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Adjusting free-growing guidance regarding aspen retention in the Cariboo-Chilcotin: Research to operational implementation

Author(s) or contact(s): T.A. Newsome and J.L. Heineman
Source: Forests, Lands, and NR Operations
Subject: Biodiversity, Broadleaf/Conifer Interactions, Forest Policy, Vegetation Management
Series: Technical Report
Other details:  Published 2016. Hardcopy is available.


Over a 6-year period, from 2008-2014, recommendations for change to broadleaf-tree-related free-growing guidelines were made for seven Cariboo Region biogeoclimatic subzones/variants. In large part, the project involved examining available research, primarily from Cariboo Region Experimental Project 1152, and verifying the extent to which it could be applied across the landscape. As a result of this work, in 2013, Chilcotin and Central Cariboo Forest District policy declared aspen a non-deleterious brush species in the SBPSxc and IDFdk4. In 2015, recommended adjustments to free-growing guidance for the IDFdk3, SBSdw1, SBSdw2, SBPSmk, and SBPSdc were incorporated into the Silviculture Survey Procedures Manual as an accepted alternative within South Area guidelines for the Williams Lake, Quesnel, and 100 Mile Timber Supply Areas. For the biogeoclimatic subzones/variants examined in this project, universal adjustments were made to the definition of a competitive broadleaf tree, and the term "conifer-brush ratio" was replaced with "brush-conifer ratio". Broadleaf trees can now be up to 125% taller than crop lodgepole pine (brush-conifer ratio of 1.25) and up to 150% taller than other acceptable conifer species (brush-conifer ratio of 1.5) before they have to be considered in free-growing surveys. The new brush-conifer ratios are used to define both countable broadleaves (i.e., those considered when assessing broadleaf density within free-growing plots) and broadleaf presence within a 1-m cylinder around crop conifers. The allowable number of occupied quadrants within the 1-m cylinder was also universally increased; whereas only one quadrant was previously allowed to be occupied, either one or two adjacent quadrants can now be occupied with countable broadleaf vegetation.

The allowable number of countable broadleaves was also adjusted from previous levels that had ranged from 400 to 1000 stems/ha, depending on conifer species and site series. Following change to free-growing guidelines for the IDFdk3, 3000 countable broadleaf stems/ha can be present in conifer plantations (regardless of conifer species) on mesic and drier site series, and 1000 countable stems/ha are allowed on wetter than mesic site series. For the SBSdw1, SBSdw2, SBPSmk, and SBPSdc, the allowable number of countable broadleaves (again regardless of conifer species) was set at 1000 stems/ha for all site series.

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Updated November 01, 2016