Pinus flexilis James is an ecologically important, highly stress tolerant species that is often the first to colonize sites following disturbance, yet P. flexilis is experiencing widespread decline and mortality, due to bark beetles and white pine blister rust (WPBR). Artificial regeneration will be needed on sites with low regeneration density to sustain the species and facilitate the effective introduction of seedlings that are resistant to WPBR and adapted to future climates. To develop forest-scale planting methods, P. flexilis seedlings (2,160) were planted in 2009 at 6 sites in the central Rockies. Seedlings were planted in a randomized block design in 6 plots per site; treatments included nurse objects (stumps we installed), canopy cover, and hydrogels. Survival was promising in 2012 but was reassessed in 2018 to determine: (1) how well the 4-yr post-planting monitoring predicts long-term (10-yr) outcomes and (2) if nurse objects, canopy cover and hydrogel influence long-term seedling performance. We collected health data using a standard 1-5 scale of healthy to old dead; measured percent canopy cover; seedling basal diameter, height, and length of new growth; and assessed nurse object condition. Data analysis was done in RStudio and SAS.
Results/Conclusions
In 2018, 58.5% of the seedlings were healthy (1 on 1-5 scale, <5% needles red/dead), seven percentage points higher than in 2012. This is attributed to the recovery of seedlings that were alive but had lower health ratings. There continues to be significant differences in survival by planting site, ranging from 75.2% to 30.3% (Χ2=274.96, df=5, p<0.0001). Survival rates continued to be higher for seedlings planted next to a nurse object (67.4% living; Χ2=22.56, df=1, p<0.0001), than those planted without an object (56.9%). There was minimal nurse object decomposition, and we did not find nurse objects interfering with seedlings. However, unlike in 2012, there was no significant relationship between survival and orientation to the nurse object (north=68%, east and south=66%, west=70%; Χ2=1.85, df=3, p=0.6039). Survival continued to be uninfluenced by hydrogel presence (63%) or absence (65%; Χ2=0.92, df=1, p=0.337). Further analyses using modeling will include canopy cover and other site variables and will be used to re-evaluate preliminary findings and analyze growth. These findings refine planting guidelines needed for P. flexilis management, conservation, and restoration efforts, particularly for deploying WPBR-resistant seedlings. Longitudinal data analyses will help inform knowledge of seedling establishment and likelihood of long-term survival.