Total Leaf Area Index Research Articles

Effect of tillage practice and planting pattern on performance of white bean (Phaseolus vulgaris L.) in Ontario

The effect of tillage system on planting pattern and cultivar choice of white bean (Phaseolus vulgaris L.) was evaluated in 1990 and 1991. In one experiment, white bean cv. OAC Gryphon was sown in three different planting patterns: rows 20 cm apart and 375 000 seeds ha−1, 40 cm apart and 375 000 seeds ha−1 and 76 cm apart and 250 000 seeds ha−1. This cultivar was grown under chisel ploughing and no-till. No interaction (tillage × planting pattern) was detected in either year. There were no significant differences in seed yields, total aboveground dry matter or leaf area index (LAI) between tillage systems and no interaction of year × tillage system. In 1990, yield increased where white bean was planted in 20 cm rows versus 40 cm rows; however, there was no significant effect of planting pattern on total aboveground dry matter or LAI. In 1991, total aboveground dry matter and LAI increased with decreasing row width. In a second experiment, the interaction effects between tillage system and seven cultivars of white bean were evaluated. Regardless of the tillage system used, the performances of two cultivars (OAC Gryphon and OAC Laser) were consistent within the 2 years of our study. It appears that the choice of cultivars of white bean may depend more on yield potential, disease resistance and adaptation to a particular region than the tillage system to be used. Key words:Phaseolus vulgaris, white bean, no-till, chisel plough, planting pattern

Canopy structure within a Quercus ilex forested watershed: variations due to location, phenological development, and water availability

Spatial and temporal changes in canopy structure were studied in 1988 and 1989 in a Mediterranean Quercus ilex forest in north-eastern Spain. Due to differences in precipitation patterns the 1989 growing season was drier than the 1988 growing season. Sampling was conducted in parallel at two sites which represent endpoints along a slope gradient within a watershed (ridge top at 975 m, and valley bottom at 700 m). At both sites, similar inter-annual changes in canopy structure were observed in response to differences in water availability. Samples harvested in the upper 50 cm of the canopy during 1989 exhibited a decrease in both average leaf size and the ratio of young to old leaf and stem biomass relative to samples obtained in 1988. At the whole canopy level, a decrease in leaf production efficiency and an increase in the stem to leaf biomass ratio was observed in 1989. Temporal changes in canopy leaf area index (LAI) were not statistically significant. Average LAI values of Q. ilex at the two sites were not significantly different despite differences in tree stature and density (4.6 m2 m−2 at the ridge top, and 5.3 m2 m−2 at the valley bottom). Vertical distribution of leaves and stems within the canopy was very similar at the two locations, with more than 60% of the total LAI in the uppermost metre of the canopy. The possible significance of such an LAI distribution on the canopy carbon budget is discussed.

Cropping systems for spring and winter cereals under simulated pasture: Sward structure

The feasibility of using mixtures of spring-planted spring and winter cereals for pasture in central and southern Alberta was demonstrated previously. In the current study cropping system treatments consisting of: spring cereal monocrops (SMC), either oats (Avenu sativa L.) or barley (Hordeum vulgare L.); winter cereal monocrops (WMC), either winter wheat (Triticum aestivum L.) or winter triticale (× Triticosecale Wittmack); binary mixtures of the spring and winter cereals planted together as intercrops (IC) in the spring at the same time; and a doublecrop (DC) system where the winter cereal was planted into the spring cereal after one clipping were grown during 2 yr at Lacombe, Alberta. Pasture was simulated by clipping the stands five times, beginning at the joint stage of the spring cereal and four times subsequently at about 4-wk intervals. Prior to each clip, tiller weight, tiller density, tiller height and leaf area index (LAI) were measured in each sward. Differences for yield among treatments within systems did not occur, so small differences in sward structure were considered to be due to a compensatory interaction of yield components which stabilized yield and were ignored. Sward structure appeared to explain differences among systems for yield distribution. Tiller density and LAI of the SMC and spring component of the IC and DC became relatively small as the season advanced, especially after cut 2. Tiller density and LAI of the WMC were maintained at high levels throughout the season after cut 1. After cut 2 the winter cereal components of the IC and DC were responsible for the maintenance of total tiller density and LAI in their respective swards. Average seasonal total LAI were 3.36, 3.02, 1.87 and 1.17 cm2 cm−2 in the WMC, IC, DC and SMC. Late planting and competition for light from the taller spring cereal component delayed tillering of the winter cereal component in the DC compared with the IC during midsummer (cuts 2 and 3) resulting in the low average LAI. In contrast, planting the spring and winter cereal components at the same time (IC) resulted in a relatively stable total tiller density, high average LAI and yield. Thus the superior yield distribution of the IC, shown previously, was due to the complementary way in which spring and winter cereal tillers responded to clipping when planting occurred at the same time. Key words: Monocrop, intercrop, double-crop, yield components

