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. 全球范围内，栖息地丧失、片段化与改造正持续威胁众多物种的存续。在小型、退化且孤立的栖息地中，物种种群与个体的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栖息地中以残存种群的形式存活较长时间，但目前学界对灭绝债务背后的种群与个体层面机制仍探索不足。
3. 本研究以西班牙加泰罗尼亚（伊比利亚半岛东北部）地区地中海半自然石灰质草原受森林侵入后的生境为研究对象，针对该区域常见的草地特化型长寿克隆植物蒙彼利埃假叶树（Aphyllanthes monspeliensis L.，天门冬科Asparagaceae）的长期存续机制展开探究。为达成研究目标，我们将评估其营养生长（地上与地下部分）与繁殖生长的各项性能指标，以及相关栖息地与景观（当前与历史）层面的驱动因子。
4. 我们证实了该物种存在灭绝债务现象：当前的植株出现频率与历史连通性（而非当前连通性）相关，同时还发现历史连通性对种子结实量存在正向影响。此外，当前的树木覆盖度会对植株个体大小以及地上/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向影响，而树木覆盖度则会提升种子结实量。由此可见，森林侵入过程也会对部分适合度性状产生正向影响，这可能是因为林木为其提供了更为湿润的微环境。
6. 综合分析表明：栖息地丧失与生境退化会导致草地特化物种蒙彼利埃假叶树的营养生长性能下降，但其对繁殖生长性能的影响则呈现相反趋势。然而，若进一步发生森林侵入，将会加剧光竞争与土壤酸化，威胁该物种的存续，并在未采取保护措施的情况下推动灭绝债务的清偿。