persistence and developmental transition of wide seismic lines in the western boreal plains of...

Persistence and developmental transition of wide seismic lines

in the western Boreal Plains of Canada

Philip Lee*,1, Stan Boutin2

Integrated Landscape Management Program, Department of Biological Sciences, University of Alberta, Edmonton, Alta., Canada T6G 2E9

Received 15 September 2004; revised 26 January 2005; accepted 21 March 2005

Available online 22 August 2005

Abstract

This study examined the fate of seismic lines utilized in oil and gas exploration in Canada’s western Boreal Plains. It retrospectively

followed the persistence, recovery and developmental transition of seismic lines established between the 1960s and the mid-1970s through to

2003. We examined lines that passed through three forest types; aspen, white spruce, and lowland black spruce. In general, the recovery rates

of seismic lines to woody vegetation were low. After 35 years, 8.2% of seismic lines across all forest types had recovered to greater than 50%

cover of woody vegetation. Only the upland forest types recovered; aspen and white spruce. Most seismic lines (w65% at 35 years) remained

in a cleared state with a cover of low forbs. The most common transition for seismic lines was to tracked access (w20% at 35 years).

Transition to other anthropogenic developments such as roads, pipelines, buildings, and timber harvest blocks was 5% after 35 years. The

pulse of industrial activity initiated in the mid-1990s greatly increased the transition rate of seismic to tracked access for a short period of

time. The discussion focused on natural and anthropogenic factors that hinder recovery and on the management directions that would

facilitate greater recovery rates.

q 2005 Elsevier Ltd. All rights reserved.

Keywords: Vehicular traffic; Oil exploration; Road development; Site remediation

1. Introduction

Seismic exploration is often the first step in the oil

extraction process. In brief, it consists of the linear

placement of sensitive receivers (geophones) on the ground,

i.e. seismic lines. Small explosive charges or mechanical

vibrations are created along the ground surface. Geophones

record the energy reflected back from subterranean rock and

hydrocarbon layers at varying depths. The intensity, wave

form, and times for reflection are used to profile the

underlying rock layers and potential hydrocarbon layers.

Solitary lines of geophones allow for a two-dimensional,

cross-sectional resolution while a network grid of geo-

phones with closer spacing produces a more detailed, three-

0301-4797/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jenvman.2005.03.016

* Corresponding author. Address: Parks Canada, #300-300 W. Georgia

Street, Vancouver, BC, Canada V6B 6B4. Tel.: C1 604 666 3154.

E-mail addresses: [email protected] (P. Lee), stan.boutin@ualberta.

ca (S. Boutin).1 Tel.: C1 780 492 5766; fax: C1 780 492 9234.2 Tel.: C1 780 492 1297.

dimensional, topographic map of rock layers. The surface

footprint of this exploration can be long linear lines of trails

cut into the forest.

A number of different methods are used to create the

transmission and receiver lines in seismic exploration. In the

boreal forest of western Canada, the primary method from the

early 1950s to 2000 was to clear vegetation using bulldozers.

This linear grid of lines, some cut as early as the 1950s, is still

evident today. Lines intersect with other lines forming an

irregularly spaced grid over the landscape. The trend has been

a reduction of lines from 8 to 5 m. In ecologically sensitive

areas, there can be a further reduction in the footprint, i.e.

narrow width, such as hand-cut, or narrow width machinery, or

minimal footprint techniques such as heliportable. While the

application of these methods is expanding, many kilometres of

seismic lines in Canada and Russia were cut and are still being

cut to the 5 m width. This paper examined the recovery of

these wider seismic lines.

Conservative estimates of wide seismic lines in north-

eastern Alberta, a primary oil producing region within

Canada, indicate a mean density of 1.5 km per km2 present

in 98% of the townships (10!10 km) (based on 2001

Alberta Base Features Map, Alberta Data Resource

Journal of Environmental Management 78 (2006) 240–250

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P. Lee, S. Boutin / Journal of Environmental Management 78 (2006) 240–250 241

Division, Sustainable Resource Development, Government

of Alberta, Edmonton, Alberta). Densities in some town-

ships reach as a high as 10 km per km2. This estimate does

not include other linear features such as roads, electrical

transmission lines, pipelines, and railways. For comparison,

the road network in the developed agricultural zone of

Alberta is 1 km per km2 (2 km right angle spacing). Unlike

other forested systems in which timber harvest or clearing

for agriculture were the first steps to development, seismic

lines were often the first step in industrial development for

much of the boreal forests in western Canada and Russia. As

industrial development proceeds, the cumulative effects of

these different anthropogenic features are an environmental

concern (Schneider, 2002; Schneider et al., 2003). The

original intent was that seismic lines would eventually

recover their former vegetation communities. Casual

observations suggest that this has not occurred, however,

this type of information can be deceptive since observers are

naturally biased in detecting lines that have not recovered. A

current ‘snapshot’ of existing seismic lines underestimates

those that have recovered. Studies need to start with an

unbiased set of seismic lines and track their development

through time. Quantitative studies on the ability of seismic

lines to recover in tundra and steppe ecosystems are not

promising (Felix et al., 1992; Marcela and Martin, 2003).

