Two years ago a property owner in Carmel, CA approached me about helping improve the health of her sick oak trees. When I inspected her oaks I found them to be severely diseased and the canopies very thin. I told her that I wasn’t sure I could save her diseased oaks, but that I felt confident I could help her other oaks. She agreed to have all her oaks treated with fire mimicry.
Two years later, the diseased oaks (first three sets of photos) are recovering nicely and the remaining oaks on both properties are showing improved canopy health. The photos below show the results of all the oaks I’ve treated on her property over the past two years. The photos show a nice response in some oaks, others showing a limited response. Overall, I’m pretty happy with the results in just two years.
Indeed, it’s becoming clear that native people of North America knew how to grow big trees! In 2006 I published a peer-reviewed chapter titled “Ecological evidence of large-scale silviculture by California Indians” in the book Unlearning the Language of Conquest (Four Arrows, ed.). In that chapter I proposed the hypothesis that “the many types of refuse mounds and middens, including shell middens, bone middens, and rock middens originate not from the gradual accumulation of the waste products of daily living, but rather from the intentional stockpiling of gathered or recycled lime-rich materials for use as mineral fertilizers.” A careful review of the literature at the time indicated to me that this hypothesis was novel to modern science, though not at all novel to traditional ecological knowledge. Furthermore, I provided evidence for the fertilization effect of midden materials on trees that I collected from a giant sequoia grove in central California and from a grove of western hemlock and Sitka spruce trees in southeastern Alaska, which I attributed to intentional tending by native people.
Now, ten years later, comes a study published in Nature Communications detailing the positive effects of shell middens on the growth and health of western redcedar trees in coastal British Columbia. The paper, “Intertidal resource use over millennia enhances forest productivity” (by A.J. Trant et al. 2016. Nature Communications 7:12491) makes several key points that are relevant to my original hypothesis. These include:
“Pockets of enhanced forest productivity are associated with increased phosphorous availability resulting from higher soil pH from the slow leaching of calcium from shell middens along with the nutrient amendments of past fires.”
“Western redcedar (Thuja plicata) trees growing on the middens were found to be taller, have higher wood calcium, greater radial growth and exhibit less top die-back.”
“Coastal British Columbia is the first known example of long-term intertidal resource use enhancing forest productivity and we expect this pattern to occur at archaeological sites along coastlines globally.”
This last point I take some exception to, as Trant et al. fail to recognize that examples of the same phenomenon were reported ten years earlier in my peer-reviewed publication noted above. I might have given them a pass for unintentionally overlooking my work, except that when I do a google search on “shell middens and tree health” my 2006 publication shows up on the first page of results. Perhaps the authors were careless in their searches, or viewed the evidence I reported as somewhat scant, which I agree it was. But any peer-reviewed hypothesis with supportive evidence, scant or not, deserves to be cited and recognized as taking precedent to any later work.
I’m not asking for any personal recognition here, rather I’m hoping to point out that in the ten years since I first published the above findings I have used midden materials (crushed shells and rocks) in the treatment of thousands of oaks and other trees, with good to excellent results (see the many previous posts on fire mimicry). This, to me, is the real evidence supporting the shell midden hypothesis, and more importantly, demonstrates the immense ecological wisdom of the native peoples of the world who discovered this relationship millennia before modern science. Hopefully the authors of the recent paper will take the next step, as I did, and use their findings to make a difference in the health of trees and forests in British Columbia!