• Coniferous to deciduous forest
    • Summary
    • Categorical attributes
    • Detail information
    • Regime shift Analysis
      • References

Coniferous to deciduous forest

Main contributors: Katja Malmborg, Linda Lindström Lindström, Lara D. Mateos

Other contributors: Garry Peterson, Juan Carlos Rocha

Last update: 2014-10-21

Summary

The regime shift is the boreal forest, where the coniferous dominated forest is slowly being replaced by deciduous trees due to recent climate warming and changes in the wildfire regime.  Coniferous trees thrive in cold, moist soil conditions, and enhance these conditions by accumulating a deep soil organic layer. The moisture of the soil prevents frequent fires from occurring, but when they do, the soil organic layer is rarely consumed in its entirety due to the high water content (Johnstone et al., 2010). Coniferous trees regenerate well in organic soil, which means that only really severe fires that consume the whole soil organic layer will alter the coniferous-promoting soil conditions (Hollingsworth et al., 2013). Deciduous trees, on the other hand, thrive in nutrient rich, dry and warm soils, which are conditions that they reinforce by keeping the decomposition rate high, making the soil organic layer shallow. Fires tend to be more frequent than in coniferous dominated forests, but not as intense. However, since the soil organic layer is so shallow, it tends to be consumed by the fire, exposing the mineral soil (Johnstone et al., 2010). Deciduous trees have well developed strategies for regenerating in mineral soil, which means that deciduous trees tend to return to these areas after a wildfire (Hollingsworth et al., 2013). A severe fire can get the system to shift from one regime to the other, while changes in climate (i.e. mainly temperature or precipitation) can change the underlying conditions to make each regime less resilient (Johnstone et al., 2010). It has been well studied in interior Alaska (Wolken et al., 2011).  Currently, warmer temperatures are decreasing the relative humidity in the boreal forest in Interior Alaska, which is both causing more frequent and severe fires, as well as altering temperature and moisture conditions in the soil to favour deciduous tree regeneration (Mann et al., 2012).  The productivity of the boreal forest in Interior Alaska is expected to decrease due to drought stress in the new regime (Beck et al., 2011).  The provisioning of wild products such as berries and game is expected to shift as some species and decrease for others, but it is unclear what the net changes will be (Chapin et al., 2008). The boreal forest is likely to become a net source of carbon to the atmosphere (McGuire et al., 2009; Schuur et al., 2009), while the air quality is expected to decrease periodically due to the increase in fire frequency (Chapin et al., 2008). Because the main driver of the regime shift is climate warming, decreasing  emissions of greenhouse gasses into the atmosphere would be the most powerful way to prevent or reverse the regime shift.  Reducing greenhouse gas emissions is a difficult and challenging intervention that requires substantial coordinated global action that seems unlikely to occur in the near future.  Fire suppression could potentially slow down the rate of change in parts of the forest, but fire supression is not feasible in most of the boreal forest.

 

Categorical attributes

Impacts

Ecosystem type:’

  • Temperate & boreal forests

Key ecosystem processes:

  • Soil formation
  • Primary production
  • Nutrient cycling
  • Water cycling

Biodiversity:

  • Biodiversity

Provisioning services:

  • Freshwater
  • Wild animal and plant products
  • Timber
  • Woodfuel

Regulating services:

  • Air quality regulation
  • Climate regulation
  • Water purification
  • Regulation of soil erosion
  • Pest & disease regulation

Cultural services:

  • Recreation
  • Aesthetic values

Human well-being:

  • Food and nutrition
  • Health (e.g. toxins
  • disease)
  • Livelihoods and economic activity
  • Security of housing & infrastructure
  • Cultural
  • Aesthetic and recreational values

Links to other regime shifts:

NA

Drivers

Key drivers:

  • Environmental shocks (e.g. fire
  • floods
  • droughts)
  • Global climate change

Land use:

  • Timber production
  • Conservation
  • Tourism

Key attributes

Spatial scale:

