Identifying Conifer Tree vs. Deciduous Shrub and Tree Regeneration Trajectories in a Space-for-Time Boreal Peatland Fire Chronosequence Using Multispectral Lidar

Abstract

Wildland fires and anthropogenic disturbances can cause changes in vegetation species composition and structure in boreal peatlands. These could potentially alter regeneration trajectories following severe fire or through cumulative impacts of climate-mediated drying, fire, and/or anthropogenic disturbance. We used lidar-derived point cloud metrics, and site-specific locational attributes to assess trajectories of post-disturbance vegetation regeneration in boreal peatlands south of Fort McMurray, Alberta, Canada using a space-for-time-chronosequence. The objectives were to (a) develop methods to identify conifer trees vs. deciduous shrubs and trees using multi-spectral lidar data, (b) quantify the proportional coverage of shrubs and trees to determine environmental conditions driving shrub regeneration, and (c) determine the spatial variations in shrub and tree heights as an indicator of cumulative growth since the fire. The results show that the use of lidar-derived structural metrics predicted areas of deciduous shrub establishment (92% accuracy) and classification of deciduous and conifer trees (71% accuracy). Burned bogs and fens were more prone to shrub regeneration up to and including 38 years after the fire. The transition from deciduous to conifer trees occurred approximately 30 years post-fire. These results improve the understanding of environmental conditions that are sensitive to disturbance and impacts of disturbance on northern peatlands within a changing climate.

Examining Drivers of Post-Fire Seismic Line Ecotone Regeneration in a Boreal Peatland Environment

“…and Alnus spp. growing on seismic lines and intersections with well pads [37,38]. Vegetation species and canopy heights were determined/measured within 202 × 1 m 2 plots, collected at 4 m intervals at the centre of seismic lines.…”

“…Vegetation species and canopy heights were determined/measured within 202 × 1 m 2 plots, collected at 4 m intervals at the centre of seismic lines. Field measurements were used in a previous study [38] to validate lidar-based vegetation structure.…”

“…A total of 155 peatlands (sample size, n = 76 bogs, and n = 79 fens) were identified. The variations in vegetation heights (across cells, described below) and classification into deciduous shrubs and conifer or deciduous trees [38] within peatlands were examined. Within classified peatland shapes, peatland forms were also determined and classified into open, shrubby, and treed peatlands based on assumed shrub (up to 3 m) and tree (>3 m) heights.…”