Other systems such as coastal vegetation communities on

the Gulf of Mexico appear to suffer no long-term effects

(Drawe and Ortega, 1996).

In one of the few studies to examine tree regeneration

along seismic lines in Alberta, Revel et al. (1984) found that

23 out of 35 seismic lines in the foothills of the Rocky

Mountains had sapling densities of lodgepole pine (Pinus

contorta), white spruce (Picea glauca, black spruce (Picea

mariana), and occasionally balsam fir (Abies lasiocarpa) in

excess of Alberta’s timber regeneration standards. How-

ever, there was a significant time lag in achieving these

densities (10–30 years) and the height of trees was

significantly shorter than those in regenerating trees

typically found after harvest. MacFarlane (2003) found no

significant differences in the understory vegetation of

seismic lines aged from less than 14 years to greater than

23 years in trembling aspen (Populus tremuloides) forests of

the northeastern Alberta. However, all vegetation commu-

nities from all ages of seismic lines were different from

interior forest communities. Online communities were

unique because they included light tolerant, disturbance

associated species. Both studies were intensive, plot-based

examinations of relatively few sites. If recovery and

transition rates are relatively low, an intensive plot-based

technique will lack sufficient sample sizes to confidently

estimate rates. Furthermore, the widespread nature of oil

and gas exploration requires sampling over a broad area to

obtain a representative sample of the population of seismic

lines. The question of what the broad, long-term patterns of

recovery and potential transition to other forms of industrial

development for seismic lines remains unexplored.

This paper reports on the fate of the wider seismic lines

established during this early phase of oil and gas exploration

in western Canada. In order to examine this question, we

surveyed an extensive sample of seismic lines from the time

they were established to when they recovered to woody

vegetation or developed into another anthropogenic feature.

Specifically, we assessed the transition of a cohort of

seismic lines from 1960 and 1970s cut through three forest

types in northeastern Alberta. These included: trembling

aspen, white spruce, and lowland black spruce. By

examining a chronosequence of aerial photos, we backdated

the seismic lines to their establishment and followed them

forward to 2002–2003.

2. Materials and methods

2.1. Study area

The study area was bordered by 110 and 1148 west

longitude (3rd and 4th west meridians) and 55 and 588 north

latitude (Fig. 1). The area is classified as the Boreal Plains

ecozone (Environment Canada, 2001) or Boreal ecoregion

(Alberta Environmental Protection, 1994). The Alberta

classification further subdivides the ecoregion into Central

Mixedwood (O80%), Boreal Highlands (15%), and

Subarctic (!5%) subregions. Over these subregions,

median winter temperatures range from K7.7 to

K18.0 8C with median summer temperatures ranging

from 9.5 to 13.5 8C. The overall mean precipitation is 240

and 64 mm in the summer and winter, respectively. Our

study focused on the Central Mixedwood and Boreal

Highlands. No seismic lines were examined from the

Subarctic. Boreal Highlands have slightly more precipi-

tation and cooler temperatures than the Central Mixed-

woods. Typical tree species in these areas include;

trembling aspen, (P. tremuloides Michx.), jack pine (Pinus

banksiana Lamb.), black spruce (Picea mariana (Mill.)

B.S.P.), white spruce (P. glauca (Moench) Voss), and

tamarack (Larix laricina (Du Roi) K. Koch). Minor species

include: balsam poplar (Populus balsamifera L.), paper

birch (Betula papyrifera Marsh.), and balsam fir (Abies

balsamea (L.) Mill).

Aspen forests are the dominant upland forest type

regenerating after stand-replacing or large gap disturbances

such as wildfire or large wind events (reviewed in Peterson

and Peterson, 1992). Aspen primarily regenerates by

suckering to very high stem densities. Densities of

100,000–200,000 stems per ha are not uncommon after

disturbances. Self-thinning reduces densities to 800–1500

stems per ha by 80 years after disturbance. Some aspen

stands with nearby seed sources develop a white spruce

subcanopy that can eventually replace or supplement

the overstory layer and create a mixedwood canopy.

These stands can eventually give way to a full white spruce

overstory with the eventual loss of aspen. Despite this

Fig. 1. Study area in northeastern Alberta. Hierarchical rectilinear grid represents the pattern of townships (10!10 km) while the subgrid (0.6!0.6 km)

represents the layout of 36 sections within each township. The insert shows an example of seismic lines within a section.

P. Lee, S. Boutin / Journal of Environmental Management 78 (2006) 240–250242

general successional trend, there is a great deal of variation

in the timing for the onset of mixedwood and full white

spruce canopies across the western Boreal Plains (reviewed

in Zasada, 1972; Kabzems and Lousier, 1992; Peterson and

Peterson, 1992). At the extremes, some aspen stands appear

to be able to replace their initial cohort with a second cohort

of aspen while some areas regenerate directly to white

spruce after disturbances.

