Kirtland's warbler occupancy and plantation density

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 si..., 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-1) 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), ..., , # 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 ...