Monitoring forest vegetation in the North Coast and Cascades Network: 2009 annual report

Acker, Steven; Boetsch, John; Bivin, Migonne; Whiteaker, Lou

Late-successional, coniferous forest is critical for ecosystem function and biological conservation in the Pacific Northwest. Such forests are well-represented in the North Coast and Cascades Network (NCCN) of the National Park Service. As part of monitoring of natural resources within the NCCN, we have begun to track trends in tree recruitment, growth, and mortality in forests representing the range of environments in network parks. We have established 35, 1-hectare plots in three parks (Mount Rainier, North Cascades, Olympic), at elevations from near sea-level to almost 1800 m. To select monitoring locations, we began by generating a spatially-balanced, random set of potential plot locations using the Generalized Random Tesselation Stratified algorithm. Initial screening was in the office, using GIS to evaluate suitability factors including safety of access routes and proximity to trails and roads. Points that passed the office screening were evaluated in the field on safety of access, forest species composition and age, and other factors. We evaluated over 1700 points in the office, 640 of which passed. Three reasons accounted for most of the rejection of points in the office: excessively steep access, excessive steepness at the proposed location, and proximity to trails (either too close or too far). We evaluated 579 points in the field, 107 of which passed. Most of the rejections of points in the field were due to forest species composition which was not one of the target types.We selected three different elevation strata at the network-level (two within each park) for forest monitoring, with plans to establish six plots within each strata-park combination. As of 2008, we established six plots in five of the six elevation strata-park combinations, and five plots in the highest-elevation stratum at North Cascades National Park. For the most part, plots are located on hillsides occupying a variety of aspects within each combination of stratum and park. A total of 21 tree species occurred within the 35 plots, 15 of which were conifers. The plots include all of the tree species which are widespread and dominant in the parks. Average density of trees varies by a factor of five (from 241 to 1213 per ha) between the various combinations of stratum and park, with the lowest elevation stratum distinguished from the other two by its low average density of trees. Basal area of live trees was less variable than stem density; high-elevation plots on average had roughly two-thirds of the basal area of plots at low and mid-elevations (overall range of average by stratum and park 44 to 75 m2/ha). Tsuga heterophylla had the highest average density in more combinations of stratum and park than any other species; Pseudotsuga menziesii had the highest average basal area in more combinations of stratum and park than any other species. Other abundant and/or dominant species were Abies lasiocarpa, A. amabilis, Picea sitchensis, Thuja plicata, and Picea engelmannii.Our first interval for measuring tree mortality was 2008 to 2009. Roughly half of the plots had no tree mortality; the overall average rate of tree mortality was 0.6%. The most common condition of trees reported dead in 2009 was standing with no obvious cause of death (over 60% of cases). The overall average rate of tree mortality was within the range to be expected for older forests in the Pacific Northwest in the absence of severe wind damage. That field crews were unable to assign a cause in most cases is not surprising, inasmuch as tree death usually results from multiple, interacting factors.

Monitoring forest vegetation in the North Coast and Cascades Network: 2009 annual report

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