Temporal patterns of forest seedling emergence across different disturbance histories data

Forest ecosystems experience a myriad of natural and anthropogenic disturbances that shape ecological communities. Seedling emergence is a critical, preliminary stage in the recovery of forests post-disturbance and is triggered by a series of abiotic and biotic changes. However, the long-term influence of different disturbance histories on patterns of seedling emergence is poorly understood.

Here, we address this research gap by using an 11-year dataset gathered between 2009 and 2020 to quantify the influence of different histories of natural (wildfire) and anthropogenic (clearcut and post-fire salvage logging) disturbances on emerging seedlings in early successional Mountain Ash forests in south-eastern Australia. We also describe patterns of seedling emergence across older successional forests varying in stand age (stands that regenerated in <1900s, 1939, 1970-90 and 2007-11).

Seedling emergence was highest in the first three years post-disturbance. Stand age and disturbance history significantly influenced the composition and abundance of plant seedlings. Specifically, in salvage logged forests, plant seedlings were the most different from similarly aged forests with other disturbance histories. For instance, relative to clearcut and unlogged, burnt forests of the same age, salvage logging had the lowest overall richness, the lowest counts of Acacia seedlings, and an absence of common species including Acacia obliquinervia, Acacia frigescens, Cassinia arcuealta, Olearia argophylla, Pimelea axiflora, Polyscias sambucifolia and Prosanthera melissifolia over the survey period.

Synthesis: Our findings provide important new insights into the influence of different disturbance histories on regenerating forests and can help predict plant community responses to future disturbances, which may influence forest recovery under altered disturbance regimes.

Methods
Please see manuscript for detailed description of methods.

森林生态系统会经历众多自然与人为干扰，这些干扰过程塑造了生态群落的结构与组成。幼苗萌发是森林受干扰后恢复过程中的关键起始阶段，其发生由一系列非生物与生物变化共同触发。然而，学界对不同干扰历史对幼苗萌发格局的长期影响仍知之甚少。

本研究利用2009—2020年间采集的11年数据集，针对澳大利亚东南部早期演替山桉（Mountain Ash）林，量化不同自然（野火（wildfire））与人为（皆伐（clearcut）、火灾后打捞采伐（salvage logging））干扰历史对幼苗萌发的影响，以此填补该研究领域的空白。本研究同时描述了不同林龄的晚期演替森林（分别为1900年以前、1939年、1970—1990年、2007—2011年更新形成的林分）的幼苗萌发格局。

幼苗萌发率在干扰后的前三年达到峰值。林龄与干扰历史对植物幼苗的群落组成与个体丰度具有显著影响。具体而言，经火灾后打捞采伐的林分中，植物幼苗群落组成与其他干扰历史下的同龄林分差异最为显著。例如，相较于同龄的皆伐未采伐火烧林分，本调查期内火灾后打捞采伐样地的物种总丰富度最低，金合欢属幼苗数量最少，且缺失斜脉金合欢（*Acacia obliquinervia*）、淡色金合欢（*Acacia frigescens*）、弧花银叶菊（*Cassinia arcuealta*）、银叶桂叶菊（*Olearia argophylla*）、轴花美柱草（*Pimelea axiflora*）、接骨木状南洋森（*Polyscias sambucifolia*）以及蜜花普罗桑特拉（*Prosanthera melissifolia*）等常见物种。

综合分析：本研究结果为不同干扰历史对森林更新的影响提供了重要新认知，同时可助力预测植物群落在未来干扰下的响应，这对变化后的干扰制度下的森林恢复具有重要指导价值。

方法：详见研究手稿以获取详细方法描述。