Completion Form

2020

The project was designed to quantitatively assess the benefits of the following variables in post-fire restoration planting protocols for aspen: site selection, addition of biochar, nursery pot size, the use of coarse woody debris, and exclosures to minimize ungulate herbivory.

Task 1: Seedling production. Aspen seedlings were produced in the Harrington Forestry Research Center in Mora, New Mexico.  This facility has successfully produced many aspen seedlings in recent years, and has experience using aspen seedlings for reclamation of mined lands.  Aspen seedlings were grown in either D16 or D40 pots (see below) and were induced to set bud early in the season to maximize root:shoot ratios, which has been shown to increase seedling success. Seeds from a mixture of maternal trees in Utah and Idaho were used to create a seed mixture which was sown in early May 2018 for planting in fall 2018, although planting was delayed until late summer 2019 (see below).

Task 2: Site selection.  Based on our previous work with aspen seedlings, we used a combination of GIS, early summer imagery, and site visits to choose five sites in the Brian Head fire footprint which were likely to retain soil moisture from winter snowmelt into the summer months. Sites with obvious extensive pocket gopher activity were avoided.  We chose three sites on private land within the Brian Head fire footprint.  Three sites had undergone salvage logging near the town of Brian Head and two sites were unlogged and located on the National Forest near Brian Head:
Salvage logged sites:
	Salvage site #1: N. 37.710296 W. -112.840533, 2901m
	Salvage site #2: N. 37.716507 W. -112.829559, 2394m
	Salvage site #3: N. 37.715028 W. -112.829306, 2952m
Unlogged sites: 
        Unlogged site #4: N. 37.69320 W. -112.76354, el. 2988m
        Unlogged site #5: N. 37.70377 W. -112.75915, el.3115m

Task 3: Exclosure construction and site preparation. At each of the five sites, we hired a Utah Conservation Corps crew to construct a 30x30m exclosure, 8' tall, using Tenax elk fencing.  At sites #1-3, we used metal corner posts and 10' tposts at 8' spacing.  At sites #5 and 6, fencing with t-posts was not approved by the USFS because archaeological clearance could not be obtained in time for construction.  Exclosure with Tenax fencing around trees was attempted in the summer 2018 but proved to be too unstable and risky with burned/fragile snags by spring 2019, so those sites were abandoned and the fencing material removed.  Exclosures on sites #1-3 were constructed during the summer 2018.  Site preparation included spot treatment with glyphosate and hand weeding to reduce competing regenerating vegetation.
Sites #1-3 were divided into plots as shown in Figures 1-3.  Plots were arranged to minimize adjacent plot types and spread plot types across the sites.  For "logs" sites, charred logs were moved from onsite into the plots (Figure 4).

Task 4: Seedling planting. Seedlings were scheduled to be planted in October 2018, but an unusual early snowfall prevented access.  Instead, the nursery held the seedlings through spring 2019 in a dark enclosure to delay budburst, and the seedlings were top-pruned and allowed to re-sprout prior to planting in late July 2019 to maximize root:shoot ratios.  For "biochar" sites, approximately 1/4 cup of biochar was added into the planting hole at the time of planting.  For "pot size" plots, trees in differing sized pots (D16 or D40; 16 and 40 cc, respectively) were planted in an alternating pattern within plots in sites #2 and 3 (Figure 2).  Because planting aspen seedlings for restoration is uncommon, it is unknown whether larger root systems (D40) might be beneficial to seedling survival, even though these larger pots might be less efficient operationally for planting.  Control plots had no treatment although any large logs on these plots were removed. A newly planted plot is depicted in Figure 5.  In all, 1120 aspen seedlings were planted in sites #1-3 in late July 2019.
       Additionally, 400 ponderosa pine (Pinus ponderosa) seedlings in SC10 pots, remaining from a similar study on Cedar Mountain, were planted in an exclosure adjacent to site #2 in late July 2019. These seedlings were also grown at the Harrington Forestry Research Center. This was an opportunistic addition to the project conducted in collaboration with Tom Kolb and Aalap Dixit from Northern Arizona University. The elevation of the planting sites is near the high end of the current distribution of ponderosa pine across its range, including southern Utah.  However, as climates shift to a hotter and drier regime in western landscape, ponderosa pine may be expected to move into higher elevations, and may be a good candidate for "assisted migration".  Like aspen, ponderosa pine is a fire-adapted species and pulses of natural regeneration frequently occur following fires. 
       Vexar tubing was not used to protect any of the planted seedlings, as originally planned, because of the heavy snow loads observed in the winter of 2018-19.  This snow load damaged the Tenax fencing on exclosures, and we were concerned that the Vexar tubing would damage seedlings during the winter. Planted aspen seedlings were marked with large colored paper clips (with different colors denoting plot type or pot size) to distinguish planted trees from subsequent suckers emerging from aspen roots extending from adjacent areas.  Soil moisture from monsoonal rains at the time of planting was high enough that additional irrigation was not necessary.  However, the monsoonal moisture did not persist, and seedlings were irrigated in mid-August 2019.  The City of Brian Head provided a water truck and volunteer driver for this irrigation. 
	Seedlings left over after planting were donated to Brian Head residents.  Contact information was collected from these residents, and a follow-up questionnaire about seedling survival will be administered at the end of the 2020 growing season.

