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Management of mountain pine beetle attacked stands : strategies for increasing midterm timber supply Bruemmer, Matthew R. 2012

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 MANAGEMENT OF MOUNTAIN PINE BEETLE ATTACKED STANDS: STRATEGIES FOR INCREASING MIDTERM TIMBER SUPPLY by MATTHEW R. BRUEMMER  A GRADUATING ESSAY SUBMITTED FOR THE REQUIREMENTS OF THE DEGREE: BACHELOR OF SCIENCE IN FORESTRY in THE FACULTY OF FORESTRY MAJOR: FOREST RESOURCES MANAGEMENT THE UNIVERSITY OF BRITISH COLUMBIA VANCOUVER SPRING 2012II  Abstract British Columbia has recently experienced the largest outbreak of mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB) in recorded history. Although the amount of timber killed has declined since 2005, the after-effects of the epidemic are still not fully understood. MPB acts like a thinning from above, allowing the release of an understory of advance regeneration and subsequent development of an uneven-aged stand of shade tolerant conifers. MPB has been most significant in the Sub Boreal Spruce (SBS) and Sub-Boreal Pine Spruce (SBPS) biogeoclimatic zones. In these zones, among others, MPB has had impacts on numerous forest values. Of significant importance are the effects of MPB on the midterm timber supply. This paper reviews, synthesizes and discusses literature on the stand dynamics and development of MPB-attacked stands as well as silviculture strategies for increasing midterm timber supply. These strategies include: leaving secondary structure in MPB-attacked stands, thinning, spacing, and fertilizing of advance regeneration and other young stands, and fill and under- planting attacked stands that are under-stocked. Forest managers need to understand the advantages and disadvantages of these strategies as well as the situations in which they are appropriate in order to make sound forest management decisions. Keywords: mountain pine beetle, stand dynamics, midterm timber supply, silviculture strategies III  Table of Contents Abstract .................................................................................................................................................. II Table of Contents .................................................................................................................................... II Index of Figures ...................................................................................................................................... IV Index of Tables ....................................................................................................................................... IV Introduction ............................................................................................................................................ 1 Background ............................................................................................................................................. 2 History of MPB .................................................................................................................................... 2 Silvics of pine ....................................................................................................................................... 3 Stand dynamics ................................................................................................................................... 3 Stand development following MPB-attack ........................................................................................... 4 Relationship between MPB and forest fire potential ............................................................................ 4 MPB and Biogeoclimatic Ecosystem Classification ................................................................................ 6 Silviculture strategies .............................................................................................................................. 7 Secondary structure ............................................................................................................................ 7 Species and stocking ........................................................................................................................ 7 Growth and release ......................................................................................................................... 9 Forest health ................................................................................................................................. 10 Management options .................................................................................................................... 10 Thinning & spacing ............................................................................................................................ 11 Fertilization ....................................................................................................................................... 11 Planting ............................................................................................................................................. 12 Discussion ............................................................................................................................................. 12 Recommendations ................................................................................................................................ 17 Conclusion ............................................................................................................................................. 18 Literature cited ...................................................................................................................................... 19 IV  Index of Figures  Figure 1: Conceptual model of forest dynamics in lodgepole pine ecosystems ......................................... 4 Figure 2: Projection of fire hazard in MPB-attacked stands over time ...................................................... 5 Figure 3: Cumulative MPB outbreak area (1960-2002) by BEC zone ......................................................... 6 Index of Tables Table 1: Summary of recent studies on regeneration in MPB-attacked stands ......................................... 