Definition: watershed productivity
Productivity is defined by ecologists as the rate of production (e.g. grams per
year) of some component of the community such as the biomass of vegetation.
When referring to “productive” SE watersheds, we employ a market-weighted bias that might gloss over some other ecologically important kinds of productivity.
In terms of annual tonnage, timber and salmon far outweigh all other Southeast commodities. We define productive watersheds, as those that–relative to their biogeographic province–rapidly grow very large trees and associated fauna, and/or host exceptional runs of salmon. This kind of productivity often appears to spring from the nature of underlying bedrock, with carbonate rocks at the rich end, and granitics toward the lean end of the spectrum.
But, as ecologist Mary Willson points out, it’s important to be clear that timber or fish productivity
“doesn’t translate directly into productivity of anything else, because habitat structure and exposure and plant defensive compounds and a zillion other things may regulate other community components.”
For example, shrub production is often inversely proportional to forest canopy production. So it could be there’s higher production of some shrub-nesting birds and blueberry parasites in the types of scrubby-forest watersheds we’ve defined [in the 2005 summary report] as “less productive.” Diversity within many taxa (e.g. bryophytes) is also probably higher in our “less productive” watersheds.
Even more relevant (and confounding) for this essay; some conditions that are
productive of certain fish species need not be productive of forests. Anan Creek
watershed has extraordinary pink salmon productivity but almost zero large-tree forest. The entire watershed is mapped as granitic. Evidently, this relatively sterile parent rock is a deal-breaker for tree production, but not for a fish that barely feeds in the freshwater portion of its life cycle. Anan’s pink productivity may have less to do with in-stream fish food than with flow-stabilization provided by the many lakes in the system.
Still, for better or worse, timber and salmon productivity tend to go
together in most watersheds. Since our greatest large-tree forests have mostly
been cut, the best single indicator of watershed productivity is probably the province ranking for pink and chum salmon. Sadly, an even more reliable productivity index is percent loss of productive old growth (POG) and large-tree forest.
The good news is that productivity and resilience tend to go hand-in-hand.
This makes many ‘hammered gem watersheds’ guaranteed long-term payoffs, given the expected volatility in nature’s “market:” i.e. the impacts of global warming and the like.