Forest fires reset genetic structure of seeders and preserve that of sprouters, evidence in South American Nothofagus

PREMOLI, A.C.; MATHIASEN, P.; KITZBERGER, T.

Bariloche

Congreso; VI Southern Connection Congress; 2010

Southern Connection

In northern Patagonia, Nothofagus species are dominant components along west-to-east precipitation gradients where fire is the predominant coarse-scale disturbance. We tested the hypothesis that genetic consequences of fire i.e. levels of diversity and spatial distribution of genotypes, vary in Nothofagus according to specific life history traits. We followed a spatially explicit sampling design to collect leaf tissue for genetic analyses using nuclear markers on mature and postfire forest stands of obligate seeders (high-elevation dry N. pumilio and low-elevation mesic N. dombeyi) and the resprouter N. antarctica. Postfire even-aged stands of obligate seeders held relatively reduced polymorphism due to drift as few remnant trees recolonize burned sites. Also a uniform spatial distribution of genotypes resulted from synchronic establishment of closely related progeny produced during masting after fire. In contrast, mature stands of seeders undergoing gap-phase regeneration yielded increased genetic diversity and a significant clustering of genotypes at short spatial scales as a result of distinct mother trees contributing to local establishment. On the other hand, sprouting after fire preserved diversity and complexity. Given that fire frequency is expected to increase under warming scenarios, actions should be taken to facilitate postfire establishment of seeders such as passive restoration of N. pumilio drylands and exclosure of herbivores within burned N. dombeyi forests.