Global Ecology Unit CREAF-CSIC-UAB, CSIC, Bellaterra, Spain.
CREAF, Cerdanyola del Vallès, Spain.
Glob Chang Biol. 2017 Oct;23(10):4267-4279. doi: 10.1111/gcb.13763. Epub 2017 Jun 12.
Global warming and recurring drought are expected to accelerate water limitation for plant communities in semiarid Mediterranean ecosystems and produce directional shifts in structure and composition that are not easily detected, and supporting evidence is scarce. We conducted a long-term (17 years) nocturnal-warming (+0.6°C) and drought (-40% rainfall) experiments in an early-successional Mediterranean shrubland to study the changes in community structure and composition, contrasting functional groups and dominant species, and the superimposed effects of natural extreme drought. Species richness decreased in both the warming and drought treatments. Responses to the moderate warming were associated with decreases in herb abundance, and responses to the drought were associated with decreases in both herb and shrub abundances. The drought also significantly decreased community diversity and evenness. Changes in abundance differed between herbs (decreases) and shrubs (increases or no changes). Both warming and drought, especially drought, increased the relative species richness and abundance of shrubs, favoring the establishment of shrubs. Both warming and drought produced significant shifts in plant community composition. Experimental warming shifted the community composition from Erica multiflora toward Rosmarinus officinalis, and drought consistently shifted the composition toward Globularia alypum. The responses in biodiversity (e.g., community biodiversity, changes of functional groups and compositional shifts) were also strongly correlated with atmospheric drought (SPEI) in winter-spring and/or summer, indicating sensitivity to water limitation in this early-successional Mediterranean ecosystem, especially to natural extreme droughts. Our results suggest that the shifts in species assembles and community diversity and composition are accelerated by the long-term nocturnal-warming and drought, combined with natural severe droughts, and that the magnitude of the impacts of climate change is also correlated with the successional status of ecosystem. The results thus highlight the necessity for assessing the impacts on ecosystemic functioning and services and developing effective measures for conserving biodiversity.
全球变暖以及反复出现的干旱预计将加速半干旱地中海生态系统中植物群落的水分限制，并导致结构和组成发生不易察觉的定向变化，而且相关证据还很缺乏。我们在一个早期演替的地中海灌丛中进行了一项长期（17 年）的夜间增温（+0.6°C）和干旱（-40%降雨量）实验，以研究群落结构和组成的变化，对比功能群和优势种，并叠加自然极端干旱的影响。在增温和干旱处理中，物种丰富度都有所下降。中度增温的响应与草本植物丰度的降低有关，而干旱的响应与草本植物和灌木丰度的降低有关。干旱还显著降低了群落的多样性和均匀度。草本植物（减少）和灌木（增加或无变化）的丰度变化不同。增温和干旱，特别是干旱，增加了灌木的相对物种丰富度和丰度，有利于灌木的建立。增温和干旱都导致了植物群落组成的显著变化。实验增温使群落组成从 Erica multiflora 向 Rosmarinus officinalis 转变，而干旱则一致地使组成向 Globularia alypum 转变。生物多样性的响应（例如，群落生物多样性、功能群的变化和组成的变化）也与冬季-春季和/或夏季的大气干旱（SPEI）强烈相关，表明该早期演替的地中海生态系统对水分限制敏感，特别是对自然极端干旱敏感。我们的结果表明，长期夜间增温和干旱，加上自然严重干旱，加速了物种组合、群落多样性和组成的变化，气候变化的影响程度也与生态系统的演替状态有关。因此，这些结果强调了评估对生态系统功能和服务的影响以及制定保护生物多样性的有效措施的必要性。