Transpiration from an Amazonian rainforest calculated from stomatal conductance measurements

A multi-layer combination equation has been used to calculate transpiration from a tropical rainforest in the central Amazon, Brazil. The five-layer formulation used through-canopy measurements of temperature and humidity deficit with leaf stomatal and boundary layer conductances scaled up to canopy layer values used a profile of canopy leaf area index derived from the literature. Net radiation input to each layer was estimated from an above canopy measurement using an extinction function and leaf area index. Transpiration calculated for hourly and daily periods in a range of seasonal conditions agreed well with those measured directly with an eddy correlation device. Four simplified forms of the transpiration calculation were also compared with the direct measurement. These simplified forms used the above-canopy or the average of the through-canopy values of weather variables and used either the average of leaf conductances multiplied by total leaf area index or the average of the layer conductances. These simplified forms of the transpiration calculation gave poorer agreement with measured transpiration.

Effects of competition from young northern hardwoods on red pine seedling growth, nutrient use efficiency, and leaf morphology

The effects of competition from three northern hardwood tree species on red pine ( Pinus resinosa Ait.) seedlings were examined on two clear-cut sites in western Maine. We examined how planted red pine seedlings altered their nutrient use efficiency and shoot morphology under changing environmental conditions and how these changes related to their ability to tolerate competition. A three-factor experimental design was used to determined the effects of species of competitors and their abundance as well as fertilization on red pine seedling growth, nutrient use efficiency, and leaf morphology. The competitors were striped maple ( Acer pensylvanicum L.), red maple ( Acer rubrum L.), and pin cherry ( Prunus pensylvanica L.) established at two densities (high and zero) with two levels of fertilization (0 and 224 g m −2 of 10-10-10 NPK commercial fertilizer). Nitrogen and phosphorus use efficiencies were calculated as total aboveground biomass divided by total nutrient content. Specific leaf area (cm 2 g −1), leaf area ratio (cm 2 g −1), and total leaf area (cm 2) were measured for all red pine seedlings. Plots were harvested at two time periods, when pine seedlings were 2 years old (1989) and 3 years old (1990). Total biomass, annual production, and leaf area index (m 2 leaf area m −2 ground surface area) were calculated for competitors on each plot. Red pine seedlings had higher specific leaf area, leaf area ratio, and nitrogen use efficiency on competitor plots than on plots free of competition, suggesting a phenotypic response to resource depletion of light and nutrients by competitors. Fertilization decreased growth of red pine seedlings and decreased nitrogen use efficiency. Red pine total leaf area and biomass were lower on the competitor plots. Higher competitor biomass, leaf area index, and nutrient uptake explained the lower growth of red pine seedlings on competition plots. Pin cherry was the most significant competitor eith striped maple being intermediate; red maple had the least effect on pine seedling growth. The results of this study indicate that the growth of red pine seedlings was governed by the availability of resources as influenced by the competitor species, the efficiency of nutrient use, and the ability of red pine to adjust its growth pattern in response to resource availability.

