Disturbance Alters the Relative Importance of Topographic and Biogeochemical Controls on Microbial Activity in Temperate Montane Forests

Abstract

Abstract:Fire and pathogen-induced tree mortality are the two dominant forms of disturbance in Western U.S. montane forests. We investigated the consequences of both disturbance types on the controls of microbial activity in soils from 56 plots across a topographic gradient one year after the 2012 High Park wildfire in Colorado. Topsoil biogeochemistry, soil CO 2 efflux, potential exoenzyme activities, and microbial biomass were quantified in plots that experienced fire disturbance, beetle disturbance, or both fire and beetle disturbance, and in plots where there was no recent evidence of disturbance. Soil CO 2 efflux, N-, and P-degrading exoenzyme activities in undisturbed plots were positively correlated with soil moisture, estimated from a topographic wetness index; coefficient of determinations ranged from 0.5 to 0.65. Conversely, the same estimates of microbial activities from fire-disturbed and beetle-disturbed soils showed little correspondence to topographically inferred wetness, but demonstrated mostly negative relationships with soil pH (fire only) and mostly positive relationships with DOC/TDN (dissolved organic carbon/total dissolved nitrogen) ratios for both disturbance types. The coefficient of determination for regressions of microbial activity with soil pH and DOC/TDN reached 0.8 and 0.63 in fire-and beetle-disturbed forests, respectively. Drivers of soil microbial activity change as a function of disturbance type, suggesting simple mathematical models are insufficient in capturing the impact of disturbance in forests.

Desirable Effects from Disturbance Ecology—A Paradox within Conservation Management

“…Another example is that disturbances could contribute to national parks' adaptation to climate change and increased temperatures [4]. The importance of natural disturbances for biodiversity is well-documented in the disturbance ecology literature [5][6][7][8], often with a more specific demarcation such as the contribution of fire to forest development [3,[9][10][11][12]. At the same time, natural disturbances are complex and difficult to define due to hierarchical relations and interactions with other small or large-scale disturbances [13].…”

Targeting Extreme Events: Complementing Near-Term Ecological Forecasting With Rapid Experiments and Regional Surveys

“…Manipulative experiments, a core tool in ecology (Hairston, 1989;Peters, 1991;Sala et al, 2000;Scheiner and Gurevitch, 2001;Weltzin and McPherson, 2003), can identify the mechanisms underpinning responses and the potential thresholds that are difficult to identify post-hoc, and have successfully been used to improve ecological forecasting (Jiang et al, 2018). Additionally, regional surveys and associated summaries are effective for change detection associated with extreme climatic events (Hughes et al, 2018;Ruthrof et al, 2018;Fettig et al, 2019;Flake and Weisberg, 2019), and are especially useful given the often spatially heterogeneous nature of many ecological disturbances (e.g., Lybrand et al, 2018). There are a range of remote sensing technologies that can be used to augment regional field surveys and forecast changes at a broader spatial scale.…”