The purpose of this pilot project was to determine whether nursery-grown aspen seedlings could be established by planting in a recent fire footprint, and whether planting seedlings near logs or with the addition of biochar would help retain soil moisture and improve seedling survival.  These are important questions because aspen stands in Utah are experiencing dramatic declines in many areas, and because fire footprints may present an opportunity to restore these forests.  Very little is known at this point about the utility of nursery-grown aspen seedlings in post-fire restoration efforts, but this could be a way to increase genetic diversity, bring in drought-adapted stock, and restore aspen to areas where it has been lost due to conifer encroachment.  
       As of June 2020, the aspen seedlings planted in three sites in the Brian Head fire footprint had survival rates ranging from 65% to 84%.  Survival was lowest in plots where seedlings were planted adjacent to logs.  This result was unexpected since logs should increase retention of soil moisture, and soil moisture was expected to be a significant source of mortality.  Interestingly, the high mortality among seedlings planted near logs was largely associated with above-ground small rodent herbivory in sites #1 and 3, as evidenced by scat piles under logs and gnawing marks on stems (Figure 6).  The logs likely provided predation shelter for the rodents.  The effect was most pronounced in site #1, where mortality rates were 70% to 81% in plots with logs, but 18% to 23% in plots without logs.  High mortality rates were coincident with signs of rodent damage (Tables 1-3).  In site #2, little evidence of rodent herbivory was present on plots with logs, and mortality rates in those plots was lower (as expected) than mortality rates in plots without logs.  The addition of biochar to planting holes had little effect on seedling survival rates (Table 4).  The size of the planting pots (D16 vs D40) also had no effect on seedling survival rates (Table 4).  
       Surviving aspen seedlings were generally in good condition as of June 2020.  If these seedlings survive another year they would be expected to develop more extensive root systems, and should begin to send up suckers of their own as they become established.  At that point, their probability of survival through climate fluctuations and even subsequent low to medium severity fire should be quite good. They will remain vulnerable to rodent herbivory and (when exclosures are removed) ungulate herbivory for the next few years. 
       Another surprise was the high survival rate of ponderosa pine seedlings at this high-altitude site. We found that first-year survival rates were approximately 90% for these seedlings, although seedlings planted from the same nursery stock on Cedar Mountain (~2800m, ~45km SSW) experienced near 100% mortality due to drought and rodent damage in the same year.  This finding suggests that 'assisted migration' of ponderosa pine seedlings sourced from lower elevations may be a viable strategy for post-fire forest restoration at higher altitudes, given the anticipated impact of climate change (tending toward hotter, drier conditions).  In both aspen and ponderosa pine, however, longer-term survival data will be important to obtain.

Overall, seedling survival rates observed in our plots during the first year were high enough to warrant pilot studies in larger areas.  However, our findings indicate that traditional strategies to protect planted tree seedlings from soil moisture loss (e.g. planting near logs) may actually increase vulnerability to rodent herbivory in aspen.  This is a novel and unexpected finding, and suggests that other aspects of site selection (e.g. absence of evidence of rodent presence, location in low-lying areas which collect runoff or snowmelt) may be especially important in seedling-based restoration for aspen.  Our findings of high survival rates among ponderosa pine seedlings is also encouraging and informative, and warrants further study to assess long-term survival at higher altitudes.  Overall, our results suggest that post-fire restoration at higher elevations in Utah with both aspen and ponderosa pine seedlings could hold promise in the future. 
       Both aspen and ponderosa pine seedlings will continue to be monitored in fall 2020 and in future years. Survival in 2020-2021 will be especially important since seedling roots will be extending past the planted root mass and becoming established.  Additionally, the survival of aspen seedlings donated to landowners in the Brian Head area will be assessed in late 2020.

Karen Mock

09/03/2020 16:35:48