DOI: 10.5061/dryad.cfxpnvx9v
title: Forest associated habitat variables influence human-tick encounters in the southeastern United States

description: Due to the increased frequency of human-tick encounters and expanding
 ranges of ticks in the United States, there is a critical need to identify
 environmental conditions associated with tick populations and their
 likelihood to contact human hosts. In a passive tick surveillance
 partnership with the United States Department of Agriculture Forest
 Inventory and Analysis (FIA) program, we identified environmental
 variables associated with tick encounters by forestry personnel. Ticks
 were identified to species and life stage and site-specific variables were
 associated with each tick using FIA forest inventory datasets and
 generalized linear and zero-inflated models. Of the 55 FIA variables
 available, we identified biotic and abiotic environmental variables
 associated with Amblyomma americanum (carbon in litter material and
 standing dead tree aboveground dry biomass), Dermacentor variabilis (live
 sapling belowground dry biomass, carbon in litter material, forest stand
 age, and elevation), and Ixodes scapularis (carbon in dead woody material
 and seedling species unevenness). We propose that land management
 decisions not only affect common flora and fauna but changes to these
 habitats can also alter the way ticks parasitize hosts and use vegetation
 to find those hosts. Testing of these results can be used with land
 management decisions to prevent future encounters and highlight risk
 areas. Foresters that inventory sites encounter ticks, which we can then
 use to better understand the environmental conditions conducive to
 increased tick abundance or habitat suitability.
description: Data for this study were obtained through a partnership with the
 USDA-FIA. Ticks were collected voluntarily according to methods outlined
 in Trout Fryxell and Vogt 2019 by FIA foresters conducting standard
 inventory operations over a period of five years (2017–2021) in the
 southeastern U.S.  Vegetation data were collected by USDA-FIA crews on
 permanent ground sampling plots located across the study area at a
 sampling intensity of 1 plot per 2,428 ha. Crews indicated where ticks
 were encountered and those plots were cross-referenced with the USDA FIA
 database.
description: # Forest associated habitat variables influence human-tick encounters in
 the southeastern United States Data for this study were obtained through a
 partnership with the USDA-FIA. Ticks were collected voluntarily according
 to methods outlined in Trout Fryxell and Vogt 2019 by FIA foresters
 conducting standard inventory operations over a period of five years
 (2017-2021) in the southeastern U.S. Vegetation data were collected by
 USDA-FIA crews on permanent ground sampling plots located across the study
 area at a sampling intensity of 1 plot per 2,428 ha. Crews indicated where
 ticks were encountered and those plots were cross-referenced with the USDA
 FIA database. Analyses were conducted to correlate tick abundance with
 different environmental variables. Missing data are coded with a decimal
 (.) The following is a table with the code followed by a definition. |
 Variable | Definition | | :------------------------------ |
 :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Number | Identification number for each vial collected | | nearby\_city | Nearby city where ticks were collected | | date | Date when ticks were collected | | crew\_size | The number of foresters present on each site where ticks were collected | | state | State where ticks were collected | | FORTYPCD | A descriptor of the species with the plurality of stocking for all live trees in the condition class that are not overtopped. Primarily derived using a computer algorithm (Arner et al. 2003). | | STDAGE | Average total age, to the nearest year, of trees in the stand-size class of the condition. | | STDSZCD | A classification of the predominant (based on stocking) diameter class of live treese within the condition. Assigned using an algorithm (Arner et al. 2003). | | SITECLCD | Code indicating the classification of forest land in terms of inherent capacity to grow crops of industrial wood based on the culmination of mean annual increment of fully stocked natural stands. | | PHYSCLCD | The general effect of land form, topographical position, and soil on moisture available to trees. | | BALIVE | Basal area in square feet per acre of all live trees 1.0 inch d.b.h./d.r.c. in the condition class. | | CARBON\_DOWN\_DEAD | Carbon, in tons per acre, of woody material &gt;3 inches in diameter on the ground, and stumps and their roots &gt;3 inches in diameter. Estimated from models based on geographic