Soil seed bank of Austrocedrus chilensis (D. Don) Pic. Serm. et Bizarri related to different degrees of fire disturbance in two sites of southern patagonia, Argentina

URRETAVIZCAYA M.F.; DEFOSSÉ G.E.

Forest Ecology and Management

Elsevier B.V.

Lugar: Diboll, USA; Año: 2004 vol. 187 p. 361 - 372

0378 1127

Austrocedrus chilensis (D. Don) Pic. Serm. et Bizarri, called locally "cypress" is among the most important native tree species that compose the temperate Subantarctic forests of Patagonia in Argentina. Cypress grows in either humid, mesic or dry sites, being fire the most important natural disturbance affecting these forests. Regeneration of cypress in burned areas is very slow, and may depend on a series of environmental and biotic factors, among which the availability of seeds could be extremely important. In this study, the dynamics of cypress soil seed bank was determined in two sites of its southern distribution area (Trevelin, 43º 12´ S, 71º 31´ W, and El Bolsón 41º 59´ S, 71º 33´ W), and for three levels of fire disturbance (treatments): undisturbed (UN); partially burned (PB) and completely burned (CB). For about two growing seasons and at tri-monthly intervals, soil seed bank was measured by both direct and indirect methods. In the direct method, seeds were visually classified in apparently viable (AVS) and apparently non-viable seeds (ANVS). The indirect method implied germination of seeds in a germination chamber after being stored to mimic natural conditions and break dormancy. For both study sites and all dates, the undisturbed treatment showed significantly higher (***P<0.001) seed numbers than the other two (partially and completely burned). Before the autumn seed rain, all seeds were classified as ANVS and did not germinate. After that seed rain, a high proportion of seeds appeared to be AVS in both sites, showing a similar trend for all treatments, although in dissimilar numbers (undisturbed > partially > completely burned). The number of AVS steadily diminished during winter and spring, to practically disappear at the beginning of the summer, coinciding with the results obtained with the germination method. This behaviour confirms that cypress has a transient type of soil seed bank, and that the size of this soil seed bank is greatly influenced by the degree of fire disturbance. The amount of AVS that reached the soil at any particular site, however, might also be conditioned by several insects that parasite seeds before the seed rain. The transient soil seed bank and the low seed density found in partially and completely burned areas appears as important constraints for cypress regeneration.(D. Don) Pic. Serm. et Bizarri, called locally "cypress" is among the most important native tree species that compose the temperate Subantarctic forests of Patagonia in Argentina. Cypress grows in either humid, mesic or dry sites, being fire the most important natural disturbance affecting these forests. Regeneration of cypress in burned areas is very slow, and may depend on a series of environmental and biotic factors, among which the availability of seeds could be extremely important. In this study, the dynamics of cypress soil seed bank was determined in two sites of its southern distribution area (Trevelin, 43º 12´ S, 71º 31´ W, and El Bolsón 41º 59´ S, 71º 33´ W), and for three levels of fire disturbance (treatments): undisturbed (UN); partially burned (PB) and completely burned (CB). For about two growing seasons and at tri-monthly intervals, soil seed bank was measured by both direct and indirect methods. In the direct method, seeds were visually classified in apparently viable (AVS) and apparently non-viable seeds (ANVS). The indirect method implied germination of seeds in a germination chamber after being stored to mimic natural conditions and break dormancy. For both study sites and all dates, the undisturbed treatment showed significantly higher (***P<0.001) seed numbers than the other two (partially and completely burned). Before the autumn seed rain, all seeds were classified as ANVS and did not germinate. After that seed rain, a high proportion of seeds appeared to be AVS in both sites, showing a similar trend for all treatments, although in dissimilar numbers (undisturbed > partially > completely burned). The number of AVS steadily diminished during winter and spring, to practically disappear at the beginning of the summer, coinciding with the results obtained with the germination method. This behaviour confirms that cypress has a transient type of soil seed bank, and that the size of this soil seed bank is greatly influenced by the degree of fire disturbance. The amount of AVS that reached the soil at any particular site, however, might also be conditioned by several insects that parasite seeds before the seed rain. The transient soil seed bank and the low seed density found in partially and completely burned areas appears as important constraints for cypress regeneration.