Twenty-five years of tree demography in a frequently burned oak woodland: implications for savanna restoration

"Twenty-five years of tree demography in a frequently burned oak woodland: implications for savanna restoration"

This article was published Dec. 9, 2021 in the journal Ecosphere. This is an open-access journal.

Read or download the article from the journal using this permanent URL (DOI) (https://doi.org/10.1002/ecs2.3844)

Abstract

Due to decades of fire suppression, much of the Upper Midwest savanna habitat has converted to oak woodland. In efforts to restore oak savanna habitat, fire has been re-introduced in many of these woodlands. A primary purpose of these burns is to kill the fire-sensitive mesophytic tree species, which had established themselves during the decades of fire suppression, reduce the number of understory trees, and preserve the larger more widely spaced oaks. It is clear from ongoing efforts that restoring oak savannas will require frequent fires over decades, but frequent fires over the long term can also threaten the desirable oaks. Long-term demographic studies at savanna restoration sites experiencing frequent fires are necessary to determine the extent to the frequent burns are supporting and/or confounding restoration goals. Results presented here are from a twenty-five-year demographic study of an Upper Midwest bur oak (Quercus macrocarpa) savanna/woodland experiencing frequent fire, during which both the survival and growth of more than 9000 trees were documented. Survival was assessed annually and growth every five years.

In the face of frequent fires, stem survival was found to be strongly associated with tree species, stem size, and stem growth. In turn, stem growth was found to be related to tree species and stem size. Decades of frequent burning in this oak woodland have substantially reduced the abundance of unwanted trees, specifically mesophytic species and Quercus ellipsoidalis, the latter which outcompetes Q. macrocarpa in the absence of fire. While Q. macrocarpa mid-sized (10–25 cm dbh) and large (≥25 cm dbh) trees are quite resistant to fire and now dominate the savanna landscape, they are not immune from fire-induced mortality.

It is recommended that the number and density of these trees should be re-evaluated every few years to ensure that desirable numbers remain. If necessary, fires should be suspended for a period of time. This will give smaller Q. macrocarpa trees time to grow larger and become more fire-resistant, thereby ensuring successive generations of Q. macrocarpa.

Citation

Davis, Mark A. "Twenty‐five years of tree demography in a frequently burned oak woodland: implications for savanna restoration." Ecosphere 12, no. 12 (2021): e03844.

Pre-print: "Post-fire Quercus alba fitness in a stressed plant community"

TPOS notes: This article is a pre-print and has not been peer reviewed.

Abstract

Prescribed burns are widely used for managing North American deciduous forests due to their ability to positively affect plant community structure and composition. This study examines the effects of neighboring herbaceous plants on the recruitment of Quercus alba (white oak) seedlings in fire-managed parts of Shawnee National Forest (Illinois, USA). Herbs were clipped to induce plant community stress and relative growth rates (RGRs) of planted white oak seedlings were assessed to determine if a competitive or facilitative dynamic is present. In addition to RGR, we observed the mycorrhizal network via fungal colonization in mesh bags to quantify belowground activity for our experimental plots. Our results supported fire's positive effects on tree recruitment and herbaceous growth. Clipping combined with fire management decreased RGR. This finding suggests that a facilitative dynamic is at play and herbaceous neighbors help white oak seedlings persist due to protection from environmental stressors (p = 0.017). Soil moisture played a large role in promoting tree fitness on each of our sites. Lower hyphal biomass was observed in areas where herbs were clipped. We further speculate that the stress caused by clipping may have suspended or eliminated the need for mycorrhizae to form, possibly due to herb mortality. Knowing how herbs and trees interact will lead to purposeful forest community planning especially in fire-managed forests where herbs are likely to dominate post-prescribed burn.

Citation:

"Post-fire Quercus alba fitness in a stressed plant community," Kevin Milla, bioRxiv 189829; doi: https://doi.org/10.1101/189829

Corresponding author: Kevin Milla, email: milla2 "at" illinois.edu