03gerhold

Gerhold: Species Response to Tree Shelters SPECIES DIFFER IN RESPONSES TO TREESHELTERSby Henry D. Gerhold Abstract. Effects of tree shelters on height, caliper, and di- cated in USDA Hardiness Zone 6. Seven species and ameter at breast height of 11 landscape tree species and cul- cultivars were planted in 6-tree plots, replicated in 3 tivars were investigated in 2 nurseries during a 4-year randomized complete blocks. Tubex® tree shelters 8 period; the ratio of height to caliper was calculated as an to 11 cm (3.1 to 4.5 in.) in diameter and 1.5 m (5 ft) indicator of trunk sturdiness. Species differed greatly in in height were placed over 3 trees in a subplot; the their responses, ranging in the fourth year from none to 44% other 3 trees served as controls. After the second and 55% height increases of Magnolia ‘Merrill’ and M.
stellata accompanied by 18% and 14% caliper increases. Acer growing season, shelters were removed from 2 trees griseum, Carpinus caroliniana, Cercis canadensis, Cornus in each subplot and from the remaining tree after the ‘Celestial’ and ‘Constellation’, Prunus serrulata ‘Kwanzan’, and P. subhirtella autumnalis exhibited more modest height Trees in Experiment 2 were planted in April and increases, but also caliper decreases, compared to controls May 1995 at Nittany Trees nursery in central Penn- without shelters. Malus ‘Adirondack’ and Syringa reticulata sylvania, near the border of USDA Hardiness Zones ‘Summer Snow’ did not benefit. Two shelter sizes and severe 5 and 6. Nine species or cultivars were planted in 9- winter weather also affected the results of some varieties.
tree plots, replicated in 3 randomized complete Key Words. Landscape trees; nursery; tree shelters; ac- blocks. Two sizes of Tree Pro Sr.® Tree Protectors were used, 9 cm (3.5 in.) and 18 cm (7 in.) in diam-eter, both 1.5 m (5 ft) in height; each size was placed Tree shelters may be able to accelerate the growth of over 3 trees in a subplot, leaving 3 trees as controls.
certain species that are compatible with overhead Shelters were removed after the second or third utility lines. If their slow growth and branching habit growing season, as they had been at Root’s Nursery.
could be improved, the limited number of species Trees were measured every year after summer suitable for planting under wires could be amplified.
growth was complete: total height, caliper at 15 cm A previous article (Witmer et al. 1997) discussed the (6 in.) above ground, and diameter at 137 cm growth responses of 14 species and cultivars grown (4.5 ft). An indicator of trunk sturdiness was calcu- in tree shelters for 1 or 2 years in 2 nurseries. Two lated by dividing caliper by height.
years later, the trees nearly had attained marketable Analyses of variance were conducted in which sizes, so that final results of the experiments can be blocks, tree varieties, and shelter treatments within varieties were the main sources of variation.
Other studies of tree shelters in nursery environ- Duncan’s New Multiple Range Test was used to sepa- ments have been conducted in California (Burger et rate means at the 0.05 significance level.
al. 1992; Burger et al. 1996; Burger et al. 1997). Themost common use of tree shelters has been in forest conditions (Brissette 1995), but they also have been Statistically significant differences were detected employed in urban situations (Jones et al. 1995).
among varieties and among tree shelter treatmentsnested within varieties (Table 1). These occurred in all years in measurements of height, caliper, and diam- The earlier report on the 2 experiments (Witmer et eter at breast height. Blocks and interactions of blocks al. 1997) described materials and methods com- with varieties and treatments had much smaller ef- pletely, so only the main features are repeated here.
fects, which were nonsignificant in most cases.
Trees in Experiment 1 were planted in May 1994 Three species suffered severe dieback and mortal- at Root’s Nursery in southeastern Pennsylvania, lo- ity presumably due to low winter temperatures: Acer Journal of Arboriculture 25(2): March 1999 Table 1. Results of analyses of variance in height, cali- from the tops of the shelters. In subsequent per, and diameter at breast height at Root’s Nursery and years, the height advantages became smaller.
Beneficial effects on heights of the 2 magnolias at Root’s Nursery and Carpinus caroliniana in thelarger shelters at Nittany Trees were especially dramatic, and the height advantage persisted af- ter removal of the shelters. Acer griseum and Cercis canadensis also retained a height advan- tage after the fourth growing season.
