Facilitation of conspecific seedling recruitment and shifts in temperate savanna ecotones

Ecological Monographs

Volumn 69, Issue 4, 1999, Pages 513-534

  Weltzin, Jake F ^a,b   McPherson, Guy R ^a  

^a UNIVERSITY OF ARIZONA   (United States)

^b UNIVERSITY OF TENNESSEE   (United States)

Author keywords

Acorn; Ecotone; Effects on seedling recruitment; Facilitation; Quercus emoryi; Safe site; Seed dispersal; Seedling establishment; Shade; Tree line

Indexed keywords

FACILITATION; RECRUITMENT; SAVANNA; SEED DISPERSAL; SEEDLING ESTABLISHMENT; SHADING; TREELINE;

NORTH AMERICA;

DICOTYLEDONEAE; QUERCUS; QUERCUS EMORYI;

EID: 0032697006     PISSN: 00129615     EISSN: None     Source Type: Journal    
DOI: 10.1890/0012-9615(1999)069[0513:FOCSRA]2.0.CO;2     Document Type: Article

References (147)

1. Albaladejo, J. 1990. Impact of degradation processes on soil quality in arid Mediterranean environments. Pages 193-214 in J. Rubio and J. Rickson, editors. Strategies to combat desertification in Mediterranean Europe. Commission of the European Communities, Report EUR 11175.
2. Allison, P. D. 1995. Survival analysis using the SAS system: a practical guide. SAS Institute, Cary, North Carolina, USA.
3. Amundson, R. G., A. R. Ali, and A. J. Belsky. 1995. Stomatal responsiveness to changing light intensity increases rain-use efficiency of below-crown vegetation in tropical savannas. Journal of Arid Environments 29:139-153.
4. Archer, S. 1994. Woody plant encroachment into southwestern grasslands and savannas: rates, patterns and proximate causes. Pages 13-68 in M. Vavra, W. Laycock, and R. Pieper, editors. Ecological implications of livestock herbivory in the West. Society for Range Management, Denver, Colorado, USA.
5. _. 1995. Tree-grass dynamics in a Prosopis-thornscrub savanna parkland: reconstructing the past and predicting the future. Écoscience 2:83-99.
6. 2? Climatic Change 29:91-99.
7. Ashton, M. S., and B. C. Larson. 1996. Germination and seedling growth of Quercus (section Erythrobalanus) across openings in a mixed-deciduous forest of southern New England, USA. Forest Ecology and Management 80: 81-94.
8. Bahre, C. J. 1977. Land-use history of the Research Ranch, Elgin, Arizona. Journal of the Arizona Academy of Science 12(supplement 2):1-32.
9. _. 1991. A legacy of change. University of Arizona Press, Tucson, Arizona, USA.
10. Bartolome, J. W., B. H. Allen-Diaz, and W. D. Tietje. 1994. The effect of Quercus douglasii removal on understory yield and composition. Journal of Range Management 47: 151-154.
11. Bazzaz, F. A., and P. M. Wayne. 1994. Coping with environmental heterogeneity: the physiological ecology of tree seedling across the gap-understory continuum. Pages 349-390 in M. M. Caldwell and R. W. Pearcy, editors. Exploitation of environmental heterogeneity by plants. Ecophysiological processes above-and belowground. Academic Press, San Diego, California, USA.
12. Belsky, A. J., R. G. Amundson, J. M. Duxbury, S. J. Riha, A. R. Ali, and S. M. Mwonga. 1989. The effects of trees on their physical, chemical, and biological environments in a semiarid savanna in Kenya. Journal of Applied Ecology 26:1005-1024.
13. Belsky, A. J., and C. D. Canham. 1994. Forest gaps and isolated savanna trees: an application of patch dynamics in two ecosystems. BioScience 44:77-84.
14. Berkowitz, A. R., C. D. Canham, and V. R. Kelly. 1995. Competition vs. facilitation of tree seedling growth and survival in early successional communities. Ecology 76: 1156-1168.
15. Blackburn, W. H., and P. T. Tueller. 1970. Pinyon and juniper invasion in black sagebrush communities in east-central Nevada. Ecology 51:841-848.
16. Borchert, M., F. W. Davis, J. Michaelsen, and L. D. Oyler. 1989. Interactions of factors affecting seedling recruitment of blue oak (Quercus douglasii) in California. Ecology 70: 389-404.
