Greater needle packing (number of needles per unit stem length) among shoots of Picea engelmanii(Parry ex. Engelm.), Abies lasiocarpa ([Hook] Nutt.), and Pinus contorta (Engelm.) collected at sun-exposed locations resulted in leaf temperatures (T1) that were well above air temperature (Ta) and which were closer to optimum for maximum photosynthesis under field conditions. Maximum photosynthesis in these species occurred at leaf temperatures well above mean maximum Ta during most of the summer growth period. An approximate doubling in needle packing on sun shoots of these species, however, led to an estimated temperature enhancement of daily photosynthetic carbon gain of 21 to 36% compared to estimations assuming T1 = Ta for the entire day. Elevated T1 due to needle packing may lead to substantial increases in summer carbon gain for conifers experiencing cold-limited, short growth seasons. © Botanical Society of America. Abstract reproduced by permission.