May 1999 Selection silvicultural systems in …web.unbc.ca/~wetbelt/docs/stevenson-et-al-1999.pdfmaintained by Global Positioning System (GPS) traverses of cut areas within this treatment

Prince GeorgeForest Region��

ForestResources &

Practices Team

May 1999Note #PG-19

• Extension • Research • Consulting •

Effects ofselection

harvesting onstand

dynamics,structural

biodiversity,and caribou

habitat.

Background

Experimentation with the selection silvicultural system in theEngelmann Spruce-Subalpine Fir (ESSF) Zone of east-centralBritish Columbia began nearly ten years ago. The initial impe-tus for partial cutting came from concerns about specific non-timber resources, such as scenic values, water quality for do-mestic use, and habitat for mountain caribou (Rangifertarandus). A set of first-generation management trials wasestablished through the Mountain Caribou in Managed For-ests program to assess whether it was feasible to use partialcutting to maintain both timber harvest and caribou habitat(Stevenson et al. 1994, Armleder and Stevenson 1996, Jullet al. 1996). One of these was a single-tree selection harvestblock at Pinkerton Mountain (CP 376), established in 1991.The results at CP 376 and the other management trials havebeen monitored and used to design new silvicultural systemsblocks.

Maintaining caribou habitat remains one of the corereasons for using the selection silvicultural system in the ESSF.Some land use plans, including the Prince George Land andResource Management Plan (LRMP) call for the use of partialcutting rather than clearcutting in specified caribou habitat

Selection silvicultural systems in mountain caribouhabitat: Logging and learning at Pinkerton Mountain

by Susan K. Stevenson, Mike Jull, and Darwyn S. Coxson

zones. But there are other reasons for using selection silvicul-tural systems in wet forest types. Forest management thatmimics natural disturbance regimes is expected to maintainbiodiversity better than past forestry practices. In the InteriorWet-belt, where forest fires and other stand-destroying eventsoccur infrequently, selection silvicultural systems are likely toproduce stands that are more natural in structure than thosethat result from clearcutting. Selection silvicultural systemshave the potential of combining timber harvesting with man-agement for a wide variety of resource objectives.

There has been little testing or monitoring of single-tree selection or group selection in the ESSF, and there iscontroversy over their potential advantages and disadvan-tages. Harvesting concerns focus on the cost and complexityof these systems. Silvicultural concerns focus on regenerationcomposition and growth, regeneration risks, logging damageto the residual stand, and windthrow potential in partial-cutstands. Wildlife habitat concerns include the short- and long-term abundance of arboreal lichens for mountain caribou for-age, and the continuing presence of wildlife trees and coarsewoody debris. The Pinkerton Mountain trial is structured toprovide a side-by-side comparison of the short- and long-termeffects of two stand management options across an equivalentrange of elevations and site types.

Project overview and objectives

Building on the results of earlier trials, a secondsilvicultural systems block at Pinkerton Mountain, CP 377,was harvested in late winter 1998. It is the first of a set ofreplicated silvicultural systems trials to be established underthe Northern Rockies Wet-belt ICH/ESSF Silvicultural Sys-tems Research Project. These trials have several purposes.They help to build a pool of local practitioners who haveexperience with design, layout, harvesting, and silviculture inpartially cut blocks. They allow us to examine the short-termand long-term responses of key indicators of stand dynamicsand biodiversity to variations in opening size and level ofvolume retention. And they serve as study sites for otherresearch projects that examine other ecosystem responses topartial cutting.

The Silvicultural Systems project is linked to otherprojects that share study sites through the Northern Wet-beltForest Research Co-operative, an informal collaboration ofFIGURE 1. Aerial view of the Pinkerton Mountain area.

Ministry of Forests, 5th Floor, 1011 - 4th Avenue, Prince George, BC V2L 3H9 Telephone: (250) 565-6100 Fax: (250) 565-4349

researchers from universities, government, and the privatesector; public groups; and forest licensees. One such project isForest Canopy Processes and Partial-Cutting SilviculturalSystems in Northern Wet-belt Forests. The Canopy projectfocuses on the effects of partial cutting on the arboreal lichensthat mountain caribou eat during winter. Some of the researchquestions that these two projects are addressing at CP 377 are:

• How do partial-cut silvicultural systems affect the devel-opment of growing stock, including stand productivity,stand structural development, species composition, loggingdamage, wind damage, and mortality?

