Increasing numbers of wintering forest birds in Swedish Lapland 1986–2017 show stronger correlations with forest development than with local weather

Björn Ferry,Håkan Rune,Ulf Andersson,Martin Green

doi:10.34080/os.v30.19633

Björn Ferry, Håkan Rune + Show 2 more

Open Access

https://doi.org/10.34080/os.v30.19633

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Abstract

After a long period of decline, the number of forest birds has increased in Sweden in recent decades. Whether this trend is due to an increase in forested area, forest quality, climate change, or a combination of these factors, remains unclear. Here, we compared forest bird data from a local winter point count route around Storuman in Swedish Lapland between 1986 and 2017, with the development of regional forest composition and local weather conditions. We suggest that rather than changes in average annual, winter, or summer local temperatures or precipitation, the main drivers behind increasing numbers of wintering forest birds in this part of Sweden are an increase in the area of denser forest and dead wood volume, and a decrease in open ground area without forest vegetation. While there may be supplementary explanations behind the increasing numbers of forest birds, such as reduced agriculture, decreasing local human population, or stronger photosynthesis, our results indicate that local land use has been favourable for forest birds in recent decades in this area.

Highlights

Biodiversity loss is a possible threat to humanity’s future (Cardinale et al 2012)
We found no significant changes in local average temperature or precipitation during the period 1986–2017, irrespective of whether we analysed annual, winter, or summer averages (Table 2)
The pattern was similar for abundance of forest birds, which significantly increased with area of middle-aged forest, standing volume of wood, and volume of dead wood, but significantly decreased with increasing area of open ground, forest ready for cutting, and older forest rich in deciduous trees (Figure 6, Appendix 2)

Summary

Introduction

Biodiversity loss is a possible threat to humanity’s future (Cardinale et al 2012). From 1970 to 2014, population sizes of mammals, birds, fish, reptiles, and amphibians around the globe declined by on average 60 % (WWF 2018). During the study period the area of older forest (>80 years old) rich in deciduous trees decreased, while the standing volume of wood increased continuously, i.e. the forests became denser.

Results

Conclusion