Consequences of various landscape-scale ecosystem management strategies and fire cycles on age-class structure and harvest in boreal forests

Abstract

At the landscape scale, one of the key indicators of sustainable forest management is the age-class distribution of stands, since it provides a coarse synopsis of habitat potential, structural complexity, and stand volume, and it is directly modified by timber extraction and wildfire. To explore the consequences of several landscape-scale boreal forest management strategies on age-class structure in the Mauricie region of Quebec, we used spatially explicit simulation modelling. Our study investigated three different harvesting strategies (the one currently practiced and two different strategies to maintain late seral stands) and interactions between fire and harvesting on stand age-class distribution. We found that the legacy of initial forested age structure and its spatial configuration can pose short-(<50 years) to medium-term (150-300 years) challenges to balancing wood supply and ecological objectives. Also, ongoing disturbance by fire, even at relatively long cycles in relation to historic levels, can further constrain the achievement of both timber and biodiversity goals. For example, when fire was combined with management, harvest shortfalls occurred in all scenarios with a fire cycle of 100 years and most scenarios with a fire cycle of 150 years. Even a fire cycle of 500 years led to a reduction in older forest when its maintenance was not a primary constraint. Our results highlight the need to consider the broad-scale effects of natural disturbance when developing ecosystem management policies and the importance of prioritizing objectives when planning for multiple resource use.Résumé : À l'échelle du paysage, un des indicateurs clés d'un aménagement forestier durable est la distribution des classes d'âges des peuplements étant donné qu'elle fournit un aperçu grossier des habitats potentiels, de la complexité structurale et du volume du peuplement et qu'elle est directement modifiée par le prélèvement de matière ligneuse et les feux de forêt. Nous avons utilisé un modèle de simulation spatialement explicite pour étudier les conséquences de plusieurs stratégies d'aménagement forestier à l'échelle du paysage en forêt boréale sur la structure des classes d'âges dans la région de la Mauricie, au Québec. Nous avons étudié trois stratégies de récolte (celle présentement utilisée dans la pratique et deux autres stratégies visant à maintenir les peuplements de fin de succession) et les interactions entre le feu et la récolte sur la distribution des classes d'âges des peuplements. Nous avons constaté que l'héritage laissé par la structure d'âge initiale de la forêt et sa configuration spatiale peuvent constituer des défis à court (<50 ans) et moyen (150-300 ans) termes pour arriver à concilier l'approvisionnement en bois et les objectifs écologi-ques. De plus, les perturbations dues aux feux, même avec des cycles relativement longs comparativement aux cycles passés peuvent compliquer encore davantage l'atteinte des objectifs de production de bois et de conservation de la biodiversité. Par exemple, lor...

Using spatially explicit simulations to explore size distribution and spacing of regenerating areas produced by wildfires: recommendations for designing harvest agglomerations for the Canadian boreal forest

“…For areas characterized by mean fire sizes or fire cycles not represented, the nearest values could be used or interpolated from other regimes in the tables. Furthermore, to take into account catastrophic events and possible interactions between cutting activities and uncontrolled fire events , Fall et al 2004, we have truncated the harvest agglomeration size distribution to 100 000 ha for the fire regime controlled by 60 000-ha mean fire size and to about the 90 th percentile of the fire size distribution for regimes with 3000-ha and 15 000-ha mean fire sizes. Resulting maximum class sizes are 5000-10 000 ha and 20 000-50 000 ha for the 3000-ha and 15 000-ha mean fire size regimes, respectively (Table 3).…”

Challenges and implications of incorporating multi-cohort management in northeastern Ontario, Canada: A case study

“…We did not include fire occurrence in the model, so if our assumption of effective fire suppression is wrong additional stand-replacing disturbances other than clearcutting can be expected (Fall et al 2004). However, in Ontario if large fires that have an impact wood supply occur, the wood supply modelling is redone.…”

“…The annual harvest rate inevitably declines when a traditional even-aged silviculture with a targeted regulated forest on short (i.e., <100 year) rotations shifts to incorporate the maintenance of older age classes, including mid-and lateseral forests. For example, Fall et al (2004) reported that a harvest rate of 65% of maximum harvest (regulated forest on a rotation age of 100 years) maintains harvest levels and older stand age classes compared to extended rotations without fire reductions. However, an analysis has yet to be done using an operational forest management plan that even currently includes some regulated constraints on the maintenance of old-growth targets and protected forested areas.…”

A Real Options Approach to Forest-Management Decision Making to Protect Caribou under the Threat of Extinction

“…We used a landscape-level disturbance simulation model (Fall et al 2004) to estimate the expected amount and variability of habitat. In overview, the simulation model captures both landscape disturbance and forest management and generates indicators of forest structure through time.…”

“…To parameterize the simulation model, estimates of the fire cycle and number of fires per year are needed (Fall et al 2004). The number of fires per year is equal to the forested area divided by mean fire size and fire cycle.…”