The impact of invasive plant species on native plants is largely assumed to be negative, but supporting evidence is sparse. A common control method of non-native plants is herbicide application, but little is known about the effects of these chemicals on non-target plant populations, or differences in these populations before and after control measures are taken. We examined the response of the forest floor plant community to herbicide-mediated reduction of Alliaria petiolata in an old-growth and a second-growth forest stand in Hueston Woods State Park, Preble and Butler Counties, OH. Fifty 1 × 1 m plots were established in each stand, and 25 plots per stand were treated with Round-up© each November 2000–2004, which reduced cover of adult Alliaria petiolata but did not suppress recruitment. Percent cover of herbs and woody plants ≤0.85 m tall was assessed in May and June, 2000–2005. To determine compositional differences between sprayed and unsprayed plots in each stand we ordinated plots based on peak cover of each species using nonmetric multidimensional scaling, tested for differences in community composition with a multiple response permutation procedure, and compared total cover of growth forms with Kruskal-Wallis tests.

Five years of Alliaria petiolata control only modestly affected the forest floor vegetation. Neither species richness nor diversity differed significantly between sprayed and unsprayed treatments in any year of the study. Community composition differed each year between stands, but treatments differed significantly only in 2002 (in the second-growth stand), and marginally in 2004 and 2005 (in the old-growth stand). Treatment affected cover of some growth forms during the study, but only in some years: in the second-growth stand sprayed plots had significantly greater cover of spring perennials and graminoids in 2003 and marginally lower cover of annuals in 2005; in the old-growth stand sprayed plots had marginally more spring perennials in 2005. Wintergreen species, particularly the exotic annual Stellaria media, had lower cover in sprayed plots in the old-growth stand in 2005. We attribute the compositional differences we observed in the forest floor community to competitive impacts of Alliaria petiolata, but suggest that effects were modest due to the persistence of rosettes in the sprayed plots.

Competitive hierarchy for four common old-field plant species depends on resource identity and availability. J. Torrey Bot. Soc. 134: 166–176. 2007.—Competition is an important factor structuring plant communities. Competitive hierarchies may facilitate prediction of the outcome of interactions among multi-species mixtures, but their utility depends upon invariance along environmental gradients. We examined interactions among four common old-field herbaceous dicots (Dactylis glomerata, Festuca elatior, Trifolium pratense, Plantago lanceolata) with pairwise monoculture and polyculture competition experiments at two levels each of light and water. We constructed competitive hierarchies for unique treatment combinations based on competitive effect and response scores. Biomass production and relative yield were affected by presence and identity of neighbor species and inter- and intraspecific competition were typically not distinguishable. Competitive effect and response scores were inversely correlated, but depended on treatment factor as well as levels within factors. Competitive rankings among these four common plant species varied along resource gradients, although the extreme ends of the hierarchy were relatively stable: under most conditions P. lanceolata was most competitive whereas F. elatior was least competitive. Results lay the groundwork for assessments of multispecies mixtures under field conditions along broader environmental gradients.

We examined the ability of Houstonia montana, a rare plant endemic to the Southern Appalachians, to grow in two markedly different habitat types. Most known populations of H. montana occur on rock outcrops with little soil development and sparse vegetation. In contrast, a few populations occur on grassy slopes with continuous soils and dense surrounding vegetation. We compared growth and life-history traits of two rock-outcrop and two grassy-slope populations. Houstonia montana was a dominant vascular plant species in all four sites, with 20–37 % ground cover on grassy slopes and 4–6% on rock outcrops. Growth began earlier in the season and plants were taller on grassy slopes than on rock outcrops. In contrast, reproductive potential, numbers of leaves, and ratios of leaves:height were markedly higher in one grassy slope site but showed no consistent pattern between habitats. Foliar nitrogen:phosphorus ratios varied widely and indicated N limitation in at least one grassy slope site and P limitation in one rock outcrop site. However, mycorrhizal colonization did not differ between habitat types. Houstonia montana exhibited variation in growth and nutrition across sites that may be unexpected for an apparently stress-tolerant plant. Our results suggest that the ability of H. montana to thrive in grassy sites depends upon rapid early-season growth, and they also raise questions about potentially important genetic variation among populations.

