Testing the relative sensitivity of 102 ecological variables as indicators of woodland condition in the New Forest, UK

Abstract

Forests globally are facing an increasing number of threats from modified disturbance regimes, novel stressors and changing environmental conditions. This has ultimately resulted in declines in the ecological condition of many forest and woodland ecosystems, leading to widespread tree mortality and stand dieback. Effective indicators of overall woodland ecological condition are therefore needed for environmental monitoring and to support management responses. To test the effectiveness of different variables that could potentially be used as indicators of woodland condition, 102 variables that describe woodland structure, composition, functioning, edaphic conditions and disturbance regimes were assessed along 12 replicate gradients of beech stand dieback. Results indicated that 35 variables differed significantly between at least two stages of the dieback gradient, indicating their sensitivity to stand dieback. Seven of these indicators related to woodland species composition, two to functional processes, 20 to structural features, four to edaphic conditions, and two to disturbance regimes. These results demonstrate that effective indicators can potentially be identified for each of the ecological categories. Effective composition indicators included species richness of ectomycorrhizal fungi, ground flora and epiphytic lichens; functional indicators were soil respiration rate and net nitrification rate; edaphic conditions included soil Na:Ca ratio, sodium cation exchange capacity, total carbon, Ca:Al ratio, structural indicators included canopy openness, litter cover, sward height, and volume of deadwood, and for disturbance was Equus dung density. Other measures, such as shrub cover and species richness of carabid beetles and spiders, were not found to vary 2 significantly along the dieback gradients, and were therefore not identified as effective indicators. These results demonstrate the value of gradient analysis for evaluating indicators of woodland condition, but also highlight the need for multi-site studies to identify indicators with wide applicability.

Climate-induced forest dieback drives compositional changes in insect communities that are more pronounced for rare species

“…deadwood), sunlight and microhabitats, increasing species richness for multiple insect groups including bees, wasps, hoverflies, saproxylic beetles, as well as multiple redlisted insect taxa following insect pest outbreaks 10 , or canopydwelling beetles in declining oak forests 9 . However, no significant change in species richness of ground-dwelling carabids and spiders has been associated with climate-induced dieback in a beechdominated forest 11 . Meanwhile, forest management practices, like salvage logging (i.e.…”

Climate-induced forest dieback drives compositional change in insect communities that is concentrated amongst rare species

“…deadwood), sunlight and microhabitats, increasing species richness for multiple insect groups including bees, wasps, hoverflies, saproxylic beetles, as well as multiple red-listed insect taxa following insect pest outbreaks 10 , or canopy-dwelling beetles in declining oak forests 9 . However, no significant change in species richness of ground-dwelling carabids and spiders has been associated with climate-induced dieback in a beech-dominated forest 11 . Meanwhile, forest management practices, like salvage logging (i.e.…”

The forest biodiversity index (FOBI): monitoring forest biodiversity potential over space and time

“…dispersal capabilities) can limit the generalisability of compositional indicators, and their representativeness of other species needs, and broader aspects of biodiversity is often untested beyond small scale case studies (Lindenmayer et al 2000, Gao et al 2015. Collecting the required taxonomic data can also be costly and often requires specialist skills or equipment (Evans et al 2019, Cosović et al 2020. Functional indicators instead focus on the physical and ecological traits associated with an organism's fitness which mediate responses to environmental changes (Noss 1990, Violle et al 2007, Feld et al 2009.…”