Schroeder 2019 reconstructed pre-settlement forest puget sound

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Schroeder, T. 2019. Pre-settlement forests around Puget Sound: eyewitness evidence. Poulsbo, Washington. 23 pp.

https://www.biorxiv.org/content/10.1101/592733v5.full.pdf

Notes[edit]

This is a citizen science project by a retired scientist from WDFW.
The GLO surveyor record and use of "witness trees" provides a rare (perhaps only?) pre-settlement view of forests in the Puget Sound region. For each township approximately 288 trees were identified in a systematic grid and measured for DBH. Surveys were completed around 1874. Hudson's Bay Company has initated grazing on South Sound Prairies in 1939. Mass mortality from disease among tribal communities preceded that date.
49,746 witness trees were extracted from 14,000 handwritten pages of field notes(!).
Most common species were Pseudotsuga, Tsuga, Thuja, Alnus, and Acer accounted for 86% of trees.
Species are unevenly distributed. Five relatively distinct areas occupied around 1/3 of the study area:
- Floodplains - Alder, Willow and Maple of smaller diameter were common in floodplains, along with larger diameter Cedar, Cottonwood and Douglas-fir
- Rain Shadow - In the rain-shadow of the Olympics, including San Juan Islands, 83% of all stems were Douglas-fir, Pine, and Alder, with Cedar and Hemlock rare. Prairies (corners with no trees) were also more common in these areas. This area was distinctive in the prevalence of large old Douglas-fir.
- Hemlock Heights - Above 1000' at the margins of Puget Sound country had much higher prevalence of Hemlock, suggesting less disturbance by fire. There was a high variation in tree diameter.
- Prairies - Oak were limited to South Sound (except a few witness trees on San Juan Island based on the mapping).
- Outwash Forest - A large area of Mason and Kitsap County was 69% Douglas-fir with extensive pine. Some small hemlock were mapped, and virtually no alder or cedar. These areas of well drained glacial outwash may have been more fire prone. Other sources indicate some prairie species, and beargrass in this landscape. While compositionally similar to the rainshadow
The remaining area composing 2/3 of the landscape was very mixed with broad representation. The increased prevalence of hemlock in the middle of Puget Sound might relate to the convergence zone.
Large trees - and average of 3.9% of trees were greater than 4 feet DBH, or approximately 1 of 26 witness trees, or a handful in each acre. Most of these were Douglas-fir or Cedar.
Within the survey notes are 781 citations of fire of some kind, over twice as many as windthrow. Windthrow observations were fairly concentrated in the vicinity of the Enumclaw plateau. There is not way to know if there was observer bias.
Henderson et al 1989 observed abundant fire scares dating around 1700 that correspond to Douglas-fir witness tree age estimates. Gavin et al 2013 suggests climate variability duing the "little ice age" may have included periods of drought. The observed large size of trees on islands may have indicated escaping large catastrophic fires.
The author suggests that separation of the Puget Lowlands from the "Hemlock Zone" defined by Franklin and Dyrness 1979 may be warranted.