Influences of gap microheterogeneity on the regeneration of Nothofagus pumilio in a xeric old-growth forest of northwestern Patagonia, Argentina

Abstract

We experimentally examined the influences of within-gap environmental heterogeneity on regeneration patterns of Nothofagus pumilio (Poepp. & Endl.) Krasser near the xeric limit of its distribution in northern Patagonia, Argentina. Results from this xeric old-growth forest are compared with patterns previously described for the same species in mesic forests. Survival of N. pumilio seedlings beneath tree-fall gaps in this relatively xeric forest appears to be strongly influenced by moisture availability. Seedlings and saplings that have survived this demographic bottleneck are found at microsites where soil water potentials are higher, such as in the shady northern edges of tree-fall gaps (Ψ = -0.46 MPa compared with less than -0.6 MPa in other gap positions) and on coarse woody debris (Ψ = -0.29 MPa, compared with -0.51 MPa on the forest floor). Although gap creation in this dry N. pumilio forest is favorable to tree regeneration by releasing light resources, decreased water resources may switch the system from a light- to a water-limited system in some positions of the gap. This may explain the lack of regeneration of N. pumilio often observed after creation of large gaps towards the xeric end of its range and needs to be considered in the management of this important timber species.