age.
Black Spruce stands typically grow in poorly drained low lying areas, and are rarely used by wintering deer. White Spruce are found on better sites, sometimes in combination with tolerant hardwoods, fir, cedar, and other trees.
The Life of a Tolerant Hardwood Stand
Tolerant (of shade) hardwood stands in the Acadian Forest are typically comprised of sugar maple, beech, and yellow birch, alone in combination with each other. The trees, which can live up to 400 years, should be selectively harvested only with >70% stocking maintained for highest production and to prevent competition from less valuable and shorter-live intolerant hardwoods. Tolerant Hardwood stands live perpetually as trees that fall are replaced by trees in the understory that receive extra sunlight and grow to fill the gaps.
The Life of a Long-lived Softwood Stand (Red Spruce, Hemlock, Cedar)
The range of Red Spruce closely matches that of the Acadian forest. Red Spruce is much longer-lived than black or white spruce, with trees sometimes growing to 300 – 400 years old; however, Red Spruce has very shallow roots, and is prone to windfall. For this reason, partial harvests should be done with particular attention to stand stability.
Hemlock is of very high value to wildlife, in particular to wintering deer, as they are extremely long-lived, windfirm, and provide highest food and shelter values. Hemlock is not common in the northernmost portion of the Upper St. John River Watershed.
Cedar are long-lived, wind-firm, and typically occur near water bodies. They provide high food and shelter value to deer, and stabilize soils to prevent soil erosion and protect water quality. Several rare plants are associated with cedar stands.
The life of an Acadian Mixedwood stand
While the Red Spruce is sometimes seen as the signature tree of the Acadian Forest since its range IS the Acadian Forest, it is mixedwood stands, which exemplify the Acadian Forest, provide a variety of sustainable wood and wildlife values. A component of hardwoods stabilizes the stand, and extends opportunities for partial harvests. Year-round resident wildlife heavily use softwood trees in hardwood dominated stands, and hardwoods in softwood dominated stands. Softwood dominated mixedwood stands are often utilized by wintering deer, who are attracted to stands containing hardwood to browse on, even though this hardwood browse is of very low nutritional value.
Mixedwood stands may become a Climax forest mix of spruce or other softwoods with tolerant hardwoods.