We investigated the spatial patterns of several woody species that colonize disturbed sites, including the native Juniperus virginiana and the exotic Lonicera maackii. Our study site was on a road cut in northern Kentucky, USA, that faced NW and consisted of nine contiguous 25-m² quadrats. The positions of all woody plants ≥ 50 cm in height were measured. Spatial patterns were quantified and compared with Ripley's K and the pair correlation function, which analyze the distribution of interplant distance at varying scales. For each woody plant, we also measured height, soil depth, and photosynthetically active radiation (PAR); the latter two measurements were taken at the four cardinal directions. Ripley's K showed that J. virginiana was distributed randomly, while L. maackii was clustered. Both J. virginiana and L. maackii were distributed independently of each other. Smaller L. maackii individuals clustered with larger ones, but this pattern was not seen in J. virginiana. Neither species appeared to associate with the other species. Mann-Whitney tests showed that L. maackii was found in areas of lower light than J. virginiana but there was only a weak indication of differences in soil depth means between these two species. These two species colonize disturbed sites in very different manners. L. maackii potentially facilitates establishment of its own species, whereas J. virginiana seedlings can only establish at some distances from parent trees. The different physiological requirements and growth forms of the two species appear to explain the lack of interaction between them. Though this project was limited to one study site, the methods can be used for multiple site analysis or on sites of varying size.

Stand reconstruction, using live trees and deadwood, provided a four to five hundred year recruitment history for the current stand structure in dry fir-pine forests of northern Washington, USA. The lengthy structural record indicated these dry fir-pine forests were resilient to change, that all forest conditions were transient, and that forests were currently transitioning away from maximum tree density levels. Historically, frequent fires maintained low tree abundance, but fire cycles lengthened in the 1860s as Euro-settlement progressed. Average stand density had already increased to 194% (SD  =  116) of 1860 levels by the start of effective fire suppression in 1915. From the 1930s to 1960s, average stand density peaked at 258% (SD  =  98) of 1860 levels. By 2000, tree mortality in these overstocked stands had reduced average stand densities to 68% (SD  =  19) of maximum levels. However, tree densities in 2000 still averaged 173% (SD  =  64) above historical levels. Although there had been significant tree recruitment and a century without fire, the trees present in the historic stands provided 75% (SD  =  13) of the basal area in 2000. Numerous understory (< 7.6 cm dbh) trees (252 trees/ha, SD  =  97) were present in 1860 stands and these trees contributed more basal area than the historic overstory in 2000. In the absence of fire and without human intervention, the sampled stands have decreased in overall tree density from maximum levels while representation of shade-tolerant species, range and evenness of age-class structure, and abundance of old forest (live tree and deadwood) legacies have increased.

This study relates contemporary patterns of species composition, stand structure, and tree regeneration in a mature western Indiana forest, Kieweg Woods, to the complex of Euro-American settlement impacts and regional environmental change. We established permanent plots at this 5 ha flat upland site to initiate a long-term program of forest monitoring; this paper reports on the results of the first stand census, as well as placing them in historical context by examining both General Land Office survey records for the surrounding landscape and the dendrochronology of several of the stand's mature trees. Reconstruction of presettlement vegetation indicates that this site was transitional between open Quercus-Carya assemblages found at the margins of prairie and the more mesophytic Fagus grandifolia-Acer saccharum forests associated with the dissected topography of the Wabash River valley. Contemporary stand composition reflects this mix of species, but with Quercus spp., Carya spp. and Liriodendron tulipifera dominating the canopy and Acer saccharum and Fagus grandifolia comprising most of the subcanopy. Dendrochronological analysis indicates that the largely shade-intolerant canopy members were recruited during a major growth release in the late nineteenth century, probably due to logging, while the subcanopy has formed under a regime of minimal disturbance. These patterns suggest an impending successional turnover in canopy composition, and highlight the role of settlement impacts in remnant forests as having altered the presettlement linkages among disturbance and site conditions, and thereby reformulated the set of species' life history characteristics best suited to dominance in the contemporary landscape.