  • Local/landscape (e.g. lake
  • catchment
  • community)
  • National (country)

Time scale:

  • Decades
  • Centuries

Reversibility:

  • Irreversible (on 100 year time scale)
  • Hysteretic (difficult to reverse)

Evidence:

  • Models
  • Paleo-observation
  • Contemporary observations

Confidence: existence of the regime shift

  • Well established – Wide agreement in the literature that the RS exists

Confidence: mechanisms underlying the regime shift

  • Well established – Wide agreement on the underlying mechanism

Detail information

Alternative regimes

The boreal forest in northern Interior Alaska is approximately 48 million hectares (Mann et al., 2012) and is bounded by the Alaska Range to the south, the Seward Peninsula to the west and Brooks Range to the north (Wolken et al., 2011). It is characterized by large areas of gently sloping uplands and flat lowlands isolated by mountain ranges and braided rivers with broad floodplains. During the past 50 years, the mean annual temperature in the interior boreal forest of Alaska has increased by 1.3 ºC (Hartmann and Wendler, 2005) and this has been strongly associated with recent increase in fire frequency and severity (Wolken et al., 2011). The annual area burned in Interior Alaska has doubled during the last decade (Kasischke et al., 2010). The forest has been dominated by coniferous trees (mainly black spruce), which is a group of species that thrive under colder, moist conditions in a deep soil organic layer. However, due to climate warming, Interior Alaska is currently  shifting towards a deciduous dominated  forest (e.g. aspen and birch) that prefer warmer and drier conditions with a shallow soil organic layer (Johnstone et al., 2010).  

 

 

Low fire frequency coniferous dominated forest

Under cold and wet conditions, coniferous trees, such as the black spruce (Picea mariana), dominate the boreal forest in Interior Alaska. The coniferous trees promote the accumulation of a deep soil organic layer, cold and moist soil temperatures, and slow decomposition rates. Due to the moistness of the soil, fires are not frequent in these forests. However, when they occur, they tend to be severe due to the high flammability of the black spruce. Due to the high water content of the soil organic layer, it will only be entirely consumed by the most severe fires (Johnstone et al., 2010). As long as the entire organic layer has not been consumed, the coniferous trees have a regenerative advantage due to their seed’s ability to sprout in moist organic soils. This means that these forests tend to return to a coniferous dominated state even after a fire (Hollingsworth et al., 2013).

 

High fire frequency deciduous dominated forest

A deciduous dominated forest, mainly consisting of aspen and birch trees in Interior Alaska, prefers and reinforces dry and warm soil conditions. Although these forests have a high organic litter production, the fast decomposition rate and the subsequent fast nutrient turnover, leaves a shallow soil organic layer and a nutrient rich mineral soil that favours deciduous tree regeneration. The warm and dry conditions in the forest lead to a comparatively high fire frequency, but due to the low flammability of the deciduous trees, the fires rarely become very severe (Johnstone et al., 2010). However, because of the shallow pre-fire soil organic layer, the fires tend to expose the mineral soil, which favours the post-fire reproduction of deciduous trees (Hollingsworth et al., 2013).

 

