Nitrogen cycling and export in California chaparral: the role of climate in shaping ecosystem responses to fire

Abstract

Climate change models predict that interannual rainfall variability will increase in California over the next several decades; these changes will likely influence how frequently California ecosystems burn and how they respond to fire. Fires uncouple N mobilization from uptake by destroying plant biomass and increasing nitrification. Following fire, autumn and winter rains can leach N into streams from slopes that have been denuded. The amount of N exported depends on how rapidly soil microbes metabolize it into mobile forms such as NO3− , and the rate that recovering plants take up available N. However, the long‐term effects of a changing climate on postfire N dynamics remain unknown. We used the ecohydrologic model RHESSys (regional hydro‐ecologic simulation system) to evaluate how interannual climate variability may affect the magnitude of N mineralization, nitrification, N export, and plant recovery following fire. N export was highest when fire was followed by drought; even though there was less water moving through the system, dry conditions prolonged the period during which N mobilization was decoupled from plant uptake. We also found that the effects of drought on N export were magnified in stands dominated by obligate seeders, which initially recovered more slowly than resprouters. These findings suggest that climate may regulate N balance most powerfully by influencing how quickly plants “turn on” and begin to immobilize N.

Sensitivity of nitrate concentration‐discharge patterns to soil nitrate distribution and drainage properties in the vertical dimension

“…We then use these values to investigate the influence of different combinations of N_decay and Ksat0 pairs on the concentration-discharge patterns. (Shields & Tague, 2012) and plot scale nitrogen cycling (Hanan et al, 2016b). The range of values of key parameters (N_decay, Ksat0) overlaps with the settings in the previous modeling studies (Hanan et al, 2016b) or derived from previous studies (Demenico & Schwartz, 1990 *From Physical and Chemical Hydrogeology (Demenico & Schwartz, 1990), the hydraulic conductivity ranges from 8 ×10 −13 m/s (unweathered marine clay) to 3 ×10 −2 m/s (gravel).…”

“…Rattlesnake Creek watershed (5.8 km 2 area) is located on the southern facing slopes of the coastal Santa Ynez Mountains and has three dominant shrub species: Ceanothus megacarpus (big pod ceanothus), Adenostoma fasciculatum (chamise) and Arctostaphylos spp. (Manzanita) (Hanan et al, 2016b). The watershed is characterized by steep slopes (slopes >20 ) and sandy loams plus rock outcrops.…”

Ecosystem processes at the watershed scale: Influence of flowpath patterns of canopy ecophysiology on emergent catchment water and carbon cycling

“…RHESSys couples elements of the ecosystem models BIOME‐BGC (Running & Hunt, ) and CENTURY (Parton, Schimel, Cole, & Ojima, ), with distributed watershed models to derive the coupling between ecosystem water use, carbon and nitrogen cycling with lateral soil water redistribution. RHESSys has been widely used to estimate spatially distributed soil moisture, ET, surface and subsurface run‐off, carbon and nitrogen cycling in different biomes and under different climate and land use change scenarios (e.g., Band, Patterson, Nemani, & Running, ; Bart, Tague, & Moritz, ; Garcia, Tague, & Choate, ; Hanan, Tague, & Schimel, ; Hwang et al, ; Lin, ; Lin, Webster, Hwang, & Band, ; Miles & Band, ; Tague & Band, ). RHESSys uses a landscape hierarchical structure over nested patch (Figure ), hillslope and watershed scales (Figure ).…”

Drought and its legacy modulate the post‐fire recovery of soil functionality and microbial community structure in a Mediterranean shrubland

“…Regarding the role of drought and fire on soil biogeochemical processes, it has been shown that soil nutrient availability, microbial activity, and biomass decrease under post‐fire severe drought conditions (Potts, Suding, Winston, Rocha, & Goulden, ; Hinojosa et al, ; Hinojosa, Parra, Laudicina, & Moreno, ; Hanan, Tague, & Schimel, ). However, under moderate drought (15% rainfall reduction), Hedo de Santiago, Lucas‐Borja, Wic‐Baena, Andrés‐Abellán, and Heras () showed that soil enzyme activities, microbial biomass, and respiration were not affected during a period of 3 years in a medium‐age (17 years since the last fire) forest.…”