Picea glauca dynamics and spatial pattern of seedlings regeneration along a chronosequence in the mixedwood section of the boreal forest

Abstract

-We studied Picea glauca dynamics in the boreal forest of Saskatchewan, Canada, using 35 stands ranging from < 1 to > 200 y after fire. We determined the spatial pattern and the importance of seedbed conditions to the recruitment of P. glauca. Basal area increased along the chronosequence peaking at 110 y after fire (51.5 m 2 ha -1 ). The ratio of softwood to hardwood increased from 0.03 (16 y) to 17.0 (172 y). Picea glauca tree density increased with stand age, highest densities were observed in a 172 y stand (1413 stems ha -1 ). Picea glauca dominated the canopy between 93 and 172 y after fire. Picea glauca snags appeared about 66 y after fire, and remained relatively low in density until 160 y. Saplings were present at varying densities along the chronosequence. Seedlings established immediately after fire and exhibited bimodality with lowest densities observed between 110 and 125 y. Analysis with Ripley's K, showed that seedlings were mainly distributed at random in young stands but were clumped at a distances < 12 m in old stands. In young stands, the majority of seedlings regenerated on the organic layer (LFH 73%), while recruitment was almost exclusively on logs in old stands (94%). Picea glauca regeneration depended on propagule availability and seedbed characteristics at early stand age. Logs and the resultant canopy gaps formed, appear to be critical for P. glauca regeneration in mature and old stands.Picea glauca / boreal forest / stand dynamics / spatial pattern / Ripley's K Résumé -Dynamique de Picea glauca et répartition spatiale de la régénération selon une chronoséquence située dans une zone de forêt mélangée de la forêt boréale. Nous avons étudié la dynamique de Picea glauca en forêt boréale du Saskatchewan au Canada, en utilisant 35 peuplements dont l'âge va de 1 à 200 ans après incendie. Nous avons étudié la répartition spatiale des semis et mis en évidence l'importance des conditions du milieu de germination pour la régénération de Picea glauca. La surface terrière augmente au cours de la chronoséquence, avec un pic à 110 ans après incendie (51,5 m 3 par ha). Le rapport bois résineux sur bois feuillu s'accroît de 0,03 (16 ans) à 17,0 (172 ans) exprimé en surface terrière. La densité de tiges de Picea glauca augmente avec l'âge du peuplement, la plus forte étant observée dans un peuplement de 172 ans (1413 tiges/ha). Picea glauca occupe une place dominante dans le couvert entre 93 et 172 ans après incendie. On voit apparaître des Picea glauca morts sur pied, environ 66 ans après incendie ; ceux-ci restent peu nombreux jusqu'à 160 ans. On constate la présence de jeunes individus, en nombre plus ou moins grand, tout au long de la chronoséquence. Les semis s'installent aussitôt après incendie. Ils sont particulièrement denses à 50 et à 172 ans, avec un minimum entre 110 et 125 ans. L'analyse, à l'aide de la fonction de Ripley's K, montre que, dans les jeunes peuplements, les semis sont répartis au hasard, alors que dans les peuplements âgés, ils sont groupés par bouquets distants de moin...

Post-harvest soil nitrate dynamics in aspen- and spruce-dominated boreal forests

“…The concern that spruce seedlings experience inadequate N nutrition on clear-cuts because of the shift to nitrate domination (Kronzucker et al, 1997) was not supported according to our results. Vegetation competition (Hangs et al, 2004) and adequate seedbed conditions (Awada et al, 2004) are probably more important than the form of available N for conifer regeneration on harvested western boreal sites.…”

Early vegetation dynamics of Pinus tropicalis Morelet forests after experimental fire (W Cuba)

“…González-Ochoa et al [27] noted that this pattern is favoured by an increase in light, an absence of humus and a nutrient increase in the upper soil layers. Furthermore, therophyte dynamics are related to germination mechanisms [2]. The majority of species that appear immediately after fire have seeds whose germination capability is induced by high temperatures during fire.…”

Short-term effects of fire on plant cover and soil conditions in two Austrocedrus chilensis (cypress) forests in Patagonia, Argentina

“…In contrast, at Bolsón site (a more humid site and with least extreme soil temperature values), this effect seems to be lessened, particularly in the first few years after the fire. Similar to what happens with cypress, in species such as Picea glauca, regeneration in the first years after the fire would depend on the presence of propagules and of the characteristics of the seed bed [4].…”

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Abstract -Early post-fire effects on plant cover, in soil temperature (0,5,20, and 30 cm depth) and moisture (0)(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36), and 40-56 cm depth) were analyzed for two years in two cypress stands in Patagonia, Argentina. Each stand (Trevelin = xeric and Bolsón = mesic) contained three treatments: unburned (UN), partially (PB), and completely burned (CB).

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