Drivers and causes of the regime shift

Shift from coniferous to deciduous-dominated forest

The main external direct driver of the regime shift is climate warming, which affects the important feedbacks of the boreal forest ecosystem. Warmer and drier climatic conditions have a direct effect on the most important soil characteristics (i.e. soil temperature, moisture and depth of the soil organic layer), influencing the vegetation cover. Coniferous trees require a cold moist soil with a deep soil organic layer in order to successfully reproduce. Deciduous trees, on the other hand, are competitively superior under warmer and drier soil conditions with a shallow soil organic layer (Johnstone et al., 2010). Extended summer seasons and the accompanying drier conditions create a suitable environment for an increase in the annual number of natural ignitions by lightning strikes (Kasischke et al., in press). Fires have an immediate effect on the environmental conditions of the forest, affecting factors such as soil moisture and the post-fire forest community composition (Kelly et al., 2012). Once established, the trees support and emphasize the conditions that favour their own reproduction and dominance. Under colder environmental conditions, coniferous trees, such as the black spruce, produce large amounts of organic litter, which, together with the presence of permafrost, maintains a moist soil and slow decomposition rates, contributing to a deep soil organic layer. Under warmer climatic conditions, deciduous trees produce ground layer fuels that decompose at fast rates, maintaining a shallow organic layer (Johnstone et al., 2010). Global socio-economic development indirectly drives climate warming, contributing to the increased atmospheric temperatures through e.g. greenhouse gas emissions (IPCC, 2011). Fire management can have a limited effect on the regime shift through fire suppression practices.

Shift from deciduous-dominated to******coniferous forest**

In order to shift from regime 2 to regime 1, a prolonged climatic cooling would be necessary. A slow change of the environmental conditions towards those that favour a coniferous boreal forest could, if the forest is left undisturbed for a sufficiently long time, lead to late successional coniferous species, like the black spruce, replacing early successional deciduous species (Rupp et al., 2002). Although the spatial scale considered is of extreme importance, sufficiently large external shocks, such as deciduous-specific insect outbreaks, could clear sufficiently large areas to advance the dominance of coniferous trees. In such hypothetical events, coniferous trees could get the opportunity to sprout and start altering the soil conditions to their own favour.

Impacts on ecosystem services and human well-being

Shift from coniferous to deciduous-dominated forest

The coniferous dominated boreal forest of Interior Alaska requires a deep soil organic layer to succeed over other classes of trees. Once the required depth is present, this has a strong reinforcing effect on the coniferous forest. This is a requisite to maintain cold moist soil conditions in which coniferous trees thrive. The cold soil temperature reduces the decomposition rate of organic litter, maintaining a deep soil organic layer (Johnstone et al., 2010).

External shocks such as severe and frequent fires or insect outbreaks might cause dramatic shifts in the soil and vegetation by impacting the soil organic layer depth and tree succession (Hollingsworth et al., 2013; McCullough et al., 1998; Wolken et al., 2011). If the severity of such external shocks is sufficient, thresholds in the most important regime characteristics will be crossed (e.g. shallow post-shock soil organic layer) creating windows of opportunity for deciduous species to dominate. Atmospheric temperature influences the frequency and severity of fires, the soil characteristics and the length of the growing season; therefore, climate warming can also cause a change in conditions that would set the grounds for a shift to a new stable state (Mann et al., 2012).

The deciduous dominated forest has a competitive advantage in warm and dry conditions with shallow soil organic layers. Again, once the required shallow layer is present, it has a strong reinforcing effect on the deciduous forest. A shallow soil organic layer maintains warm and dry soil conditions that speed up the decomposition of organic litter, maintaining the required depth of soil organic layer (Johnstone et al., 2012).

Shift from deciduous-dominated to******coniferous forest**

A future shift from regime 2 to regime 1 could occur if the environmental and climatic conditions became colder and moist again. However, this is an unlikely scenario in the near future. As discussed previously, the climatic conditions alter the soil characteristics, which in turn influence the vegetation cover and the fire regime of the forest.

Management options

The primary tactic used for reducing impacts of fire and enhance resilience (i.e. maintain structures, feedbacks, functions and processes of regime 1) is fire suppression to reduce the fire severity (Chapin et al., 2008). Decrease in fire severity could prevent the fire from consuming the soil organic layer, which in turn favours the conditions for coniferous tree. Fire suppression should be maintained in Alaska since it minimizes the risk fire imposes to life and property in communities. However, distant fires should be allowed to burn under controlled conditions, since it could have a cooling effect at a regional scale due to the higher albedo of post-fire deciduous species compared to the previous coniferous forest (Chapin et al., 2008).

