As mentioned above, Smil estimates that the world average for wind, hydro and solar power production is 1 W/m2, 3 W/m2 and 5 W/m2 respectively. In order to match these power densities, plantation yields must reach 17 t/ha, 50 t/ha and 83 t/ha for wind, hydro and solar respectively. This seems achievable for tropical plantations – Smil estimate that large scale plantations with eucalyptus, acacia, leucaena, pinus and dalbergia in tropical and subtropical regions yield 20–25 t/ha, equivalent to 1.20–1.50 W/m2. It also seems achievable for elephant grasses, e.g. miscanthus (10–40 t/ha, or 0.6–2.4 W/m2), and napier (15–80 t/ha, or 0.9–4.8 W/m2), but unlikely for forest and many other types of biomass crops – Smil's estimate for natural temperate mixed forests is 1.5–2 dry tonnes per hectare (2–2,5 m3, equivalent to 0.1 W/m2), ranging from 0.9 m3 in Greece to 6 m3 in France).