The Influence of American Chestnut

ARTICLE IN PRESS Pedobiologia 50 (2007) 553—562 www.elsevier.de/pedobi The influence of American Chestnut (Castanea dentata) on nitrogen availability, organic matter and chemistry of silty and sandy loam soils Charles C. RhoadesÃ US Forest Service, Rocky Mountain Research Station, 240 W. Prospect, Fort Collins, CO 80526, USA Received 28 September 2006; accepted 1 October 2006 KEYWORDS Summary Tree species effects; American chestnut trees once dominated vast areas of deciduous forest in eastern Soil nitrogen cycling; North America, but the exotic chestnut blight almost eliminated the species from Net mineralization; the region. Introduction of blight-resistant American chestnut hybrids will probably Soil texture; start in the next decade after many years of tree breeding. What were the historic Parent material; effects of chestnut on forest soils, and what changes may follow reintroduction of Forest restoration hybrid chestnuts? A site in southern Wisconsin provided an opportunity to examine the effect of chestnut trees on soil properties. At this site, 600 km northwest of chestnut’s historic distribution, naturalized chestnuts have spread throughout an intact mixed-species forest from nine planted trees. The site contains soil developed on a silty loess-mantled ridge that abuts sandier hillslopes, allowing the effects of individual chestnuts to be examined on two soil types. I sampled and analyzed forest floor and mineral soils beneath canopies of individual American chestnuts and the surrounding mixed-species deciduous forest on fine-silt and sandy-loam soil types. On sandy loam soils, total soil carbon (C) and nitrogen (N), inorganic N and net mineralization and nitrification rates were 10–17% higher beneath chestnut canopies compared to soils beneath mixed-species deciduous forest. The pool of total soil N beneath chestnut canopies was positively related to the silt content of the sandy loam soils. In contrast, there were no differences between properties of chestnut canopy and mixed-species deciduous forest soils on the fine silt texture class. On sandy loam soil conditions common throughout the pre-blight distribution of American chestnut, soil biogeochemical processes differ beneath individual chestnut trees relative to a diverse mixture of deciduous species. These findings suggest that widespread chestnut reintroduction has the potential to alter both stand- and watershed-scale processes. Published by Elsevier GmbH. ÃTel.: +1 970 498 1250; fax: 1 970 498 1212. E-mail address: [email protected]. 0031-4056/$ - see front matter Published by Elsevier GmbH. doi:10.1016/j.pedobi.2006.10.003 ARTICLE IN PRESS 554 C.C. Rhoades Introduction tions differed between subcanopy soils beneath a variety of African savanna species and adjacent American chestnut (Castanea dentata [Marsh.] open areas to a greater extent in sandy soils as Borkh.), was a dominant component of the eastern compared to fine-textured soils (Campbell et al., deciduous forest until 1904 when chestnut blight 1994; Charreau and Vidal, 1965; Kamara and caused by Cryphonectria parasitica (Murr.) Bar., Haque, 1992). Cation exchange capacity was lower was introduced to North America (Russell, 1987). in the sandy soils such that subcanopy organic Before the pathogen eliminated chestnut from the matter inputs had greater effect on the size of the forest overstory, chestnut occupied a wide range of exchange complex (Campbell et al., 1994). Simi- landscape positions and soil types and occurred larly, the N2-fixing alder, Alnus crispa (Ait.) Pursh., within many forest associations (Braun, 1950; significantly enriched soil N capital and availability Keever, 1953; Russell, 1987). Throughout much of on sandy, nutrient-poor floodplains but had little its native range, chestnut was an abundant overs- influence in upland sites with silty texture and tory species on xeric ridges and more mesic higher N soils in northwestern Alaska (Rhoades hillslopes and coves (DeFriese, 1884; Hawley and et al., 2001). These studies indicate that ante- Hawes, 1912; Russell, 1987). Chestnut occurred on cedent soil properties that regulate exchange both north- and south-facing slopes and on soils reactions and organic matter dynamics may deter- formed from shale, sandstone, and occasionally mine the imprint of trees on soil biogeochemical limestone parent material (Braun, 1935), though processes. the tree was most common on well-drained, acidic Chestnut blight disease spared few locations soils (Russell, 1987; Stephenson et al., 1991). where it is possible to estimate the potential of Blight-resistant hybrid chestnuts will be available American chestnut to influence biogeochemical for introduction to North American forests within processes and edaphic patterns of forest ecosys- the next decade (Hebard, 