Lowland black spruce is found at the extreme end of the

vegetation types that characterize peatlands on the western

Boreal Plains of Alberta. The overall gradient of mire types

includes: bogs, poor fen, wooded rich fen, sedge fen, and

extreme-rich fen (reviewed in Szumigalski, 1995). Wooded

bogs are characterized by large raised plateaus (0.3–0.5 m)

in peatland complexes. These plateaus are ombrotrophic,

i.e. precipitation is the only source of water. The relief is

characterized by hummocks interspersed with small pools.

These pools may have water year round. The cover of trees

within wooded bogs is dominated by slow growing black

spruce and seldom exceeds 35%. The shrub cover features

labradour tea (Ledum groenlandicum, Oeder), bog cran-

berry (Vaccinium vitis-idaea L.), and small bog cranberry

(Oxycoccus microcarpus Turcz.). There are few herbaceous

species with most of the ground stratum covered by mosses

including; Sphagnum fuscum (Schimp.), S. magellanicum

(Brid.), S. angustifolium (C. Jens ex Russ.), and Poly-

strichum strictum (Brid.). Poor fens often surround wooded

bogs. These fens may have a similar topography to bogs but

are wetter and more minerotrophic, i.e. more input from

water sources with dissolved ions.

2.2. Sample design

The developmental trajectory of seismic lines was

determined through the examination of aerial photographs.

Alberta has a good library of publicly available aerial

photographs. Between 1949 and 1950, the entire northern

portion of the province was photographed. This was prior to

any seismic line or many other developments. We used 1978

as benchmark year because this was the first year a complete

set of township maps with all seismic lines was produced.

These maps were released from 1980 to 1982 but were all

derived from interpretation of 1978 aerial photographs (Phase

III maps, Alberta Data Resource Division, Sustainable

Resource Development, Government of Alberta, Edmonton,

Alberta).

Table 1

Description of categories for the aerial photo-interpretation of seismic lines

Category Features Description

Revegetationa Seismic Less than 12% cover of woody

vegetation

25% recovered 13–39% cover of woody vegetation



100% recovered Greater than 88% cover of woody

vegetation

Transportation Tracked access Visible vehicle tracks

Gravel road Presence of raised road bed and

gravelled surface often bordered by

a cleared ditch

Paved road Presence of raised road bed and

paved surface always bordered by a

cleared ditch

Others Clearcut Clearing for timber harvest

Facilities Buildings, parking lots, oil or gas

facilities, etc.

Gravel pit Presence of moved soils and gravel

sorting piles

Pipeline Presence of compressor stations,

clearings at access points, and

wider than seismic lines

Well pad Recti-linear pads often with well

heads in the centre

a Woody vegetation does not have to match the height of the surrounding

vegetation.


Of the 864 townships (10!10 km) within the study area,

we randomly selected 628 townships. Within each town-

ship, we further selected a section (36 sections per

township) at random and selected a segment of seismic

line (0.5 km) nearest to the section centre. The entire length

of each segment had to be bordered on both sides by one of

three forest types; aspen, white spruce, and lowland black

spruce. If this sample as unsatisfactory then the next nearest

segment of seismic line would be selected along that line

provided it was still within the section. If this proved to be

unsatisfactory, a nearest segment on the next seismic line

nearest the section centre was examined. This was repeated

until each line within a section was examined. If no suitable

seismic line was found, then another section was been

selected and the procedure repeated. There was nothing

ecologically significant about the scale of townships and

sections. It was chosen because many of the aerial photo and

map resources are catalogued by section and township. Use

of townships greatly facilitated searching for aerial

photographs and data gathering.

For the 628 sites, there were 8815 photographs available

between 1949 and 2004. Of these, 3242 were examined.

Multiple sets from the same year, poor quality, and aerial

photos taken prior to the presence of seismic lines were not

examined. Furthermore, photographs with a resolution less

than 1:40,000 were generally avoided if higher resolution

photographs were available G2 years. In general, photo-

graphs taken during and after 1978 were of a better quality

and temporal resolution. The median resolutions for pre-

1978 and post-1978 photographs were 1:31,680 and 1:20,

000, respectively. Pre-1978, no colour photographs were

examined. After 1978, approximately 10% of photographs

were colour. Pre-1978, 15% of photographs were sensitive

to infrared waves while 36% were sensitive to infrared

waves after 1978. The mean (GS.D.) interval between

photographs for pre-1978 and post-1978 photographs were

7.9G7.7 and 2.6G2.4 years, respectively.

We examined seismic lines originally cut through three

forest types. These included; aspen-dominated (O80% canopy

cover), white spruce-dominated (O80%), and lowland black

spruce (O15%). All forests adjacent to seismic lines were

judged to be greater than 40 years of age (based on height and

canopy density) when the seismic line was cut. The dataset did

not include seismic lines that had burned during the period of

examination. Although mixedwood forests (e.g. aspen and

white spruce) are a commonly classified forest type, we only

workedwithsinglespecies types. Initialobservationsofseismic

lines cut within stands classified as mixedwood canopies based

on Alberta Vegetation Inventory (Alberta Environmental

Protection 1991) indicated that 0.5 km segments of seismic

line were usually bordered by either aspen or white spruce. We

only rarely found a intermingling of aspen and spruce at the

scale of 50–100 m, on either side of the seismic line. Hence, we

had no separate category for mixedwood forests.

