Temperate Mountain Forest Biodiversity under Climate Change: Compensating Negative Effects by Increasing Structural Complexity

Abstract

Species adapted to cold-climatic mountain environments are expected to face a high risk of range contractions, if not local extinctions under climate change. Yet, the populations of many endothermic species may not be primarily affected by physiological constraints, but indirectly by climate-induced changes of habitat characteristics. In mountain forests, where vertebrate species largely depend on vegetation composition and structure, deteriorating habitat suitability may thus be mitigated or even compensated by habitat management aiming at compositional and structural enhancement. We tested this possibility using four cold-adapted bird species with complementary habitat requirements as model organisms. Based on species data and environmental information collected in 300 1-km2 grid cells distributed across four mountain ranges in central Europe, we investigated (1) how species’ occurrence is explained by climate, landscape, and vegetation, (2) to what extent climate change and climate-induced vegetation changes will affect habitat suitability, and (3) whether these changes could be compensated by adaptive habitat management. Species presence was modelled as a function of climate, landscape and vegetation variables under current climate; moreover, vegetation-climate relationships were assessed. The models were extrapolated to the climatic conditions of 2050, assuming the moderate IPCC-scenario A1B, and changes in species’ occurrence probability were quantified. Finally, we assessed the maximum increase in occurrence probability that could be achieved by modifying one or multiple vegetation variables under altered climate conditions. Climate variables contributed significantly to explaining species occurrence, and expected climatic changes, as well as climate-induced vegetation trends, decreased the occurrence probability of all four species, particularly at the low-altitudinal margins of their distribution. These effects could be partly compensated by modifying single vegetation factors, but full compensation would only be achieved if several factors were changed in concert. The results illustrate the possibilities and limitations of adaptive species conservation management under climate change.

Automated Detection of Forest Gaps in Spruce Dominated Stands Using Canopy Height Models Derived from Stereo Aerial Imagery

“…Gap characteristics such as number, density, size, spatial coverage and form have been confirmed as valuable predictors in various habitat models: Zellweger et al [6] and Braunisch et al [15] used the density (number of gaps per ha) to model the effect of forest structural complexity on multi species occurrence of four temperate mountain forest bird species: Capercaillie, Hazel Grouse (Bonasa bonasia), Three-toed Woodpecker (Picoides tridactylus) and Pygmy Owl (Glaucidium passerinum). Derived metrics describing the geometry of gap have been used for example by Braunisch and Suchant [71] to define an optimal proportion of gap area for the Capercaillie-friendly habitats, or by Getzin et al [28] who used a perimeter-to-area ratio and gap shape complexity index to assess floristic diversity of the forest understory.…”

“…Getzin et al [28] showed that very high-resolution images from unmanned aerial vehicles (UAV) can be used to effectively assess forest gaps and associated plant biodiversity in temperate forests. In recent years many studies confirmed the benefit from including forest structure parameters such as canopy cover and forest gaps derived from LiDAR into habitat models showing LiDAR to deliver precise, reproducible and high resolution information for answering a variety of ecological questions [5,6,15,29].…”

“…Canopy cover [4], vertical variation of the canopy height [5] and forest gaps [6] are considered important structural elements in forest ecology to which various conservation relevant forest species are associated [7]. Presence or absence of many animal species such as European nightjar (Caprimulgus europaeus) [8], Capercaillie (Tetrao urogallus) [9], Grey-headed woodpecker (Picus canus) [10], various chiroptera [11][12][13], saproxylic beetles [14] or bird species assemblages [6,15] are expected to depend on semi-open forest habitats. Gaps in forest canopies also play a key role in various ecological processes such as the regeneration of trees and ground vegetation development, with the associated light regime being a main driver for composition and diversity of understory biota [16].…”

Forest conversion can help to mitigate impacts of climate change on common forest birds

“…All these changes can affect bird abundances and bird community composition. Climate change affects not only composition and configuration of forests (Bolte and Degen 2010) but also forest structure and the relative performance of tree species (Hanewinkel et al 2013), which may on the one hand amplify negative climate-related impacts on species' habitats but also offers additional potential for mitigation (Braunisch et al 2014). …”

“…Generally, the reliable prediction of ecological and biogeographic responses to climate change and future climate-driven land-use changes poses a serious challenge for ecologists (Jackson et al 2009). Intensive research has been conducted on projecting climate-driven changes of species distributions, but few studies have attempted to include both climate and land-use variables for predicting species distribution change (Jetz et al 2007;Braunisch et al 2014). Typically, spatial studies on the impact of climate change have focused on the prediction of range contractions and range shifts but not on the changes of population size.…”