List of references used in the meta-analysis.
Aanderud ZT, Shuldman MI, Drenovsky RE, Richards JH (2008) Shrub-interspace dynamics alter relationships between microbial community composition and belowground ecosystem characteristics. Soil Biology & Biochemistry 40 (9): 2206-2216.
Abella SR, Springer JD (2008) Canopy-tree influences along a soil parent material gradient in Pinus ponderosa-Quercus gambelii forests, northern Arizona. Journal of the Torrey Botanical Society
135: 26-36
Abril A, Villagra P, Noe L (2009) Spatiotemporal heterogeneity of soil fertility in the Central Monte desert (Argentina). Journal of Arid Environments 73 (10): 901-906.
Alban, D.H. 1969. The influence of western hemlock and western redcedar on soil properties. Soil
Science Society of America Proceedings 33: 453-457
Amiotti NM, Zalba P, Sánchez LF, Peinemann N (2000) The impact of single trees on properties of loess-derived grassland soils in Argentina. Ecology 81: 3283-3290
Barth RC, Klemmedson JO (1982) Amount and distribution of dry matter, nitrogen, and organic carbon in soil-plant systems of mesquite and palo verde. Journal of Range Management 35: 412-418.
Barton AM, Wallenstein MD (1997) Effects of invasion of Pinus virginiana on soil properties in serpentine barrens in southeastern Pennsylvannia. Journal of the Torrey Botanical Society 124:
297-305
Beatty SW (1984) Influence of microtopography and canopy species on spatial patterns of forest understory plants. Ecology 65: 1406-1419
Belsky A, Amundson R, Duxbury J, Riha S, Ali A, Mwonga S (1989) The effects of trees on their physical, chemical, and biological environments in a semi-arid savanna in Kenya. Journal of
Applied Ecology 26: 1005-1024
Belsky A, Mwonga S, Amundson R, Duxbury J, Ali A (1993) Comparative effects of isolated trees on their undercanopy environments in high- and low-rainfall savannas. Journal of Applied Ecologu
30: 143-155
Belsky AJ, Mwonga SM, Duxbury JM (1993) Effects of widely spaced trees and livestock grazing on understory environments in tropical savannas. Agroforestry Systems 24 (1): 1-20
Bochet E, Rubio JL, Poesen J (1999) Modified topsoil islands within patchy Mediterranean vegetation in
SE Spain. Catena 38: 23-44
Boettcher SE, Kalisz PJ (1990) Single-tree influence on soil properties in the mountains of eastern
Kentucky. Ecology 71: 1365-1372
Broquen P, Candan F, Falbo G, Girardin JL, Pellegrini V (2005) Impact of Pinus ponderosa on acidification at forest-steppe transition soils, SW Neuquén, Argentina. Bosque (Valdivia) 26: 63-
74
Butterfield BJ, Briggs JM (2009) Patch dynamics of soil biotic feedbacks in the Sonoran Desert. Journal of Arid Environments 73 (1): 96-102.
Camargo-Ricalde SL, Reyes-Jaramillo I, Montano NM (2010) Forestry insularity effect of four Mimosa
L. species (Leguminosae-Mimosoideae) on soil nutrients of a Mexican semiarid ecosystem.
Agroforestry Systems 80 (3): 385-397.
Cardelus CL, Mack MC, Woods C, DeMarco J, Treseder KK (2009) The influence of tree species on canopy soil nutrient status in a tropical lowland wet forest in Costa Rica. Plant and Soil 318: 47-
61.
Carnevale NJ, Torres PS, Vilche MS (2005) The relationship between the chemical properties of native woody species and the soil, in a secondary forest of the Eastern Chaco (Argentina). Journal of
Sustainable Forestry 20: 85-100

Charley, J.L., West, N.E., 1975. Plant-induced soil chemical patterns in some shrub dominated semidesert ecosystems of Utah. Journal of Ecology 63: 945–963.