• How do partial-cut silvicultural systems affect the lossand creation of structural biodiversity attributes, specifi-cally wildlife trees and coarse woody debris?

• How do the changes in canopy architecture brought aboutby partial cutting affect the distribution and abundance,physiological activity, growth and fragmentation, andlitterfall rates of arboreal forage lichens?

Site description

The study area is located in the Cariboo Mountainsabout 90 km ESE of Prince George, British Columbia, in theWet Cool Quesnel variant of the Engelmann Spruce-SubalpineFir Zone (ESSFwk1) and the Quesnel Highlands Ecosectionof the Columbia Mountains and Highlands Ecoregion (Figure3). The mesic to subhygric site is on a southwest-facing slope atan elevation of 1350 to 1470 m. Slopes are moderate, rangingfrom 0 to 40% . Pre-harvest basal area was approximately 35m2/ha, composed of 78% subalpine fir (Abies lasiocarpa) and22% Engelmann spruce (Picea engelmannii). The stand isuneven-aged and many of the trees occur in clumps, separatedfrom one another by gaps in the canopy. The originalunderstorey vegetation was dominated by white-floweredrhododendron (Rhododendron albiflorum) in the shrub layerand Sitka valerian (Valeriana sitchensis), Indian hellebore(Veratum viride), five-leaved bramble (Rubus pedatus), andoak fern (Gymnocarpium dryopteris) in the herb layer.

Prescribed harvest treatments

The silvicultural systems applied at the PinkertonMountain site include two contrasting types of uneven-agedselection systems: group selection (GS) on a 59-hectare treat-ment unit, and single-tree selection (STS) on a 40-hectare treat-ment unit (Figure 3). In the selection areas, wildlife-tree re-serves totalling approximately 6 hectares were retained. Thereis a 25-hectare unharvested control area just outside the north-west boundary of the block.

Prescription objectives

The operational motivation for partial-cutting atPinkerton Mountain results from its status as “Caribou Me-dium” habitat, as designated by the Ministry of Environment,Lands and Parks and approved under the Prince George Landand Resource Management Plan. Forestry activities in Cari-bou Medium areas must maintain mountain caribou habitatvalues, as described by Stevenson et al. (1994). The generalmanagement intent is to maintain late seral stand conditions andhigh proportions of large trees which bear abundant arboreal li-chens for forage. Partial cutting systems should remove no morethan 30% of the timber volume from the stand every 80 years.

Target stand conditions

Thirty percent basal area removal (or 70% retention)was prescribed for both GS and STS treatment units. Up toone-third of this basal area removal (or 10% of the pre-harvesttotal) in both units was anticipated in the cutting of designated

FIGURE 2. The group selection unit (left) and the single tree selection unit (right).

FIGURE 3. PinkertonMountain study area.


skid trails, assuming a maximum width of four metres andspacing of approximately 40 metres. Twenty percent of thebasal area and volume in the areas in between designated trailswas marked for harvest removal (Figure 4).

The 30% removal was expected to yield approxi-mately 80 to 100 m3/ha, providing a marginal but adequateeconomic return for costs.

Group selectionGroup selectionGroup selectionGroup selectionGroup selectionIn the group selection system, the level of removal

and timing of future stand entries is controlled by area regula-tion (Smith 1986), and removal is measured as the total per-cent of the area harvested in a given period. To maintain thepre-existing clumpy nature of the stand, we also defined thedesired shape of harvest groups. Rather than geometric shapes,harvest groups were irregularly-shaped aggregations of one orseveral pre-existing clumps of trees ranging from 0.1 to 0.4hectares, with a target mean opening size of 0.25 hectares(Figure 5). This approach works with, rather than against, theexisting spatial structure of the stand, and avoids arbitrarydivision of natural clumps by regular geometric harvest bounda-ries. It also provides a less regular, more “natural” appearanceto the final partial-cut stand. Area-based regulation of cut ismaintained by Global Positioning System (GPS) traverses ofcut areas within this treatment unit.

