DOI: 10.5061/dryad.0zpc8674s
title: Data from: Kirtland's warbler occupancy and plantation density

description: Early studies into the habitat preferences of the Kirtland’s warbler (KW;
 Setophaga kirtlandii) suggested that these birds exhibited a
 preference for areas with high jack pine stem densities; therefore, jack
 pine plantations established as part of the KW recovery and conservation
 programs have been planted using a 1.5 x 1.8 m spacing (3,588 trees ha-1).
 In contrast, traditional pine plantations in the Lake States established
 for roundwood production are typically planted on a 2.1 x 2.4 m spacing
 that equates to 1,922 trees ha-1. Over more than 40 years, tree spacing in
 KW habitat plantations has gone largely unchanged, and until very recently
 there has never been an attempt to verify that these tighter spacings
 actually provide better KW habitat than would a traditional forestry
 spacing. We used a retrospective approach to assess the impacts of tree
 density on KW occupancy and observed an unexpected negative relationship
 between realized plantation density and maximum occupancy by KW singing
 males. This finding should be interpreted with caution due to the limited
 nature of this study; however, a lack of a positive relationship is
 entirely plausible given the narrow range of densities encountered in
 plantations, as well as the fact that uniform spacing of plantations
 should allow for the achievement of optimal jack pine cover at lower
 densities than would be required in a natural-origin stand.
description: We took advantage of unintended variability in plantation spacing
 to conduct a retrospective assessment of KW usage of plantations across a
 range of realized plantation densities. Our approach was to use MDNR
 regeneration survey data to determine realized plantation density and then
 to relate this to KW occupancy using KW census data. We used digital
 3-year post-planting surveys from 2004 - 2010. The maximum density of KW
 (males ha<sup>-1</sup>) was used as the metric for analyses
 and was calculated for each stand by taking the number of singing males
 from the peak year of occupancy and dividing that by the size (ha) of the
 stand. In addition to jack pine stem density, we attempted to account for
 other factors known to influence local KW density, including stand age,
 stand size, geographic location, and the amount of occupiable habitat in
 the surrounding landscape. Therefore, for each stand in our analysis we
 also considered the following as covariates: stand size (ha), functional
 unit size (ha), stand year of origin, KW Management Area (KWMA), and a
 measure of habitat connectivity. We calculated a simple metric of habitat
 connectivity to include in our analysis by summing the total area of
 potentially occupiable habitat within a defined radius of each stand. For
 each stand, at the year of peak occupancy, we summed the area (ha) of all
 jack pine between 5-23 years of age (potentially occupiable habitat)
 within a 5-km, or 10-km, radius of the centroid of that stand.
description: # Kirtland's warbler occupancy and plantation density
 This dataset has
 Kirtland's warbler census data for dedicated jack pine plantations on
 Michigan DNR forest land in relation to the realized stem density of those
 plantations ## Description of the data and file structure Functional Unit:
 We defined functional unit as a group of adjacent KW stands that were
 within 8 years of age of each other, representing available KW habitat on
 a broader scope than a single stand. This parameter identifies which
 functional unit each stand belongs to. Functional_Unit_Ha: This parameter
 defines the area in hectares of each functional unit FCS-Key: This
 represents the unique MDNR stand identifier number. Stand_Origin_Year:
 This represents the year in which the plantation was established Age: Age
 of the stand in 2022 Stand_Hectares: Area of the stand in hectares
 KWMU_Mgmt_Block: KW Management Unit represents which one of 16 unique
 areas on MDNR land designated for KW management and is a proxy for
 geographic location Trees_per_ha: Stand density at three-years post
 planting KW_Max_Density_birds_per_ha: The maximum KW density recorded in
 birds per hectare for that stand according to digitized KW Census data
 Connectivity_5kmArea_Ha: summed area (hectares) of all jack pine between
 5-23 years of age (potentially occupiable habitat) within a 5-km radius of
 the centroid of that stand Connectivity_10kmArea_Ha: summed area
 (hectares) of all jack pine between 5-23 years of age (potentially
 occupiable habitat) within a 10-km radius of the centroid of that stand
 Peak_Occupancy_Year: the calendar year in which peak KW occupancy occurred