Oak Regeneration Management
| Project: | Evaluation of selected techniques to enhance artificial regeneration of California white oaks |
| Project Leader: | Adams, T.E., Jr., and K. Rice |
| Summary: | 1988 Public Serv. Research and Dissemination Program, 1987-88 Summary Report.: p. 2. This study is stressing the impact of natural agents (excluding large herbivores) on directly-seeded acorns and on nursery transplants at research locations in six counties across the state. After the oak seedlings emerge in the spring, researchers will assess interactions between these seedlings and annual vegetation to develop a model to understand temporal partitioning of soil moisture among competing plant species. By comparing response of oak to varying treatments used to control annuals, especially from summer varieties, affects oak survival and growth. |
| Project: | Artificial regeneration of blue and valley oak in California |
| Project Leader: | Adams, T.E., Jr., P.B. Sands, and W.H. Weitkamp |
| Summary: | 1988 Range Sci. Rep. No. 16 UCDavis Agron. & Range Sci. Dept. 16: pp. 1-9. Suspected elements of poor valley oak and blue oak regeneration are being studied in three regions using artificial regeneration techniques. Plantings of acorns and nursery stock have been made within deer-proof exclosures to examine the impacts of weed competition, fertilization, and small mammals and insects. Results suggest weed control and protection from small mammals and insects will be necessary for successful artificial regeneration of blue and valley oak in many areas of the state. |
| Project: | Blue and Valley Oak Seedling Establishment on California's Hardwood Rangelands |
| Project Leader: | Adams, T.E., Jr., P.B. Sands, W.H. Weitkamp, and N.K. McDougald |
| Summary: | 1991a. Proc., Symp. on Oak Woodlands and Hardwoods Rangeland Mgmt., USDA For. Serv. Tech. Rep. PSW-126.: pp. 41-47. Factors contributing to poor establishment of blue oak and valley oak in California oak-grassland savannas were studied in a series of acorn seeding experiments initiated in 1985. Exclusion of large herbivores permitted examination of herbaceous interference and small mammal and insect depredation. With few exceptions, the addition of screen protection to discourage predation significantly enhanced survival and growth. Shade provided by window screen cages is suspected of making an unmeasured positive contribution. Interaction between herbaceous control and protection appears to develop with time. |
| Project: | Blue oak seedling regeneration on California rangelands |
| Project Leader: | Adams, T.E., Jr., P.B. Sands, W.H. Weitkamp, and N.K. McDougald |
| Summary: | 1991b. Proc., IVth International Rangeland Congress 1: pp. 67-71. Control of herbs appears essential to achieve adequate emergence and first-year survival of blue oak seedlings. Limited data on long-term survival suggests seedling mortality over time is reduced by herb control. Screens protected seedlings against insects and small mammals. Window screen cages provided the best protection from predation, but they may modify the microenvironment. They provide shade, the effects of which we could not separate from protection. Predation in our studies may have been affected by concentrated planting patterns and characteristics of the exclosures. |
| Project: | Oak seedling establishment on California rangelands |
| Project Leader: | Adams, T.E., Jr., P.B. Sands, W.H. Weitkamp, and N.K. McDougald |
| Summary: | 1992 J. Range Manage. 45: pp. 93-98. Factors responsible for poor recruitment of blue oak and valley oak need to be determined on California hardwood rangelands so that management strategies for enhancement of recruitment can be developed. To examine selected factors, exclusive of large herbivore impacts, a series of acorn seeding experiments was initiated in 1985 in 6 counties on representative sites. At each site, the experimental treatments were the factorial combination of herbs vs. no herbs and screen protection vs. no protection. With few exceptions, the addition of screen protection discouraged predation and significantly enhanced survival and growth. |
| Project: | Enemies of white oak regeneration in California |
| Project Leader: | Adams, T.E., Jr., P.B. Sands, W.H. Weitkamp, and N.K. McDougald, and J. Bartolome |
| Summary: | 1987 Proc., Symp. Multiple-use Mgmt of Calif. Hardwood Res. USFS Gen. Tech. Rep. PSW-100.: pp. 459-462. Blue oak and valley oak acorns and nursery stock were planted in six counties during the 1985-1986 growing season, but each plant material was not planted at all sites. Results suggest weed competition was a major cause of poor emergence and survival of seedlings developing from field-planted acorns and survival of transplanted nursery stock. These problems were aggravated by use of a slow release fertilizer placed beneath acorns and transplants. Small mammals and insects were responsible for additional mortality at all locations. |
