Data from: Early plant recruitment stages set the template for the development of vegetation patterns along a hydrological gradient

1. Recruitment processes are critical components of a plant's life
cycle. However, in comparison with later stages in the plant life cycle
(e.g. competition among adults), relatively little is known about their
contribution to the regulation of plant species distribution. Particularly
little is known about the individual contributions of the three main
recruitment processes—germination, seedling survival, and seedling
growth—to community assembly, while quantitative information on these
contributions is essential for a more mechanistic understanding of the
regulation of plant species distribution and biodiversity. 2. Riparian
zones along streams provide a globally-relevant case study for evaluating
the importance of the different stages of plant recruitment. The natural
hydrological gradients of stream riparian zones are currently being
restored after a period of worldwide habitat degradation. To identify how
recruitment contributes to vegetation patterns and biodiversity in
riparian zones, we carried out field experiments at restored lowland
streams. We quantified the germination of introduced seeds, and survival
and growth of introduced seedlings of 17 riparian plant species across a
gradient from the stream channel to upland. 3. The hydrological gradient
of riparian zones acted as a strong environmental filter on all three
recruitment processes, through imposing an abiotic limitation (excess
water) at low elevations and a resource limitation (water shortage) at
higher elevations. Other variables, such as soil organic matter content
and nutrient availability, only affected recruitment marginally. 4.
Species-specific patterns of environmental filtering initiated niche
segregation along the riparian gradient during all three recruitment
processes, but particularly during germination and seedling growth. These
recruitment niches appeared strongly related to indicator values for adult
distribution optima, suggesting that at least some riparian plant species
may have evolutionary adaptations that promote recruitment under
favourable hydrological conditions for adult growth and reproduction. 5.
Our results suggest that strong environmental filtering during germination
and seedling growth plays an important role in determining later adult
distributions, by forming the spatial template on which all subsequent
processes operate. In addition to well-known mechanisms, such as
competitive exclusion at the adult stage, environmental filtering during
early recruitment stages already strongly affect plant distribution and
diversity.