Abstract. We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above-ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan.Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above-ground architecture of these two species. In all stands light capture of plants increased with their above-ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better-lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands 'later successional' species had higher light harvesting efficiencies for the same plant height than 'early successional' species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves.This shows how plant stature, plasticity in above-ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series.Keywords: Canopy structure; Grazing; Light acquisition efficiency; Photon flux; Plant architecture; Plant size inequality; Plasticity.Nomenclature: Makino (1962);Ohwi (1965).Abbreviations: LAI = Leaf area index; LAR = Leaf Area Ratio; LMR = Leaf Mass Ratio; PPFD = Photosynthetically active photon flux density; SLA = Specific Leaf Area.

Abstract. We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above-ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan.Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above-ground architecture of these two species. In all stands light capture of plants increased with their above-ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better-lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands 'later successional' species had higher light harvesting efficiencies for the same plant height than 'early successional' species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves.This shows how plant stature, plasticity in above-ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series.Keywords: Canopy structure; Grazing; Light acquisition efficiency; Photon flux; Plant architecture; Plant size inequality; Plasticity.Nomenclature: Makino (1962);Ohwi (1965).Abbreviations: LAI = Leaf area index; LAR = Leaf Area Ratio; LMR = Leaf Mass Ratio; PPFD = Photosynthetically active photon flux density; SLA = Specific Leaf Area.

Inland dunes in northwestern Europe support a number of dry vegetation types. These ecosystems are poor in nutrients and it has been suggested that accumulation of nutrients triggers succession in such systems.We studied the accumulation of organic matter and N and P over a 30 months period in two adjacent ecosystems, the Spergulo-Corynephoretum and the Genisto-Callunetum. Amounts of plant matter and soil organic matter significantly accumulated during the sampling period in the Genisto-CaUunetum but not in the SperguloCorynephoretum. While nutrient concentrations of live and dead phytomass in the Spergulo-Corynephoretum were significantly higher than in the Genisto-Callunetum, total nutrient contents in the systems showed the opposite pattern. N and P concentrations in litter were relatively high compared with the other fractions of plant matter and the amount of N significantly increased in both ecosystems during the sampling period. Soil moisture contents showed a seasonal pattern. It was highest in the top soil layer and higher in the Genisto-Callunetum than in the Spergulo-Corynephoretum.The estimated annual increase of total N in these two ecosystems was consistent with rates of atmospheric N deposition (wet fall ÷ dry fall) measured in comparable Dutch sites.