Data from: 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 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.

关于科特兰莺（Kirtland’s warbler，KW；学名Setophaga kirtlandii）栖息地偏好的早期研究表明，这类鸟类倾向于选择杰克松（jack pine）植株密度较高的区域；因此，作为KW恢复与保护项目一部分而建立的杰克松人工林，采用了1.5×1.8米的株距（即每公顷3588株）进行种植。对比之下，美国湖州区（Lake States）为生产圆木而建立的传统松林人工林，通常采用2.1×2.4米的株距，相当于每公顷1922株。40多年来，KW栖息地人工林的植株间距基本保持不变，且直到最近，从未有人尝试验证这种较密的间距是否真的比传统林业间距更适合KW栖息。我们采用回顾性方法评估植株密度对KW栖息地占用率的影响，发现人工林实际密度与KW鸣唱雄鸟的最大占用率之间存在意外的负相关关系。由于本研究的局限性，这一发现应谨慎解读；不过，考虑到人工林中植株密度的范围较窄，且人工林的均匀间距应能在比天然林更低的密度下实现杰克松的最优覆盖，因此不存在正相关关系的结论是完全合理的。