Brian J. Stocks

Climate Change and Forest Disturbances

tudies of the effects of climate change on forestshave focused on the ability of species to tolerate tem-perature and moisture changes and to disperse,but they haveignored the effects of disturbances caused by climate change(e.g.,Ojima et al.1991).Yet modeling studies indicate the im-portance of climate effects on disturbance regimes (He et al.1999). Local, regional, and global changes in temperatureand precipitation can influence the occurrence, timing, fre-quency,duration,extent,and intensity of disturbances (Baker1995, Turner et al. 1998). Because trees can survive fromdecades to centuries and take years to become established,climate-change impacts are expressed in forests, in part,through alterations in disturbance regimes (Franklin et al.1992, Dale et al. 2000).Disturbances,both human-induced and natural,shape for-est systems by influencing their composition,structure,andfunctional processes.Indeed,the forests of the United Statesare molded by their land-use and disturbance history.Withinthe United States,natural disturbances having the greatest ef-fects on forests include fire,drought,introduced species,in-sect and pathogen outbreaks, hurricanes, windstorms, icestorms, and landslides (Figure 1). Each disturbance affectsforests differently. Some cause large-scale tree mortality,whereas others affect community structure and organizationwithout causing massive mortality (e.g., ground fires). For-est disturbances influence how much carbon is stored intrees or dead wood. All these natural disturbances interactwith human-induced effects on the environment,such as airpollution and land-use change resulting from resource ex-traction, agriculture, urban and suburban expansion, andrecreation.Some disturbances can be functions of both nat-ural and human conditions (e.g., forest fire ignition andspread) (Figure 2).

Climate Change and Forest Fire Potential in Russian and Canadian Boreal Forests

In this study outputs from four current General Circulation Models (GCMs) were used to project forest fire danger levels in Canada and Russia under a warmer climate. Temperature and precipitation anomalies between 1 × CO2 and 2 × CO2 runs were combined with baseline observed weather data for both countries for the 1980–1989 period. Forecast seasonal fire weather severity was similar for the four GCMs, indicating large increases in the areal extent of extreme fire danger in both countries under a 2 × CO2 climate scenario. A monthly analysis, using the Canadian GCM, showed an earlier start to the fire season, and significant increases in the area experiencing high to extreme fire danger in both Canada and Russia, particularly during June and July. Climate change as forecast has serious implications for forest fire management in both countries. More severe fire weather, coupled with continued economic constraints and downsizing, mean more fire activity in the future is a virtual certainty. The likely response will be a restructuring of protection priorities to support more intensive protection of smaller, high-value areas, and a return to natural fire regimes over larger areas of both Canada and Russia, with resultant significant impacts on the carbon budget.

Climate change and forest fires

This paper addresses the impacts of climate change on forest fires and describes how this, in turn, will impact on the forests of the United States. In addition to reviewing existing studies on climate change and forest fires we have used two transient general circulation models (GCMs), namely the Hadley Centre and the Canadian GCMs, to estimate fire season severity in the middle of the next century. Ratios of 2 x CO2 seasonal severity rating (SSR) over present day SSR were calculated for the means and maximums for North America. The results suggest that the SSR will increase by 10-50% over most of North America; although, there are regions of little change or where the SSR may decrease by the middle of the next century. Increased SSRs should translate into increased forest fire activity. Thus, forest fires could be viewed as an agent of change for US forests as the fire regime will respond rapidly to climate warming. This change in the fire regime has the potential to overshadow the direct effects of climate change on species distribution and migration.

Fire, Global Warming, and the Carbon Balance of Boreal Forests

Fire strongly influences carbon cycling and storage in boreal forests. In the near-term, if global warming occurs, the frequency and intensity of fires in boreal forests are likely to increase significantly. A sensitivity analysis on the relationship between fire and carbon storage in the living-biomass and ground-layer compartments of boreal forests was performed to determine how the carbon stocks would be expected to change as a result of global warming. A model was developed to study this sensitivity. The model shows if the annual area burned in boreal forests increases by 50%, as predicted by some studies, then the amount of carbon stored in the ground layer would decrease between 3.5 and 5.6 kg/M2, and the amount of carbon stored in the living biomass would increase by 1.2 kg/M2. There would be a net loss of carbon in boreal forests between 2.3 and 4.4 kg/M2, or 27.1- 51.9 Pg on a global scale. Because the carbon in the ground layer is lost more quickly than carbon is accumulated in living biomass, this could lead to a short-term release of carbon over the next 50-100 yr at a rate of 0.33-0.8 Pg/yr, dependent on the distribution of carbon between organic and mineral soil in the ground layer (which is presently not well-under- stood) and the increase in fire frequency caused by global warming.

