Fig. 1. From left to right: (A) a defect-free tree with neither codominant stems nor a double crown; (B) a tree with codominant stems; (C) a tree with a double crown; (D) a codominant stem that has split into a double crown. Diameter at breast height (DBH) was measured by the harvester during the field study. Consequently, breast height is approximately 1.3 m above ground level. The forking always occurred above the breast-height level in our study.

Table 1. Random effect (i.e., block) estimates (s tree^{–1}) from the linear mixed model (LMM) analysis for the dependent variables. Diameter at breast height (DBH) is provided in cm. The number of trees (n) in the final dataset was 1503. All trees were lodgepole pines (*Pinus contorta* Douglas ex Loudon). |

| Dependent variable | Mean DBH^{ (a} | n |

Total time | Crane-out | Processing |

Estimate | p-value | Estimate | p-value | Estimate | p-value |

Block 1: operator A, old machine | 0.097 | 0.947 | 0.118 | 0.799 | –0.023 | 0.983 | 25.8 | 579 |

Block 2: operator A, new machine | –3.269 | 0.026 | –1.239 | 0.008 | –1.971 | 0.071 | 23.0 | 391 |

Block 3: operator B, old machine | 3.565 | 0.018 | 0.673 | 0.164 | 2.824 | 0.012 | 25.1 | 191 |

Block 4: operator B, new machine | –0.393 | 0.790 | 0.448 | 0.340 | –0.830 | 0.449 | 23.6 | 342 |

Table 2. Fixed effect estimates (s tree⁻¹) from the LMM analysis for the dependent variables. The machine was either repositioned during the crane-out work element or not (driving: yes/no). Driving and processing did not occur simultaneously. The covariate DBH should be provided in cm. |

Dependent variable | Effect | Estimate | Standard error | t-value | p-value |

Total time | Intercept | 46.03 | 2.25 | 20.43 | <0.001 |

DBH | 0.80 | 0.05 | 17.46 | <0.001 |

Codominant stems: | No | –31.31 | 0.96 | –32.47 | <0.001 |

Yes | 0 | | | |

Double crown: | No | –1.81 | 0.58 | –3.14 | 0.002 |

Yes | 0 | | | |

Driving: | No^{ (a} | –6.94 | 0.44 | –15.84 | <0.001 |

Yes | 0 | | | |

Crane-out | Intercept | 13.43 | 0.87 | 15.52 | 0.001 |

DBH | 0.00 | 0.02 | 0.07 | 0.941 |

Codominant stems: | No | –1.29 | 0.41 | –3.14 | 0.002 |

Yes | 0 | | | |

Double crown: | No | 0.01 | 0.25 | 0.05 | 0.956 |

Yes | 0 | | | |

Driving: | No^{ (a} | –6.80 | 0.19 | –36.40 | <0.001 |

Yes | 0 | | | |

Processing | Intercept | 32.50 | 1.83 | 17.80 | <0.001 |

DBH | 0.80 | 0.04 | 20.21 | <0.001 |

Codominant stems: | No | –30.03 | 0.83 | –36.08 | <0.001 |

Yes | 0 | | | |

Double crown: | No | –1.83 | 0.50 | –3.67 | <0.001 |

Yes | 0 | | | |