Effective management for deadwood‐dependent lichen diversity requires landscape‐scale habitat protection

Abstract

Habitat loss is considered a major threat for biodiversity. However, the scales on which its effects occur are still insufficiently understood, namely, is the amount of available habitat important for species richness on both local and landscape scales? We studied the effects of local and landscape‐scale habitat amount on local‐scale species density of deadwood‐dependent lichens in Swedish boreal forests. Creation and retention of deadwood are common practices to benefit forest biodiversity, and recognizing the relevant scale is critical for them to be successful. We surveyed deadwood‐dependent lichens in 90 unmanaged forest stands that differed in the local and landscape habitat amount. The local habitat amount was measured as the amount of deadwood in the sampled stands (m2 deadwood ha−1), while six alternative proxies were used to estimate the landscape habitat amount, that is, the amount of deadwood in the surrounding landscapes. Lichen species density (number of species per standardized deadwood area of 3.7 m2) was modelled as a function of local and landscape habitat amount at multiple scales (300 m–5 km from the stands). Lichen species density increased with the landscape habitat amount. The proportion of old forests (>100 years, including newly clear‐cut stands that until recently were old forests) within 5 km from the stands explained species density better than the other proxies of landscape habitat amount. Local deadwood amount did not affect species density, and there was no interaction between the local and landscape habitat amount. Synthesis and applications: To promote the conservation of deadwood‐dependent lichens, the amount of old forests in managed forest landscapes should be maintained or increased. A certain amount of deadwood hosted more lichen species when situated in a landscape with more old forest, while there was no effect of the local deadwood amount. This suggests that management aimed at increasing the local species density of deadwood‐dwelling lichens should focus on creating and maintaining habitat in the surrounding landscape rather than only adding deadwood to that local site. In other words, effective management for deadwood‐dependent lichen diversity requires landscape‐scale habitat protection.

Time-lag effects of habitat loss, but not fragmentation, on deadwood-dwelling lichens

“…This is in contrast with the habitat amount hypothesis (Fahrig 2013), which predicts that the focal patch area should not affect species density within a sample area, when the landscape habitat amount has been accounted for. Furthermore, it is in contrast with a previous study that did not observe any effects of local dead wood amount on lichen species density in old pine forests (Hämäläinen et al 2023). Our result implies that larger patches of old forest can maintain higher local species density, at least in some regions.…”

“…old forest, in the landscape had in most cases a positive effect on the species density of deadwood-dwelling lichens. However, these effects were rarely significant, and typically quite weak in comparison to previous studies that have found lichen diversity to increase with landscape habitat amount in boreal (Kärvemo et al 2021;Hämäläinen et al 2023) and temperate forests (Paltto et al 2006). Moreover, in some cases, the present amount of habitat in the southern study region had a negative (though weak) effect on lichen species density.…”

“…We calculated habitat amount and fragmentation in the landscapes surrounding the study stands using ArcMap 10.8 (Esri Inc. 2021). We defined habitat as old forest (> 100 years), since our previous study found it to explain the species density of deadwooddwelling lichens better than other tested variables (Hämäläinen et al 2023). To examine the potential time-lag in lichen responses to changes in the landscape, we calculated the habitat amount and fragmentation in two periods: at the time of the lichen survey (present landscape) and in the 1960s (ca.…”

“…In addition, they typically contain more dead wood than younger forests (e.g. Fridman and Walheim 2000) and can therefore function as a proxy for deadwood-dwelling lichen habitat (Hämäläinen et al 2023). Data on forest age were obtained from the SLU Forest Map, which is produced from a combination of satellite data and field data from the Swedish National Forest Inventory.…”

Young Generations’ Perception of the Role of Deadwood in Forests: Comparison between Italy and Türkiye

“…Furthermore, the structural-functional role of deadwood in forests has been widely recognized by the scientific community and decision makers in the last two decades [15]. Numerous studies have shown the importance of deadwood as microhabitats for saproxylic insects [16], fungi [17], bacteria and actinobacteria [18], bryophytes [19], lichens [20], amphibians [21], small mammals [22], and birds [23].…”