quantifying peatland burning and resistance to wildfire ......gc.ca/datamart/ download/nfdbpoly?...

Current Advances in Geology and Geoscience [CAGG]

Volume 2020 Issue 01

April 07, 2020 Curr Advnc Geo & GeoSci, Volume 01(01): 19–37, 2020

Quantifying Peatland Burning and Resistance to Wildfire Activity in the Eastern Canadian TaigaYisa Ginath Yuh*

University of Quebec at Rimouski (UQAR), 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada

Received: March 30, 2020; Accepted: April 04, 2020; Published: April 07, 2020

R-Infotext Citation: Yuh YG (2020) Quantifying Peatland Burning and Resistance to Wildfire Activity in the Eastern Canadian Taiga. Curr Advnc Geo & GeoSci 01(01): 19–37.

Abstract

Northern peatlands occupy about 5–25% of boreal landscapes, yet their vulnerability to burning is still poorly understood, while their resistance to wildfire activity still forms knowledge gaps in boreal fire ecology. In this paper, i aim at addressing these knowledge gaps by: (i) quantifying the extents of peatland burning in northern Quebec, based on three characteristics of peatlands that describe resistance: size, amount and distance of peatlands to surrounding uplands; (ii) quantify the resistance of peatlands to wildfire spread; and (iii) quantify the effects of topography, fire weather indices (FWI) and lakes on peatland burning. Using peatland maps obtained from the northern Quebec eco-forestry inventory project, i applied the geoprocessing clip tool in ArcGIS to extract burnt peatland areas from large fire perimeters obtained from the Canadian National Fire Database (CNFDB). I further applied the geometry tool in ArcGIS to calculate burnt areas based on sizes, amount and distance of surrounding uplands to peatlands, using six fire zones that describe the North-East and South-East gradients of fire activity. I further applied a binomial logistics regression as well as a stepwise multiple linear regression approach in R to quantify the effects of peatlands to wildfire spread, as well as evaluate peatland resistance under the control of topography, FWI and lake abundance. I thus found out that, the quantity of extremely smaller peatlands burnt was 10–15 times greater than large and extremely large peatlands, with amount burnt reducing North-East and South-East of the fire activity gradient. Also, fires were less likely to spread under increase peatland sizes, and more likely to spread under increase peatland distance. In addition, FWI contributed immensely in diminishing peatland resistance to burning, while lakes, slope and elevation positions contributed in increasing such resistance. These findings provide baseline information required for regional wildfire management in Northern forest ecosystems dominated by peatlands.

Keywords: wildfire spread, wildfire activity, peatland resistance, peatland burning.

Research Article

Introduction

Wildfire is an important disturbance of forest ecosystems worldwide [4, 5, 1, 25, 26]. Historical records for the years 1960 – 2000 showed that global average area burned was approximately 300 – 450 Mha [31, 40, 43]. These estimates were based on data collected from the most fire-prone regions around the world, with the boreal region of North America being the most affected [23, 34].

In Canada and USA, the effects of fires on forest ecosystems have received considerable attention [14,

16, 37, 45]. In the Canadian boreal forest for example, studies have shown that, wildfires burned an average of 2 million hectares of land per year, between the years 1959–1997 [34]. Decadal statistics show increase trends in fire activity and burned areas from an approximated average of 6000 fires and below 1 million hectares burned per year in the early 1920s to approximately 8000 fires and 2 million hectares burned by the year 2013 [35]. But how these fires affect wetlands (particularly peatlands) still form a major knowledge gap in boreal fire disturbance ecology.

Peatland Burning


Peatlands are vegetated or non-vegetated areas of land which accumulate peat due to the slow decomposition of organic matter, often in response to deficient drainage conditions. In the boreal region, they are classified into two main types: bogs and fens. Bogs are sphagnum dominated peatlands [17] that are considered “ombrotrophic” because they receive their water and nutrient supply from rainfall. Conversely fens are graminoid dominated and receive their nutrient and water supply from surrounding mineral soil and water bodies (lakes, rivers, streams etc.). Hence, they are considered as being “minerotrophic” [10, 30].

Peatlands occupy approximately 1.14 million km2 of boreal landscapes [38] and several studies suggest they may influence fire probabilities [2, 7, 32, 41]. They have been shown to form fuel breaks that act as natural barriers to fire spread [6, 15, 32]. Their high moisture content and often high abundance can limit the activity of fires and lengthen fire intervals [12, 32]. Their frequency and severity of drying are predicted to increase under high fire weather severity as a result of climate change [11, 22, 39], but how such drying will impact fire activity still remains an open question that needs to be answered, hence a significant challenge for regional wildfire management [9]. There is, therefore, a need to understand the contributions of peatlands to boreal landscape resistance to wildfires. There is equally a need to understand the contributions of fire weather severity and other landscape factors (e.g. topography and lake abundance) on peatland burning. Such information will help improve regional wildfire adaptation planning.

In general, wetlands are known to interrupt fuel continuity thereby acting as natural breaks or barriers to fire spread [6, 15, 24]. With water bodies, their resistance effects on fire activity have been characterized in terms of sizes, directions, shapes, distances and orientations of water bodies [13, 24]. With peatlands, knowledge gaps still exist on the effects of such landscape characteristic to wildfire activity.

In this study therefore, I seek to: (i) quantify or measure the extents of peatland burning in northern Quebec (Eastern Canadian Taiga) within a period of 16 years (2001 – 2016), based on three characteristics of peatlands that describe resistance: size, amount and distance of peatlands to surrounding uplands; (ii)

quantify the resistance of peatlands to wildfire spread; and (iii) quantify the effects of topography, fire weather indices (FWI) and lakes on peatland burning.

