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Tree Damage after Fertilization of Thinned Lodgepole Pine, Douglas-fir, and Spruce Stands in the British Columbia Interior Synthesis Report on up to 18-year Responses from EP886

Author(s) or contact(s): Woongsoon Jang, Bianca N.I. Eskelson, and Louise de Montigny
Source: Ministry of Forests, Lands, Natural Resource Operations and Rural Development
Subject: fertilization, Douglas-fir, lodgepole pine, spruce, forest health, natural disturbances
Series: Technical Report
Other details: Published 2019
 

Abstract

As a silvicultural practice, forest fertilization has emerged to mitigate risks and
reduce the effect of damage agents on timber supply due to climate change and
on subsequent extensive landscape-scale natural disturbances in British Columbia.
In total, 61 installations were established in the central and southern
interior of British Columbia to quantify fertilization responses of major commercial
tree species. One-time fertilization with two to five kinds of fertilizer
blends was applied, and the stand ages at fertilization ranged from 9 to 58
years. Plots were repeatedly measured at 3-year intervals, although a few plots
were measured 2–4 years after fertilization. The repeated measurements (up
to 18 years after fertilization) indicated that trees were damaged by various
damage agents in the experimental sites, and that the fertilization may have
been associated with the damage agents’ activities. This report provides a
descriptive overview of the damage that occurred after fertilization in the
EP886 installations.

First, the major damage agents after fertilization were identified by comparing
proportions of damage records for each plot. Second, to account for
different measurement years since fertilization, annual damage rates were
calculated. The damage record proportions and damage rates were summarized
at different scales (i.e., plot and installation), and by size classes, age,
and fertilization treatments.

The results of the analyses indicated the following:
1. The four most prevalent damage agents after fertilization were squirrels
(accounting for 11.8% of total damage records), western gall rust (16.4%),
mountain pine beetle (19.5%), and white pine weevil (10.8%).
2. Squirrels, western gall rust, and mountain pine beetle were observed
only in lodgepole pine stands, whereas white pine weevil was exclusively
observed in spruce stands. The four major damage agents were not observed
in Douglas-fir stands.
3. The squirrel attack was concentrated in the stand age class of 25–30 years,
which implied a potential association between susceptibility and stand age.
4. Throughout the study periods, fertilized plots showed slightly lower average
plot-level damage than control plots for squirrel (0.1%) but higher damage
rates for western gall rust (1.0%), mountain pine beetle (5.2%), and white
pine weevil (6.6%).
5. Annual damage rate throughout the study periods after fertilization for
squirrel, western gall rust, mountain pine beetle, and white pine weevil
were 1.1, 1.2, 1.8, and 3.3%, respectively. Those annual damage rates for
control plots were 1.0, 1.1, 1.2, and 2.9%, respectively.

The results presented are purely descriptive. Further analyses are required
to assess more detailed associations between fertilization and tree damage. The
findings in this study will provide insights for further research, and subsequent
research efforts will provide useful information about the relationship between
fertilization and forest health for managing interior British Columbia forests
sustainably.

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Updated April 09, 2019