Single-tree selectionSingle-tree selectionSingle-tree selectionSingle-tree selectionSingle-tree selectionIn the single-tree selection system, level of removal

and timing of future stand entries is controlled by BDq regula-tion (Alexander and Edminster 1977, Guildin 1990), inwhich the residual stand is defined by setting stand targets forresidual basal area (B), maximum residual diameter (D), andthe shape of the post-harvest diameter distribution (q) (Figure 6).

We used operational cruise data to assess pre-harveststand structure and basal area, and determine targets for theresidual stand. The cumulative target basal area was deter-mined by the 30% constraint on level of removal in caribouhabitat. There was no maximum residual diameter; instead, amaximum harvested diameter was set at 52.5 cm dbh (exceptfor trees that had to be removed to clear skid trails). This wasdone because the largest trees carry lichen loading and wildlifetree values proportionately far greater than their contributionof 6% of the total stand basal area, and were expected to berelatively windfirm compared to codominant and intermedi-ate trees. To determine residual stand diameter distribution,we compared the diameter distributions that would result fromvarious q-values. The q-value of 1.2 was selected because itallows relatively high retention of larger diameter classes.

Marking rules for the STS unit followed the principleof “cutting the worst first”, and at a minimum, maintaining orincreasing the proportion of spruce relative to subalpine fir inthe residual stand.

Treatment layout

Designated skid trails

Layout of cut and leave trees in the GS and STS unitswas carried out by Northwood Inc.’s consultants in the sum-mer of 1996. The first step for both units was laying out


Marking rules for the Single Tree Selection (STS) Harvest Unit

1. Retain all trees greater than 52.5 cm dbh.2. Leave all trees where the pre-harvest live basal area is less than 25 m2/ha. (A range of basal areas from 15 to 55 m2/ha existed in the pre-harvest stand);3. Mark trees for cutting according to the following marking rules for each diameter class:

Diameter classDiameter classDiameter classDiameter classDiameter class Marking rule Percent removalMarking rule Percent removalMarking rule Percent removalMarking rule Percent removalMarking rule Percent removal17.5-22.4 Cut 4 trees of every 7 57%22.5-27.5 Cut 2 trees every 5 40%27.5-32.4 Cut no trees 0%32.5-37.5 Cut 1 tree of every 5 20%42.5-52.5 Cut 2 trees of every 6 33 %

4. Select individual trees for cutting according to the following specifications:

a)a)a)a)a) TTTTTree speciesree speciesree speciesree speciesree species Subalpine fir = first choice for cutting ; Engelmann spruce = second choice (Retention of spruce was encouraged as it iscurrently less abundant than subalpine fir, and an increase in the relative proportion of subalpine fir is not desired.)b)b)b)b)b) TTTTTree class / qualityree class / qualityree class / qualityree class / qualityree class / quality Take the worst, leave the best (Wherever possible, the marking objective is to cull the poorer grades of trees from thestand to establish a vigorous stand of trees capable of using the increased growing space available after the partial cut.)c)c)c)c)c) Lichen Loading Lichen Loading Lichen Loading Lichen Loading Lichen Loading If a choice is to be made between two trees of equal status, the one with the least amount of lichen is to be marked-to-cut.

designated skid trails by flag-ging the routes and recordingGPS locations. A minimumdistance between skid trails of40 metres was used to pro-vide a maximum long-line dis-tance of 20 metres. In theGS treatment, “speed trails”at distances of 70 to 100metres apart were laid out toprovide a series of fast skid-ding corridors between skidtrails attached to the groupharvest openings and land-ings. Trees or groups of treesto be logged were marked onlyafter the locations of desig-nated skid trails were known.

Single-tree selection

Marking rules provided to the marking crews weredeveloped co-operatively by licensee foresters and research-ers (Crampton 1996).

