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Moss and organic soil keep permafrost closer to the surface

Across four Canadian boreal sites, moss and organic-matter thickness lowered active-layer thickness; the tobit model explained 73% of ALT variation.

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What happened to ALT as moss thickened?

ALT decreased, following exponential decay (shallow moss changes matter most).

How much ALT variation did the cross-site model explain?

73% (adjusted McFadden pseudo R² = 0.734).

Did organic-matter thickness affect ALT?

Increasing OM thickness decreased ALT overall, with an OM×slope interaction.

Why use tobit regression?

17 burned plots had ALT > 150 cm, beyond the probe, so the response was censored.

Which land-cover contrasts were sampled?

Unburned and burned black-spruce stands (MSU, BS, MSB, BB) with different moss, moisture, and LAI.

Where was ALT greatest vs smallest?

Greatest at MSB, intermediate at BB, smallest at MSU and BS.

What other predictors entered the final model?

OM, moss, understory and tree LAI, slope, deep and surface moisture, plus interactions.

Why does ALT matter for the carbon cycle?

Thaw exposes previously frozen permafrost carbon to microbial decomposition.

Was fire part of the design?

Yes—burned vs unburned Boundary Creek/black-spruce comparisons, with some burned ALTs off-scale.

What complementary analysis accompanied tobit models?

Structural equation modelling for more mechanistic pathways among vegetation, soil, and ALT.