area, forest type, and live tree carbon density (Smith and Heath 2008). | | CARBON\_LITTER | Carbon, in tons per acre, of organic material on the floor of the forest, including fine woody debris, humus, and fine roots in the organic forest floor layer above mineral soil. Estimated from models based on geographic area, forest type, and (except for nonstocked and pinyon-juniper stands) stand age (Smith and Heath 2002). | | CARBON\_SOIL\_ORG | Carbon, in tons per acre, in fine organic material below the soil surface to a depth of 1 meter. Does not include roots. Estimated from models based on geographic area and forest type (Smith and Heath 2008). | | CARBON\_STANDING\_DEAD | Carbon, in tons per acre, in standing dead trees 1.0 inch diameter, including coarse roots, is estimated from models based on geographic area, forest type, and (except for nonstocked stands) growing-stock volume (Smith and Heath 2008). | | CARBON\_UNDERSTORY\_AG | Carbon, in tons per acre, in the aboveground portions of seedlings and woody shrubs. Estimated from models based on geographic area, forest type, and (except for nonstocked and pinyon-juniper stands) live tree carbon density (Smith and Health 2008). | | CARBON\_UNDERSTORY\_BG | Carbon, in tons per acre, in the belowground portions of seedlings and woody shrubs. Estimated from models based on geographic area, forest type, and (except for nonstocked and pinyon-juniper stands) live tree carbon density (Smith and Heath 2008). | | lt\_baf | Cross-sectional area, including bark, at the point of diameter measurementc of all live trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in square feet per acre. | | lt\_tpa | Number of all live trees 5.0 inches d.b.h./d.r.c. in the condition class, on a per acre basis. | | lt\_DB\_AG | Oven-dry biomass in the aboveground portion, excluding foliage, of all live trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | lt\_C\_AG | Carbon in the aboveground portion, excluding foliage, of all live trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | lt\_C\_BG | Carbon, in pounds, of coarse roots &gt;0.1 inch in root diameter for live trees 5.0 inches d.b.h./d.r.c. in the condition class, on a per acre basis | | dt\_baf | Cross-sectional area, including bark, at breast height (4.5 ft above the ground) of all standing dead trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in square feet per acre. | | dt\_tpa | Number of all standing dead trees 5.0 inches d.b.h./d.r.c. in the condition class, on a per acre basis. | | dt\_DB\_AG | Oven-dry biomass in the aboveground portion, excluding foliage, of all standing dead trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | dt\_DB\_BG | Oven-dry biomass of the belowground portion, including coarse roots with a root diameter 0.1 inch, of all standing dead trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | dt\_C\_AG | Carbon in the aboveground portion of all standing dead trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | dt\_C\_BG | Carbon of coarse roots &gt;0.1 inch in root diameter of all standing dead trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | qmd | Diameter, in inches, corresponding to the mean basal area of all live trees 5.0 inches d.b.h./d.r.c. in the condition class. | | ls\_baf | Cross-sectional area, including bark, at breast height (4.5 ft above the ground) of all live trees 1.0 inches to &lt;5.0 inches d.b.h./d.r.c. in the condition class. Expressed in square feet per acre. | | ls\_tpa | Number of all live trees &gt;1.0 inch d.b.h./d.r.c. and &lt;5.0 inches d.b.h./d.r.c. in the condition class, on a per acre basis. | | ls\_DB\_AG | Oven-dry biomass in the aboveground portion, excluding foliage, of all live trees 1.0 inch d.b.h./d.r.c. and &lt;5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | ls\_DB\_BG | Oven-dry biomass of the belowground portion, including coarse roots with a root diameter 0.1 inch, of all live trees 1.0 inches to &lt;5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | ls\_C\_AG | Carbon in the aboveground portion, excluding foliage, of all live trees 1.0 inches to &lt;5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | ls\_C\_BG | Carbon of coarse roots &gt;0.1 inch in root diameter of all live trees 1.0 inches to &lt;5.0 inches d.b.h./d.r.c. in the condition class. Expressed in pounds per acre. | | ltH\_baf | Cross-sectional area, including bark, at the point of diameter measurement of all live Angiospermae trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in square feet per acre. | | ltH\_tpa | Number of all live Angiospermae trees 5.0 inches d.b.h./d.r.c. in the condition class, on a per acre basis. | | ltS\_baf | Cross-sectional area, including bark, at the point of diameter measurement of all live