PS 45-103 - A comparison of the understory vegetation composition in western larch (Larix occidentalis) and lodgepole pine (Pinus contorta) 30-40 years post-planting.

Background/Question/Methods

To adapt to changing climate and habitat envelopes, the feasibility of planting western larch (Larix occidentalis) north of its natural range as an assisted migration practice is being explored in north-central British Columbia. From a silvicultural climate adaptation standpoint, larch is a suitable species, capable of withstanding projected increasing temperature. However, due to its deciduous nature questions have arisen around how larch in plantations may modify understory vegetation composition, a key factor important in maintaining ecological and habitat conditions. This research investigated if there was a significant difference in the richness and abundance of total understory vegetation, along with individual shrubs, herbs, forbs and bryophyte groups, between 40-year-old, managed lodgepole pine (Pinus contorta) and western larch in plantations north and west of Prince George British Columbia. The two treatment types were 100% western larch cover and 100% lodgepole pine cover. Each treatment had two stands and within each stand ten, 2m x 2m plots divided into four 1m quadrats to measure all species percent cover using ocular estimates. From the four quadrats, total richness and abundance were calculated through averages. The differences in richness were assessed using two-way ANOVA (p=0.05) and abundance was assessed using a two-way MANOVA test (p=0.05).

Results/Conclusions

The results showed there was no significant difference in total species richness between western larch and lodgepole pines stands (p=0.504). There was a significant difference between the richness of bryophytes (p=0.000238) and lichen (p=0.0498) between western larch and lodgepole pine stands. In addition, there was a significant difference in bryophyte percent cover between the two treatment types (p=0.004882). Over 75% and up to 100% of the plots in the larch treatments do not have as high a percent cover as any of the plots in the pine treatments. This data shows that there are significant differences in the understory composition between western larch and lodgepole pine sites including the observed reduction of bryophytes and terrestrial lichens. These species groups contribute to a variety of ecological functions including carbon balance and cycling, water retention and forage habitat for caribou in winter months. Bryophytes also insulate and regulate water retention in soil and are essential for maintaining microhabitats for soil fauna. Larch is a viable species to meet silvicultural goals under future climate pressures. However, a reduction of bryophyte cover may have consequences for the soil ecological community and ungulate browse.