CLBMON-09 Kinbasket Reservoir monitoring of revegetation efforts and vegetation composition analysis: year 5 – 2015

Author: V.C. Hawkes, M.T. Miller

Monitoring of vegetation enhancement projects undertaken after 2011 including (1) wood debris removal and log boom exclosure trials at Canoe Reach; (2) sedge planting trials at Km 88, Bush Arm; and (3) mound and windrow construction trials at Bush Arm Causeway, Bush Arm.

At most sites, vegetation on driftwood-covered shorelines responded positively to the removal of debris within two months of clearing, with short-term increases in both total cover and species richness observed relative to untreated controls. During the subsequent inundation cycle some sites were buried again by debris and, as a result, plant cover and richness had declined again by 2015. However, at VP-N, a previously highly impacted, remnant wetland site, the log boom exclosure was successful at preventing debris from re-encroaching. Here, the native plant community continued to show rapid recovery between 2014 and 2015. A floristic inventory of VP-N in July 2015, one year after debris removal, yielded 62 established and regenerating vascular plant species—nearly half the cumulative total of 128 species recorded to date for the entire Canoe Reach drawdown zone. It is thus apparent that targeted wood debris removal has the potential to be an effective management technique for enhancing vegetation growth in the drawdown zone, particularly if it is supplemented by placement of protective log boom exclosures (or other measures to protect the shoreline) in areas with active wood debris drifting.

At Km 88, the survival of sedge plugs two years after planting ranged from 43 to 100 per cent, with an overall survival of 74 per cent. The estimated establishment rate of approximately 17,000 sedge plants per hectare thus far appears to be exceeding the targeted objective, as proposed in the planting prescription, of between 5,000 and 15,000 plants per hectare. The high survival rate to date can likely be ascribed to a combination of site selection (Km 88 was specifically chosen for its ecological suitability as a receptor site) and the utilization of older (2-yr old versus 1-yr old), more robust nursery stock.

While getting new sedges to establish is an important step in expanding the vegetation cover at Km 88, more time will be needed to determine if these introductions have the ability on their own to alter the successional trajectory of the sites toward something more resembling a mature KS (Kellogg’s Sedge) community type. Nevertheless, localized increases in sedge cover may already be providing ancillary wildlife services; we saw indications in 2015 that local waterfowl populations (most likely Canada geese) have begun to utilize the sedge plantings as a spring food source.

For the mound and windrow trials, pre-impact baseline data on vegetation and substrate conditions were collected at five proposed construction sites in 2015: Bush Arm Causeway (north and south), Chatter Creek, Goodfellow Creek, and Hope Creek. The five sites differed with respect both to substrate composition and the plant species currently supported, differences that will need to be factored in when eventually assessing the effectiveness of physical works. A total of seven mounds were constructed. In addition, three wood-choked ponds at the north Causeway site were cleaned of debris. Three other sites (Chatter Creek, Goodfellow Creek, and Hope Creek) were not treated in 2015 due to access and time constraints. The efficacy of the mounds and windrows in promoting vegetation establishment and increasing local diversity will be assessed over time, commencing in 2017 after at least one growing season has passed.

Preliminary results suggest that adjusting the timing and reducing the duration and depth of inundation could translate into increased success for future revegetation attempts.

At most sites, vegetation on driftwood-covered shorelines responded positively to the removal of debris within two months of clearing, with short-term increases in both total cover and species richness observed relative to untreated controls. During the subsequent inundation cycle some sites were buried again by debris and, as a result, plant cover and richness had declined again by 2015. However, at VP-N, a previously highly impacted, remnant wetland site, the log boom exclosure was successful at preventing debris from re-encroaching. Here, the native plant community continued to show rapid recovery between 2014 and 2015. A floristic inventory of VP-N in July 2015, one year after debris removal, yielded 62 established and regenerating vascular plant species—nearly half the cumulative total of 128 species recorded to date for the entire Canoe Reach drawdown zone. It is thus apparent that targeted wood debris removal has the potential to be an effective management technique for enhancing vegetation growth in the drawdown zone, particularly if it is supplemented by placement of protective log boom exclosures (or other measures to protect the shoreline) in areas with active wood debris drifting.

At Km 88, the survival of sedge plugs two years after planting ranged from 43 to 100 per cent, with an overall survival of 74 per cent. The estimated establishment rate of approximately 17,000 sedge plants per hectare thus far appears to be exceeding the targeted objective, as proposed in the planting prescription, of between 5,000 and 15,000 plants per hectare. The high survival rate to date can likely be ascribed to a combination of site selection (Km 88 was specifically chosen for its ecological suitability as a receptor site) and the utilization of older (2-yr old versus 1-yr old), more robust nursery stock.

While getting new sedges to establish is an important step in expanding the vegetation cover at Km 88, more time will be needed to determine if these introductions have the ability on their own to alter the successional trajectory of the sites toward something more resembling a mature KS (Kellogg’s Sedge) community type. Nevertheless, localized increases in sedge cover may already be providing ancillary wildlife services; we saw indications in 2015 that local waterfowl populations (most likely Canada geese) have begun to utilize the sedge plantings as a spring food source.

For the mound and windrow trials, pre-impact baseline data on vegetation and substrate conditions were collected at five proposed construction sites in 2015: Bush Arm Causeway (north and south), Chatter Creek, Goodfellow Creek, and Hope Creek. The five sites differed with respect both to substrate composition and the plant species currently supported, differences that will need to be factored in when eventually assessing the effectiveness of physical works. A total of seven mounds were constructed. In addition, three wood-choked ponds at the north Causeway site were cleaned of debris. Three other sites (Chatter Creek, Goodfellow Creek, and Hope Creek) were not treated in 2015 due to access and time constraints. The efficacy of the mounds and windrows in promoting vegetation establishment and increasing local diversity will be assessed over time, commencing in 2017 after at least one growing season has passed.

Preliminary results suggest that adjusting the timing and reducing the duration and depth of inundation could translate into increased success for future revegetation attempts.