Reducing air temperature is essential to be able to restore regime 1. Alaska itself accounts for a miniscule proportion of global greenhouse gas emissions and consequently to climate warming (Chapin et al., 2008). Therefore, reducing Alaska’s emissions will not have a major impact on global climate change. Global abatement of emissions is the long-term solution. Regardless of global greenhouse gas emission policies, it is highly likely that recent warming and wildfire frequency will continue for several decades in Alaska due to the multidecadal lag in the climate system (IPCC, 2007). This makes the reduction of emissions an inefficient short-term solution.  Secondary challenges that face efforts to achieve reduced emissions include restricting the economy and changing the focus of developed nations on a continued economic but sustainable growth. Educating global public about the social impacts of climate change in Alaska and other parts of the world (e.g. reduction in ecosystem services) may promote the willingness to reduce emissions (Chapin et al., 2008).

In summary, this means that the regime shift from coniferous to deciduous dominated forest in theory could be reversible through manipulation of e.g. soil conditions or local climate. However, due to projected global socio-economic development and climate change, it is highly unlikely that reversing the regime shift will be possible during the next 100 years.

Regime shift Analysis

Feedback mechanisms

Reinforcing feedback loops:

R1. Soil temperature reinforcing feedback (local, well established):

Regime 1: A low deciduous:coniferous abundance ratio i.e. black spruce dominated forest (Picea mariana), prefers cold environments and thick layers of organic litteron top of the mineral soil. The deeper the soil organic layer is, the more insulated the mineral soil becomes, which in a cold environment such as interior Alaska means that the soil will stay cold despite warm summer temperatures. This in turn will prevent permafrost from melting. Permafrost limits the percolation of rainwater through the soil, increasing the soil moisture. This reinforces a coniferous dominated forest (Johnstone et al., 2010).

Regime 2: The deciduous dominated forest tends to have a shallow soil organic layer, which makes the soil more susceptible to temperature shifts. In average, this means that the soil is warmer, which leads to permafrost melting and the soil becoming drier. The warmer, drier conditions favour deciduous tree regeneration (Johnstone et al., 2010).

Two important delays are present in R1 feedback, both related to the time required for the vegetation to reorganize and have a significant effect on their surrounding environment. It takes time for the trees to create their preferred soil conditions such as accumulation of required depth of the soil organic layer and soil moisture. At the same time, there is a delay between the soil characteristics present and an observable change in the deciduous:coniferous abundance ratio, since the trees need several decades to be established and exert their dominance.

R2. Decomposition reinforcing feedback (local, well established):

Regime 1: The coniferous dominated forest promotes a deep soil organic layer which functions as an insulator limiting the increase of soil temperature during the summer months. The cold soil temperatures leads to low rates of decomposition of organic litter, that in turn will further deepen the soil organic layer (Johnstone et al., 2010).

Regime 2: The deciduous dominated forest promotes a shallow soil organic layer which increases the soil’s sensitivity to atmospheric temperature. On average, this makes the soil warmer than in the coniferous dominated regime. The warm soil stimulates fast decomposition rates. Combined with the high organic litter production, this creates high nutrient turnover and a shallow soil organic layer, which are conditions that deciduous trees thrive in (Johnstone et al., 2010).

R3. Regime shift reinforcing feedback (local, well established):

Regime 1: Coniferous trees like black spruce, have developed regeneration mechanisms that have made them competitively superior when a deep soil organic layer is present. At the same time, the black spruce have high production of organic litter to the forest floor, reinforcing its own regeneration (Johnstone et al., 2010 ; Hollingsworth et al., 2013).

Regime 2: On the other hand, deciduous trees species are competitively superior when a shallow soil organic layer is present. A shallow soil organic layer is maintained by these species through the creation of soil conditions (i.e. temperature, moisture and nutrient turnover) which allows them to remain competitively superior (Johnstone et al., 2010 ; Hollingsworth et al., 2013).