Cheng XL, An SQ, Liu SR, Li GQ (2004) Micro-scale spatial heterogeneity and the loss of carbon, nitrogen and phosphorus in degraded grassland in Ordos Plateau, northwestern China. Plant and
Soil 259: 29-37
Coile, T.S. 1938. Forest soil fertility: influence of stand composition on nitrogen transformation in the surface soil. Soil Science Society of America Proceedings 3: 225-229
Cross A, Perakis SS (2011) Complementary models of tree species–soil relationships in old-growth temperate forests. Ecosystems 14: 248-260
Cross AF, Schlesinger WH (1999) Plant regulation of soil nutrient distribution in the northern
Chihuahuan Desert. Plant Ecology 145 (1): 11-25
Cruz C, Bio AMF, Jullioti A, Tavares A, Dias T, Martins-Loucao MA (2008) Heterogeneity of soil surface ammonium concentration and other characteristics, related to plant specific variability in a Mediterranean-type ecosystem. Environmental Pollution 154 (3): 414-423.
Dahlgren RA, Singer MJ, Huang X (1997) Oak tree and grazing impacts on soil properties and nutrients in a California oak woodland. Biogeochemistry 39 (1): 45-64
Dean WRJ, Milton SJ, Jeltsch F (1999) Large trees, fertile islands, and birds in arid savanna. Journal of
Arid Environments. 41: 61-78
DeLuca TH, Zackrisson O (2007) Enhanced soil fertility under Juniperus communis in arctic ecosystems. Plant and Soil 294 (1-2): 147-155.
Dijkstra FA, Smits MM (2002) Tree species effects on calcium cycling: the role of calcium uptake in deep soils Ecosystems 5: 385-398
Dockersmith IC, Giardina CP, Sanford RL (1999) Persistence of tree related patterns in soil nutrients following slash-and-burn disturbance in the tropics. Plant and Soil 209 (1): 137-156
Dong, X.W., X.K. Zhang, X.L. Bao, and J.K. Wang. 2009. Spatial distribution of soil nutrients after the establishment of sand-fixing shrubs on sand dune. Plant Soil Environ. 55: 288-294
Dossa EL, Diedhiou S, Compton JE, Assigbetse KB, Dick RP (2010) Spatial patterns of P fractions and chemical properties in soils of two native shrub communities in Senegal. Plant and Soil 327 (1-2)
:185-198.
Eldridge DJ, Wong VNL (2005) Clumped and isolated trees influence soil nutrient levels in an
Australian temperate box woodland Plant and Soil 270: 331-342
Facelli JM, Brock DJ (2000) Patch dynamics in arid lands: localized effects of Acacia papyrocarpa on soils and vegetation of open woodlands of south Australia. Ecography 23 (4): 479-491
Finzi AC, Breemen Nv, Canham CD (1998) Canopy tree-soil interactions within temperate forests: tree species effects on carbon and nitrogen. Ecological Applications 8: 440-446
Finzi AC, Canham CD, VanBreemen N (1998) Canopy tree soil interactions within temperate forests:
Species effects on pH and cations. Ecological Applications 8: 447-454
Fisher RF (1995) Amelioration of degraded rain forest soils by plantations of native trees. Soil Sci Soc
Am J 59: 544-549
Frias-Hernandez JT, Aguilar-Ledezma AL, Olalde-Portugal V, Balderas-Lopez JA, Gutierrez-Juarez G,
Alvarado-Gil JJ, Castro JJ, Vargas H, Albores A, Dendooven L, Miranda LCM (1999) Soil characteristics in semiarid highlands of central Mexico as affected by mesquite trees (Prosopis laevigata). Arid Soil Research and Rehabilitation 13 (3): 305-312
Frost WE, Edinger SB (1991) Effects of tree canopies on soil characteristics of annual rangeland.
Journal of Range Management 44: 286-288
Fujinuma R, Bockheim J, Balster N (2005) Base-cation cycling by individual tree species in old-growth forests of Upper Michigan, USA. Biogeochemistry 74 (3): 357-376.
Gallardo A (2003) Effect of tree canopy on the spatial distribution of soil nutrients in a Mediterranean
Dehesa Pedobiologia 47: 117-125

Gersper, P. L., and N. Holowaychuk. 1970. Effects of stemflow water on a Miami soil under a beech tree. II Chemical properties Soil Science Society of America Proceedings 34: 786-794.
Gersper, P.L. and N. Holowaychuk. 1971. Some effects of stem flow from forest canopy trees on chemical properties of soils. Ecology 52: 691-702.
