Heterogeneity promotes resilience in restored prairie: implications for the ‘environmental heterogeneity hypothesis’

Enhancing resilience in formerly degraded ecosystems is an important goal of restoration ecology. However, evidence for the recovery of resilience and its underlying mechanisms requires long-term experiments and comparison to reference ecosystems. We used data from an experimental prairie restoration that featured long-term soil heterogeneity manipulations and data from comparable remnant (reference) prairie to (1) quantify the recovery of ecosystem functioning (i.e., productivity) relative to remnant prairie, (2) compare resilience of restored and remnant prairies to a natural drought, and (3) test whether soil heterogeneity enhances resilience of restored prairie. We compared sensitivity and legacy effects between prairie types (remnant and restored) and among four prairie sites that included two remnant prairie sites and prairie restored under homogeneous and heterogeneous soil conditions. We measured sensitivity and resilience as the proportional change in aboveground net primary productivity (ANPP) during and following drought (sensitivity and legacy effects, respectively) relative to average ANPP based on four pre-drought years (2014-2017). In non-drought years, total ANPP was similar between remnant and restored prairie, but remnant prairie had higher grass productivity and lower forb productivity compared to restored prairie. These ANPP patterns generally persisted during drought. Sensitivity of total ANPP to drought was similar between restored and remnant prairie, but grasses in restored prairie were more sensitive to drought. Post-drought legacy effects were more positive in restored prairie, and we attributed this to the more positive and less variable legacy response of forb ANPP in restored prairie, especially in the heterogeneous soil treatment. Our results suggest that productivity recovers in restored prairie and exhibits similar sensitivity to drought as remnant prairie. Furthermore, imparting heterogeneity promotes forb productivity and enhances prairie resilience to drought.

Methods

These data pertain to Figure 1 in Wojciechowski et al. (Ecological Applications).

Grass, forb, and total aboveground net primary productivity (ANPP) were determined for the same time period (2014-2019) using the same methods in remnant and restored prairie experiments. In all experiments, plant material was harvested from 0.1 m2 quadrats at peak biomass. Biomass was sorted into grasses, forbs, and litter produced in the sampling year. All biomass was dried at 60oC and weighed to estimate ANPP (Briggs and Knapp 1991). In the restoration experiment, we harvested biomass from twelve quadrats in each plot (n = 4 per heterogeneity treatment). In REMIRT, ANPP was estimated from six quadrats in each of 6 control plots. In REMBGP, ANPP was estimated from two quadrats in each of 4 control plots. Biomass in each sample was multiplied by 10 to report ANPP values as g/m2/yr.

提升退化后生态系统的恢复力是恢复生态学的重要目标。然而，要获取恢复力恢复及其内在机制的相关证据，需要开展长期实验并与参照生态系统进行对比。本研究结合长期土壤异质性操控实验的草原恢复数据，以及与实验区匹配的残存（参照）草原数据，开展了三项研究内容：（1）量化相对于残存草原的生态系统功能（即生产力）恢复程度；（2）对比恢复草原与残存草原对自然干旱的恢复力；（3）验证土壤异质性是否可提升恢复草原的恢复力。本研究对比了两类草原（残存草原与恢复草原）间以及4个草原样地间的敏感性与遗留效应，4个样地包含2个残存草原样地，以及分别在均质与异质土壤条件下恢复的草原样地。本研究将敏感性与恢复力定义为：相较于干旱前4年（2014-2017年）的地上净初级生产力（aboveground net primary productivity, ANPP）平均值，干旱期间与干旱后地上净初级生产力（ANPP）的比例变化（分别对应敏感性与遗留效应）。在非干旱年份，残存草原与恢复草原的总ANPP并无显著差异，但残存草原的草本生产力更高、杂类草生产力更低。上述ANPP分布模式在干旱期间整体保持一致。两类草原的总ANPP对干旱的敏感性并无差异，但恢复草原中的草本对干旱的敏感性更高。干旱后的遗留效应在恢复草原中更为积极，本研究将这一现象归因于恢复草原（尤其是异质土壤处理样地）中杂类草ANPP的遗留响应更积极且变异性更低。研究结果表明，恢复草原的生产力可得到恢复，且对干旱的敏感性与残存草原相当；此外，引入土壤异质性可提升杂类草生产力，并增强草原对干旱的恢复力。

研究方法
本数据集对应Wojciechowski等人发表于《Ecological Applications》的论文中的图1。
草本、杂类草及总地上净初级生产力（ANPP）的测定周期为2014-2019年，所有实验采用统一方法开展。所有实验均在生物量峰值期，从0.1 m²的样方中采集植物样品。将采集的生物量按当年产生的草本、杂类草和枯落物进行分类，随后在60℃下烘干并称重，以此估算ANPP（参照Briggs与Knapp 1991年的方法）。在恢复实验中，每个样地内采集12个样方的生物量（每个异质性处理组n=4）。在REMIRT样地中，从6个对照样地的每个样地内选取6个样方估算ANPP；在REMBGP样地中，从4个对照样地的每个样地内选取2个样方估算ANPP。将每个样品的生物量乘以10，将ANPP单位换算为g/m²/yr。