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10 results for “krummholz”
Pocket gopher esker-krummholz distance data for Martinelli slope and North of Tvan, 1995.
Two ares of Niwot Ridge were examined for simultaneous occurrences of krummholz and eskers created by Thomomys talpoides (Northern pocket gopher) burrowing, to establish a relationship between snowpack and gopher habitat. The krummholz east and northeast of the Martinelli slope and the krummholz north of T-van were surveyed for the abundance of gopher eskers. Using a tape measure, the minimum and maximum distances of the eskers from the krummholz vegetation were measured, with a value of 0 m indicating that the nearest soil core was immediately adjacent to or actually underlying a branch of the tree. With the use of a compass, both the northernmost and southernmost bearings were measured from the krummholz to the esker. The krummholz were tagged at the northeasternmost point whenever possible for consistency, or the northernmost branches of the leeward side of the tree island. All measurements were taken from the nearest protruberance of the krummholz.
Krummholz island soil C and N data for East of Tvan, 1994.
Previous work has shown that passage of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) tree islands across tundra lowers the soil carbon and nitrogen storage capacity of the top 15cm of soil (A horizon) (Pauker and Seastedt 1996). This data forms part of a study which seeks to further examine how changes in carbon storage capacity are associated with changes in soil physical properties. Soils were collected in 1994. We sought to determine whether there were changes in natural abundance of C and N isotopes associated with previously reported changes in C and N content. Any such changes in natural abundance of C and N isotopes may indicate differences in inputs to the ecosystem or differences in ecosystem processes that may account for the differences in N and C content that have been observed. In addition to measuring ratios of natural isotopes of C and N, we also measured C and N contents to provide a comparison with previous studies. To convert % N and C values to kgs of N and C per m2, we used bulk density values, averaged across sampling dates that had been previously measured for these sites. Metadata for these data are available at: https://portal.lternet.edu/nis/mapbrowse?scope=knb-lter-nwt&identifier=131 When N and C soil contents were considered on a percentage basis, levels at windward sites were significantly lower than those of undisturbed tundra, but levels directly beneath krummholz were not significantly different from tundra soils. Bulk density was significantly lower under krummholz than other sites. Thus when N and C amounts were expressed on a volume (Kg/m2, to a depth of 15cm), they were significantly lower in both krummholz and windward sites than in undisturbed tundra. D13C values of soils under krummholz were significantly less negative under krummholz than from windward or undisturbed tundra sites. A less negative d13C value is indicative of less discrimination and may be attributable to either vegetation differences
Krummholz island soil inorganic and organic property data for East of Tvan, 1995 - 1996.
Previous work has shown that passage of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) tree islands across tundra lowers the soil carbon and nitrogen storage capacity of the top 15cm of soil (A horizon) (Pauker and Seastedt 1996). This study shows that levels of KCl extractable ammonium and percent organic matter were also significantly higher in the A horizon of undisturbed tundra sites compared with soils underneath or immediately adjacent to (windward or leeward) the krummholz. The response of soil KCl extractable NO3- also showed this trend but was not statistically significant. Holtmeier and Broll (1992) suggested that the depletion of organics and nutrients following the passage of tree island may be associated with a reduced clay content. We analyzed a subsample of these soils for cation exchange capacity (CEC) and texture. We did not find significantly lower clay content in soils under or adjacent to krummholz compared with those from undisturbed tundra. In fact, percent clay was greater in krummholz and windward sites than in tundra sites. The percent clay of windward sites was significantly greater in windward soils than either krummholz or tundra soils. Clearly, depletion of organics following the passage of tree islands does not appear to be associated with a depleted clay content. We found that CEC was very highly significantly correlated with percent organic content (using percent organic data only from the subset of soils on which CEC was measured). Therefore, the CEC content of these soils would appear to be strongly associated with the organic content but not with the clay content. Percent soil moisture was significantly higher directly underneath the krummholz compared with the other sites. There was no effect of treatment on pH. We also investigated whether the organic matter lost in association with krummholz colonization (i.e. 1m from the tree) was replenished as tundra vegetation recolonized in the wake of the tree is
Krummholz island soil N and root ingrowth data for East of Tvan, 1996 - 1997.
