Data from: The abundance and distribution of guilds of riparian woody plants change in response to land use and flow regulation

1. Many riparian ecosystems in Mediterranean Europe are affected by land
use and flow alteration by dams. We focused on understanding how these
stressors and their components affect riparian forests in the region. We
asked: (i) are there well-defined, responsive riparian guilds?; (ii) do
dam-induced stream flows determine abundance and distribution of riparian
guilds? and (iii) what are the main drivers governing composition and
cover of riparian guilds in regulated rivers? 2. We inventoried the cover
of riparian woody species in free-flowing rivers and downstream of dams.
We performed a cluster analysis and ordination to derive riparian guilds,
using abundance data from 66 riparian woody species and 26 functional
plant traits. We used a reduced set of principal components for the
environment, land use and hydrology, and general linear modelling to
explore the effect of these factors (separately and combined) on riparian
guilds. 3. We found that: (i) four dominant guilds are responsive to
disturbance in Southwestern European streams, namely the obligate
riparian, water-stress tolerant, deciduous competitive, and Mediterranean
evergreen guilds ; (ii) a set of land use and hydrological variables
differentially affect the diverse co-occurring riparian guilds; (iii)
frequency and duration of high flow pulses and the low-flow conditions
were major drivers of change in landscapes dominated by intensive
agriculture and forestry; (iv) storage reservoirs reduced the cover of
obligate riparian and Mediterranean evergreen guilds, and increased the
abundance of water-stress tolerant and deciduous competitive guilds, while
run-of-river dams, having limited water storage, reduced both obligate and
deciduous competitive guilds. 4. Synthesis and applications. Future
research, especially in Southwestern Europe, should address the resilience
of riparian guilds and the effects of interacting landscape factors and
stressors on guild distribution. Stream flow regulations downstream of
reservoirs should focus on specific flow components, namely the magnitude
of flows, and frequency and duration of extreme flow events. For
successful mitigation of the dam-induced effects on riparian vegetation,
river management plans must incorporate the environmental and land use
site-specific contexts.