Functional diversity of ground‐layer plant communities in old‐growth and managed northern hardwood forests

Abstract

Questions: Do ecological sorting processes and functional diversity of forest ground-layer plant communities vary among mature (65-85-yr-old) even-aged, managed uneven-aged and old-growth forest stands? How does functional diversity relate to environmental variables within stands? Location: Northern temperate deciduous forests of Wisconsin and the Upper Peninsula of Michigan, USA. Methods: Ground-layer species cover and light availability were measured at each of four old-growth, even-aged second-growth, and managed uneven-aged stands (n = 12 stands total). We used mixed-effect models and fourth-corner analysis to assess relationships among forest structure, species traits and the three components of functional diversity (functional richness, evenness, divergence) based on 32 leaf, reproductive and whole plant traits from 111 species. Results: We identified differences in leaf phenology and morphology, life form and dispersal among stand types at the community level. Ground-layer plant communities of even-aged and uneven-aged stands were at opposite ends of a spectrum of strategies aimed at tolerating stressful vs competitive environments, respectively. In even-aged stands, communities were characterized by species adapted to relatively dark and closed conditions (heavy-seeded tree saplings, spring ephemerals). In contrast, managed uneven-aged stands were characterized by species with potential for quick returns on investment of nutrients and dry mass in leaves (i.e. early summer species with high specific leaf area, low leaf dry matter content and high phosphorus concentration). Old-growth stands had fewer trait associations than managed stands, and were characterized by ferns and species with either ballistic or wind-assisted seed dispersal. Functional diversity metrics were related in complex ways to light, management and soil texture. Managed stands had higher functional richness and divergence than old-growth stands, which, instead, showed higher functional evenness. Conclusions: Even-aged and managed stands support ground-layer species with a distinct set of traits relative to those found in old-growth forests. Although there is broad interest in uneven-aged management as a means to restore the structures and functions of old-growth forests, uneven-aged management does not, at least initially, produce ground-layer plant communities more similar to old-growth forests than even-aged management. We elucidated a set of life-history traits providing a synthetic view of vegetation response to forest management. Functional diversity of ground-layer plant communities was related to differences in environmental conditions related to forest structure, suggesting that habitat filtering contributes to compositional differences at the community level. We discussed these differences with reference to plants' general strategies and carbon econom

Relationships between overstory and understory structure and diversity in semi-natural mixed floodplain forests at Bosco Fontana (Italy)

“…In the moist plot, LAI proved to be uncorrelated between the two layers, thus it could be hypothesized that this stand reflects a more mature successional stage, in which the higher resource availability have promoted niche differentiation and favored late-successional (habitat-specialist) species (Campetella et al 2004), and where the overstoryunderstory dynamics are close to the equilibrium (Aubert et al 2003). Taken together, the above results agree with previous reports indicating that different overstory structures can determine different environmental conditions, which drive different plants strategies aimed at tolerating stressful vs. competitive, resource-rich environments (Wright 2002, Sabatini et al 2013. In general, our results emphasize the importance of the understory layer (often neglected in forest management decision) because of its crucial role in driving the future dynamics of the forests (Gilliam 2007).…”

“…In the last decades, the number of studies conducted in natural forests sharply increased (Falinski 1989, Scheller & Mladenoff 2002, Campetella et al 2004, Petritan et al 2012, Sabatini et al 2013. Forest stand structure is an important factor in determining species diversity (Larsson 2001, Marchetti 2004, Corona & Marchetti 2007 which is a combination of species richness and their relative abundance (Newton 2007).…”

Wild boar rooting intensity determines shifts in understorey composition and functional traits

“…We sampled overstorey structure since it exerts an infl uence on the composition, diversity and spatial pattern of ground-layer plants (Burrascano et al 2011, Sabatini et al 2014a, and on the functional traits of the herb layer (Sabatini et al 2014b). We sampled overstorey structure through a variable radius plot, using a wedge prism, centered on the 400 m 2 plots used for the vegetation sampling (Avery and Burkhart 2002).…”

“…Among these species, Allium triquetrum and Ranunculus ficaria are vernal geophytes, a functional group typical of deciduous forests. These plants are characterised by a high SLA owing to their need to attain high photosynthetic rates to effectively take advantage of the enhanced amount of light reaching the forest floor prior to the leafing of the overstorey (Wright et al 2004, Sabatini et al 2014b. Although no facilitative role of Ruscus aculeatus was demonstrated so far (Brooker et al 2008), these vernal geophytes have low dispersal ability, and are likely to be facilitated by a dense Ruscus aculeatus thicket, which may provide protection from the direct predation by the wild boar (Cuevas et al 2010, Perea andGil 2014).…”

Multi‐scale spatial controls of understory vegetation in Douglas‐fir–western hemlock forests of western Oregon, USA

“…As most studies have focused on a single factor and/or scale, less is known about how factors interact across scales to influence the spatial patterning of understory vegetation. Yet, because most plant species are limited to the understory, which functions to provide a range of ecosystem services (e.g., Gilliam 2007, Neill and Puettmann 2013, Sabatini et al 2014, understanding the processes underlying spatial patterns carries important implications for forest management and conservation (Levin 2000, Rietkerk et al 2004, Peters et al 2007, Puettmann et al 2009). …”