Mesophication of Eastern Deciduous Forests Is it happening, why and is there anything to be done?

Abundance and Value of Oaks Oak harvest species trees Native to almost every state Associated with 68 of 90 forest cover types across U.S. (Eyre, 1980) 1/4 all growing stock on timberland in eastern forests is in oaks Provides food and habitat Treasured for historic, cultural and property values

What is “Mesophication”? Mesophication coined by Nowacki & Abrams (2008) – use of geospatial and fire scar data – derive past and current fire regimes – project changes in forests Pre-European settlement – diverse array of fire-adapted vegetation communities – eg. Grasslands, savannahs, oak woodlands – Open-canopy forests Native American land use – like a “keystone” species – low to mixed-severity burns – mosaic of burned and unburned areas

Post –European settlement shift in competitive balance – Extensive timber harvesting of oak forests – Introduction of invasive plants from Europe – slash and burn in some places – Suppression fire to protect property in new agricultural areas cascade of structural and compositional changes – Grasslands, savannahs and oak woodlands replaced by closed-canopy forests – Changes in closed-canopy microclimate and leaf litter and woody debris

maple, beech, birch, cherry, tulip popular and black gum positive feedbacks for continued “mesophytic” communities

Evidence for the Mesophication Hypothesis? Empirical Observations – Reports by forest managers – Variety of scale of studies – aerial, canopy gap, random sampling – Historical records Experimental Methods – Fire (size, frequency and severity) – Harvested sites – clear-cut and selective thinning – Fire surrogates (herbicides, disease, herbivory) – Physiological responses of trees to fire

Major Ecoregion Divisions of the U.S. from Fei et. al. 2011

Change in Oak Abundance in Eastern United States Mean annual change in (a) rel density, (b) rel volume, and (c) importance value (IV) for all oak species in the eastern U.S.

Declines in oak abundance in 81% forested areas (IV) 17% Rel Density Central Hardwood Region 25% Rel Density Forest- Prairie Region Near universal increase in Shingle and Water Oaks Rel Vol in 76% of area Northern Region Increase in total oak volume in 4 Ecoregions No species had universal increase or decrease Results and Trends

Major Conclusions: Oak declines in Density and Volume relative to other species Absolute Volume oak growing stock is increasing Variations in Density and Volume by region and species Concerns: Why does this matter? Forests aging insufficient oak regeneration ; lacking sapling size in midstory ½ oak is in sawtimber size; ¼ in seedling/sapling sizes Regional Trends: What can they suggest? Gains and losses strongly clustered in space Variety of ecological and socioeconomic factors on multiple scales

Establish baseline data from “Old-Growth” Forests Central Appalachian Forest (Chapman and McEwan, 2012) Hypothesized shift in oak to maple dominance over a 10-year interval Not a clear transition Acer increase density ground-layer, shrub-layer decrease Quercus cover and density changes minor in both layers Caveats of an “Old Growth” Study: How is tree regeneration different in younger forests ? How are ephemeral patterns in understory layers related to the future of the overstory ? Continued long-term quantification of changes across all woody strata

What sort of process is “Mesophication”? Implies a deterministic process – Non-Equilibrium model - change in competitive ranking – Disturbance will slow decline of oaks? – Frequency and type of disturbance required? What sort of Disturbance / Succession? – Not discrete – happens continuously – Is it predictable? – Related to change in fire or some other unknown? – Happening to oak/hickory forest selectively?

Canopy Gap Formation Uniform age to complex age Monoculture to polyculture Density-dependent to density-independent mortality Stand-replacing to gap-phase local successional changes create distinct microenvironments provide a mechanism for regeneration and recruitment Forest Stand Dynamics

Species-Gap Area Curve - 40 Gaps in a Mixed-Oak Woodland High species richness with 34 species in canopy gaps Sapling richness increased with gap size Sapling density increased with size of gap from Hart and Kupfer (2011 ) Pogue Creek Natural Area, Tennessee

from Hart and Kupfer (2011) Sugar and Red Maple and Beech widespread and abundant Oak / Hickory regeneration mostly on xeric sites Gap composition varied according to gradients of gap formation mechanism, size, aspect and soils Composition and Density in the Canopy Gaps

Attempts to Model Vegetation Changes at Fine-Scale Random Stratified Sampling in Wayne National Forest Use of multivariate analysis and Structural Equation Modeling Vegetation responds to fine-scale environmental gradients Thresholds between community states maintaining maple-beech Influence of canopy on the sapling and ground flora layers from Gilliam 2007 Conclusion: Shift in Dominance from Oak Hickory to Maple

Climate Regime Change -temp and moisture change -reconstruct drought patterns and oak regeneration Native American populations -low density mid-1600s to 1800s Paucity of fire scar data Coincident with demise of the Chestnut Increased browser and acorn-eater populations Oak acorns in a complex web of interactions -eg. squirrels as both predators and dispersers of acorns Other animal population changes populations -Wild Turkeys (forest floor disturbance) -Passenger pigeons (light gaps) Alternative Explanations of “Mesophication”

Arthur et al. 2012

Sugar maple, American beech and yellow birch trees