| Project: | Oak seedling establishment by artificial regeneration on California rangelands |
| Project Leader: | Adams, T.E., Jr., P.B. Sands, W.H. Weitkamp, and M.E. Stanley |
| Summary: | Proc., Symp. on Oak Woodlands: Ecology, Management, and Urban Interface Issues. San Luis Obispo, CA., Mar. 19-22, 1996. Poor recruitment in many stands of oaks (Quercus spp.) on California's rangelands has raised concern about the sustainability of the state's hardwood resource. Studies using spatial and temporal replication were initiated to examine factors suspected of contributing to poor seedling regeneration of blue and valley oaks. Information from these studies will help refine survival curves that can be used in planning oak restoration and mitigation. Ref.147\64.01. |
| Project: | Resampling VTM plots in blue oak cover type series |
| Project Leader: | Allen-Diaz, B.H., and B.A. Holzman |
| Summary: | 1993 Report for Forest and Rangeland Resources Assessment Program (FRRAP), Calif. Dept. of Forestry and Fire Protection, July 1993 July: p. 70. Understanding recent change within the blue oak woodlands is the focus of this study. The transitional cover types such as Blue oak-Foothill pine/Grass and Blue oak/Buck brush/Grass persist on the landscape due to continuous changes in blue oak communities through time as well as in response to human disturbances such as harvesting and fire suppression. Grazing did not appear to significantly affect overstory vegetation change. Although it is the ecological changes that were of most interest in this study, it is the cultural impacts that will significantly determine the future of the blue oak woodlands in California. |
| Project: | Blue oak stand age structure |
| Project Leader: | Bartolome, J.W., and M.P. McClaran |
| Summary: | 1985 Proc., UC Sierra Foothill Range Field Station Beef and Range Field Day: p. 26. Stand age structure, vertical growth rates, fire dates and fire free periods were measured for blue oaks in the Campbell and Koch pastures. The faster vertical growth rates for sprouts compared to seedlings is probably related to the greater success of establishment from sprouts compared to establishment from seedlings because it reduces the period of time that terminal buds are within the reach of browsing deer and livestock. |
| Project: | Understory forage production in blue oak woodlands |
| Project Leader: | Bartolome, J.W., and M.P. McClaran |
| Summary: | 1987 Proc., UC Sierra Foothill Range Field Station Beef and Range Field Day: p. 56. Preliminary guidelines for managment of hardwood range published by UC Cooperative Extension in 1985 suggest that in areas with more than 20 inches of annual rainfall, tree cover of 50 percent or more suppresses the understory. During this study our results showed location combined with plant species composition offers potential as a useful guide to predict the effects of blue oak canopy removal or retention. Along a rainfall gradient within the blue oak woodland with 50 percent canopy, suppression of understory production occurs above 50 cm rainfall. The canopy has no effect or an enhancement below 50 cm annual precipitation. |
| Project: | Effect of forest soil inoculum on Mycorrhizal root development and growth of valley oak seedlings |
| Project Leader: | Berman, J., and C. Bledsoe |
| Summary: | Proc., Symp. on Oak Woodlands: Ecology, Management, and Urban Interface Issues. San Luis Obispo, CA., Mar. 19-22, 1996. In this study a field experiment and a green house experiment were carried out to assess the effects of mycorrhizal infection on valley oak seedling growth. This information could be a valuable aid in efforts to reintroduce valley oaks to disturbed riparian areas. These studies suggest that forest soil used as inoculum can increase percent mycorrhizal infection on valley oak seedling roots. The effect of mycorrhizal infection on growth should be evaluated in a longer-term study. Ref.251\64.01. |
| Project: | Soil water potentials provide evidence of hydraulic lift and oak root activity in a California blue oak woodland |
| Project Leader: | Bledsoe, C. S., and C. S. Milikin |
| Summary: | Proc., Symp. on Oak Woodlands: Ecology, Management, and Urban Interface Issues. San Luis Obispo, CA., Mar. 19-22, 1996. Blue oaks and annual grasses coexist in an environment that appears to be unfavorable toward growth during hot dry summers. To see how the dry summer affects root activity, soil water potential was measured with thermo-couple psychrometers at four depths. Because root uptake decreases soil water potential below 25 cm (evaporation is minimal) and grasses senesce by June, the decreases in soil water potential suggest that oak root activity continues throughout the summer. After sunrise soil water potential decreased rapidly, after sunset soil water potential gradually increased. These patterns occurred between late May and October, when soils were drier, and were observed throughout the soil profile. Ref.252\64.01. |