The previous delay mentioned in R1 between the deciduous:coniferous abundance ratio and the depth of the soil organic layer, is also apparent in the opposite direction. It takes time for the forest community composition to adjust to the environmental conditions such as changes to the depth of the soil organic layer.

R4. Albedo reinforcing feedback (regional, speculative):

Regime 1:Lower atmospheric temperatures shorten the growth season of the forest, maintaining the high albedo snow longer in the spring. A high albedo lowers the atmospheric temperature by reflecting more solar radiation.

Regime 2: However, the previous scenario is highly unlikely. Instead, due to climate warming, the opposite reinforcing feedback is happening (Mann et al., 2012).

Balancing feedback loops:

The mechanisms driving the balancing feedback loops are the same for both regimes.

B1. Coniferous forest balancing feedback (regional, speculative):

Coniferous forests develop under moist and cold conditions, leading to low frequency of fires However, when fires occur they tend to be more severe due to the accumulated highly flammable biomass. Severe fires burn the soil organic layer, decreasing its depth, and opening the door for deciduous trees to dominate (i.e. a balancing loop). However, if the severity is not strong enough, the remaining depth of the soil organic layer will still be enough for the coniferous forest to reinforce itself (i.e. regime reinforcing loop, see R3) (Johnstone et al., 2010 ; Kelly et al., 2012).

B2. Forest Heterogeneity balancing feedback(regional, speculative):

Severe fires contribute to a more heterogeneous forest which limits the spread and severity of subsequent fires.This balancing loop has the potential to limit the speed at which the regime shift takes place (Johnstone et al., 2010 ; Kelly et al., 2012).

B3. Fuel quantity balancing feedback 1 (local, speculative):

An increase in fire severity will burn the soil organic layer, decreasing its depth, which is translated into a decrease in the availability of fuel for subsequent fires (Johnstone et al., 2010 ; Kelly et al., 2012).

B4. Fuel quantity balancing feedback 2 (local, speculative):

See B3 (Johnstone et al., 2010 ; Kelly et al., 2012).

B5. Insect outbreak balancing feedback (local/regional, contested):

Fire severity has a direct impact on insect outbreaks by acting as a pest-control and influencing insect diversity. Insects affect forest productivity and fuel quantity by for example killing the trees. The fuel quantity has a direct impact on how severe fires can be (McCullough et al., 1998).

B6. Growth season balancing feedback(regional, speculative):

A coniferous dominated forest has a lower albedo, which decreases the atmospheric temperature. With colder temperatures, the growth season decreases, which decreases the storm season. Since lightning is the most important cause of extensive wildfire ignition (Kasischke et al., in press), it increases the overall frequency of fires. From this point on, see B1. Deciduous-dominated forest, on the other hand, have a higher albedo, which decreases the atmospheric temperature, which makes the growing season longer, and so on.

B7. Albedo balancing feedback (regional, speculative):

A coniferous dominated forest (i.e. low deciduous:coniferous abundance ratio) has a lower albedo than a deciduous dominated forest (Rupp et al., 2002). A lower albedo will cause higher local atmospheric temperatures (Blok et al., 2011), increasing the soil temperature. This will melt the permafrost and decrease the soil moisture as water percolates down the soil (Wolken et al., 2011). A drier soil favours the thrive of deciduous forests. The strength of this balancing feedback depends on the regional extent of vegetation change affecting the albedo (Johnstone et al., 2010; Mann et al., 2012).