17. Borelli, S., P. F. Ffolliott, and G. J. Gottfried. 1994. Natural regeneration in encinal woodlands of southeastern Arizona. Southwestern Naturalist 39:179-183.
18. Bragg, W. K., A. K. Knapp, and J. M. Briggs 1993. Comparative water relations of seedling and adult Quercus species during gallery forest expansion in tallgrass prairie. Forest Ecology and Management 56:29-41.
19. Bray, J. R. 1960. The composition of savanna vegetation in Wisconsin. Ecology 41:721-732.
20. Breshears, D. D., J. W. Nyhan, C. E. Heil, and B. P. Wilcox. 1998. Effects of woody plants on microclimate in a semiarid woodland: soil temperature and evaporation in canopy and intercanopy patches. International Journal of Plant Sciences 159:1010-1017.
21. Brown, D. E., editor. 1982. Biotic communities of the American southwest - United States and Mexico. Desert Plants 4:1-342.
22. Callaway, R. M. 1992a. Effects of shrubs on recruitment of Quercus douglasii and Quercus lobata in California. Ecology 73:2118-2128.
23. _. 1992b. Morphological and physiological responses of three California oak species to shade. International Journal of Plant Science 153:434-441.
24. Callaway, R. M., and C. M. D'Antonio. 1991. Shrub facilitation of coast live oak establishment in central California. Madrono 38:158-169.
25. Callaway, R. M., E. H. DeLucia, D. Moore, R. Nowak, and W. H. Schlesinger. 1996. Competition and facilitation: contrasting effects of Artemisia tridentata on desert vs. montane pines. Ecology 77:2130-2141.
26. Callaway, R. M, N. M. Nadkarni, and B. E. Mahall. 1991. Facilitation and interference of Quercus douglasii on understory productivity in central California. Ecology 72: 1484-1499.
27. Canfield, R. H. 1941. Application of the line interception method in sampling range vegetation. Journal of Forestry 39:388-394.
28. Clements, F. E., J. Weaver, and H. Hansson. 1926. Plant competition: an analysis of the development of vegetation. Carnegie Institute, Washington, D.C., USA.
29. Darley-Hill, S., and W. C. Johnson. 1981. Acorn dispersal by the blue jay (Cyanocitta cristata). Oecologia 50:231-232.
30. Davis, M. A., K. J. Wrage, and P. B. Reich. 1998. Competition between tree seedlings and herbaceous vegetation: support for a theory of resource supply and demand. Journal of Ecology 86:652-661.
31. Davis, O. K. 1994. The correlation of summer precipitation in the southwestern USA with isotopic records of solar activity during the Medieval Warm Period. Climatic Change 26:271-287.
32. Day, P. R. 1965. Particle fractionation and particle-size analysis. Pages 545-567 in C. A. Black, editor. Methods of soil analysis, part I. Physical and mineralogical properties. Agronomy Monographs 9. American Society of Agronomy and Soil Science Society of America, Madison, Wisconsin, USA.
33. De Steven. D. 1991a. Experiments on mechanisms of tree establishment in old-field succession: seedling emergence. Ecology 72:1066-1075.
34. _. 1991b. Experiments on mechanisms of tree establishment in old-field succession: seedling survival and growth. Ecology 72:1076-1088.
35. Dreimanis, A. 1962. Quantitative gasometric determination of calcite and dolomite by using Chittick apparatus. Journal of Sedimentary Petrology 32:520-529.
36. Espelta, J. M., M. Riba, and J. Retana. 1995. Patterns of seedling recruitment in west-Mediterranean Quercus ilex forests influenced by canopy development. Journal of Vegetation Science 6:465-472.
37. Evans, R. A., and R. M. Love. 1957. The step point method of sampling - a practical tool in range research. Journal of Range Management 10:208-212.
38. Fisher, R. A. 1958. Statistical methods for research workers. Thirteenth edition. Hafner, New York, New York, USA.
39. _. 1960. The design of experiments. Seventh edition. Hafner, New York, New York, USA.
40. Franco, A. C. and P. S. Nobel 1989. Effect of nurse plants on the microhabitat and growth of cacti. Journal of Ecology 77:870-886.