Biomass burning and global change

The burning of living and dead biomass, including forests, savanna grasslands and agricultural wastes is much more widespread and extensive than previously believed and may consume as much as 8700 teragrams of dry biomass matter per year. The burning of this much biomass releases about 3940 teragrams of total carbon or about 3550 teragrams of carbon in the form of CO2, which is about 40% of the total global annual production of CO2. Biomass burning may also produce about 32% of the world’s annual production of CO, 24% of the nonmethane hydrocarbons, 20% of the oxides of nitrogen, and biomass burn combustion products may be responsible for producing about 38% of the ozone in the troposphere. Biomass burning has increased with time and today is overwhelmingly human‐initiated.

Fire, climate change, and carbon cycling in the boreal forest

Preface Introduction Section I: Information Requirements and Fire Management and Policy Issues The Role of Boreal Ecosystems in the Global Carbon Cycle Boreal Forest Fire Emissions and the Chemistry of the Atmosphere The Eurasian Perspective of Fire: Dimension, Management, Policies and Scientific Requirements Fire Management in the Boreal Forests of Canada Effects of Climate Change on Management, Policy and Mitigation Options in the Boreal Forest Section II: Processes Influencing Carbon Dynamics in the Boreal Forest The Distribution of Forest Ecosystems and the Role of Fire in the North American Boreal Region Extent, Distribution and Ecological Role of Fire in Russian Forests Long-term Perspectives on Fire-Climate-Vegetation Relationships in the North American Boreal Forest Controls on Patterns of Biomass Burning in Alaskan Boreal Forests Post-Fire Stimulation of Microbial Decomposition in Black Spruce (Picea mariana L.) Forest Soils: A Hypothesis The Influence of Fire on Long-Term Patterns of Forest Succession in Alaskan Boreal Forests Section III: Spatial Data Sets for the Analysis of Carbon Dynamics in Boreal Forests And much more....

Satellite analysis of the severe 1987 forest fires in northern China and southeastern Siberia

Meteorological conditions, extremely conducive to fire development and spread in the spring of 1987, resulted in forest fires burning over extremely large areas in the boreal forest zone in northeastern China and the southeastern region of Siberia. The great China fire, one of the largest and most destructive forest fires in recent history, occurred during this period in the Heilongjiang Province of China. Satellite imagery is used to examine the development and areal distribution of 1987 forest fires in this region. Overall trace gas emissions to the atmosphere from these fires are determined using a satellite-derived estimate of area burned in combination with fuel consumption figures and carbon emission ratios for boreal forest fires.

DETERMINING EFFECTS OF AREA BURNED AND FIRE SEVERITY ON CARBON CYCLING AND EMISSIONS IN SIBERIA

The Russian boreal forest contains about 25% of the global terrestrial biomass, and even a higher percentage of the carbon stored in litter and soils. Fire burns large areas annually, much of it in low-severity surface fires – but data on fire area and impacts or extent of varying fire severity are poor. Changes in land use, cover, and disturbance patterns such as those predicted by global climate change models, have the potential to greatly alter current fire regimes in boreal forests and to significantly impact global carbon budgets. The extent and global importance of fires in the boreal zone have often been greatly underestimated. For the 1998 fire season we estimate from remote sensing data that about 13.3 million ha burned in Siberia. This is about 5 times higher than estimates from the Russian Aerial Forest Protection Service (Avialesookhrana) for the same period. We estimate that fires in the Russian boreal forest in 1998 constituted some 14–20% of average annual global carbon emissions from forest fires. Average annual emissions from boreal zone forests may be equivalent to 23–39% of regional fossil fuel emissions in Canada and Russia, respectively. But the lack of accurate data and models introduces large potential errors into these estimates. Improved monitoring and understanding of the landscape extent and severity of fires and effects of fire on carbon storage, air chemistry, vegetation dynamics and structure, and forest health and productivity are essential to provide inputs into global and regional models of carbon cycling and atmospheric chemistry.

