Diversity, functional structure and functional redundancy of woodland plant communities: How do mixed tree species plantations compare with monocultures?

Abstract

Managing forest plantation stands in a way that retains productivity targets, but that also fosters biodiversity and stand resilience are key sustainable forest management goals. Current forestry policy advocates a diversification of forest stands to achieve these goals, favouring mixed age structures and polycultures over single-aged monocultures. Evidence is lacking, however, to support this management recommendation for biodiversity gains and related ecosystem service delivery. We used indices of taxonomic diversity and functional structure to compare ground vegetation communities in mixed and pure stands of Scots pine (Pinus sylvestris) and pedunculate oak (Quercus robur) in each of three study regions. We categorised the 91 vascular plant species identified into functional effect and response groups. We tested the hypotheses that ground vegetation communities (i) differ significantly in structure and composition between Scots pine and oak monocultures and (ii) show enhanced levels of taxonomic and functional diversity and functional redundancy in mixed stands of Scots pine and oak compared with monocultures. We explored the implications of any differences in the functional structure of ground vegetation communities in the different stand types on two ecosystem services: nutrient availability and levels of resource provisioning for herbivores. Nine functional response groups (RG) and seven functional effect groups (EG) were identified with considerable overlap in the RG and EG species grouping. Three RGs had traits characteristic of forests (spring flowering herbs, tree saplings and shrubs/ climbers), one RG had traits characteristic of open habitats (annual ruderals) and the remaining RGs had more generalist traits (anemochorous perennials, graminoids and short perennials). No significant differences were found among stand types in terms of taxonomic diversity or richness of the different functional trait groups. Ground vegetation communities in the three study regions also had similar levels of functional redundancy across stand types. However, Scots pine and oak monocultures harboured significantly different abundances of species with distinct functional traits. In all three study regions, anemochorous perennials were significantly more abundant in Scots pine monocultures than oak monocultures, while two core forest groups (shrubs/ climbers, spring flowering herbs) were significantly more abundant in oak monocultures. Mixed stands had intermediate abundances of these functional groups. These differences have implications for the comparative availability of food resources and shelter for wildlife, but also the mobilisation and temporal availability of nutrients in the two monocultures. Thus, mixtures of Scots pine and pedunculate oak can temper significant tree species identity influences on ground vegetation functional diversity

Mapping the effectiveness of nature‐based solutions for climate change adaptation

“…Our map revealed 91 cases that reported ecological outcomes of nature‐based interventions in addition to effectiveness in reducing a climate impact. Of these, most had positive outcomes, such as an increased number of species, functional diversity, or higher plant or animal productivity (e.g., Barsoum et al., 2016; Biel, Hacker, Ruggiero, Cohn, & Seabloom, 2017; Liquete, Udias, Conte, Grizzetti, & Masi, 2016). Moreover, 47 of these positive cases also reported benefits to address one or more climate impacts.…”

Trends in evergreen oak suitability from assembled species distribution models: assessing climate change in south-western Europe

“…Preservation of older, larger and well-connected Q. ilex stands in agricultural areas is essential for specialist insects and biodiversity in general (Ruiz-Carbayo et al 2016). This is also important in forest plantations, in which finding a balance between productivity and biodiversity is a key goal in management (Barsoum et al 2016). Quercus suber decline can alter soil respiration and nutrients having effects in other successional forest species and implying vegetation shifts (Ávila et al 2016;Ibáñez et al 2016).…”

Getting the message right on nature‐based solutions to climate change

“…A recent systematic map of 376 peer‐reviewed studies (Chausson et al, 2020) showed that most (73%) of the 91 cases that reported on ‘ecological outcomes’ showed benefits, such as an increased number of species, functional diversity, or higher plant or animal productivity (e.g. Barsoum et al, 2016; Liquete et al, 2016) with only 1% showing exclusively negative effects, and 24% reporting mixed or unclear effects. Of the cases with positive ecological outcomes, 47 were reported to also have benefits for adaptation (none were negative, four were mixed).…”