41. Garcia-Moya, E., and C. M. McKell. 1970. Contribution of shrubs to the nitrogen economy of a desert-wash plant community. Ecology 51:81-88.
42. Germaine, H. L., and G. R. McPherson. 1998. Effects of timing of precipitation and acorn harvest date on emergence of Quercus emorvi. Journal of Vegetation Science 9:157-160.
43. Germaine, H. L., and G. R. McPherson. 1999. Effects of biotic factors on emergence and survival of Quercus emoryi at lower tree line, Ecoscience 6:92-99.
44. Gordon, D. R., and K. J. Rice. 1993. Competitive effects of grassland annuals on soil water and blue oak (Quercus douglasii) seedlings. Ecology 74:68-82.
45. Gordon, D. R., J. M. Welker, J. W. Menke, and K. J. Rice. 1989. Competition for water between annual plants and blue oak (Quercus douglasii) seedlings. Oecologia 79:533-541.
46. Griffin, J. R. 1971. Oak regeneration in the upper Carmel Valley, California. Ecology 52:862-868.
47. _. 1973. Xylem sap tension in three woodland oaks of central California. Ecology 54:152-159.
48. _. 1977. Oak woodland. Pages 383-415 in M. Barbour and J. Major, editors. Terrestrial vegetation of California. John Wiley, New York, New York, USA.
49. _. 1980. Animal damage to valley oak acorns and seedlings, Carmel Valley, California. Pages 242-245 in T. R. Plumb, technical coordinator. Proceedings of the symposium on the ecology, management, and utilization of California oaks. U.S. Forest Service General Technical Report PSW-44.
50. Grover, H. D., and H. B. Musick. 1990. Shrubland encroachment in southern New Mexico, USA: an analysis of desertification processes in the American Southwest. Climatic Change 17:305-330.
51. Grubb, P. J. 1977. The maintenance of species richness in plant communities: the importance of the regeneration niche. Biological Review 52:107-145.
52. Gurevitch, J., and S. L. Collins. 1994. Experimental manipulation of natural plant communities. Trends in Ecology and Evolution 9:94-98.
53. Harper, J. L. 1977. Population biology of plants. Academic Press, London, UK.
54. _. 1982. After description. Pages 11-24 in E. I. Newman, editor. The plant community as a working mechanism. The British Ecological Society, Oxford, UK.
55. Harper, J. L., J. N. Clatworthy, I. H. McNaughton, and G. R. Sagar. 1961. The evolution of closely related species living in the same area. Evolution 15:209-277.
56. Hastings, J. R. and R. M. Turner. 1965. The changing mile. University of Arizona Press, Tucson, Arizona, USA.
57. Haworth, K., and G. R. McPherson. 1994. Effects of Quercus emoryi on herbaceous vegetation in a semiarid savanna. Vegetatio 112:153-159.
58. Haworth, K.,and G. R. McPherson. 1995. Effects of Quercus emoryi trees on precipitation distribution and microclimate in a semiarid savanna. Journal of Arid Environments 31: 153-170.
59. Herrera, C. M., P. Jordano, L. López-Soria, and J. A. Amat. 1994. Recruitment of a mast-fruiting, bird-dispersed tree: bridging frugivore activity and seedling establishment. Ecological Monographs 64:315-344.
60. Hill, J. D., C. D. Canham, and D. M. Wood. 1995. Patterns and causes of resistance to tree invasion in rights-of-way. Ecological Applications 5:459-470.
61. Houle, G. 1995. Seed dispersal and seedling recruitment: the missing link(s). Ecoscience 2:238-244.
62. Hubbard, J. A., and G. R. McPherson. 1997. Acorn selection by Mexican jays: a test of a tri-trophic symbiotic relationship hypothesis. Oecologia 110:143-146.
63. Hubbard, J. A., and G. R. McPherson. In press. Do seed predation and dispersal limit downslope movement of the semidesert grassland/oak woodland ecotone in the American Southwest? Journal of Vegetation Science.
64. Jackson, J. T. and O. W. Van Auken. 1997. Seedling survival, growth and mortality of Juniperus ashei (Cupressacae) in the Edwards Plateau region of central Texas. Texas Journal of Science 49:267-278.
