Pseudotsuga macrocarpa (Vasey) Mayr

A relict species endemic to a small area of southern California, Pseudotsuga macrocarpa is aptly named, having comfortably the largest seed cones in the genus at 9–18 cm long, although usually smaller in cultivation in Europe. It is closely related to P. menziesii but distinct on account of its cones, stiffer more radially arranged needles, and for being a smaller tree, rarely exceeding 20 m tall except in the most sheltered sites where individuals to 44 m have been recorded (Lipscomb 1993); its range also lies wholly outside that of P. menziesii (Gibson 1913).

Except on a very local scale Pseudotsuga macrocarpa has never really been persecuted for its timber, which is ‘inferior in most ways to that of the Douglas Fir, lighter, weaker, and less elastic’ (Gibson 1913). Its IUCN assessment Near Threatened stems from the significant risk posed by fire, especially in the drier forest community under a Mediterranean climate with long, hot summers. Fire prevention measures and fire-fighting by forest management have mitigated this threat thus far, but in a warming climate this risk will likely increase, especially in light of the increasing human presence (Thomas 2019; Farjon 2017). Although many populations occur in protected areas such designations offer no protection against fire, but P. macrocarpa has exhibited some resilience against relatively intense fires thanks to its thick bark and ability to resprout (Steel, Safford & Viers 2015).

The American botanist C.C. Parry collected Pseudotsuga macrocarpa in 1850, but both he and Torrey initially mistook it for P. menziesii, hence Sargent later (1897) attributed the discovery to the Lieutenant Ives Exploring Expedition whose participant J.S. Newberry collected material in November 1857; once more material was available to testify to its distinctiveness, Torrey described Bigcone Douglas Fir in 1860, albeit as a variety of P. menziesii (Hermann 1982). Even by the end of the 19th century P. macrocarpa was not thought to be in cultivation on either side of the Atlantic (Sargent 1897) and while it seems reasonable to assume that it would have been attempted in a few of the early American collections, the earliest documented introduction to cultivation would appear to be that of Capt. H. Clinton-Baker who introduced seed to Britain in 1910, the same year he also introduced P. japonica (Bean 1976). This introduction may have been the source of trees at the Arboretum National des Barres, France, where by the early 1960s there were trees reaching ‘a vigorous and healthy 50 ft. [15.2 m], coning freely’ (Mulligan 1962).

In the same year a tree Clinton-Baker had planted at his home in Bayfordbury, Hertfordshire, UK, was c. 11.6 m × 22 cm dbh, and in 1964 the larger of two trees grafted in 1925 at Bedgebury, Kent, was 18.2 m × 53 cm dbh (Bean 1976). By 2015 the Bedgebury trees were 31.5 m × 95 cm dbh (the UK and Ireland champion) and 28 m × 78 cm dbh; others exceeding 20 m grow at the Sir Harold Hillier Gardens, Hampshire (21.4 m in 2013), Parc Cefn Onn, Glamorgan (23 m in 2013), Borde Hill, West Sussex (23 m in 2015) and Avondale Forest Park, Wicklow (23.5 and 24.5 m in 2000) (Tree Register 2023). Smaller trees grow in several collections across southern Britain but it remains rare, and not being so hardy as Pseudotsuga menziesii it requires some shelter when young (Rushforth 1987); it also benefits from meaningful summer heat, but young trees are thriving as far north as the Yorkshire Arboretum (pers. obs.). It is cultivated in a few specialist collections in the western USA, including the San Francisco Botanical Garden (pers. obs.). P. macrocarpa has been noted for its drought tolerance and it may prove a useful ornamental in various landscapes that must adapt to the warmer and drier conditions of the future.