Importance Of Site Conditions Research Articles

Similarity of nutrient uptake and root dimensions of Engelmann spruce and subalpine fir at two contrasting sites in Colorado

Nutrient uptake capacity is an important parameter in modeling nutrient uptake by plants. Researchers commonly assume that uptake capacity measured for a species can be used across sites. We tested this assumption by measuring the nutrient uptake capacity of intact roots of Engelmann spruce ( Picea engelmanni Parry) and subalpine fir ( Abies lasiocarpa (Hook.) Nutt.) at Loch Vale Watershed and Fraser Experimental Forest in the Rocky Mountains of central Colorado. Roots still attached to the tree were exposed to one of three concentrations of nutrient solutions for time periods ranging from 1 to 96 h, and solutions were analyzed for ammonium, nitrate, calcium, magnesium, and potassium. Surprisingly, the two species were indistinguishable in nutrient uptake within site for all nutrients ( P > 0.25), but uptake rates differed by site. In general, nutrient uptake was higher at Fraser ( P = 0.01, 0.15, 0.03, and 0.18 for NH 4 +, NO 3 −, Ca 2+, and K +, respectively), which is west of the Continental Divide and has lower atmospheric deposition of N than Loch Vale. Mean uptake rates by site for ambient solution concentrations were 0.12 μ mol N H 4 + g fwt − 1 h − 1 , 0.02 μ mol N O 3 − g fwt − 1 h − 1 , 0.21 μ mol C a 2+ g fwt − 1 h − 1 , and 0.01 μ mol M g 2+ g fwt − 1 h − 1 at Loch Vale, and 0.21 μ mol N H 4 + g fwt − 1 h − 1 , 0.04 μ mol N O 3 − g fwt − 1 h − 1 , 0.51 μ mol C a 2+ g fwt − 1 h − 1 , and 0.07 μ mol M g 2+ g fwt − 1 h − 1 at Fraser. The importance of site conditions in determining uptake capacity should not be overlooked when parameterizing nutrient uptake models. We also characterized the root morphology of these two species and compared them to other tree species we have measured at various sites in the northeastern USA. Engelmann spruce and subalpine fir were indistinguishable in specific root length and diameter distribution, while most of the other 10 species had statistically distinct diameter distributions across five diameter classes < 2 mm. Based on specific root length, subalpine fir and Engelmann spruce had significantly coarser roots than red pine ( Pinus resinosa Soland), yellow birch ( Betula allegheniensis Britt.), sugar maple ( Acer saccharum Marsh.), chestnut oak ( Quercus prinus L.), black cherry ( Prunus serotina Ehrh.), and red spruce ( Picea rubens Sarg.). White oak ( Quercus alba L.), balsam fir ( Abies balsamea (L.) Mill.), American beech ( Fagus grandifolia Ehrh.) and loblolly pine ( Pinus taeda L.) were intermediate in SRL (indistinguishable from Engelmann spruce and subalpine fir by ANOVA). Species that differ more in physiology and morphology than the two species we compared would likely show dissimilar uptake characteristics even at the same site.

Short-term effects of selection and clear cutting on the shrub and herb layer vegetation during the conversion of even-aged Norway spruce stands into mixed stands

The conversion of even-aged Norway spruce (Picea abies (L.) H. Karst.) stands into more site adapted mixed stands is the main silvicultural goal in Germany and many other European countries. The conversion will primarily be achieved with the help of selection cutting, removing single target diameter trees and creating small gaps. At sites highly susceptible to windthrow, however, small scale clear cutting (up to 1ha) might be an appropriate alternative. Both selection and clear cutting will affect the understorey vegetation, an important component of forest biodiversity and ecosystem functioning. Thus, with the help of a BACI-experiment (before–after/control–impact), the short-term effects of selection and small scale clear cutting on the herb and shrub layer vegetation were studied at two sites in the Solling Hills (Lower Saxony, Germany). Both treatments led to an increase in herb and shrub layer species numbers, due to persistent and invading (mainly pioneer tree species and indicators of disturbance) species and to a shift in plant traits. Most responsible for the changes in vegetation was a higher light availability, and to a lesser degree soil disturbance. The number of annuals and ruderals, however, increased only immediately after clear cutting, whereas on selection cutting plots the numbers remained high. Gaining in number and coverage were competitive perennials (Epilobium angustifolium, Juncus effusus, Rubus idaeus) especially on the clear cuttings, fulfilling a nutrient retention function. The competitives did not deter tree species from regenerating in the clear cut plots, whereas on selection cutting plots the large expansion of R. idaeus appeared to be hindering tree colonisation. Suffering under clear cut conditions were predominantly shade-tolerant, closed-forest species, but no loss of these species could be detected. This indicates the potential for a fast recovery of these forest species, as soon as, pioneer trees expand.Although the vegetation changed in similar directions at both study sites, differences in species numbers and composition were found, indicating the importance of site conditions in the beginning of succession.In conclusion, our study shows no overall negative effects on shrub and herb layer biodiversity and trait composition after clear cutting. It is suggested that small scale clear cutting may be considered an appropriate alternative to silvicultural methods which cause a moderate rate of disturbance, to reach the goal of Norway spruce forest conversion.