Harsh winters presumably caused some die- back in 1996 or 1997 at Nittany Trees. Practi- cally all of the affected trees were within shelters: 4 of 9 Carpinus trees in each of the shelter sizes, 8 of 9 Magnolia trees in each of the shelter sizes, 3 of 9 Cornus ‘Celestial’ trees in small shelters, and 2 of 9 Cornus ‘Constellation’ The caliper growth of trees in shelters was greatly depressed by the end of the second growing season in most cases (Table 3). The 2 magnolias were an exception at both nurseries, even though their height growth as a percentage * = significant at 0.05% level.
ns = nonsignificant.
Table 2. Heights of trees (feet) grown for the first 2 years at Root’s Nursery in 9-cm (3.5-in.) shelters and at Nittany Trees in 9- and 18-cm (3.5- and 7-in.) shelters, compared to trees grown all 4 years without shelters (percentage of control).
and Carpinus japonica (7 trees inshelters died and 9 trees in shel- Gerhold: Species Response to Tree Shelters of the control exceeded all other species. In the The shelters required little maintenance after fourth year at Root’s Nursery, the magnolias were the they were installed shortly after planting. A few of only varieties for which the calipers of sheltered trees them were bent over by a wet, heavy snowfall be- were greater than for the controls. At Nittany Trees, cause their wooden stakes were defective. Branches the dieback of sheltered trees, to the ground in many inside the shelters remained relatively small. They cases, reduced calipers substantially.
could be pruned quickly when shelters were taken The sturdiness indicator of trees within shelters, off. The plastic shelters appeared to deteriorate very expressed as caliper of the trunk divided by height, was reduced the most at the end of the second grow-ing season (Table 4). After the tops of trees emerged from shelters and they were removed, sturdiness im- Tree shelters were found to be useful in the nursery proved but was still inferior to the controls. The one production of some species but not others. The exception, Malus ‘Adirondack’, had a higher sturdi- heights of Magnolia ‘Merrill’ and Magnolia stellata in ness value because its height was depressed by shel- shelters were about half again as tall as the controls, ters proportionally more than its caliper. The and their calipers were also somewhat greater. This reduction in sturdiness was not a severe problem, size advantage occurred in USDA Hardiness Zone 6, but a few trees tended to bend over and were fas- but near the edge of Zone 5 it was nullified by die- tened to the stakes that were left in place after shel- back after severe winters. The modest height in- ters were removed. The 18-cm (7-in.) shelters creases of Acer griseum, Cercis canadensis, Cornus caused less of a reduction in sturdiness than the 9- ‘Celestial’, and Cornus ‘Constellation’ in shelters were offset by decreases in caliper and sturdiness; growing Table 3. Calipers of trees (inches) grown the first 2 years at Root’sNursery in 9-cm (3.5-in.) shelters and at Nittany Trees in 9- and 18- cm (3.5- and 7-in.) shelters, compared to trees grown all 4 years with- out shelters (percentage of control).
(1-in.) in caliper. The same mayapply to Carpinus caroliniana in Journal of Arboriculture 25(2): March 1999 Table 4. Sturdiness (caliper/height) of trees grown for the first 2 years at Root’s Nursery in 9-cm (3.5-in.) shelters and at Nittany The utility of tree shelters in the nurs- Trees in 9- and 18-cm (3.5- and 7-in.) shelters, compared to trees grown all 4 years without shelters (percentage of control).
landscape trees depends on ascertain-ing biological effects, which then must obtained with magnolias in a warmer portion of Har- stallation of the larger ones should be considered in diness Zone 5. Acer griseum, Carpinus caroliniana, relation to their biological benefits.
Cercis canadensis, and Cornus kousa ∞ florida hybrids Additional benefits of shelters may apply in some also showed some promise. The faster growing situations. Where wildlife problems occur, shelters Prunus serrulata and P. subhirtella varieties appeared protect against deer browsing and rubbing their ant- to benefit only marginally. Malus and Syringa lers, and also against bark gnawing by mice and reticulata, each represented by only 1 cultivar, grew voles. Furthermore, pruning can be deferred for 2 years and thus reduce costs and perhaps alleviate thescheduling of labor.
The results of these 2 experiments are consistent Brissette, J.C. (Ed.). 1995. Proceedings of the tree shelter with other studies (Burger et al. 1992; Burger et al.
conference. USDA Gen. Tech. Report NE-221, 80 pp.