I thus hypothesise that: (i) area burned will be extremely lower in large and extremely large peatlands than in small and extremely smaller peatlands; (ii) the quantity of uplands burnt increases with increase distance of uplands to surrounding peatlands; (iii) Peatlands act as natural barriers to wildfire spread. Consequently, the attributes of peatlands such as size and distance of surrounding uplands to peatlands act as active bottom-up controls to wildfire spread.

Methodology

The Study Area

The study area covers the La Grande hydroelectric complex between latitudes 51° and 55° N and between the James Bay and longitude 700W in northern Québec. The area comprises large hydroelectric reservoirs and associated infrastructures such as power transmission lines, airports, roads etc., which are at risk of burning. Burn rates are high and have averaged about 2–3 % of the land area per year since 1840, including fires more than 60km across every 20–30 years [7, 14].

The landscape topography is characterized by a hilly terrain with elevations progressively increasing from 0 to about 550m above sea level [36] from west to east. Mean annual temperatures vary between -30C to 2.40C from North to South, with the coldest month being January and the warmest month being July. Annual precipitations stand at approximately 680mm, with approximately 40% falling as snow (between October-May). Fuels in this area are made of open woodland stands dominated by black spruce (Piceamariana) and jack pine (Pinusbanksiana). Ombrotrophic and minerotrophicpeatlands cover about 5–25% of the study area and decrease in cover from west to east. This decreasing peatland abundance gradient (Figure 1) is paralleled by a gradient of increasing lake abundance from about 5% to 25% of the landscape area.

Data Acquisition

Datasets used in verifying our research hypothesis include: peatlands, lakes, fire polygons for the periods 2001–2016,

Peatland Burning


fire weather indices (FWI) and topography (aspect, slope and elevation) (Table 1).

Peatland polygons for the N-E zone of the study area were obtained from the Northern Quebec cartography project (projet de cartographie du Nord québécois) while those of the S-E zone were obtained from the Northern Quebec eco-forestry inventory project (projetd’inventaire écoforestier du Nord (PIEN)) of the Québec government (https://geoegl.msp.gouv.qc.ca/igo/mffpecofor/?id= cc2567a4c0). Fire polygons (fire progression maps) for the period 2001–2016 (comprising both large and small fires), compiled by provincial and federal agencies, were obtained from the Canadian national fire database (CNFDB) (http://cwfis.cfs.NRCan.gc.ca/ datamart/download/nfdbpoly?token=a756f62ea0b8e06b 1bd844e085845dfa). Daily FWI based on reanalysis of

weather data were obtained from the Copernicus fire danger forecast project (ECMWF) (http://apps.ecmwf.int/datasets/data/geff-reanalysis/). Data for lakes as well as topography were obtained from the open access geospatial database of Natural resource Canada (http://ftp.maps.canada.ca/pub/nrcan_rncan/vector/canvec/fgdb/Hydro).

Data Analysis

Quantification of peatland burning by fire zone

Because I seek to quantify peatlands burning based on the North-East (N-E) and South-East (S-E) gradient of fire activity in the study area, I divided the study area into six fire zones or eco-zones (Figure 2). Zones A – C represent the N-E gradient of fire activity, while zones D–F represent the S-E gradient.

Figure 1: Map of the study area (Eastern Canadian Taiga) showing the distribution of peatlands as well as the 2001 – 2016 fires

http://cwfis.cfs.NRCan.gc.cahttp://apps.ecmwf.int/datasets/data/geff-reanalysis/http://apps.ecmwf.int/datasets/data/geff-reanalysis/http://ftp.maps.canada.ca/pub/nrcan_rncan/vector/canvec/fgdb/Hydrohttp://ftp.maps.canada.ca/pub/nrcan_rncan/vector/canvec/fgdb/Hydro

Peatland Burning


Table 1: Data required for verifying the research hypothesis.

Category Data type Description Source

Bogs and fens Peatlands

Digitized peatlands of Northern and Southern eco-forestry zones of Quebec. Datasets for the N-E zonewere obtained from the projet de cartographie du Nord québécois while those of the southern zone were obtained from projetd’inventaireécoforestier du Nord (PIEN)

https://geoegl.msp. gouv.qc.ca/igo/ mffpecofor/?id= cc2567a4c0

Water bodies Lakes and riversLakes and rivers in Canada - CanVec Series - Hydrographic features

http://ftp.maps.canada.ca/ pub/nrcan_rncan/vector/ canvec/fgdb/Hydro/

Fire weather severityFire weather indices (FWI

The data contains reanalyzed FWI for the periods 2001–2016 provided by the European Copernicus fire danger forecasting project through the Global ECMWF fire forecast (GEFF) real time system

http://apps.ecmwf.int/ datasets/data/geff-reanalysis/

TopographyAspect, slope and elevation

The data contains Digital Elevation Model (DEM) data generated for the whole of Canada from which aspect and slopes were extracted using ArcGIS

http://ftp.geogratis.gc.ca/ pub/nrcan_rncan/elevation/ cdem_mnec/doc/

Fire polygons

Fire progression maps for the period 2001–2016

Fire perimeters as provided by Canadian fire management agencies.

http://cwfis.cfs.NRCan.gc.ca/datamart/download/nfdbpoly? token=a756f62ea0b8e06b 1bd844e085845dfa

For each of the six fire zones, I applied the geometry tool in ArcGIS 10.6 to calculate the shape area (in hectares) of total peatlands burnt within the course of 16 years (i.e. between the years 2001–2016). Calculations were based on the three characteristics of peatlands that describe resistance: size, amount and distance of surrounding upland to peatlands [24]. Quantification was done on each fire zone (Figure 2), i.e. based on the N-E and S-E fire activity gradient. The quantification approach involved applying the geoprocessing clip tool in ArcGIS in order to clip peatland areas overlaid by the 2001–2016 fire perimeters (polygons) and then applying the geometry tool to calculate shape areas and amount of burnt peatlands based on the attribute tables of the clipped peatland data. The 16 year time period was selected in order to calibrate fire polygons from the CNFDB with MODIS fire data thereby ensuring accuracy. In carrying

out these geoprocessing techniques, only fires greater than 200 ha were used, as large fires in Canada have been shown to account for more than 97% of total area burned [34].