We initially selected segments of seismic line at random

with respect to these forest types. However, we switched to

a stratified random sample in later selection. This was an

effort to obtain more white spruce samples. Lowland black

spruce makes up approximately 38% of the forested

landbase in this area, aspen makes up 22%, and white

spruce makes up less than 12%. At the end of sampling

phase, there were 228, 225, and 175 samples from lowland

black spruce, aspen, and white spruce forests, respectively.

For each segment of seismic line, historic aerial

photographs were examined to determine the year the

seismic was cut. Photographs were examined from that time

forward to determine whether the seismic line had recovered

or transitioned to another feature. Table 1 describes all

categories that were detected. Transition dates were

interpolated halfway between the last photograph taken

prior to the appearance of a feature and the next photograph

with that feature. A number of studies have used aerial

photography to detect disturbance associated with seismic

lines or pipelines (e.g. Radforth, 1973; Raynolds and Felix,

1989). These studies used higher resolution photographs to

provide detailed descriptions of the traffic disturbance. As

an example, Raynolds and Felix (1989) used 1:6000

photography to breakdown disturbance into four categories

and seven vegetation categories in the Arctic National

Wildlife Refuge, Alaska. Our categories were less detailed.

As an example, we found it possible to discern the presence

or absence of tracked access using stereo pairs under 2 to

4!magnification on 1:40,000 photographs.

We followed the standard guidelines and criteria for

photo interpretation according to the Alberta Vegetation


Inventory (Alberta Environmental Protection, 1991). This

interpretation system is the standard method for the

inventory of forested lands in Alberta. Recovery was

based on the return of woody vegetation detectable on

aerial photography. Woody vegetation was readily dis-

tinguishable from grasses and herbs. It was not possible to

distinguish tall shrubs from trees (except conifers) within

the same canopy strata nor can we measure stem density or

stem height with accuracy. Hence, our measurement of

recovery is not to timber regeneration standards. However,

the return of a woody vegetation triggers a significant

ecological recovery of biotic communities after timber

removal (reviewed in Song, 2002). We categorized woody

vegetation in 5 cover classes (Table 1) based on relative

cover of the line to the surrounding forest.

Time (years)

0 5 10 15 20 25 30 35

Pro

port

ion

0.00

0.05

0.10

0.15

0.20

0.250.60

0.70

0.80

0.90

1.00

SeismicWoody vegetationRoadsTracked accessOther industrial

Fig. 2. Overall proportion of seismic lines plotted against the time since

establishment in forested ecosystems in the western Boreal Plains of

northeastern Alberta, Canada. Seismic lines either retained their status quo

with low ground cover or transitioned to other anthropogenic features.

These included; woody revegetation (50% cover), tracked access, roads, or

other industrial features. Symbols represent inflection points on the graphs

rather than the temporal availability of data.

2.3. Analysis

Seismic transition data were analysed using techniques

commonly applied to the analysis of population survivor-

ship data (Lee, 1992). A nonparametric method was used

since not all the seismic lines had recovered or been

transformed into another anthropogenic feature, i.e. right

censored data. All lines were backdated; hence, there was no

left censored data. The remaining data were uncensored.

The product-limit method was used to estimate the survival

function of the seismic lines, their recovery, and transition

to other features (Kaplan and Meier, 1958).

Curves for recovery or transition to other anthropogenic

features were estimated from the time of seismic line

establishment to its recovery or transition. Values at each

time interval were calculated using the failure values (0–1)

from the product-limit analysis. These were then scaled

according to the overall transition over the entire time

period. As an example, the overall transition from seismic to

recovery was rescaled to 8.2% after 35 years. Comparisons

between seismic survival, recovery, and transition functions

from different forest types were made using a log rank test

(Mantel, 1966; Peto and Peto, 1972). All analyses were

performed on the JMP statistical package (ver. 5.0, SAS,

2002). All statistical tests were considered significant when

P!0.05.

Generalized curves such as exponential, Weibull,

lognormal, or gamma are often fitted to survival data

(Lee, 1992). Fitting curves to this data is mathematically

possible, however, we felt they were inappropriate. The

temporal pattern of the seismic line transition is largely

driven by contingency factors that are historical shifts in

industrial development. They are unlikely to re-occur in the

same manner. Hence, we felt curve fitting was inappropriate

particularly for predictive purposes. Instead, we chose to

present the raw data with error bars. Median, quartile,

min/max values for the annual rates of change are presented

since the distributions of annual rates were not normally

distributed.