| Project: | Effect of blue oak canopy on annual forage production |
| Project Leader: | Connor, J.M., and B.L. Willoughby |
| Summary: | Proc., Symp. on Oak Woodlands: Ecology, Management, and Urban Interface Issues. San Luis Obispo, CA., Mar 19-22, 1996. Production of annual forage was compared at four sites under four blue oak canopy levels (0, 25, 50, and 75 percent), over five years. Long-term precipitation averages 28.5 inches. Significant differences in herbaceous forage production occurred among years, with the highest rainfall season being the most productive and the drier years generally being less productive. The effects of canopy cover varied from year to year; canopy significantly depressed forage yield in two of the five years. High rainfall years appeared to favor herbaceous plant growth under the higher canopy levels. Ref.254\64.01. |
| Project: | Biogeochemistry in oak woodlands of the Sierra foothills |
| Project Leader: | Dahlgren, R., and M. Singer |
| Summary: | 1993. Proc., UC Sierra Foothill REC Beef and Range Field Day. pp. 29-30. Our study has focused on nutrient cycling; the movement of nutrients in, out of, and within the ecosystem. The flow of nutrients through the oak woodland ecosystem has been studied for a four year period in the Schubert Watershed. Fluxes of nutrients in ecosystem waterflows (precipitation, canopy throughfall, soil solutions and stream water), plant uptake, and litterfall were monitored. Removal of Oaks leads to a loss of nutrients from the ecosystem. Ref.171\61.49. |
| Project: | Nutrient cycling in managed and non-managed oak woodland-grass ecosystems |
| Project Leader: | Dahlgren, R., and M.J. Singer |
| Summary: | 1994. Rep. to Integrated Hardwood Range Management Program. 91 pages. This research project examining oak woodland nutrient cycling shows that oak trees play a major role in maintaining the nutrient status of these ecosystems. Each year, a typical blue oak will return approximately 1, 0.1, 2, and 0.8 kg of nitrogen, phosphorus, calcium and potassium, respectively, to the soil surface in the form of litterfall (e.g. leaves, twigs and acorns) and canopy throughfall (canopy leaching). While these values may appear low, multiplying by all the oak trees in a watershed results in very large quantities of nutrients. Ref.177\62.11. |
| Project: | Nutrient cycling in grazed and ungrazed oak woodland rangelands |
| Project Leader: | Dahlgren, R., and M.J. Singer |
| Summary: | 1995. Proc., UC Sierra Foothill REC Beef and Range Field Day. pp. 27-33. Oak trees play a critical role in sustaining ecosystem productivity through their role in cycling nutrients to the soil surface, preventing nutrient leaching losses, increasing water infiltration, and attenuating water erosion and stream sediment concentrations. Moderate intensity grazing does not appear to have any serious detrimental effects on nutrient cycling in these oak woodland ecosystems. Oak tree removal will lead to a significant loss of nutrients from these ecosystems leading to a long-term decrease in ecosystem productivity. Careful removal of oaks does not significantly change stream flow patterns or amounts. Ref.241\63.53. |
| Project: | Hydrologic impacts of blue oak harvesting and evaluation of the modified USLE in the Northern Sierra Nevada |
| Project Leader: | Epifanio, C.R. |
| Summary: | 1989 Thesis, Univ. of Calif., Davis: p. 144. The original objective of this project was the determination of the impacts of vegetation-type conversion and other range management techniques on water yield and water quality from a rangeland watershed. Six years data for rainfall, runoff and sediment yield for two watersheds, S1 and S2, have been reduced, tabulated, placed into a computer database and statistically analyzed. The watersheds were found to be sensitive to rain intensity and amount. Runoff tends to increase linearly with rainfall. In view of the fact that the SCS tolerable annual soil loss limits for the SFRFS are 5 tons per acre per year, none of the watersheds posed serious erosion problems during the study period. |
| Project: | Understory - canopy relationships in oak woodlands and savannas |
| Project Leader: | Frost, W.E., J.W. Bartolome, and J.M. Connor |
