Boreal canopy lichens declined from several drivers
Over a decade of Swedish forest inventory, hair lichens Alectoria, Usnea, and Bryoria became less common, with losses tied to forestry, nitrogen, and climate together—not one driver alone.
Source
Multiple drivers of large-scale lichen decline in boreal forest canopies
Study at a glance
- Design
- Cohort — Repeat Swedish National Forest Inventory plots relating canopy-lichen change to forestry, N deposition, and climate
- N
- NFI plots measured ~10 years apart (1993–2002 vs 2003–2012) with at least one live Picea ≥150 mm DBH
- Population
- Filamentous lichens on spruce in productive Swedish boreal forest
- Outcome
- Large-scale canopy-lichen decline has multiple interacting drivers: logging cycles, nitrogen sensitivity, and warming/rain
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Boreal canopy lichens declined from several drivers
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Relative loss rates were 1.70%, 1.25%, and 0.50% per year for the three lichens.
This corresponds to 1.70%, 1.25% and 0.50% relative loss rates per year, assuming constant loss rates over the 10‐year period.
51.6% of Alectoria occurrences were lost in region 3.
More than half of the Alectoria occurrences (51.6%) was lost in region 3 (Figure ), followed by substantial decreases of Usnea in regions 3 (20.2%) and 4 (30.1%), whereas Bryoria decreased in regions 1 (13.6%) and 2 (6.3%).
What they did
Authors used Swedish NFI plots measured 10 years apart (1993–2002 vs 2003–2012) to track occurrence and thallus length of three filamentous canopy lichens on spruce, then related changes to forestry, N deposition, and climate variables.
What they found
National occurrence fell for all three genera (Alectoria relative loss ~1.70%/year). More than half of Alectoria records were lost in region 3. Drivers interacted: logging cycles, N sensitivity, and warming/rain all mattered, and traits such as color and dispersal shaped which genus declined where.
The limits
What it doesn't show
NFI presence on host trees does not measure biomass in the upper canopy or prove which single driver would reverse the trend if managed alone.
Key terms
- Hair lichens
- Filamentous epiphytes in genera Alectoria, Bryoria, and Usnea that hang in boreal canopies.
- Swedish NFI
- National Forest Inventory with permanent plots remeasured on a 10-year cycle.
- Occurrence
- Whether a lichen genus is present on sampled host trees in a plot.
- N deposition
- Atmospheric nitrogen input that can harm N-sensitive lichens even as national S/N pollution has fallen since 1980.
- Functional traits
- Color, dispersal, N sensitivity, and water storage that mediate lichen responses to global-change drivers.
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Hair lichens that declined:
Common questions
Which lichens declined?
Alectoria, Usnea, and Bryoria canopy hair lichens.
How fast did Alectoria occurrence fall nationally?
About 1.70% relative loss per year over 10 years.
What data source?
Swedish National Forest Inventory, two 10-year periods.
One driver only?
No—forestry, N deposition, and climate interact.
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