8 Table 2: Advantages and disadvantages of silviculture strategies that can potentially increase midterm timber supply ........................................................................................................................................ 16  1  Introduction British Columbia has experienced an unprecedented outbreak of mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB) in its interior lodgepole pine (Pinus contorta Dougl.) forests. These outbreaks are naturally occurring periodic disturbances in lodgepole pine forests that have been documented in western Canada for over 85 years (Carroll, Taylor, Alfaro, & Safranyik, 2006). The current outbreak peaked in the summer of 2005 and has declined to an estimated annual volume of 39 million m3 of timber killed in the summer of 2010 (Walton, 2011). The BC Ministry of Forests, Lands and Natural Resource Operations (MFLNRO) estimates that a cumulative total of 726 million m3 of timber has been killed by MPB covering an area of approximately 17.5 million hectares. (BC MFLNRO, 2011). The industry and governments’ response to the epidemic has been to salvage as much of the dead lodgepole pine as possible under temporarily elevated (‘uplifted’) annual allowable cuts in order to recover economic value before the trees deteriorate (Lewis, 2010). In their 2011 update on the infestation the BC MFLNRO projected that:  “In the province’s pine units, 62 percent of the merchantable pine volume on the timber harvesting land base at the start of the current outbreak will be killed by 2016 if the infestation continues to behave as projected.” MPB has had significant impacts on numerous forest values including timber supply, wildlife, hydrology, visual quality and recreation among others. All of these values are important and require attention; of particular importance are the impacts of the MPB epidemic on the midterm timber supply. Timber supply is the quantity of timber available for harvest over time (BCMoFR, 2007) – the midterm is the period of time 10-50 years into the future (Coates, 2006). It is projected that midterm harvest levels will be 33 percent lower than the pre-outbreak allowable annual cut levels (BCMoFR, 2007). This is an issue that has been widely discussed in recent times. It has raised many questions about how to best manage MPB-attacked stands and which strategies could best contribute to an increase in midterm timber supply. According to Dhar and Hawkins (2011):  “There is a great amount of completed and ongoing research regarding the management of MPB-attacked stands. However, this information needs to be gathered, synthesized, and presented such that it is widely available to managers, practitioners, and researchers alike.” 2  The objective of this paper is to explore the stand dynamics of MPB-attacked stands and to synthesise and present information on silvicultural strategies for their management in a form that is readily available for forest managers to utilize. It is my goal to present and discuss various silvicultural strategies that may help alleviate the problem of midterm timber supply, and to present options for forest managers to consider. Background It is critical to understand the ecology and stand dynamics of the forest types affected by MPB in order to make sound forest management decisions regarding their future. The following sections address the ecology and silvics of lodgepole pine, the stand dynamics of pine forests, the natural role MPB plays in different ecosystems, and the range of stand types affected by MPB. History of MPB MPB is a native insect and has been present in BC’s forests for millennia (Taylor & Carroll, 2003). Outbreaks have been well documented since the beginning of the 1900s and the current outbreak is the largest ever recorded (Taylor & Carroll, 2003). MPB preferentially attack larger lodgepole pine trees (Safranyik & Carroll, 2006) that are greater than 80 years of age (Taylor & Carroll, 2003). This is because for successful reproduction, MPB require trees with thicker phloem which is well correlated to stem diameter (Safranyik & Carroll, 2006). Normally, MPB kill the oldest and weakest trees in a forest contributing to ecological processes and the maintenance of biological and structural diversity (Roe & Amman, 1970). However, under epidemic conditions such as those experienced in BC, MPB-attack healthy, mature and immature trees (Safranyik & Carroll, 2006). In order for a MPB outbreak to occur two requirements must be satisfied – a sustained period of favourable weather over several years, and an abundance of susceptible host trees (Taylor & Carroll, 2003). MPB populations have normally been regulated by extreme cold winter temperatures (Safranyik & Carroll, 2006); however, recent warming trends linked to climate change have led to high rates of brood survival and an expansion of MPB’s suitable range (Carroll et al. 2003). Additionally, over the past 100 years the amount of mature lodgepole pine on the BC landscape has increased significantly in all habitat types (Carroll et al. 2003). This can be attributed to past forest management strategies that avoided harvesting lodgepole pine as well as successful fire suppression. Intensive logging of lodgepole pine forests didn’t begin until the 1960s. At this same time fire suppression success increased greatly 3  and today initial attack success rates are greater than 95% (Taylor & Carroll, 2003). Consequently, disturbance rates in lodgepole pine forests have been greatly reduced over the past century leading to an abundance of host trees (Taylor & Carroll, 2003).  