3. Results

3.1. Overall transition patterns

In general, the historic, 5–8 m seismic lines cut using

bulldozers were relatively persistent features in the forested

boreal landscape. Only 8.2% of seismic lines in all forested

stands had recovered to greater than 50% cover of woody

vegetation (Fig. 2). Temporal patterns suggested a lag of up

to 15 years for recovery. The median recovery rate was

0.21% per annum (Table 2). Most seismic lines remained

cleared with only a covering of grasses and herbs. After 35

years, 64.4% of seismic lines were in this state. The

remaining, 35.6%, had either recovered or been transformed

into another feature (Fig. 2). The median annual rate for the

transition of seismic was K0.80% per annum (Table 2).

The majority of transitional states for seismic lines was into

other anthropogenic features. Of these, the establishment of

vehicular tracks in 20% of the seismic lines after 35 years

indicated that these had become regularly travelled transpor-

tation routes (Fig. 2). The transition of seismic lines into

vehicle tracked roads expanded greatly from 22 to 25 years

then plateaued thereafter. Conversion of seismic lines to roads

and other industrial developments was relatively slow but

constant. After 35 years, 3.0 and 2.3% of the seismic lines were

roads and other industrial developments, respectively. Annual

median rates for the development into tracked access, roads,

and other industrial developments were 0.32, 0.053, and

0.035% per annum, respectively (Table 2).

3.2. Comparisons amongst forest types

Recovery varied greatly amongst forest types. Most

notably, we observed no recovery in lowland black

Table 2

Percent change per annum for the loss of seismic lines, recovery to woody vegetation (50% cover), and the transition rates of seismic into tracked access, roads,

and other industrial features

Feature Median 25% Quartile 75% Quartile Minimum Maximum

Loss of seismic K0.80 K1.40 K0.44 K5.25 0.00

Recovery toRwoody vegetation 0.21 0.017 0.37 0.017 0.75

Transition to tracked access 0.32 0.040 0.96 0.027 3.35

Transition to roads 0.053 0.046 0.11 0.040 0.21

Transition to other industrial features 0.035 0.021 0.054 0.018 0.24


spruce. Out of 228 seismic lines, no lines recovered to

the minimum criteria of at least 13% woody vegetation

(relative to surrounding forest) to be included in the 25%

category of recovery. At 50% recovery, there was no

statistical difference in the temporal patterns of recovery

for seismic lines in aspen and white spruce forests

(Fig. 3a; PZ0.11). After 35 years, 10.4 and 9.6% of

seismic lines in aspen and white spruce forests,

respectively, had 50% woody revegetation.

Time (years)

0 5 10 15 20 25 30 35

Pro

port

ion

0.00

0.02

0.04

0.06

0.08

0.10

0.12(a)

(

Time (years)

0 5 10 15 20 25 30 35

Pro

port

ion

0.00

0.05

0.10

0.15

0.20

0.25

0.30(c)

(

Fig. 3. a–d Proportion of seismic lines transformed within aspen (C), white spruc

Symbols represent inflection points on the graphs rather than the temporal availabil

50% woody vegetation cover. Only aspen and white spruce forests are shown sin

proportion of seismic remaining untransformed for each forest type. For the sake

transformed to vehicle access as evidenced by tracks; (d) is the proportion of sei

border have data that extends greater than 35 years while lines stopping before 3

There was no statistical difference for the overall

transition curves for seismic lines in white spruce and

aspen forests (Fig. 3b; PZ0.27). However, there were

significant statistical differences between lowland black

spruce and the other forest types (PO0.03). The transition

rate within lowland black spruce was less than either aspen

or white spruce. After 35 years, lowland black spruce

retained 70% of the original seismic lines while aspen and

white spruce retained 60 and 62%, respectively. The curve

Time (years)

0 5 10 15 20 25 30 35

Pro

port

ion

0.00

0.01

0.02

0.03

0.04

0.05

0.06d)

Time (years)

0 5 10 15 20 25 30 35

Pro

port

ion

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00b)

e (B), and lowland black spruce (&) forests with time after establishment.

ity of data. Bars represent standard error: (a) is the proportion of recovery to

ce we found no examples of recovery in lowland black spruce forests; (b)

of clarity, error bars were not included; (c) is the proportion of seismic line

smic transformed to gravel or paved roads. Lines that extend to right-side

5 years have no data beyond that point.


for lowland black spruce diverged from the other two forest

types after 15 years.

There were sufficient sample sizes to compare transition

to tracked access and roads amongst forest types. The

transition of seismic lines to tracked vehicular access did not

significantly differ amongst forest types for the entire 35

year period (PZ0.29; Fig. 3c). However, the amount of

tracked access at the end of 35 years was different. The

amount of tracked access was 24, 21, and 16% for lowland

black spruce, white spruce, and aspen, respectively.

Standard error bars indicated that these differences were

significant (Fig. 3c; P!0.05). Despite the relatively small

sample sizes (NZ20), the number of seismic lines that

developed into roads did exhibit some differences amongst

forest types (Fig. 3d). Overall temporal trends were not

significantly different between aspen and white spruce

forests (PZ0.25) while both were significantly greater than

lowland black spruce (P!0.03). There were insufficient

samples to compare the transition to other industrial features

amongst forest types.