Gimeno-Garcia E, Andreu V, Rubio JL (2001) Influence of mediterranean shrub species on soil chemical properties in typical Mediterranean environment. Communications in Soil & Plant
Analyisis 32: 1885-1898
Graham S, Wilson BR, Reid N, Jones H (2004) Scattered paddock trees, litter chemistry, and surface soil properties in pastures of the New England Tablelands, New South Wales. Australian Journal of Soil Research 42: 905-912
Grieve IC (1977) Some relationships between the vegetation patterns and soil variability in the Forest of
Dean, U.K. Journal of Biogeography 4: 193-199
Gutierrez JR, Meserve PL, Contreras LC, Vasquez H, Jaksic FM (1993) Spatial distribution of soil nutrients and ephemeral plants underneath and outside the canopy of Porliera chilensis shrubs
(Zygophyllaceae) in arid costal Chile. Oecologia 95 (3): 347-352
Jeddi K, Chaieb M (2009) Using trees as a restoration tool in Tunisian arid areas: effects on understorey vegetation and soil nutrients. Rangeland Journal 31 (4): 377-384.
Kamara CS, Haque I (1992) Faidherbia albida and its effects on Ethiopian highland Vertisols.
Agroforestry Systems 18: 17-29
Kamei J, Pandey HN, Barik SK (2009) Tree species distribution and its impact on soil properties, and nitrogen and phosphorus mineralization in a humid subtropical forest ecosystem of northeastern
India. Canadian Journal of Forest Research 39: 36-47
Kellman, M. 1979. Soil enrichment by neotropical savanna trees. Journal of Ecology 67: 565-577
Knops JMH, Koenig WD (1997) Site fertility and leaf nutrients of sympatric evergreen and deciduous species of Quercus in central coastal California. Plant Ecology 130: 121-131
Ko LJ, Reich PB (1993) Oak tree effects on soil and herbaceous vegetation in savannas and pastures in
Wisconsin. Am Midland Naturalist 130: 31-42
Kreibich H, Lehmann J, Scheufele G, Kern J (2003) Nitrogen availability and leaching during the terrestrial phase in a várzea forest of the Central Amazon floodplain. Biology and Fertility of
Soils 39: 62-64
Li PX, Wang N, He WM, Krusi BO, Gao SQ, Zhang SM, Yu FH, Dong M (2008) Fertile islands under
Artemisia ordosica in inland dunes of northern China: Effects of habitats and plant developmental stages. Journal of Arid Environments 72 (6): 953-963.
Lodhi MAK (1977) The influence and comparison of individual forest trees on soil properties and possible inhibition of nitrification due to intact vegetation. American Journal of Botany 64:260-
264
Lovett GM, Mitchell MJ (2004) Sugar maple and nitrogen cycling in the forests of eastern North
America. Frontiers in Ecology and the Environment 2 (2): 81-88
Marcos E, Calvo L, Marcos JA, Taboada A, Tarrega R (2010) Tree effects on the chemical topsoil features of oak, beech and pine forests. European Journal of Forest Research 129 (1): 25-30.
Mertens J, Van Nevel L, De Schrijver A, Piesschaert F, Oosterbaan A, Tack FMG, Verheyen K (2007)
Tree species effect on the redistribution of soil metals. Environmental Pollution 149 (2): 173-
181.
Mohr D, Simon M, Topp W (2005) Stand composition affects soil quality in oak stands on reclaimed and natural sites. Geoderma 129 (1-2): 45-53.
Mohr D, Topp W (2005) Hazel improves soil quality of sloping oak stands in a German low mountain range. Annals of Forest Science 62 (1): 23-30.
Moore TR (1980) The nutrient status of subarctic woodland soils. Arctic and Alpine Research 12: 147-
160

Moro MJ, Pugnaire FI, Haase P, Puigdefabregas J (1997) Mechanisms of interaction between a leguminous shrub and its understorey in a semi-arid environment. Ecography 20 (2): 175-184
Norden, U. 1994. Influence of tree species on acidification and mineral pools in deciduous forest soils of South Sweden. Water, Air, Soil Pollution 76: 363-381
Onipchenko VG, Makarov MI, van der Maarel E (2001) Influence of alpine plants on soil nutrient concentrations in a monoculture experiment. Folia Geobotanica 36 (3): 225-241
Oostra S, Majdi H, Olsson M (2006) Impact of tree species on soil carbon stocks and soil acidity in southern Sweden. Scandinavian Journal of Forest Research 21 (5): 364-371.
