Prescribed fire is increasingly used to restore and maintain upland oak (Quercus L. spp.) ecosystems in the central and eastern US. However, little is known about how prescribed fire affects recently fallen acorns under different fine fuel loads, which can vary with stand composition and basal area, burn season, and fire frequency. We conducted plot-level (1 m2) burns in an upland oak stand in northern Mississippi, USA, during December 2018, using single (i.e., ambient), double, and triple fine fuel loads, representative of those in nearby unburned and recently fire-treated, closed-canopy stands. Pre burn, we placed 30 acorns each of white oak (Quercus alba L.) and Shumard oak (Quercus shumardii Buckley) ~1 cm below the litter surface in five plots of each fuel treatment. Immediately post burn, we planted unburned and burned acorns in a greenhouse. After ~50% of each species’ unburned acorns germinated, we measured percent germination and height, basal diameter, and leaf number of germinating seedlings weekly for 11 weeks. Then, we harvested seedlings to determine above- and belowground biomass. The single fuel treatment reduced acorn germination rates of both species to ~40% compared to ~88% in unburned acorns. When burned in double and triple fuel loads, acorns of both species had a <5% germination rate. There was no difference in basal diameter, leaf number, or biomass of seedlings from burned versus unburned acorns for either species. However, seedlings originating from burned acorns of both species were ~11% shorter than those from unburned acorns. Thus, both species responded similarly to fuel load treatments. Acorns of both species exhibited greater survival with lower fine fuel loads, and consequently lower percent fuel consumption. Acorns germinating post fire generally produced seedlings with growth patterns similar to seedlings originating from unburned acorns. These findings indicate that regular, repeated prescribed fires or canopy reductions that limit fine fuel accumulation and create heterogeneous fuel beds are likely to increase acorn germination rates relative to unburned sites or those with recently introduced fire.

中文翻译：

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增加精细燃料负荷对橡树种子萌发和橡树幼苗早期生长的影响

在美国中部和东部，越来越多的人使用指定的火种来恢复和维持山地橡木（Quercus L. spp。）生态系统。但是，对于在不同的细燃料负荷下规定的火灾如何影响最近倒下的橡子，人们知之甚少，这些燃料随林分组成和基础面积，燃烧季节和火灾频率而变化。我们于2018年12月在美国密西西比州北部的一个高地橡木林进行了小区级（1 m2）燃烧，使用了一次（即环境），两倍和三倍的精细燃料负荷，代表了附近未燃烧和最近发生的大火。处理过的封闭式棚架。燃烧前，我们在每种燃料处理的五个地块中，在枯枝落叶表面下方约1 cm处分别放置30橡子，分别是白橡树（Quercus alba L.）和Shumard橡树（Quercus shumardii Buckley）。燃烧后，我们立即在温室中种植未燃烧和燃烧过的橡子。在每种物种的约50％未燃烧的橡子发芽后，我们连续11周每周测量发芽率和高度，基径和发芽幼苗的叶数。然后，我们收获了幼苗，以确定地上和地下的生物量。单一燃料处理将两个物种的橡子发芽率降低至〜40％，相比之下，未燃烧的橡子则为〜88％。当以两倍和三倍的燃料负荷燃烧时，两种橡子的发芽率均小于5％。对于两种物种，从燃烧过的橡子和未燃烧的橡子的幼苗的基径，叶数或生物量都没有差异。但是，来自两种物种的燃烧橡子的幼苗比未燃烧的橡子的幼苗短约11％。因此，两个物种对燃料负荷处理的反应相似。两种橡子在较低的精细燃料负荷下均表现出更高的存活率，因此燃料消耗百分比也更低。火后发芽的橡子通常产生的幼苗具有与未燃烧的橡子相似的生长模式。这些发现表明，相对于未燃场所或最近发生火灾的地区，经常性，反复性的规定性起火或冠层减少会限制精细燃料的积累并形成不均匀的燃料床，可能会增加橡子的发芽率。