Impact of riparian buffer guidelines on old growth in western boreal forests of Canada

Abstract

As timber harvest expands over a previously unharvested landbase, riparian buffers will make up an increasing proportion of old-growth forests. This study examined the impact of different criteria for the formulation of riparian buffers on the temporal supply of old-growth forests in western boreal Canada. Three common criteria were applied through computer simulation over an ∼313 000-ha timber merchantable landbase for a 200-year time horizon. Guideline criteria included: (1) broad prescriptive approach, i.e. few-sizes-fit-all; (2) special management of fish-bearing streams; and (3) two-zone, partial harvest buffers. While the numerical results are specific to this study area, they suggested five general results applicable to forest planning. (1) Regardless of the criteria for buffers, old growth accumulated over the first 40-60 years thereafter it dropped to 2-4 per cent of the total landbase after 100 years. (2) Guidelines recognizing fish-bearing water bodies retained more old growth, particularly conifer, because of their application to higher elevation and more intermittent stream types. Few-sizes-fit-all retained the most deciduous and mixed-wood old growth, i.e. low elevation forest types. Two-zone buffers exhibited less temporal variance but an overall lower amount of old growth. (3) Operational and field interpretations of the few-sizes-fit-all guidelines retained three times more riparian area and three to seven times more old growth than just the planning phase alone. (4) Old-growth mixed-wood forests virtually disappeared from both timber harvest and riparian landbases. (5) The primary location of old growth shifted from the harvest to the riparian landbase.