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Forest management and carbon storage in British Columbia Xu, Yuanyuan Apr 30, 2014

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 Forest Management and Carbon Storage in  British Columbia  By Yuanyuan Xu  B.S.F., The University of British Columbia, 2014  A GRADUATING ESSAY SUBMITTED IN PARTIAL FULFILLMENT OF THE  REQUIREMENTS FOR THE DEGREE OF   BACHELOR OF SCIENCE  in Forest Resources Management  The Faculty of Forestry  FRST 497   THE UNIVERSITY OF BRITISH COLUMBIA  (Vancouver)   April 2014  ©Yuanyuan Xu, 2014   ii Abstract Forest ecosystems play a significant role in the global carbon cycle. Through the process of photosynthesis, live trees are able to sequester carbon from the atmosphere and store it in biomass and soil, which helps to ease climate change. Besides above ground woody biomass, forest soil is another critical part of carbon storage; about 58% of the carbon in a forest stand is stored in soil. With disturbance (e.g., harvesting, fire, insects infection), forests release carbon dioxide to the atmosphere, converting forests from a net carbon sink to a carbon source. Forest management activities can either increase or decrease the carbon storage of forests. In general, reducing the harvest level, extending rotation intervals and replacing clear cutting harvest systems will reduce carbon emissions during and post disturbance. Protecting forests from fire and insects infection also significantly contributes to carbon sequestration and help reducing carbon emissions. The outbreak of mountain pine beetle is the main factor that converted BC from a carbon sink to a carbon source since 2003. Thus, addressing effective solutions to control the mountain pine beetle population is critical for carbon recovery in BC province. Key words: carbon sequestration; climate change; forest protection; forest management; BC province;   ACKNOWLEDGEMENT I would like to acknowledge and thank my primary adviser, Peter L Marshall, who helped me with the selection of essay topic and encouraged me to improve myself. This essay would not have been possible without Dr. Marshall’s professional suggestions and patient guidance.  I would like to thank Professor Gary Bull for providing background about carbon stocks in his lecture and giving me the opportunity to do carbon stock and carbon credits in my group project to have a better understanding on this topic.  iii Table of Content 1.0 INTRODUCTION ............................................................................................. 1 2.0 FUNCTIONS OF FORESTS IN CARBON STORAGE .................................. 2 2.1 THE STATUS OF FOREST IN THE GLOBAL CARBON POOL ..................................... 2 2.2 CARBON SINK AND CARBON SOURCE ................................................................ 4 3.0 EFFECT OF FOREST ACTIVITY ON CARBON STORAGE....................... 6 3.1 SILVICULTURE SYSTEMS .................................................................................... 6 3.1.1 Old-growth Harvesting VS. Secondary-growth Harvesting ........................ 6 3.1.2 Clear Cutting with an Even-aged Management System Versus Patch Cutting with an Uneven-aged Management System ........................................................ 7 3.1.3 Optimal Rotation Intervals ........................................................................ 9 3.2 IMPACT OF NATURAL DISTURBANCE ON CARBON SEQUESTRATION ....................11 3.2.1 Forest Fire ............................................................................................... 11 3.2.2 Mountain Pine Beetle Epidemic .............................................................. 13 4.0 DISCUSSION .................................................................................................. 15 5.0 CONCLUSIONS .............................................................................................. 18 5.1 GENERAL CONCLUSIONS ................................................................................. 18 5.2 SUGGESTIONS FOR IMPROVING MANAGEMENT ACTIVITIES ............................... 18 6.0 REFERENCES ................................................................................................ 