Gymnospermae trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in square feet per acre. | | ltS\_tpa | Number of all live Gymnospermae trees 5.0 inches d.b.h./d.r.c. in the condition class, on a per acre basis. | | lsH\_baf | Cross-sectional area, including bark, at breast height (4.5 ft above the ground) of all live Angiospermae trees 1.0 inches to &lt;5.0 inches d.b.h./d.r.c. in the condition class. Expressed in square feet per acre. | | lsH\_tpa | Number of all live Angiospermae trees 1.0 inches to &lt;5.0 inches d.b.h./d.r.c. in the condition class, on a per acre basis. | | baf\_prop1 | Proportion of total live tree basal area for the most dominant tree species in the condition class, i.e., the species with the greatest proportion of live tree basal area. | | baf\_prop2 | Proportion of total live tree basal area for the second most dominant tree species in the condition class, i.e., the species with the second greatest proportion of live tree basal area. | | tpa\_prop1 | Proportion of total live tree density for the most dominant tree species in the condition class, i.e., the species with the greatest proportion of live tree density. | | tpa\_prop2 | Proportion of total live tree density for the second most dominant tree species in the condition class, i.e., the species with the second greatest proportion of live tree density. | | tpa\_total | Number of all live trees &lt;1.0 inch diameter and 6 inches tall (softwoods) or 12 inches tall (hardwoods) in the condition class, on a per acre basis. | | tpa\_hw | Number of all live Angiospermae trees &lt;1.0 inch diameter and 12 inches tall in the condition class, on a per acre basis. | | seedling\_tpa\_prop1 | Proportion of total seedling density for the most dominant species in the condition class, i.e., the species with the greatest proportion of seedling density. Note: as a formula this is max(seedling density for species i on plot j / total seedling density on plot j). | | seedling\_tpa\_prop2 | Proportion of total seedling density for the second most dominant tree species in the condition class, i.e., the species with the second greatest proportion of seedling density. | | RDDISTCD | The straight-line distance from plot center to the nearest improved road, which is a road of any width that is maintained as evidenced by pavement, gravel, grading, ditching, and/or other improvements. | | WATERCD | Water body &lt;1 acre in size or a stream &lt;30 feet wide that has the greatest impact on the area within the sampled portions of any of the four subplots. | | ELEV | Distance the plot is located above (or below, if negative) sea level. Rounded to the nearest foot. | | ECOSUBCD | Code identifying an area of similar surficial geology, lithology, geomorphic process, soil groups, subregional climate, and potential natural communities. | | SPCD | FIA tree species code | | prop\_baf\_sp | Proportion of the total number of live trees per acre | | prop\_tpa\_sp | Proportion of the total number of live trees per acre | | avg\_ht | Average length (height) in feet of all live trees 5.0 inches d.b.h./d.r.c., as measured from ground level to the highest remaining portion of the tree still present and attached to the bole, in the condition class | | baf\_adj\_tot | Cross-sectional area, including bark, at the point of diameter measurement of all live trees 5.0 inches d.b.h./d.r.c. in the condition class. Expressed in square feet per acre. | | SLOPE | The predominant or average angle of the slope across the subplot, to the nearest 1 percent. Valid values are 0 through 155. | | amblyomma\_americanum\_larvae | Total number of Amblyomma americanum larvae | | amblyomma\_americanum\_nymph | Total number of Amblyomma americanum nymphs | | amblyomma\_americanum\_male | Total number of Amblyomma americanum males | | amblyomma\_americanum\_female | Total number of Amblyomma americanum females | | ixodes\_scapularis\_larvae | Total number of Ixodes scapularis larvae | | ixodes\_scapularis\_nymph | Total number of Ixodes scapularis nymphs | | ixodes\_scapularis\_male | Total number of Ixodes scapularis males | | ixodes\_scapularis\_female | Total number of Ixodes scapularis females | | dermacentor\_variabilis\_larvae | Total number of Dermacentor variabilis larvae | | dermacentor\_variabilis\_nymph | Total number of Dermacentor variabilis nymphs | | dermacentor\_variabilis\_male | Total number of Dermacentor variabilis males | | dermacentor\_variabilis\_female | Total number of Dermacentor variabilis females | | amblyomma\_americanum\_num | Total number of Amblyomma americanum ticks | | ixodes\_scapularis\_num | Total number of Ixodes scapularis ticks | | dermacentor\_variabilis\_num | Total number of Dermacentor variabilis ticks | | total | Total number of ticks |