The marking crew covered the entire STS treatmentunit in a series of systematic transects. Along each transect,initial prism sweeps determined the pre-harvest basal area andthe number of trees available to be cut, based on the targetbasal area. The target basal area determines the minimumnumber of trees to be kept in a given area. The crew kept acontinuous tally of the number of trees marked and not markedin each diameter class.

The decision to mark an individual tree was based notonly on the marking rules, but also on practical falling issuesand the location of a tree in relation to a skid trail. As well,trees immediately adjacent to natural openings were not cut.After the crew finished marking in an area, they took finalprism sweeps to ensure that the target basal area range wasachieved.

Group selection

The GS openings were designed to have a minimumwidth of one tree length (about 30 metres) and a maximumwidth of about two tree lengths (about 60 metres). These sizelimits were achieved by harvesting aggregations of one or moreadjacent natural clumps up to the prescribed area size limits.

In planning the GS unit, the implications of currentharvest decisions for future harvest entries were considered.Harvest openings were spread more or less uniformly through-out the entire block. Their spatial distribution was planned sothat future harvests could be similarly distributed and not havetheir access compromised by poor skid trail layout. Wherepossible, openings were at least 50 metres apart and weredesigned to resemble a parallelogram or a teardrop oriented at35 to 45 degrees to the skid road. This angle was planned toallow a straight line skid from the upper to lower end of theopening and onto the skid trail.

Trees on the outside perimeter of the planned openingwere marked with orange paint above the level of thesnowpack, and with orange dots at the base. All marked treesand unmarked trees within the opening were to be cut. Tofacilitate layout and future tracking of harvested areas, GPSlocations were recorded for boundaries of marked groups.Although this latter procedure may not be required by regu-lations at time of writing, it is recommended.

The Silviculture Prescription for the GS unit indi-cates that the openings accounted for 24% of the total area ofthe unit, with skid trail area making up an additional 3%.

Harvesting

The GS and STS units were harvested in March andApril, 1998, by the forest licensee, Northwood Inc. under asingle cutting permit, CP 377. Snow depth at that time was aboutone metre of settled spring snowpack in a low-snow year.

A Timbco 455C feller-buncher with a 22" (56 cm)diameter “hot saw” was used in both units. One feature of thistype of feller-buncher particularly suited to partial-cutting in

(The marking rules were determined by the numberof stems in the pre-harvest stand in excess of the targetJ curve.)


confined stand conditions is its “zero tail-swing” — that is, itsrotating chassis does not extend beyond the dimensions of itstracks. This feature allows a reasonably experienced operatorto cut selected trees, and to turn and manoeuvre in close prox-imity to leave-trees, without striking or damaging their boles.Generally, this machine was able to move on the springsnowpack and harvest trees throughout the spruce-fir standwith little evidence of its passage off the skid trails other thanthe cut stumps of selected marked-to-cut trees.

The Timbco feller-buncher was used to fell trees bothon and off designated skid trails. Trees selected for cutting upto 20 metres away from designated skid trails were not droppedat the stump after cutting and oriented at an angle to the skidtrail as they would be in traditional hand-falling. Rather, thebuncher was able to hold a cut tree upright, back up to the skidtrail, and place the tree on the skid trail in the intended skid-ding direction.

Logs were skidded to the landings and roadsides bytwo D6 tracked grappled skidders. Cut trees were delimbedat roadside and cut to truck length by a button-top processor(stroke delimber) and stacked for log hauling three monthslater, in July 1998.

The on-site logging supervisor considered the desig-nated skid trails to be an advantage to logging productivity. Inhis recent experience with randomly-skidded selection cuttingelsewhere, he had observed that fallers and skidder operatorsspent much time locating marked trees and manoeuvring cuttrees around leave-trees. Designated skid trails seemed to solvethis problem and made the falling and skidding more orderlyand efficient.

Regeneration Methods

In August 1998 an excavator with a five-tine sitepreparation rake and mechanical thumb attachment was usedto pile logging debris in roadside accumulations and landings.In the GS unit, harvested openings were mounded with asmall excavator bucket to create warmer micro-sites for plant-ing of spruce seedlings. The STS unit was not mounded dueto limitations on summer equipment access, and risk of ma-chine damage to advance regeneration.

