Canadian Forest Service Publications
Heatsum-emergence relationship in Douglas-fir seedlings. 1978. Bloomberg, W.J. Canadian Journal of Forest Research 8(1): 23-29.
Issued by: Pacific Forestry Centre
Catalog ID: 1946
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Usefulness of classifying Douglas-fir seed lots using heatsum–emergence relationship parameters was examined by (1) comparing nursery emergence with that predicted by the relationship, (2) testing seed lots for conformity to the relationship, and (3) computer simulation of emergence under various temperature regimes. The emergence parameters used were threshold heatsum (degree-hours above 0 °C that must be accumulated before emergence starts), emergence coefficient (percentage emergence per thousand degree-hours above the threshold), slow emergence percentage (percentage emergence at which the emergence rate is reduced), and slow emergence factor (amount by which the emergence coefficient is reduced). Emergence of seed lots at two nurseries was accurately predicted by a computer model based on the heatsum–emergence relationship. Five seed lots sown in growth chambers under two temperature regimes showed good conformity to the relationship. Computation of emergence percentage and days to 50 or 100% emergence was carried out by a computer model using various emergence parameter values chosen from the observed range and simulated temperature regimes comprising daily heatsums at the 0.5-cm soil depth for 40 days after sowing. These heatsums were derived by regression equation from air temperatures at a forest nursery and were increased or decreased to represent warm or cool regimes or combinations of both. Generally, emergence percentage increased and number of days to 50 or 100% emergence decreased as emergence coefficient and slow emergence percentage increased and threshold heatsum decreased. Emergence percentage was affected by temperature regime only at low emergence coefficients. Number of days to 100% emergence was affected by temperature regime only at average or high emergence coefficients.