Growth and foliar nutrition of juvenile western hemlock and western redcedar plantations on low- and medium-productivity sites on northern Vancouver Island: response to fertilization and planting density

Abstract

A factorial trial was established to examine the effects of planting density and fertilization on the growth of western redcedar (Thuja plicata Donn ex D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) on nutrient-poor (CH) sites and nutrient-medium (HA) sites. Two levels of NPK fertilization were crossed with three levels of planting density (500, 1500, and 2500 stems/ha). Fifteen years after establishment and 10 years after the last fertilizer application, height, individual stem volume increment, stand volume, 5 year periodic annual increment (PAI), and 5 year periodic height increment were all increased by fertilization. Fertilization of CH sites increased annual stand volume increment by 753%-2552% and 122%-209% for hemlock and cedar, respectively; fertilization of HA sites increased PAI by 94%-264%. Volume growth response to fertilization was greater on HA than on CH sites. Increasing stand density reduced height growth on CH sites but not on HA sites. These results suggest that competition for nutrients can be a significant growth-limiting factor even before canopy closure occurs and that treatment of ericaceous sites may not be justified by productivity increases.Résumé : Un dispositif factoriel a été mis en place pour étudier les effets de la densité de plantation et de la fertilisation sur la croissance du thuya géant (Thuja plicata Donn ex D. Don) et de la pruche de l'Ouest (Tsuga heterophylla (Raf.) Sarg.) établis sur des stations pauvres (CH) et modérément riches (HA) en nutriments. Deux niveaux de fertilisation en NPK ont été appliqués dans chacun des trois niveaux de densité de plantation (500, 1500 et 2500 tiges/ha). Quinze ans après l'établissement et 10 ans après l'application de la dernière fertilisation, la hauteur, l'accroissement en volume des tiges individuelles, le volume du peuplement, l'accroissement annuel périodique quinquennal (AAP) et l'accroissement périodique quinquennal en hauteur ont tous augmenté à cause de la fertilisation. La fertilisation des stations CH a augmenté l'accroissement annuel en volume du peuplement de 753 % à 2552 % pour la pruche et de 122 % à 209 % pour le thuya. La fertilisation des stations HA a augmenté l'AAP de 94 % à 264 %. À la suite de la fertilisation, la réaction de la croissance en volume des stations HA a été supérieure à celle des stations CH. L'augmentation de la densité des peuplements a réduit la croissance en hauteur sur les stations CH, mais pas sur les stations HA. Ces résultats indiquent que la compétition pour les nutriments peut être un facteur important pour limiter la croissance des arbres avant même que survienne la fermeture de la canopée. De plus, il est possible que le traitement des stations à éricacées ne soit pas justifié par des augmentations de la productivité.[Traduit par la Rédaction]

Soil greenhouse gas and nutrient dynamics in fertilized western Canadian plantation forests

“…There have been a number of replicated, meso-scale experimental fertilization trials in Western Canada extending, at time of writing, up to nearly 4 decades across different forest types and Biogeochemical Ecosystem Classification (BEC, Meidinger and Pojar 1991) zones (e.g. Brockley 2007, record case of 25 fold over controls by Negrave et al (2007) in a y.o. cedar-hemlock coastal forest.…”

Soil carbon, nitrogen and phosphorus stoichiometry (C : N : P) in relation to conifer species productivity and nutrition across British Columbia perhumid rainforests

“…With mean annual precipitation near 3500 mm, these perhumid rainforests are at the extreme range in rainfall for the Pacific west coast (Carpenter et al, 2014). The evidence for P constraints outlined in this trial have been substantiated by fertilizer studies along northern Vancouver Island (Blevins et al, 2006;Negrave et al, 2007), but other areas in the Pacific Northwest have shown more variation in growth response to added P (Radwan et al, 1991;Mainwaring et al 2014). Lower precipitation levels or differences in soil mineralogy could mediate rates of soil podzolization and reductions in Pi so the full regional extent of these presumed P deficiencies should be examined and tested more thoroughly.…”

Contrasting conifer species productivity in relation to soil carbon, nitrogen and phosphorus stoichiometry of British Columbia perhumid rainforests

“…With mean annual precipitation near 3500 mm, these perhumid rainforests are at the extreme range in rainfall for the Pacific west coast (Carpenter et al, 2014). The evidence for P constraints outlined in this trial have been substantiated by fertilizer studies of very similar perhumid forests along northern Vancouver Island (Blevins et al, 2006;Negrave et al, 2007), but other areas in the Pacific Northwest have shown more variation in growth response to added P (Radwan et al, 1991;Mainwaring et al, 2014). Lower precipitation levels or differences in soil mineralogy could mediate rates of soil podzolization and reductions in P i so the full regional extent of these presumed P deficiencies should be examined and tested more thoroughly.…”