Background
Altona Flat Rock, NY
- The Altona Flat Rock is a unique jack pine dominated sandstone pavement barrens, unlike the surrounding hardwood forest is highly fire dependent due to jack pine serotinous cones.
- In 2018 a wildfire took place burning about 200 hectares of the Flat Rock, providing the opportunity to study post-disturbance recovery of this system.
Objectives
- We were interested to see how jack pine seedlings would regenerate in a post-disturbance fire regime and whether or not the seedling densities would increase since the 2018 disturbance.
- Our main objective here was to understand what factors influence which seedlings will survive to form the mature forest.
- We were particularly interested in fine-scale factors such as soil depth, the percentage of ground cover that was rock, duff, grass, moss, or blueberry, and the soil depth interactions between these previously listed factors.
Methods
- We established three random sites each containing three, 1 meter square plots which we subset into a 10 x 10 cm grid and measured fine-scale variables; we determined the rooting substrate and percent cover of competing vegetation, along with the number of Jack Pine seedlings.
- Seedlings were individually tagged so that we could track survival and growth through time for each individual; This was monitored each fall and spring since 2018 for survival and since fall 2019 for height.
- We started tracking survivorship back in fall 2018 and began taking both height and survivorship data in fall 2019 tracking these factors till fall 2021.
Figures
We used linear regression in RStudio to determine the effects of measured variables on survival and height.
Analysis
- Initial seedling densities in fall 2018 ranged from 353,000 to 1,070,000 seedlings/ha across the three sites.
- Continued germination through 2019 offset mortality and maintained the initial density at one site, however, significant mortality occurred at the other two sites, reducing densities by 40-75%.
- Following the 2019 growing season no new seedlings have germinated and densities have continued to decline at all three sites.
- Seedling densities as of fall 2021 ranged from 57,000 to 893,000 (reductions of 16-84%).
- Survival was highly correlated with soil depth, % rock and % grass.
- In 2019 average seedling height was 3.56 cm across the three sites. By 2021 average seedling height was 10.04 cm, with the tallest seedling being 32 cm.
- Height was strongly correlated with soil depth and %duff.
- These results help elucidate the ongoing successional process and how the forest is recovering back towards its pre-disturbance state.
Explanations
- At low soil depths, seedlings aren’t growing well because little/thinner layers of soil means less moisture and no nutrients. While on the other hand, higher soil depths would subsequently have more moisture and nutrients, explaining why survivorship and height growth did particularly well.
- A higher percentage of duff could help with soil retention, absorbing all the vital nutrients the seedlings need for successful germination, explaining why a high percentage of duff at high soil depths resulted in greater height growth (cm).
- Less competition due to lower percentages of vaccinium and tufts of grass can also explain the trends in seedling height growth where height does extremely well, growing tall.
- The more percentage of rock could result in higher amounts of surviving seedlings because the rock took up the space for any of the other microsite variables, resulting in little to no competition for those seedlings, allowing them to flourish.
Importance
- Examining these fine-scale factors in post disturbance regeneration is essential for future understanding and research in how jack pine seedlings will react and survive in a competitive, post-fire ecosystem and how the forest as a whole recovers back to its pre-disturbance state.
- Observing these various competitive factors on a fine scale will give us a bigger picture understanding of what should or can be manipulated for future germination success in these seedlings.
- This research should be continued for the next several years to see how jack pine reacts to increasing or decreasing inter/intra specific competition and if there were to be another wildfire, how this would affect the seedlings previously measured this growing season.