65. Jackson, L. P., I. V. Hall, and L. E. Aalders. 1972. Lowbush blueberry seedling growth as affected by soil type. Canadian Journal of Soil Science 52:113-115.
66. Jensen, T. S., and O. F. Neilson. 1986. Rodents as seed dispersers in a heath-oak wood succession. Oecologia 70: 214-221.
67. Joffre, R., and S. Rambal. 1988. Soil water improvement by trees in the rangelands of southern Spain. Acta Oecologia 9:405-422.
68. Johnson, P. S. 1992. Oak overstorey/reproduction relations in two xeric ecosystems in Michigan. Forest Ecology and Management 48:233-248.
69. Jordan, P. W., and P. S. Nobel. 1979. Infrequent establishment of seedlings of Agave deserti (Agavaceae) in the northern Mojave Desert. American Journal of Botany 66:1076-1084.
70. Kadmon, R., A. Yair, and A. Danin. 1989. Relationship between soil properties, soil moisture, and vegetation along loess-covered hillslopes, northern Negev, Israel. Catena Supplement 14:43-57.
71. Keeney, D. R., and D. W. Nelson. 1982. Nitrogen - inorganic forms. Pages 643-698 in A. L. Page, editor. Methods of soil analysis, part 2. Chemical and microbiological properties. Second edition. Agronomy Monographs 9. American Society of Agronomy and Soil Science Society of America, Madison, Wisconsin, USA.
72. Kollmann, J., and H.-P. Schill. 1996. Spatial patterns of dispersal, seed predation and germination during colonization of abandoned grassland by Quercus petraea and Corylus avellana. Vegetatio 125:193-205.
73. Kosmas, C., N. Moustakas, N. G. Danalatos, and N. Yassoglou. 1994. The effect of rock fragments on wheat biomass production under highly variable moisture conditions in Mediterranean environments. Catena 23:191-198.
74. Koukoura, Z., and J. Menke. 1995. Competition for soil water between perennial bunch-grass (Elymus glaucus B.B.) and blue oak seedlings (Quercus douglasii H. and A.). Agroforestry Systems 32:225-235.
75. Kruskal, W. H., and W. A. Wallis. 1952. Use of ranks in one-criterion analysis of variance. Journal of the American Statistical Association 47:583-621.
76. Kullman, L. 1989. Recent retrogression of the forest-alpine tundra ecotone (Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) in the Scandes Mountains, Sweden. Journal of Biogeography 16:83-90.
77. Leopold, A. 1924. Grass, brush, timber and fire in southern Arizona. Journal of Forestry 22:1-10.
78. Ludwig, D., B. H. Walker, and C. S. Holling. 1997. Sustainability, stability, and resilience. Conservation Ecology (1):7 [online: 〈http://www.consecol.org/voll/issl/art7〉].
79. Malanson, G. P. 1997. Effects of feedbacks and seed rain on ecotone patterns. Landscape Ecology 12:27-38.
80. Marshall, J. T. 1957. Birds of the pine-oak woodland in southern Arizona and adjacent Mexico. Pacific Coast Avifauna Number 32, Cooper Ornithological Society, Berkeley, California, USA.
81. Matsuda, K., and J. R. McBride. 1986. Difference in seedling growth morphology as a factor in the distribution of three oaks in central California. Madrono 33:207-216.
82. McClaran, M. P., L. S. Allen, and G. B. Ruyle. 1992. Livestock production and grazing management in the encinal oak woodlands of Arizona. Pages 57-64 in P. F. Ffoliott, G. J. Gottfried, D. A. Bennett, V. M. Hernandez C., A. Ortega-Rubio, and R. H. Hamre, technical coordinators. Ecology and management of oak and associated woodlands: perspectives in the southwestern United States and northern Mexico. U.S. Forest Service General Technical Report RM-218.
83. McClaran, M. P., and J. W. Bartolome. 1989. Fire related recruitment in stagnant Quercus douglasii populations. Canadian Journal of Forest Research 19:580-585.
84. McClaran, M. P., and J. W. Bartolome. 1990. Comparison of actual and predicted blue oak age structures. Journal of Range Management 43:61-63.
85. McClaran, M. P., and G. R. McPherson. 1995. Can soil organic carbon isotopes be used to describe grass-tree dynamics at a savanna-grassland ecotone and within the savanna? Journal of Vegetation Science 6:857-862.