| Summary: | Proc., Symp. on Oak Woodlands: Ecology, Management, and Urban Interface Issues. San Luis Obispo, CA.,Mar 19-22, 1996. We summarize available information about the relationships between oak overstory and understory plants. Understory biomass productivity and plant species composition vary considerably in California's oak woodlands and savannas. Factors discussed include geographic location, overstory species composition, overstory density and distribution, and animal utilization. Management implications are summarized for different woodland types around the state. Ref.256\64.01. |
| Project: | Grazing compatible with blue oak regeneration |
| Project Leader: | George, M.R., and L.M. Hall |
| Summary: | 1991 Report for Forest and Rangeland Resources Assessment Program (FRRAP), Calif. Dept. of Forestry and Fire Protection, Aug 1991.: p. 32. Cattle have been implicated as a principal cause for poor oak regeneration in California's hardwood rangelands. The effects of stock density and season of grazing was evaluated on blue oak establishment. Seven hundred and twenty blue oak seedlings were planted on ten-foot centers in thirty plots in three annual grassland pastures at the Sierra Field Station. Steers were allowed to graze one plot per week at low, medium, and high stock densities during the months of January, April and July of 1990. It is clear that cattle damage to oak seedlings varies tremendously depending on season of grazing and, to a lesser degree, stock density. |
| Project: | Competitive Effects of Grassland Annuals on Soil Water and Blue Oak (Quercus Douglasii) Seedlings |
| Project Leader: | Gordon, D.R., and K.J. Rice |
| Summary: | 1993 Ecology 74(1): pp. 68-82. Four California annual grassland species were used to examine the hypothesis that different plant species have equivalent competitive effects. We investigated the effects of the annuals on soil water availability and the growth responses of blue oak to neighbor-induced water depletion. Neighborhoods of annuals were composed of species from the California annual grassland with differing phenology and morphology that were hypothesized to show non-equivalent competitive effects on both a per-individual-and a per-unit-tissue basis. |
| Project: | Soil Water Effects on Blue Oak Seedling Establishment |
| Project Leader: | Gordon, D.R., K.J. Rice, and J.M. Welker |
| Summary: | 1991 Proc., Symp. on Oak Woodlands and Hardwoods Rangeland Mgmt., USFS Tech. Rep. PSW-126: pp. 54-58. A field experiment was conducted to examine the effects of soil water availability on blue oak seedling establishment. Soil water and plot size, depending on the site, and initial acorn weight and parent tree all influenced oak seedling growth. Survival and height in subsequent growing seasons was dependent on early growth. Soil water availability in the first growing season, therefore, influences both oak seedling establishment and growth in subsequent years. |
| Project: | Competition for soil water between annual plants and blue oak (Quercus douglasii) seedlings |
| Project Leader: | Gordon, D.R., J.M. Welker, J.W. Menke, and K.J. Rice |
| Summary: | 1989 Oecologia 79: pp. 533-541. We examined the competitive effects of two annual species on soil water potential and blue oak seedling growth and water relations. Two densities of the annual grass and one density of the annual forb comprised plant neighborhoods around the oak seedlings grown in 1 m deep boxes. Rates of soil water depletion differed among neighborhoods. These results suggest that the annual species are not equivalent competitors for water: fibrous grass roots had greater competitive effect than did forb tap-roots. |
| Project: | The effects of season of grazing and stock density on blue oak (Quercus douglasii) regeneration in the sierra foothills of California |
| Project Leader: | Hall, L.H. |
| Summary: | 1991. M.S. Thesis, Univ. of Calif., Davis. 43 pages. This study investigated the effects of stock density and season of grazing on blue oak establishment. Seven hundred and twenty year- old blue oak seedlings were planted on ten-foot centers in 30 plots in three annual grassland pastures at the Sierra Foothill Range Field Station east of Marysville. Steers were allowed to graze one plot per week at low, medium and high stock densities during the months of January, April, and July. One half of all tree planting spots received a herbicide application prior to planting to eliminate grass competition. Low stock density does not have a significant detrimental effect on oak establishment in winter. Grazing damage and browsing by deer increased dramatically in the spring and summer periods. In summer deer browsing damage in the control plots exceeded cattle damage in the experimental plots. Grazing damage was mainly due to nipping and rarely due to girdling or uprooting. Trampling damage was usually minimal. Herbicide application did not have any effect on the incidence of trampled or grazed trees. Ref.309/ 64.47. |
