Monthly Precipitation Records, 2012-2016
Looking for a weather/die-off correlation in monthly reports: we do
not know if ferns are resilient against pronounced summer drought and
heat in years of average (or better) rainfall. Nor do we know yet if extreme-but-only-in-summer weather is what we have actually had. As a first step towards assessing that, here are the monthly records from
SeaTac airport.
It may be that near zero rainfall in some summer months (in contrast to the average summer montly rainfall of one inch) over repeated and nearly consecutive years, takes a toll. We see such summers, with two bone-dry months in 2012 and 2015. 2013 had one dry month.
Perhaps the strongest argument against the weather hypothesis, in which weather is the driving cause, if not the proximal cause, is that most of the sword ferns in Seward's old-growth forest are in good health. The die-off is three years-old, spreads radially uphill and down, now occupying 5 acres (completely dead) and >20 acres (the total affected area).
It may be that near zero rainfall in some summer months (in contrast to the average summer montly rainfall of one inch) over repeated and nearly consecutive years, takes a toll. We see such summers, with two bone-dry months in 2012 and 2015. 2013 had one dry month.
Perhaps the strongest argument against the weather hypothesis, in which weather is the driving cause, if not the proximal cause, is that most of the sword ferns in Seward's old-growth forest are in good health. The die-off is three years-old, spreads radially uphill and down, now occupying 5 acres (completely dead) and >20 acres (the total affected area).
One other thing about the drought hypothesis is that drought would work against a fungal disease. More likely the disease has been facilitated by increased spring rains that leave the soil saturated during warmer weather. Not saying that is the case because I haven't looked at rain and temperature records, but warm/wet is something that facilitates fungual disease while warm/dry does not.
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