Both units were planted by Northwood Inc. in Sep-tember 1998 with 1+0 PSB 415 Engelmann spruce stock.The GS openings were planted to a target stocking standard of1000 sph. Both spruce and subalpine fir are preferred species,so quality subalpine fir natural regeneration will also besilviculturally acceptable. The STS unit was planted to anestimated 100 to 150 sph outside the drip line of leave trees, inorder to augment the spruce composition of understorey layers.

Acceptable inter-tree spacing was modified to 1.0metre in the GS unit to facilitate cluster planting. The Silvicul-ture Prescription did not include reforestation of naturallyunstocked wet openings or microsites, but rather, concentratedon regenerating areas in the vicinity of harvested trees.

Studies of stand dynamics

In partial-cut silvicultural systems, structural elementsof the original forest, including living trees, standing deadtrees, and fallen trees, are carried forward into the post-harvest

stand. Stands resulting from partial cutting willbe structurally complex along both horizontaland vertical dimensions. However, the long-term effects of various patterns and scales ofpartial cutting on stand dynamics and biodiver-sity are poorly known. At Pinkerton Moun-tain we are investigating the effects of singletree selection and group selection on post-har-vest stand attributes, dynamics, and structuralbiodiversity.

Stand development and growthand yield study

A network of 24 permanent growthand yield sample plots (8 per treatment, includ-ing the control unit) have been established toexamine medium to long-term stand responseto the different treatments. Response variablesbeing examined include future stand basal areaand volume growth, regeneration abundanceand vigour, regeneration growth rates and spe-cies composition, and damage and mortalitypatterns for all sizes of trees.

Wildlife trees and coarse woody debris

Along with the tree measurements that will allow in-terpretations about stand dynamics, we are collecting a varietyof assessments that will allow us to make interpretations abouthabitat for wildlife. Disturbances in the forest, whether theyare caused by humans or other disturbance agents, affect bothforest productivity and biodiversity. Most of the structuresand attributes that distinguish a wildlife tree froma tree with no special habitat value result fromdamage agents, such as disease, insects, wind,snow, lightning, sudden temperature changes,and mechanical damage. The processes thattransform a live standing tree into a log on theforest floor are also processes of damage andmortality. The information we are collectingallows us to assess the immediate impact of par-tial cutting on wildlife trees and coarse woodydebris, and provides baseline data for the long-term monitoring of biodiversity structures.

All the sample trees in our plots areassessed for the presence of Wildlife Tree Types(Keisker 1999) – configurations of habitatfeatures that appear to be required by one ofmore wildlife species. For example, WildlifeTree Type 1 (WT1) – hard outer wood sur-rounding decay-softened inner wood – isneeded by Three-Toed Woodpeckers and otherstrong cavity excavators as a substrate for theexcavation of nestholes. WT4 – large exca-vated or natural cavities – is commonly usedby various small owls, bats, squirrels, and mem-bers of the weasel family for nesting, denningor resting. Wildlife Tree Types may occur in

FIGURE 7. The “zero tail-swing” feller-buncher was able to harvest trees inconfined spaces without damagingleave trees.

FIGURE 8. Partial cutting may haveboth short-term and long-term effects onthe occurrence of wildlife trees andcoarse woody debris.


living or dead trees, and are not mutually exclusive. A giventree may have zero, one, or more Types. We used the numberof Types associated with each sample tree as a single variableto characterize the habitat value of that tree.

Although 30% removal of basal area was planned forboth harvest treatments, we expected partial cutting to affectthe abundance of wildlife trees differently in the two treat-ment units. Any trees that can be dangerous to workers —which includes many of the dead and dying trees — must beremoved in a harvesting area. In a single tree selection unit,harvesting can potentially take place throughout the unit, anda high proportion of the dead and dying trees are subject toremoval. In a group selection unit, worker activity is concen-trated in the harvest openings, and fewer of the potentiallydangerous trees are likely to affect the work areas.