Partitioning ozone fluxes to sparse grass and soil and the inferred resistances to dry deposition

A two-source (Penman-Monteith type) model, used in a preceding companion study as a diagnostic tool to partition objectively half-hourly measurements of evapotranspiration into bare soil and plant components and to derive in situ estimates of the bulk plant and soil resistances to evaporation, is extended to include ozone deposition. At the time this study was performed, the total leaf area index (LAI) of the site varied between 0.5 and 0.8. Live plant material accounted for 60–75% of the LAI while the remaining LAI was dead plant material. For present purposes this two-source model augments measurements of the major components of the surface energy balance and other micrometeorological measurements with measurements of the ambient ozone concentration and eddy correlation measurements of the total dry depositional flux of ozone. This study employs the bulk canopy resistances estimated previously with this model along with additional ozone measurements: (1) to partition the ozone dry deposition flux into bare soil and plant components in a region of partial canopy cover and (2) to estimate the intrinsic soil resistance to ozone destruction. The results of this study suggest: (a) that the plant component probably receives no more than 25% of the total ozone depositional flux and this percentage decreases as the soil water available to the plants decreases and (b) that the soil resistance to ozone destruction has a near-surface boundary layer component of about 0.7 s cm −1 and an intrinsic component of about 1.0 s cm −1.

Estimating leaf area index and light extinction coefficients in stands of Douglas-fir (Pseudotsugamenziesii)

Both photosynthetically active radiation penetrating the overstory canopy and overstory leaf area index were determined in forty-three 12 × 12 m plots in even-aged Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stands. Stands were located on the east side of Vancouver Island, British Columbia, between 300 and 800 m on flat to south-facing slopes and were from a wide range of stem densities and stocking levels. In nine core plots total tree leaf area index was estimated using regression equations from individual-tree stem diameter and stand relative density. A single extinction coefficient did not govern the attenuation of photosynthetically active radiation with respect to leaf area index. For a given leaf area index, the extinction coefficient was smaller at low relative densities because of the presence of canopy gaps. Light attenuation models assuming a single extinction coefficient seriously underpredict stand leaf area index, especially at low stand densities. A modified Beer's Law model was used to predict light penetration, which implicitly accounted for foliage clumping.

Spatial Variability of Canopy Foliage in an Oak Forest Estimated with Fisheye Sensors

Abstract The vertical distribution of forest canopy elements is an important factor in canopy-atmosphere exchange processes and knowledge of the shape of the average vertical profile of leaf area density is a critical input to models of these processes. This study was conducted to determine the spatial variability of Leaf Area Index (LAI) in an oak forest when estimated with indirect fisheye techniques. A 35 mm camera with a 180° hemispherical lens and a LI-COR LAI-2000 Plant Canopy Analyzer (wavelengths < 490 nm) were used simultaneously to estimate vertical leaf area profiles and the horizontal variability in an oak forest in central Pennsylvania. Measurements were made at eight different heights in the canopy and repeated at nine different locations. The two sensors were in reasonable agreement. The photographic technique estimated the total leaf area index (LAI) to be 3.58, and the light sensor estimates resulted in an estimate of 3.40. The average precision was 8% for the LAI-2000 and 17% for the photographic technique. The point-to-point spatial variability of the LAI estimates was low when the whole canopy was measured from the ground and quite high when measuring the upper canopy. Ground level estimates of LAI using these fisheye techniques spatially average the canopy to the point where only four replications were necessary to sample the total LAI with 90% confidence. For. Sci 38(4):854-865.

Ear Position and Vertical Distribution of Leaf Area in Corn

AbstractLeaf area distribution determines the interception of radiation for photosynthesis. A method of analysis was developed to quantifiy differences in vertical leaf area distribution in a corn (Zea mays L.) canopy. A third‐order polynomial accurately described the relationship between leaf area index (LAI) and plant height (both normalized with respect to their maxima) for a range of normal and “leafy” licensed and experimental plant lines during the late vegetative and early grainfilling stages (r2≥0.85). The shape of the polynomial reflected the bell shape of individual leaf area versus leaf number curves, with the densest leaf area in the mid‐portion of the canopy. When ear position was marked on the polynomial plot, the proportion of leaf area above the ear was easily compared among lines. The proportion of total LAI above the ear varied from 0.52 to 0.83 in 1986 and from 0.63 to 0.86 in 1987. The actual LAI above the ear was in a relatively narrow range of 2.0 to 3.2 for all tested licensed lines. The analysis described will facilitate comparison of ear position and vertical distribution of leaf area among different plant lines and crop management practices.