3.3. Levels of recovery

In both aspen and white spruce forests, proportion of

seismic recovery decreased as the cover criteria was

increased (Fig. 4a,b). Recovery trajectories for 50 and

75% cover in aspen forests were statistically similar (PZ0.37) while 25 and 100% were respectively, greater (P!0.05) and lesser (P!0.05) than 50 and 75% (Fig. 4a).

Seismic lines cut through white spruce forests exhibited a

similar pattern. There was no significant difference between

the 50 and 75% cover trajectories (PZ0.52) while 25 and

100% were respectively, greater (P!0.05) and lesser (P!0.05) than 50 and 75% (Fig. 4b).

Fig. 4. Proportion of recovered seismic lines with time since establishment in as

presented; 25% (C), 50% (B), 75% (&), and 100% (,) cover to woody veg

temporal availability of data. Bars represent standard error.

4. Discussion

The results of this study suggest that wide seismic lines

cut into forested boreal landscapes become persistent

features. After 35 years, more than 60% of the seismic

lines were still present. Recovery to woody vegetation

occurred in a small percentage (w8%) with the remainder

retaining the low herbaceous understory associated with the

original seismic line or developing into a more permanent

anthropogenic feature such as roads. Even without the

transition to roads, the time to a near complete recovery (!5% remaining) of a cohort of seismic lines would be

approximately 112 years based on median recovery rates

(Table 2).

The historical development of the northeast boreal in

Alberta has produced at least one significant pulse of seismic

transition into another feature primarily for vehicle traffic.

The timing and magnitude of the seismic transition coincides

with a pulse of tracked access development from 22 to 25

years. For the first 22 years, median transition rates for

seismic into tracked access was 0.479% per annum. During

the pulse of development, the rate increased to 1.44% per

annum, then declined to 0.027% per annum for the 10 years

afterwards. Since most (O70%) of the seismic lines in this

study were cut from 1970 to 1977, this corresponds to an

activity period from approximately 1992 to 2003. This

pattern suggests an increased industrial development that

was, in part, facilitated by an increased use of seismic lines as

transportation corridors. After the network was developed to

service the pulse of growth, there was little further transition

of seismic lines into transportation corridors.

We offer two potential explanations for the pulse of

seismic transition into tracked access. In Alberta, the 1990s

to the early 2000s were an unprecedented period of

pen (a) and white spruce (b) forests. Four different levels of recovery are

etation. Symbols represent inflection points on the graphs rather than the


industrial development in northeastern Alberta. The total

volume of timber harvested in Alberta doubled from

approximately 9 million m3 in 1990 to 20 million m3 in

1999 as a consequence of new allocations of deciduous and

mixedwood forests (Stelfox and Wynes, 1999). Within our

study area, the world’s largest single line pulp mill was built

in 1992 and granted a tenure of 6 million ha (Alberta Pacific

Forest Industries, 2001). The land tenure for this single mill

represents 88% of the study area. The increased timber

activity required access into forested areas for activities

such as research, inventory, harvest, and extraction. Access

continued after harvest for the monitoring of regeneration

and silvicultural treatments.

Aside from forestry, the oil and gas sectors greatly

increased in the mid 1990s. This was largely spurred by the

recovery and increase in oil and natural gas prices. From

1990 to 2000, the cumulative number of oil and gas wells

has nearly doubled from approximately 88,000 to 160,000

wells (Canadian Association of Petroleum Producers,

2000). A similar increase in the price of oil and changes

to oil and gas exploration license structure gave rise to a

pulse of seismic activity in the 1970s.

Lastly, improvements to off-road vehicles has made

travel on seismic lines much easier. In particular, the

increased use and availability of four-wheel drive trucks,

sports utility vehicles, and all terrain vehicles has facilitated

the transition of seismic lines into a transportation network.

Like elsewhere in North America, the use of both four wheel

drive trucks and off-road vehicles by industry and

recreational users has greatly increased. From 1990 to

2001, purchases of new trucks in Alberta increased 84%

(estimates derived from Statistics Canada, 1990, 2003). In

contrast, the population increased by 17% over the same

period (Statistics Canada, 2004). Over a period of 1997–

2001, the sales of smaller, all terrain vehicles tripled

(reported in Lai, 2004).

The large proportion of recleared seismic lines reflects

their high re-use. Oil and gas exploration and extraction

agreements encourage the development of new lines and re-

use of existing lines. Since 1976, license (exploration) and

lease (extraction) agreements have specifically applied to

mineral rights at a particular depth and above. They do not

apply to layers below the explored or extraction layer. These

changes were originally brought in to spur drilling and

prevent ‘sterilization’ of the deeper deposits by licenses and

leases applied to shallower layers. These changes had their

desired effect in that much of the seismic lines used in this

study and mapped in Phase III maps were the result of

increased exploration activity. A point worth noting is that

when seismic lines are re-used they are generally cleared

back to the original width.

