Data from: Contrasting habitat and landscape effects on the fitness of a long-lived grassland plant under forest encroachment: do they provide evidence for extinction debt?

1. Habitat loss, fragmentation and transformation threaten the persistence of many species worldwide. Population and individual fitness are often compromised in small, degraded and isolated habitats, but extinction can be a slow process and extinction debts are common. 2. Long-lived species are prone to persist as remnant populations in low quality habitats for a long time, but the population and individual-level mechanisms of extinction debt remain poorly explored so far. 3. We here investigate the mechanisms involved in the long-term persistence of the common grassland specialist, long-lived, clonal plant Aphyllanthes monspeliensis L. (Asparagaceae). after forest encroachment into semi-natural Mediterranean calcareous grasslands in Catalonia (NE Iberian Peninsula). For this purpose we assess vegetative (aboveground and belowground) and reproductive plant performance indicators and their habitat and landscape (current and historical) drivers. 4. We confirm the existence of an extinction debt for this species, since current plant frequency is related to historical but not current connectivity, and we also find a positive effect of historical connectivity on seed set. In addition, current tree cover negatively affects individual size and aboveground/belowground biomass ratio, and biotic soil acidification leads to a reduction in the flowering probability of individuals and stems. 5. However, we also find that current connectivity negatively affects flowering and that tree cover enhances seed set. The forestation process, thus, also exerts a positive effect on some fitness traits, probably by providing a moister environment. 6. Synthesis. Habitat loss and deterioration result in a decreased vegetative performance of Aphyllanthes monspeliensis, a grassland specialist, but show contrasting effects on its reproductive performance. However, further forest encroachment would increase light competition and soil acidification, threatening its persistence and promoting the payment of the extinction debt if no conservation measures are taken.

1. 生境丧失、破碎化与改造正威胁着全球众多物种的存续。在小型、退化且孤立的生境中，物种种群与个体适合度往往会受到损害，但物种灭绝往往是一个缓慢的过程，灭绝债务（extinction debt）现象十分普遍。
2. 长寿物种易于在低质量生境中以残存种群的形式长期存续，但目前学界对灭绝债务背后的种群与个体水平灭绝机制仍鲜有探索。
3. 本研究以伊比利亚半岛东北部加泰罗尼亚地区地中海石灰质半自然草原被森林侵占后的常见草原特化长寿克隆植物——蒙彼利埃无叶草（Aphyllanthes monspeliensis L.，天门冬科Asparagaceae）为研究对象，探究其长期存续的相关机制。为此，我们评估了该植物的营养（地上与地下）及繁殖性能指标，并分析了其生境与景观（当前与历史）层面的驱动因子。
4. 本研究证实了该物种存在灭绝债务：当前植株出现频率与历史连通性相关，而非当前连通性；同时我们还发现历史连通性对种子结实量具有正向影响。此外，当前林木盖度会对植株个体大小及地上/地下生物量比产生负面影响，而生物性土壤酸化则会降低植株与茎秆的开花概率。
5. 但我们同时发现，当前连通性会对开花产生负面影响，而林木盖度则会提升种子结实量。由此可见，森林化过程对部分适合度性状也存在正向作用，这可能是因为林木为植株提供了更为湿润的微环境。
6. 综合分析：生境丧失与退化会导致草原特化物种蒙彼利埃无叶草的营养性能下降，但对其繁殖性能却产生了截然相反的影响。然而，若不采取任何保护措施，进一步的森林侵占会加剧光竞争与土壤酸化，威胁该物种的存续，并推动其灭绝债务的偿付。