Course:CONS200/2019/The relationship between forest harvesting methods and wildfire intensity in the dry southern interior forests of British Columbia
- 1 Introduction
- 2 Forest characteristics
- 3 The social impact of wildfires
- 4 Forest harvesting and wildfire intensity
- 5 Other opinions regarding forest fire intensity in harvested settings
- 6 Management objectives for forest fuel reduction
- 7 Conclusion
- 8 References
Fires are one of the primary disturbances of dry interior forests in the Pacific Northwest, specifically in British Columbia. Pre Euro-American settlement, frequent low intensity fires played a large role in the spread of certain plants, and removing small trees and shrubs from forests, with little impact on larger more mature fire-resistant trees such as western larch, ponderosa pine, and Douglas-fir.
Logging in North America is a controversial practice regarding its relationship for wildfire intensity and prevention. Significant debate occurs regarding the most efficient practice for mitigating high-intensity forest fires in the Western forests of North America, or if prevention is even a worthwhile task for the success of our forests and the communities that surround them. Forest stand characteristics vary in the Pacific Northwest including topography, species composition, and climatic conditions. It is argued that natural, unnatural, pre and post harvesting factors associated with these forests can influence the potential intensity of wildfires.
The simple principles of fuel reduction treatments include: “reduction of surface fuels, increasing the height to live crown, decreasing crown density, and retaining large trees of fire-resistant species” . Clear-cut logging, overstory or understory thinning, and small controlled burns have been prescribed as a way to achieve these objectives. Of which, overstory and understory thinning have been proven to be the most successful and cost effective . Small controlled burning of forests has been proven to be inherently risky. Following the extremely prolific case of the 2002 Biscuit Wildfire in Oregon, US President George W. Bush pushed the timber industry to thin trees in order to prevent fires of this severity in the future, generating a great debate around public land management . However, ambiguities in thinning policy can potentially lead to larger more fire resistant trees being removed due to their commercial value. Commercial interest has the ability to become an obstacle to successful fire suppression. For example: BC provincial mandated removal of natural defences such as broadleaf trees in order to make way for more commercially viable Douglas fir and pine species . Hence, policy regarding fire suppression is extremely complex and there are many other factors including logging methods that influence the risk of high-intensity wildfires, such as the maturity of trees thinned and how susceptible they are to fires.
Many individuals argue that wildfires are expedited and that the removal of trees was found to be the primary cause of forest fires and their intensity . Furthermore, forest health is at greater risk of mortality and disease where logging occurs, increasing fuels for fires . Others believe that the intensity of wildfires is influenced by climate change, rather the practice of forest harvesting . Climate change is said to cause temperature increases, less snowpack, earlier spring melt and other contributing factors which are potential causes of reduced forest resilience, increasing fire spread and vigor .
Forest fires have huge implications for the people involved in fire suppression, taxpayers, general forest users, and those living near forests. Hence, it is extremely important that forest policy works to reduce the risk of high-intensity fires, placing public safety, economic wellbeing, and environmental health at its heart .
Policy geared towards logging conducted directly as a treatment can be beneficial. However, clear-cut logging isn’t necessarily good for preventing fires and may be shown to increase intensity in some cases, although more evidence of this is needed. This wiki will highlight the pros and cons of logging practices on wildfire management as it pertains to the intensity of wildfires in forests in the Pacific Northwest.
Geographically, the dry forests of the interior of British Columbia are primarily situated between the Coast Mountains to the East, and the Cascade and Rocky Mountain ranges to the West. The northern boundary is loosely identified within the Cariboo Plateau south of the city of Prince George. The Okanagan and Thompson regions are a continuation of the arid basins stretching up from across the US border. Similar climatic conditions exist East of the Cascade Mountains and within the Rocky Mountain Trench. As with most of BC, the landscape profile was formed with the recession of glaciers over 10,000 years ago. This has left a rugged and diverse topography with a mix of rolling hills, flatlands and steep slopes along river valleys and terraces.
In British Columbia, the Biogeoclimatic Ecosystem Classification (BEC) guide is a system for assigning ecological zones to areas based on topographic, climatic, vegetation and soil features. Within this framework, the forests that are considered dry typically fall into the Interior Douglas Fir Zone (IDF), or the Ponderosa Pine Zone (PP). However, these forests extend beyond the borders of BC into the North-Western United States, where the BEC system is not in use. For this reason, the BEC classification system is not necessary to describe the general forest type in question.