Silvics of pine  Lodgepole pine has very large ecological amplitude, it occurs in all Biogeoclimatic Ecosystem Classification (BEC) zones in BC on many different sites, from low to high elevation, warm to cold, dry to wet and on most soil types (Shore, Safranyik, Hawkes, & Taylor, 2006). Generally, lodgepole pine is considered to be highly intolerant of shade – for this reason it grows best as a pioneer species following disturbances such as fire (Shore et al. 2006). In fire-prone ecosystems, its serotinous cones allow it to regenerate and occupy sites very rapidly following fires. Stand dynamics The dynamics of lodgepole pine forests in the BC Interior are tied to the local disturbance regime. The predominant disturbances in these forests are fires and MPB-attacks. Following a stand-replacing forest fire, lodgepole pine generally forms homogenous even-aged stands (Alfaro & Hawkes, 2012). In ecosystems where lodgepole pine dominates, even-aged stands are formed of lodgepole pine in the dominant and sub-canopy with very little regeneration in the understory (Alfaro & Hawkes, 2012). In ecosystems with multiple species, even-aged stands can be of mixed-species and levels of regeneration can be more variable. In the absence of fire, MPB plays a lead role in driving stand dynamics. Consecutive MPB-attacks contribute to the conversion of even-aged stands to un-even aged stands (Shore et al. 2006). Mixed severity surface fires also lead to the creation of un-even aged lodgepole pine stands (Alfaro & Hawkes, 2012). In this regime some pine survives a fire and form the dominant and sub-canopy. The difference between the even-aged and un-even aged stands is that in the latter there is more light penetrating the forest floor allowing the regeneration of numerous seedlings (Alfaro & Hawkes, 2012). Figure 1 conceptualizes the dynamics of these forests and the effects of the two different disturbance types. 4  Figure 1: Conceptual model of forest dynamics in lodgepole pine ecosystems  Source: (Alfaro & Hawkes, 2012) Stand development following MPB-attack MPB acts as a natural thinning agent, killing the largest trees in a stand and opening up the canopy like a thinning-from-above treatment (Alfaro & Hawkes, 2012). This allows growing space (light, water, nutrients, area) to become available for surviving suppressed and understory trees; promoting their growth and release. The residual stand following an attack will be comprised of trees in intermediate layers, non-host species, and advanced regeneration (Shore et al. 2006). Common species found in the understory are usually shade tolerant, such as Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), subalpine fir (Abies lasiocarpa (Hook.) Nutt), hybrid spruce (Picea glauca x engelmannii) and Engelmann spruce (Picea engelmannii Parry ex Engelm.) (Shore et al. 2006). The release of these shade-tolerant species results in the conversion of even-aged lodgepole pine stands to uneven-aged stands of shade tolerant conifers (Griesbauer & Green, 2006). In the absence of stand-replacing fire these trees will form the new forest. Relationship between MPB and forest fire potential The mortality imposed on lodgepole pine forests following MPB-attack can impact future forest fire potential (Hawkes, Taylor, Stockdale, & Shore, 2003) by increasing the quantity and modifying the distribution of fuels in the forest (Shore et al. 2006). In the first few years following MPB-attack most of 5  the dead needles are retained on killed trees. Foliar moisture content is very low; therefore the likelihood of crown fire is increased (Shore et al. 2006). Once needles drop to the ground and dead trees begin to fall, the likelihood of crown fire decreases, however, the increased surface fuel loading could contribute to a stand-replacing crown fire in residual trees (Shore et al. 2006). Hawkes et al. (2003) noted that 90% of dead trees will have fallen to the ground within 14-years post attack. At this point the fire hazard rises to high or extreme depending on the distribution of fuels resulting from fallen trees as well as the presence of regeneration (Needoba & Blackwell, 2008). Figure 2 conceptualizes changes in fire hazard throughout stand development post MPB-attack. Some researchers question this scenario however, and report that there is little empirical evidence of increased fire incidence in MPB affected stands (Carroll et al. 2006). Figure 2: Projection of fire hazard in MPB-attacked stands over time  Source: (Needoba & Blackwell, 2008) 6  MPB and Biogeoclimatic Ecosystem Classification  The range of MPB is determined by the distribution of suitable host trees and by climate. In BC this has historically corresponded to the southern half of the province (Carroll et al. 2006). According to Carroll et al. (2006), “The majority of mountain pine beetle outbreaks occurred in the Sub Boreal (SBS) zone, followed by the Sub-Boreal Pine Spruce (SBPS), Interior Douglas-Fir (IDF), and Engelmann Spruce Subalpine Fir (ESSF), Montane Spruce (MS), and Interior Cedar Hemlock (ICH) zones.” Between 1960 and 2002 MPB outbreaks have occurred largely in the SBS, SBPS, IDF, ESSF and MS zones (Figure 3). Figure 3: Cumulative MPB outbreak area (1960-2002) by BEC zone  Source: (Carroll A. L., Taylor, Alfaro, & Safranyik, 2006) MPB outbreaks affect stand dynamics differently in each BEC zone. This is due to differences in the disturbance regime, and the presence of non-pine species and their role in succession. In the SBPS zone, fire is a frequent disturbance and lodgepole pine is considered a climax species (Carroll et al. 2006). Succession to spruce would be very slow as there is little spruce in the understory and a limited seed 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Th o u sa n d s o f h ec ta re s (h a)  BEC Zone Area (ha)7  source. Therefore, following MPB-attack in the SBPS, the residual stand is primarily composed of smaller diameter lodgepole pine that survived the infestation (Carroll et al. 2006). In zones such as the SBS, ESSF, and ICH mixed species stands are more common. Lodgepole pine is typically a post-fire pioneer species in these zones and MPB-attacks accelerate the successional process to non-host species (Carroll et al. 2006).  Silviculture strategies The initial and post-infestation stand structure and dynamics inform various silvicultural strategies. Strategies that have the potential to improve midterm timber supply include leaving stands with secondary structure un-salvaged, thinning, fertilizing, and planting.  