Abstract
AbstractOaks (Quercus spp.) are currently declining worldwide due to a multitude of threats. Woodland management is often heavily focused on thinning and burning nontarget species to reduce competition and promote oak dominance in the overstory. These techniques have typically been developed in temperate regions, such as eastern U.S. forests, but whether they are the most effective strategy for promoting oak regeneration in semiarid woodlands has not been sufficiently examined. We conducted our study on the eastern Edwards Plateau in central Texas, where several oak species are codominant with Ashe juniper (Juniperus ashei) over karst limestone terrane. These juniper‐oak woodlands provide habitat for many endemic species and play an essential role in the maintenance of key aquifers. A history of canopy clearing and a severe drought in 2011 generated patches of living and dead juniper‐oak canopy interspersed with canopy gaps in our study area. In November 2013, we planted 200 shin oak (Quercus sinuata var. breviloba) acorns in each of three habitat treatments, replicated six times: (1) live canopy, (2) dead canopy, and (3) open invasive grassland. We monitored emergence and survival each year, harvesting five seedlings from each replicate in October 2017 to assess shoot height, rooting depth, biomass, ectomycorrhizal colonization, and foliar nutrients. Canopy trees, living or dead, significantly enhanced seedling emergence and survival. Survival was positively associated with increasing Ashe juniper and oak basal area, shrub cover, and soil organic matter, and negatively associated with increasing canopy gap size (complete mortality in gaps >220 m2). Seedling biomass increased significantly in dead and open treatments along with foliar nutrients N, P, and S (dead treatments) or S and Fe (open treatments), whereas ectomycorrhizal colonization and foliar nutrients Ca, Mg, and Mn increased under living canopy. Our findings suggest that oak regeneration in these juniper‐oak woodlands closely resembles that of Mediterranean regions, where canopy facilitates seedling survival. Both living and dead trees and shrubs enhanced oak regeneration, with seedling survival depending on proximity to larger trees, living roots, shrubs, and juniper‐oak canopy. Planting acorns under canopy is an inexpensive, sustainable, and effective restoration practice in drought‐prone ecosystems.
Highlights
With over 500 species distributed worldwide (McShea and Healy 2002), Quercus is a diverse genus occupying a wide variety of habitat conditions, ranging from lowland to mountainous, mesic to xeric, and closed-canopy forests to scrublands (Johnson et al 2005)
We conducted our study on the eastern Edwards Plateau in central Texas, where several oak species are codominant with Ashe juniper (Juniperus ashei) over karst limestone terrane
The semiarid woodlands of the eastern Edwards Plateau appear to more closely resemble those of Mediterranean regions
Summary
With over 500 species distributed worldwide (McShea and Healy 2002), Quercus is a diverse genus occupying a wide variety of habitat conditions, ranging from lowland to mountainous, mesic to xeric, and closed-canopy forests to scrublands (Johnson et al 2005). Oak species richness is exceptionally high in North America (200–240 species), in mountainous regions of Mexico and the southeastern United States (Valencia-A 2004, Nixon 2006), much of the available research on oak management strategies is derived from forests in the eastern United States In these temperate forests, management-intensive xerifying disturbance regimes of prescribed burns and canopy thinning are aimed at promoting oak dominance in the overstory by reducing midcanopy structure and allowing light to reach regenerating seedlings (McShea and Healy 2002, Johnson et al 2005, Brose et al 2013). Successful strategies for managing oak regeneration in temperate regions may not be the most appropriate for more xeric ecosystems
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