Environmental Engineering Reference
In-Depth Information
Cool, temperate, moist forests store between 250 and 650 t C/ha, while boreal
forests have a total phytomass usually no greater than 60-90 t C/ha and an aboveg-
round living component of only 25-60 t C/ha, or 50-120 t/ha: the Russian mean
is about 80 t/ha, the European and U.S. averages are around 100 t/ha, and the
Canadian means range from just around 40 t/ha in the drier western provinces to
about 55 t/ha in eastern Ontario and Quebec (Kurz and Apps 1994; Potter et al.
2008). Actual timber (roundwood) harvests are only a small fraction of the standing
aboveground phytomass; in temperate forests they are no higher than 1.5-2 t/ha.
The most extensive ecosystems with the highest recorded stores are in the
old-growth formations of western North America, which benei t from abundant
moisture in maritime locations (Edmonds 1982). Mature stands of Douglas i r
(
Pseudotsuga menziesii
) and noble i r (
Abies procera
) store up to 1,700 t/ha, and
the aboveground maxima for the Pacii c coastal redwoods (
Sequoia sempervirens
)
are around 3,500 t/ha, three times as much as the richest tropical rain forests. These
forests also contain the biosphere's most massive organisms, giant sequoias (
Sequoi-
adendron giganteum
), with a phytomass in excess of 3,000 t and a life span of more
than 3,000 years.
Keith, Mackey, and Lindenmayer (2009) found another instance of high carbon
density in an Australian (highlands of Victoria) evergreen temperate forest domi-
nated by
Eucalyptus regnans:
its average aboveground carbon content in living
tissues is 1,053 t/ha and the total is 1,867 t C/ha (more than 3,700 t/ha) in all (living,
roots, and dead) phytomass in stands with trees older than 100 years. Douglas i rs,
sequoias, and
Eucalyptus regnans
are also the world's tallest trees. Douglas i rs can
reach 110 m, the tallest coastal redwood (
Sequoia sempervirens
) is nearly 116 m,
and the record height for
E.
regnans
is about 125 m (Carder 1995; Gymnosperm
Database 2011). However, as with every large tree, most of the phytomass of these
giants is dead wood. Another remarkable attribute of old-growth forests is that,
contrary to the standard belief that they are carbon neutral, they continue to accu-
mulate phytomass (Luyssaert et al. 2008).
Even those ecosystems that have relatively low stores of woody phytomass, such
as chaparral (the arid shrubland of southern California) and temperate woodlands,
typically store more phytomass per unit area than do the richest grasslands. Tall
tropical grasslands can have phytomass densities surpassing 30 t/ha, temperate
grasslands store usually around 20 t/ha, and the short-grass tundras average no
more than 5 t/ha. Unlike in forests, most of the grassland phytomass is stored
belowground: the mean global root:shoot ratio is about 3.7 (Jackson et al. 1996),
and in many grasslands it is in excess of 6 (Yang et al. 2010). In contrast, both
