The physiological basis for regeneration response to variable retention harvest treatments in three pine species

摘要

Variable retention harvesting (VRH) is promoted for enhancing biodiversity and ecosystem processes in managed forests, but regeneration responses to the complex stand structures that result from VRH are poorly understood. We analyzed foliar stable carbon isotope ratios (delta C-13), oxygen isotope ratios (delta O-18), light-saturated photosynthetic rates (A(max)), stomatal conductance (g(s)) and sizes of pine seedlings in Pinus resinosa stands treated with VRH systems that created different spatial patterns of overstorey retention. Pinus banksiana, P. resinosa and Pinus strobus seedlings in dispersed retention, aggregated retention between small gaps and aggregated retention between large gaps treatments had greater delta C-13, A(max), g(s), diameter and height than seedlings in unharvested treatments, but seedling performance was similar among VRH treatments when averaged across stands. There were no significant differences in delta O-18 associated with any treatment. These results indicate seedling photosynthetic capacity, water relations and growth were improved by VRH, but the spatial pattern of retention had surprisingly little impact on average performance in the first 4 years after harvesting. This suggests retention treatments that produce different residual stand structures can promote similar mean rates of early seedling development when performance is averaged across all of the neighbourhood environments within each treatment.