North American coniferous forests have undergone dramatic changes over the past few decades. More intense, prevalent outbreaks of native bark beetles, owing to milder winters and drier environments due to climate change, have dramatically altered many landscapes. Healthy forests have been replaced by stands of defoliated snags. In Colorado, the spruce beetle (Dendroctonus rufipennis) has affected over 1.5 million acres of Engelmann spruce – subalpine fir forest over the past two decades. Beetle-killed trees generally allow more light to reach the forest floor, more woody debris to be available, and moisture dynamics to be altered because of increased snow depth and earlier snow melt. Research has quantified how bark beetle outbreaks have affected vascular plant and bird communities, but little work has been done on the particular impact on lichen communities.
Lichen abundance and species composition data were collected in spruce-fir forests of northwestern Colorado in the summer of 2018. Forty-four plots in affected and unaffected forest were surveyed; affected forest plots spanned areas affected from 1996 – 2017 as detected by aerial survey data. Environmental data, such as canopy, coarse woody debris, and vascular plant cover were also collected at each plot.
Results/Conclusions
We found that forest structure did not differ by time since spruce beetle disturbance. Specifically, there were no significant differences in canopy cover, amounts of coarse or fine woody debris, basal area, moss cover, or understory plant cover between plots from five impact classes: impact detected between 1996 – 2003, 2004 – 2006, 2007 – 2011, 2012 – 2017, or unaffected forest (individual ANOVAs p ≥ 0.137). We also found that age since disturbance groupings of plots did not align with patterns in community structure of lichens in the genus Peltigera, an important ground-dwelling foliose taxon (MRPP, p = 0.8606). Peltigera, along with Cladonia, was the most speciose genus and had the highest cover of ground-dwelling species.
The lack of significant differences of forest and lichen community structure between age classes indicates that categorization by time since disturbance may not inform how lichen communities are impacted by spruce beetle. Instead, looking into other variables, such as disturbance intensity or structural characteristics like canopy cover, may better explain lichen community response to spruce beetle disturbance.