Examining the potential of western larch, Siberian larch, and ponderosa pine as regeneration species in Cariboo Region ecosystems: 22-year results from EP904.02.
Experimental Project 904.02 (EP904.02) was established in 1987 to examine the performance of western larch (Larix occidentalis), Siberian larch (Larix sibirica), and ponderosa pine (Pinus ponderosa) at ICHwk2, SBSmw, ESSFwk1, and SBPSxc sites in the Cariboo Region. Survival and growth of these non-native species over a 22-year period were compared with that of lodgepole pine (Pinus contorta var. latifolia), Douglas-fir (Pseudotsuga menziesii), and hybrid spruce (Picea engelmannii × glauca), which are common forest components in this region. Subsequent to the installation of this experiment, climate change-related forest health issues became an important management concern, and the extension of species beyond their natural range was considered as a mitigation strategy. Western larch was a good candidate for assisted migration, and interim guidelines are now in place that allow this species to be planted in many Cariboo Region ecosystems. As a result of these recent changes, our 22-year western larch results are especially relevant to current forest management. Lodgepole pine, Douglas-fir, and hybrid spruce survived and grew according to general expectations for the individual biogeoclimatic units, except that lodgepole pine sustained high (40%) first-year mortality at the ESSFwk1 site. At all locations, lodgepole pine grew more rapidly in early years than Douglas-fir or hybrid spruce, and continued to be larger at age 22. Douglas-fir, once established, survived and grew well at the ICHwk2 and SBSmw sites but did poorly at the SBPSxc installation. Hybrid spruce exhibited better overall survival than any other species but grew considerably more slowly than lodgepole pine or Douglas-fir throughout the 22-year assessment period. Western larch had higher survival and better growth at the ESSFwk1 than the ICHwk2 or SBSmw sites, possibly because the seedlot used at the ESSF-wk1 installation was better adapted to moist conditions than that used elsewhere. After 22 years, 79% of western larch survived at the ESSFwk1 site, and trees were approximately as tall as lodgepole pine. Within its current range, western larch is not common in the ESSF zone, and we speculate that if a more suitable seedlot had been used at our ICHwk2 and SBSmw sites, western larch growth would have at least equalled that at the ESSFwk1 location. Western larch had very low survival and was unable to increase in height at the SBPSxc site, apparently because it was as ill-suited as Douglas-fir to the harsh climatic conditions of the Chilcotin plateau. Siberian larch survival was equal to or better than that of western larch at all the experimental locations, but after 22 years, it was approximately 1 m shorter than western larch at the ESSFwk1 and SBSmw sites. Both larches sustained considerable forking damage, but from a growth and yield perspective, Siberian larch had the more serious defects. At the SBPSxc site, severe forking notwithstanding, Siberian larch had the second-best survival after lodgepole pine and was the only other species that was even marginally able to withstand the climatic limitations of that location. Ponderosa pine survived and grew reasonably well at the SBSmw and ICHwk2 sites, but tended to increase in diameter at the expense of height and was subjectively observed to have large branches and wide crowns, traits that do not suggest high economic value. Like all other species except lodgepole pine, ponderosa pine did poorly at the SBPSxc site.