Sizes of burnt peatlandswere calculated based on five peatland size categories: extremely small, small, medium, large and extremely large peatlands. Extremely small peatlands were classified as peatlands with size range of between 0–50 ha. Small peatlands were classified as peatlands with size ranges of between 51–100 ha. Medium peatlands had sizes of between 101–300 ha, while large and extremely large peatlands had sizes of between 301–500 ha and greater than 500 ha respectively. These five size categories were selected in order to show how peatlands burn by size (i.e. compare area burnt between extremely small, small, medium, large and extremely large peatlands) thereby depicting resistance.

http://ftp.maps.canada.ca/%20pub/nrcan_rncan/vector/%20canvec/fgdb/Hydro/http://ftp.maps.canada.ca/%20pub/nrcan_rncan/vector/%20canvec/fgdb/Hydro/http://ftp.maps.canada.ca/%20pub/nrcan_rncan/vector/%20canvec/fgdb/Hydro/http://apps.ecmwf.int/%20datasets/data/geff-reanalysis/http://apps.ecmwf.int/%20datasets/data/geff-reanalysis/http://ftp.geogratis.gc.ca/%20pub/nrcan_rncan/elevation/%20cdem_mnec/doc/http://ftp.geogratis.gc.ca/%20pub/nrcan_rncan/elevation/%20cdem_mnec/doc/http://ftp.geogratis.gc.ca/%20pub/nrcan_rncan/elevation/%20cdem_mnec/doc/http://cwfis.cfs.NRCan.gc.ca/datamart/download/nfdbpolyhttp://cwfis.cfs.NRCan.gc.ca/datamart/download/nfdbpolyhttp://cwfis.cfs.NRCan.gc.ca/datamart/download/nfdbpoly

Peatland Burning


Figure 2: Fire zones or ecozones illustrating gradient of wildfire patterns across peatlands.

Amount of burnt peatlands were calculated based on the total number of peatlands burnt by size category, while distance of burnt uplands to peatlands was calculated based on the total area of uplands burnt at distances of 100m, 1000m and 10000m to peatland size categories.

Quantification of peatland resistance to wildfire spread

In order to quantify the resistance of peatlands to wildfire spread, i used the three characteristics of peatlands that best describe resistance as described with water bodies in [24] (i.e. size, amount and distance). These three landscape resistance factors (in polygon shapefiles) were converted to raster files in ArcGIS, re-sampled at a fine spatial (pixel) resolution of 30m, and projected to similar coordinate reference systems for the study area

(NAD_1983_Quebec_Lambert). The rasterized peatland and lakes were quantified at a 100000ha spatial scale using a neighbourhood moving windows approach using the focal statistics tool in ArcGIS.

Because the resistance of peatlands to wildfire also depends on other environmental factors that have been proven to diminish or increased resistance (e.g. topography, fire weather severity and lakes), i included these factors in the analysis. Topography was measured in terms of aspect, slope and elevation, while fire weather severity was expressed in terms of fire weather indices (FWI), and lakes added in terms of lake sizes. These explorative variables were also resampled at a 30m spatial resolution and projected to a similar coordinate reference system for the study area (NAD_1983_Quebec_Lambert).

Peatland Burning


Table 2: Characterization of landscape predictors to wild fire activity

Type of variable

Landscape characteristics Spatial scales (ha)

Possible prediction assumptions

Peatlands Size of peatlands 100000 probability of wildfire spread decreases with increase peatland sizes

Distance of upland pixels to peatlandsat 1000m units

Probability of wildfire spread increases as the distance of surrounding uplands to peatlands increases

Amount of peatlands Probability of wildfire spread increases as the amount of peatlands increases

Weather severity

Fire weather indices (FWI) NA The resistance of peatlands to wildfires decreases with increase fire weather severity

Topography Aspect, slope and elavation

100000 Topographic parameters act as active bottom up controls to fire spread but their effects on peatland resistance to fire spread still remains unknown.

Lakes Lake size 100000 The resistance of peatlands to wildfires increases under increase lake abundance

Regression analysis

For the entire study area, I generated 50000 random points in R in order to sample pixel values of both peatland and non-peatland sites. Sampling was done based on their landscape characteristics: size, amount and distance. Because peatland amounts represented the counts of peatlands in the entire study area, i excluded it in the regression analysis in order to avoid over sampling with peatland sizes (sampling bias). I further used the same random points to sample lake and non-lake sites as well as topographic variables and fire weather indices. I further used the same points to sample fire spread values from the 2001 – 2016 fire progression maps. In sampling the fire progression maps, only fires greater than 200 ha were selected. Because i also intended to quantify the contributions of topography, FWI and lakes on peatland resistance to burning, i used the generated sample points to sample presence data for peatland area burnt. The sampled peatland data served as the main predictor variables while the topography, fire weather and lake datasets served as the predictor effect variables. Fire spread values, as well as peatland area burnt, were used as response variables.

A binomial logistic regression modeling approach was applied using a Generalized Linear Model (GLM)

[21] from the R package “glm”, with family as “binomial and link as “logit”, to predict the probability that the 2001–2016 fires spread across a site (30m pixel) based on the size of peatlands, as well as distance of surrounding uplands to peatlands. In addition, a second GLM was built to quantify the interactive effects of peatlands with lakes, topography and FWI, considering that these factors are all important in driving wildfire activity.

