Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT, United States of America.
PLoS One. 2019 Mar 18;14(3):e0207047. doi: 10.1371/journal.pone.0207047. eCollection 2019.
Non-native, early-successional plants have been observed to maintain dominance for decades, particularly in semi-arid systems. Here, two approaches were used to detect potentially slow successional patterns in an invaded semi-arid system: chronosequence and direct observation. Plant communities in 25 shrub-steppe sites that represented a 50-year chronosequence of agricultural abandonment were monitored for 13 years. Each site contained a field abandoned from agriculture (ex-arable) and an adjacent never-tilled field. Ex-arable fields were dominated by short-lived, non-native plants. These 'weedy' communities had lower species richness, diversity and ground cover, and greater annual and forb cover than communities in never-tilled fields. Never-tilled fields were dominated by long-lived native plants. Across the chronosequence, plant community composition remained unchanged in both ex-arable and never-tilled fields. In contrast, 13 years of direct observation detected directional changes in plant community composition within each field type. Despite within-community changes in both field types during direct observation, there was little evidence that native plants were invading ex-arable fields or that non-native plants were invading never-tilled fields. The more-controlled, direct observation approach was more sensitive to changes in community composition, but the chronosequence approach suggested that these changes are unlikely to manifest over longer time periods, at least in part because of disturbances in the system. Results highlight the long-term consequences of soil disturbance and the difficulty of restoring native perennials in disturbed semi-arid systems.
非本地、早期演替的植物已被观察到能维持几十年的优势，特别是在半干旱系统中。在这里，我们使用了两种方法来检测入侵半干旱系统中潜在的缓慢演替模式：时间序列和直接观察。对代表农业废弃 50 年时间序列的 25 个灌丛草原地点的植物群落进行了 13 年的监测。每个地点都包含一个废弃的农田（前耕地）和一个相邻的从未耕种过的田地。前耕地主要由短命的非本地植物占据。这些“杂草”群落的物种丰富度、多样性和地面覆盖度较低，一年生植物和草本植物的覆盖度较大，而从未耕种过的田地中的群落则较高。从未耕种过的田地主要由长寿命的本地植物占据。在整个时间序列中，前耕地和从未耕种过的田地中的植物群落组成都没有变化。相比之下，13 年的直接观察检测到了每种田地类型中植物群落组成的定向变化。尽管在直接观察期间，两种田地类型的群落内部都发生了变化，但几乎没有证据表明本地植物正在入侵前耕地，或者非本地植物正在入侵从未耕种过的田地。更受控制的直接观察方法对群落组成的变化更敏感，但时间序列方法表明，这些变化不太可能在更长的时间内表现出来，至少部分原因是系统中的干扰。研究结果突出了土壤干扰的长期后果，以及在受干扰的半干旱系统中恢复本地多年生植物的困难。