2001; McKinstry, 2005). tems. An isolated stand of American chestnut Hybrid chestnuts are generated through a backcross located 600 km beyond the tree’s native range in breeding process that combines blight-resistance southwestern Wisconsin, affords a rare opportunity from Asian chestnuts (C. mollisima or C. crenata) to investigate the effect of chestnut trees on soil with desired growth, form and nut characteristics chemistry and nutrient dynamics (Cummings-Carlson of the American chestnut (Burnham, 1981). Poten- et al., 2002; McEwan et al., 2006; Paillet and Rutter, tial for widespread dissemination of hybrid chest- 1989). Chestnuts radiated from nine planted trees nut provokes questions regarding forest ecosystem throughout 36 ha of mixed hardwood forest and now dynamics and species replacement. Persistence of comprise about 30% of the overstory basal area chestnut logs for a half-century (Hedman et al., (McEwan et al., 2006). Individual chestnuts are 1996; Muller, 2003) combined with the previous adequately dispersed so that soils beneath chestnut abundance of the species suggests that biogeo- crowns can be compared to soils influenced by the chemical characteristics of the American chestnut mixture of species in the surrounding forest. The may have historically influenced soil properties. forest encompasses an abrupt transition between Individual trees alter the biogeochemistry of soils silt loess and sandstone parent materials thus within discrete zones of influence around trees allowing an assessment of the influence of individual isolated in savanna ecosystems (Belsky et al., 1989; American chestnut trees on the soil properties of silt Kellman, 1979) as well as those embedded within and sandy loam soils. In the absence of common- closed-canopy forest (Finzi et al., 1998; Zinke, 1962). garden plantation trials it is impossible to fully Species-level variation in tree effects relate to negate the possibility that effects attributed to differences in the amount and chemical composition individual chestnut may have resulted from a priori of organic matter inputs, in nutrient uptake and in microsite soil differences. However, this disjunct the capacity to fix atmospheric nitrogen, as well as stand provides a worthwhile first estimate of the secondary factors that follow from the effects of potential for chestnut to influence soil properties these differences on soil biota (Binkley, 1995; differently than co-occurring hardwood species. Rhoades, 1997). The resulting diversity of soil conditions has been described as a ‘‘mosaic of profiles reflecting the chemical characteristics of ground Materials and methods cover vegetation and individuals of the various tree species present’’ (Boettcher and Kalisz, 1990). Site description Characterization of tree effects on soil properties must consider species influences along with site The study was conducted in the Driftless Area of conditions. For example, C and cation concentra- southwest Wisconsin, near West Salem (431 570N; ARTICLE IN PRESS American Chestnut effects on distinct soils 555 911 030W). Mean annual precipitation and tempera- native range such as Tilia americana L. and Ulmus ture are 820 mm and 8.5 1C (at La Crosse, 10 km americana L. from site); half the annual precipitation occurs from May to August (NOAA, 2005). This region of bluffs and ravines remained unglaciated during the Sampling and analysis Pleistocene (Albert, 1995). The study area consists of a silt loess-mantled ridge and adjacent sandy Sampling was designed to compare the effects of loam hillslopes formed on sandstone residuum individual chestnut trees on chemical properties of (Hole, 1976; Hole and Germain, 1994). The ridge- the litter layer and surface mineral horizon of two top Greenridge soil series are fine silty (28% sand, soil series with fine silt and sandy loam texture 65% silt and 7% clay) mesic Typic Hapludalfs (NRCS, classes (Table 1). In May 2002, twenty chestnut 2005; Simonson 2006). The sideslope Council soil trees were selected within the two areas mapped series are sandy loam (61% sand, 33% silt and 6% as (1) Greenridge fine silts on the broad central clay) mesic Typic Hapludalfs (Table 1). The ridgetop ridge and (2) Council sandy loams on the surround- Greenridge loess soils also have higher pH, extrac- ing slopes. Crowns of sample trees were contiguous table cations (K+,Ca2+,Mg2+) and total N and C. with adjacent deciduous species, but were at least Montmorillonite is the dominant clay mineral in two canopy heights (430 m) away from the nearest Driftless Area loess soils, with lesser amounts of neighboring chestnut canopy. Sampled chestnuts illite (NRCS, 2005). The textural and mineralogical averaged 44 cm diameter at 1.3 m height, had 4.5 m differences between the loess and

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