In order to verify the contributions of FWI, topography and lakes on peatland burning, a stepwise multiple linear regression was further applied with the PredictEffect function from the R package ‘effects’, using presence data only. Model accuracies were evaluated using the Receiver Operator Characteristics (ROC) and area under the curve (AUC) (roctab command in STATA) (StataCorp 2013) at 95% confidence intervals.

Results

Quantification of burnt peatlands by fire zone

My findings show that, in all fire zones, extremely smaller peatlands had the greatest surface area burnt by size and amount, followed by small peatlands, medium peatlands, large peatlands and extremely large peatlands (Figures 3,

Peatland Burning


Table S1). The only exception was in fire zone A where medium peatlands burnt more than small peatlands (i.e. 124 ha burnt for medium peatlands and 106 ha for smaller peatlands) (Figure 3a, Table S1). In addition, my findings also showed that the largest fire sizes and numbers occurred within extremely smaller peatlands, followed again by small peatlands, medium peatlands, large peatlands and extremely large peatlands (Table S1). These results clearly reveal that, the resistance of peatlands to burning increases with increase peatland sizes (i.e. from extremely small to extremely large peatlands). Thus, large and extremely large peatlands are less susceptible to burning due to high moisture contents on peat surfaces, thus highly resistant. Conversely, extremely smaller and small peatlands contain low moisture content on peat surfaces, hence more susceptible to drying and burning.

Like size and amount, a large area of uplands burnt more quickly with increasing distance to extremely smaller peatlands followed again by small peatlands, medium peatlands, large peatlands and extremely large peatlands in all fire zones (Figures 4, Table S2). Thus, as peatland distance increases in all peatland size class, fire sizes and numbers increase within uplands. This finding thus reveals that uplands are more likely to burn further away from peatlands in my study area.

With respect to the N-E and S-E gradient of fire activity, this study provide evidence that, the burning of peatlands decreases as fires spread from North to East and South to East of its activity gradient i.e. burning decreases from fire zone A to fire zone C, and from fire zones D to fire zone F (Figures 5). In addition, peatlands burn less frequently than expected. For example, in fire zone A, peatlands cover a total surface area of 270336 ha, but only 1800 ha of peatland area has been burnt within a period of 16 years, forming an estimated overall burn rate of 0.66%. In fire zone B, peatlands cover a total surface area of 118332 ha, but only 351 ha of peatland area has been burnt within a period of 16 years, forming an estimated overall burn rate of 0.29%. In fire zone C, peatlands cover a total surface area of 193563 ha, but only 135 ha of peatland area has been burnt, forming an estimated overall burn rate of 0.07%. In fire zone D, peatlands occupy a total surface area of 1820876 ha, but only 149462 ha of peatlandhas been burnt, forming an estimated overall burn rate of 8.2%. In fire zone E, peatlands occupy a total surface area of 297455 ha, but only 25251 ha of peatlandhas been

burnt, forming an estimated overall burn rate of 8.5%. In fire zone F, peatlands occupy a total surface area of 152250 ha, but only 5873 ha of peatlandhas been burnt, forming an estimated overall burn rate of 3.86%. Thus, the highest proportions of peatlands burnt were in fire zones D and E.

Resistance of peatlands to wildfire spread

My findings show that peatlands act as natural barriers to wildfire spread, i.e. the spread of wildfires decreases with increase peatland size (Figure 7a) and increases with increase peatland distance from surrounding uplands (Figure 7b). These findings were deduced based on model estimates (mean of the marginal posterior distribution) + sd (standard deviation of the marginal posterior distribution) (Table 3). Thus, the probability of wildfire to spread across peatlands decrease with increase peatland sizes (-0.035 + 0.004) and increases with increase distance of peatlands to surrounding uplands (0.045 + 0.009). These resistance effects were realistically achieved based on the interactive contributions of other landscape factors such as FWI, topography and lakes. For example, FWI and slope positions proofed to be powerful determinants of wildfire occurrence and spread across the study area (0.309 + 0.093), (2.625 + 2.630), while increase lake abundance and aspect positions diminished wildfire activity considerably (-0.011 + 0.005), (-0.375 + 0.046). Elevations also played quite a considerable positive role on wildfire activity (0.197 + 0.019).

Contributions of topography, FWI and lakes to peatland burning

Because topography, FWI and lakes played considerable roles in controlling wildfire activity across the study area, their impacts on controlling the resistance of peatlands to burning varied considerably. For example, my findings show that, lakes contribute in increasing peatland resistance to burning i.e. the burning of peatlands decreases under increase lake abundance (-0.059 + 0.001) (Figure 8b). FWI played a very strong impact in reducing peatland resistance to burning i.e. peatlands show high burn probability under increase FWI (0.717 + 0.032) (Figure 8a). Like lakes, Slope and elevation positions played very strong roles in increasing peatland resistance to wildfires (-7.282 + 0.783), (-0.331 + 0.007) (Figures 8d and 8e), while aspect contributes in diminishing such resistance (0.039 + 0.022) (Figure 8c).

Peatland Burning


Figures 3: Quantity of peatlands burnt by size within fire zones: (a) Fire zone A; (b) Fire zone B; (c) Fire zone C; (d) Fire zone D; (e) Fire zone E; and (F) Fire zone F

Peatland Burning


Figures 4: Quantity of peatlands burnt by distance to surrounding uplands within fire zones: (a) Fire zone A; (b) Fire zone B; (c) Fire zone C; (d) Fire zone D; (e) Fire zone E; and (F) Fire zone F

Peatland Burning


Figures 5: Gradient of peatland area burnt in the study area: (a) Fire zones A-C representing the North-East fire activity gradient; (b) Fire zones D-F representing the South-East fire activity gradient.

Peatland Burning


Figure 6: Map of peatlands burnt between fire zones in the study area. Map shows amount of peatlands burnt by size categories (extremely large, large, medium, small and extremely small). The map data was used to calculate peatland area burnt by size and distance, as well as number of fires that burnt peatlands (Tables S1 and S2).

