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D. Michael Glenn and Michael J. Newell

reduced fruit number and yield ( Tworkoski et al., 1997 ) while increasing branch angle ( Welker and Glenn, 1995 ). Long-term studies in rain-fed peach production demonstrated that sod competition, while reducing pruning weights and sucker weights in most

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James F. Cahill and Eric G. Lamb

, competition, and multitrophic interactions. This is further complicated by the recognition that these factors are themselves dependent on variable climatic conditions and nutrient inputs. In this article, we summarize some recent advances addressing questions

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Justine E. Vanden Heuvel and Carolyn J. DeMoranville

key times of competition among organs through the growing season. Materials and Methods Sample collection. ‘Stevens’, ‘Howes’, and ‘Early Black’ uprights were collected on a weekly basis in 2002 and on a biweekly basis in 2003 and 2004 from State Bog

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David E. Yarborough and Prasanta C. Bhowmik

The competitive effects of bunchberry Cornus canadensis L. on native stands of blueberries Vaccinium angustifolium Ait. was assessed in 1986 and 1987, and in the greenhouse in 1987 with replacement series experiments. In the field, blueberry and bunchberry fruit were harvested in August and all aboveground growth was cut, the species were separated, and dry weight was determined. The relative yield total (RYT), defined as the dry weight (DW) of the combined aboveground portions of the blueberry and bunchberry divided by their respective DW at 100% cover, was >1 and showed an increase with increasing proportion of bunchberry. Blueberry relative yield, defined as the DW of the aboveground portion divided by the DW at 100% cover, was >1, but bunchberry relative yield DW was ≤1. Regression of individual on associate DW yield indicates blueberry is as aggressive as bunchberry. Blueberry fruit count and yield decreased with increasing bunchberry density. In the greenhouse study, plant count and cover were assessed weekly, and leaf area index (LAD and DW were obtained at the end of the study. RTY > 1, and combined DW increased with increasing proportion of bunchberry. The LAI of blueberry or bunchberry was higher in mixtures than in pure stands. Blueberries are competitive with bunchberry, but in native fields, open areas among clones allow faster growing bunchberry to spread without competition.

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Joshua I. Adkins, Joshua H. Freeman and Stephen M. Olson

linear increase in triploid yield in response to the lower competition. The degree of competition from in-row pollenizers grown in the commercially common arrangement where pollenizers are placed equidistant from neighboring triploids has not been

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R. Kjelgren and L.A. Rupp

We investigated how shelters and competing herbaceous vegetation affected tree growth and water relations during establishment. A bunch-type forage grass was concurrently seeded around 1-year-old bigtooth maple (Acer grandidentatum) and gambel oak (Quercus gambelii) planted in a silt loam field soil. During the second year following planting, irrigation was withheld, and midday water potential was measured twice to determine differences in water stress. At the end of the season, we measured total survival, elongative growth, and leaf area, as well as root growth of trees without competition. In the presence of competing vegetation, trees in shelters were less water stressed by –1.0 MPa than those without shelters. All maples without shelters and with competition died, and oak survival was 28%. Survival of both species in shelters was 86%. All trees without competing vegetation survived, but shelters affected maples differently than oaks. Maples without shelters had multiple stems that resulted in less shoot elongation and coarse roots but higher leaf area than those in shelters, and there were no differences in midday water potential. By contrast leaf area, elongation, and root growth of oaks in shelters were not different from those without shelters, but water potential was less negative. Tree shelters mitigated the effects of competition during establishment, but overall growth in shelters varied with species as oaks did not grow as well as maples.

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D. M. Glenn and W. V. Welker

The effect of ground covers on water uptake was studied using peach trees grown in a 4-part split root system. In 1992, one section of the root system was in bare soil and 3 sections were in combination with `K-31' tall fescue. In 1993, K-31 was eliminated in 2 additional sections, leaving 1 section in combination with `K-31'. When grass transpiration was suppressed by covering the K-31, tree water uptake/cm of root length was greater in the presence of grass compared to bare soil under well watered conditions. These data indicate that peach trees compensate for interspecific competition by increasing root hydraulic conductivity.

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Mary Hockenberry Meyer and Joe Paul

Many different vegetatively propagated cultivars of Miscanthus sinensis Anderss. are popular ornamental grasses sold at garden centers and nurseries. Large stands of the “wild type” or species (not ornamental cultivars) of this grass have self-seeded near Asheville, N.C.; Valley Forge, Pa.; and Washington, D.C. In order to document the competitive ability of this self-seeded naturalized species, a greenhouse competition study was conducted with Panicum virgatum L. `Forestburg' (P), switchgrass, and several non-native, naturalized biotypes of Miscanthus sinensis (M) grown from seed collected from the above locations. Seedlings were transplanted into #1 (2.88 L) containers in nine different planting arrangements: 2M; 4M; 8M; 2M2P; 4M4P; 8M8P; 2P; 4P; 8P, and grown for 15 weeks. Growth measurements were taken during the 15 weeks. At harvest, shoot and root dry weights were calculated. Panicum had significantly larger root (0.50 g vs. 6.00 g) and shoot (6.96 g vs. 2.3 g) biomass, respectively, than Miscanthus. Intraspecific competition in monocultures was significantly higher for Panicum than Miscanthus. Panicum showed higher competitive ability than all Miscanthus biotypes, with one exception: root dry weights of one Pennsylvania biotype. Panicum increased in dry weight at the expense of Miscanthus. Panicum dominated Miscanthus during the 15 weeks and, in this study, proved to be a better competitor than Miscanthus. Miscanthus and Panicum did not fully share the common limiting resources and they showed partial resource complementarity. Miscanthus biotype variation was evident; the highest dry weights were from a Pennsylvania biotype and the smallest weights were from a Washington, D.C., biotype.

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Tijana Blanusa, Eleni Vysini and Ross W.F. Cameron

water availability enhanced efficiency of flower production ( P = 0.001). Petunia plants that experienced both reduced water supply and competition within the container produced significantly more flowers/g dry weight (5.4) than well-watered, single

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Thomas Tworkoski

Peach [(Prunus persica (L.) Batsch., `Rutgers Redleaf'] trees were grown for two seasons in a greenhouse with three pruning treatments (none, shoot tips removed, and half the shoots removed) and three grass treatments (no grass competition; perennial ryegrass, Lolium perenne L., `Linn'; and tall fescue, Festuca arundinacea Schreb, `Kentucky 31'). Competing grass reduced shoot growth, leaf area, and weight of fine roots in shallow soil, but did not affect the growth response to pruning. Regrowth from pruned trees was such that the shoot: root ratio was restored to that of unpruned trees. Leaf water potential, stomatal conductance, and photosynthesis had decreased markedly by 48 hours after irrigation ceased in trees without competition (larger trees) and to a similar level by 96 hours in trees with competition (smaller trees). Apparently, the reduced leaf area of peach trees grown with grass competition delayed water stress. Leaf abscisic acid levels were not directly affected by grass competition but increased as leaf water potential decreased. Grass competition modified morphology and reduced tree size, but did not affect shoot growth following pruning.