Trees affect soil chemistry and nutrient availability via a broad range of processes. Effects can vary dramatically among species, whose distinctive spatial “footprints” can vary for different nutrients. Potentially overlapping effects of neighboring trees in mixed-species stands make footprint shape and interspecific interactions important: If interactions are non-additive, then not only abundance but also spatial configuration influence tree species’ effects on ecosystem properties. We used spatially explicit neighborhood-scale data on tree distributions to fit maximum likelihood models of exchangeable calcium, magnesium, and potassium in surface soils of four sites in northern hardwood forests in northwestern Connecticut, USA. The models incorporated parent material, site, and tree species or functional group configuration to predict availability of the three cations. Site had a stronger effect than species for all cations (there was no species effect for potassium), even after accounting for variation in parent material. Species’ spatial footprints extended further from the stem for calcium than magnesium, which is consistent with the relative importance of litterfall versus stemflow transfer of these nutrients. The magnitude of species effects on calcium and magnesium varied widely. Functional groups made up of species with positive or negative effects provided parsimonious models for magnesium and calcium, and the best model for calcium included a non-additive, antagonistic effect whose strength varied by site. This non-additive effect suggests that the degree of intermingling of tree species from negative- and positive-effect functional groups may influence stand-level availability of calcium, a key nutrient for forest health in these ecosystems.
Soil Sample Data with 4 Site Codes
Soil Sample Data documentation.
137 records, each representing a point at which soil samples were obtained.
Variables are "SITECODE", "SITENUM", "TDIST" (m), "X" (m), "Y" (m), "EL.CA.MOL" (mol/m2), "EL.MG.MOL" (mol/m2), "EL.K.MOL" (mol/m2), "EX.CA.MOL" (mol/m2), "EX.MG.MOL" (mol/m2), "EX.K.MOL" (mol/m2)
"SITECODE", values 1-4, is code indicating area of landscape where samples were taken. In the accompanying manuscript, corresponding locations and codes are 1=Camps Pond (A), 2=Wangum (D), 3 = #4 Trail (B), 4 = Backgate (C).
"SITENUM", values 1-104 (not inclusive). SITENUM 1-18 and 52-95 are at Camps Pond. SITENUM 19-30 are at Wangum, SITENUM 31-36 are at #4 Trail. SITENUM 101 is at Backgate, and SITENUM 104 is at #4 Trail.
"TDIST" indicates distance along transect, in meters. SITENUM 101 consists of two parallel transects: the first transect has distances from 0-100, and second, from 200-300 (i.e., the different transect is indicated by adding 200 to each distance along it). SITENUM 104 consists of a single 200 m transect with soil sample sites at 5 m intervals. Every record is defined by a unique combination of "SITENUM" and "TDIST".
"X" and "Y" are xy coordinates (in m) where soil sample was taken. There is a unique XY coordinate reference system at each value of "SITENUM".
"EL.CA.MOL" (mol/m2), "EL.MG.MOL" (mol/m2), "EL.K.MOL" (mol/m2), "EX.CA.MOL" (mol/m2), "EX.MG.MOL" (mol/m2), "EX.K.MOL" (mol/m2) are values of exchangeable calcium, magnesium and potassium.
Tree Map Data Checked 2015
The file "Tree Map Data Checked 2015.txt" provides tree map data for plots where soil samples were taken.
Variables are "SITENUM", "X" (m), "Y" (m), "Z" (m), "DBH" (cm), and "SPECIES".
It has original site numbers (not grouped into 4 sites, and not numbered consecutively).
1:18 - Camps Pond
19:30 - Wangum
31:36 - #4 Trail
51-98: Sites originally sampled by Feike Dijkstra, n=18, all at Camps Pond
104: Transect #1 at #4 Trail
101: “Back Gate” transects #1 and #2
X, Y, and Z are local tree-location coordinates. Each SITENUM has a common coordinate reference system.
DBH is tree's breast-height diameter.
SPECIES is a four-letter acronym that is a concatentation of the first two letters of the genus and species. Acronyms and associated species are given below
"species","binomial"
"acpe","Acer pennsylvanica"
"acru","Acer rubrum"
"acsa","Acer saccharum"
"beal","Betula alleghaniensis"
"bepa","Betula papyrifera"
"bepo","Betula populifolia"
"crb","Crataegus brainerdii"
"caca","Carpinus caroliniana"
"caov","Carya ovata"
"fram","Fraxinus americana"
"fagr","Fagus grandifolia"
"havi","Hammamelis virginiana"
"masy","Malus sylvestris"
"osvi","Ostrya virginiana"
"pran","Prunus angustifolia"
"pprr","Picea rubens
"prse","Prunus serotina"
"pist","Pinus strobus"
"qual","Quercus alba"
"quru","Quercus rubra"
"tsca","Tsuga canadensis"