Drivers

Important shocks that contribute to the regime shift:

Fire (local and regional, well established):Fire constitutes a natural, dramatic disturbance shaping the boreal forest landscape by abruptly influencing the vegetation composition and structure. If the fire is severe enough, the whole soil organic layer will be consumed, which will make the post-fire conditions favour regeneration of deciduous species, since they have been shown to be competitively superior for sprouting in mineral soil (Hollingsworth et al., 2013). The persistence of the new, deciduous dominated regime will depend on the climatic conditions - warmer drier conditions benefit deciduous trees, while colder, moist conditions could gradually shift the system back to a coniferous dominated regime (Johnstone et al., 2010)

Insect outbreaks (regional, speculative): Insect outbreaks have the potential to be a major shock and greatly affect forest structure in boreal forests (McCullough et al., 1998). However, in present conditions in Interior Alaska, the insect infestations only constitute localized disturbances (Rupp et al., 2002), which is why it has not been included as a disturbance in the present system analysis. In a future warmer climate, there is a risk that insect might become more common and therefore insect outbreaks have the potential to become a more dominant disturbance shock in the future.

The main external direct drivers that contribute to the shift include:

Climate warming (regional, well established): The boreal forest is expected to be one of the biomes most sensitive to climate change (Lynch et al., 2004), and the link between climate warming and increase in fire is well established (Kelly et al., 2012). The increase in temperature is expected to increase soil temperature and lengthen the growing season (Mann et al., 2012). To date, observed temperature increase is believed to be the main driver behind the increase of fire frequency and severity in Interior Alaska. As a consequence of projected decreases in relative humidity, the occurrence and extent of fires will potentially increase by up to 60 percent by 2039 (McCoy and Burn, 2005). An increase in fires will greatly affect the composition and structure of the boreal forest, and the projected drier conditions will increase the probability of local-scale tree stands shifting from regime 1 to regime 2 after a severe fire, which in turn will lead to a gradual regional shift (Mann et al., 2012).

Fire management and forestry practices (local, contested): Due to the large areal extent of Interior Alaska, the fires are at present not managed in the entire region. This means that fire management as such is not a major driver in all of Interior Alaska. However, where the risk for human life and property is high, an area which constitutes 17 percent of the total Interior Alaska, active fire suppression is practiced. There, fire management is decreasing the severity of wildfires in the forest, possibly counteracting the regime shift (Chapin et al., 2008). This partial fire suppression is possibly affecting the structure of the forest, slightly increasing its heterogeneity.

The main external indirect drivers that contribute to the shift include:

Population increase (regional, speculative): The population in Alaska is projected to increase by 25 percent by 2030 relative to 2006 (Huntsinger et al., 2007). This population increase might potentially increase the area where active fire suppression is deemed necessary, which means that the impact of fire management would increase.

Socio-economic global development and climate change-regulating policies (global, well-established): The global socio-economic and population development has a major effect on the extent of climate change, due to its importance for e.g. greenhouse gas emissions through land use and burning of fossil fuels. The nature of the international action taken, e.g. the kind of climate change-regulating policies instituted, will also have a major effect on the future global climate (IPCC, 2011).

Slow internal system changes that contribute to the regime shift include:

Change in soil characteristics (local, well-established): The characteristics of the soil, mainly the depth of the soil organic layer and soil moisture, affect the species composition of the forest, e.g. if it is dominated by coniferous or deciduous trees (see feedback loop descriptions). Shocks, such as fire, and drivers, such as climate, can change these characteristics and thus cause internal system changes.

Summary of Drivers # Driver (Name) Type (Direct, Indirect, Internal, Shock) Scale (local, regional, global) Uncertainty (speculative, proposed, well-established) 1 Fire Shock Local and regional Well established 2 Insect outbreaks Shock Local and regional Speculative 3 Climate warming Direct Regional Well established 4 Fire management and forestry practices Direct Local Constested 5 Population increase Indirect Regional Speculative 6 Socio-economic global development and climate change regulating policies Indirect Global Well established 7 Change in soil characteristics Internal Local Well established Key thresholds Threshold 1: Depth of the soil organic layer: The depth of the soil organic layer is the most important soil characteristic defining the dominant vegetation in the boreal forest. If the soil organic layer reaches a certain depth (or lack of depth), the ecosystem will shift from one tree species type dominance to the other (Johnstone et al., 2010).