The most common natural disturbance type in the dry interior forests is wildfire. It's fire regime cycle has traditionally been described as low severity and high frequency. This means that in their natural state these areas will see frequent fires on short intervals that lightly burn the understory. Recent studies have challenged this assumption however, as some experts are now describing them as mixed severity. This means that along with frequent stand maintaining fires, naturally occurring high intensity burns are more frequent than previously understood.
The dry forests of the interior are dominated by Douglas fir, with ponderosa pine occurring in the driest of ecosystems. Lodgepole pine occurs in significant frequency in the higher elevation stands; particularly in the Cariboo plateau. Fir dominated stands are characterized by wide spacing between stems, and low understory cover. The natural state of these forests is similar to a parkland type landscape, due to the high frequency of stand maintaining fires. This leaves only sporadic shrub species in the undergrowth, and an overstory dominated by veteran fir and pine that have survived multiple fires in their lifespan. This resiliency is due to their thick fire resistant bark, which is an ecological adaptation suited to this climate. With the onset of fire suppression policies, many forests of this type have experienced an overgrown understory, along with a higher stem density than the natural state.
In recent years Canada has been experiencing an increased prevalence and severity of forest fires leading to higher impacts on affected communities “including large numbers of evacuations, high property damage, poor air quality and costly fire-suppression efforts” . In 2017, British Columbia had a record high fire year costing $500 million in fire suppression, burning over 1.2 million hectares of land, leading to roughly 65,000 evacuees . Wildfires have immense effects on ecological environments and pose huge risks to local communities.
Fires can destroy culturally and economically viable lands damaging livelihood security, capabilities, social cohesion, and threaten the subsistence of otherwise unemployed peoples living on First Nations reserves . In addition, large amounts of displacements cause significant disturbances to education, social isolation, and insecurity that exacerbate the social impacts of the disaster . This has significant implications for environmental justice as First Nations people of BC as due to their remote rural locations are at far greater risk . According to Todd Kuiack an Emergency Management Director for Indigenous Services Canada, on reserve First nations communities have a 33 times greater chance of being evacuated due to wildfires than those off-reserve . Such communities do not always have the social, human, and economic capital in order to tackle big issues such as wildfires without government support. Municipalities in BC fall under provincial jurisdiction, whereas, First Nation reserves fall under federal jurisdiction, often making it more difficult for resources to be diffused into these areas as opposed to other urban and less remote rural areas .
Forest harvesting and wildfire intensity
In the scope of forestry there are three main types of forest harvesting systems: Shelterwood harvesting, selective harvesting, and most famously recognized Clear-Cut harvesting. The type of harvesting system being practiced is critical to understand, as it can help in predicting the intensity of a wildfire, if one were to occur. Based on the research collected, these harvesting systems are assumed to be on conventional terrain (ground based harvesting operations), as the majority of forest harvesting in the interior of British Columbia is conducted this way.
Shelterwood harvesting is a type of seed tree system, where after harvesting manual tree planting is not required because healthier trees with good genetics are retained in the setting to re-seed the void areas left behind from harvesting activities. The objective of Shelterwood systems is to harvest the forest over several cycles and through a long period of time. Shelterwood systems are designed to remove trees in each pass with poor genetics, diseased, or undesirable species while still balancing economics and stand longevity. Typically in the interior this system is implement in a mature Douglas fir/ponderosa Pine stands. Its significance to wildfire intensity is that this harvesting method can lower the intensity of wildfires by removing the ladder fuels in the forest structure. Research shows that “understory fuel development is thought to have propagated crown fires that have killed old-growth stands not normally subject to fires of high intensity”. Shelterwood harvesting can help reduce the chance of a low intensity ground fire climbing to the forest canopy developing into a high intensity fire.
Selective harvesting is similar to Shelterwood harvesting as both systems still retain a percent of forest stand cover. However, with selective harvesting corridors and patches or “islands” of forest are left. The objective with this system is to remove selective groups of trees within the forest. Generally this type of harvesting creates a mosaic on the landscape of forested and non-forested sections.
Clear-cut harvesting is the simplest and most cost efficient method of harvesting, it is achieved by cutting all of the trees inside a setting with the exception of wildlife sensitive areas. The objective is to regenerate a new forest with healthier trees while also generating a market and value for the existing timber.