Although fire exclusion is thought to be linked with declining plant diversity in oak forests, few studies have examined long-term changes in their shrub and ground layers resulting from repeated burning. In this study, we compare the composition and structure of woody understory and ground layer vegetation in burned and unburned oak forest after 17 years of annual dormant season low-intensity burns. Over time, burned forest had 97% reduction of shrubs and small saplings, but only 38% loss of stems in the > 5–10 cm size class. Canopy openness was similar in burned and unburned forest plots prior to the onset of burning, but it was significantly greater in burned forest after 17 years of fire. Ground layer vegetation structure also changed significantly, with responses differing by guilds. Spring herbs were the dominant guild before burning and did not change over time. However, cover and abundance of summer herbs increased over time in burned forest, probably in response to greater light assimilation under the more open canopy. This resulted in greater overall species richness in burned plots without loss of the spring herbs. Burning eliminated most alien shrubs, although common buckthorn persisted in small numbers. The alien herb garlic mustard also persisted and had greater abundance in burned plots, apparently by re-colonizing from unburned micro-habitats and adjacent forest. These results indicate that long-term burning can eliminate shrub and small sapling canopy cover, thereby increasing canopy openness and promoting greater richness and cover of summer forbs. Fire also probably had a positive effect on seedling establishment through removal of litter. Resulting tradeoffs to this gain in diversity include loss of native vines, shrubs, understory trees and forest interior bird habitat, as well as persistence of alien plants.

In 2004 we remeasured trees in 42 permanent vegetation plots that had been established in Adirondack spruce-fir, northern hardwood, and pine-dominated stands in 1984. Over the 20-yr interval, live basal area (BA) in red spruce and/or balsam fir-dominated plots decreased by 15%. Blowdown was a major cause of balsam fir, but not red spruce mortality in two plots. Excluding the two blowdown plots, balsam fir live BA increased by 17%, while red spruce live BA decreased by 42% (P < 0.05). There was no significant change in the overall live BA of northern hardwood plots. However, excluding beech, the pooled northern hardwoods showed a significant decrease (P ≤ 0.05) in live BA over the 20-yr interval. In contrast to the spruce-fir and northern hardwood plots, the live BA of pine-dominated plots increased by 19% over the 20-yr interval (P ≤ 0.01). Changes in sapling densities in the spruce/fir plots were not significant, though fir in the 2–9.9 cm dbh class reached densities of > 3000 stems ha⁻¹ in four plots where they filled large gaps. There was a trend toward increased red spruce sapling density (P ≤ 0.10) in the upper northern hardwood zone (600–950 m). Sugar maple sapling density and BA decreased significantly (P ≤ 0.05) in the northern hardwood plots during the twenty-year interval.

We conducted a biogeochemical analysis of four Adirondack northern hardwood forests (two old-growth and two maturing second-growth) to elucidate correlations among stand age, site conditions and several nutrient cycling processes. One each of the old-growth and maturing forests were located on base-rich sites, while the other two were on base-poor sites. At each site we analyzed soil solution chemistry and estimated nutrient flux rates; measured annual litter production, and nutrient and lignin content; measured annual N mineralization and nitrification rates; and characterized herb- and canopy-layer vegetation, and coarse woody debris volumes. Vascular plant communities of the two base-rich sites were dominated by several rich-site indicator species, while such indicators were lacking at the base-poor sites. Tree basal areas and annual litter production did not differ among the study sites, but the old-growth stands contained 3-fold more coarse woody debris than the maturing stands. Foliar litter N concentrations did not differ among the study sites, but foliar litter from the base-rich sites had higher Ca² and lower lignin concentrations than the base-poor sites. Differences in foliar litter quality among the sites were due, in part, to intraspecific variation in litter chemistry. There were no consistent differences between the old-growth and maturing stands in soil solution nutrient concentrations or fluxes. Soil solution H concentrations were higher and Ca:Al ratios lower at the two base-poor sites. Annual, net N mineralization rates did not differ among the sites, but net nitrification rates in the organic soil horizons at the rich old-growth site were more than twice those at the other sites. High levels of net nitrification and N leaching were observed only in the base-rich old-growth site. Our data suggest that net forest nutrient retention may be a function of interacting mechanisms associated with forest developmental stage, community composition and site conditions.