Secondary structure For various reasons, a large portion of the land base infested by MPB will not be salvage-harvested (Griesbauer & Green, 2006). These un-salvaged stands will either be left to recover on their own or will require some form of management intervention to improve future yields. Many of these stands currently support varying levels of understory trees, surviving lodgepole pine trees, and non-host species. These trees form what is known as “secondary structure”. Secondary structure includes seedlings, saplings, sub-canopy, and canopy trees that will likely survive MPB-attack (Coates, Delong, Burton, & Sachs, 2006). Stands developing from secondary structure and advance regeneration may restock and add volume quickly, providing opportunities for midterm harvests (Griesbauer & Green, 2006). Many factors regarding the management of stands with secondary structure will need to be considered in order to make sound management decisions. Griesbauer & Green (2006) note that stands developing from advance regeneration after MPB-attack will differ in species composition, abundance and spatial distribution of regeneration, and health and long-term viability of regeneration.  Each of these factors needs to be considered when considering secondary structure as a source of midterm timber supply.  Species and stocking Recent studies have shown that large amounts of regeneration exist in MPB-attacked stands throughout BC (Hawkins & Dhar, 2011).  Table 1 summarizes some of these studies and presents results on the amount of regeneration found in MPB-attacked stands. 8  Table 1: Summary of recent studies on regeneration in MPB-attacked stands Geographic area and biogeoclimatic zone (when available) No. of samples Age Regeneration species composition Density Distribution Health Data Holder Northern interior 35 - Mostly subalpine fir Less Patchy - Coates (2008) Flathead area, southeast BC 22 70 Mostly subalpine fir Less Patchy - Pantage Creek (SBSdw2) 12 28 Diverse species High Wide Good Statland (2008) Takysie Lake (SBSdk) 15 79 Mostly pine High Wide Good SBSdw3, SBSmc3, SBSdk 50 - Lodgepole pine, white spruce High - - Delong et al. (2008) IDF, SBPS, SBS zones 56 - Pine High - - Zumrawi et al. (2008) MSxk2, MSdm3, IDFdk1, IDFdk2 167 - Mostly subalpine fir Modera te Clumpy - Vyse (2008) SBSdk, SBSmc,SBSdw, SBSmc 500 80 Mostly non-pine species Variable - - Burton and Brooks (2008) MS, Merritt 28 - Subalpine fir, lodgepole pine, interior spruce, Douglas-fir High Clumpy - Nigh et al. (2008) Lakes TSA, SBSdk 302 100+ Lodgepole pine, spruce, subalpine fir Low Sparse Good  Rakochy (2005) SBS, six subzones, Prince George TSA 525 60- 250 Diverse species Less Variable Good Balliet (2010) Source: (Hawkins & Dhar, 2011) In a report for the Chief Forester, Coates et al. (2006) concluded that approximately 20-30% of stands in north central BC have enough secondary structure to produce a midterm harvest opportunity if left un- salvaged. Coates also noted that roughly 40-50% of pine-leading stands have sufficient understory 9  densities to be considered stocked without further intervention. Simulations show that these stands can contribute up to 200-300m3/ha of harvestable volume within the next 25-40 years. Although many stands have significant amounts of understory regeneration, the spatial distribution of this regeneration must be considered when determining if stands are well stocked. Spatial patterns such as clumping often occur as a result of snag decay processes in MPB-attacked stands as well as the presence and distribution of a seed source (Griesbauer & Green, 2006). Sampling of stands with clumpy distributions may indicate that the total number of stems per hectare is of an acceptable level; however, it would not indicate if these stems were well spaced which may result in poor overall site occupancy. Clumpy distributions may also result in decreased productivity in the long run as trees within clumps compete with one another for resources (Griesbauer & Green, 2006). Stand development in MPB-attacked stands often results in the regeneration of shade tolerant species in the understory. Subalpine fir is a common shade tolerant species found in many MPB-attacked stands. In certain subzones, however, forest managers are reluctant to consider it as desirable a timber species based on assumptions that it is less productive, more susceptible to disease and less valuable than species like interior spruce (Vyse, Ferguson, Huggard, Roach, & Zimonick, 2009). In these subzones future intervention such as spacing and fill-planting may be required in order to achieve a stand of well- spaced, acceptable species. Growth and release The growth and release potential of secondary structure will be important to know in order to make predictions of future yields.  Recent studies examining the release of advance regeneration have found variable results. Successful growth and release is a function of species, health, understory light environment and the degree of canopy mortality. Advance regeneration of shade tolerant species such as Douglas-fir, subalpine fir, and interior spruce have shown strong release responses as compared to shade intolerant lodgepole pine (Griesbauer & Green, 2006). This can be attributed to shade tolerant species’ ability to adjust their crown physiology and structure in response to changing light regimes (Griesbauer & Green, 2006).  The remaining stand structure following MPB-attack will have a large effect on the changes in light regimes. Coates & Hall (2005) developed a model to predict the changes in understory light environment following MPB-attack. As snags deteriorate, the light conditions for regeneration improve steadily. Coates & Hall estimated that the understory light environment would remain fairly constant for 10  5 years following MPB-attack and that residual stems could shade understory regeneration for up to 10 years, with some snags remaining for up to 15 years. This study also showed that stands with a well- developed immature spruce component recover quickly, and if they are left un-salvaged they can contribute to a midterm timber supply.   Forest health The health of secondary structure is of critical importance as it will affect the release potential of regeneration as well as long term yields from stands. Following MPB-attack the health of secondary structure is affected by both biotic and abiotic agents. Generally, abiotic damage is more common – falling branches and stems from dead overstory pine can cause damage and mortality (Hawkins & Dhar, 2011). Poor form is also common as a result of factors such as snow creep (Lewis, 2010). Increased exposure as a result of overstory mortality and decay also increases the potential for radiation frost damage, and soil moisture regime can impact regeneration health (Hawkins & Dhar, 2011).  