Data set creator(s): Timothy Seastedt
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Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) tree islands modify the characteristics of surface soils in alpine tundra. Soil C content of the approximate A horizon (top 15 cm) of soil was measured during the summer of 1994 on windward, leeward, upslope and downslope sides, and interiors of tree islands on Niwot Ridge, Colorado, USA. A subset of samples from these sites were also used for CHN analysis and were measured for total phosphorus using persulfate digestions and colorimetric measurements. Results indicate significant (p<.0001) reductions of percent of dry mass represented by C in soil and significant (p<.04) declines in absolute C storage among soils on the windward sides of tree islands as compared to the upslope and downslope controls, and a tendency for reduced C on the leeward sides as well. Surface organic matter (O horizon) accumulations averaging 9.6 +/- 1.02 kg/m^2 are found in the interior of tree islands, but this material, in addition to roots, is not stabilized in the A horizons of soil. The movement of tree islands can therefore be regarded as disturbances to soil building processes in alpine tundra. Timberline forest and adjacent tundra patches of similar aspect and slope were also sampled for comparisons of soil C content. Results indicated similar C storage beneath trees and tundra at this lower elevation. The wind-induced movement of tree islands across the tundra creates enhanced snowpack within the trees and on their leeward sides. Shading and moisture conditions of the soil are altered, leading to C deposition and decomposition dynamics which differ from that of unimpacted tundra surface soils. However, at timberline, adjacent tundra lacks the ability to exhibit the enhanced C storage of alpine tundra at higher elevations. Snowpack within trees and adjacent tundra at timberline may be relatively constant such that biophysical factors affecting soil characteristics are relatively unchanged by plant life-form.
Study sites were located on a south-facing slope adjacent to the east side of the Niwot Ridge Saddle at an approximate elevation of 3600 m (treeline data), south-facing slopes on Niwot Ridge at an approximate elevation of 2400 m (timberline data), and randomly selected subalpine fir and Engelmann spruce tree islands in dry meadows on Niwot Ridge (tree island data). Contact Tim Seastedt for location of original data.
1994-6-28 to 1994-7-12
length of krummholz tree island, width of krummholz tree island, distance of soil core from leeward side of krummholz tree island, scar length of krummholz tree island, sample depth, organic matter content as a proportion of dry mass, total phosphorus, total nitrogen, total carbon, carbon/nitrogen ratio
Elevation: 3500 m
Niwot Ridge (USFS - UNESCO Biosphere Reserve)
Located in: USFS - UNESCO Biosphere Reserve
(Click to learn more about these locations)
More data from: Saddle, S slope of Niwot Ridge
Core Data Set: No
Discipline: Plant/vegetation ecology, Biogeochemistry
The field data and the organic matter data were manually entered from laboratory data sheets using an EasyEntry form. The resulting files were processed and archived on niwotlter (NWT LTER server).
The CHN and total phosphorus analysis were performed by the Stable Isotope/Soil Biology Laboratory of the University of Georgia Institute of Ecology. Detailed information concerning the methods used in the Dumas combustion assays performed to determine total N and total C, as well as the persulfate digestions and colorimetric assays performed to determine total phosphorus are available from the Laboratory via the World Wide Web at http://ash.ecology.uga.edu/. The total N, total C, C/N ratio, and total P data were provided by Tim Seastedt in a 24 December 1996 email message. An ASCII version of the original message has been archived as /data1/Datman/Tims/Som/Lifeform/Archive/email.cnp. A copy of the message was reformatted using various Unix commands, and the data were joined with the data in this file. Empty columns were added to the records for samples which were not sent for further analysis in order to maintain a consistent format. The following quality control comments were included in the 24 December 1996 email:
Determined mean TP% NBS 2710 = 0.108%
Determined range = 0.100% -- 0.112%
NBS certified mean TP% = 0.106%
NBS certified range = 0.091% -- 0.121%
Our tree island samples were collected in minimal snow cover soil described by Burns (1980) as follows: The soil is composed of Pergelic Cryumbrept of a loamy-skeletal, mixed type, probably eolian in origin with moderately thick, fine-textured A horizons overlying a cambic B horizon. Where A horizons are not thick enough to be classified as umbric epipedon, soil is classified as Dystric Pergelic Cryochrept of a coarse-loamy, mixed type. These latter characteristics described the soil on the windward side of tree islands, which was confirmed by Holtmeier et. al. (1992). Less than 15% rock cover occurs on the ground surface, although extremely rocky areas found in this soil type are have been interpreted to be edges of buried patterned ground, suggesting extensive permafrost in the past. Vegetation communities dominating this dry meadow area are primarily Association Selaginello-Kobresietum myosuroidis, and Association Caricetum elynoidis with some areas of Acomastylis (Geum) rossii (Burns 1980). Pocket gopher (Thomomys talpoides) disturbance occurs regularly in the Acomastylis (Thorn 1982), leaving esker-like mounds of soil on the surface. Various forbs and willows (Salix brachycarpa) tend to invade the wind-sheltered leeward side of tree islands, and are eventually either killed by the advancing tree, or become mixed with the branches of the island (Marr 1977).