20       iv List of Figures Figure 1 Forest Carbon Cycle, taken from (Hoberg, 2013) ___________________________ 3  Figure 2 The GHG sources and sinks in the forest ecosystem, taken from (Hoberg, 2013) _________________________________________________________________________________________ 5  Figure 3 The area of old-growth forests (unprotected, protected, managed) and secondary growth forest (unprotect and protect) in BC, taken from (Sierra Club BC, 2013) __________________________________________________________________________________ 7  Figure 4 The amount of live carbon stores over harvest rotation intervals for different percentage partial cutting, taken from (Harmon et al., 2009) _________________________ 9  Figure 5 The prediction of forest carbon sequestration in wood, soil and live trees after a forest fire, taken from (Fire Science Brief, 2010) ____________________________________ 12  Figure 6 Total carbon stock change for control, Beetle and Beetle & additional harvest scenario, taken from (Kurz et al., 2008) _____________________________________________ 15   List of Tables Table 1 Estimate of global forest area, carbon stock in living biomass and growing stock (IPCC, 2007). __________________________________________________________________________ 4  1 1.0 Introduction In recent years, the public has paid more attention to climate change as it became a critical issue globally. Retaining a stable climate is vital since climate change will severely affect plants. Greenhouse gases are the main driver of global warming and CO2 is the most common greenhouse gas in the atmosphere. Therefore, carbon sequestration is important to ease global warming. According to the IPCC report (2013), CO2 increased by 40% from 278 ppm to 390.5 ppm between 1750 and 2011.   Forests are large storehouses of carbon accumulated in the trees and soils (Beer et al., 2010). According to the IPCC (2000), approximately 1150 Pg, over half of the terrestrial soil and vegetation carbon is found in the forests. Global forests store about 861 ± 66 Pg C, with 383 ± 30 Pg C (44%) in the upper 1 m soil and, 363 ± 28 Pg C (42%) in live biomass, 73 ± 6 Pg C (8%) in deadwood and 43 ± 3 Pg C (5%) in litter (Pan et al., 2011). Since 1850 one-third of CO2 emission has been caused by deforestation, which explains 20% of the rise in recent decades (IPCC 2000). As a result, managing forests sustainably with considerations of timber value, carbon, biodiversity, non-timber products, and visualization is critical for social development and stability.   In Canada, 77% of forests are managed (Thompson & Pitt, 2003). Residual carbon storage varies among harvesting systems. In addition, managed forests are also affected by natural disturbances (e.g., fires, insect attack). These management regimes and disturbance result in changes in species composition, age structure and the amount of carbon they store (Chen et al, 2013).  Past research has compared the influence of reducing harvest levels or promoting growth rates on carbon sequestration and impacts of various disturbance regimes on forests  2 carbon fluxes and stocks (Harmon et al., 1990; Masek & Collatz, 2006; Kurz et al., 2008; Man et al., 2013). Forests have a significant impact on the carbon cycle and forest management helps to stabilize the sequestration of carbon from the atmosphere (Pacala, 2004). Canada contains the second largest forest area in the world.  This paper will focus on above ground woody biomass in temperate forests in BC, Canada. I will illustrate some general ideas about the function of forests in carbon storage. I will then summarize the results of relevant research and analyze the impacts of each forest management activity and disturbance regime in terms of carbon storage and provide feasible suggestions for foresters to manage forest stands for increasing carbon stock.   2.0 Functions of Forests in Carbon Storage 2.1 The Status of Forest in the Global Carbon Pool Carbon sequestration is a process removing carbon from the atmosphere and depositing of in a reservoir (Daniels, 2014). Carbon storage is the amount of carbon kept in forests, consisting of two parts generally: carbon stored in above ground woody biomass and forest soil carbon storage (Nowak, 2002).  Figure 1 shows the forest carbon cycle. Carbon is stored in many pools, and emitted from and added to each carbon pool over time. Harvesting, decomposition and fire emit greenhouse gases (GHG) to the atmosphere, while forest growth removes carbon from the atmosphere (Hoberg, 2013).  3  Figure 1 Forest Carbon Cycle, taken from (Hoberg, 2013).  Forests are the biggest carbon pool in the terrestrial ecosystem (Kauppi & Posch, 1989). Approximately 1 ton of carbon dioxide can be absorbed from the atmosphere with only 1 m3 of wood growth (Zhang & Pen, 2008). Vegetation carbon storage occupies 29% of the total forest ecosystem carbon pool, while soil carbon storage occupies 58%. The carbon storage in the soil is 6,600 billion tones while the carbon storage in the forest vegetation is 3,300 billion tones (IPCC, 2007). Forest carbon storage for different regions is shown in Table 1. Thus, forests make a significant contribution to the carbon dioxide concentration in the atmosphere not only from the perspective of forest total carbon storage, but also in terms of the forest capacity to sequestrate carbon.     