In the group selection area, the proportion of sampletrees with one or more Wildlife Tree Types that remained afterharvesting was about the same as the overall proportion ofsample trees that remained in the residual stand. Relativelyfew trees with Wildlife Tree Types were removed outside thegroup selection openings. In the single tree selection area,71.3% of the sample trees in general were still present afterlogging, but only 56.8% of the sample trees with one or moreWildlife Tree Types were still present. The removal of treeshaving value to wildlife was disproportionately greater thanthe overall level of removal – but not by as much as we hadexpected.

All the Wildlife Tree Types that were present in thestand before harvesting were still present after harvesting. Themost conspicuous reduction was in WT6 (cracks, loose bark,or deeply furrowed bark), an attribute that occurs most oftenin the study area in subalpine fir that have been dead longenough to have loose, peeling bark, but still have most oftheir full height. Because they often have butt-rot, and are tallenough to make a large area hazardous, they are likely to be felled.

One of the objectives of the study is to monitor theeffects of damage agents, including logging damage, on wild-life tree attributes. Very few damaged trees were located in thesample plots. In the group selection area eight (3.9%) of 205

sample trees had minor dam-age and the rest were undam-aged. Of the 237 sample treesin the single tree selection areafour (1.7%) had major dam-age, five (2.1%) had minordamage and the rest were un-damaged.Coarse Woody Debris Typeshave also been identified(Keisker 1999). Examples ofCoarse Woody Debris Typesare CWD1 — large con-cealed spaces used for denningand escape cover by grouse,hares, some mustelids, andother mammals; and CWD5– large or elevated, long ma-terial clear of dense vegeta-

tion used as travel lanes by tree squirrels and chipmunks. Thepartial cut harvesting had very little immediate effect on eitherthe occurrence of Coarse Woody Debris Types in the studyarea or on Coarse Woody Debris volume. Estimated volumeof coarse woody debris in the group selection area was 270+ 49 (SE) m3/ha before logging and 293 + 40 m3/ha afterlogging. In the single tree selection area, pre-harvest volumewas 295 + 34 m3/ha and post-harvest volume was 286 +24 m3/ha. Neither of those changes was statistically significant.

Canopy studies

Partial cutting affects the microclimate in the canopyand its architecture – the size and shape of tree crowns, theoverlap of branches of different trees, the spatial relationshipsbetween old trees and young trees. Our research examineswhich elements of canopy microclimate and architecture aremost important to the productivity of the arboreal lichenseaten most by mountain caribou – the dark brown beardlichens, Bryoria spp., and the light green beard lichen, Alectoriasarmentosa.

Canopy microclimate

As non-vascular plants, lichens do not have access togroundwater or water from their host tree. Their metabolicactivity depends on direct exposure to precipitation, or insome cases, delayed exposure, as from snowmelt in the canopy.The main factor controlling lichen growth rates is thus thelength of time that the thallus — the body of the lichen —remains moist during and after precipitation. This is control-led primarily by regional climate. Lichens are most abundantin areas with high rain and snowfall and in areas with frequentfog and mist. Once lichens have absorbed water from rainwa-ter or snowmelt, the length of time they can remain wet thenbecomes important. The effect of air movement on watervapour changes dramatically from the top to the bottom of a forestcanopy. Near the ground surface the air is comparatively still andhumid. In the upper canopy average wind speed is higher, result-ing in more removal of water vapour away from lichen thalli. Atthe same time lichens in the upper canopy are exposed to moresunlight, which also increases drying rates.

These interacting profiles of air movement and sun-light create unique environments for lichen growth in subalpinespruce-fir forests. In the upper canopy lichens dry rapidlyafter each precipitation event (Figure 9). In contrast, lichens inthe lower canopy remain moist much longer, increasing thelength of time they have for growth and reproduction. Ourmeasures of lichen thallus wetting in intact old-growth forestshow the cumulative impact of these different growth envi-ronments. For both Alectoria and Bryoria, the total durationof wetting in the lower canopy is almost twice that of the samelichen species growing in the upper canopy. The removal oftrees by selection harvesting shifts these gradients of moistureand light downwards in the remaining canopy, exposing lowercanopy lichen communities to microclimate conditions morelike that of undisturbed upper canopy forest. Our microclimatemeasurements set the stage for understanding the changes weobserve in the growth, distribution, and biomass of the lichens.Arboreal lichen studies

FIGURE 9. Duration of wetting of Alectoria andBryoria at two canopy heights, June - September1998.