Figures 7: Probability of wildfire spread under the influence of peatland: (a) effects of peatland size; (b) effects of peatland distance.

Peatland Burning


Figures 8: Effects of topograpgy, fwi and lakes on peatland burning : (a) effects of fwi; (b) effects of lakes; (c) effects of aspect; (d) effects of slope; (e) effects of elevation.

Peatland Burning


Table 3: Model prediction results showing the effects of peatlands and other environmental predictors on wildfire spread.

estimate sd CI 2.5%

CI 97.5%

Intercept* 219.4 10.85 198.2 240.7

Peatland size -0.035 -0.004 -0.042 -0.027

Peatland distance

0.045 0.009 0.028 0.062

FWI 0.309 0.093 0.127 0.492

Lake size -0.011 0.005 -0.001 0.020

Aspect -0.375 0.046 -0.467 -0.283

Slope 2.625 2.630 2.109 3.141

Elevation 0.197 0.019 0.158 0.235

Table 4: Model prediction results showing the contributions or effects of fwi, topography and lakes on peatland burning.

estimate sd CI 2.5%

CI 97.5%

Intercept* 315.7 6.377 303.2 328.2

FWI 0.717 0.032 0.654 0.779

Lake abundance

-0.059 0.001 -0.062 -0.057

Aspect 0.039 0.022 -0.003 0.081

Slope -7.282 0.783 -7.436 -7.129

Elevation -0.331 0.007 -0.345 -0.316

Discussion

My study provides evidence that the burning of peatlands depends on their landscape resistance characteristics such as size, amount and distance of surrounding uplands to peatlands. These landscape resistance characteristics have been reported with other wetlands (e.g. rivers and lakes) in the boreal region of Saskatchewan [24]. Thus, by quantifying these landscape characteristics between six fire zones that describe the North-East and West-East gradients of fire activity in the Eastern Canadian Taiga (Figure 2), my findings have shown that, the quantity of extremely smaller peatlands burnt within the course of 16 years is 10–15 times greater than medium size, large and extremely large peatlands burnt (Figures 3). Furthermore,

my findings have shown that uplands areas are more susceptible to burning at increase distances to peatlands, with the most abundant quantities of area burnt recorded at distances to extremely smaller peatlands. These findings thus provide evidence that smaller peatlands have an extremely high potential for burning than large peatlands, with fires more likely to occur nearer or further away than in large peatlands. The underlying peats (ground fuels) of smaller peatlands are highly vulnerable to fires and as such represent a high proportion of fuels consumed during forest fires [1]. Thus, the resistance of peatlands to wildfire activity increases with increase peatland sizes and reduces with increase distance of peatlands to surrounding uplands. These findings thus support the general evidence that peatlands act as natural barriers to wildfire spread [32], hence, highly resistant to burning due to their high moisture content [42] particularly in large and extremely large peatlands which burnt at very low proportions in our study area. Such resistance to burning was well supported by the low percentage rates of burning found in all six fire zones in my study area. i.e. in fire zone A, average peatland burnt was rated at 0.66%, in fire zone B, it was rated at 0.29%, in fire zones C, D, E and F, average burn rates were measured at 0.07%, 8.2%, 8.5% and 3.86% respectively. With increase distances, large areas of uplands proofed to burn at high proportions, providing evidence that fires occur prefentially in boreal uplands of northern Quebec than in peatlands.

My findings further reveal that, the gradient of peatland burning decreases North-East and West-East of the study area (Figures 5). Peatlands cover about 5–25% of the study area [7], hence their decrease abundance from North to East, as well as from South to East decreases their rate of burning along the N-E and S-E fire activity gradient. This evidence was more pronounced with increase lake abundance West-East of the study area (Figure 1). This gradient of lake abundance contributes immensely to poor peatland drainage conditions, hence causing fire escapes [27, 44]. The combination of this wetland conditions seem to interrupt fuel continuity in the study area thereby acting as natural breaks or barriers to fire spread [3, 6, 12, 16, 20, 24]. This findings thus proof that both wetland conditions act as strong bottom-up controls to wildfire activity.

My findings also show that FWI, topography and lakes play vital roles in increasing or reducing the resistance of

Peatland Burning


peatlands to burning across the study area. For example, FWI proofed to be a powerful determinant of peatland burning, i.e. under increase FWI, the probability of peatlands to burn was approximately 70%. This finding corresponds to already documented evidence that, boreal peatlands burn at high severity under increase fire weather severity [41]. Their high moisture contents have been predicted to diminish under increase fire weather severity as a result of climate change [11, 22, 39], hence making them more vulnerable to burning [41]. Thus fire weather indices act as active or strong bottom-up controls to peatland burning in the eastern Canadian Taiga. The relationship between fire weather and fire activity is very important in boreal fire disturbance ecology since variation in weather severity often determines the extent at which soils and vegetation will dry sufficient enough to act as flammable fuels.

With topography, slope and elevation positions contributed immensely in increasing the resistance of peatlands to burning, while aspect played a significant contribution in diminishing such resistance. In general, topography has been shown to play a vital role in controlling the spatio-temporal variability in forest fire activity [8, 28, 29, 33] through interaction with fuels and weather. However, their influence on peatland fires has not been previously reported. In this study, we therefore provide evidence that slope and elevation position contributes in slowing down the burning of peatlands in our study area while large areas of peatlands burnt strongly depend on aspect positions. We thus recommend that more research be done to document more evidence on Western boreal peatlands.

