Stability of the large tree component in treated and untreated late-seral interior ponderosa pine stands (1)

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Date: May 2008
From: Canadian Journal of Forest Research(Vol. 38, Issue 5)
Publisher: NRC Research Press
Document Type: Report
Length: 3,981 words
Lexile Measure: 1380L

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Abstract: Ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) stands with late-seral features are found infrequently, owing to past management activities throughout western North America. Thus, management objectives often focus on maintaining existing late-seral stands. Observations over a 65 year period of stands with no past history of harvest showed substantial ingrowth in the smaller diameter classes and elevated rates of mortality among the largest mature trees in the stand. Adjacent stands, with combinations of thinning and prescribed fire, had far fewer high-risk mature trees and generally lower rates of mortality after treatment. Forecasts using individual-tree diameter growth and mortality models suggest that observed declines in these stands with remaining old trees and a dense understory will continue in the absence of any treatment. Increased vigor in thinned stands appeared to be offset by an increase in mortality of large trees when thinning was followed by prescribed fire.

Resume : Partout dans l'ouest de l'Amerique du Nord, il est peu frequent de rencontrer des peuplements de pin ponderosa (Pinus ponderosa Dougl. ex P. & C. Laws.) aux derniers stades de succession ecologique a cause du type d'amenagement pratique dans le passe. Par consequent, les objectifs d'amenagement sont souvent axes sur le maintien des peuplements aux derniers stades de succession ecologique qui existent encore. Des observations s'etalant sur une periode de plus de 65 ans dans des peuplements qui n'ont pas ete recoltes dans le passe montrent que le recrutement est eleve dans les classes inferieures de diametre et que le taux de mortalite est eleve parmi les plus gros arbres matures. Il y a beaucoup moins d'arbres matures a haut risque et le taux de mortalite est generalement plus faible dans les peuplements adjacents apres qu'ils aient ete soumis a diverses combinaisons d'eclaircie et de brulage dirige. Des previsions basees sur la croissance en diametre des arbres et des modeles de mortalite indiquent que le declin va se poursuivre en l'absence de traitements dans les peuplements ou de vieux arbres persistent et dont le sous-etage est dense. Dans les peuplements eclaircis, l'augmentation de la vigueur semble contrebalancee par un accroissement de la mortalite chez les gros arbres lorsque l'eclaircie est suivie d'un brulage dirige.

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Introduction

Ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) is widely distributed throughout western North America. The species is important in interior forests both commercially and for its contribution to forest structure and habitat. Throughout its range, stand structures have changed substantially during the last century, primarily owing to two factors: past harvesting practices and fire exclusion (Skinner and Chang 1996; Taylor 2000; Fitzgerald 2005).

The exclusion of fire in forests dominated by western pine has led to increases in density among small trees (Laudenslayer et al. 1989; Dolph et al. 1995). The occurrence of this phenomenon is ubiquitous; thus, the open park-like stands thought to be common before European settlement are now rarely encountered. Furthermore, widespread harvesting of interior pine stands has removed much of the large-tree...

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Gale Document Number: GALE|A180697306