Biotic damage also occurs in advance regeneration in MPB-attacked stands.  Animal browsing is common in many species, with subalpine fir being the most susceptible, followed by spruce and lodgepole pine (Lewis, 2010). Western gall rust and dwarf mistletoe (Arceuthobium americanum Nutt. Ex Engelm.) can also be found in certain stands. Dwarf mistletoe can be a problem where the overstory had high levels of infection prior to MPB-attack. These stands will almost certainly have high levels of infection in the understory (Lewis, 2010). These stands would be ideal candidates for salvage harvesting. Stands with a high component of subalpine-fir may be at a risk due to health problems such as insect attack (e.g. Western Balsam bark beetle (Dryocetes confusus)) and stand development problems associated with productivity (Griesbauer & Green, 2006).  Another potential problem is damage from root diseases such as Inonotus tomentosus (Lewis, 2010). Tomentosus primarily affects spruce – stands with a significant amount of root disease may require a higher harvest priority, and future stand management should focus on less susceptible species (Lewis, 2010).   Management options In general, three management options are available for dealing with MPB-attacked stands with secondary structure. These include full salvage, careful salvage protecting residual trees, and no-salvage in order to retain secondary structure (Coates et al. 2006). Clearcutting and replanting attacked stands is a common practice, however this practice has been shown to not contribute to midterm timber supply (Runzer, Hassegawa, Balliet, Bittencourt, & Hawkins, 2008). In contrast, protecting residual trees and 11  advance regeneration during salvage operations could reduce rotation ages by 10-30 years in some areas (Coates, 2006).  In a recent assessment, Coates & Sachs (2011) identified a threshold of 4 -6 m2/ha of residual secondary structure basal area in MPB-attacked stands that recover fairly well. These stands would be ideal candidates to leave un-salvaged as they would develop into viable stands that could provide a midterm timber supply. Coates and Sachs found that stands in the SBS posed the greatest risk for future timber supply since 30% of pine leading stands in this zone fell below the 6 m2/ha threshold. Stands in the ESSF and ICH pose few problems as 90% of stands in the ESSF and 100% of stands in the ICH currently have levels of secondary structure in excess of 10 m2/ha (Coates & Sachs, 2011).  Thinning & spacing Stands with well-developed secondary structure following MPB-attack may require further intervention in order to ensure trees are well spaced and will form a future commercially viable forest. Where stands have clumpy distributions of advance regeneration, they may require thinning and spacing in order to achieve a well-spaced condition (Griesbauer & Green, 2006). In addition; thinning of previously established stands of young lodgepole pine may be a useful strategy to consider for increasing midterm timber supply. Fire origin stands in the stem exclusion stage of development generally have high stocking; these stands would be ideal candidates for thinning treatments (Brockley, 2005). Positive benefits have also been noted when thinning is done in combination with fertilization as these treatments accelerate stand development and shorten rotation length (Brockley, 2005). Fertilization Fertilization along with thinning are primary silvicultural strategies available for increasing the operability of established stands and reducing rotation ages (Brockley, 2005). Generally, fertilization accelerates stand development and increases piece size in natural or planted stands (Brockley, 2005). It is particularly useful at releasing dense, height suppressed fire-origin stands of lodgepole pine (Brockley, 2005).  Fertilization may also be useful at releasing advance regeneration in MPB-attacked stands that may otherwise be slow to release or have diminished growth response (Griesbauer & Green, 2006). However, there are a limited number of studies done on the response of understory trees to fertilization treatments in MPB-attacked stands. Regardless, fertilization as well as thinning should be considered as possible management strategies for increasing midterm timber supply. 12  Planting In many instances planting may be an appropriate and necessary silviculture strategy in the management of MPB-attacked stands. Planting is currently used to re-establish stands following clearcut salvaging, however, because of the time needed to reach harvestable size, this treatment has no contribution to midterm timber supply (Runzer et al. 2008). Fill-planting may be required in stands that have an existing understory but still require further stocking to meet appropriate standards and ensure long term site productivity (Griesbauer & Green, 2006). Where stands with little understory regeneration are not to be salvaged for economic or other reasons, under-planting is a potential strategy to return theses stands to productivity in the longer term. However, under-planting has historically been costly and unsuccessful (Runzer et al. 2008). This can be partially attributed to the light conditions in the understory of attacked stands. Results of trials showed that 10,000 stems/ha of lodgepole pine regeneration died when established 1 year post attack, but when planting was delayed 10 years, 300 stems/ha survived (Coates & Hall, 2005). Conversely, Coates & Hall (2005) showed that mortality rates of interior spruce and subalpine fir were lower than lodgepole pine at the same understory light levels. They also noted that planting either subalpine fir or spruce substantially increased the yield of stands after 100 years compared to no management intervention. Discussion The scale of the current MPB epidemic is unprecedented and its impacts on numerous forest values are significant. A drop of 33% to the mid-term allowable annual cut in the interior of BC is expected (BCMoFR, 2007). However, the best strategies for dealing with MPB-attacked stands in ways that increase mid-term timber supply still appear to be uncertain.  The most promising silviculture strategy for increasing midterm timber supply appears to be leaving secondary structure in MPB-attacked stands. Models such as SORTIE-ND have shown that stands with high levels of residual structure (>4-6m2/ha) have a good potential to contribute to midterm timber supply (Coates, 2006). Leaving secondary structure in MPB-attacked stands could also achieve other resource objectives such as hydrologic recovery, biodiversity, visual quality, and wildlife habitat. This could be achieved in a cost-efficient manner as stands with good secondary structure may not require further treatment until they reach their planned rotation age. However, the health of secondary structure as well as the future productivity of stands originating from advance regeneration still remain uncertain and represent a significant knowledge gap in the understanding of the management of these 13  stands (Hawkins & Dhar, 2011). Future growth and yield will also depend on the species composition, stocking and spacing, release potential and future growth of advance regeneration.  These factors will need to be addressed when making management decisions. The issues with subalpine fir regeneration will need to be resolved – if forest managers continue to assume that it is not an acceptable species in certain ecosystems then further treatments will be required to achieve a desired stand condition. Research has shown that subalpine fir grows at a similar rate as Engelmann spruce on the same site and has comparable timber value (Vyse et al. 2009). Furthermore, subalpine fir plays an important ecological role in ESSF forests (Vyse et al. 2009). If markets exist for subalpine fir and managers decide that it is an acceptable species then treatment costs will likely be reduced. The degree of MPB-attack as well as the amount and condition of residual structure in stands is highly variable. Therefore, management of stands with secondary structure will have to be done on a stand by stand basis. Current forest inventory data does not provide information on the abundance of understory trees (Hawkins & Dhar, 2011); making the identification of stands with sufficient secondary structure very difficult at the landscape level (BCMoFR, 2007). Ground sampling would be required to achieve an accurate estimate of the abundance of secondary structure (BCMoFR, 2007); however, this would be extremely costly and time consuming. Perhaps one of the largest issues with leaving secondary structure in stands is the increased potential for future forest fires in non-salvaged stands. Canopy death from MPB-attack leads to a fuel build-up in stands. This increase in fuel loading could pose a serious risk for many values including timber. Careful assessments of fuel loading in stands will need to be done in order to make informed management decisions about leaving secondary structure. The potential risk of fire may outweigh the benefits of not salvaging stands with high levels of secondary structure. However there is a difference of opinion on the fire hazard associated with MPB-attacked stands. According to Carroll et al. (2006) there is little empirical evidence supporting the theory that there is greater incidence of fire or greater area burned following MPB-attack. Clearly further research is required in this field as it will be critical to understand the risk of fire when making management decisions with regards to leaving secondary structure in un- salvaged MPB-attacked stands. One of the advantages of managing secondary structure in MPB-attacked stands is that it is easily quantifiable. Coates & Sachs (2011) suggested that a simple basal area measure may be adequate for determining if stands can contribute to midterm timber supply. If models such as SORTIE-ND could 14  accurately predict what threshold of residual structure is required then basic cruising would be able to determine if stands could contribute to midterm timber supply. Other silviculture strategies such as thinning and fertilizing may also be required in combination with leaving secondary structure in stands in order to achieve a desired future stand condition. Fertilizing and thinning treatments may reduce rotation age allowing midterm harvest opportunities. However, research on the release of understory regeneration in MPB-attacked stands following fertilization treatment is limited and further research on this strategy will be required if it is to be considered a viable strategy for increasing midterm timber supply.  Thinning and fertilizing may be viable options in younger stands that have not been attacked by MPB. Of particular interest are young fire and harvest-origin stands. Fertilization of these stand types have shown promising results and when done in combination with thinning further benefits are noted. The cost of these treatments may be an issue in certain situations; however, if applied in appropriate situations and in the appropriate stand types fertilizing and thinning can reduce the rotation age of stands and allow midterm harvest opportunities. Of important note is the risk of MPB-attack in young stands as high levels of attacks were noted in these stands in recent surveys(BCMoFR). The risk of future attack will need to be considered when employing these treatments. Planting is an important silviculture strategy in many situations but has limited use for enhancing mid- term timber supply. This strategy would likely be most successful when done in stands that have some existing understory. Fill-planting would increase the stocking of such stands as well as allow forest managers flexibility to make decisions regarding species composition of future stands. However, the success of under-planting has generally been low. Further testing of species selection and timing of under-planting would be required to determine how to best increase success rates of this treatment.  