Pallant, E. and S.J. Riha. Surface soil acidification under red pine and norway spruce. Soil Science
Society of America Journal 54: 1124-1130
Pandey CB, Singh L (2009) Soil Fertility Under Homegarden Trees and Native Moist Evergreen Forest in South Andaman, India. Journal of Sustainable Agriculture 33 (3): 303-318
Payán F, Jones DL, Beer J, Harmand J-M (2009) Soil characteristics below Erythrina poeppigiana in organic and conventional Costa Rican coffee plantations. Agroforestry Systems 76: 81-93
Perakis SS, Kellogg CH (2007) Imprint of oaks on nitrogen availability and delta N-15 in California grassland-savanna: a case of enhanced N inputs? Plant Ecology 191 (2): 209-220.
Peréz FL (1992) The influence of organic matter addition by caulescent Andean rosettes on superficial soil properties Geoderma 54: 151-171
Peréz FL (2001) Geoecological alteration of surface soils by the Hawaiian silversword (Argyroxiphium sandwicense DC.) in Haleakala's crater, Maui. Plant Ecology 157: 215-233
Perroni-Ventura Y, Montana C, Garcia-Oliva F (2010) Carbon-nitrogen interactions in fertility island soil from a tropical semi-arid ecosystem. Functional Ecology 24 (1): 233-242
Powers JS, Kalicin MH, Newman ME (2004) Tree species do not influence local soil chemistry in a species-rich Costa Rican rain forest. Journal of Tropical Ecology 20: 587-590
Reed SC, Cleveland CC, Townsend AR (2008) Tree species control rates of free-living nitrogen fixation in a tropical rain forest. Ecology 89: 2924-2934
Reich PB, Oleksyn J, Modrzynski J, Mrozinski P, Hobbie SE, Eissenstat DM, Chorover J, Chadwick
OA, Hale CM, Tjoelker MG (2005) Linking litter calcium, earthworms and soil properties: a common garden test with 14 tree species. Ecology Letters 8 (8): 811-818
Rhoades CC (2006) The influence of American Chestnut (Castanea dentata) on nitrogen availability, organic matter and chemistry of silty and sandy loam soils. Pedobiologia 50 (6): 553-562
Rhoades CC, Eckert GE, Coleman DC (1998) Effect of pasture trees on soil nitrogen and organic matter: implications for tropical montane forest restoration. Restoration Ecology 6: 262-270
Rhoades CC, R.L. Sanford J, Clark DB (1994) Gender dependent influences on soil phosphorus by the dioecious lowland tropical tree Simarouba amara. Biotropica 26: 362-368
Riha, S.J., B.R. James, G.P. Senesac, and E. Pallant (1986) Spatial variability of soil pH and organic matter in forest plantations. Soil Science Society of America Journal 50: 1347-1352
Rossi BE, Villagra PE (2003) Effects of Prosopis flexuosa on soil properties and the spatial pattern of understorey species in arid Argentina. Journal of Vegetation Science 14 (4): 543-550
Ryan, P.J. and J.W. McGarity. 1983. The nature and spatial variability of soil properties adjacent to large forest eucalypts. Soil Science Society of America Journal 47: 286-293.
Schade JD, Hobbie SE (2005) Spatial and temporal variation in islands of fertility in the Sonoran Desert.
Biogeochemistry 73: 541-553
Schroth AW, Friedland AJ, Bostick BC (2007) Macronutrient depletion and redistribution in soils under conifer and northern hardwood forests. Soil Science Society of America Journal 71 (2): 457-468
Seastedt TR, Adams GA (2001) Effects of mobile tree islands on alpine tundra soils. Ecology 82: 8-17
Sedia EG, Ehrenfeld JG (2006) Differential effects of lichens and mosses on soil enzyme activity and litter decomposition. Biology and Fertility of Soils 43 (2):177-189

Sharma R, Dakshini KMM (1991) A comparative assessment of the ecological effects of Prosopis cineraria and P. juliflora on the soil of revegetated spaces Vegetatio 96: 87-96
Shiels AB and Sanford RL. 2001. Soil nutrient differences between two krummholz-form tree species and adjacent alpine tundra. Geoderma 102: 205–217.