The abundance of forage lichens for caribou reflects the com-bined influence of several factors: the availability of lichenfragments to colonize trees, the availability of suitable surfacesfor the lichens to grow on, and favourable microclimatic con-ditions. The canopy structure of large old-growth trees pro-vides both long-lasting surfaces for colonization by lichensand a microclimate that promotes continued lichen growth.Managers need to know at what point changes in stand struc-ture influence this complex of interacting factors such thatlichen growth and colonization are no longer adequate to meetmanagement objectives. We are examining this question bystudying three parts of the system in natural forest standsand in stands modified by partial cutting. These systemcomponents are:

BiomassBiomassBiomassBiomassBiomassThe biomass of lichens in the canopy affects forage

availability for caribou as well as other ecological processes,such as nutrient cycling. Ours is one of the first researchstudies to measure lichen abundance by directly accessing theupper canopy using rope-based climbing techniques. We havefound marked height-dependant zonation of canopy lichenspecies (Figure 10; Campbell 1998), presumably in responseto microclimate gradients.

LitterfallLitterfallLitterfallLitterfallLitterfallThe rate at which lichens are removed from the canopy

interacts with biomass to determine the long-term persistenceof lichens in forest stands. The long strands of lichens areeasily fragmented by wind action during storms, some fallingonto lower branches, and some falling to the forest floor. In-creased exposure brought about by partial cutting may alterlitterfall rates. In extreme cases, residual lichens can be scouredfrom forest stands after partial cutting. We are monitoringlichen litterfall to determine how partial cutting affects theremoval of lichens from the canopy.

Growth ratesGrowth ratesGrowth ratesGrowth ratesGrowth ratesLichens that remain in the canopy after harvesting

must show continued high growth rates to balance normallitterfall and other mortality. We are measuring the growthrates and fragmentation rates of Alectoria and Bryoria in thelower canopy and mid-canopy of trees in the partially cut andunharvested areas. By monitoring the growth rates of thelichens in combination with microclimate measurements, weexpect to have a better understanding of the short-term re-sponses of the lichens to partial cutting, and a better basis forpredicting longer-term responses.

Conclusion

This project has been set up to provide both short-term and long term benefits. One of our goals in establishinga silvicultural systems trial at Pinkerton Mountain was to in-crease operational experience with the kind of partial cuttingthat is currently recommended in mountain caribou habitat.Several key points have emerged from our experience atPinkerton Mountain.

• Detailed pre-harvest planning is essential. While it may

appear to increase overall costs, it is better seen as an invest-ment that will be repaid by increased efficiency of harvest-ing and silviculture operations, less damage to the residualstand, and a layout that allows for future stand entries.

• Designated skid trails laid out on the ground before treeswere marked for cutting made logging operations moreorderly and efficient than in selection harvested blockswithout an overall skidding plan.

• The small, “zero tail-swing” feller-buncher used in boththe group selection and single tree selection areas allowedthe operator to manoeuvre close to the leave-trees with-out striking their boles and to carry a harvested tree up-right from the stump to the skid trail.

• To maintain the naturally clumpy structure of the stand,group selection openings were laid out so that pre-exist-ing clumps of trees were either retained or harvested as aunit. Use of GPS technology made it practical to createopenings that were irregular rather than geometric in shape.

Another goal was to determine the immediate impactof partial cutting on the structure of the residual stand. Whilenot all the data have been analyzed yet, our preliminary resultsshow that:

• Fewer than 4% of the sample trees in the residual standsustained logging damage. Fewer than 1% were rated ashaving major damage.