Short‐term N2O, CO2, NH3 fluxes, and N/C transfers in a Danish grass‐clover pasture after simulated urine deposition in autumn

AbstractUrine patches are significant hot‐spots of C and N transformations. To investigate the effects of urine composition on C and N turnover and gaseous emissions from a Danish pasture soil, a field plot study was carried out in September 2001. Cattle urine was amended with two levels of 13C‐ and 15N‐labeled urea, corresponding to 5.58 and 9.54 g urea‐N l–1, to reflect two levels of protein intake. Urine was then added to a sandy‐loam pasture soil equivalent to a rate of 23.3 or 39.8 g urea‐N m–2. Pools and isotopic labeling of nitrous oxide (N2O) and CO2 emissions, extractable urea, ammonium (NH4+), and nitrate (NO3–), and plant uptake were monitored during a 14 d period, while ammonia (NH3) losses were estimated in separate plots amended with unlabeled urine. Ammonia volatilization was estimated to account for 14% and 12% of the urea‐N applied in the low (UL) and high (UH) urea treatment, respectively. The recovery of urea‐derived N as NH4+ increased during the first several days, but isotopic dilution was significant, possibly as a result of stress‐induced microbial metabolism. After a 2 d lag phase, nitrification proceeded at similar rates in UL and UH despite a significant difference in NH4+ availability. Nitrous oxide fluxes were low, but generally increased during the 14 d period, as did the proportion derived from urea‐N. On day 14, the contribution from urea was 23% (UL) and 13% (UH treatment), respectively. Cumulative total losses of N2O during the 14 d period corresponded to 0.021% (UL) and 0.015% (UH) of applied urea‐N. Nitrification was probably the source of N2O. Emission of urea‐derived C as CO2 was only detectable within the first 24 h. Urea‐derived C and N in above‐ground plant material was only significant at the first sampling, indicating that uptake of urine‐C and N via the leaves was small. Urine composition did not influence the potential for N2O emissions from urine patches under the experimental conditions, but the importance of site conditions and season should be investigated further.

Importance of site conditions and time since abandonment for coppice vegetation on Langeland, Denmark

In 57 sample plots in neglected coppices on Langeland, Denmark (14—c. 125 years since last coppicing) the cover of trees and shrubs was analysed by the method of Domin‐Krajina and the ground layer by the frequency method of Raunkiær. The data were analysed by DC A. The tree and shrub layer showed significant correlations with topsoil pH and litter depth. The ground layer was significantly correlated with inclination, area of the wood in which the coppice was situated, light, topsoil pH and the tree layer, and to a lesser extent with litter depth, but was not correlated with time since last coppicing. It is suggested that for some stands the suppression of Corγlus avellana by tree species (Quercus robur, Fagus sylvatica, Carpinus betulus) which form a permanent litter layer and acidify the soil is more important to the ground layer than the time elapsed since last coppicing per se. Formation of a permanent litter layer reduces species density, e‐specially of some forest species without clonal growth. One main reason for the lack of correlation between the ground layer and time since coppicing may be the great environmental variation in the neglected coppices on Langeland. Another reason seems to be the absence of competitive forest species (which otherwise would benefit from non‐intervention) due to the isolated position of the coppiced woods. It is concluded that neglect in excess of c. 35 years beyond the normal coppice rotation has some effect on the composition of the tree and shrub layer, but not a direct effect on the ground layer.

Residential Preferences in China

This study is an analysis of residential preferences of a sample of students at six Chinese universities. Respondents indicated the importance of site conditions in their residential preferences. Associations between conditions and choices were measured by regression and factor analyses. Implications for migration policies and regional development are discussed. (EXCERPT)