Oak regeneration at the arid boundary of the temperate deciduous forest biome: insights from a seeding and watering experiment

Abstract

Previous studies found that pedunculate oak, one of the most widespread and abundant species in European deciduous forests, regenerates in open habitats and forest edges, but not in closed forest interiors. However, these observations usually come from the core areas of the biome, and much less is known about such processes at its arid boundary, where limiting factors may be different. In a full factorial field experiment, we tested the effects of different habitats (grassland, forest edge, forest interior) and increased growing season precipitation on the early regeneration of pedunculate oak in a forest-steppe ecosystem in Central Hungary, at the arid boundary of temperate deciduous forests. In the grassland habitat, seedling emergence was very low, and no seedlings survived by the fourth year. In contrast, seedling emergence was high and similar at forest edges and forest interiors, and was not affected by water addition. Most seedlings survived until the fourth year, with no difference between forest edge and forest interior habitats in numbers, and only minor or transient differences in size. The lack of oak regeneration in the grassland differs from previous reports on successful oak regeneration in open habitats, and may be related to a shift from light limitation to other limiting factors, such as moisture or microclimatic extremes, when moving away from the core of the deciduous forest biome towards its arid boundary. The similar number and performance of seedlings in forest edges and forest interiors may also be related to the decreasing importance of light limitation.

How climate, topography, soils, herbivores, and fire control forest–grassland coexistence in the Eurasian forest‐steppe

“…But now, after two decades of case studies in Eastern Central Europe (e.g. Bátori et al ., 2018 ; Erdős et al ., 2014 a , 2018 b , 2019 a , 2021 ; Tölgyesi et al ., 2020 ), Kazakhstan (e.g. Bátori et al ., 2018 ; Tölgyesi et al ., 2018 ), Mongolia (e.g.…”

“…Similarly, Pinus sylvestris is limited primarily by low soil moisture (Dulamsuren et al ., 2013 ). Quercus robur acorns in the sandy forest‐steppes of the Carpathian Basin are often unable to germinate in grassland patches, and those that do germinate eventually suffer drought‐induced mortality (Erdős et al ., 2021 ). In addition to low moisture availability, extreme cold winters, which are typical of the interior of Eurasia due to the large distance from oceans and the dry, seldom overcast sky, can also decrease tree recruitment and growth (D'Odorico et al ., 2013 ).…”

“…At the arid southern edge of the forest‐steppe in Kazakhstan, mid‐summer topsoil can be drier under forest tree canopies than in adjacent open steppes (Tölgyesi et al ., 2018 ). In climatically less harsh sites, such as the sand regions of the Carpathian Basin, forest topsoil tends to be moister than that of the steppe patches (Erdős et al ., 2018 b , 2021 ) but deeper soils are desiccated, with the rate of desiccation dependent on whether trees are deciduous or evergreen (Tölgyesi et al ., 2020 ). It is an open question though, whether the moisture surplus in the topsoil is solely a consequence of the reduced evaporation due to the cool shaded microclimate or if trees bring deep water up to the topsoil via hydraulic lift, as occurs in many semi‐arid regions (Yu & D'Odorico, 2015 ).…”

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

“…Restoration efforts that introduce Quercus seedlings often focus either on planting seedlings directly into open fields or on planting seedlings as advanced regeneration under an established forest canopy. Quercus seedlings that are planted in open fields may require more intervention for survival than seedlings planted within established forests (Martínez‐Garza & Howe 2003; Griscom & Ashton 2011; Dey et al 2012; Hanberry et al 2014; Erdős et al 2021). Quercus seedling success is related to temperature fluctuations, water availability, light availability, and microsite conditions, indicating that established forests may provide more habitable microsites for seedling establishment (Arthur et al 2012; Dey et al 2012; Urli et al 2015; Erdős et al 2021), except for their reduced light availability (Bobiec et al 2018; Mölder et al 2019).…”

“…Quercus seedlings that are planted in open fields may require more intervention for survival than seedlings planted within established forests (Martínez‐Garza & Howe 2003; Griscom & Ashton 2011; Dey et al 2012; Hanberry et al 2014; Erdős et al 2021). Quercus seedling success is related to temperature fluctuations, water availability, light availability, and microsite conditions, indicating that established forests may provide more habitable microsites for seedling establishment (Arthur et al 2012; Dey et al 2012; Urli et al 2015; Erdős et al 2021), except for their reduced light availability (Bobiec et al 2018; Mölder et al 2019). Forests are likely to have more developed soils than old fields, since established plants can alter soil nutrients, chemistry, and provide organic matter to the soil system (Bronick & Lal 2005).…”