| Project: | Effects of cattle grazing on planted oak seedlings |
| Project Leader: | Hall, L.M. |
| Summary: | 1991 Proc., UC Sierra Foothill Range Field Station Beef and Range Field Day: pp. 42-45. The results of this study indicate that cattle damage oak seedlings at medium and high stock densities particularly in the spring and summer months. At low densities in the winter and spring, however, it is quite possible that oak regeneration and livestock production are not mutually exclusive. The detrimental effects of deer at critical times of the year can be just as significant as cattle damage and should not be underestimated. Further investigations on the seasonal grazing of oak seedlings would help clarify the effect of livestock on oak seedlings. |
| Project: | Effects of cattle grazing on blue oak seedling damage and survival |
| Project Leader: | Hall, L.M., M.R. George, D.D. McCreary, and T.E. Adams, Jr. |
| Summary: | 1992 J. Range Manage. 45: pp. 503-506. Cattle grazing has been suggested as a principal cause for poor oak recruitment in California's hardwood rangelands. This study evaluated the effects of stock density and season of grazing on blue oak establishment. In December 1989, seven hundred and twenty blue oak seedlings were planted on 3-m centers in 30 plots in 3 annual grassland pastures. Browsing and trampling damage were estimated at the end of each treatment. Analysis of variance revealed significant differences between seasons but not between control and ungrazed plots within seasons. Damage was greatest during the summer season but there was no difference between grazed plots and those protected from cattle grazing. |
| Project: | Influence of tree canopies on grassland productivity and nitrogen dynamics in deciduous oak savanna |
| Project Leader: | Jackson, L.E., R.B. Strauss, M.K. Firestone, and J.W. Bartolome |
| Summary: | 1990. Agriculture, Ecosystems and Environment 32: pp. 89-105. In oak and annual grassland savanna in the foothills of the Sierra Nevada, CA, soils under deciduous blue oak canopies have higher nitrogen turnover and inorganic N availabilty than surrounding open grassland soils. Over 3 years of study, annual above- and below- ground productivity and plant N accumulation in both communities were generally very similar. Although the two areas differ in species composition, rates of seedling establishment, seasonal phenology, and dry weight and N allocation patterns, these differences are not great enough to affect productivity at this site. Even if forage production in the blue oak savanna does not benefit from the presence of oak canopies, soils under oaks harbor a reservoir of soil organic N that could be rapidly lost or redistributed if oaks are removed for management purposes. Ref.302\64.38. |
| Project: | The effect of Blue oak removal on herbaceous production on a foothill site in the northern Sierra Nevada |
| Project Leader: | Jansen, H.C. |
| Summary: | 1986. Proc., Symp. on Multiple-Use Mgmt. Calif. Hardwood Res. USDA Forest Service Tech. Rep. PSW-100. pp. 343-350. The effect on herbaceous production of blue oak canopies of 25, 50, and 75 percent, and the effect of complete removal of such canopies were determined over a 7-year period for a single site in the foothills of the northern Sierra Nevada. Tree covered plots produced 12% less than grassland plots, while cleared plots produced 46% more than tree covered plots. Percentage differences in production were about the same for the middle and end of the growing season, but were considerably less at the beginning of the growing season. Tree canopy, whether present or removed, has no discernable correlation with production due to tree size, stocking and other plot effects. Ref.266\64.03. |
| Project: | Long-term effects of Blue oak removal on forage production, forage quality, soil, and oak regeneration |
| Project Leader: | Kay, B.L. |
| Summary: | 1987. Proc., Symp. Multiple-Use Mgmt. of Calif. Hardwood Res. USDA Forest Service Tech. Rep. PSW-100. pp. 351-357. Herbaceous forage response to the killing or removal of blue oak trees was measured for 21 years in the north-Sierra foothills of California. Inceased herbage was noted in all but three of the first 15 years, but not after the fifteenth year. Forage increases during this 15-year period averaged 66 percent if the roots were killed and 45 percent if only the tops were killed. Naturally occurring grasslands within the area averaged 26% higher forage production than the tree covered areas. Percent increases due to tree removal were the greatest in the driest years. Ref.267\64.03. |
| Project: | Effect of blue oak removal on herbaceous forage production in the North Sierra Foothills |
