Effects of land use change and Quercus rubra introduction on Vaccinium myrtillus performance in Pinus sylvestris forests

Abstract

Tree species diversity can positively affect numerous forest functions. This is why Scots pine monocultures, widely promoted in Central Europe since the 18th Century, are converted into mixed stands, also with broadleaved species of alien origin. Here we studied the impacts of Northern red oak (Quercus rubra) introduction and forest continuity (ancient vs. recent forests) on bilberry (Vaccinium myrtillus) – a dominant component of the forest understory and very important ecosystem services provider in temperate coniferous (Pinus sylvestris) forests. We measured bilberry cover, density and height of shoots, fruit productivity (number and biomass of berries) as well as biomass of stems and leaves. 2000 bilberry shoots (ramets) were collected in 200 plots located in four types of Scots pine forest in central Poland: recent and ancient forests, with and without Q. rubra. At the individual (ramet) level we found decreased aboveground biomass and fruiting leaf mass fraction of bilberry in recent pine monoculture and in both types of forest with Q. rubra. Presence of Q. rubra also modified the trajectory of the allometric relationship between biomass and height: plants with the same height had lower biomass. At the population level we found a decrease of shoot density, biomass and fruiting, which resulted from effects at the individual shoot level and from lower density. At the ecosystem level these relationships were modified by decreased cover of bilberry in the understory layer and bilberry fruit biomass in recent forests (with and without Q. rubra) and in ancient forest with Q. rubra. Results clearly indicated that V. myrtillus benefited from the continuity of Scots pine forests and declined after Q. rubra introduction. As V. myrtillus serves as shelter and provides food for numerous animal species, decreases in bilberry cover and biomass can have far-reaching consequences for biodiversity and population dynamics of numerous species which occur naturally in Scots pine forests. Results show that it can also result in a decrease in availability of non-wood forest products. Therefore, as part of sustainable forest management, we suggest limiting admixture of invasive Q. rubra (as well as other broadleaved species) into pine monocultures in areas with abundant V. myrtillus cover.