Data Package Metadata   View Summary

SAMPLING BACKGROUND

The bird area has been used extensively for studies of bird populations since the 1970s. The area is forested by typical northern hardwood species (sugar maple, beech and yellow birch) over about 85% of its area, and by patches of red spruce and balsam fir over the remaining 15%. Tree inventory data were originally collected in the summer of 1981 along four transects, each 2 to 3 km long. In 1991 the transects were made permanent with PVC stakes placed every 25 m, the trees tagged and surveyed. Surveys assessing tree health and vigor of >= 10cm trees have continued every odd number year since 1991. Measurement of tree dbh is repeated every 10 years. This dataset includes vigor data for alternate years beginning in 1991 through 2019 and dbh measurements from 1991, 2001, and 2011. An initial survey of trees >= 2 to <=1 0 cm dbh was taken in 1991 and again in 2001 and 2011. These data are also included in this dataset.

SAMPLING DESIGN

The inventory is representative of approximately 2.5 km-squared of mid elevation northern hardwood forest. It consists of a total inventory of all trees ≥10 cm dbh, within each of four 10 m wide belt transects. The parallel transects are placed approximately 100 m apart and run roughly in an east-west direction for 2200 to 2900 m. Each transect is divided into between 88 and 116 contiguous plots, each 25 m long and 10 m wide, for a total of 397 plots. The lengths of these plots are not always exactly 25 meters, due to drift or imprecise placement of the end stakes. The actual measured length of the plot is used to calculate the area of the plot. Specific description of the transects: Birdline 5: 88 plots; 1246 trees; 2.2 km length: plots 1-88: start at Bear Brook edge. Birdline 9: 104 plots; 1434 trees; 2.6 km length: plots 89-192: start HB Rd. Birdline 13: 116 plots; 1584 trees; 2.9 km length: plots 193-308: start below HB Rd. Birdline 17: 89 plots (but last plot ends in Beaver pond); 1429 trees; 2.2 km: plots 309-397: start below HB Rd.

In 1991, each live stem >= 10 cm dbh was tagged with a unique number. This allows us to track the fate of each tree and its progression from live to standing dead to snag to "down wood" at which point it is no longer followed. Trees dead in the initial survey were not tagged, but were included in the dataset with a diameter measurement. Each inventory year, (which occurs on odd calendar years) new tags are placed on stems that have grown into the 10 cm diameter class. An initial survey of smaller trees (>= 2 to <= 10 cm dbh) was taken in 1991. Temporary circular plots (3 meter radius) were defined at even numbered plot stakes along the transects. Diameter and species was recorded for each live tree within the size range. Surveys of smaller trees (>= 2 to <= 10 cm dbh) were repeated in 2001 and 2011.

DATA DESCRIPTION

The data consist of the diameters (dbh) of all the trees >= 10 cm dbh, live and dead, along each of four belt transects (6015 individual stems – this varies as stems are recruited in and fall out as down trees). An assessment of health or vigor was also recorded for each tree. Live trees were noted "sick" if they had very sparse foliage or yellowing foliage in the mid-summer sampling. Dead trees were recorded as standing dead trees (trees dead but retaining most of their fine branches) or as snags (trees broken off above dbh or with only their major large branches still intact). Trees were recorded as down when they fell completely to the ground or when snags broke off below dbh and thus left nothing to measure. Tree vigor is assessed every two years and diameter is remeasured every ten years. All stems that met the size criteria were measured individually, and in some years it was noted whether a stem was part of a group of stems from the same tree (i.e. multiple stems that split from a single trunk below breast height). For the Bird area, whether or not a stem was part of a group was not recorded until 1991. A survey of trees >= 2 to <= 10 cm dbh was taken in 1991. The data consist of the diameters of live trees within subplots along each belt transect (521 individual stems).