4 Table 1 Estimate of global forest area, carbon stock in living biomass and growing stock (IPCC, 2007). Area Forest area (*106hm2) Carbon stock in living biomass (*106t) Annual added value of forest accumulation in 2005 (*106m3) 2000 2005 Asia 571.577 130.533 222.933 47.111 Europe 1001.394 158.033 160.967 107.264 North America 705.849 153.633 155.467 78.582 Oceania 206.254 41.800 41.800 7.631 South America 831.540 354.400 335.500 128.944  2.2 Carbon Sink and Carbon Source Forests can either be carbon sinks or carbon sources. Carbon dioxide is absorbed from the atmosphere and stored in living biomass through photosynthesis. As a result, trees are carbon sinks during growth. Meanwhile, respiration of vegetation and litter or snag decomposition will release carbon dioxide into the atmosphere as well. In addition, forests can also be a net carbon source following disturbance (e.g., fire, disease, pests attack, harvesting), when forests may release more carbon than they absorb (Goodale et al., 2002).   Figure 2 shows the GHG sources and sinks in the forest ecosystem. BC changed from a carbon sink to a carbon source overall because of the mountain pine beetle infestation in 2003 (Hoberg, 2013). In general, forests located in high or middle latitudes in the world are net carbon sinks with 7 billion tons carbon sequestration per year, while the forests in low latitude areas are carbon sources, releasing 1.6 billion tons carbon each year (Zhang & Pen, 2008). Deforestation and forest degradation, especially human activities that destroy tropical forests, are the main causes of low latitude forest becoming carbon sources. According to the BC government (2013), logging without burning released 63.1 million tons of CO2 in 2011 while logging and burning emit 7.9 million tons of CO2 and  5 2.4 million tons of CO2 was released by wildfire. In 2011, the overall carbon sequestration was 38.5 million tons and the total carbon emission was 73.4 million tons; thus, the net carbon emissions were 34.9 million tons (Sierra Club BC, 2014).   Figure 2 The GHG sources and sinks in the forest ecosystem, taken from (Hoberg, 2013)  Forest planners would like to increase carbon sequestration and decrease carbon emission in order to ensure forests are net carbon sinks. Forest management can regulate the capacity of forest carbon sequestration effectively. In general, three main approaches can be used: (1) protect the existing forests from deforestation or degradation and avoid conversion to other land cover types; (2) increase forest areas through afforestation or reforestation; (3) apply alternate forest management practices (Newell & Stavins, 2000).   6 3.0 Effect of Forest Activity on Carbon storage 3.1 Silviculture Systems 3.1.1 Old-growth Harvesting VS. Secondary-growth Harvesting Old growth stands have higher carbon sequestration capabilities compared to second-growth stands. Old-growth stands have sequestrated carbon for centuries and if these forests are harvested, the carbon that is stored in the woody biomass and soil may re-emit into the atmosphere by decaying (Butler, 2008). Although old-growth stands are a global carbon pool, international treaties do not protect them well since many people believe that the old growth forests no longer sequester carbon. However, Luyssaert (2008) found that the net carbon balance of the forest is usually positive between the ages of 15 and 800. No matter the soil type, carbon storage below ground for old-growth forest stands is higher than that for second growth stands (Fredeen et al., 2005). Specifically, woody biomass in old-growth stands is 78 Mg C·ha–1 in coarse soils and 35 Mg C·ha–1 in fine soils. However, in second-growth stands carbon storage in above ground woody biomass ranges from 75 Mg C·ha–1 in coarse soils to 33.8 Mg C·ha–1 in fine soils (Fredeen et al., 2005).   Logging old-growth stands release CO2 and contributes to the increase in overall carbon emissions in BC (Black et al., 2008). MacKinnon and Vold (1998) found that 47% of forests are old-growth in central British Columbia. However, many disturbances such as harvesting, diseases, and insect infections may convert old-growth stands into younger stands (Kurz & Apps, 1999). These conversions may produce large quantities of carbon emissions. From the Sierra Club of BC’s report (2013), there are approximately 1.5 million ha of unprotected old-growth stands on Vancouver Island. As is shown in Figure 3, only a few old-growth forests are protected or managed appropriately (green zones  7 represent protected old-growth forests while red zones represent unprotected old-growth forests). Among the unprotected old-growth stands, approximately 6000 ha are highly productive areas with critical carbon storage capacity and these areas may be the target of harvesting. These forests can sequester roughly 13 times British Columbia’s annual carbon emissions. Logging unprotected old-growth forests in 2011 resulted in 3 million tons loss in carbon storage, which is equivalent to the official reduction in BC annual emissions between 2007 and 2010 (Sierra Club BC, 2013).  