Maximum Productivity Study

- Growth and Yield -

Objectives

The primary objectives of the "maximum productivity" study are to compare the effects of different regimes and frequencies of repeated fertilization on the growth and development of young lodgepole pine and interior spruce managed stands, and to determine optimum fertilization regimes for maximum stand volume production.

Plot Establishment

The protocol used for the establishment and measurement of the eight "maximum productivity" field installations is consistent with standards developed by the Forest Productivity Council of British Columbia. Each installation contains 18 rectangular, 0.164-ha treatment plots. Each treatment plot consists of an inner, square 0.058-ha "assessment" plot surrounded by a treated buffer. The assessment plot is offset at one end of the treatment plot to reserve an enlarged buffer area for future destructive sampling. Three sides of the assessment plot are surrounded by a 6.04 m buffer; the buffer on the fourth side is 15.1 m wide.

Each treatment plot contains approximately 180 crop trees, equivalent to a stand density of 1100 stems per hectare at 3-m square spacing. Growth analyses for each plot are based on periodic measurement of 64 permanently tagged trees within the inner assessment plot. Conifer and broadleaf ingress is periodically removed from treatment plots.

At each study site, treatment plots are systematically located so that within- and between-plot conditions (e.g., stand density, tree height, tree dbh, soil characteristics, and minor vegetation) are as uniform as possible. The outer boundaries of adjacent treatment plots are separated by a minimum distance of 5 m. A minimum distance of 20 m separates the outer treatment plot boundaries from major disturbances (e.g., roads or large stand openings).

Experimental Design

At four study sites (Kenneth, Crow Creek, Tutu Creek, and Hand Lake), treatments were randomly assigned to each of the plots such that each treatment was applied to three plots (i.e., completely randomized experimental design). At the four remaining sites (Sheridan Creek, McKendrick Pass, Lodi Lake, and Crater Lake), geographic separation of plots or possible site differences (e.g., slope position) dictated a randomized complete block experimental design. In these cases, treatment plots were grouped into three "blocks" (e.g., 6 plots per block) such that site and stand conditions were as uniform as possible within each block (e.g., upper, middle, lower slope position). Each of the six treatments was randomly assigned to one plot within each block.

Measurement

All of the "maximum productivity" installations are currently on a 3-year re-measurement cycle. The diameter at breast height (dbh), total height, height to live crown, and crown width of all 64 tagged trees within each treatment plot are recorded at each measurement.

The development of apparent leaf area index (LAI) is measured at each installation, timed to coincide with the 3-year remeasurement cycle. Field measurements are made in late spring immediately prior to bud flush following the fall remeasurement. Leaf area is measured with a Li-Cor LAI-2000 plant canopy analyzer. Within each treatment plot, measurements are obtained at a height of 80-100 cm above the ground at the nine permanently marked points. Two readings are obtained at each point, one facing northwest and the other facing northeast. Simultaneously, above canopy light measurements are collected in an open area adjacent to the study site where the light sensor has an unobstructed view of the sky.

Foliar Sampling

Replicated samples of current year´s foliage are collected from control, ON1 and ON2 treatment plots each fall (late September to late October). For all other treatments (i.e., NB, NSB, and Complete), foliage is collected in the fall prior to each fertilizer application and after the 1st and 6th growing seasons following fertilization.

Foliage is collected from 10 representative healthy dominant or codominant trees evenly distributed within each assessment plot. Samples are collected from the lower portion of the top 1/3 of the live crown, consistent with standardized foliar sampling guidelines. Whenever possible, the same trees are sampled each year. One composite sample, consisting of equal amounts of foliage from each of the 10 trees per treatment plot, is submitted to the Ministry of Forests analytical laboratory for chemical analysis.

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Summary of Results

At least 6 years of growth measurements have been obtained from seven of the eight "maximum productivity" installations. Research highlights to date include:

• Young spruce plantations are apparently particularly well suited to "high input" silviculture. Although four of the five lodgepole pine stands have produced significant growth gains following periodic and yearly fertilization, the responses to date have been more variable and smaller than those obtained at the spruce study sites. These species differences are consistent with those previously reported from similar studies with Scots pine and Norway spruce.
• Foliar nutrient imbalances and growth disruptions have apparently been induced by large, and frequent, N additions at some pine study sites.
• The largest spruce responses have been associated with the most intensive fertilization treatments. Annual fertilization produced 6-year stand volume increments that ranged from 213-280% higher than control values.
• In one spruce stand, 9-year stand volume increment in the ON2 treatment was almost four times larger than in the unfertilized stand. This represented an absolute volume gain of 45 m3/ha.

Figure 1. Leaf area index by treatment nine years after installation establishment at: a) Sheridan Creek (lodgepole pine) and b) Crow Creek (spruce)

It´s too early to reliably predict the potential impacts of intensive fertilization on harvest yields and/or rotation length of managed interior spruce and lodgepole pine forests in the B.C. interior. However, preliminary responses from "maximum productivity" research installations appear to be tracking along pathways similar to the Scots pine and Norway spruce "optimum nutrition" studies in Sweden. The Swedish results suggest that the growth of Norway spruce can potentially be doubled in southern Sweden, and more than tripled in the north, by frequent application of balanced fertilizers. Growth projection models estimate that the rotation length for Norway spruce can be shortened by 20-30 years in the south and by 40-60 years in the north. In the B.C. interior, productivity gains and accelerated stand development of similar magnitude would be of huge benefit in addressing future timber supply challenges.

It´s important to continue monitoring stand development in all "maximum productivity" installations to see whether these early species growth trends continue, and to determine how closely growth gains from periodic fertilization (i.e., every 6 years) of spruce and pine will approximate the responses achieved by yearly nutrient additions.

Figure 2. Stand volume development at: a) Sheridan creek (lodgepole pine) and b) Crow Creek (spruce) "maximum productivity" installations.

Publications

A complete description of preliminary results is provided in the following publication:

Brockley, R.P. and D.G. Simpson. 2004. Effects of intensive fertilization on the foliar nutrition and growth of young lodgepole pine and spruce forests in the interior of British Columbia (E.P. 886.13): establishment and progress report. B.C. Ministry of Forests, Victoria. Technical Report 018. [PDF]

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Last Modified: 2007 APR 20.  Ministry contact: Frank van Thienen
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