Ste-Marie C, Pare D, Gagnon D (2007) The contrasting effects of aspen and jack pine on soil nutritional properties depend on parent material. Ecosystems 10 (8):1299-1310
Su YZ, Zhao HL, Li YL, Cui JY (2004) Influencing mechanisms of several shrubs on soil chemical properties in semiarid Horqin Sandy Land, China. Arid Land Research and Management 18 (3):
251-263
Thompson DB, Walker LR, Landau FH, Stark LR (2005) The influence of elevation, shrub species, and biological soil crust on fertile islands in the Mojave Desert, USA. Journal of Arid Environments
61 (4):609-629
Tiedemann AR, Klemmedson JO. 1973. Effect of mesquite on physical and chemical properties of the soil. Journal of Range Management 26: 27-29
Turner DP, Franz EH (1985) The influence of western hemlock and western redcedar on microbial numbers, nitrogen mineralization, and nitrification. Plant and Soil 88: 259-267
Vinton MA, Burke IC (1995) Interactions between individual plant species and soil nutrient status in shortgrass steppe. Ecology 76 (4): 1116-1133
Wang FM, Li ZA, Xia HP, Zou B, Li NY, Liu J, Zhu WX (2010) Effects of nitrogen-fixing and nonnitrogen-fixing tree species on soil properties and nitrogen transformation during forest restoration in southern China. Soil Science and Plant Nutrition 56 (2): 297-306
Washburn CSM, Arthur MA (2003) Spatial variability in soil nutrient availability in an oak-pine forest: potential effects of tree species. Canadian Journal of Forest Research 33:2321-2330
Weiss L, Shiels AB, Walker LR (2005) Soil impacts of bristlecone pine (Pinus longaeva) tree islands on alpine tundra, Charleston Peak, Nevada. Western North American Naturalist 65: 536-540
Wezel A, Rajot JL, Herbrig C (2000) Influence of shrubs on soil characteristics and their function in
Sahelian agro-ecosystems in semi-arid Niger. Journal of Arid Environments 44 (4): 383-398
Whitford PC, Whitford PB (1978) Effects of trees on ground cover in old-field succession. American
Midland Naturalist 99: 435-443
Wick B, Tiessen H (2008) Organic matter turnover in light fraction and whole soil under silvopastoral land use in semiarid Northeast Brazil. Rangeland Ecology & Management 61: 275-283
Wieder WR, Cleveland CC, Townsend AR (2008) Tropical tree species composition affects the oxidation of dissolved organic matter from litter. Biogeochemistry 88 (2): 127-138
Wilson B, Growns I, Lemon J (2007) Scattered native trees and soil patterns in grazing land on the
Northern Tablelands of New South Wales, Australia. Australian Journal of Soil Research 45:
199-205
Wilson BR (2002) Influence of scattered paddock trees on surface soil properties: A case study of the
Northern Tablelands of NSW. Ecological Management & Restoration 3: 211-219
Wilson BR, Moffat AJ, Nortcliff S (1997) The nature of three ancient woodland soils in southern
England. Journal of Biogeography 24: 633
Yadessa A, Itanna F, Olsson M (2009) Scattered trees as modifiers of agricultural landscapes: the role of waddeessa (Cordia africana Lam.) trees in Bako area, Oromia, Ethiopia. African Journal of
Ecology 47: 78-83
Yin CH, Feng G, Zhang FS, Tian CY, Tang CX (2010) Enrichment of soil fertility and salinity by tamarisk in saline soils on the northern edge of the Taklamakan Desert. Agricultural Water
Management 97 (12): 1978-1986
Zhang TH, Su YZ, Cui JY, Zhang ZH, Chang XX (2006) A leguminous Shrub (Caragana microphylla) in semiarid sandy soils of north China. Pedosphere 16 (3): 319-325