Figure 3 The area of old-growth forests (unprotected, protected, managed) and secondary growth forest (unprotect and protect) in BC, taken from (Sierra Club BC, 2013).  3.1.2 Clear Cutting with an Even-aged Management System Versus Patch Cutting with an Uneven-aged Management System  To quote the Silvicultural System Guidebook (1995), “a clearcut system is a silvicultural system that removes trees in the entire stand from an area of more than one hectare, and greater than two tree heights in width, in single harvesting operations”. Partial cutting is  8 defined as the removal of a part of stand of trees (Society of American Forests Website, 2014).   In general, the fewer the live trees are removed, the higher the carbon that remains stored in forest landscapes (Harmon & Marks, 2002). In other words, the amount of carbon stored is closely related to the percentage removed. Moreover, when the rotation interval length is short, the difference in carbon storage between partial cutting and clear cutting is greater. Specifically, for 20 year intervals, forests with 20% partial harvesting can contain 180 Mg/ha of above ground woody biomass in carbon, almost 6 times the carbon storage of clear cutting (Harmon et al., 2009). However, in the case of clear cutting, the removal of the whole tree will reduce carbon storage more than only removing stems (Jiang et al., 2002).   As is shown in Figure 4, more live carbon is kept in all rotation years under the aggregated partial cutting system. However, for dispersed partial cutting, the situation is more complex. When rotation intervals exceed 120 years, complete cutting stores more live carbon than 80% dispersed partial cutting.   Although the trends for aggregated partial cutting are similar to dispersed partial cutting, the average dead carbon stores are higher for aggregated partial cutting. Compared to clear cutting, 20% partial harvesting retains 1.7 times of the average carbon stores in soil assuming a 20 year cutting cycle (Harmon et al., 2009). On the whole, a partial harvesting has a higher level of carbon stored than clear cutting, but a lower carbon storage level compared to no harvesting. This occurs because partial cutting leaves live carbon in forests, which increases the average carbon stored (Thornley & Cannell, 2000).    9     Figure 4 The amount of live carbon stores over harvest rotation intervals for different percentage partial cutting, taken from (Harmon et al., 2009)    3.1.3 Optimal Rotation Intervals The amount of carbon stored in forests is affected by rotation length. In general, carbon that stored in forests will increase when the interval between harvests become longer (Smithwick et al., 2007). Two main reasons account for this circumstance. First of all, when the rotation interval increases, the input through photosynthesis will increase, which leads to an increase in the carbon stored (Harmon et al., 2009). Secondly, the 05010015020025030035020 50 80 100 125 150 200 250Live Carbon Storage (Mg/ha) Rotation Intervals (yrs) Aggregated Partial Cutting  100%80%60%40%20%05010015020025030035020 50 80 100 125 150 200 250Live Carbon Storage (Mg/ha) Rotation intervals (yrs) Dispersed Partial Cutting 100%80%60%40%20% 10 amount of carbon removed relates to the average carbon stored (Olson, 1963).   A stand dominated by Douglas-fir recently logged released 22 tons of CO2 each year. A similar stand logged twelve years ago, was also regarded as a carbon source, released an average of 5 tons of carbon dioxide annually (Gurney et al., 2002). The above figures indicate that a stand harvest with short intervals is a sizeable carbon source after disturbance occurs and continues to be an emission source over time. Forests release carbon immediately after logging, the amount that escapes relates to the amount of legacy carbon stored in soil and dead materials such as snags, and the rate of regeneration (Harmon 2001).    Conversion from short rotation intervals to longer ones could lead to increases in carbon storage (Seely et al., 2002). However, shorter rotation intervals may cause a smaller portion of the harvested material being converted to long-term forest products (Bourque et al., 2007).   