Background information and definitions
Watering seedlings can relieve drought stress in young trees and may therefore enhance their survival and growth. However, it may also enhance growth of undesired competing plants.
Supporting evidence from individual studies
A replicated, randomized, controlled study in 2004–2004 in one site in southern Spain (Mendoza, Zamora & Castro 2009) found that watering sown seeds increased or had no effect on the emergence and survival of trees, depending on species. In 2003, watering increased seedling emergence during the first two years for three of six species: holly oak Quercus ilex (watered: 43–57%; unwatered: 37–49%), common whitebeam Sorbus aria (watered: 7–34%; unwatered: 4-24%) and common yew Taxus baccata (watered: 23–39%; unwatered: 1–9%). In 2004, at the same site, watering increased seedling emergence during the first two years for two of five species: Scotch pine in open areas and woodland (watered: 37–42%; unwatered: 22–24%), but not shrubland, and whitebeam in woodland (watered: 32%; unwatered: 12–28%), but not open or shrubland. In 2003, watering increased seedling survival of all six species during the first two years across all three habitats (watered: approx. 0–100%; unwatered: approx. 0–90%; data taken from graphs). In 2004, watering did not increase seedling survival, except for Scotch pine in open areas and scrubland (watered: 2–39%; unwatered: 0–5%) and whitebeam in open areas (watered: 0–40%; unwatered: 0–19%). Experiments contained 180 (in 2003) and 90 (in 2004) plots (20 × 20 cm) across three open areas, scrubland and woodlands. Each plot contained the following seeds: 5 holm oak; 5 Pyrenean oak Q. pyrenaica; 15 Italian maple Acer opalus; 15 common whitebeam; 15 Scotch pine; 10 common yew (only in 2003). Half of the plots were watered during the year of sowing (2 l of water to a 30 × 30 cm area, frequency unknown). The year 2004 was wetter than 2003 (mean volumic water content of unwatered plots in summer: 2003: 8%; 2004: 18%).Study and other actions tested