• Group selection harvesting had little effect on wildlifetrees outside the harvest openings. Single tree selectionhad a greater impact on wildlife trees in the residual stand,but not as much as expected – 57% of the sample treeswith wildlife habitat attributes were still present after thesingle tree selection harvest.

• Partial cutting had very little immediate effect on eitherthe volume of coarse woody debris or its wildlife habitatattributes.

Since maintaining habitat for mountain caribou is part

FIGURE 10. Abundance of Alectoria, Bryoria and foliose lichens at differentheights in the canopy.


For further information contact:

Susan StevensonSilvifauna Research

101 Burden Street, Prince George, BC V2M 2G8Telephone: (250) 564-5695

Fax: (250) 562-8419email: [email protected]

of the rationale for partial cutting in the ESSF, it is important toevaluate its success. Over the next few years, we expect tolearn more about how partial cutting affects the microclimatein the canopy and the productivity of the caribou forage li-chens that grow there. This information will help managersdecide whether selection silvicultural systems are in fact ap-propriate in mountain caribou habitat, and what type of pre-scription is most effective in promoting the abundance of for-age lichens.

To make informed decisions about what silviculturalsystems to use to meet resource objectives, managers need toknow the implications of their decisions for a variety of re-source values. In the long term, the stand structural informa-tion we have collected at Pinkerton Mountain before andafter harvesting will become the baseline for continued moni-toring of a variety of stand dynamics processes, and continuedreporting of our results to managers.

FIGURE 11. Rope-basedclimbing techniquesallow access to thecanopy for studies ofmicroclimate, lichenabundance, and lichengrowth rates.

References

Alexander, R.R. and C.B. Edminster. 1977. Uneven-aged man-agement of old-growth spruce-fir forests: cutting meth-ods and stand structure goals for the initial entry. USDAFor. Serv., Rocky Mtn. For. Range Exp. Sta., Res. Pap. RM-186.

Armleder, H.M. and S.K. Stevenson. 1996. Using alternativesilvicultural systems to integrate mountain caribou and tim-ber management in British Columbia. Rangifer Special Is-sue No. 9:141-149.

Campbell, J. 1998. Canopy research in north-central BritishColumbia: an exploration of lichen communities. MScthesis. Univ. of Northern BC, Prince George, BC.

Crampton, D. 1996. Operational comparison of group and sin-gle-tree selection systems in mountain caribou habitat. Un-published contract report, ArborEcos Forest Managementand Research Consulting Ltd, Invermere BC. Submitted tothe Prince George Forest Region, British Columbia Minis-try of Forests, Prince George, BC. 7 pages.

Guildin. 1990. BDq Regulation of Sierra-Nevada mixed coni-fers. J. Forestry 6(2):27-32.

Jull, M., C. DeLong, A. Eastham, R.M. Sagar, S. Stevenson andR.L. DeLong. 1996. Testing silvicultural systems for theESSF: early results of the Lucille Mountain Project. PrinceGeorge Forest Region Research Note # PG-01. PrinceGeorge, BC.

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Acknowledgements

The Northern Rockies Wet-belt ICH/ESSF Silvicultural Systems Research Project and For-est Canopy Processes and Partial-Cutting Silvicultural Systems in Northern Wet-belt Forestsare funded by the Forest Renewal Plan of British Columbia. We appreciate the participationof our industrial partners: the licensee, Northwood Inc.; the Silviculture Prescription/layoutcontractor, Forey Management Ltd.; and the harvesting contractor, Warmac Ventures Ltd.We acknowledge the contributions of many colleagues, especially D. Crampton (planning theprescription and training the layout crew), R. Sagar (microclimate data), and J. Clements and K.Jordan (canopy access). The Borealis Communications Group designed and produced thepublication.

Disclaimer

Any mention of product or commercial names is purelyfor descriptive purposes and is not intended as an endorse-ment or approval by the authors or any other party, of anyproduct or service to the exclusion of other products thatmay be equivalent or suitable.

Documents

May 1999 Selection silvicultural systems in …web.unbc.ca/~wetbelt/docs/stevenson-et-al-1999.pdfmaintained by Global Positioning System (GPS) traverses of cut areas within this treatment