| Project Leader: | Kay, B.L., and O.A. Leonard |
| Summary: | 1979 Proc., Symp. Ecology, Manage.and Util.of Calif.Oaks, Claremont,CA: pp. 1-5. Herbaceous forage production beneath blue oak trees increased when the trees were killed. Forage yields were greater in 11 years of the 13 years following treatment averaging 66 percent if the roots were killed and 45 percent if only the tops were killed. Percent increases were greatest in the driest years. Yields when trees and roots were killed > tops only removed > naturally occurring grassland > under live trees. When trees were killed the botanical composition improved and total ground cover increased. Bulk density of soil increased. |
| Project: | Comparisons of water stress and stomatal conductance in different size classes of Quercus douglasii from different sites |
| Project Leader: | Matzner, S., K. Rice, and J. Richards |
| Summary: | Proc., Symp. on Oak Woodlands: Ecology, Management, and Urban Interface Issues. San Luis Obispo, CA. , Mar 19-22, 1996. Patterns of water stress and its effect on stomatal conductance were determined for different size classes of Quercus douglasii a species which is not regenerating throughout much of its range. Measurements were made on seedlings, saplings and adults at three sites that differed in annual precipitation and temperature extremes. Although differences between size classes, sites, and years were discovered, there was no evidence that blue oaks in regeneration and nonregeneration areas differ in their water relations. Ref.258\64.01. |
| Project: | Age structure of Quercus douglasii in relation to livestock grazing and fire |
| Project Leader: | McClaran, M.P. |
| Summary: | 1986. Ph.D. Thesis, Univ. of Calif., Berkeley. 119 pages. Blue oak size poorly predicts tree age and is of little value in describing stand age structure. The variation in growth rates among neighboring trees is the main limitation of the predictive ability of tree size. Stand age structure cannot be described by size distribution because they are different. Therefore the validity of earlier predictions of blue oak age structures based on tree size should be questioned. Age structure and size-age relationship results are of possibly equal importance as an injection of evidence into the current political discussion of blue oak regeneration, stating that there is no simple or quick fix solution. Ref.78\63.99. |
| Project: | Comparison of fire history estimates between open-scarred and intact Quercus douglasii |
| Project Leader: | McClaran, M.P. |
| Summary: | 1988 The American Midland Naturalist 120: pp. 432-435. Reservation has been expressed regarding relying on samples from trees with open scars to estimate fire history. A greater probability of scarring for open-scarred trees is one reason commonly given for restricting samples. Fire scars in 181 scarred Quercus douglasii cross sections were dated from two different stands. Open-scarred trees were twice as likely to scar as intact trees, but the average number of scars tree were similar. Time since last fire is critical, as scars may heal before sampling. This suggests that fire history estimates will be most affected by sample restriction in areas with long periods of fire suppression. |
| Project: | Fire-related recruitment in stagnant Quercus douglasii populations |
| Project Leader: | McClaran, M.P., and J.W. Bartolome |
| Summary: | 1989 Can. J. For. Res. 19: pp. 580-585. Blue oak age structure, stem analysis, and fire-scar history from more than 500 individuals on two sites in central California, U.S.A., revealed (i) meager tree recruitment since the 1940s and few trees older than 150 years, (ii) increased fire frequency following Anglo-American settlement in 1848 until fire suppression efforts in the 1940s, (iii) a positive association between tree ages and fire dates, and (iv) superior vertical growth to 135 cm of postfire sprouts (trees with ground-level ages within 1 year after fires) on the site with less livestock browsing pressure. |
| Project: | Effect of Quercus douglasii (fagaceae) on herbaceous understory along a rainfall gradient |
| Project Leader: | McClaran, M.P., and J.W. Bartolome |
| Summary: | 1989. Madrono 36(3): pp. 141-153. Variation in effect of approximately 50% Quercus douglasii (blue oak) cover on herbaceous understory biomass and composition was studied along a rainfall gradient between five sites. Biomass and composition were compared between understory and adjacent open grassland at each site to evaluate changes in canopy effect along the gradient. We conclude that variation in canopy effect on biomass resulted from changes in relative production between understory and open grassland, not from differences in relative composition. Ref.274\64.10. |