Currently, licenses require the establishment of explora-

tory drilling within four years or the tenure reverts back to

the government (Alberta Energy Utilities Board, 2002). A

combination of changes in market forces and prices,

strategic company positioning, bet-hedging strategies, and

unproductive wells cause many of the licenses to revert back

to the government. One estimate suggests that 75% of

licenses have reverted back to the government (Alberta

Energy Utilities Board, 2002). If a license reverts back to

the government, they can turnaround and resell the license.

Changes in markets and prices, differences in corporate

strategies, and financial resources may prompt other

companies to purchase the license and attempt to develop

it. Also, the licenses represent a commodity. Companies that

hold undeveloped licenses maintain an asset. The relatively

frequent transfer of licenses adds to the likelihood that

seismic lines will be recleared. Companies may attempt to

re-explore part or the whole seismic grid to more favourably

place well sites. They may also use seismic lines to access

other leases they hold. Furthermore, seismic data is

proprietary information and companies may not divulge

previous data to new license holders. This may necessitate

new, additional seismic programs. The overall result is that

the recovery of seismic lines is often determined by spatially

and temporally dynamic forces that are neither predictable

nor consistently applied.

This study was not designed to determine specific

mechanisms for the lack of recovery, these have been the

subject of a number of other studies. However, the results of

these studies can provide insights in the patterns exhibited in

ours. Recovery back to aspen forests is hampered by the

apical dominance from surrounding, taller, clones in the

adjacent forest. In order to overcome this dominance,

elevated light levels with the resultant increases in soil

temperature are required to stimulate suckering of aspen

roots within the seismic lines. Light levels are greater on the

edges of seismic lines resulting in greater aspen suckering

than in the adjacent, closed forest (MacFarlane, 2003).

However, sucker densities were less than in open clearcuts.

This maybe due to the shading created within 5–8 m wide

seismic lines for at least part of the day. Light intensities of

even half of full sunlight are sufficient to reduce the

suckering to 10% of full sunlight. Temperatures greater than

15 8C are required for the initiation of suckering (Maini,

1966; Maini and Horton, 1966). Groot et al. (1997) found

the % radiation on 9 m strip cuts similar to seismic lines

varied from 40% of open areas at 2 m from the southern

forested edge to 70% on the northern edge. The mean daily

maximum taken between July 20 and August 2, in strips cuts

was 14.6 and 13.8 8C respectively (northern Ontario,

Canada, 47843 0N, 83811 0W). As a result, aspen stem

densities within 9 m strip cuts was 66% less than in

clearcuts but the height of stems was similar to those in

clearcuts (Groot et al., 1997). Development of fine roots that

are critical for the uptake of water and soil nutrients was

reduced in temperatures lower than 6 8C resulting in the

impairment of growth and productivity (Landhausser and

Lieffers, 1998; Wan et al., 1999).

Unlike aspen, white spruce regenerates from seed. Revel

et al. (1984) found that establishment of saplings in 23 of 35

test plots exceeded forestry stocking standards but that


growth was slow with most saplings less than 2 m tall after

10 or more years. Densities of saplings were negatively

correlated to the presence of grasses and low herbaceous

understory. These were argued to be competitors. The

exception was at the intersection of seismic lines. They

suggested that the larger cleared area allowed a greater total

amount of sunlight throughout the day. This facilitated

higher growth rates in saplings. Other instances of poor

stocking and overall lower vegetation cover were attributed

to a combination of physical damage by the tires or tracks of

vehicles, soil compaction, water channelization and the

subsequent erosion of soils on and adjacent to the line.

For lowland black spruce, all seismic lines were clearly

visible after 35 years and longer in some of the older

samples. A greater number of samples may have yielded

some natural recovery but it would have been at a rate less

than 0.4% (!1/228) over 35 years. A review of the

literature yielded no studies on the mechanisms that prevent

regeneration of black spruce on seismic lines. We can only

draw on findings from other similar ecosystems and

speculate on the mechanisms from casual observations.

One possible mechanism is the loss of hummocks on cleared

seismic lines. The use of bulldozers and other clearing

equipment removes the vegetation but more importantly it

removes the hummocks and flattens the terrain. The loss of

the hummocks greatly reduces the number of sites for

seedling establishment of black spruce. Furthermore,

flattening of the terrain and the compaction created by

tracks alters the local hydrology and converts what had been

a bog to a wetter poor fen dominated by sedges. Vehicle

tracks often fill with water year round (personal obser-

vation). A similar transition from a shrub-dominated

community to a sedge community was found on seismic

lines subject to winter traffic in moist tundra and dryas

terraces in Arctic Wildlife Refuge in northeastern Alaska

(Felix et al., 1992). They found very little resistance to

vehicular traffic and that after 4–5 years there was very little

recovery of the vegetation. Like our study, they found a

conversion from a drier woody stem community to a wetter

sedge-dominated community.