In closing, the most common silviculture strategy currently used in the management of MPB stands is the classic clearcut and replant strategy. This strategy has its advantages: recovery of economic value from MPB-killed trees before they decay, rapid return of land to timber productivity through reforestation, reduction of forest fire potential, and short term socio-economic benefits to communities. However, it is well documented that this strategy has no contribution to midterm timber supply (Runzer et al. 2008) as well as potential negative impacts on values such as biodiversity, hydrology and wildlife. If midterm timber supply is the most salient issue facing communities in interior BC than alternative strategies should be considered, each of which has advantages and disadvantages (Table 2). 15  Implementation of these strategies also requires some changes in policy. The current policy framework in BC provides very little incentive for forest managers and companies to consider strategies that offer little financial return for a long period of time. If the problem of midterm timber supply is to be resolved then new, creative prescriptions that account for the structure and variability of MPB-attacked stands will need to be drafted. A policy framework that encourages forest managers to draft these prescriptions is required. 16  Table 2: Advantages and disadvantages of silviculture strategies that can potentially increase midterm timber supply Advantages Disadvantages Secondary structure  Stands with secondary structure of good health, vigour, stocking and spacing with >4- 6m2/ha have the potential of contributing to midterm timber supply  A simple basal area measure in stands can determine if stands exceed a certain threshold  Cost is low if stands already meet appropriate stocking requirements  Can fulfill other resource objectives such as hydrologic recovery, visual quality, wildlife and biodiversity  Stands are highly variable and are difficult to measure at a landscape level  Uncertainties surrounding future growth, yield and health of stands   Species composition may not be acceptable (e.g. Subalpine fir)  Further treatments may be required to achieve a desired stand condition (i.e. thinning, planting)  Potential for future forest fires may be increased in stands originating from secondary structure  Thinning and spacing  Spacing of advanced regeneration can help achieve a desired future condition in MPB- attacked stands  Thinning of young fire or harvest-origin stands can reduce rotation age  Combining with fertilization leads to improved height and diameter growth  Cost and area required to treat is high  Safety of workers in dead stands would be a concern Fertilization  Increases operability of stands and reduces rotation age  Young fire or harvest-origin stands show good release potential  May help release advance regeneration in stands with a well-developed understory  Response of advanced regeneration is uncertain  Cost & effectiveness   Planting  Fill-planting in stands with a developed understory can help achieve a desired future stand condition in MPB-attacked stands  Allows forest managers flexibility with regards to species composition of future stands  Under-planting of dead stands that will not be salvage harvested can reduce recovery time  Under-planting has historically been unsuccessful  Safety of planters working in dead stands would be a concern  Cost and area required to treat is high 17  Recommendations To improve the quality of information and decision-making concerning mid-term timber supply enhancement strategies, the following recommendations are made:  inventory the amount of area that is well stocked with understory regeneration – this knowledge will be critical for making stand and landscape level management decisions;  undertake further research on the health and vigour as well as the release and growth of secondary structure – this is important to know when predicting future yields of stands originating from MPB-attack;  focus management strategies on the SBS and SBPS zones – these are the most heavily impacted BEC zones and levels of secondary structure are variable; the ESSF and ICH require little management intervention as levels of secondary structure are very high;  salvage merchantable stands with a high percentage of dead lodgepole pine and little secondary structure where this is consistent with other management objectives – these stands likely would be slow to recover on their own and would have little contribution to midterm timber supply;  leave stands with >4-6m2/ha of secondary structure un-salvaged – these stands if healthy and well stocked, will likely contribute to midterm timber supply;  undertake further research on the risk of wildfire in MPB-attacked stands – this will be critical to understand when considering management options;  salvage stands close to communities with high risk of fire to reduce threats to human property;  consider subalpine-fir as an acceptable species – it can provide ecological benefits as it is a natural component of certain ecosystems;  consider careful partial harvesting strategies in mixed species stands that protect understory – these strategies could reduce rotation length;  draft new, creative silviculture prescriptions that account for structure in pine leading stands – the classic clearcut and re-plant approach will not contribute to midterm timber supply;  establish a regulatory framework that is flexible and accounts for the high variability of stands impacted by MPB. 18  Conclusion The scale of the problem created by MPB is substantial and its impacts on the interior forests of British Columbia are significant. As of 2011, in the interior of BC the equivalent of roughly 20 years of AAC, totalling 726 million m3 of timber has been killed by MPB. Although MPB is on the decline in BC, the after-effects on forest and human communities in the interior of the province will be significant and long lasting. The fall-down effects from MPB will be substantial as mid-term harvest levels will be reduced by roughly one third below pre-MPB levels.   