Leaf nitrogen distribution and whole canopy photosynthetic carbon gain in herbaceous stands

The amount of photosynthetically-active photon flux density incident upon a leaf and the nitrogen content of that leaf strongly affect the photosynthetic carbon gain of that leaf. Therefore, the canopy structure of a stand, affecting the light climate in the canopy, and the leaf nitrogen distribution pattern in the canopy, affect the carbon gain of the whole canopy. This review discusses the results of studies directed to this problem and obtained so far in open and in dense canopies of stands of herbaceous, monocotyledonous or dicotyledonous, plants in their growing or flowering stages. It is found that the leaf nitrogen distribution pattern in the canopy is vertically non-uniform, and in dense stands more strongly so than in open stands. The leaf nitrogen distribution pattern in most canopies closely approaches an optimal pattern in that it maximizes whole canopy potential carbon gain as calculated for the actual total leaf nitrogen content and leaf area index of the stand. The resulting increase in potential carbon gain as compared to a uniform leaf nitrogen distribution pattern is considerable and it is larger in dense stands than in open stands. For at least some dense stands simulation studies show that with the available total leaf nitrogen content, whole canopy carbon gains could still be considerable higher had a lower leaf area index been developed.

Short-term effects of nitrogen on the growth and nitrogen nutrition of small swards of white clover and perennial ryegrass in spring

Small swards of white clover and perennial ryegrass were established in Perlite in a heated glasshouse, as either monocultures or mixtures of equal plant numbers. On 26th March, 1984 the swards were moved outside and their growth studied over the period to 29th May. All swards received a basal level of nitrate N to simulate soil mineralization and two-thirds received additionally the equivalent of 80 kg N ha−1. Over the experimental period (26th March-29th May) clover maintained its proportion of total mixture dry weight In swards given ‘fertilizer’-N and increased its proportion in those given only ‘basal’ N, However, clover declined as a percentage of total mixture dry weight during the first period of the experiment when total leaf area index (LAI) and ambient temperatures were low, and increased its percentage later when temperature and LAI had risen. Changes in tiller and stolon growing point numbers were not good indicators of changes in dry weight. Relative yields and relative replacement rates also were not good indicators of relative performance in mixture. Where ‘fertilizer’-N was applied, clover derived less of its nitrogen from that source than grass although their uptakes per unit shoot dry weight were similar.

Effects of water level fluctuation on the growth of Nelumbo nucifera Gaertn. in Lake Kasumigaura, Japan

AbstractInvestigations were made of the growth of Nelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass of N. nucifera from the maximum of 291 g d.w. m−2 in July to a minimum of 75 g d.w. m−2. The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m2 m−2 in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m2 m−2. The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day−1, respectively. The sudden rise in water level (25 cm day−1) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival of N. nucifera in Lake Kasumigaura.

Forest Structure and Productivity in Puerto Rico's Luquillo Mountains

Net aboveground primary production (NPP) at 725 m in elevation in the colorado forest (montane rain forest, sensu Beard; lower montane wet forest, sensu Holdridge) of the Luquillo Mountains of Puerto Rico averaged 7.60 t/ha yr on two 0.4-ha permanent plots and was determined by summing aboveground biomass accrual (0.59 t/ha yr), litterfall (6.80 t/ha yr), and herbivory (0.21 t/ha yr). The total leaf area index (trees, epiphytes, and ground vegetation) was 4.95 m2/i2, the aboveground woody volume and biomass, 220 m3/ha and 130 t/ha, respectively, and standing herbivory and the herbivory rate, 5.1 and 4.0 percent/yr, respectively. The mean standing crop of litter was 680 g/m2, with a turnover rate of 0.78 times per year. Of the structural features studied over a 600-m elevational gradient in the Luquillo Mountains, the number of trees per hectare, basal area, and soil organic matter increased with elevation; whereas, the specific leaf area, canopy height, range of tree diameters, forest volume and biomass, leaf area index, and species richness declined. Of the dynamic features studied, ingrowth and mortality of trees, tree growth (diameter, volume, and biomass growth), litterfall, loose litter, standing herbivory and herbivory rates, litter turnover, aboveground woody NPP, and total NPP all declined with an increase in aboveground elevation. The structural and floristic impoverishment of forests and changes in forest dynamics with ascent in the Luquillo Mountains reflect cooler temperatures, fog, and heavier rainfalls that interact to produce saturated soils and retard the mineralization of organic matter.