Burger, D.W., G.W. Forister, and R. Gross. 1997. Short- 1996; Burger et al. 1997), although the other 2 stud- and long-term effects of treeshelters on the root and ies were conducted with different species in a stem growth of ornamental trees. J. Arboric. 23(2): Mediterranean-type climate. Species differed in their responses to shelters. Generally they were taller than Burger, D.W., G.W. Forister, and P.A. Kiehl. 1996. Height, controls initially, and caliper growth was reduced.
caliper growth, and biomass response of ten shade tree Root growth also was decreased in 1 study (Burger et species to treeshelters. J. Arboric. 22(4):161–166.
al. 1997) and can be anticipated in other cases in Burger, D.W., P. •Svihra, and R. Harris. 1992. Treeshelter use in producing container-grown trees. HortScience27(1):30–32.
Gerhold: Species Response to Tree Shelters Jones, R.H., A.H. Chappelka, and D.H. West. 1995. Use of Zusammenfassung. In einer vierjährigen Periode plastic shelters for low-cost establishment of street wurden in zwei Baumschulen die Auswirkungen von trees. South. J. Appl. For. 20(2):85–89.
Baumschutzhüllen auf die Höhe, Umfang und Durchmesser Witmer, R.K., H.D. Gerhold, and E.R. Ulrich. 1997. Tree in Brusthöhe von elf Baumarten untersucht. Das Verhältnis shelters accelerate slow-growing species in nurseries. J.
zwischen der Höhe und Umfang wurde dabei als ein Indikator für die Baumvitalität kalkuliert. Die Baumartenreagierten sehr unterschiedlich und rangierten in dem 4.
Jahr von Null bis zu 44 und 55 % Höhenzuwachs bei der Magnolia ‘Merrill’ und M. stellata mit 18 und 14 %Umfangzuwachs. Acer griseum, Carpinus caroliniana, Cercis canadensis, Cornus ‘Celestial’ und ‘Constellation’, Prunus serrulata ‘Kawanzan’ und P. subhirtella autumnalis zeigten mehr moderate Höhenzuwachsraten, aber auch schwacheUmfangentwichlung im Vergleich mit zwei Kontrollen ohneSchutz. Malus ‘Adirondack’ und Syringa reticulata ‘SummerSnow’ profitierten nicht davon. Zwei verschiedene Schutz-hüllengrößen und harte Winterbedingungen beeinflußtenebenfalls die Ergebnisse von einigen Baumarten.
Resumen. Los efectos de protectores de árboles en altura, Résumé. Les effets des ombrières d’arbres sur la hauteur, calibre y diámetro a la altura del pecho de 11 especies de le calibre (diamètre de la souche) et celui du DHP du tronc árboles urbanos (de paisaje) y de cultivo fueron investigados ont été étudiés sur 11 espèces et cultivars différents présents en dos viveros durante un periodo de cuatro años. La relación dans deux pépinières durant quatre années. Le ratio du cali- altura a calibre fue calculada como un indicador de la bre par rapport à la hauteur a été calculé comme indice de fortaleza del tronco. Las especies tuvieron una gran solidité du tronc. La réponse des espèces variait grandement, diferencia en sus respuestas, fluctuando en el cuarto año de nulle à 45 et 55% d’accroissement en hauteur pour le desde cero hasta 44 y 55 por ciento de incremento en la Magnolia ‘Merrill’ et le M. stellata accompagnée d’un altura de la Magnolia ‘Merril’ y M. stellata, acompañado por accroissement du calibre de 18 et 14%. Acer griseum, 18 y 14 por ciento de incremento en el diámetro del tronco.
Carpinus caroliniana, Cercis canadensis, Cornus ‘Celestial’, Acer griseum, Carpinus caroliniana, Cercis canadensis, C. ‘Constellation’, Prunus serrulata ‘Kwanzan’ et P.
Cornus ‘Celestial’ y ‘Constelación’, Prunus serrulata subhirtella autumnalis avaient des croissances en hauteur ‘Kwanzan’ y P. subhirtella autumnalis exhibieron incrementos plus modeste, mais aussi des diminutions de calibre, más modestos en la altura, pero también decreció el diámetro comparativement aux arbres-contrôle sans protection. Malus del tronco, comparado con los controles sin protectores. Malus ‘Adirondack’ et Syringa reticulata ‘Summer Snow’ sont restés ‘Adirondack’ y Syringia reticulata ‘Summer Snow’ no se inchangés. Les dimensions des deux ombrières et les condi- beneficiaron. Dos tamaños de protector y el clima de un tions climatiques sévères de l’hiver ont aussi affecté les invierno severo también afectaron los resultados de algunas résultats chez certaines variétés.

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