Wildfire intensity from both selective harvesting and clear-cut harvesting can greatly vary depending on how the harvesting slash is dealt with. In harvested areas with low amounts slash remaining post harvest, the fire intensity is lower because much of the biomass that would typically be consumed in a high intensity wildfire has already been removed from the forest floor. For harvested areas with high amounts of slash reaming the fire intensity is increased as the ground is loaded with a greater amount of fine fuels rather then if the forest was left natural. High intensity fires are classified by the resulting exposure of mineral soil from the burn. By controlling the amount of residual biomass left from harvesting, the intensity of a wildfire in the setting can be controlled.
Additionally, post harvest silviculture practices can impact the intensity of a future wildfire. A large contributor to post harvest to wildfire intensity is remaining logging slash, part of silviculture is to manage logging slash residue. There is a fine balance in managing harvesting waste so that after harvesting the site is not fuel loaded, however there is still enough residue left for decomposition and nutrient recycling. Common methods of removing harvesting slash are, either by pile burning or wood chipping. It is import to remember “[in] many forest ecosystems biomass production exceeds decomposition; this accumulated biomass fuels fires when lightning or people ignite fires in hot, dry, windy conditions”. Research shows that “[in] some drier forest types, such as the semi-arid ponderosa pine ecosystems, tree density far exceeds historical norms and these can fuel unusually intense fires”. Aside from tree density, species composition is an added factor that can impact the intensity of a wildfire. Depending on the forest attributes, such as aspect, and soil nutrients, often dictates the type of forest that will regenerate. For example on southern facing slopes the forest will typically be drier and have less ground vegetation, on northern facing slopes the forest are usually damper with more under story vegetation as it is not directly exposed to the sun. In some cases it may argued that forest harvesting does not impact the intensity of a wildfire, while it is the silviculture prescriptions post harvest that impact its potential intensity.
Other opinions regarding forest fire intensity in harvested settings
There have been many opinions, and ideas regarding the cause of forest fire intensity in harvested settings in the dry inlands of the pacific northwest. Mountainous landscapes are shaped and influenced by natural and anthropogenic disturbances. There is no doubt that as global, economic, climatic and management patterns shift, these changes will in turn affect ecological landscapes. Beyond the argument that wildfires are expedited and that the removal of trees was found to be the primary cause of forest fires and their intensity, there are additional opinions regarding the effect of forest wildfire intensity and the relative causes in harvested settings rather than the practice of forest harvesting being the primary cause.
As climatic changes and regimes are on the climb in the interior portions of many continents, it is expected that an increase in temperatures could rise 2-6 degrees celsius as well as a decrease in summer precipitation by 10-30%. Climate change is said to cause temperature changes, less snow-pack, earlier spring melt and other contributing factors which are the cause of increasing fire spread and vigour. The change in climate doesn’t only decrease the period of time where harvested settings are exposed to cooler, wetter climates, but it also changes the way the native tree species grow in the soil. Not having enough atmospheric and soil moisture can cause deficiencies, and a consequence of this is that mortality rates of trees increase, both in juvenile and established forests. Invasive plant species also thrive in areas where native species are weak and out-compete the native vegetation. Native species are extremely important for the success of different ecosystems. When non-native species begin to take over, they begin to add more thick vegetation in the understory, which creates more fuels for fires.
The practice of forest high-grading can also lead to an increase in forest wildfire intensity post-harvesting. High-grading is the act of harvesting the most merchantable trees in a given area. This isn't necessarily the issue. After this, the low quality trees that are left behind, which are often left with disease and other deformities, will begin to naturally regenerate. This can cause an abundance of dense understory, which can significantly increase the amount of fuels that will burn during a wildfire.
Fire suppression is also said to increase the intensity. Fire naturally regenerates soils, vegetation and forest ecosystems, and when intense suppression is done, it only increases the likelihood for it to later burn, when fuels density has grown. There is a fine line between wildfire suppression and allowing it to burn its course.
The cause of forest fire intensity in harvested settings is a disputable subject with evidence supporting many different theories. The most important consideration is that no two situations will be identical and that there can be many ways to mitigate and manage for wildfires before, during and post harvest.
