Vegetation structure (DP1.10098.001)

Vegetation Structure data are collected from Distributed and Tower plots. Each Distributed plot is sampled in a given bout if at least one tree with Diameter at Breast Height (DBH) ≥ 10 cm or one palm tree or large tree fern is present. If trees with DBH ≥ 10 cm, palm trees, and large tree ferns are absent, all smaller qualifying vegetation is considered: both woody and non-woody perennial vegetation are sampled if all qualifying individuals of both types comprise ≥ 10% aerial cover of the plot. For example, a Distributed plot with 10% aerial cover comprising a mix of small shrubs and yucca would be sampled for yucca even if total yucca cover is < 10% aerial cover. Ferns, Xerophyllum, and Yucca have additional sampling criteria within Distributed plots: These three growth forms are not measured when the NLCD vegetation type of the plot is Deciduous Forest, Evergreen Forest, or Mixed Forest. In addition, when Distributed plot NLCD vegetation type is not forest, ferns are only sampled when aerial cover is ≥ 50% within the plot. Tower plots are sampled if at least one tree with DBH ≥ 10 cm or one palm tree, or one large tree fern is present in ≥ 10% of Tower plots, or if smaller qualifying individuals comprise ≥ 10% of aerial cover averaged across all Tower plots. Within both Distributed and Tower plots, all woody individuals with DBH ≥ 10 cm, all palm trees, and all large tree ferns are mapped and measured throughout the plot sampling area. Individuals with DBH < 10 cm are mapped if a) individuals with DBH ≥ 10 cm are absent from the plot, and b) they are visible to airborne remote-sensing instruments. If stem density thresholds are met, individuals with DBH < 10 cm and non-woody perennial vegetation, such as ferns and saw palmetto, may be measured within nested subplots in order to standardize the sampling effort across plots. At all sites at which qualifying woody or non-woody perennial vegetation is present, Distributed plots are sampled every 5 years. At most sites with qualifying vegetation, a spatially-balanced subset of n=5 tower plots are sampled annually, and the full complement of Tower plots is sampled every 5 years. At slow-growth-increment sites (RMNP, YELL, NIWO, WREF, SJER, SOAP, TEAK, BONA, DEJU, HEAL), dendrometer bands are measured annually on a subset of individuals within Tower plots. At desert sites with sensitive vegetation and soils (i.e., MOAB, JORN, SRER, ONAQ), there is no annual Tower plot measurement and the full complement of Tower plots is measured every 5 years only. Ferns are only sampled in Tower plots when all Tower plots are sampled every 5 years; that is, ferns are not measured annually in the n=5 Tower plot subset. At all sites, Distributed plot sampling and sampling of the full set of Tower plots is scheduled in a staggered manner such that sites generate data either from all Distributed plots or all Tower plots every 2-3 years. Sites that do not have qualifying vegetation are surveyed every 5 years to determine whether ingrowth of qualifying vegetation has occurred. At sites with seasonal senescence, the onset of sampling in a given year is triggered by senescence of canopy or understory individuals. Sampling must be completed before growth begins the following season and within 4 months of sampling onset. At sites with no distinct season, sampling begins within ± 2 weeks of the same date, and must be completed within 60 days of sampling onset. The Teakettle site (TEAK) in California is an exception: Here, site logistics dictate a late June sampling start date. See NEON.DOC.000987 for more details. Instrumentation: