Partial harvesting in the Canadian boreal: Success will depend on stand dynamic responses

Abstract

In the past 10 to 15 years, alternative silvicultural treatments involving partial harvesting have been developed for boreal forests, with the goal of achieving a balance between biodiversity maintenance and continued timber production. Most prior research has focussed on the impacts of partial harvesting on biological diversity, while stand dynamic responses remain little studied. In this paper we explore partial stand harvesting in the Canadian boreal-its rationale, current extent, and impact on stand dynamic patterns. Empirical studies from the boreal and elsewhere indicate that residual trees of many species respond to partial harvesting with enhanced growth, commonly showing a lagged response after which peak growth occurs five to 25 years following harvest. Post-harvest mortality is also prevalent but much more variable, with losses of residual trees ranging from nearly zero to more than 50% above background mortality rates in the initial years following harvest. With the exception of strip cutting in parts of northern Ontario and Quebec (HARP/CPPTM), operational partial harvesting in the Canadian boreal currently involves very low levels of retention. Available data suggest that such low retention levels, particularly when spatially dispersed, generally result in unacceptably high rates of post-harvest mortality, which are unlikely to be offset by increases in residual tree growth. There is an urgent need for development of spatially explicit stand simulation models that will allow accurate yield predictions for partial harvest systems to assess their feasibility in boreal forest management.Key words: ecosystem management, natural disturbance emulation, boreal forest, partial cut, structural retention, growth response, windthrow, post-harvest mortality RÉSUMÉ Au cours des dix à quinze dernières années, des traitements sylvicoles alternatifs comprenant une coupe partielle ont été élaborés en forêt boréale, dans le but d'obtenir un équilibre entre le maintien de la biodiversité et la production continue de matière ligneuse. La majeure partie de la recherche réalisée à ce jour a porté sur les impacts de la coupe partielle sur la diversité biologique, tandis que les réactions au niveau de la dynamique du peuplement recevaient peu d'attention. Dans cet article, nous explorons la coupe partielle des peuplements dans les forêts boréales du Canada : le rationnel, le niveau actuel d'utilisation et les conséquences sur les patrons de dynamique des peuplements. Les études empiriques en provenance des forêts boréales et des autres forêts indiquent que les arbres résiduels de plusieurs espèces réagissent à la coupe partielle par un accroissement de la croissance, démontrant généralement une réaction déphasée suivie d'un pic de croissance survenant entre 5 et 25 ans après la récolte. La mortalité après coupe est également présente quoique plus variable, avec des pertes parmi les arbres résiduels avec des taux de zéro à plus de 50 % de mortalité par rapport au milieu naturel au cours des premières années suivant...

Elevated mortality of residual trees following structural retention harvesting in boreal mixedwoods

“…Additionally, the majority of observations have been from the U.S Pacific Northwest and British Columbia (Thorpe and Thomas 2007). To our knowledge, this study is the first in this region to demonstrate elevated mortality rates of retention trees following harvesting.…”

“…It is assumed that the retention of later seral conditions will contribute to sustaining ecosystem functions and biological diversity at the stand level (Franklin et al 1997, Bergeron et al 2002. Thus, it has been widely promoted and adopted as a forest management strategy in boreal and temperate forest ecosystems (Bourgeois et al 2007, Thorpe andThomas 2007). However, since the policies and guidelines of this harvesting practice have been developed predominantly from expert opinion (Halpern et al 2005), many details regarding how to best implement retention systems are still unclear.…”

Differentiation of Alternate Harvesting Practices Using Annual Time Series of Landsat Data

“…This is best exemplified through the range in greenness values of the time series, which show clearcut with residual practices to be not significantly different from partial cuts. As clearcut residual polygons retain large mature trees to aid in regeneration, the average greenness of the polygon has less deviation from the pre-change spectral response [40]. Depending on the configuration of the residual cover, it may confound the automated detection and attribution of the change event using the Landsat time series.…”

Effects of partial harvesting on vertebrate species associated with late-successional forests in Ontario’s boreal region

“…It is believed that partial harvesting can emulate various nonstand-replacing disturbances that are common in boreal forests (e.g., insects, wind), and enable the development of late-seral stand structures that do not arise within conventional rotation lengths under clearcut management (Franklin et al 1997, Harvey et al 2002, Thorpe and Thomas 2007. Numerous wildlife species are associated with mature-and old-forest habitats in Ontario's boreal region, and it is hoped that by maintaining structural characteristics of these habitats, partial-harvest silviculture could provide suitable conditions for late-successional species.…”