En skov er et plantesamfund eller en biotop, hvori træer udgør hovedbestanddelen. Endvidere må det kræves, at der er tale om et større areal, minimum 0,5 hektar og en minimumsbredde på 20 meter med træer højere end 5 meter og at trækronerne dækker mere end 10 %.[1] Skov forekommer naturligt overalt på Jorden, bortset fra områder med for lav temperatur eller for tørt klima. Klimaet er afgørende for, hvilken skovtype, der udvikles.
^Skovstatistik 2018 (Webside ikke længere tilgængelig) Thomas Nord-Larsen, Vivian Kvist Johannsen, Torben Riis-Nielsen, Iben Margrete Thomsen og Bruno Bilde Jørgensen (2019). Institut for Geovidenskab og Naturforvaltning, Københavns Universitet, Frederiksberg. 40 s. ill. ISBN978-87-7903-813-4 (web)
^Penn State. (2004, May 6). Missing Chemical Important To Air Pollution Estimates. ScienceDaily Citat: "..."We think we measured all major components of the hydroxyl radical reactants, but there is something still unaccounted for,” says Brune. "We know that something we cannot identify is reacting with the hydroxyl radicals and we know it is temperature dependent and not light dependent. We just do not know what it is."..."
^Carnegie Mellon University. (2014, May 15). Emissions from forests influence very first stage of cloud formation. ScienceDaily Citat: "...This new study uncovers an indispensable ingredient to the long sought-after cloud formation recipe -- highly oxidized organic compounds..."It turns out that sulfuric acid and these oxidized organic compounds are unusually attracted to each other. This remarkably strong association may be a big part of why organics are really drawn to sulfuric acid under modern polluted conditions," Donahue said...The fine-tuned model not only predicted nucleation rates more accurately but also predicted the increases and decreases of nucleation observed in field experiments over the course of a year, especially for measurements near forests. This latter test is a strong confirmation of the fundamental role of emissions from forests in the very first stage of cloud formation, and that the new work may have succeeded in modeling that influence..."