Management objectives for forest fuel reduction
Historically, the dominant natural disturbance regime in these forests was fire. It both initiated new growth and aided in the natural self thinning of the forest. Before the west was settled by Europeans, the use of fire was harnessed by the Indigenous peoples of the region to keep the forests healthy and clear unwanted underbrush that would hinder development and allow fire to escalate easily. However, for much of the last century, the official policy in both Canada and the US has been that of fire suppression. This has been justified to protect human life, property, and merchantable timber. The suppression of fire has led to an excess of fuels on the forest floor as well as increased canopy density. With fire being an integral part of the ecosystem for millennia, many fire-resistant plant species developed in this environment. With the exclusion of fire, many of these species have been out-competed by other, less resistant species. This has contributed to the uncharacteristically high fire intensity seen in the region.
Ladder fuels, understory thinning, and prescribed burns
As knowledge of fire ecology has grown, there has been a greater focus on stand maintenance to mitigate wildfire. This includes prescribed burns and mechanical fuel treatments in order to eliminate excess fuel accumulation. The excess understory acts as “ladder fuel”, that enable ground fires to easily climb into the forest canopy, greatly increasing severity. Resilience to first and even second entry wildfires has increased substantially following treatment in a fire suppressed forest.
Understory and brushing treatments are an effective way to mitigate wildfire intensity. This involves removing excess brush and non-merchantable timber from a forest. This process can either be mechanized or done manually. Clearing the fuels from the forest floor is intended to mimic the natural state of these forests; open and clear with a mature overstory and abundant room for ungulate travel. One criticism of biomass removal is a potential decrease in carbon storage. The paradox of this is that large scale forest fires are one of the leading causes of atmospheric CO2 emissions, due to the release of stored carbon in biomass. It has been found that most of the carbon stored in a forest is in the overstory layer, which is not removed in a fuel treatment. By removing understory vegetation, it reduces the risk for large wildfires, while retaining most of the forests carbon sequestration ability.
Prescribed burning is a useful, yet controversial practice. Typically, a low intensity fire will be implemented on a stand following a mechanical brushing treatment. This is considered one of the most effective methods at reducing fuel build up and restoring the natural forest structure. There is some stigma attached to this method, however. Communities are generally wary of any intentionally lit fires, considering the risks involved. Choosing the right climatic conditions and ensuring the public are well informed are important requirements for a successful prescribed burning treatment.
Commercial, or overstory thinning is a harvest practice that involves removing a determined amount of merchantable trees from a stand, leaving most of the canopy intact. This provides interim revenue before the end of the rotation cycle, while reducing competition for the remaining stems which allows for increased annual increment growth. It also prevents the spread of crown fires and decreases the amount of fuel accumulation of the forest floor. Some landowners or tenure holders may choose to carry out a commercial thinning operation for these reasons, with the additional benefit of reducing wildfire risk. Removing some of the basal area can mimic the density found in the natural state of these forests.
Wildfires have been on a steady rise over the past few years in British Columbia. Historical wildfire records and patterns have been changing, and it is no different in the dry inlands of the pacific northwest. Communities, both rural and urban have been exposed to the threats and destruction caused by outraging fires, leaving massive amounts of change for everyone to deal with. People and animals are relocated, towns are at the risk of burning up, people are losing their jobs, and the province is watching BC's natural resources go up in flames. Contrary to the wildfires potential to be incredibly dangerous, fire is a natural occurrence and is important for certain ecological benefits and ecosystems. Working with the natural resources in British Columbia comes with a heavy amount of responsibility and the forest harvesting management methods that were discussed, all relate to the intensity of wildfires in some capacity some being greater than others. It is however critical to note that the act for forest harvesting isn't necessarily the main and only contributing factor to the fire intensity relative to the location it is burning in. Pending on the harvesting system being implemented and the associated management objectives for fuel reduction in the same setting needs to be well planned out and implemented to have any type of success. Collecting surrounding area wildfire, climate, ecosystem and wildlife data, looking at future climatic trends, post harvesting management objectives are all additional contributors to the potential intensity. With many components to this dynamic, non-linear wildfire intensity trend, ensuring adequate forest management during all levels of harvesting is extremely important. By managing our forests with wildfire intensity management being a major objective, it helps reduce the negative impacts on the social, economic and environmental spectrums, and it will ensure that our forests will be healthy, and habitats won't be unnecessarily destroyed, so the dry inlands of British Columbia can thrive for decades to come.
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