Are the declining trends in forest grouse populations due to changes in the forest age structure? A case study of Capercaillie in Finland

Abstract

In Finland, Capercaillie (Tetrao urogallus) populations have a history of serious decrease starting from the mid-20th century. The decline is temporally in line with the expansion of modern forestry practices that created major changes in the landscape. We used tetraonid route-censuses from 18 forestry board districts and Finnish forest inventories (data on forest stand structure) to analyze the decline in 1965-1988. We used information theoretical model selection to evaluate a set of log-linear second order autoregressive models, allowing for spatially correlated process errors. The average trend throughout the country corresponded to an annual decline of 4.01% (mean of local trends) ± 0.24% (SEM), parallel to a half-life of 17 years. The decline was surprisingly uniform throughout the country (SD = 1.01%) and most parsimoniously explained by a geographically constant log-linear trend. At the large scale of observation applied here, population trends could not be explained by the proportional increase of younger forest age classes (<40 years old and <80 years old, respectively). Our analysis does not support the hypothesis that the decline in Capercaillie numbers is due to changes in the forest age structure, but we cannot exclude the possibility that other factors behind the decline may have interacted with forestry in general. From a conservation point of view, we caution against overemphasizing the role of forest age especially at large spatial scales, but leaning also on other research, we recommend that more management efforts would go into the preservation of the overall forest cover and the original physiognomy in single forest patches.

Declining reproductive output in capercaillie and black grouse – 16 countries and 80 years

“…However, today's habitat structure in Fennoscandia has not been shown to limit chick production under contemporary densities (i.e. Sirkiä et al, 2010) and the suggested habitat requirements for both capercaillie and black grouse are not as rigid as previously suspected (e.g. Sirkiä et al, 2011a, b;Lande et al, 2014).…”

“…Long-term declines in population densities of capercaillie (Tetrao urogallus) and black grouse (Lyrurus tetrix) have been documented from continental Europe, the British Isles and throughout the continuous boreal forests of Fennoscandia (Wegge, 1979;Lindén & Rajala, 1981;Helle & Helle, 1991;Baines & Hudson, 1995;Moss et al, 2000;Lindén & Helle, 2003;Storch, 2007;Ludwig et al, 2008;Sirkiä et al, 2010). These declines began earlier in the southern than in the northern range (Lovel, 1979, and references therein).…”

“…In Abernethy, Scotland, where foxes are controlled and pine martens are protected, pine martens were the only predators recorded predating capercaillie nests (Summers et al, 2009). Sirkiä et al (2010) proposed that capercaillie persistence at a landscape scale relates to conifer forest cover in general, and is independent of configuration of stand age-classes. A similar hypothesis has also been put forward for black grouse in relation to abundance of birch (Betula pubescens) (Lindén & Helle, 2003).…”

“…In the Fennoscandian context, intensified land-use refers primarily to the expansion of modern forestry which has been the focus of several studies (i.e. Lindén & Helle, 2003;Storch, 2007;Sirkiä et al, 2010). In continental Europe and Britain, landuse change also refers to the intensification of agriculture and changes in grazing pressure by livestock, as well as increased browsing by ungulates.…”

Wildlife monitoring in Finland: online information for game administration, hunters, and the wider public

“…Studies dealing with population dynamics, factors affecting long-term changes in grouse populations, comparisons with adjacent areas' predator-prey interactions, and biodiversity aspects, as well as wildlife-habitat relationships and landscape ecology, have made fruitful use of the wildlife triangle data (Kurki et al 1998;Lindén et al 2000;Ranta et al 2006;Elmhagen et al 2010;Sirkiä et al 2010;Kojola et al 2014;among others).…”