Conclusion

The findings of this study supports the three initial hypothesis that, (i) area burned is extremely lower in large and extremely large peatlands than in small and extremely smaller peatlands; (ii) the quantity of uplands burnt increases with increase distance of uplands to surrounding peatlands; (iii) Peatlands act as natural barriers to wildfire spread. Consequently, the attributes of peatlands such

as size and distance act as active bottom-up controls to wildfire spread. In addition, the gradient of peatlands burning decreases N-E and W-E of the study area. Furthermore, FWI contribute immensely in decreasing peatland resistance to wildfires, whereas lakes, slopes and elevations contribute in increasing such resistance.

Although the interactions between peatlands, lakes, topography and fwi seem spatially complex, they collectively act as important bottom-up and top-down factors that determine areas of high fire risk. In addition, they are surrounded by old forest stands that have found refuge due to escaping fires. Thus, interacting all these factors in a spatially explicit burn probability model will help identify areas at high risk of burning. Such risk maps will enable identify the exposure of values at risk (VARs) (e.g. infrastructures, villages, roads and airports) to wildfires.

I therefore recommend further studies to be conducted on the interactive effects of forested and non-forested peatlands as well as fuel age on the spatial variability of wildfires. Such studies will contribute immensely in providing more insights on peatland resistance to wildfires in the study area, and will as such enable a realistic mapping of the risk of fire exposure to infrastructures (VARs).

Acknowledgement

Special thanks go to Professor Dominique Arseneault of the University of Quebec at Rimouski (UQAR), and Dr. Marc Andre parisien and Yan Boulanger of Natural Resource Canada, for their contributions towards developing the research concepts. Further thanks go to the Quebec government as well as the federal government for providing free and open access data on mapped peatlands and fire perimeters across the study area.

Data Availability

Data used for this research has been clearly referenced in the text, but can be obtained from the corresponding author upon request.

Peatland Burning


Supplementry materialsTable S1. Amount and area of peatlands burnt by size classes, including number and size of fires measured per peatland size class

Fire zone

Size class (ha)

Size type

Total peatland area (ha)

Peatland area burnt

(ha)

% area burnt by fire zone

Peatland amount

(N)

Amount of peatland burnt (N)

Fire size (ha)

Number of fires

(N)

Zone A 0–50 ES 166973 1475 82 12414 446 1452 36

51–100 S 38011 106 6 784 21 104 7

101–300 M 26786 124 7 300 11 122 4

300–500 L 22922 96 5 183 1 94 1

500+ EL 15645 0 0 51 0 0 0

Total 270336 1800 100 13732 479 1772 48

Zone B 0–50 ES 91696 324 92 11054 245 319 33

51–100 S 12042 19 5 289 13 19 8

101–300 M 8014 2 1 107 3 2 2

300–500 L 4053 6 2 46 5 6 3

500+ EL 2527 0 0 11 0 0 0

Total 118332 351 100 11507 266 346 46

Zone C 0–50 ES 109795 119 88 11511 112 117 25

51–100 S 24301 16 12 557 1 16 1

101–300 M 18338 0 0 284 0 0 0

300–500 L 16584 0 0 132 0 0 0

500+ EL 24545 0 0 94 0 0 0

Total 193563 135 100 12578 113 133 26

Zone D 0–50 ES 512832 73730 49 18732 4271 73131 87

51–100 S 272654 29674 20 3986 831 29440 63

101–300 M 230640 23736 16 2010 389 23551 50

300–500 L 215689 11959 8 1211 155 11867 38

500+ EL 589060 10364 7 792 69 10287 26

Total 1820876 149462 100 26731 5715 148277 264

Zone E 0–50 ES 196280 21342 84 13317 3029 21210 153

51–100 S 44503 2052 8 913 179 2040 64

101–300 M 27875 1430 6 316 76 1421 32

300–500 L 18548 427 2 139 14 424 11

500+ EL 10248 0 0 33 0 0 0

Total 297455 25251 100 14708 3298 25095 260

Peatland Burning


Fire zone

Size class (ha)

Size type

Total peatland area (ha)

Peatland area burnt

(ha)

% area burnt by fire zone

Peatland amount

(N)

Amount of peatland burnt (N)

Fire size (ha)

Number of fires

(N)

Zone F 0–50 ES 101041 4676 80 6166 1267 4634 81

51–100 S 21380 438 7 442 56 434 24

101–300 M 10605 206 4 129 18 204 12

300–500 L 9964 193 3 79 18 192 9

500+ EL 9260 361 6 30 6 359 5

Total 152250 5874 100 6846 1365 5824 131

Table S2. Sizes and number of fires measured at 100m, 1000m and 10000m distance to peatlands by size class

Fire zone

Size class (ha)

Size type

Peatland area (ha)

Number of fires

at 100m distance

(N)

Size of fires at 100m

distance (ha)

Number of

fires at 1000m distance

(N)

Size of fires at 1000m distance

(ha)

Number of


(N)

Size of fires at

10000m distance

(ha)

Zone A 0–50 ES 166973 36 86422 43 90939 47 92693

51–100 S 38011 11 55817 13 59126 34 81774

101–300 M 26786 4 49164 8 51147 23 62611

300–500 L 22922 2 6612 6 51629 35 79164

500+ EL 15645 0 0 0 0 9 11436

Total 270337 53 198015 70 252841 148 327678

Zone B 0–50 ES 91696 41 130377 46 132653 56 142098

51–100 S 12042 9 63594 16 72864 39 130808

101–300 M 8014 3 26268 6 57366 27 118645

300–500 L 4053 3 41281 3 41281 7 49571

500+ EL 2527 0 0 0 0 0 0

Total 118332 56 261520 71 304164 129 441122

Zone C 0–50 ES 109795 29 130874 41 143410 53 154713

51–100 S 24301 2 15057 9 20833 27 103228

101–300 M 18338 0 0 0 0 17 89074

300–500 L 16584 0 0 1 614 7 6412

500+ EL 24545 0 0 0 0 1 361

Total 193563 31 145931 51 164857 105 353788

Peatland Burning


Fire zone

Size class (ha)

