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Long‐term dynamics of shrub facilitation shape the mixing of evergreen and deciduous oaks in Mediterranean abandoned fields
Journal of Ecology ( IF 5.3 ) Pub Date : 2019-11-19 , DOI: 10.1111/1365-2745.13309 Verónica Cruz‐Alonso 1 , Pedro Villar‐Salvador 1 , Paloma Ruiz‐Benito 1, 2 , Inés Ibáñez 3 , José M. Rey‐Benayas 1
中文翻译：
灌木促进的长期动态影响了地中海荒地中常绿和落叶橡树的混合
更新日期：2019-11-19
Journal of Ecology ( IF 5.3 ) Pub Date : 2019-11-19 , DOI: 10.1111/1365-2745.13309 Verónica Cruz‐Alonso 1 , Pedro Villar‐Salvador 1 , Paloma Ruiz‐Benito 1, 2 , Inés Ibáñez 3 , José M. Rey‐Benayas 1
Affiliation
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- Recovery of Mediterranean forests after field abandonment is a slow process, even without propagule limitations. This is mainly due to stressful conditions for seedling establishment. In this context, shrubs play a critical role in facilitating tree recruitment, but how this process unfolds after field abandonment is not entirely known. We evaluated the long‐term dynamics of facilitation by the nurse shrub Retama sphaerocarpa in the recruitment of two ecologically contrasting oaks, the evergreen Quercus ilex and the deciduous Quercus faginea.
- Thirty years after field abandonment, we dated shrubs and oaks established in an old field to estimate the annual recruitment rates and investigate temporal recruitment patterns. For oaks, we differentiated recruitment at two microsites: open areas or under shrub. To assess how nurse shrubs modulated environmental stressors, we modelled oak recruitment as a function of climatic variables. For the evergreen oak, we assessed these effects within each microsite. Finally, we estimated the annual interaction index between shrubs and evergreen oak juveniles as a function of climatic conditions.
- Each species showed different recruitment pulses during colonization. Recruitment rate was the highest for the shrub, followed by the evergreen oak. Oak colonization under shrubs was appreciable 20 years after field abandonment, when shrub cover reached 2.2%, and concentrated under medium and large shrubs older than 7 years. Shrubs not only accelerated evergreen oak colonization but also attenuated the fluctuations of recruitment pulses. For the evergreen oak, the interaction index indicated facilitation dominance in years with more arid summers (precipitation < 47 mm and heat waves longer than 8 days) and competition in wetter summers.
- Synthesis. Oak colonization in Mediterranean abandoned fields progressed slowly, and only two decades after abandonment pioneer shrub population grew to a level in size and number that could effectively trigger facilitation and accelerate tree recruitment. The shrub nurse effect was unbalanced between oak species, only benefiting the evergreen oak, and it was more prevalent in arid years. Our study illustrates the build‐up of shrub facilitation during forest recolonization and the varying nature of this process among climatically different years and ecologically distinct species. This information provides insights for assessing and managing Mediterranean forest recovery.
中文翻译：
灌木促进的长期动态影响了地中海荒地中常绿和落叶橡树的混合
- 即使没有繁殖限制，放弃田野后恢复地中海森林也是一个缓慢的过程。这主要是由于幼苗生长的压力条件。在这种情况下，灌木在促进树木募集方面起着关键作用，但是在田间弃耕后该过程如何展开尚不完全清楚。我们评估了护士灌木Retama sphaerocarpa在招募两种具有生态反差的橡树（常绿栎树和落叶栎树）中的长期促进作用。
- 废弃田地三十年后，我们对在一个旧田里建立的灌木和橡树进行了测年，以估算年招聘率并调查临时招聘模式。对于橡树，我们区分了在两个微场所的招聘：开放区域或灌木下。为了评估护士灌木是如何调节环境压力的，我们将橡树募集作为气候变量的函数进行了建模。对于常绿的橡树，我们评估了每个微型站点内的这些影响。最后，我们估算了灌木和常绿橡树幼虫之间的年度相互作用指数随气候条件的变化。
- 每个物种在定殖过程中显示出不同的募集脉冲。灌木丛的招聘率最高，其次是常绿橡树。田间废弃20年后，灌木丛中的橡树定植量可观，当时灌木覆盖率达到2.2％，并集中在年龄大于7年的中型和大型灌木丛中。灌木不仅加速了常绿橡树的定殖，而且减弱了补充脉冲的波动。对于常绿的橡树，相互作用指数表明年份在干旱较多的夏季（降水量<47 mm，热浪超过8天）的促进作用占主导地位，而在潮湿的夏季则表现出竞争优势。
- 合成。地中海废弃土地上的橡树殖民化进展缓慢，仅在废弃的先锋灌木种群数量增加到可以有效触发便利化并加快树木采伐的规模和数量之后的仅仅二十年。灌木护理效果在橡树种之间是不平衡的，仅使常绿橡树受益，并且在干旱年份更为普遍。我们的研究说明了森林重新定居过程中灌木林易化性的建立，以及这一过程在气候不同年份和生态上不同物种之间的不同性质。这些信息为评估和管理地中海森林恢复提供了见识。
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