What is good for birds is not always good for lichens: Interactions between forest structure and species richness in managed boreal forests

Abstract

Forestry in the boreal region increasingly replaces natural disturbances in shaping biodiversity. Large-scale removal of small diameter trees (thinning), is ubiquitous in northern European forestry, yet an understanding of how it relates to biodiversity across taxa is lacking. To address this, we examined how two forest structural elements, commonly impacted by forest thinning (i.e. vegetation density in the understory and overstory), are correlated with the species richness of forest-dwelling birds and epiphytic lichens. These taxa were chosen because they likely have opposing habitat demands: epiphytic lichens potentially benefitting from more light in open forests, and birds benefitting from structurally complex forests for foraging, nesting and cover. We used remote sensing tools, already applied in forestry planning, to see if management recommendations could be found that balance the needs of both taxonomic groups within the same forests. Our results show that richness in epiphytic lichens and forest-dwelling birds is not correlated and that a high species richness (~15 birds & ~40 epiphytic lichens) in both taxa is only predicted in the same stand under a specific vertical distribution and density of the forest’s vegetation: this occurs when the vegetation above 3 m is open (to promote epiphytic lichen richness) and below 3 m is dense (to promote bird richness). Dense vegetation up to 7 m above ground has a diverging effect on forest birds (positive) and epiphytic lichens (negative). A larger stem diameter further increases species richness in both taxa. Our study provides results that are directly implementable in forestry planning over large areas with the help of remote sensing tools (LiDAR).

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