Responses to canopy openings in architectural development of saplings ineight deciduous broadleaved tree species

摘要

Crown-architectural responses to small canopy openings, in relation to relative height growth rate (RHGR), were examined in saplings (0.5-2.3 m tall) of eight deciduous broad-leaved tree species in northern Japan. Five species were lateral-growth type with high leaf-support cost (branch mass per leaf area) to display many small leaves over a wide area. while three species were vertical-growth type with low leaf-support cost due to a small number of large leaves along a main trunk. In closed-canopy conditions, the lateral-growth species showed a greater increase in leaf area with increasing sapling size than the vertical-growth species. Net production rate (NP) per leaf area was not clearly different between the two groups. As a result, NP per sapling also increased to a greater extent with increasing sapling size for the lateral-growth species. The NP per leaf area was increased in canopy openings for the two groups, but this increase was not clearly distinguished between the two groups. The vertical-growth species supported greater leaf area per sapling in canopy openings because of the low cost of leaf support, which resulted in a greater increase in NP per sapling compared with the lateral-growth species. The lateral-growth species allocated more to trunk in canopy openings, keeping leaf area constant and decreasing the cost of leaf support. The RHGR of the vertical-growth species tended to be greater than that of the lateral-growth species in closed-canopy conditions. RHGR of all species was increased in canopy openings to a similar degree in both groups. Multiple regression analysis showed that RHGR of the lateral-growth species depended on both NP per sapling and allocation to trunk, while that of the vertical-growth species depended strongly on NP per sapling alone. Thus, saplings of each group responded to canopy openings in contrasting ways to increase RHGR.