4.1. Future management directions

Barring a wholesale decrease in the industrial develop-

ment of the western Boreal Plains, it seems the recovery of

seismic lines will be best facilitated by a multifaceted

approach involving some seismic line closure and natural or

recovery through silviculture, and replacement with no or

very narrow lines. The results of this study offer some

insights into these management directions. Furthermore, the

study points out the critical areas for research as we begin to

trade-off different elements such as the pre-emptive

development of a roaded transportation network versus its

ad hoc development through the use of existing seismic

lines.

1. Closure and recovery of seismic lines—After a period of

non-use, seismic lines should be actively closed to

further use. We can take advantage of the period of

inactivity to identify lines with a low probability of re-

use and target their closure to further access. Access

closure can be done through a number of methods such

as laying trees across access points, gates, and soil and

debris berms. If seismic lines become active as

transportation routes then those segments maybe further

developed into the road network. In order to facilitate all

these activities, there needs to be an active tracking and

reclamation goals for seismic lines.

2. Application of silvicultural treatments—Given the

large area of open seismic, ground preparation and

planting of trees is likely to be an expensive

proposition and may only be feasible in cases of

critical wildlife habitat for endangered species such as

woodland caribou or other areas where the control of

access is critical. One unexplored possibility is the

rescheduling of timber harvest into areas adjacent of

seismic lines. Silviculture can be done at the same time

as the harvest areas. For lines through aspen forests, it

would alleviate the problems with apical dominance

while producing more favourable physical conditions

for clonal regeneration. For lines through spruce

forests, seismic lines could be replanted along with

the rest of the cutblock.

3. Development of a road network—The utility of this

strategy depends upon whether a road network at

lower linear density than the existing seismic lines

has less ecological impact than the ad hoc use of

seismic lines. If seismic lines fall into a consistent

usage pattern then they may be further developed into

roads. However, it is unlikely that this pattern is very

efficient. Most seismic lines were cut along ordinal or

subordinal compass directions. Tracked access winds

its way along several linear segments usually

avoiding wet or steep terrain. Along with the road

network, there should be a harmonizing of all linear

corridors including pipelines, electrical transmission

lines, and railways. A planned road network would

have to efficiently replace the current ad hoc network

patterns while facilitating orderly development of a

region.

4. Re-use of seismic lines—The re-use of seismic lines

prevents the cutting of new lines, hence, should be

encouraged. Nonetheless, the switch to minimal or

very narrow seismic lines will mean that even re-used

wide seismic lines will eventually have to be closed.

A priority list should be established for their closing

and recovery. We suggest that the currently recovered

lines, i.e. those supporting woody vegetation, would

be the easiest to close. Then lines not being used in a

current license or lease would be next. As lines are

closed, they are not reopened with wide clearances. In

this manner, the current backlog of wide seismic is


constantly ‘ratcheted’ to a recovered state or to

minimal or very narrow seismic.

5. Activity in lowland black spruce—Given that we

found no recovery in lowland black spruce, we would

question whether it is appropriate to continue a

practice of using seismic lines that leave any footprint

in lowland black spruce and perhaps all peatlands.

Minimal footprint methods such as heliportable should

be used in all peatlands. Furthermore, lowland black

spruce may require remediation to facilitate recovery.

The large backlog of seismic lines in peatlands would

suggest that remediation methods would have to be

cost effective and work in concert with natural

patterns of vegetation recovery. Lowland black spruce

and perhaps all peatlands should receive priority in the

phasing out of wide seismic lines. Even the

disturbance created by narrower but more frequently

spaced lines for three-dimensional seismic exploration

needs to be carefully evaluated.

5. Conclusions

The current backlog of wide (5–8 m) seismic lines is a

persistent feature on the boreal landscape of Alberta. Lines

cut into aspen and white spruce forests recover at relatively

slow rates to a cover of woody vegetation. Lines cut into

lowland black spruce have yet to significantly recover to

woody vegetation even after 35 years. In part, the high level

of re-use and conversion to tracked access prevents many

lines from recovering. To avoid compounding the impact of

the wide seismic lines with other new anthropogenic

developments, i.e. cumulative effects, a concerted effort

should be made to recover or transition the old seismic lines

to minimal or very narrow seismic. This is probably best

expedited through a mixed strategy utilizing: closing and

recovery of wide seismic no longer used for exploration,

remediation of seismic lines in critical habitats, and

development of an efficient road and linear corridor

network. Given the lack of recovery in lowland black

spruce, these areas should receive priority in the recovery of

seismic lines and application of minimal footprint seismic

lines.

Acknowledgements

We would like to thank C. Gray, A. Krowski, and M.

Lankau for technical support on this project. We acknowl-

edge a critical review of this paper by J. Doubt and the

comments from the editor and four anonymous reviewers.

All have greatly improved the manuscript. This research

was supported by Natural Sciences and Engineering and

Research Council-Alberta Chamber of Resources Integrated

Landscape Management Chair to S. Boutin.

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