Size type

Peatland area (ha)

Number of fires

at 100m distance

(N)

Size of fires at 100m

distance (ha)

Number of


(N)

Size of fires at 1000m distance

(ha)

Number of


(N)

Size of fires at

10000m distance

(ha)

Zone D 0–50 ES 512832 89 740822 92 908963 47 92693

51–100 S 272654 67 865428 78 874685 34 81774

101–300 M 230640 52 848459 64 860103 23 62611

300–500 L 215689 44 1413142 61 1444165 35 79164

500+ EL 589060 26 678338 33 690192 9 11436

Total 1820875 278 4546189 328 4778108 148 327678

Zone E 0–50 ES 196280 158 992478 179 1004482 202 1053609

51–100 S 44503 66 630527 93 830190 188 1001563

101–300 M 27875 34 533409 45 595996 144 898646

300–500 L 18548 14 324779 23 426256 140 1013738

500+ EL 10248 5 176109 5 176109 28 302314

Total 297454 277 2657302 345 3033033 702 4269870

Zone F 0–50 ES 101041 87 491474 99 500303 132 648783

51–100 S 21380 29 491474 43 344617 107 504705

101–300 M 10605 12 263275 21 286548 66 401505

300–500 L 9964 9 176296 13 191316 66 572407

500+ EL 9260 5 22558 7 27647 25 172985

Total 152250 142 1445077 183 1350431 396 2300385

References

1. Amiro BD, Todd JB, Wotton BM, Logan KA, Flannigan MD, et al. (2001) Direct carbon emissions from Canadian forest fires, 1959–1999. Canadian Journal of Forest Resource 31: 512–525.

2. Barrett CM, Kelly R, Higuera PE, Hu FS (2013) Climatic and land cover influences on the spatiotemporal dynamics of Holocene boreal fire regimes. Ecology 94: 389–402. [View]

3. Bergeron Y (1991) The influence of island and mainland lakeshore landscapes on boreal forest fire regimes. Ecology 72: 1980–1992.

4. Bond WJ, van Wilgen BW (1996) Fire and Plants. Pp. 42–38. Chapman and Hall, London.

5. Bond WJ, Dickinson KJM, Mark AF (2004) What limits the spread of fire dependent vegetation? Evidence from

geographic variation of serotiny in a New Zealand shrub. Global Ecology and Biogeography13:115–127.

6. Cyr D, Bergeron Y, Gauthier S, Larouche AC (2005) Are the old-growth forests of the Clay Belt part of a fire-regulated mosaic? Canadian Journal of Forest Research 35: 65–73.

7. Erni S, Arseneault D, Parisien MA, Bégin Y (2017) Spatial and temporal dimensions of fire activity in the fire-prone eastern Canadian taiga. Glob Chang Biol 23: 1152–1166. [View]

8. Estes BL, Knapp EE, Skinner CN, Miller JD, Preisler HK (2017) Factors influencing fire severity under moderate burning conditions in the Klamath Mountains, northern California, USA. Ecosphere 8: e01794.

9. Flannigan M, Cantin AS, De Groot WJ, Wotton M, Newbery A, et al. (2013) Global wildland fire season severity in the 21st century. Forest Ecology and Management 294: 54–61.

http://www.ncbi.nlm.nih.gov/pubmed/23691658http://www.ncbi.nlm.nih.gov/pubmed/27514018

Peatland Burning


10. Godwin KS, James PS, Donald JLJ, Barbara LB (2002) Linking landscape properties to local hydrogeologic gradients and plant species occurrence in New York fens: a hydrogeologic setting (HGS) framework. Wetlands 22: 722–737.

11. Granath G, Moore PA, Lukenbach MC, Waddington JM (2016) Mitigating wildfire carbon loss in managed northern peatlands through restoration. Sci Rep 6: 28498. [View]

12. HellbergE, Niklasson M, Granström A (2004). Influence of landscape structure on patterns of forest fires in boreal forest landscapes in Sweden. Canadian Journal of Forest Research 34: 332–338.

13. Heinselman MI (1981) Fire intensity and frequency as factors in the distribution and structure of northern ecosystems. Pp. 7–57 in. H Mooney, IM Bonnicksen, NL Chnstensen, IF Lotan, WA.

14. Héon J, Arseneault D, Parisien MA (2014) Resistance of the boreal forest to high burn rates. Proc Natl Acad Sci U S A 111: 13888–13893. [View]

15. Heyerdahl EK, Brubaker LB, Agee JK (2001) Spatial controls of historical fir regimes: a multiscale example from the Interior West, USA. Ecology 82: 660–678.

16. Hollingsworth TN, Johnstone JF, Bernhardt EL, Chapin FS 3rd (2013) Fire severity filters regeneration traits to shape community assembly in Alaska’s boreal forest. PLoS One 8: e56033. [View]

17. Keddy PA (2010) Wetland Ecology: Principles and Conservation (2nd ed.). Cambridge University Press. ISBN 978-0521739672.

18. Krawchuk MA, Moritz MA, Parisien MA, Van Dorn J, Hayhoe K (2009) Global pyrogeography: the current and future distribution of wildfire. PLoS One 4: e5102. [View]

19. Krawchuk MA, Moritz MA, Parisien M-A, Van Dorn J, Hayhoe K (2009a) Global pyrogeography: macro-scaled statistical models for understanding the current and future distribution of fire. PLoS ONE 4: e5102.

20. Larsen CPS (1997) Spatial and temporal variations in boreal forest fire frequency in northern Alberta. Journal of Biogeography 24: 663–673.

21. McCullagh P, Nelder JA (1989) Generalized Linear Models, Vol. 37 of Monographs on Statistics and Applied Probability, 2edn, Chapman and Hall, London.

