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Comparing the influence of wildfire and prescribed burns on watershed nitrogen biogeochemistry using 15N natural abundance in terrestrial and aquatic ecosystem components.

Stephan K, Kavanagh KL, Koyama A - PLoS ONE (2015)

Bottom Line: We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire.In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations.S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns.

View Article: PubMed Central - PubMed

Affiliation: Forest, Rangeland, and Fire Sciences, University of Idaho, Moscow, ID, United States of America; Department of Life and Physical Sciences and Cooperative Research, Lincoln University, Jefferson City, Missouri, United States of America.

ABSTRACT
We evaluated differences in the effects of three low-severity spring prescribed burns and four wildfires on nitrogen (N) biogeochemistry in Rocky Mountain headwater watersheds. We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire. To better understand fire effects on the entire watershed ecosystem, we measured N concentrations and δ15N in both the terrestrial and aquatic ecosystems components, i.e., soil, understory plants in upland and riparian areas, streamwater, and in-stream moss. In addition, we measured nitrate reductase activity in foliage of Spiraea betulifolia, a dominant understory species. We found increases of δ15N and N concentrations in both terrestrial and aquatic ecosystem N pools after wildfire, but responses were limited to terrestrial N pools after prescribed burns indicating that N transfer from terrestrial to aquatic ecosystem components did not occur in low-severity prescribed burns. Foliar δ15N differed between wildfire and prescribed burn sites; the δ15N of foliage of upland plants was enriched by 2.9 ‰ (difference between burned and unburned watersheds) in the first two years after wildfire, but only 1.3 ‰ after prescribed burns. In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations. S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns. These responses are consistent with less altered N biogeochemistry after prescribed burns relative to wildfire. We concluded that δ15N values in terrestrial and aquatic plants and streamwater nitrate concentrations after fire can be useful indicators of the magnitude and duration of fire effects and the fate of post-fire available N.

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Foliar δ15N values in burned (B) and unburned (U) watersheds of prescribed burn (P) and wildfire (W) sites.Foliar δ15N values are averaged across all (A) upland species and (B) riparian species. Error bars represent 1 SE across four species. Each species’ value was obtained by first averaging across sites; the variability across sites per species is presented in Table 2. Data for the fourth post-fire year represents only the Danskin Creek wildfire site. Note that averaging across species obscures species × treatment interactions to some extent (see text).
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pone.0119560.g002: Foliar δ15N values in burned (B) and unburned (U) watersheds of prescribed burn (P) and wildfire (W) sites.Foliar δ15N values are averaged across all (A) upland species and (B) riparian species. Error bars represent 1 SE across four species. Each species’ value was obtained by first averaging across sites; the variability across sites per species is presented in Table 2. Data for the fourth post-fire year represents only the Danskin Creek wildfire site. Note that averaging across species obscures species × treatment interactions to some extent (see text).

Mentions: Following the fire, foliar δ15N of upland plants was generally higher in burned than unburned plots, but the magnitude of enrichment differed between wildfire and prescription-burned sites (Table 2). All upland species from WB plots had significantly higher foliar δ15N than in WU plots across all three post-fire years (P = 0.01). All species showed a consistent pattern in foliar δ15N with no statistically significant interaction effects among species, treatment, and post-fire year. The difference in foliar δ15N between WB and WU persisted for several years. The average differences were 3.0 ‰ and 2.8 ‰ in the first and second post-fire year, respectively. These differences decreased to 1.4 ‰ by post-fire year 3 (P < 0.001). In addition, data from the Danskin Creek wildfire site indicated that the burned-unburned differences in post-fire year 3 persisted in post-fire year 4 (Fig 2A).


Comparing the influence of wildfire and prescribed burns on watershed nitrogen biogeochemistry using 15N natural abundance in terrestrial and aquatic ecosystem components.

