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To investigate the cover, frequency, biomass, and productivity of endolithic and epilithic lower plants on temperate zone cliff faces, rock samples were randomly collected from the Niagara Escarpment in southern Ontario, Canada. Chlorophyll was extracted using dimethyl sulfoxide (DMSO), and CO2 gas exchange was measured in the laboratory using infrared gas analysis. Epilithic surface cover averaged 26% for cyanobacteria, 3% for green algae, and 20% for lichens. Endoliths were present below 6% of the surface area, with chasmoendoliths about twice as common as cryptoendoliths. Fungi were by far the most common organisms. The cliffs contained 73.0 mg chi a and 19.8 mg chi b per square meter; 15% and 23% of these, respectively, were in the endolithic zone. Biomass of primary producers (algae, cyanobacteria, and lichen photobionts) was 1.5-73 g dry mass m(-2) total, and 0.3-14 g m(-2) in the endolithic zone alone. Photosynthetic carbon uptake was 0.0021 mg CO2 cm(-2) h(-1) at 700 mu mol m(-2) s(-1) photosynthetically active radiation (PAR). At PAR = 130 mu mol m(-2) s(-1), a small amount of carbon was released (0.5 mg CO2 m(-2) s(-1)); dark respiration was 0.0096 mg CO2 cm(-2) h(-1). The upper limit for carbon fixation by primary producers was estimated from this to be 2.3 mg CO2 cm(-2) yr(-1), but endolithic and epilithic zones as a whole were shown to be net consumers of CO2. Cover, occurrence, biomass, and productivity of endoliths and epiliths showed most of their variability on a scale smaller than a square meter; there was little or no consistent variation from north to south or from cliff top to bottom. Seasonal changes were absent when chlorophyll and gas exchange rates were expressed on a unit cliff surface basis. Gas exchange on a chlorophyll a basis, as well as the chi a:phaeophytin a ratio, showed a general decline between spring and fall.