In peatlands, micro-topography strongly affects understory plant communities. Disturbance can result in a loss of micro-topographic variation, primarily through the loss of hummocks. To address this, mounding treatments can be used to restore micro-topography. We examined the effects of mounding on the understory vegetation on seismic lines in wooded fens. Seismic lines are deforested linear corridors (~3-8 m wide), created for oil and gas exploration. Our objectives were to compare the recovery of understory communities on unmounded and mounded seismic lines and determine how recovery varies with micro-topographic position. Recovery was evident in the unmounded seismic lines, with higher shrub and total understory cover at the ‘tops’ of the small, natural hummocks than at lower micro-topographic positions —much like the trends in adjacent treed fens. In contrast, mounding treatments that artificially created hummocks on seismic lines significantly changed understory communities. Mounded seismic lines had higher forb cover, much lower bryophyte cover, less variation along the micro-topographic gradient, and community composition less similar to the reference sites than were unmounded seismic lines, due to higher abundance of marsh-associated species. Our results suggest mounding narrow seismic lines can be detrimental to the recovery of the understory communities in treed peatlands.

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Treed peatlands are dominated by bryophytes, particularly Sphagnum spp., which create the characteristic hummock-hollow microtopography. This, in turn, shapes the distribution of bryophyte communities. Disturbances can lead to a loss of this microtopographic variation, impacting the bryophyte community. Seismic lines are deforested linear disturbances (approximately 3-8 m wide) created during oil and gas exploration and very extensive in Alberta, Canada. Loss of microtopographic variation leads to slow tree recovery on seismic lines in treed peatlands. To facilitate tree establishment, mounding is being applied to restore the microtopography on seismic lines. We compared bryophyte communities on unmounded and mounded seismic lines (18 years after seismic line creation, 3 years after mounding), and in adjacent treed fens as the reference, to evaluate how recovery varies with microtopographic position (i.e., top of hummock, slope or side of the hummock, and level ground). We found that recovery on the unmounded seismic lines was underway 18 years after seismic lines were created, while mounding redisturbed the sites and thus set back recovery, at least in the short term (3 years post-mounding). In unmounded seismic lines, Sphagnum cover was similar to that of reference treatments at all microtopographic positions. In contrast, mounded seismic lines had lower Sphagnum cover and higher cover of true mosses (sans feather mosses) than reference and unmounded treatments. Overall, these results show mounding sets back the recovery of bryophyte communities-the very organisms responsible for the microtopographic variation we are trying to establish. Further monitoring is needed to understand how this changes over time.

Questions Edge influence on forest biodiversity is an important environmental effect associated with habitat fragmentation, but extrapolating the influence of edges across the broader landscape has been difficult, especially for situations where multiple edges exist in close proximity. We asked whether there were differences in edge effects between two types (3 m vs 8 m width) of low‐severity linear disturbance (seismic lines) and whether there were interactions of edge effects when seismic lines occur in dense networks; that is, do multiple narrow seismic lines have a stronger or weaker edge influence than a single narrow seismic line. Location Treed peatlands in northeastern Alberta, Canada. Methods Seismic lines are created during oil and gas exploration and are responsible for dissection of boreal forests in western Canada. We sampled vascular plants along transects perpendicular to seismic lines in moderate‐rich and poor treed fens. We used the “Randomization Test of Edge Influence” (RTEI) to calculate the magnitude and distance of edge effects and then compared these between narrower (3 m) versus wider (8 m) lines and between single narrow lines versus multiple narrow lines (parallel and ~50 m apart). Results In moderate‐rich fens, we found a positive edge influence on understorey diversity from both wide and narrow seismic lines. We also found a weakening edge interaction on diversity, that is, single narrow seismic lines had a stronger edge influence on diversity than did multiple narrow seismic lines. In treed poor fens, multiple narrow seismic lines had a negative edge effect on tree density, understorey abundance, richness, and composition. In addition, we found strengthening edge interactions in treed poor fens on tree density, graminoid cover, and understorey composition. Conclusions Even narrow linear disturbances, such as seismic lines, can have significant edge effects and these are exacerbated when lines occur in dense networks.