LWD STUDY

LWD IN PLUM CREEK LAB 11 REPORT STUDY TO DETERMINE POTENTIAL FOR LARGE WOODY DEBRIS AND HABITAT CREATION IN PLUM CREEK

J. GARRETT SIBINGA

.1 DATA COLLECTION N 500 FEET

the study began with data collected from the OSIP website. target of the site map includes four tiles from OSIP covering oberlin and its surrounding area. satellite images demarcate the site boundaries. these were later overlayed with spatial data.

initial site map

.2 DATA PROCESSING N 500 FEET

lidar files provide spatial data from aerial scanners. these files are converted into raster data for efficient storage and retrieval.

1:4000 scale: trees, buildings and water have unique, recognizable footprints in the raster image.

.3 TERRAIN MAPPING N 500 FEET

maps are created from data embedded in the laser scan files. terrain maps are built for both bare earth elevation model and treetop elevation model. using pre-defined classes, trees and ground elevations are mapped separately.

bare earth elevation map HIGH

LOW

.4 TREETOP MAPPING N 500 FEET

high vegetation data is used to map tree top elevation. tree top elevation model creates a secondary terrain that drapes over the bare earth model. the two layers can then be used to make calculations for a third elevation model, treetop height.

tree top elevation map HIGH

LOW

.5 HEIGHT CALCULATION N 500 FEET

elevation data for the bare earth model is subtracted from elevation data for treetop elevation model. this function yields tree height data - the difference between the two layers. a third elevation layer is created from this data, which models just tree height.

tree height elevation map TREES APPEAR IN BLUE

.6 PROXIMITY CALCULATION N 625 FEET

target length of plum creek is drawn onto the map. distances from point location to streambed are calculated using data from tree raster layer. mapped above are distances from the streambed within the dataframe.

N

distance gradient map + streambed vector map

P L U M C R E E K MARKED IN BLUE

1 0 0 0

F E E T

N

.7 OVERLAP CALCULATION N 625 FEET

after distance from the streambed is computed, it is measured against tree height. any cell with a tree height greater than distance from the streambed creates an overlap. these cells house potential large woody debris.

overlap raster data display data is exported for biomass index calculation.

TOTA L H E I G H T x TOTA L # x 2 . 5 (C E L L S I Z E )

5563

x

x

71426

3 9 7, 3 4 2 , 8 3 8

x

9 9 3 , 3 57,0 9 5

2.5 2.5

.8 DISCUSSION SECTION the lab has some necessary concessions and sources of error.

1. data used. the lab relies on data from ogrip, requiring lidar, tiffs, and grid data. the data that actually gets used is seven years out of date. for features that are purely geographic this would not be that big of a deal, but because trees are organic and therefore comparatively unstable, it makes a big difference.

2. no defined method for measuring the streambed. there is no instruction on a specific map layer to draw from, or degree of accuracy to draw it with. this could lead to inconsistencies with the data returned from the proximity calculations and in turn the overlap calculations.

3. unrealistic biomass total. the calculation for the final biomass amount is unrealistic. multiplying by the width of a cell (2.5) assumes that a tree takes up the entire cell. trees are not solid cubes rising to their full height, so it creates an exaggerated total. suggestions for future research. when the new lidar files are released by ogrip, it would be interesting to check fallen trees totals within the sample area against population totals for the creek’s indigenous creatures.