Genetic Diversity and Structure in Austrocedrus chilensis Populations: Implications for Dryland Forest Restoration

Abstract

In South America, 94% of dry-temperate lands present some degree of environmental degradation, highlighting the need for ecological restoration. We analyzed geographic patterns of genetic variation in Austrocedrus chilensis, a dominant conifer of the steppe-forest ecotone in the eastern Andes, to examine its potential for restoration. We sampled 67 locations in Argentina and estimated genetic parameters to determine the effects of historical factors affecting diversity, together with inbreeding and gene flow, using 12 allozyme loci. Genetic diversity decreased southwards in eastern populations, which are marginal for the range of the species and patchily distributed, while high genetic admixture was detected in continuous western populations, possibly reflecting postglacial migrations from northern and eastern sources. Higher inbreeding (F IS > 0.14) was recorded in northern compared with southern populations, attributed to the impact of recent bottlenecks resulting from anthropogenic fires. Gene flow was found to be moderate overall (F ST = 0.12). The implications of these results for restoration actions focusing on Austrocedrus were explored. Relatively small, inbred yet genetically diverse northern populations should be the subject of passive restoration efforts, while experimental common gardens should be established toward the south, to support active restoration approaches. This illustrates how ahead of time information on patterns of genetic variation can support restoration efforts for dryland tree species.

Forest Landscape Restoration in the Drylands of Latin America

“…For example, the genetic structure of monospecific dryland forests of southern Argentina was assessed, focusing on the monotypic conifer Austrocedrus chilensis. While in the north marginal populations were relatively small and inbred yet genetically diverse, toward the south larger and relatively continuous populations had reduced diversity and showed signals of genetic admixture, highlighting the need for active restoration efforts (Souto et al 2011). This illustrates the risk of assuming that relatively small, isolated populations are genetically impoverished, and large continuous populations are highly genetically variable (Souto et al 2011).…”

How Many Seed Transfer Zones Are Necessary for the Preservation of the Genetic Identity of Austrocedrus chilensis Natural Populations in Argentina?

“…Souto et al () found higher levels of diversity and differentiation not only at species level but also at population level. As a general result, this could be attributed to sampling differences, because Souto et al () over‐represented the marginal forest patches from the steppe, which turned out to be the most diverse in both studies.…”

“…Souto et al () revealed eight enzymes, whereas Pastorino and Gallo () revealed just seven, of which five were coincident. One of the non‐coinciding enzymes in the set utilized by Souto et al () is cathodal peroxidase (Per Cat E.C.1.11.1.7).…”

“…Souto et al () revealed eight enzymes, whereas Pastorino and Gallo () revealed just seven, of which five were coincident. One of the non‐coinciding enzymes in the set utilized by Souto et al () is cathodal peroxidase (Per Cat E.C.1.11.1.7). Peroxidases are known to vary occasionally in relation to the environment (Bergmann et al ; Bergmann & Hattemer ), a feature that should be tested on the species of interest before using this kind of enzyme in population genetic studies.…”

“…Unless additional information is presented showing genetic isolation between particular forest fragments, a distance of less than 5.000 m cannot be accepted as enough evidence of isolation. Under this conservative assumption, the 67 sampling points of Souto et al () would represent only 38 populations.…”