Zhao et al 2010 Nitrogen and phosphorus transformations in the rhizospheres of three tree species in a nutrient-poor sandy soil. Applied Soil Ecology 46: 341-346
Zinke, P.J. and R.L. Crocker. 1962. The influence of giant Sequoia on soil properties. Forest Science
8: 2-11

Supplemental Methods
Not all studies included in this meta-analysis reported standard deviations associated with measured variables. In this case, the inverse of sample size can be used as a metric of within-study precision, because studies with greater replication can be safely assumed to be more precise (Gurevitch and
Hedges 1999). To examine sensitivity of our results to the metric of within-study error, we re-analyzed our data using 1/N as the metric of study precision for all experiments included in the meta-analysis, including those for which SD was reported. In these analyses, effect size estimates were slightly greater, but highly correlated with estimates derived using SD of the IPE (R
2
= 0.86, P < 0.001). This suggests that our results are highly robust to the assumption that sample size is a good surrogate for within-study error. We also examined the correlation between effect sizes and N pairwise
, or the number of comparisons used to generate each IPE, to test whether effect sizes were systematically larger or smaller in publications that examined a larger suite of species. Finally, we used weighted meta-regressions to determine whether there were systematic changes in effect size over time (i.e. publication year). Effect sizes exhibited non-significant negative correlations with N pairwise and year (see Figure S1b, c below), suggesting that neither the number of plant treatments included in a study nor publication year influenced the magnitude of the IPE.

Table S1 . Mean (and range) of mean annual temperature (

C), mean annual precipitation (mm), and latitude in each ecosystem category used in the meta-analysis.
Ecosystem MAT MAP |latitude|
Desert
Dry forest
Grassland
Tundra
Wet forest
15.4 (9.0 – 21.0) 181 (52 – 375) 25.3 – 41.7
19.2 (14.5 – 27.9) 710 (450 – 1050) 2.75 – 39.25
12.6 (5.7 – 21.0) 377 (259 – 500) 18.1 – 43.0
2.0 (-2.0 – 6.0) 803 (650 – 1000) 8.9 – 43.6
10.5 (0.7 – 26.5) 1319 (490 – 5000) 0.1 – 48.8

Table S2. Back-transformed effect sizes and confidence intervals within each subgroup of the metaanalysis. Effect sizes are presented as % difference between soil properties in Trt
A
vs. Trt
B
.
Subgroup
Effect size Lower limit Upper limit
Grand mean
Soil horizon
40.9 32.8 49.4
Organic
50.4 36.2 66.1
Mineral
40.0 31.9 48.5
Biome
Desert
36.6 14.4 63.0
Dry forest
34.8 20.2 51.2
Grassland
34.3 19.7 50.8
Tundra
50.2 22.7 83.9
33.5 23.5 44.3
Wet forest
Soil property
Al
43.7 3.5 99.6
Bases
81.1 42.8 129.7
Bulk density
22.5 -1.8 52.9
Carbon
42.5 29.7 56.6
Ca
64.9 50.6 80.6
CEC
17.7 0.2 38.3
C:N
30.4 9.2 55.7
EC
127.9 74.2 198.1
K
51.8 37.7 67.3
Mg
46.1 33.0 60.4
Soil moisture
12.1 -0.3 26.1
Na
31.5 13.4 52.6
N (inorganic)
64.0 48.3 81.4
N (total)
48.3 35.1 62.8
Organic matter
44.2 28.7 61.6
P (labile)
57.3 42.5 73.6
P (total)
30.1 13.0 49.7 pH
20.5 12.1 29.6
S
41.0 -5.3 110.0
65.5 30.2 110.4
Zn
Successional stage
Primary
47.0 30.1 66.2
Secondary
47.4 31.9 64.8
24.1 8.7 46.9
Plantation
Matrix type
41.4 26.0 58.8
Grass
None (closed canopy)
38.4 27.0 50.8
Shrubs
26.1 -11.6 80.0
Mineral soil
46.7 30.3 65.2

Figure S1a. Funnel plot showing within-study variances as a function of effect size. b. Relationship between mean effect size and Npairwise, or number of treatment comparisons within a study. c.
Relationship between mean effect sizes and publication year.