Fig 15. A Principle Coordinate Analysis ordination showing the trajectory of vegetation changes over time in control, simulated 50% kill, simulated 100% kill, and salvage logged stands one year prior to treatment, one year post-treatment, five years post-treatment, and seven years post-treatment.
Results & Discussion Although vegetation communities in all treatments changed over time in the same direction, the level of disturbance impacted the extent of change (Fig 15). The salvage treatments had the largest change, although by 2016 the trajectory turned back and started to return in the direction from which they originated. The 100% kill had the next strongest change in community composition. The control and 50% kill treatments appeared to have changed in a similar direction and length, indicating that the 50% kill may not result in substantially different communities compared to the control. As higher severity disturbances have increased impacts to the environment, it makes sense that the vegetation would also change more under higher disturbance intensities.
Functional groups reacted differently among the treatment types. Graminoids were associated with salvage logging, while forbs were not common in this treatment type. Bryophytes were associated with treatment sites that left a standing canopy, as well as shrubs to a lesser extent (Fig 16). Looking closer at each individual group (Fig 17), as the level of disturbance increased (50% to 100% to salvage), graminoid cover increased. Graminoids are often the first to colonize disturbed areas, so they may have increased in cover as increasing amounts of resources became available due to increased light reaching the forest floor in the 100% kill and salvage treatments, and possibly increased nutrients. Canopy disturbance (50% and 100% kill) resulted in a slight increase in shrub cover, while salvage logging decreased the amount of cover. This may have been due to increases in resource availability, but the salvage logging process may have damaged the shrubs growing in those stands. The increase and then decrease of forb cover in the control treatment may have been due to annual variation. This trend was also seen in the 100% kill treatment, while 50% kill had no changes in cover quantity. Salvage logging resulted in an immediate reduction of forb cover, most likely due to the damage of forbs during the the clear cutting process. Bryophyte cover increased then decreased in the control and 50% kill treatments, most likely due to annual variations. Bryophyte cover decreased immediately in the salvage treatment, followed by a recovery in 2016. It seems that as increased light levels reached the forest floor, bryophyte cover decreased. This could have been due to damage during the salvage logging process, or a decrease in shade, which often prevents the desiccation of bryophytes.
Fig 16. A Principle Coordinate Analysis ordination showing the trajectory of functional vegetation groups (shrubs, forbs, bryophytes, and graminoids) over time in control, simulated 50% kill, simulated 100% kill, and salvage logged stands from one year prior to treatment until seven years post-treatment.
Fig 17. Percent cover for a) graminoids, b)shrubs, c) forbs, and d) bryophtes by treatment and year. Lower case letters represented significant differences between years within a treatment and upper case letters represented significant differences between treatments within each year.
Fig 18. A Principle Coordinate Analysis ordination showing the trajectory of changes for individual species over time in control, simulated 50% kill, simulated 100% kill, and salvage logged stands one year prior to treatment, one year post-treatment, five years post-treatment, and seven years post-treatment.
Dominant species for each of these functional groups (Fig 18) were clumped in the same vicinity as where the functional group vectors were found, and they are all commonly found species found in boreal forests in Alberta. The dominant grass species were Calamagrostis spp. (Caspp) and Leymus innovatus (LEIN). The dominant shrub species were Alnus crispa (ALCR) and Vaccinium vitis-idaea (VAVI). The dominant bryophytes were feathermosses that are typically found under lodgepole pine overstories, and included Ptilium crista-castrensis (PTCR), Pleurozium schreberi (PLSC), and Hylocomium splendens (HYSP). There was slightly more variety in terms of dominant forbs, and those included Aralia nudicaulis (ARNU), Cornus Canadensis (COCA), Linnaea borealis (LIBO), and Lycopodium annotinum (LYAN). This indicates that although the trajectory of vegetation communities may be shifting in the treated stands, invasive species do not seem to be in these communities, and native species are still dominating the understory.