Growth and life span of the leaves of Nelumbo nucifera Gaertn. in Lake Kasumigaura, Japan

Growth of leaves of Nelumbo nucifera Gaertn. in Lake Kasumigaura was investigated with special emphasis on leaf dynamics. Floating leaves were found throughout the growing period, while emergent leaves were not found until July. However, emergent leaves contributed approximately 75% of the total leaf area index at its seasonal maximum, 2.76 m 2 m −2. Mean leaf life span of emergent leaves with thick laminae and stiff petioles was much longer than that of floating leaves (44.5 vs. 17.1 days).

Vertical distribution of leaf area in Larixoccidentalis: a comparison of two estimation methods

Total leaf-area index and the vertical distribution of leaf-area index were described for an unthinned stand (density 11 250 stems/ha) and a thinned stand (density 1660 stems/ha) of 30-year-old Larixoccidentalis Nutt. Two independent methods were used to estimate leaf-area index in each of the two stands. The first method is based on allometric relationships that are applied to stem measurements, and the second method is based on gap-fraction analysis of fisheye photographs. Leaf-area index estimates obtained by the two methods were not significantly different. The gap-fraction method provides a desirable alternative because much less fieldwork is required, however, use of this method is limited to canopies where the light-blocking elements are randomly displayed. Total leaf-area index values for the unthinned and thinned stands were 5.0 and 3.6, respectively. The vertical distribution of leaf-area index in the unthinned stand resembled a normal distribution. The vertical distribution of leaf-area index in the thinned stand would have resembled a normal distribution, except that thinning operations resulted in a truncated distribution of leaf-area index at the canopy base.

A Global Climatology of Albedo, Roughness Length and Stomatal Resistance for Atmospheric General Circulation Models as Represented by the Simple Biosphere Model (SiB)

Components of the Simple Biosphere Model (SiB) of Sellers et al. (1986) were used to generate global monthly fields of surface albedo (0.4-4.0 microns), roughness length and minimum surface (stomatal) resistance. SiB consists of three submodels which describe the roles of radiative transfer, turbulent transfer and surface resistance in determining the energy balance of the vegetated land surface. These three submodels were detached from SiB and used on the SiB parameter set (total and green leaf area index, leaf angle orientation, canopy dimensions, etc.) to calculate global monthly fields of albedo, roughness length and minimum stomatal resistance at 1 x 1 deg resolution. Time series of various parameters are also displayed for each vegetation type for specified grid points. The SiB results compare reasonably well with appropriate measurements obtained from the literature and have the additional merit of being mutually consistent; the three submodels use many common parameters, which ensures that, for each grid area, the calculated surface properties are closely interrelated as is the case in nature. The derived fields provide a check on the operation of the submodels and the correctness of the parameter set. They can also be used as prescribed fields for GCMs that do not have biophysically based land surface parameterizations.

Canopy profiles of some Piedmont hardwood forests

Relationships between canopy profiles and site quality were examined in 11 old, uneven-aged (>180 years) hardwood forests in the Piedmont of eastern North Carolina. Site fertility was indexed by extractable soil calcium and phosphorus, by the content of calcium, phosphorus and nitrogen in litter fall, and by the aboveground net primary productivity of each stand. Canopy profiles were indexed by the leaf area index for each 3.3-m height interval. Total leaf area index correlated highly with most measures of site fertility, but we found no clear patterns between canopy profiles and any measure of site fertility. We conclude that site fertility is reflected in broad ecosystem-level variables such as total leaf area index and stand productivity, but that detailed patterns such as canopy profiles relate strongly to specific stand composition, age structure, and history.

Biomass and Leaf-Area Estimates for Varnishleaf Ceanothus, Deerbrush, and Whiteleaf Manzanita

