Structural and functional responses of riparian vegetation to human disturbance: performance and spatial scale-dependence
Aguiar, Francisca C.; Ferreira, M. Teresa Albuquerque; Segurado, Pedro
published: Aug 1, 2009
ArtNo. ESP141017503006, Price: 29.00 €
Successful protection, enhancement and management of surface inland waters require bioassessment and monitoring of ecological quality, as recognized by the Water Framework Directive (WFD; EU/2000/60). In the present paper, we aimed at assessing the response to disturbance of structural and functional components of the riparian ecosystem in order to develop a plant-based index of biotic integrity (Riparian Vegetation index, RVI). Further, the implications of Mediterranean conditions and the spatial scale dependency in the index performance and its component metrics were investigated and discussed. Aquatic and bankside plant species were sampled at more than 400 sites of Portuguese rivers, in Spring-Summer of 2004 and 2005. Over 300 plant attributes were pre-screened to select 32 candidate metrics. Both single stressors and composite stressor indices were used in this study. Two spatial scale-approaches were evaluated: the Local River Type - LRT - which follows the Portuguese river typology, and the Regional River Type - RRT -, which clusters the LRT into North and South types. Composition (e.g. cover and number of alien and endemic species) and functional metrics associated with life cycle and reproduction (e.g. numbers of perennial species), or with trophic status (e.g. proportion of nitrophyllous species) were the most responsive to disturbance across types. Overall, the RVI displayed a reliable response to disturbance; although the local approach has a higher discriminatory efficiency, the macro scale approach had a more consistent response to multifaceted human disturbances and a more robust performance, essential for environmental-decision making. Results substantiate the hypothesis that plant-based indices of integrity are scale-dependent, an important consideration in the development of typological-adapted methods either for the WFD implementation or for other assessment and monitoring purposes. Future work is required to calibrate the index for inter-annual variability in plant structure and composition, which is especially relevant in Mediterranean-type rivers.