Forest Investment Account (FIA) - Forest Science Program
FIA Project M075012

    Treatment of Repressed Lodgepole Pine Stands
Project lead: Newsome, Teresa
Author: Newsome, Teresa A.
Imprint: [BC] :, 2007
Subject: Forest Investment Account (FIA), Pinus Contorta, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
In 1996, a joint industry-government committee, the Timber Investment Strategy Committee (TISC), made reference to the existing inventory database which listed over 130,000 ha of height repressed lodgepole pine stands in the Cariboo Forest Region (TISC 1996). These stands were in height class 1 (under 10.4 m tall) and in age classes 2, 3 and 4 (21 to 80 years old). Many of these stands are growing at a site index less than 7, and provide minimal contributions to the Annual Allowable Cut (AAC). This poor growth is associated with high densities of pine establishing after wildfires and persisting over time. Height repression in lodgepole pine has previously been studied, with little evidence of response to treatment (e.g., Goudie 1980; Bassman 1985; Keane 1985; Worrall 1995). As part of the Cariboo Timber Investment Strategy, forest licensees and the Ministry of Forests deemed it a high priority to return these forest types to their potential productivity. With the timber fall down that is expected to result from accelerated harvest of mountain pine beetle (MPB) killed stands, there is a critical need to increase forest productivity wherever possible. In addition to the issue of productivity, a significant area occupied by repressed pine stands is located within the ~1.5 million ha range of the northern caribou in the west Chilcotin. This ungulate is blue-listed provincially and threatened nationally. Their principle winter food source is terrestrial lichen which is found growing under older pine canopies and studies have shown that the lichen do not survive well following clearcutting (Miege et al. 2001). Increased rates of harvesting in MPB affected stands have the potential to decrease lichen abundance. Despite the fact that terrestrial lichen is common in repressed pine stands, the Northern Caribou Strategy (Youds et al. 2002) identified these stands as having little value for caribou due to the high stem density acting as a physical barrier to movement. Thinning treatments could facilitate caribou movement through the stands, although the effect of these treatments on lichen species composition and abundance must also be considered. Thinning treatments applied to improve growth of repressed pine stands have the potential to provide caribou habitat, but the effects must be carefully studied. In 1997, an industry/MOFR group was formed to address the Chilcotin repressed pine issue. Two approaches to the management of these stands were identified. The first approach was application of stand tending treatments to existing stands. Not only were these stands very dense but pre-treatment foliar analysis indicated severe nutrient deficiencies, particularly in nitrogen, sulfur and boron. Therefore, the recommended stand tending treatments included a combination of thinning and fertilization. The second approach was site rehabilitation + stand replacement (i.e., removal of the existing repressed pine stand, in some cases followed by site preparation, and then planting lodgepole pine seedlings). Limiting factors for seedling development on these sites include severe climate conditions (dry and cold), cold and sometimes dry soils, nutrient deficiencies, as observed in the existing stands, and vegetation competition from grasses. The first trial established to explore these issues, supported by West Fraser Ltd., was located approximately 80 km west of Williams Lake in the SBPSdc subzone. The 36 year-old pine stand originated from the Rosita Fire (from which the trial is named) and was approximately 3-m tall, with approximately 40,000 stems/ha. The study included both stand replacement and stand tending options. Early results showed that pine were responding positively to stand tending treatments, which in this case consisted of fertilization treatments applied with and without thinning. At about the same time, Farnden and Herrring (2002) were reporting similar findings in another study near Prince George. As a result, partners involved in the present project agreed to more fully explore stand tending options in two additional experiments. These were installed in repressed pine stands in the more extreme climate of the SBPSxc subzone where a majority of repressed pine stands as well as a substantial portion of caribou habitat are located Tolko Industries Ltd supported a trial at Luck Mountain, approximately 30 km NW of Alexis Creek. This trial replicated all the stand tending treatments and one site rehabilitation + stand replacement treatment from the Rosita Fire trial in a ~70 year-old, ~3 m tall stand with ~30,000 trees/ha. An additional stand tending treatment was also added to examine the effects of fertilization followed by thinning two years later. It was hoped that early fertilization would allow the most vigorous stems to be easily identified for retention as crop trees during thinning operations. The third trial, supported by Yun Ka Whu’ten Holdings ltd., was located near Anahim Lake to examine the effects of fertilization on repressed pine stands that had been thinned 5 to 7 years previously. A substantial growth response to the increased growing space from thinning alone was expected but not realized. On these sites three different fertilizer formulations were tested to determine which nutrients were critical. Early results from all three experiments indicate a very positive pine growth response occurs where appropriate fertilizer blends were applied. Mean leader length has consistently increased by 300-400% from fertilizer application in comparison with the untreated control (i.e., 28 cm versus 7 cm respectively). Thinning in combination with fertilization is generally producing the largest overall growth increases. Seven years after fertilization at the Rosita Fire, pine are continuing to grow at an accelerated rate that is more reflective of the expected site index. Early results from the Rosita Fire experiment are published in Newsome and Perry (2002). If long-term release from height repression is possible (as suggested by Farnden and Herring 2002), it is important to know which treatments are most effective, the degree to which the growth improvements are sustained over time, and what the expected site index and volume increments will be. All three experiments are designed to collect data that can be used in growth and yield models that project future stand development. If it appears that the repressed stands can be stimulated to reach a harvestable state within approximately 50-60 years, the projected costs and benefits of site rehabilitation + stand replacement versus tending of existing stands can be compared.
Contact: Newsome, Teresa, (250) 398-4408,


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Updated August 16, 2010 

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