Pothole Creek
Study Area

Related Work

Stand Modelling
Demonstration Area

• IDF Timber Supply
• Area Land Base
• Development of Area
• Growth and Yield Studies
• Silviculture Trials
   • Fill Planting
   • Stand Tending

Silviculture Trials

In the summer of 1997, two silviculture trial areas were established within the Pothole Creek Demonstration Area, in order to demonstrate potential fill planting and and spacing treatments.

Site Preparation and Fill Planting

1. To determine the suitability of an excavator for preparing sites for fill planting within the openings of low-stocked interior Douglas-fir stands, and
2. To determine the suitability of interior Douglas-fir (Fdi), Ponderosa pine (Py), lodgepole pine (Pl), and western larch (Lw) for planting on these machine prepared sites.

Site Preparation
Before work began, areas of difficult terrain and scattered clumps of residual trees which had to be avoided were identified and discussed with the operatior while walking portions of the site. A CAT 320L excavator with a VH mulcher head was used for site preparation. The head is a hydraulically operated rotating disk mounted onto the boom arm of the excavator, which breaks and mixes the upper 50 to 75 cm of the soil, producing a plantable spot approximately 1 m in diameter. Approximately 3400 plantable spots were created in four days (40 hours), creating a trial area of about 7.1 ha, including portions that were not treated such as rocky outcrops, patches of residual trees, and larger exclusions around several draws which contained trees, rock, and steep slopes. This work was completed in late fall 1997.

Fill Planting
In the early spring of 1998, 7750 seedlings were planted in the prepared area, including 2250 Fdi, 2250 Pl, 2250 Py and 1000 Lw seedlings. A survival study involving 500 of the prepared spots was developed. Each spot was tagged and planted with four seedlings (one of each species). Information on the local aspect, slope, crown closure and surrounding basal area at each spot was recorded. No consideration of microsite was applied during planting. A post-planting survey in late summer 1998 showed survival and growth to be excellent, despite a very hot, dry summer. However, browsing (most likely from hares) affected many of the seedlings. A further 5750 seedlings were planted throughout the rest of the area at two seedlings per prepared spot.

Results

An August 1999 assessment of the 500 survival study plots determined that mortality was high at 64%. Western larch was found to be the most successful species, followed by interior Douglas-fir. The lodgepole pine and Ponderosa pine had suffered heavy browsing damage. By the fall of 2000, the survival was 51% for western larch, 49% for interior Douglas-fir, 26% for lodgepole pine and 18% for Ponderosa pine. The Douglas-fir was most heavily browsed at 62% of live trees, followed by 53% for Ponderosa pine, 44% for lodgepole pine, and 23% for western larch. Both mortality and browsing seemed to have levelled off by this time. The study replication was found to be insufficient to determine any trends in the relationship between survival and slope, aspect, canopy closure or surrounding basal area.

Stand Tending

The stand tending trial area included three different stand types: patchy, older interior Douglas-fir (Fdi), a young, more even-aged mix of Fdi and lodgepole pine (Pl), and a drier, western-facing hillside of multi-layered Fdi stands. The objectives were:

1. To provide a visual demonstration of alternative spacing regimes in these stand types, and
2. To provide an opportunity for the BC Ministry of Forests Research staff to evaluate spacing regimes in concert with their studies on site-limiting factors.

The three spacing treatments were as follows:

Area 1: "Best Tree" (2.5 ha)
This regime was developed following the recommendations of Dr. Ken Mitchell (BC Ministry of Forests Research Branch) to preserve and provide adequate growing space for the trees with the highest crop tree potential (those with vigorous crowns, good form, and freedom from disease), with even spacing a secondary goal. The general target was to achieve 800 to 1,000 stems per hectare final density, with space around crop stems equivalent to the height of the tree to a maximum of four metres. Deformed and diseased stems were to be cut out, and nothing above 17.5 cm diameter at breast height (DBH) removed. This treatment is within the patchy, older stand in the southern-most part of the stand tending trial, and borders on the MOF Research area (see Figure 6).

Area 2: 2.0 m x 2.0 m spacing (2.5 ha)
This treatment was applied to the denser, more even-aged Fdi and Pl mixed stands. The desired result was a standard spacing regime of a 2.0 m x 2.0 m inter-tree distance, with a minimum of one metre allowed. Deformed stems were to be removed; all trees 12.5 cm DBH and larger were to be left. To ensure that the later removal of larger diameter stems in the next harvest would not create gaps, stems over 30 cm DBH were to be ignored during spacing decisions.

Area 3: 3.4 m (2.2 ha)
This area was also located within the more even-aged Fdi and Pl mixed stand type, and had the same objectives as Area 2, but at wider spacing (3.4 m x 3.4 m inter-tree distance) and with the additional requirement that all trees under 50 cm height were to be preserved.

Area 4: Space to a reverse J-curve: Target q=1.7 (0.5 ha)
This regime was developed for the drier, western-facing hillside in the north end of the trial area. The objective was to achieve some form of classic single-tree selection treatment for the lower layers of the canopy, and to determine if "rules" could be developed for spacing crews to follow that would create a preconceived diameter distribution. A pre-treatment sample was taken to estimate the current diameter frequency distribution. Then a "q" value of 1.7 was selected to smooth the frequency into the classic reverse J shape. This projected diameter distribution was then translated into spacing rules for each diameter class (DBH) as follows: trees less than 1.3 m height: cut 1 of every 2 trees; 0 to 7.5 cm diameter: cut 3 of every 4 trees; 7.6 to 12.5 cm diameter: cut 3 of every 4 trees; 12.5 to 17.5 cm diameter cut 1 of every 2 trees. Clumps of trees were to be spaced individually by removing deformed and diseased stems first, and then thinning the larger diameter classes before the smaller ones. No trees over 17.5 cm were to be removed, and spacing was reduced to half distances adjacent to openings.

Results
Clear communication and ongoing consultation with the spacing crew were essential for achieving the objectives for each treatment area. The reasoning behind each selected spacing regime was discussed, and "rule cards" for each treatment were developed for the workers to carry. This assisted crews in taking responsibility for producing a treatment rather than for performing an activity.

In post-treatment discussions with the workers, the crew unanimously agreed that clear direction and the pre-treatment discussion of the goals for the areas had helped them gain confidence in their tree selections. They felt more likely to take interest in the work and act conscientiously if they had a sense of helping to create a particular stand condition. The spacing conducted in Area 1 was the most time consuming because the larger stems required limbing and bucking. However, they enjoyed the freedom of selecting quality stems and removing those that were deformed and rotten. The spacing in Areas 2 and 3 were more standard and, in some places, rules were overlooked resulting in tighter spacing than desired. The reverse J-curve spacing was the most interesting for the crew, but also the most inconsistently applied between cutters. The crew felt that the regime was possible to standardize, but would always require close supervision and clear instructions to the spacing crew. It was agreed that productivity would improve once the crew became familiar with what was to be accomplished. The ultimate objective would be for a crew to space an entire area such as the treatment unit in a continuous pass, adjusting their spacing according to the differences in stand structure.

During the summer of 1998, a fire destroyed the reverse J-curve spacing (Area 4). A new area was spaced in November of 1999 to replace this treatment (Figure 7). The spacing rules were changed to reflect the different initial stand structure: spruce and aspen stems left unless diseased or excessively dense, root disease patches flagged and avoided, one meter minimum inter-tree distance for stems = 5 cm DBH, with no minimum distance for smaller stems, all trees under 1.3 m height left unless diseased or of poor form, and the upper threshold for cutting was reduced to 15 cm DBH.