Relationships between charcoal particles in air and sediments in west-central Siberia

Production and size of charred particles determine transport and deposition in lakes. Lack of such data is a principal obstacle to interpretation of past fire from charcoal profiles. Our two-part analysis includes a calibration study, to assess charred-particle production and transport during fire, and a study of charred particles in sediment. The calibration step establishes the magnitude and size distribution of particle accumulation from traps during a controlled burn of Pinus sylvewtris forest in west-central Siberia. This high-intensity fire consumed 3.71 kg m-2 of fuels and produced 0.0729 kg m-2 of airborne particles, for an emission factor of 0.02 kg kg-1. Particle flux to the ground was 1 to 3 mm2cm-2 yr-1 inside the burn; it declined sharply within 5 m of the burn edge, and it was variable but without trend to a distance of 60 m. Particle-size distributions were conservative, with a slope of 2 on plots of log frequency versus log diameter, and sediment data suggest this slope may steepen as sources bcome more remote and as large particles are progressively lost due to settling. Deposition from the plume is similar to accumulation rates in sediment, with apparent upward bias in sediments as expected from broad geographic patterns in charcoal distributions. During the mid-Holocene charred-particle accumulation in lake sediments (101 mm2 cm-2 yr-1 was greater than observed in particle traps within the experimental burn. Particles were larger, suggesting nearby sources. Rates decreased by 3800 BP to values lower than average rates in particle traps, and samples were depleted in large particles. Low rates and infrequent large particles indicate sources were distant. Accumulation rates and particle sizes were again high from 3400 to 2800 and from 1400 to 700 BP. Close correspondence between the accumulation rates during the experimental burn and in sediments and particle evidence for source area, as well as their agreement with particle-trap data from the experimental burn, suggest that, in this region, fire may have been more frequent and closer in the mid-Holocene than today. We cannot rule out the possibility, however, that changes in charred particle accumulation also reflect changes in supply of sediment to the core site.

Modeling of carbonaceous particles emitted by boreal and temperate wildfires at northern latitudes

For the first time, a spatial and monthly inventory has been constructed for carbonaceous particles emitted by boreal and temperate wildfires in forests, shrublands, and grasslands, with burned area data statistics, fuel load maps, fire characteristics, and particle emission factors. The time period considered is 1960–1997, and an important year-to-year variability was observed. On average, boreal and temperate vegetation fires represent 4% of global biomass burning, but during extreme years, their contribution may reach 12%, producing 9% and 20% of black carbon (BC) and particulate organic matter (POM), respectively, emitted by worldwide fires. The North American component of the boreal forest fires (Canada and Alaska) represents 4 to 122 Gg C yr-1 of BC and 0.07 to 2.4 Tg yr-1 of POM emitted, whereas the Eurasiatic component (Russia and northern Mongolia) may vary in the 16 to 474 Gg C yr-1 range for BC and between 0.3 and 9.4 Tg yr-1 for POM, with however great uncertainty. Temperate forests in conterminous United States and Europe have a much lower contribution with an average of 11 Gg C yr-1 of BC and 0.2 Tg yr-1 of POM. Grassland fires in Mongolia represent significant BC and POM sources which may reach 62 Gg C and 0.4 Tg, respectively. Finally, an annual average of BC emissions for shrubland fires in both the Mediterranean region and California is 20 Gg C yr-1, with average POM emissions of 0.1 Tg yr-1. These source maps obtained with a high spatial resolution (lox lo) can now be added to previous ones developed for other global carbonaceous aerosol sources (fossil fuel combustion, tropical biomass burning, agricultural and domestic fires) in order to provide global maps of particulate carbon emissions. Taking into account particle injection height in relation with each type of fire, our source map is a useful tool for studying the atmospheric transport and the impact of carbonaceous aerosols in three-dimensional transport and climate models.