Quantifying habitat impacts of natural gas infrastructure to facilitate biodiversity offsetting

Abstract

Habitat degradation through anthropogenic development is a key driver of biodiversity loss. One way to compensate losses is "biodiversity offsetting" (wherein biodiversity impacted is "replaced" through restoration elsewhere). A challenge in implementing offsets, which has received scant attention in the literature, is the accurate determination of residual biodiversity losses. We explore this challenge for offsetting gas extraction in the Ustyurt Plateau, Uzbekistan. Our goal was to determine the landscape extent of habitat impacts, particularly how the footprint of "linear" infrastructure (i.e. roads, pipelines), often disregarded in compensation calculations, compares with "hub" infrastructure (i.e. extraction facilities). We measured vegetation cover and plant species richness using the line-intercept method, along transects running from infrastructure/control sites outward for 500 m, accounting for wind direction to identify dust deposition impacts. Findings from 24 transects were extrapolated to the broader plateau by mapping total landscape infrastructure network using GPS data and satellite imagery. Vegetation cover and species richness were significantly lower at development sites than controls. These differences disappeared within 25 m of the edge of the area physically occupied by infrastructure. The current habitat footprint of gas infrastructure is 220 ± 19 km(2) across the Ustyurt (total ∼ 100,000 km(2)), 37 ± 6% of which is linear infrastructure. Vegetation impacts diminish rapidly with increasing distance from infrastructure, and localized dust deposition does not conspicuously extend the disturbance footprint. Habitat losses from gas extraction infrastructure cover 0.2% of the study area, but this reflects directly eliminated vegetation only. Impacts upon fauna pose a more difficult determination, as these require accounting for behavioral and demographic responses to disturbance by elusive mammals, including threatened species. This study demonstrates that impacts of linear infrastructure in regions such as the Ustyurt should be accounted for not just with respect to development sites but also associated transportation and delivery routes.

Keywords: Compensation; Uzbekistan; ecological impact assessment; residual impact; semi-arid.

Figure 1

Geography of Central Asia, Uzbekistan, and the Ustyurt plateau. Circles on the detailed map are survey locations, with transects roughly equally distributed across the eight locations. Maps created using Garmin “BaseCamp”™ software.

Figure 2

Design of spine and rib transects: the main 500-m spine transect originates from the center of disturbance with 20-m rib transects bisecting it at set intervals: 25-m intervals between 0 and 100 m (where 0 m is the center of disturbance), 50-m intervals between 100 and 300 m, and 100-m intervals between 300 and 500 m, giving increased sampling effort closer to the disturbance. The line-intercept method was used to collect species richness and vegetation cover data along each rib. Secondary disturbances (i.e. small tracks) were also recorded.

Figure 3

Boxplots showing differences in vegetation responses at the 0-m “rib” transect of control and disturbed sites. Differences in both species richness (z = −6.2, P < 0.001) and cover (t = −4.7, P < 0.001) are significant.

Figure 4

Interaction plots for richness and cover with distance. Hollow points represent disturbed sites, solid points represent controls. Graphs produced using “Sciplot” with 95% confidence intervals displayed.

Figure 5

Mapping of spatial extent of gas infrastructure. (A) mapped using GPS data, where lines = roads, tracks, and pipelines, circles = settlements with gas infrastructure, triangles = known facilities used or created by the gas industry. Black lines = mapped using GPS data, gray lines = known infrastructure not mapped using GPS data; (B) linear infrastructure mapped using Google Earth (2012). White lines represent linear infrastructure – roads, railways, pipelines – associated with the oil and gas industry. Note that the large white region near the center of this figure corresponds to a dried-up saline lake.