Conclusion
Forested headwater streams drain much of the land area in North America
(Colvin et al., 2019) and are a major contributor of C to the atmosphere
(Cavallaro et al., 2018). Regeneration of pine stands following harvest
of old-growth forests is a common land cover change in the western
United States (Collins et al., 2011) that will have lasting consequences
for the quantity and composition of DOM exported from forest hillslopes
and watershed C cycling. We found that the DOM exported from
second-growth hillslopes was five times more reactive than that from
old-growth, though the total amount of C released was ten times lower.
As such, export of bioavailable C from second-growth was roughly half of
that released from old-growth forest, reducing the amount of DOM
available to stream microbes. The slow recovery of these forests
reinforces the persistent effects of land cover change on DOM
composition and reactivity in headwater ecosystems.