Both canopy and understory traits act as response–effect traits in fire‐managed forests

Abstract

Citation: Refsland, T. K., and J. M. Fraterrigo. 2017. Both canopy and understory traits act as response-effect traits in fire-managed forests. Ecosphere 8(12):e02036. 10. 1002/ecs2.2036 Abstract. Community-level shifts in the distributions of plant functional traits associated with environmental change are expected to influence ecosystem functioning. However, few studies have identified traits that both respond to environmental change and affect ecosystem properties, thus limiting potential to scale the effects of environmental change through the community level. We measured canopy and understory plant functional traits, characterizing the most abundant functional trait value (community-weighted mean; CWM) and the functional diversity (FD), across a soil resource gradient in fire-managed mixeddeciduous forests to determine how traits both respond to a disturbance-resource gradient and affect stocks of active and stable soil organic carbon (SOC) fractions. We expected that understory traits would respond mainly to fire and canopy traits would respond mainly to soil resources. We further hypothesized that fire and resource conditions affect SOC stocks (1) through mass-ratio, by influencing trait abundance; (2) through non-additive effects, by influencing the FD of plant communities; or (3) directly, through either combustion or environmental controls on SOC stocks. Understory traits responded to soil resource conditions and fire, whereas only canopy CWM leaf dry matter content (LDMC) varied with resource conditions; no canopy traits varied with fire. Among the response traits, canopy CWM LDMC and diversity in the maximum height of the understory were related to SOC stocks, suggesting they play dual roles as response and effect traits. SOC stocks were primarily associated with mass-ratio effects from canopy leaf traits and secondarily with non-additive effects from the canopy and understory. There were also strong, fraction-dependent patterns in SOC stocks with fire disturbance. Repeatedly burned forests characterized by resource conservative traits (i.e., high canopy CWM LDMC) had a higher relative proportion of active SOC, whereas unburned forests characterized by resource acquisitive traits (i.e., high canopy CWM leaf nitrogen content) had a higher relative proportion of stable SOC. Our results suggest that canopy community-aggregated leaf traits and diversity in understory size traits can act as both response and effect traits in disturbed forests. Predicting forest SOC stocks using a response-effect trait framework will thus require knowledge of both canopy and understory trait distributions, as well as disturbance history.

Linking understory species diversity, community‐level traits and productivity in a Chinese boreal forest

“…In our study, community aggregated traits included LCC, LDMC, LNC, PH, and SLA. Considering these functional traits are highly related to the light‐capturing capacity, photosynthetic rate and growth rate (Meers et al., ; Refsland & Fraterrigo, ; Sabatini et al., ), our study suggested that understory productivity was higher in communities composed of species with traits on the fast‐growth end of the leaf economics spectrum (Reich, ). In contrast, we found functional diversity (FDis), representing multiple trait axes, did not affect UABP.…”

“…There are a large number of potentially related traits for a given ecosystem process (Pérez‐Harguindeguy et al., ). We selected six functional traits for all recorded understory species, which are closely related to understory light capture, resource utility, growth, and productivity (Meers, Kasel, Bell, & Enright, ; Refsland & Fraterrigo, ; Sabatini et al., ). Specifically, leaf area (LA, mm 2 ) is related to species' ability to capture light resources, which affects the photosynthetic rate.…”

Niche Breadth: Causes and Consequences for Ecology, Evolution, and Conservation

“…For example, on a given focal niche axis, the idea that variable performance of narrow NB species would translate into variable ecosystem functioning in changing environments (discussed above) seems most applicable when the traits that respond to the environment and that shape NB ("response" traits) also drive ecosystem functioning ("effect" traits; Lavorel and Garnier 2002). However, the overlap between these response and effect traits remains an area of active research (Funk et al 2017;Refsland and Fraterrigo 2017). Ecosystem functioning depends on the relative abundances of effect traits, so we envision two general pathways by which traits, NB, and ecosystem functioning interact.…”

The role of understory phenology and productivity in the carbon dynamics of longleaf pine savannas

“…Understory vegetation is thought to play a key role in carbon dynamics of ecosystems across the globe. Uncertainties exist, however, regarding the total carbon found in this vegetation strata (Johnson et al 2017, Refsland andFraterrigo 2017), and these uncertainties are expected to increase as climatic extremes become more common and severe (IPCC 2014). These shifts in climate, particularly drought, will have a direct effect on ecosystem structure (both understory and overstory), function (phenology and physiology), and ultimately their management strategies (Rich et al 2008, Becknell et al 2015.…”