Some researchers (e.g., Dewar & Cannell et al., 1992; Pussinen et al., 2002; Seely et al., 2002) hold the opinion that harvesting with short rotation intervals could increase carbon stored in forest products. When the highest annual increment of trees is achieved at short harvest rotation intervals, the average amount of carbon absorbed begins to decline (Pussinen et al., 2002). Thus, harvesting with short rotation intervals, especially harvesting at the peak of mean annual increment years could maximize carbon stored in forest systems as long as there is no carbon loss during manufacturing (Harmon et al., 2009). However, almost all forest products, except biofuels, suffer a large amount of carbon loss during the manufacturing processes (Harmon et al., 1996). In other words, harvesting with short rotation intervals will lead to more carbon stored in forest products;  11 however, this increase cannot offset the loss of carbon stored in forest ecosystems as forest products lose carbon storage during manufacturing.  3.2 Impact of Natural Disturbance on Carbon Sequestration 3.2.1 Forest Fire  Protection from fire or insects attack seems more important for increasing carbon sequestration controlling harvesting since there will be more carbon emissions during and after the disturbance. Although harvesting reduces the interval between disturbances and forest carbon storage will decrease, forest carbon storage can still be expected to increase when forest is protected from fire or disease (Kurz, 1998, Seely 2002).   Fires, especially stand replacing fires or high intensity fires, release a sizable amount of carbon dioxide from living biomass and soil to the atmosphere (Auclair & Carter, 1993). Annual carbon losses in Canadian forests due to fire are approximately 10% to 30% of net primary production (Harden et al., 2000). In addition, the US will experience an increase of 25% to 50% of the area burned over the next 100 years based on current climate model predictions (Neilson & Drapek, 1998). Thus, understanding the short term and long term effects of forest fires is critical for understanding the carbon budget over climate change periods.  There is a difference between long-term and short-term fire effects. Forests will be a net carbon source post-fire and may recover to become again a carbon sink after a long period without further disturbances.  The short-term effect of a stand-replacing fire is that carbon is released to the atmosphere through combustion during the fire, converting stands from carbon sinks to carbon  12 sources. The capacity for carbon sequestration is diminished as almost all living biomass in forests is killed and dead biomass cannot sequester carbon through photosynthesis (Kasischke & Stocks, 2000). Decomposition of dead biomass can last for numerous decades and the carbon released by decomposition can reach up to three times that which occurs during initial combustion (Auclair & Carter, 1993). Although the landscape will experience regeneration after a fire, carbon losses through decomposition can still exceed the carbon that sequestrated by new growth for several decades after a fire (Crutzen & Goldammer, 1993). Figures 5 indicate the prediction of forest carbon sequestration in wood, soil and live trees after fire. Carbon recovery will not occur until 80 years after a stand-replacing fire (Fire Science Brief, 2010).  Figure 5 The prediction of forest carbon sequestration in wood, soil and live trees after a forest fire, taken from (Fire Science Brief, 2010).  The long-term fire effect on the carbon balance depends on regeneration and fire frequency after the disturbance. When forests convert to grassland rather than regenerating to another forest after a stand-replacing fire, more carbon will be lost from the landscape and the carbon sequestration process is slower, which means it takes longer period for carbon recovery (Fire Science Brief, 2010). Fire frequency plays an important  13 role since, the forests will still be a carbon source over the long term if another disturbance occurs before the stands recovered. If forests regenerate and last long enough before the next disturbance occurs, the carbon that is lost can be recovered by the natural resilience of the forests (Smith & Resh, 1999; Litton et al., 2004).  3.2.2 Mountain Pine Beetle Epidemic  Forest insect epidemics can also produce large carbon emissions to the atmosphere by reducing tree growth rate and causing tree mortality (Mattson & Addy, 1975). It is difficult for unhealthy trees to uptake carbon as usual and the decay of dead trees will release carbon as well. Mountain pine beetle (Dendroctonus ponderosae), a native insect in North American, is the most common insect epidemic currently occurs in western North American, and large-scale outbreaks have major impacts on mature pine forests (Safranyik, 1974; Brooks et al., 2004).   