Photosynthetic production of ground vegetation in different-aged Scots pine (Pinus sylvestris) forests
2011
Kulmala, L. | Pumpanen, J. | Kolari, P. | Muukkonen, P. | Hari, P. | Vesala, T.
The photosynthesis of ground vegetation is dependent on species composition and environmental factors that are extremely diverse during forest succession. However, present in situ measurements over the gross primary production (GPP) of ground vegetation are unable to cover this variability. The primary objective of the present study was to estimate the GPP of ground vegetation in five differently aged Scots pine (Pinus sylvestris L.) forests in southern Finland during the growing season of 2006 by using temperature, soil moisture, photosynthetically active radiation, and biomass of the ground vegetation to run a known process-based model. The GPP of ground vegetation was approximately 350 g·m-2 at the 6- and 12-year-old sites and 168, 146, and 41 g·m-2 thereafter at the 20-, 45-, and 120-year-old sites, respectively. The values decreased with stand age, because as the stand ages, light availability decreases, the dominant species below the canopy show lower rates of photosynthesis than species in open areas, and the biomass of the ground vegetation decreases. Grasses and herbs took up nearly half of the value at the youngest site but their role decreased thereafter, whereas low shrubs were responsible for most of the GPP of ground vegetation below closed canopies.
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