Fig. 4.
The acoustic emission rate per 10 minutes (AEs/10 min) related to maximum AEs/10 min (a–d) and the relative AE rate (AEs/10 min related to all AE signals detected at the same time interval) (e–g) clustered by the following peak amplitude (PAAE) ranges: 30.5 dB ≤ PAAE < 40 dB, 40 dB ≤ PAAE < 50 dB, 50 dB ≤ PAAE < 60 dB, and PAAE ≥ 60 dB at 5% steps of relative water loss. Error bars represent 1 standard error. Significant differences between juvenile (open symbols, dashed lines; n = 12) and mature (closed symbols, solid lines; n = 12) Norway spruce (Picea abies) beams are marked with * at the corresponding relative water loss if significant at the 0.05 level, with ** if significant at the 0.01 level, and with *** if significant at the 0.001 level.