Threshold 2: Atmospheric temperature: The atmospheric temperature is the most important climatic factor defining the direction of the regime shift. Since the forests have been shown to create self-regenerative conditions, the stickiness of the regimes mean that the gradual change in temperature will probably not lead to a gradual change in tree species dominance. However, when a sufficiently large change in temperature has occurred, a threshold will probably be crossed, leading to a switch from one set of self-reinforcing feedbacks to another (Johnstone et al., 2010; Beck et al., 2011).

Leverage points Atmospheric temperature (global, certain):

Since climate warming is the strongest driver of regime 2, a decrease in temperature by reducing input of warming greenhouse gases in the atmosphere would have the largest impact for restoring regime 1 (Chapin et al., 2008) . Lower temperature would imply a decrease in, soil moisture, growing season, humidity and insects outbreaks which in turn are conditions that favours the coniferous forest in regime 1 (see feedbacks). However, climate change is a global driver which is due to major global causes, hence not realistic to manage at a regional scale.

Fire management and forestry practices (local, certain):

Another leverage point originates from fire management practices, which is the most direct effect humans can have on fire regime dynamics. Through changes in fire suppression management, the fire severity and forest heterogeneity can be influenced . A decrease in fire severity implies deeper soil organic layer which favours the coniferous trees (see B1). Forestry practices could enhance the heterogeneity of the forest which limits the spread and severity of the fires (see B2 feedback.) (Johnstone et al., 2010 ; Kelly et al., 2012). Allowing distant fires (i.e. fires not too close to communities) to burn under controlled conditions conditions could have a cooling effect at regional scale in interior Alaska due to higher albedo of post-fire deciduous species compared to previous coniferous forest (Chapin et al.,2008).

Summary of Ecosystem Service impacts on different User Groups References (if available) Provisioning Services Freshwater ? Food Crops Feed, Fuel and Fibre Crops Livestock Fisheries Wild Food & Products +/- Chapin et al., 2008 Timber - Beck et al., 2011; Keyser et al., 2000 Woodfuel + Chapin et al., 2008 Hydropower Regulating Services Air Quality Regulation - Chapin et al., 2008 Climate Regulation - Keyser et al., 2000; McGuire et al., 2009; Schuur et al., 2009 Water Purification ? Soil Erosion Regulation ? Pest & Disease Regulation - McCullough et al., 1998; Wolker et al., 2011 Pollination Protection against Natural Hazards Cultural Services Recreation - Aesthetic Values - Cognitive & Educational Spiritual & Inspirational Uncertainties and unresolved issues

It is unclear if the observed recent increase in fire frequency and severity will be a permanent change in the fire regime in Interior Alaska, or if it is part of the period of regime shift. It is possible that the high accumulation of organic litter in the coniferous dominated forest, combined with the new, warmer conditions, is promoting more frequent and more severe fires. However, once the soil organic layer has burned and the forest has properly shifted from a coniferous to a deciduous dominated system, the fires will possibly decrease in frequency again due to the smaller amounts of organic litter on the forest floor. Mature deciduous forests tend to have lower fire frequency than coniferous forests (Johnstone et al., 2010). However, different models predict that due to the warmer, drier conditions and longer summer season, fires might keep on being as frequent as now, or even increase until 2020, when the fire regime might stabilize (Mann et al., 2012).

Since the main driver behind the regime shift is climate warming, the inherent weaknesses of climate models translate into the predictions of how vegetation cover might change. Especially precipitation patterns tend to be hard to model with high certainty (McCoy and Burn, 2005). Since the change in relative humidity is of great importance for the shift from coniferous to deciduous trees as well as for the fire regime in Interior Alaska, the projections presented in this report share the same uncertainties as the climate models that have been used in our references.

Citation

Acknowledge this review as:

Katja Malmborg, Linda Lindström Lindström, Lara D. Mateos, Garry Peterson, Juan Carlos Rocha. Coniferous to deciduous forest. In: Regime Shift Database, www.regimeshifts.org. Last revised: 2014-10-21

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