Previous work has shown that passage of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) tree islands across tundra lowers the soil carbon and nitrogen storage capacity of the top 15cm of soil (A horizon) (Pauker and Seastedt 1996). The presence of tree islands (krummholz) on the tundra acts as a 'snowfence' causing snow to drift within the krummholz and in a semi-circular area leeward of the krummholz. This drifting causes soil within and leeward of the krummholz to have a much deeper, more consistent and longer lasting snow-cover than the adjacent tundra soils. The snowdrifts form a permanent cover over the leeward and krummholz sites from November through June, helping to insulate the soils beneath from the extreme low temperatures and supplying significantly more meltwater in the spring. In contrast, high winds cause the adjacent tundra to be free from snow and exposed to extremely cold temperatures for much of the winter. Studies have shown that atmospheric nitrogen deposition accumulates on snowpacks throughout the winter months and that this is released as a 'pulse' of nitrogen ions at snowmelt (Williams et al. 1996). We hypothesized that accumulation of snowpacks in krummholz and leeward sites may alter nitrogen dynamics in these areas relative to tundra, by either (a) affecting microbial activity via its insulating effect or (b) accumulating large amounts of atmospherically deposited N and releasing it as a pulse at snowmelt. This study sought to examine the nitrogen inputs into tundra, krummholz, and leeward soils over an entire winter season (using buried ion exchange resin bags which collect ions percolating down at snowmelt and early spring rains) and over a short period in spring, immediately following snowmelt (using microlysimeters to collect soil water over a 24 hour period). Belowground NPP (determined from root ingrowth cores) and d13C values of tundra and krummholz vegetation are also presented in this file. NH4+ and NO3-
Krummholz island plant species density data for East of Tvan, 2000.
Species richness (density) on one meter sq. plots were measured on windward and leeward sides of krummholz trees previously studied by Seastedt and colleagues. Species richness of adjacent dry meadow tundra areas was also sampled. The results indicate that species richness is initially increased by the passage of tree islands. Richness was higher in leeward areas than on either windward or open tundra sites. The hypothesis that successional species must tolerate low nitrogen conditions found in the windward sites of tree islands was not supported by findings obtained here.
Alpine tundra and krummholz soil temperature data for Saddle and North of Tvan, 1994 - 1999.
Growing season soil temperatures (typically at 2 depths in a given location) were measured (1) to quantify the soil temperature environment across the landscape mosaic of alpine tundra, and (2) to compare temperatures between tundra and adjacent krummholz vegetation. Measurements were made at sites differing in aspect (south-facing and north-facing) and moisture conditions (dry, mesic, and wet). In addition, soil temperature was measured at a site characterized by persistent snow cover, as well as at sites within and adjacent to a krummholz patch. Data are presently collected using an Omnidata DP212 datapod.
Krummholz island size, soil inorganic, and organic property data for Saddle, S slope of Niwot Ridge, 1994.
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.
Krummholz island soil bulk density data for East of Tvan, 1994 and 1996.
Previous work has shown that bulk density is lower in the A horizon of soils directly under tree islands (Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa)) than in adjacent tundra soil. We compiled a dataset of bulk densities from soils that had been previously collected at several dates in 1994 and 1996. The results from this large dataset confirmed those of Pauker and Seastedt (1996): soils within tree islands had lower bulk densities than those of other sites.
Winter damage is more important than summer temperature for maintaining the krummholz growth form above alpine treeline
<p><span><span><span><span><span><span><span><span><span><span><span>1. Understanding the processes that control alpine treelines, the elevational limits of tree growth forms, has been a central question in ecology and is growing in importance with concern over climate change. Cool summer air temperatures are currently thought to be the ultimate limiter of upright tree growth at alpine treelines globally. However, winter damage has long been recognized as a shaping force near alpine treelines. Low-growing krummholz growth forms provide an opportunity to test hypotheses about the controls of upright growth in environments above current treelines.</span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span>2. To distinguish between effects of growing season temperature, winter damage and their interaction on preventing upright growth in krummholz, we conducted a field experiment on krummholz growth forms of <i>Pinus albicaulis </i>over the summer and winter of 2015-2016 at 10 mountain top sites in the Tobacco Root Mountains, Montana, USA. We experimentally manipulated four factors using a fully crossed design: shoot position (natural low position in the krummholz mat vs. propped up above the krummholz mat), summer warming (warming chamber vs. ambient), winter exposure (shelter cage vs. exposed), and elevation position (local high vs. low krummholz limits). We also conducted an observational study of the climatic conditions associated with recent natural emergent stem establishment from krummholz. </span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span>3. Experimentally propped shoots that were exposed in winter experienced the highest mortality (10-50%), while propped shoots in shelter cages and shoots located within the krummholz mat, whether caged or not, had low mortality (0-10%). Summer warming had little influence on shoot mortality. Surviving mat shoots had marginally higher growth rates than surviving propped shoots during the early growing season after treatments were established. Natural emergent stem establishment was associated with warmer than average summer temperatures, but also warmer winter temperatures, lower winter wind speeds, and lower snowpack.</span></span></span></span></span></span></span></span></span></span></span></p> <p><span><span><span><span><span><span><span><span><span><span><span>4. <i>Synthesis</i>. Our results suggest winter damage plays a more important role than does growing season temperature in maintaining the krummholz growth form. While warming may increase opportunities for emergent shoot establishment above krummholz mats, establishment of upright trees in the krummholz zone will also require climatic change that reduces wind and snow transport which cause winter damage.</span></span></span></span></span></span></span></span></span></span></span></p>
Winter damage is more important than summer temperature for maintaining the krummholz growth form above alpine treeline
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