86. McClaran, M. P., and G. R. McPherson. In press. Oak savanna in the American southwest. In R. C. Anderson, J. S. Fralish, and J. Baskin, editors. Savanna, barren and rock outcrop plant communities of North America. Cambridge University Press, New York, New York, USA.
87. McLean, E. O. 1982. Soil pH and lime requirement. Pages 199-224 in A. L. Page, editor. Methods of soil analysis, part 2. Chemical and microbiological properties. Second edition. Agronomy Monographs 9. American Society of Agronomy and Soil Science Society of America. Madison, Wisconsin, USA.
88. McPherson, G. R. 1992. Ecology of oak woodlands in Arizona. Pages 24-33 in P. F. Ffoliott, G. J. Gottfried, D. A. Bennett, V. M. Hernandez C., A. Ortega-Rubio, and R. H. Hamre, technical coordinators. Ecology and management of oak and associated woodlands: perspectives in the southwestern United States and northern Mexico. U.S. Forest Service General Technical Report RM-218.
89. _. 1993. Effects of herbivory and herbs on oak establishment in a semiarid temperate savanna. Journal of Vegetation Science 4:687-692.
90. _. 1997. Ecology and management of North American savannas. University of Arizona Press, Tucson, Arizona, USA.
91. McPherson, G. R., T. W. Boutton, and A. J. Midwood. 1993. Stable carbon isotope analysis of soil organic matter illustrates vegetation change at the grassland/woodland boundary in southeastern Arizona, USA. Oecologia 93:95-101.
92. McPherson, G. R., G. A. Rasmussen, D. B. Wester, and R. A. Masters. 1991. Vegetation and soil zonation associated with Juniperus pinchotii Sudw. trees. Great Basin Naturalist 51:316-324.
93. McPherson, G. R., and H. A. Wright. 1990. Establishment of Juniperus pinchotii in western Texas: environmental effects. Journal of Arid Environments 19:283-287.
94. Menaut, J. C., J. Gignoux, C. Prado, and J. Clobert. 1990. Tree community dynamics in a humid savanna of the Côte-d'Ivoire: modelling the effects of fire and competition with grass and neighbors. Journal of Biogeography 17:471-481.
95. Muick, P. C. 1991. Effects of shade on blue oak and coast live oak regeneration in California annual grasslands. Pages 21-24 in B. Standiford, editor. Symposium on oak woodlands and hardwood rangeland management. U.S. Forest Service General Technical Report PSW-126.
96. Muick, P. C., and J. W. Bartolome. 1987. An assessment of natural regeneration of oaks in California. Report to California Department of Forestry, Forest and Rangeland Resource Assessment Program, California, USA.
97. Munn, L., N. Harrington, and D. R. McGirr. 1987. Rock fragments. Pages 259-282 in R. D. Williams and G. E. Schuman, editors. Reclaiming mine soils and overburden in the western United States. Analytic parameters and procedures. Soil Conservation Society of America, Ankeny, Iowa, USA.
98. Neilson, R. P. 1993. Transient ecotone response to climatic change: some conceptual and modeling approaches. Ecological Applications 3:385-395.
99. Neilson, R. P., and L. H. Wullstein. 1983. Biogeography of two southwest American oaks in relation to atmospheric dynamics. Journal of Biogeography 10:275-297.
100. Nelson, D. W., and L. E. Sommers. 1982. Total carbon, organic carbon and organic matter. Pages 539-580 in A. L. Page, editor. Methods of soil analysis, part 2. Chemical and microbiological properties. Second edition. Agronomy Monographs 9. American Society of Agronomy and Soil Science Society of America. Madison, Wisconsin, USA.
101. Noble, I. R. 1993. A model of the responses of ecotones to climate change. Ecological Applications 3:396-403.
102. Nyandiga, C. O., and G. R. McPherson. 1992. Germination of two warm-temperate oaks, Quercus emoryi and Quercus arizonica. Canadian Journal of Forest Research 22:1395-1401.
