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Fertilizer x Thinning Interactions in Lodgepole Pine (EP 886.01d)

Last updated on August 22, 2023

Introduction

Many experiments have compared fertilization growth responses in thinned and unthinned stands. However, few studies have examined the effects of fertilization across a range of post-thinning densities. Given the large impacts of juvenile thinning on stand structure and development, it is likely that the level of post-thinning density may also affect tree and stand growth following fertilizer application.

In 1992, the B.C. Ministry of Forests, Research Branch established an experiment to determine the effects of different levels of post-thinning density, with and without repeated fertilization, on the growth and development of young, harvest-origin lodgepole pine. The site is located southeast of Williams Lake within the moist-cool subzone of the SBPS biogeoclimatic zone. The unthinned, harvest-origin stand was approximately 10 years old at the time of installation establishment.

Objectives

To determine the effects of different post-thinning stand densities on the growth and development of unfertilized and fertilized lodgepole pine, and to examine the nature of fertilizer x thinning interaction.

Treatments

Factorial combinations of three post-thinning densities (600, 1100, and 1600 stems per hectare) and two levels of fertilization (unfertilized, fertilized) are replicated three times and arranged in a completely randomized design. Treatment plots are rectangular, and vary in size from 0.09 to 0.24ha depending on post-thinning density. Each treatment plots consists of an inner, square assessment plot (with 64 tagged trees) surrounded by a treated buffer. The assessment plot is offset at one end of the rectangular treatment plot to reserve an enlarged buffer at one end of the treatment plot for future destructive sampling. There are also three replicates of small, unthinned control plots that are large enough to contain at least 200 trees.

A balance fertilizer blend is applied to the fertilized treatment plots every 5 years. Fertilizer application rates are as follows (kg/ha): 200N, 100K, 100P, 75S, 38Mg, 3B.

This installation is re-measured at 5-year intervals. Measurements include diameter at breast height, total height, height to live crown, crown width, tree form and damage). Leaf area development is also being monitored within each treatment plot. Foliar nutrient data are obtained from all treatment plots prior to, and one year after, every fertilizer application.

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