Compared to previous recorded outbreaks, the outbreak in 2006 was the most severe in intensity and scale ever recorded in BC (Safranyik, 2006). The area presently attacked by the mountain pine beetle in BC exceeds 18.1 million hectares. Timber losses are approximately 710 million cubic meters since the epidemic began (British Columbia Government website, 2014). However, the population of the mountain pine beetle is declining now because most of their preferred hosts (lodgepole pine trees) have been killed in the past decade (British Columbia Government Website, 2014). There will be an estimated average of  36 g carbon released per m2 of area per year during 2000 to 2020 in the affected region of  374,000 km2 (Kurz et al., 2008). Due to large-scale outbreaks and control difficulty, the impact of insect epidemics on forest carbon emission is much larger than forest fire (Walton, 2010). Carbon released from the beetle outbreak in BC in the worst years was equivalent to nearly 75% of the carbon emissions annually from forest fires across the whole of Canada (Kurz et al., 2008).  14  Climate change is the main reason attributed to causing the large-scale outbreaks of mountain pine beetle. Mountain pine beetle can multiply rapidly in conditions of warmer temperatures and reduced precipitation (Goheen, 2007). Compared to the average temperature increase globally, the temperature is increasing faster in interior BC (Osborn, 2014). The warmer temperature in winter allows more beetles to survive through winter (Goheen, 2007). With the suitable habitat conditions for these insects, the recent outbreak expanded northward and to higher elevations than has occurred in the past (Williams & Liebhold, 2002).  The Ministry of Forests increased the annual allowable cut in the outbreak region and reallocated the harvest to salvage dead trees (Kurz et al., 2008). Figure 6 indicates the total carbon stock change for control (forests without beetle), beetle (forests with beetle but no additional harvest) and beetle and additional harvest scenarios. As is shown in figure 6, controlled forests can recover from a carbon source to a carbon sink in a short period after harvesting. However, carbon in the forests that are attacked by beetle is unable to recover within 20 years. Although the salvage harvesting helps reduce more carbon storage immediately after harvesting, transfer from beetle-killed timber to forest products is 31 Mt carbon, about 13% of the total harvest (Kurz et al., 2008). As a result, salvage harvesting can provide additional economic value and forest products can store carbon, while the timber in the stands without salvage harvesting will decay and release more carbon into the atmosphere.    The intensity of fire will increase following mountain pine beetle attack, as there are more dead trees. The water content of dead trees is low, which means these coarse fuels are easy to burn. In addition, ignition is easy as fine fuels (e.g., litters, snags) are  15 abundant in unhealthy forests. As a result, the probability of extreme fire (high intensity) is abnormally high in forests with beetles (Daniels, 2013). Extreme fires are hard to control and suppressed.  Figure 6 Total carbon stock change for control, Beetle and Beetle & additional harvest scenario, taken from (Kurz et al., 2008).  4.0 Discussion Several approaches can be used to increase carbon storage, including increasing the optimal rotation age, choosing an optimal harvesting system, protecting old-growth forests from logging, and protecting forests from fires and insect epidemics. Based on an empirical model, Sohngen & Mendelsohn (2003) believe that carbon sequestration by forestry can account for one-third of total carbon reduction.  Intermediate rotation intervals can increase carbon storage more effectively than  16 longer rotation intervals because the capacity of carbon sequestration declines in older forests (Johnsen et al., 2001). Although the carbon absorption rate is lower in older forests, there is large amount of live and dead carbon stored in those forests. Also, stand-replacing disturbances of old-growth stands lead to massive carbon emissions. Most of the old-growth stands in BC are not appropriately protected or managed. Thus, we need to protect old-growth forests from disturbances in order to prevent the release of carbon to the atmosphere. The optimal rotation interval for carbon sequestration in second-growth forests is difficult to determine and there is limited research on this field. I believe it will be a big challenge to study rotation intervals and it will be valuable to find an approach to determine optimal rotation intervals for different stand compositions and environmental conditions.   