Effects of forest wildfire on inner-Alpine bird community dynamics

Abstract

As major disturbance agents, natural catastrophes impact habitats, thereby maintaining the dynamics of ecological communities. Such discrete events are expected to positively affect biodiversity because they generate high habitat heterogeneity and thus numerous ecological niche opportunities. Species typical of open and semi-open habitats, which are often of high conservation concern in modern anthropized landscapes, may benefit most from recurrent natural catastrophes that regularly reset ecosystems. We investigated bird community changes and species-specific responses to wildfire at two recently burnt temperate, montane-subalpine forest stands in an inner-Alpine Swiss valley, with a special focus on red-listed and conservation priority species. We compared bird community changes in burnt forests (spanning 13 years) with bird assemblages occurring in adjacent non-burned forest stands that served as quasi-experimental controls. Strong species-specific responses to wildfire were evidenced, resulting in a dramatic post-fire decrease in overall bird abundance and species richness. Yet, red-listed bird species and conservation priority species in Switzerland were substantially more common in burnt than in control forest stands. Many red-listed species showed a bell-shaped numeric response to wildfire over time, suggesting low habitat suitability just after fire, high habitat suitability at pioneer and early stages of vegetation succession, followed by a long-term decrease in suitability while vegetation becomes denser, especially at ground level. As established for Mediterranean regions where wildfires are especially frequent, this study shows that forest fires can also boost the populations of red-listed and priority bird species typical of open and semi-open habitats in temperate biomes. Prescribed forest fire might represent a management option for preserving threatened elements of biodiversity despite the intense public debate it will trigger.

Fig 1. Number of territories in relation to years after fire.

Shown are regression lines and 95% confidence intervals for the burnt forest (solid line, red) and control forest (dashed line, green) for Common Cuckoo (a), Eurasian Wryneck (b), Common Redstart (c), Eurasian Linnet (d), Rock Bunting (e), Ring Ouzel (f), Crested Tit (g), and Black Grouse (h).

Fig 2. Average number of territories per 10 ha over all species in relation to years after fire.

Shown are regression lines and 95% confidence intervals for the burnt forest (solid line, red) and control forest (dashed line, green).

Fig 3. Disturbance index values in relation to years after fire.

Shown are regression lines and 95% confidence intervals, for (a) Swiss red-listed bird species, where red = higher red-listed species, green = least concern species, and (b) Swiss priority bird species, where red = Swiss priority species, green = non-priority species.