Thinning, fire, and oak regeneration across a heterogeneous landscape in the eastern U.S.: 7-year results

Abstract

We document an increase in oak and hickory advance regeneration, depending on landscape position, in the sixth year following mechanical thinning and repeated prescribed fires in southern Ohio, USA. Oak-dominated communities provide a multitude of human and natural resource values throughout the eastern United States, but their long-term sustainability is threatened throughout the region by poor regeneration. This study was established to assess regeneration following midstory thinning (late 2000) and prescribed fire application (2001 and 2005) at two sites in southern Ohio. Each of the four 20+ ha treatment units (two thin and burn, two untreated controls) were modeled for long-term moisture regime using the integrated moisture index (IMI), and a 50 m grid of sampling points was established throughout the units. Vegetation and canopy openness were sampled at each gridpoint before and after treatments, in 2000, 2001, 2004, and 2006. The thin and burn treatment generally resulted in more advance regeneration (>50 cm height) of oak and hickory. The second fires in 2005 created additional landscape heterogeneity by causing variable tree mortality, and thus canopy openness, across the IMI gradient. The drier landscape positions generally had more intense fires, more canopy openness, and more oak and hickory advance regeneration; several other tree species also exhibited marked landscape variation in regeneration after treatments. Though advance regeneration of several competing species became abundant after the initial treatments, the second fires reduced the high densities of the two major competitors, Acer rubrum and Liriodendron tulipifera. Two simple models were developed: (1) a model of oak ''competitiveness'' based on the plot data related to advance regeneration of oaks and competitors and (2) a model estimating the probability of a plot becoming 'competitive for oak' based on canopy openness, IMI class, and number of oak and hickory seedlings present. For dry or intermediate sites with at least 5000 oak and hickory seedlings/ha, opening the canopy to 8.5-19% followed by at least two fires should promote oak and hickory to be 'competitive' over about 50% of the area. However, no appreciable oak and hickory regeneration developed on mesic sites. Overall, these results suggest promise for partial harvesting and repeated fires as a management strategy to reverse the accelerating loss of oak dominance in the central hardwoods region. Published by Elsevier B.V.

The fire—oak literature of eastern North America: synthesis and guidelines

“…Most reported ambiguous effects (Franklin et al 2003, McGee et al 1995, Merritt and Pope 1991 on the oak reproduction with some showing positive outcomes (Barnes andVan Lear 1998, Schuler et al 2013) and a few showing negative outcomes (Arthur et al 1998, Luken andShea 2000). Two oak sites that were part of the National Fire and Fire Surrogate Project illustrate this confusion as they report differing outcomes between sites as well as among topographic positions (Iverson et al 2008, Waldrop et al 2008). …”

“…The burn-only treatment changed stand structure by reducing the sapling/shrub layer, but it did little to thin the overstory. Iverson et al (2008) used the same study area in Ohio as Waldrop et al (2008) to compare treatment impacts as they varied across different positions of the landscape. Study plots in Ohio were larger than those in North Carolina (50 acres vs. 20 acres) thus allowing a comparison of treatment impacts across dry and mesic sites.…”

“…The study by Iverson et al (2008) on relatively large (>50 acre) treatment units showed some promise as well as some of the problems that managers face. Though thinning and burning increased the density of oak advance regeneration, there also was ample competition from species that had different strategies in dealing with the new conditions brought about by the thinning and burning.…”

Fire in upper Midwestern oak forest ecosystems: an oak forest restoration and management handbook

“…Such combinations of disturbance may even set succession back-generally the goal for mixed oak and maple stands. Although it is not possible to create perfect conditions for oaks everywhere within one site, or on all types of sites across the landscape (Iverson et al 2008a), there are a number of factors that affect oak regeneration at various stages from germination, establishment, and recruitment. The list of factors varies from region to region and stand to stand.…”

Composition and carbon dynamics of forests in northeastern North America in a future, warmer worldThis article is one of a selection of papers from NE Forests 2100: A Synthesis of Climate Change Impacts on Forests of the Northeastern US and Eastern Canada.

“…Note, these maps reflect habitat suitability and not necessarily where the species will actually be within the next 100 years. For example, most oaks and hickories have difficulty regenerating (e.g., Sutherland and Hutchinson 2003), so that projected oakhickory expansions may not materialize for a long time (Carmel and Flather 2006;Iverson et al 2008a). …”