Arboriculture & Urban Forestry 33(4): July 2007 255 urban roads and paved areas would be sampled (as described previously). For the second stage of sampling, field crews visited each selected QQS sample unit and systematically sampled a vari- able number of variable-area plots that combined to cover urban portions of the total QQS area. The field crew began from an arbitrarily determined point along the edge of a QQS (generally determined by road access) and then moved across the QQS systematically in a serpentine pattern. Permission to sample on private land was obtained in the field, or occasion- ally in advance; a portion of potential sample space was not sampled as a result of lack of landowner permission. Variable area rectangular plots were systematically established using one of the following three methods applied to the four dif- ferent IFMAP LULC classes: 1. If the area was either high- or low-intensity urban resi- dential or commercial, each ownership was considered a variable area plot. Lot dimensions (property bound- aries within the QQS) were approximated by a rectangle and all trees inside the rectangle were part of the po- tential sample population (including all buildings, paved and mowed areas within the property bound- aries). 2. Roads/paved areas were measured as variable area rect- angles bounded by the outer edge of sidewalks, curbs, or pavement; as such, they included pavement side- walks and mowed areas if they were between the side- walk and the curb or pavement. Trees that were grow- ing outside of this envelope (most typically trees that were planted between the sidewalk and a lawn or struc- ture) were not considered as road trees/paved area trees (these trees ended up in one of the other urban stratum). 3. If the area was a park or a golf course, then beginning from an arbitrary starting point along the edge of the QQS, the field crew defined a series of plot boundary lines that were approximately equidistant between two areas of treed space (e.g., two rows of planted trees along a fairway) creating variable area rectangular plots, which included intervening areas between groups of trees or isolated trees (e.g., mowed grass). The third stage of sampling involved selecting sample trees of all species within plots that met the common minimum size standard for saw timber trees in Michigan: 20 cm (8 in) or greater stem diameter at breast height (1.37 m [4.5 ft]) dbh. Live, dying, standing dead trees were all measured; stumps were measured at stump height (typically ≈10 to 20 cm [4 to 8 in]) aboveground level. On each tree selected, the following was recorded for estimating saw timber quantity, quality, and accessibility: species (if identifiable, e.g., on stumps and dead trees), stem diameter (at breast or stump height as above), and total tree height and total saw timber log length in the main stem to an approximately 20 cm (4 in) top diameter outside bark (DOB) (measured with a Wheeler pentaprism, Forestry Suppliers Inc., Jackson, MS), also known as “merchantable” height (Avery and Burkhart 1994). If the main stem forked, the largest of the forks was followed to assess merchantable height; the other forks were considered part of the crown’s branches. The number of 2.4 m (8 ft) branch logs in a tree’s crown with a minimum 20 cm (4 in) small end diameter DOB in the tree’s crown (8 ft [2.4 m] is the standard log length on Michi- gan timberlands) was also tallied on any tree with large enough branches in its crown. In typical forest inventories, tree branches are not tallied and saw timber volume is esti- mated only for the main stem using information on merchant- able height, dbh, and some geometric model of a tree’s stem (e.g., a stem taper model; Zakrzewski and MacFarlane 2006). Urban (i.e., open)-grown trees have a much greater propor- tion of wood and larger branches in their crowns relative to forest-grown grown trees, however, so merchantable (sense Avery and Burkhart 1994) crown wood was tallied to account for this potential source of saw timber. To assess wood quality, each tree was assigned a saw log grade using six grading classes for hardwoods (Rast et al. 1973): (0) no saw volume, (1) grade 1 saw timber, (2) grade 2 saw timber, (3) grade 3 saw timber, (4) construction grade, and (5) local use class, which aligned with tree grading classes used by the U.S.D.A. Forest Service in the national forest inventory (Miles et al. 2001). Only four grading classes were used for softwoods: (0) no saw volume, (1) grade 1 saw timber, (2) grade 2 saw timber, and (3) grade 3 saw timber, consistent with common softwood grading rules (Avery and Burkhart 1994). Crown logs were not graded as a result of lack of an objective standard for doing so. To assess the accessibility of merchantable wood in it, each tree was classified into one of three accessibility classes rep- resenting the effort that would be involved in extracting the timber from the tree: 1. Easily accessible tree could be cut into relatively long sections and could be felled with minimal risk of property damage; cut sections could be loaded readily onto a vehicle for transport. 2. Moderately accessible tree could be cut into mer- chantable-length sections but would require additional effort to access with enhanced risk of property damage; cut sections would have to be transported a modest distance to be loaded onto a vehicle for transport (a truck could not drive up near the tree). 3. Difficult to accessmuch of the tree would have to be cut into submerchantable lengths to remove and/or trees could not be accessed without major effort (e.g., a large tree build into a deck) or a high likelihood of property damage. ©2007 International Society of Arboriculture
July 2007
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