Playing with fire: Age structure across a chronosequence of fire-disturbed jack pine stands

Madelyn Lehman, James Wholey, Mark Lesser

Center for Earth and Environmental Science, SUNY-Plattsburgh

Background

The history of disturbances on a landscape gives rise to different aged forest patches that in turn differ in structure and in resilience and recovery potential following new disturbances. By understanding disturbance-structure interactions, we can learn how ecosystem properties are affected (e.g., wildlife habitat).

The Altona Flat Rock is an approx. 2,000 ha sandstone pine barrens dominated by Pinus banksiana (jack pine), which relies on fire to open cones for seed dispersal, reduce understory competition, and expose mineral soil. The Flat Rock burned in 1919, 1940, 1957, and 2018, however the exact extents and spatial configurations of these disturbances is unknown.

Objectives

Our goal is to determine how past disturbance has shaped the landscape of the Altona Flat Rock and gain an understanding of the spatial extents of the past fires at the Flat Rock. By determining the timeframe of area fires using the spatial arrangement of stand ages we hope to gain an insight to the differences in forest structure over time and determine the long-term growth patterns of Jack Pine. The spatial arrangement of stand ages will provide insight into landscape level response and resilience to future disturbances and provide insight to changes in forest structure and wildlife populations. Expanding our understanding of the age structure across jack pine stands at the Altona Flat Rock will give us a better understanding of the degree of serotiny in a population of jack pine at their southern range limit.

Methods

In fall of 2022, we increment-cored three trees at each of three randomly selected sites within each of 20 one km2grid cells spanning the Flat Rock (total 60 sites). The following year, we returned to 15 sites which had shown high variability in stand age. We cored 10 more trees at each of these 15 sites to expand our right width index and better understand the age structure of these stands.

We cored each tree as close to the root collar as possible and recorded the coring height. One tree in each plot was cored 10 cm higher than the first in order to model the difference against height to establish an annual growth rate; this model was used to determine the establishment age of each tree.

Age structure was spatially interpreted across the landscape using GIS, J2X was used to measure tree rings, and COFECHA was used to cross-date the series of cores.

Results

Map of the Altona Flat rock showing estimated previous burn areas and the corresponding ages of Jack Pine. Many tress have survived the 2018 burn as well as young stands appear in the 1919 burn area because of mechanical cone opening following the 1998 ice storm.

Linear regression demonstrating the backdating process used to determine stand establishment year. We determined an average annual growth rate based on the differences between the core 1 and core 2 of the trees we cored twice. This rate of 0.35 years of growth per cm was used to backdate the remainder of the stands and find establishment years.

Box plot demonstrating frequency in which trees established >5 years prior to, within 5 years of, and >5 years following a major disturbance event. A nearly equal amount of trees established >5 years pre-disturbance as established within 5 years of a disturbance. Fewer trees established >5 years post-disturbance.

Bar plot demonstrating the range in establishment years among each plot. Many plots have a large range of establishment years due to incomplete serotiny as well as trees surviving through disturbances.

Conclusions

Stand age did not seem to align with disturbance how we expected. We expect that uneven stands due to incomplete serotiny and adult survival through disturbance will homogenize the landscape of the Altona Flat Rock over time, rather than there being many even-aged stands across the area. We expect these to be a result of a few different events:

Incomplete serotiny in a range-edge population
Adult survival through low-intensity fire events
Following damage from a 1998 ice-storm, mechanical treatments were used to open cones and regenerate the jack pine population
Altona, NY was well known in the1930s for commercial blueberry picking; berry pickers would burn the plants in a pruning effort at the end of each season, which could explain the spike 1930 spike in stand establishment

In addition to the incomplete serotiny of rear-edge Jack Pine populations

Rear-edge populations of Jack Pine use bet-hedging and rely on continuous regeneration to ensure steady recruitment in when fire is uncommon or uncertain
Jack Pine cones in rear-edge populations become more serotinous with age, which should allow for continuous seed dispersal between fires
Cones from rear-edge stands have been found to hold more seeds, less empty seeds, and lighter seeds

References

Pelletier, E., and de Lafontaine, G.. 2023. Jack pine of all trades: Deciphering intraspecific variability of a key adaptive trait at the rear edge of a widespread fire-embracing North American conifer. American Journal of Botany 110( 2): e16111. https://doi.org/10.1002/ajb2.16111

Ransom, S. (2015). Pickin' Berries. On Down the Saranac [Audio File]. Retrieved from https://open.spotify.com/track/3GL9oVI1lvFmUZXTIqtmFQ

Rowland, B. (2010). Blueberries' vast potential goes untapped. Press Republican. Retrieved 2023, from https://www.pressrepublican.com/news/local_news/blueberries-vast-potential-goes-untapped/article_0a7deaec-7e40-5e36-9e43fbce9d5d9eaa.html.

Sargis, G. & Adams, K. Effects of an Ice Storm on Fuel Loadings and Potential Fire Behavior in a Pine Barren of Northeastern New York. Scientia Discipulorum, 1(1). http://hdl.handle.net/1951/70003