Institute for Transportation

Reduced treatability in heartwood can cause reduced
retention and penetration of preservatives into
heartwood. This can reduce the durability of heartwood
compared to the treated sapwood. From an anatomical
point of view, the factors which contribute to the lower
treatability of heartwood include its high extractive
content, high rate of aspirated pits, and smaller pore
sizes. Generally, in wood members that consists of
treated sapwood and untreated heartwood, the
durability of treated sapwood is much higher. Untreated
heartwood of southern pine, Douglas-fir, Englemann
spruce, eastern spruce, red pine, white pine, eastern
larch, eastern hemlock, and eastern fir lasts longer in
outdoor exposure in the colder northern regions
(Wisconsin and Maine) than in warmer southern
regions (Mississippi). In the southern regions, the
median life of the stakes for these species ranges from
about two to four years with the exception of southern
pine which ranges from about five to seven years.
Eastern spruce and white pine appear to possess lower
durability (about two to three years) among all the
species studied. In the northern region, the median life
of the species range from five to ten years with the
exception of southern pine which lasts about eight to
fifteen years.