rufa group): their contribution to soil C and N pools and CO 2 emissions in subalpine conifer forests

Transcription

1 Red wood ants (Formica( rufa group): their contribution to soil C and N pools and CO 2 emissions in subalpine conifer forests Anita C. Risch (Syracuse University,USA) Martin F. Jurgensen (Michigan Technological University, USA) Martin Schütz (Swiss Federal Institute (Swiss Federal Institute for Forest, Snow and Landscape Research, Switzerland) Deborah S. Page-Dumroese (USDA Forest Service, USA)

2 Ants are important components of soil invertebrate community Biodiversity Ecosystem engineers Provider of habitat

3 Red wood ants (Formica rufa-group) build large aboveground nests composed of organic material (twigs, needles, wood, resin)

4 Wood ants (Formica rufa-group) are ubiquitous in many European forests Little is known on the contribution of these mounds to ecosystem C and N pools and CO 2 fluxes in forest ecosystems

5 Study area

6 Switzerland Swiss National Park

7 Climate (Inner-alpine, continental) Mean annual temperature 0.2 ± 0.7 C Mean annual precipitation 925 ± 162 mm Elevation 1650 to 3150 m a.s.l. Tree species Mountain pine (Pinus montana) European larch (Larix decidua) Stone pine (Pinus cembra) Norway spruce (Picea abies) Scots pine (Pinus sylvestris)

8 Mountain pine (MP) Four forest ecosystem in different successional stages Mountain pine/larch (MP/L) Mixed (Mix) Stone pine/larch (SP/L) Successional development Risch et al. 2004

9 Methods Ant mound survey: same stands/plots as forest survey Ant mounds (40 m circle) Heights (N/E/S/W) Diameter 1 (NS) Diameter 2 (EW) 70 m 70 m Forest structure and composition Total of 16 stands

10 Methods Mound C/N and CO 2 sampling Two mounds closest to stand center Side view View from top Top 10 cm Top 1/3 20 cm North 1/3 2/3 40 cm bottom 2/3 West East bottom South = Samples for C and N analyses = CO 2 emission (bi-monthly, June September)

11 Mound C and N pools

12 Number of mounds per hectare # mounds/ha a b c c MP MP/L Mix SP/L Number of mounds dependent on tree species composition, canopy closure and exposition

13 3 Mound volume a 2.5 Average volume (m 3 ) b b b MP MP/L Mix SP/L Highest volume in oldest SP stands

14 C/N concentrations of mound material Mound C and N concentration not different (46.9%, 1.02%), but higher than forest floor (38.5%, 0.88%) Mound C:N ratios not different, and similar to forest floor (47)

15 Mound C pools 1.4 a 1.2 t C/ha in ant mounds b 0.99 b b MP MP/L Mix SP/L

16 Contribution of mounds to forest floor C pools % 0.9% 2.0% 5.0% 20 t C/ha MP MP/L Mix SP/L

17 Contribution of mounds to forest floor N pools MP: 3 kg/ha MP/L: 4 kg/ha Mix: 7 kg/ha SP/L: 21 kg/ha Only 0.8 to 4.8%

18 Mound CO 2 emissions

19 Mound CO 2 emissions Range 0.8 to 8.6 g CO 2 /m 2 /h average for the individual mounds over the entire period (Max 15.3) No difference in emission among stand types

20 Mound vs forest floor CO 2 emission Ant mounds 8 Forest floor g CO 2 /m 2 /hr June 17 July 7 July 21 Aug 4 Aug 18 Sep 8 Date Mounds are hot spots (3.5 to 12.4 times higher than FF) On a hectare basis underestimation of 0.7 to 2.5%

21 Potential sources of CO 2 Respiration of ants and other invertebrates Organic matter decomposition Root respiration

22 Mound CO 2 emissions North-South diameter in cm June 19, 13.30pm, cloudy, 23 C East-West diameter in cm Aerial view of mound g CO 2 /m 2 /hr Top 3rd is location of breeding chamber

23 Changes in CO 2 emission June 18, 4.30pm, cloudy, 23 C July 12, 8.45am, sunny, 13 C July 23, 11.00am, few clouds, 14 C g CO 2 /m 2 /hr North-South diameter in cm August 6, 3.30pm, cloudy, 20 C August 21, 9.00am, cloudy/after rain, 13 C September 11, 2.30am, few clouds/after rain, 11 C East-West diameter in cm Ant respiration seems to be the dominate source of CO 2

24 Overall conclusions

25 Conclusions Red wood ant mounds do NOT Contribute much to ecosystem C and N pools Contribute much to ecosystem CO 2 fluxes Red wood ant mounds are CO 2 hot spots Increasing spatial heterogeneity / patchiness Keystone structures Tews et al. 2004

26 Questions?

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