103. Odum, H. T. 1971. Environment, power, and society. Wiley-Interscience, New York, New York, USA.
104. Olsen, S. R., and L. E. Sommers. 1982. Phosphorus. Pages 404-430 in A. L. Page, editor. Methods of soil analysis, part 2. Chemical and microbiological properties. Second edition. Agronomy Monographs 9. American Society of Agronomy and Soil Science Society of America. Madison, Wisconsin, USA.
105. Parker, V. T., and C. H. Muller. 1982. Vegetational and environmental changes beneath isolated live oak trees (Quercus agrifolia) in a California annual grassland. American Midland Naturalist 107:69-81.
106. Pase, C. P. 1969. Survival of Quercus turbinella and Quercus emoryi in an Arizona chaparral community. Southwestern Naturalist 14:149-156.
107. Petranka, J. W., and J. K. McPherson. 1979. The role of Rhus copallina in the dynamics of the forest-prairie ecotone in north-central Oklahoma. Ecology 60:956-965.
108. Pigott, C. D., and S. Pigott. 1993. Water as a determinant of the distribution of trees at the boundary of the Mediterranean zone. Journal of Ecology 81:557-566.
109. Poesen, J., and H. Lavee. 1994. Rock fragments in top soils: significance and processes. Catena 23:1-28.
110. 2 concentrations? Pages 177-195 in Christian Körner and F. A. Bazzaz, editors. Carbon dioxide, populations, and communities. Academic Press, San Diego, California, USA.
111. 2, soil water, and shrub/ grass ratios on rangelands. Journal of Range Management 50:278-284.
112. Prentice, I. C. 1986. Vegetation responses to past climatic variation. Vegetatio 67:131-141.
113. Primack, R. B., and S. L. Miao. 1992. Dispersal can limit local plant distribution. Conservation Biology 6:513-519.
114. Richardson, M. L., S. D. Clemmons, and J. C. Walker. 1979. Soil survey of Santa Cruz and part of Cochise and Pima Counties, Arizona. Soil Conservation Service, U.S. Department of Agriculture, Washington, D.C., USA.
115. Sanchini, P. J. 1981. Population structure and fecundity patterns in Quercus emoryi and Quercus arizonica in southeastern Arizona. Dissertation. University of Colorado, Boulder, Colorado, USA.
116. SAS Institute. 1989. SAS/STAT User's Guide, version 6. Fourth edition. SAS Institute, Cary, North Carolina, USA.
117. _. 1996. SAS/STAT software: changes and enhancements through Release 6.11. SAS Institute, Cary, North Carolina, USA.
118. Scheiner, S. M. 1993. MANOVA: Multiple response variables and multispecies interactions. Pages 94-1 12 in S. M. Scheiner and J. Gurevitch, editors. Design and analysis of ecological experiments. Chapman and Hall, New York, New York, USA.
119. Schlesinger, W. H., J. F. Reynolds, G. L. Cunningham, L. Huenneke, W. M. Jarrell, R. A. Virginia, and W. G. Whitford. 1990. Biological feedbacks in global desertification. Science 247:1043-1048.
120. Scholes, R. J., and S. R. Archer. 1997. Tree-grass interactions in savannas. Annual Review of Ecology and Systematics 28:517-544.
121. Schupp, E. W. 1995. Seed-seedling conflicts, habitat choice, and patterns of plant recruitment. American Journal of Botany 82:399-409.
122. Schupp, E. W., and M. Fuentes. 1995. Spatial patterns of seed dispersal and the unification of plant population ecology. Ecoscience 2:267-275.
123. Shapiro, S. S., and M. B. Wilk. 1965. An analysis of variance test for normality (complete samples). Biometrika 52:591-611.
124. Skarpe, C. 1991. Spatial patterns and dynamics of woody vegetation in an arid savanna. Journal of Vegetation Science 2:565-572.
125. Soil Conservation Service. 1994. Soil survey of Fort Huachuca, Cochise County, Arizona. Prepared for the U.S. Department of the Army. U.S. Department of Agriculture, Soil Conservation Service, Washington, D.C., USA.
126. Soil Survey Staff. 1994a. National soil survey handbook. U.S. Department of Agriculture, Soil Conservation Service. Washington, D.C., USA.
127. _. 1994b. Keys to soil taxonomy, Sixth edition. U.S. Department of Agriculture, Soil Conservation Service. Washington, D.C., USA.
