Growth and Yield
Red spruce is a medium-size tree at maturity, reaching 30 to 61 cm (12 to 24 in) in d.b.h. and 18 to 23 m (60 to 75 ft) in height in the Northeast, and up to 35 m (115 ft) in the Appalachian Mountains. Its maximum age is about 400 years (22). The American Forestry Association lists a tree 133 cm (52.5 in) in d.b.h. and 33.5 m (110 ft) tall in Great Smoky National Park in North Carolina as the largest living red spruce.
The rate of red spruce's growth is strongly influenced by light conditions. Although trees can live in dense shade for many years, once they reach sapling to pole stage nearly full sunlight is beneficial. Understory trees no more than 1.2 or 1.5 m (4 to 5 ft) tall may be more than 50 years old, whereas trees of the same age in the open may be approaching small sawtimber size (22).
Under favorable conditions, red spruce may reach an average d.b.h. of 10 cm (4 in) and height of 7 m (23 ft) in 20 years, and be over 23 cm (9 in) in d.b.h. and 19 m (62 ft) tall in 60 years (22).
Diameter growth of red spruce has been related to vigor, live crown ratio (ratio of live crown to total height), live crown length, and initial diameter at breast height (6,32). High vigor red spruce with a live crown ratio of 0.5 or better averaged 4.3 cm (1.7 in) of diameter growth in 10 years. Growth rates of trees with smaller crown ratios and less vigorous trees decreased progressively to an average of 0.8 cm (0.3 in) in 10 years for trees of low vigor or with crown ratios smaller than 0.4 (22). A tree classification for red spruce is shown in table 1 (11).
|Tree class |
Average 10-year growth in d.b.h.
|A, superior ||I ||Dominant and |
|B, good||I ||Dominant and |
|0.3 to 0.5||3.3||1.3|
|C, acceptable||II||Overtopped |
|D, inferior||Intermediate||0.3 to 0.5||1.5||0.6|
|E, undesirable ||III||Intermediate |
0.3 or less
¹Ratio of live crown to total height.
In one study (40), average net annual growth in softwood stands (66 to 100 percent softwood species) that can be expected from stands receiving minimal silvicultural input was found to be about 3.5 m³/ha (50 ft³/acre). In mixed-wood stands (21 to 65 percent softwood species) this dropped to about 2.8 m³/ha (40 ft³/acre), although the majority of the growth was contributed by softwoods. A further breakdown of the data shows the contributions of spruce, most of which was assumed to be red spruce, to be 51 percent in softwood stands and 39 percent in mixed-wood stands.
Yields per acre, in total volumes of all trees larger than 1.5 cm (0.6 in) in d.b.h. (inside bark and including stump and top but not butt swell), are given in table 2 (33).
|12.2 m |
or 40 ft
|15.2 m |
or 50 ft
|18.3 m |
or 60 ft
|21.3 m |
or 70 ft
¹Base age 50 years when age is measured at d.b.h.- total tree age is estimated to be 65 years at the time.
These yields are normal yields from even-aged stands growing primarily on old fields. Therefore, they are higher than yields that might be expected from more irregular stands such as those developing after cutting (22).
Site index has not been of great utility in rating the potential productivity of spruce-fir sites because of the tolerance of the species and its ability to survive in a suppressed state. Site index at base age 50 years is as good a measure of productivity as any of several growth functions, however (39). Recently, polymorphic site index curves were developed for even-aged spruce and fir stands in northern Maine; they should be valuable for estimating site productivity (20).
Other yield tables for the Northeast (48) take into consideration stand density, composition, and time since cutting. These tables give merchantable volume of spruce and fir combined in trees 15.2 cm (6 in) in d.b.h. and larger from a 0.3 m (1 ft) stump to a 7.6 cm (3 in) top, diameter inside bark, and are somewhat conservative. Yields of merchantable volume for different stand densities from 10 to 50 years after cutting, where 90 percent of the trees are spruce and fir growing on predominantly softwood sites, are given in table 3.
|Density index (regional average 100)|
|Years since cut||50||100||150|
The development of stand projection growth models that permit computer simulation of red spruce tree growth for various management practices and silvicultural treatments over a range of stand conditions has flourished in recent years. For example, the model FIBER was developed in the Northeast (43) for spruce-fir, northern hardwood and a range of Mixedwood forest types between the two. Such models have proved very useful for forest management planning.
In recent years, interest in total biomass yield and productivity has increased, and in the future is likely to become more important in management considerations. As an example, above-ground biomass and productivity values of typical red spruce stands in Canada are given in table 4 for stands in a steady state, across a moisture regime catena (17).
|Moisture regime|| |