Stephan K, Kavanagh KL, Koyama A - PLoS ONE (2015)

Foliar δ15N values in burned (B) and unburned (U) watersheds of prescribed burn (P) and wildfire (W) sites.Foliar δ15N values are averaged across all (A) upland species and (B) riparian species. Error bars represent 1 SE across four species. Each species’ value was obtained by first averaging across sites; the variability across sites per species is presented in Table 2. Data for the fourth post-fire year represents only the Danskin Creek wildfire site. Note that averaging across species obscures species × treatment interactions to some extent (see text).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401779&req=5

pone.0119560.g002: Foliar δ15N values in burned (B) and unburned (U) watersheds of prescribed burn (P) and wildfire (W) sites.Foliar δ15N values are averaged across all (A) upland species and (B) riparian species. Error bars represent 1 SE across four species. Each species’ value was obtained by first averaging across sites; the variability across sites per species is presented in Table 2. Data for the fourth post-fire year represents only the Danskin Creek wildfire site. Note that averaging across species obscures species × treatment interactions to some extent (see text).
Mentions: Following the fire, foliar δ15N of upland plants was generally higher in burned than unburned plots, but the magnitude of enrichment differed between wildfire and prescription-burned sites (Table 2). All upland species from WB plots had significantly higher foliar δ15N than in WU plots across all three post-fire years (P = 0.01). All species showed a consistent pattern in foliar δ15N with no statistically significant interaction effects among species, treatment, and post-fire year. The difference in foliar δ15N between WB and WU persisted for several years. The average differences were 3.0 ‰ and 2.8 ‰ in the first and second post-fire year, respectively. These differences decreased to 1.4 ‰ by post-fire year 3 (P < 0.001). In addition, data from the Danskin Creek wildfire site indicated that the burned-unburned differences in post-fire year 3 persisted in post-fire year 4 (Fig 2A).

Bottom Line: We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire.In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations.S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns.

View Article: PubMed Central - PubMed

Affiliation: Forest, Rangeland, and Fire Sciences, University of Idaho, Moscow, ID, United States of America; Department of Life and Physical Sciences and Cooperative Research, Lincoln University, Jefferson City, Missouri, United States of America.

ABSTRACT
We evaluated differences in the effects of three low-severity spring prescribed burns and four wildfires on nitrogen (N) biogeochemistry in Rocky Mountain headwater watersheds. We compared paired (burned/unburned) watersheds of four wildfires and three spring prescribed burns for three growing seasons post-fire. To better understand fire effects on the entire watershed ecosystem, we measured N concentrations and δ15N in both the terrestrial and aquatic ecosystems components, i.e., soil, understory plants in upland and riparian areas, streamwater, and in-stream moss. In addition, we measured nitrate reductase activity in foliage of Spiraea betulifolia, a dominant understory species. We found increases of δ15N and N concentrations in both terrestrial and aquatic ecosystem N pools after wildfire, but responses were limited to terrestrial N pools after prescribed burns indicating that N transfer from terrestrial to aquatic ecosystem components did not occur in low-severity prescribed burns. Foliar δ15N differed between wildfire and prescribed burn sites; the δ15N of foliage of upland plants was enriched by 2.9 ‰ (difference between burned and unburned watersheds) in the first two years after wildfire, but only 1.3 ‰ after prescribed burns. In-stream moss δ15N in wildfire-burned watersheds was enriched by 1.3 ‰, but there was no response by moss in prescription-burned watersheds, mirroring patterns of streamwater nitrate concentrations. S. betulifolia showed significantly higher nitrate reductase activity two years after wildfires relative to corresponding unburned watersheds, but no such difference was found after prescribed burns. These responses are consistent with less altered N biogeochemistry after prescribed burns relative to wildfire. We concluded that δ15N values in terrestrial and aquatic plants and streamwater nitrate concentrations after fire can be useful indicators of the magnitude and duration of fire effects and the fate of post-fire available N.

Show MeSH
Related in: MedlinePlus