128. Sork, V. L. 1985. Germination response in a large-seeded neotropical tree species, Gustavia superba (Lecythidaceae). Biotropica 17:130-136.
129. _. 1993. Evolutionary ecology of mast-fruiting in temperate and tropical oaks (Quercus spp.). Vegetatio 107/108: 133-147.
130. Steenbergh, W. F, and C. H. Lowe. 1969. Critical factors during the first years of life of the saguaro (Cereus giganteus) at Saguaro National Monument. Ecology 50:825-834.
131. Steenbergh, W. F., and C. H. Lowe. 1977. Ecology of the saguaro. II. Reproduction, germination, establishment, growth, and survival of the young plant. National Park Service Science Monograph Series number 8. National Park Service, Washington, D.C., USA.
132. Tiedemann, A. R., and J. O. Klemmedson. 1973. Effects of mesquite on physical and chemical properties of the soil. Journal of Range Management 26:27-29.
133. Tiedemann, A. R., and J. O. Klemmedson. 1977. Effect of mesquite trees on vegetation and soils in the desert grassland. Journal of Range Management 30:361-367.
134. Vetaas, O. R. 1992. Micro-site effects of trees and shrubs in dry savannas. Journal of Vegetation Science 3:337-344.
135. von Ende, C. N. 1993. Pages 113-137 in S. M. Scheiner and J. Gurevitch, editors. Design and analysis of ecological experiments. Chapman and Hall, New York, New York, USA.
136. Walker, B. H., and I. Noy-Meir. 1982. Aspects of the stability and resilience of savanna ecosystems. Pages 556-590 in B. J. Huntley and B. H. Walker, editors. Ecology of tropical savannas. Springer-Verlag, Berlin, Germany.
137. Walter, H. 1954. Die verbuschung, eine erscheinung der subtropischen savannengebiete, und ihre ökologischen urscachen. Vegetatio 5/6:6-10.
138. Welker, J. M., and J. W. Menke. 1990. The influence of simulated browsing on tissue water relations, growth, and survival of Quercus douglasii (Hook and Arn.) seedlings under slow and rapid rates of soil drought. Functional Ecology 4:807-817.
139. Weltzin, J. F., S. Archer, and R. K. Heitschmidt. 1997. Small-mammal regulation of vegetation structure in a temperate savanna. Ecology 78:751-763.
140. Weltzin, J. F., and G. R. McPherson. 1995. Potential effects of climate change on lower tree lines in the southwestern United States. Pages 180-193 in L. F. DeBano, G. J. Gottfried, R. H. Hamre, C. B. Edminster, P. F. Ffolliott, and A. Ortega-Rubio, technical coordinators. Biodiversity and management of the Madrean Archipelago: the sky islands of southwestern United States and Northwestern Mexico. U.S. Forest Service General Technical Report RM-264.
141. Weltzin, J. F., and G. R. McPherson. 1997. Spatial and temporal soil moisture resource partitioning by trees and grasses in a temperate savanna, Arizona, USA. Oecologia 112: 156-164.
142. Weltzin, J. F., and G. R. McPherson. In press. Implications of precipitation redistribution for shifts in temperate savanna ecotones. Ecology.
143. Williams, K., S. D. Davis, B. L. Gartner, and S. Karlsson. 1991. Factors limiting the establishment of a chaparral oak, Quercus durata Jeps., in grassland. Pages 70-73 in Symposium on oak woodlands and hardwood rangeland management. U.S. Forest Service General Technical Report PSW-126.
144. Wilson, J. B., and A. D. Q. Agnew. 1992. Positive-feedback switches in plant communities. Advances in Ecological Research 23:263-336.
145. Wilson, S. D. 1998. Competition between grasses and woody plants. Pages 231-254 in G. P. Cheplick, editor. Population biology of grasses. Cambridge University Press, Cambridge, UK.
146. Young, M. D., and O. T. Solbrig. 1993. The world's savannas: economic driving forces, ecological constraints and policy options for sustainable land use. Parthenon Publishing Group, Carnforth, UK.
147. Zar, J. H. 1996. Biostatistical analysis. Prentice Hall, Upper Saddle River, New Jersey, USA.