The timberline study area covered south-facing slopes at an approximate elevation of 3400 m. We sampled a variety of sites at this elevation whose soil types could be described as Dystric Cryochrept (Burns 1980, Holtmeier et al. 1992).
Seven subalpine fir and 5 Engelmann spruce tree islands were selected randomly in dry meadows on Niwot Ridge. The length and width at greatest points were measured at each tree island. In addition, an estimate of the disturbed area windward of the trees was also measured. Soil cores were taken to a depth of 15 cm using 3.6 cm diameter PVC pipes. Single soil cores were taken at 5 m and 1 m in the windward direction of the windward side, at 5 m and 1 m in the leeward direction of the leeward side, 5 m upslope and 5 m downslope, and 2 samples from the interior of the tree island whose distances were recorded from leeward edge.
We attempted to remove the litter and fragmented organic matter (the O horizon) of the tree island soils. No O horizon existed on tundra soils. Twelve paired timberline forest and adjacent tundra plots were selected based on their similarity in slope and aspect. Four soil cores were randomly selected from each plot and, after removal of O horizon material from forested soils, cores were taken to a depth of 15 cm.
Organic matter and soil C was estimated using loss on ignition techniques. All cores were allowed to air dry overnight, and were then passed through a 2-mm sieve. The sieved soil samples were dried to a constant weight in a drying oven at 105 degrees C. Crucibles were heated to 550 degrees C to ensure removal of organics, and rinsed with distilled, deionized water and dried between sets of samples. Approximately 2 g of air dried soil was placed in previously weighed crucibles, and the crucible + sample weight was recorded. After pre-charring, samples were muffled for 2 hours at 550 degrees C and reweighed after allowing rehydration at 105 degrees C. Bulk density data were obtained by taking two 15-cm deep cores at 6 windward and 6 upslope sites of previously sampled tree islands, air drying these samples, and averaging dry weights of the sieved material. Amount of detritus in the interior of tree islands was calculated by taking 2 samples of 0 horizon material from 6 previously sampled tree islands and averaging the dry weights of these samples. Sample identification codes are comprised of 6 characters. The first 2 characters represent the lifeform type and are either TT (krummholz tree island), TP (tundra plot), or FP (forest plot). The middle 2 characters (3 and 4) are comprised of digits that represent the plot number for the particular lifeform type. The final 2 characters (5 and 6) indicate the location of the soil core collected, with W1 representing a core collected 5 m from the windward edge of the tree island, W2 representing a core collected 1 m form the windward edge of the tree island, L1 representing a core collected 5 m from the leeward edge of the tree island, L2 representing a core collected 1 m from the leeward edge of the tree island, B1 representing a core collected 5 m downslope from the edge of the tree island, T1 representing a core collected 5 m upslope from the edge of the tree island, K1 representing the most windward core taken from within the tree island, K2 representing the most leeward core taken from within the tree island, and S# representing a core taken from a randomly selected location within the plot (# is a digit).
The carbon fraction can be estimated by multiplying the organic matter fraction by 0.44.
Sample identification codes, followed by associated descriptive comments, are:
TT05L1: disturbed Acomastylis
TT06L1: dying Kobresia
TT04K2: willow at leeward
TT06L2: disturbed Kobresia, Acomastylis
TT06W2: gravel garden
TT02W1: Kobresia, Acomastylis mix
TT04L1: snowdrift impacted
TT04T1: developing Kobresia
TT03B1: Kobresia, Acomastylis mix
TT03L2: disturbed Acomastylis
TTO4L2: disturbed Acomastylis
TT04W2: gravel garden
TT01L2: Kobresia, solifluction ridge
TT03W2: disturbed Acomastylis
TT03L1: disturbed Acomastylis
TT10L2: gopher garden
TT08T1: undisturbed Kobresia
TT10L1: gravel garden
TT11T1: undisturbed Kobresia
TP09S2: composite of 2 cores
TP07S2: mesic meadow
FP06S4: composite of 2 cores
TP05S4: wet meadow
TT12W2: gravel garden
TT12L1: mixed Acomastylis, Kobresia
TT12B1: gopher garden
Six samples from 6 of the tree islands indicated 9.6 kg C/m^2 (with a standard error of 1.02 kg C/m^2) in the O horizon. Bulk density of 0-15 cm tundra soil was 0.50 g/cm^3 of sieved soil (standard error=.03; n=6). Bulk density of 0-15 cm windward side (of tree islands) soil was 0.57 g/cm^3 of sieved soil (standard error=.04; n=6).
It was determined that the 28 June 1994 TP02S2 record with a crucible number of 14 should have a sample code of TP02S3, and was changed accordingly.