Harvesting causes CO2 emissions during and in the post-disturbance; however, different harvesting systems will have different amounts of carbon emissions. From a perspective of economics, social and sustainable forest management, it is not feasible to prevent harvesting. Partial cutting with uneven-aged management is suggested as a more carbon-friendly approach since more live trees are left in the stands to absorb carbon. Unlike tropical forests, reforestation (natural or artificial) generally occurs immediately after harvesting (Prentice et al. 2001). As a result, clear cutting will convert older stands, often with multiple ages, into younger, more homogenous stands (Wells et al., 1998). With little structure and species complexity, homogenous forests have low resilience to natural disturbances, especially for insect epidemics. In conclusion, partial cutting contributes to the creation of uneven aged stands is preferred in forest management. However, the impact of leaving trees to naturally regenerate needs to further study since the growth rate of regeneration will affect the speed and amount of carbon sequestered.   17  Furthermore, increasing soil nutrients through soil management or fertilization will increase carbon the rate of carbon sequestration due to faster tree growth and decrease the time to achieve a given carbon storage amount (Seely et al., 2002). However, research on quantifying the effect of fertilization on carbon sequestration is limited, and it is uncertain whether increasing carbon inputs through litter decomposition will increase or reduce the rate of labile decomposition (Black et al., 2008).   Forest fire prevention can protect forests and halt carbon emissions to the atmosphere. However, fire prevention may lead to higher risk of stand replacing fires. Low intensity or high frequency fires will consume fuels (e.g., wood debris, litters, and snags) on the ground. Without abundant fuels, it is difficult for high-intensity crown fires or stand-replacing fires to occur. Forest fire prevention can lead to large amount of fuels accumulating and increase the risk of crown fires. However, the impact of fire prevention on the risk of crown fire and insect epidemics should be further studied.   The mountain pine beetle outbreak was the main cause of BC’s conversion from a carbon sink to a carbon source. Thus, controlling mountain pine beetle infestations is the first step to improving carbon storage and bringing BC back to a carbon sink. However, it is a great challenge to control insect epidemic and to manage lodgepole pine stands on such as a large scale. At the present time, managers usually use salvage logging to reduce economic and carbon losses, and research is required to propose a better way for salvage logging to maximize carbon storage and enhance the mid-timber supply.   18  5.0 Conclusions 5.1 General Conclusions The forest ecosystem plays a significant role in the global carbon cycle. Through photosynthesis, live trees are able to sequestrate carbon from the atmosphere and store the carbon in biomass and soil. With disturbance (e.g., harvesting, fire, insects infection), forests will release carbon dioxide to the atmosphere, converting forests from a net carbon sink to a carbon source.   Afforestation and reforestation are two effective ways to enhance carbon stock, as well as selections of optimal forest management activities. Reducing harvest levels, extending rotation intervals, replacing clear cutting harvest system, and protecting forests from fire and insects will generally reduce carbon emissions. Improving forest stands vigour by fertilization enhances carbon sequestration by increasing tree growth rates.   Future studies on carbon sequestration should focus on developing empirical models to predict optimal rotation intervals, and addressing effective solutions to control the mountain pine beetle population.   5.2 Suggestions for Improving Management Activities  Protect or manage for carbon effectively these old-growth stands in BC.  Model and choose an optimal rotation interval for second growth stands.  Partial cutting with uneven-aged management is better for carbon than clear cutting.  Choose species that adapt well to stand conditions and that have a high capability  19 for carbon sequestration. Stand conditions change with climate change; thus, the potential species of stands might change.  Fertilizing stands when regeneration occurs or the competition between the younger generation and older trees is heavy.  Protect forests from fire, especially fire caused by human activity.   Manage fuels in forests that have high risk of crown fire. A few prescribed burns could be introduced to reduce the amount of fuels in the stands to avoid stand-replacing fires.  Salvage logging in stands affected by mountain pine beetle, to convert dead trees into wood products to store carbon longer.  Managing stands infected by mountain pine beetle with clear cutting and pesticides, reduce the percentage of pine in regeneration. Planting stocks with genetic of high resilience to mountain pine beetle infection instead of relying on natural regeneration.          20 6.0 References Auclair, A., & Carter, T. (1993). Forest wildfires as a recent source of CO2 at northern latitudes. 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