Native tree and shrub canopy facilitates oak seedling regeneration in semiarid woodland

Abstract

Oaks (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.

Oak seedling performance and soil development across a forest restoration chronosequence following agriculture in the American Midwest—a greenhouse experiment

“…The soil conditions in the older forest restorations that contained more C and N corresponded to larger Q. macrocarpa seedlings, suggesting that older restorations may harbor enough C and N to promote establishment. We found more Ca in soils collected from older sites, and Ca abundance can increase the success of Quercus seedlings (O'Donnell et al 2020). Conversely, soil P was least abundant in older restorations in this study, which is similar to other findings that as agricultural fields are left fallow and no longer fertilized, P slowly depletes from the system (Wardle et al 2004).…”

Drivers of oak establishment in Mediterranean old fields from 25-year-old woodland islets planted to assist natural regeneration

“…A similar pattern was shown by O'Donnell et al (2020), who reported increased seedling emergence and survival up to 3 m from the forest edge. We observed the opposite trend in the most sun-exposed orientation, the southern orientation.…”

Mycorrhizal Fungi Associated With Juniper and Oak Seedlings Along a Disturbance Gradient in Central Mexico

“…Changes in ECM and AM plant densities may also impact plant demography and community structure through neighboring interactions mediated by beneficial and pathogenic soil fungi (Liang et al, 2020). On the other hand, access to an existing mycorrhizal network can favor the establishment and survival of emerging seedlings (Taudiere et al, 2015;O'Donnell et al, 2020). For example, AM fungi can facilitate the establishment of Juniperus seedlings in Quercus-dominated stands (Bush, 2008) as well as the survival of Q. rugosa seedlings (Olivera-Morales et al, 2011).…”

“…Thus, seedlings of plant species that typically form ECM associations, such as oak, pine and fir, are occasionally colonized by AM fungi (Dickie et al, 2001;Wagg et al, 2008;Toju et al, 2013). Moreover, sharing AM fungi through common mycorrhizal networks likely contributes to ECM seedling survival until they are able to form more stable associations with ECM fungi (Selosse et al, 2006;O'Donnell et al, 2020). For example, laboratory experiments demonstrated that these early successional AM associations in ECM seedlings correlated with positive growth response and phosphorus (P) uptake (Lapeyrie and Chilvers, 1985;Van Der Heijden and Kuyper, 2001), but negative or neutral effects have also been reported (Egerton-Warburton and Allen, 2001;Kariman et al, 2012;Holste et al, 2017).…”