Table 2 Summary statistics calculated from the count of years in the current and previous 3 years in which cells with tree-ring dates are in the MFN.

Calculations for cells with dates reflect the MFN status for each subperiod of all cells for which any tree-ring date between A.D. 500 and 1400 is present. Calculations for local cells are based on only those cells with tree-ring dates in a given year or any of the previous 3 years. Period boundaries are as given in the text and in Table 1. x̄ is the mean, σ is the SD, G1 is an unbiased estimator of skewness, and G2 is an unbiased estimator of kurtosis. See also Fig. 5.

 Exploration Exploitation Cells withdates Local cells Cells withdates Local cells BM III x̄ (σ) 2.63 (1.39) x̄ (σ) 3.16 (1.11) x̄ (σ) 2.66 (1.40) x̄ (σ) 2.85 (1.37) G1 −0.64 G1 −1.24 G1 −0.69 G1 −0.94 G2 −0.88 G2 0.68 G2 −0.85 G2 −0.45 P I x̄ (σ) 2.54 (1.47) x̄ (σ) 2.87 (1.35) x̄ (σ) 2.54 (1.45) x̄ (σ) 2.94 (1.29) G1 −0.55 G1 −0.99 G1 −0.55 G1 −1.03 G2 −1.12 G2 −0.30 G2 −1.10 G2 −0.12 P II x̄ (σ) 2.47 (1.44) x̄ (σ) 2.73 (1.28) x̄ (σ) 2.61 (1.42) x̄ (σ) 2.69 (1.37) G1 −0.48 G1 −0.71 G1 −0.64 G1 −0.70 G2 −1.12 G2 −0.60 G2 −0.95 G2 −0.80 P III x̄ (σ) 2.53 (1.40) x̄ (σ) 2.60 (1.37) x̄ (σ) 2.50 (1.42) x̄ (σ) 2.65 (1.36) G1 −0.56 G1 −0.61 G1 −0.50 G1 −0.63 G2 −0.98 G2 −0.90 G2 −1.09 G2 −0.88 P IV x̄ (σ) 2.79 (1.34) x̄ (σ) 2.81 (1.33) — — G1 −0.85 G1 −0.85 — — G2 −0.51 G2 −0.50 — —