22. Moore PD (2002) The future of cool temperate bogs. Environment and Conservation 29: 3–20.

23. National Intelligence Fire Center (2017) Total Wildland Fires and Acres (1960–2017). National Interagency Fire Center: Boise, ID, USA.

24. Nielsen SE, DeLancey ER, Reinhardt K, Parisien M-A (2016) Effects of Lakes on Wildfire Activity in the Boreal Forests of Saskatchewan, Canada. Forests 7: 265.

25. Northoff E (2003) Fires are increasingly damaging the world’s forests. FAO, Rome, Italy. See http://www.fao.org/english/newsroom/news/2003/21962-en.html.

26. North MP, Stephens SL, Collins BM, Agee JK, Aplet G, et al. (2015) ENVIRONMENTAL SCIENCE. Reform forest fire management. Science 349: 1280–1281. [View]

27. Ouarmim S, Ali AA, Asselin H, Hély C, Bergeron Y (2015) Evaluating the persistence of post - fire residual patches in the eastern Canadian boreal mixedwood forest. Boreas 44 :230–239.

28. Povak NA, Hessburg PF, Salter RB (2018) Evidence for scale-dependent topographic controls on wild?re spread. Ecosphere 9: e02443.

29. Rollins MG, Morgan P, Swetnam T (2002) Landscape-scale controls over 20th century fire occurrence in two large Rocky Mountain (USA) wilderness areas, Landscape Ecology 17: 539–557.

30. Rydin H, John K J (2013) The Biology of Peatlands, 2nd edn. Oxford: OUP, p. 11. ISBN 978-0-19-960299-5.

31. SchultzMG, Heil A, Hoelzemann JJ, Spessa A, Thonicke K, et al. (2008) Global wildland fire emissions from 1960 to 2000. Global Biogeochemical Cycles 22: GB2002.

32. Senici D, Chen HYH, Bergeron Y, Ali AAT (2015) The effects of forest fuel connectivity on spatiotemporal dynamics of Holocene fire regimes in the central boreal forest of North America. Journal of Quaternary Science 30: 365–375.

33. Stambaugh MC, Guyette RP (2008) Predicting spatio-temporal variability in fire return intervals using a topographic roughness index. Forest Ecology and Management 254: 463–473.

34. Stocks BJ, Mason JA, Todd JB, Bosch EM, Wotton BM, Amiro BD, Flannigan MD, Hirsch KG, Logan KA, Martell DL, Skinner WR (2002) Large forest fires in Canada, 1959–1997. Journal of Geophysical Research 108: D1.

35. Stocks BJ (2013) Evaluating Past, Current and Future Forest Fire Load Trends in Canada. A January 2013 report. Available at: https://www.ccfm.org/pdf/2%20Fire%20Load%20Trends.pdf

36. Stockwell C, Mcglynn J, Emslie R (1968) Géologie du bouclier canadien. Géologie et Ressources Minérales du Canada, Partie A. Commission géologique du Canada, Ottawa, Ontario.

37. Stralberg D, Wang X, Parisien M.-A, Robinne FN, Solymos P, et al. (2018) Wildfire-mediated vegetation

http://www.ncbi.nlm.nih.gov/pubmed/27346604http://www.ncbi.nlm.nih.gov/pubmed/25201981http://www.ncbi.nlm.nih.gov/pubmed/23418503http://www.ncbi.nlm.nih.gov/pubmed/19352494http://www.fao.org/english/newsroom/news/2003/21962-en.htmlhttp://www.fao.org/english/newsroom/news/2003/21962-en.htmlhttp://www.ncbi.nlm.nih.gov/pubmed/26383934https://www.ccfm.org/pdf/2%20Fire%20Load%20Trends.pdfhttps://www.ccfm.org/pdf/2%20Fire%20Load%20Trends.pdf

Peatland Burning


change in boreal forests of Alberta, Canada. Ecosphere 9: e02156.

38. Tarnocai C (1984) Peat resources of Canada.National Research Council Canada, Division of Energy, NRCC No 24140, 17 p.

39. Tarnocai C (2006b) The effect of climate change on carbon in Canadian peatlands. Global and Planetary Change 53: 222–232.

40. Tansey K, Grégoire JM, Defourny P, Leigh R, Pekel JF, van Bogaert E, Bartholomé EA (2008) New, global, multi-national (2000–2007) burnt area product at 1-km resolution. Geophysical Research Letters 35: L01401.

41. Turetsky MR, Amiro BD, Bosch EM, Bhatti JS (2004) Historical burn area in western Canadian peatlands and its relationship to fire weather indices. Global Biogeochemical Cycles 18: GB4014.

42. Turetsky MR, Benscoter B, Page S, Rein G, van der Werf GR, et al. (2015) Global vulnerability of peatlands to fire and carbon loss. Nature Geoscience 8: 11–14.

43. van der Werf GR, Jan D, Simon NT, James T, Randerson PS, et al. (2008) Climate regulation of fire emissions and deforestation in equatorial Asia. Proceedings of the National Academy of Sciences105: 20350–20355.

44. Wallenius TH, Kuuluvainen T, Vanha –Majamaa I (2004) Fire history in relation to site type and vegetation in Vienansalo wilderness in eastern Fennoscandia, Russia. Canadian Journal of Forest Research 34: 1400–1409.

45. Whitman E, Parisien MA, Thompson DK, Hall RJ, Skakun RS, et al. (2018) Variability and drivers of burn severity in the northwestern Canadian boreal forest. Ecosphere 9: e02128.

*Corresponding author: Yisa Ginath Yuh, University of Quebec at Rimouski (UQAR), 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada;

Email: [email protected]

quantifying peatland burning and resistance to wildfire ......gc.ca/datamart/ download/nfdbpoly?...

Documents