2 samples were collected on 12 July 1994 for TP07S3, but it is unkown which sample was sent for CHN analysis and total phosphorus measurement. Therefore, the CHN and phosphorus data provided for TP07S3 were added to the original records for both samples.
soil carbon storage, tree islands, krummholz, timberline, alpine tundra, dry meadow, windward, leeward, subalpine fir, Engelmann spruce, organic matter content, phosphorus, nitrogen, carbon, scar length, carbon/nitrogen ratio, Biogeochemistry, soil and microbial pools and fluxes, saddle, south slope of Niwot Ridge, Niwot Ridge LTER, NWT
COL1. label=date, type=string, units=none, missing value indicator=NaN, minimum=1994-06-28, maximum=1994-07-12, precision=, definition=date sample was collected (yyyy-mm-dd)
COL2. label=samp_id, type=string, units=none, missing value indicator=NaN, minimum=, maximum=, precision=, definition=sample identification code
COL3. label=island_length, type=real, units=meter, missing value indicator=NaN, minimum=, maximum=, precision=, definition=length of krummholz tree island
COL4. label=island_width, type=real, units=meter, missing value indicator=NaN, minimum=, maximum=, precision=, definition=width of krummholz tree island
COL5. label=distance_edge_to_core, type=real, units=meter, missing value indicator=NaN, minimum=, maximum=, precision=, definition=distance from leeward edge of krummholz tree island to soil core location
COL6. label=trailing_scar_length, type=real, units=meter, missing value indicator=NaN, minimum=, maximum=, precision=, definition=length of trailing scar associated with krummholz tree island
COL7. label=core_depth, type=real, units=meter, missing value indicator=NaN, minimum=, maximum=, precision=, definition=depth of soil core
COL8. label=cruc_num, type=integer, units=none, missing value indicator=NaN, minimum=, maximum=, precision=, definition=crucible number
COL9. label=cruc_wt, type=real, units=gram, missing value indicator=NaN, minimum=, maximum=, precision=, definition=crucible weight
COL10. label=cruc+soil_wt, type=real, units=gram, missing value indicator=NaN, minimum=, maximum=, precision=, definition=crucible + soil sample weight
COL11. label=cruc+ash_wt, type=real, units=gram, missing value indicator=NaN, minimum=, maximum=, precision=, definition=crucible + soil ash weight
COL12. label=org_content, type=real, units=none, missing value indicator=NaN, minimum=, maximum=, precision=, definition=organic matter content as a proportion of dry mass
COL13. label=tot_P, type=real, units=percent, missing value indicator=NaN, minimum=, maximum=, precision=, definition=total phosphorus
COL14. label=tot_N, type=real, units=percent, missing value indicator=NaN, minimum=, maximum=, precision=, definition=total nitrogen
COL15. label=tot_C, type=real, units=percent, missing value indicator=NaN, minimum=, maximum=, precision=, definition=total carbon
COL16. label=C/N_ratio, type=real, units=none, missing value indicator=NaN, minimum=, maximum=, precision=, definition=carbon:nitrogen ratio
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Marr, J.W. 1977. The development and movement of tree islands near the upper limit of tree growth in the Southern Rocky Mountains. Ecology 58: 1159-1164.
Burns, S. 1980. Alpine soil distribution and development, Indian Peaks, Colorado Front Range. Ph.D. dissertation, University of Colorado, Boulder. 360 pp.
Thorn, C.E. 1982. Gopher disturbance: Its variability by Braun-Blanquet vegetation units in the Niwot Ridge alpine tundra zone, Colorado Front Range, U.S.A. Arctic and Alpine Research 14:45-51.
Holtmeier, F-K, and G. Broll. 1992. The influence of tree islands and microtopography on pedoecological conditions in the forest-alpine tundra ecotone on Niwot Ridge, Colorado Front Range, U.S.A. Arctic and Alpine Research 24: 216-228.
Pauker, S.K., and T.R. Seastedt. 1996. Effects of mobile tree islands on soil carbon storage in tundra systems. Ecology, 77(8):2563-2567.
The initial iteration of the documentation section of this file was generated on 1 September 1994 by Rick Ingersoll using a manuscript supplied by Sheridan Pauker and Tim Seastedt on 11 August 1994. [RCI 1 September 1994] Additional comments were provided by Tim Seastedt on 6 September 1994 and these were incorporated into the documentation section on 6 September 1994. The file was put under sccs control on that date as well.[RCI 6 September 1994] Total C, N, and P data were inserted into the data section and appropriate comments were inserted into the abstract and comments section on 2 January 1997. Updated information regarding the Paulker and Seastedt Ecology article was added to the citations section and a correction regarding sample TT02S3 was made at that time as well.[MAH 2 January 1997] The title, keywords, and units were edited, labels shortened, and definitions added.[HCH 18 May 2016]
Seastedt, Timothy. 2019. Krummholz island size, soil inorganic, and organic property data for Saddle S slope of Niwot Ridge from 1994-6-28 to 1994-7-12. http://niwot.colorado.edu
This material is based upon work supported by the National Science Foundation under Cooperative Agreement #DEB-1637686. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necesarily reflect the views of the National Science Foundation.
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