The stands impacted by MPB are highly diverse and the conditions following attack are highly variable. The stand dynamics and development following MPB-attack still appear to be poorly understood. Understanding of these processes will be critical for making management decisions in these stands. Currently, the most widely used strategy for dealing with MPB-attacked stands is to clearcut and replant; however, this strategy does not contribute to midterm timber supply. Alternative silviculture strategies do have the potential to increase midterm timber supply. These strategies include: leaving secondary structure in MPB-attacked stands, thinning, spacing and fertilizing of both advance regeneration and other young stands. Fill and under-planting attacked stands is less effective in the mid- term, but will improve the long term quality of these stands. Forest managers will need to understand the issues, strengths and weaknesses of these strategies and consider them in making management decisions. Forest managers will need to use a combination of strategies and treatments, while making management decisions on a stand by stand basis. These strategies should be creative, account for the variability and structure in MPB-attacked stands, and reflect the ecology of the forests in question while still providing society with the goods and services they require.  19  Literature cited Alfaro, R., & Hawkes, B. (2012, 03 05). Natural Resources Canada; Canadian Forest Service. Retrieved from Stand development following mountain pine beetle outbreaks in south-central British Columbia: http://cfs.nrcan.gc.ca/projects/63 Axelson, J. N., Alfaro, R. I., & Hawkes, B. C. (2008). Influence of fire and mountain pine beetle on the dynamics of lodgepole pine stands in British Columbiam, Canada. Forest Ecology and Management, 1874-1882. Axelson, J. N., Alfaro, R. l., & Hawkes, B. C. (2010). Changes in stand structure in uneven-aged lodgepole pine stands. The Forestry Chronicle, 87-99. BC MFLNRO. (2011). Retrieved 02, 24, 2012, from Beetle facts: http://www.for.gov.bc.ca/hfp/mountain_pine_beetle/facts.htm BCMoFR. (2007). Timber supply and the mountain pine beetle infestation in British Columbia 2007 update. Victoria: Forest Analysis Branch. Brockley, R. P. (2005). Effects of post-thinning density and repeated fertilization on the growth and development of young lodgepole pine. Vernon: NRC Research Press. Carroll, A. L., Taylor, S. W., Alfaro, R. I., & Safranyik, L. (2006). Forest, climate and mountain pine beetle outbreak dynamics in western canada. Victoria: Natural Resources Canada: Canadian Forest Service. Carroll, A., Taylor, S. W., Regniere, J., & Safranyik, L. (2003). Effect of climate change on range expansion by the mountain pine beetle in British Columbia. The bark beetles, fuels, and fire bibliography, Paper 195. Coates, D. (2006). Silvicultural approaches to managing MPB damaged stands: regeneration and mid- term timber supply. Northern Silviculture Commitee 2006 Winter Workshop. Prince George: BC Forest Service. Coates, D. K., & Hall, E. C. (2005). Implications of alternate silvicultural strategies in mountain pine beetle damaged stands. Smithers: Bulkley Valley Centre for Natural Resources Research & Management. 20  Coates, D., & Sachs, D. L. (2011). MPB impacted stands assessment project - Current state of knowledge regarding secondary structure. Smithers: Ministry of Forests, Lands and Natural Resources Operations. Coates, K. D., Delong, C., Burton, P. J., & Sachs, D. L. (2006). Abundance of secondary structure in lodgepole pine stands affected by the mountain pine beetle: Report for the Chief Forester. Smithers: British Columbia Forest Service. Griesbauer, H., & Green, S. (2006). Examining the utility of advance regeneration for reforestation and timber production in unsalvaged stands killed by the mountain pine beetle: Controlling factors and management implications. BC Journal of Ecosystems and Management, 81-92. Hawkes, B., Taylor, S., Stockdale, C., & Shore, T. (2003). Impacts of mountain pine beetle attack on stand and ecosystem dynamics. Victoria: Natural Resources Canada: Canadian Forest Service. Hawkins, C. D., & Dhar, A. (2011). Regeneration and growth following mountain pine beetle attack: A synthesis of knowledge. BC Journal of Ecosystems and Management, Volume 12, Number 2. Hawkins, C., & Rakochy, P. (2007). Stand-level Effects of the Mountain Pine Beetle in the Central British Columbia Interior. Victoria: Natural Resources Canada. Lewis, K. J. (2010). Forest health and mortality of advance regeneration following canopy tree mortality caused by the mountain pine beetle. Victoria: Natural Resources Canada; Canadian Forest Service. Mitchell, J. (2005). Review and Synthesis of Regeneration Methods in Beetle-killed Stands Following Mountain Pine Beetle. Vancouver: Forest Engineering Reasearch Institute of Canada. Needoba, A., & Blackwell, B. (2008). Post moutain pine beetle impact assessment of Ts'il?os Provincial Park. North Vancouver: BA Blackwell and Associates. Roe, A. L., & Amman, G. D. (1970). The mountain pine beetle in lodgepole pine forests. Ogden: USDA Forest Service. Runzer, K., Hassegawa, M., Balliet, N., Bittencourt, E., & Hawkins, C. (2008). Temporal composition and structure of post-beetle lodgepole pine stands: Regeneration, growth, economics and harvest implications. Victoria: Natural Resources Canada, Canadian Forest Service. 21  Safranyik, L., & Carroll, A. L. (2006). The mountain pine beetle - A synthesis of biology, management, and impacts on lodgepole pine. Victoria: Natural Resources Canada. Shore, T. L., Safranyik, L., Hawkes, B. C., & Taylor, S. W. (2006). Effects of the mountain pine on lodgepole pine stand structure and dynamics. In The mountain pine beetle - A synthesis of biology, management, and impacts in lodgepole pine (pp. 95-114). Victoria: Natural Resources Canada: Canadian Forest Service. Taylor, S., & Carroll, A. (2003). Disturbance, forest age, and mountain pine beetle outbreak dynamics in BC: A historical perspective. Victoria: Natural Resources Canada. Vyse, A., Ferguson, C., Huggard, D. J., Roach, J., & Zimonick, B. (2009). Regeneration between lodgepole pine dominated stands attacked or threatened by the mountain pine beetle in south central interior, British Columbia. Forest Ecology and Management, 36-43. Walton, A. (2011). Provincial-level projection of the current mountain pine beetle outbreak: Update of the infestation projection based on the 2010 provincial aerial overview of forest health and the BCMPB model (year 8). Victoria: BC Forest Service. 

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