Post-fire regeneration of <i>Pinus</i><i>albicaulis</i>: height–age relationships, age structure, and microsite characteristics

Abstract

We studied post-fire Pinusalbicaulis Engelm. seedling establishment in the Sleeping Child and Saddle Mountain burns of western Montana 26 and 28 years, respectively, after fire. Pinusalbicaulis seeds are dispersed primarily by Clark's nutcracker (Nucifragacolumbiana Wilson) in caches of 1–15 or more seeds. Consequently, P. albicaulis seedlings and trees often occur in clusters. In the Sleeping Child burn we collected regeneration data from 63 quadrats along a 3.6-km transect and from 14 quadrats along a 20.6-km road transect; in the Saddle Mountain buhn we collected data from 41 quadrats along a 3.2-km transect. We determined regression models for height versus age and age versus height relationships for P. albicaulis and Abieslasiocarpa (Hook.) Nutt. and used the latter regression models to construct regeneration age structures for both bums. For both conifers a disproportionately high percentage of regeneration was established between 1977 and 1985, about 17–25 years after fire. Thus, major regeneration was episodic. A small increase in mean seasonal rainfall between 1977 and 1985 possibly contributed to this recruitment surge. Age differences of 1–8 years occurred among seedlings in 65–86% of the seedling and tree clusters sampled, suggesting delayed germination of some cached seeds. Pinusalbicaulis regeneration was more frequently associated with Vacciniumscoparium Leiberg and less frequently associated with Xerophyllumtenax (Pursh) Nutt. and Luzulahitchcockii Hamet-Ahti relative to the overall frequency of occurrence of these plants among quadrats.