Abstract To help foresters assess site occupancy of seed-established stands of varnishleaf (Ceanothus velutinus var. laevigatus) deerbrush (Ceanothus integerrimus), and whiteleaf manzanita (Arctostaphylos viscida), we developed equations for estimating their aboveground biomass and leaf area. From 9 to 14 pure stands from 2 to 20 years old were selected for each species in southwest Oregon and northern California. Individual stems of Ceanothus species and whole bushes of manzanita were destructively sampled Regression equations for leaf and total biomass of manzanita plants and for stems of Ceanothus sp. showed that these variables were highly correlated with trunk or stem diameter (r² = 0.85 - 0.99). Total biomass, leaf biomass, and leaf area index (LAI) of stands can be estimated accurately from measurements of stem or trunk basal area (r² = 0.87 - 0.99). Stand age (yr) and average stem length (cm) are also reliable estimators (r² = 0.74 - 0.82). It appears that stands of varnishleaf attain a maximum LAI of 5.5 m²/m² by 7 years, whereas the maximum values for deer-brush and manzanita were 2.8 and 3.5, respectively, at about 15 years. Stands of all three species apparently continue to produce net biomass well beyond 16 years of age. West. J. Appl. For. 2(4):124-128, October 1987.

The effect of nitrogen in spring on shoot number and leaf area of white clover in mixtures

AbstractSwards of perennial ryegrass/white clover were cut to 3 cm in March and allowed to regrow for approximately thirteen weeks. Half the swards received nitrogenous fertilizer at the time of cutting (+N treatment) while the other half received none (—N treatment).About four weeks after the application of treatments, the number of clover shoots in the — N treatment was significantly higher than that in the +N; at this stage total leaf area index on both treatments was low, but significantly greater in the + N. After 30 days, more light was reaching ground level in the — N treatments, and about 40 days after cutting there was between 17 and 50% more clover in the — N treatment than the +N.It is suggested that the inhibition of stolon branching with a consequent restriction in the rate of increase of clover leaf area is a major factor in the adverse effect of N fertilizer on clover.

Mount St. Helens Ash: Recreating Its Effects on the Steppe Environment and Ecophysiology

The 18 May 1980 ash fall from Mount St. Helens was experimentally reproduced in May 1982 by applying silt—sized ash to a stand of the Artemisia tridentata/Agropyron spicatum association in south—central Washington. Compared to the adjacent control site, ash caused an immediate increase in albedo from 13% to 28%, while other parameters of the energy budget were simultaneously lowered: net radiation by °20%, soil surface temperatures by as much as 10°C, and soil heat flux by as much as 50%. The ash's mulching action initially increased water availability and delayed leaf abscission in Artemisia tridentata (Big sagebrush) by 2 wk in summer 1982. But after summer 1982 water availability declined, while water use increased, illustrating the diverse effects of the ash. Increased reflection from the ash—covered surface increased the radiation load on plant canopies. In turn, air temperature at 0.5 m increased, latent heat flux often doubled in summer, and xylem pressure potentials decreased. Available water at the —1 m soil depth eventually decreased as much as 40%. This decrease was the result of the increase in latent heat flux and the decline in infiltration through the stratified layer created by the ash cap. The sudden alteration of the soil surface by an ash layer revealed the close coupling of the water use of A. tridentata with available soil water. In summer in both 1982 and 1983, predawn xylem pressure potential declined as soil water potentials approached —4.5 MPa on both sites. Total shrub leaf area index routinely decreased 75% as large (> 2 cm long) spring—emergent leaves were shed. Highest leaf conductance (0.3 to 0.5 s/cm) and highest transpiration occurred among the remaining smaller (<2 cm long) leaves after leaf abscission in spring. Water conservation through leaf area reduction followed by high transpiration rates apparently allows the development of inflorescences during the dry, hot summer, culminating in autumn flowering and seed maturation. Lupinus sulphureus on the ash—covered surface exhibited no difference from conspecifics on the control site in xylem pressure potentials, but did have higher leaf conductances during the 1st yr following the ash fall; no differences were observed in the 2nd yr. Lupinus sulphureus aestivated °2 wk earlier on control sites the 1st yr following ash deposition. The responses to ash that we measured were probably the maximum expressed by Big sagebrush; the thin layer of ash to the east and the coarse—textured ash to the west did not significantly alter the movement of water. Short—term increases in A. tridentata in the Pacific Northwest °6700 yr BP may have been caused by similar decreases in soil temperature and increases in aridity with the deposition of Mazama ash. In addition to allowing assessment of the effects of the 18 May 1980 ash fall on arid steppe, application of ash provided an unexpected level of precision in detecting the often subtle effects that occur when some microenvironmental parameters change while the overall macroclimate remains the same.