The objective of this study was to assess nutrient losses, via soil solutes, from discrete zones of recent, single-tree gaps in an old-growth, northern hardwood forest. Growing season flux rates of all solutes did not differ between the “undisturbed” zones (areas 5 m away from gap-making trees) and “crownfall” zones (areas associated with fallen tree crowns) of the twelve tree-fallgaps we studied. Under assumptions of partial root gap formation (50% root mortality), total cation and anion fluxes were 2-fold greater, and DON and total N fluxes were 2- to 3-fold greater in the “proximate” zones (areas 0–2 m from stumps of snapped, gap-making trees) compared to the crownfall and undisturbed zones. The “pit” zones (areas of disturbed soil associated with tipped-up trees) exhibited 3- to 6-fold greater NH₄ , NO₃⁻, and total dissolved N fluxes, and 2-fold greater total cation and anion fluxes than the undisturbed and crownfall zones. We estimated that proximate and pit zones associated with both recent and old tree-fall gaps accounted for 12% and 0.3%, respectively, of the total stand area in this old-growth forest. At the stand level, root throw pits contributed < 1% of the estimated NO₃⁻, total dissolved N, total cations and total anions leaching from the system. Under assumptions of partial root gap formation proximate zones contributed 24–27% of the flux of these solutes. We conclude that the pit zones were inconsequential for nutrient loss and, while proximate zones contributed substantially more to nutrient losses from this system, the majority of nutrients leached from this system (∼ 75%) were leached from undisturbed forest zones. Our results indicate that efforts to account for mechanisms of nutrient loss from old-growth forests must consider variation in leaching rates associated with discrete microenvironments within gaps, and focus greater attention on nutrient retention capacity of the live, intact forest matrix.

The pinyon pines (Pinaceae, Pinus subsections Cembroides and Rzedowskianae) are a widely distributed group of site generalist species that dominate many of the middle to upper elevation semi-arid regions of North America. We investigated the physiological and morphological response of Pinus cembroides var. bicolor Little across an elevational gradient in the Davis Mountains of west Texas to test the hypothesis that variability in needle morphology, relative water content, and transpiration allow this species to exist across a range of elevations and local site conditions. Results from our study showed significant increases in P. cembroides needle length, mass, and area and plant water status (relative water content and transpiration) with elevation. Our findings suggested that this species is able to adapt to changes in local environment over short distances, which is an important factor responsible for the wide distribution of pinyon pines in North America.

Two hundred and sixty-one vascular plant species were documented for Yucca House National Monument and surrounding lands including seven new records for Montezuma County. This work was part of a biological inventory throughout the National Park Service as part of the Natural Resource Challenge, a legislative and administrative mandate. The study area is in the Montezuma Valley, where most land is in private or tribal ownership, and opportunities for plant surveys are limited. The flora includes three species tracked by the Colorado Natural Heritage Program: Centaurium exaltatum (Griseb.) W. Wight ex Piper (desert centaury), Penstemon breviculus (Keck) Nisbet & R.C. Jackson (shortstem beardtongue), and Penstemon lentus Pennell (handsome beardtongue).

Plant anatomists are generally agreed on the histological products of successive cambia: bands of secondary phloem and associated secondary xylem (“vascular increments”) embedded in a background of conjunctive tissue (parenchyma, sometimes fibers). Interpretations have varied widely on the ontogeny of this plan. Studies have usually involved one or a few species. The study of numerous taxa, especially in centrospermoid families, leads to the conclusion that there is a common plan, although variations on it are manifold. A master cambium produces secondary cortex externally and, internally, rays, conjunctive tissue, vascular cambia, secondary phloem, and secondary xylem. Secondary phloem and secondary xylem are formed from the vascular cambium in each vascular increment. Vascular cambia function indefinitely, so that a master cambium and a series of vascular cambia (each in a vascular increment) function indefinitely. The master cambium either remains active as long as an axis is actively growing (although it may become quiescent following the initiation of each vascular increment and associated conjunctive tissue), or, less commonly, may be reinvented in the secondary cortex. In order to establish a framework for interpretations, the varied appearances of each of these tissues in genera that have successive cambia is discussed. Themes that particular genera represent are then examined: diversification in ray types and raylessness (Nyctaginaceae); diversification in conjunctive tissue (Aizoacaeae); rays as key structural elements (Gnetaceae); successive cambia as an apomorphy (Chrysanthemoides); protraction of cambial activity (Menispermaceae); and cambial fracture and parenchyma proliferation (Bauhinia, Mendoncia). In some taxa, such as Gnetum africanum and the large tropical lianas (Bauhinia, Menispermaceae) a master cambium is absent; new vascular cambia arise by one or a few cell divisions in cortical parenchyma, followed by rapid tangential widening of the vascular cambium. Pervasive ecophysiological themes in plants with successive cambia are examined: storage and retrieval; promotion of mechanical strength and longevity of vascular tissues; and modes of lianoid structure. Because the background tissue in plants with successive cambia is conjunctive tissue, not secondary xylem, the terms “included phloem: and “interxylary phloem” are inapplicable. The term “lateral meristem” is abandoned in favor of “master cambium.”