Arboriculture & Urban Forestry 36(3): March 2010 Following the tropical storms during the summer of 2004, a large number of red maples were blown over and suffered branch failure. This is consistent with the medium-low wind resistance rating reported by Duryea et al. (2007). Root de- velopment varies with soil conditions; in wet soils the taproot is short and the lateral roots become extensive, while in well- drained sites the taproot grows deep and the lateral roots are less prominent. The majority of the wind-thrown trees appeared to have occurred in the wetter soils, consistent with an explana- tion based on a shallower root system. Many of the wind-thrown trees developed adventitious roots and coppice shoots, which is a common response to flooding or injury (Kozlowski 1985; Schnelle et al. 1989). Secondary pathogens in the form of can- kers were evident on many of the maples both alive and dead. Survival for all three sizes of red maples was poor, with the #7 size faring the worst. This conforms to findings (Struve 2009), which note that larger caliper trees have higher mortality than smaller caliper trees. Although vine entanglement and collateral herbicide damage likely were contributing factors, secondary pathogens associated with heat stress, wind throw, and branch failure may also have contributed heavily to mortality. Longleaf Pine Longleaf pine seedlings have a grass stage during which they delay trunk development and instead develop a stout taproot; this grass stage ranges from one to 15 years (Duncan and Duncan 1988; Brown and Kirkman 1990; Myers 1990). The longer grass stage delays early height growth and is associated with poorer site condi- tions (Boyer 1990). When the trunk does start to develop, it grows at the rate of 0.9 to 1.5 m the first year (My- ers 1990). In the present study, the longleaf pines in #1 containers did not fare as well as those in #3 containers in terms of survival or growth. The #1 trees may be espe- cially vulnerable to damage due to their small size while in the grass stage. Damage was noted by armadillo bur- rows, trampling by feral hogs, trampling and browsing by white-tailed deer, and fire ant colonies extending up the trunks during periods of high groundwater. Inclusion of #7 trees in additional research is suggested, due to the unusual seedling-to-sapling transition of longleaf pine. CONCLUSIONS In determining optimum planting container size, cost must be balanced with performance. While costs vary, the ap- proximate cost to install these three species of trees in re- cent wetland restoration projects in this area was USD $35 per #7 tree, $10 per #3 tree, and $5 per #1 tree. For the three species studied, the #3 trees had the best sur- vival, the greatest canopy development, and equal or greater overall height. There appears to be no advantage gained in planting the larger #7 containers, and at the current inter- mediate cost, the #3 size trees appear to offer the best over- all value.When restoration projects occur as a requirement of an environmental regulatory permit, specific growth crite- ria are expected to be attained within five years. While the #3 trees had the best results, the question remains which, if any, of the three sizes examined would be in compliance with typi- 97 cal permit conditions. Three common growth criteria refer- enced in permits are height, percent survival, and percent cover. The typical height criterion is 3.7 m after five years from the date of planting. All container sizes of bald cypress and red maple met this criterion. Although data for #7 longleaf pines are not represented, both the #3 and #1 pines fell substantially short of this requirement. This indicates the 3.7 m height criteria can be achieved by baldcypress and red maple in better than average con- ditions, but may not be practical for many sites or for all species. The criterion for survival has been expressed as percent sur- vival, or as density. Previous permits typically required 85% sur- vival of trees planted 3 m on center. Current permits typically require a density of 174 trees per hectare (436 trees per acre), which is equivalent to 100% survival of an initial 3 m on cen- ter spacing. Baldcypress survival was greatest for the #3 con- tainer-grown trees and was 74%. Red maple survival was again best for the #3 trees, but was only 52%. Longleaf pine survival was better for the #3 size and was 62%. Neither the 85% sur- vival nor the 174 trees per hectare/100% survival standards ap- pear to be achievable with the standard initial planting density. The percent cover criteria vary widely from 30% to 75%. For simplicity, 50% will be used as the requirement. To calculate this value from the canopy diameter data, canopy was assumed to be a uniform circle and trees were assumed to be planted uni- formly 3 m on center. The resulting area was then adjusted to account for mortality by multiplying by percent survival. Bald- cypress cover was best for the #3 container size and was 34%. Red maple cover was best for the #3 container size at 31%. Lon- gleaf pine cover was best for the #3 container size and was 20%. The 2.4 m reference line in Figure 2 is the canopy diameter re- quired to provide theoretical 50% cover based on the assump- tions of 100% survival at planting densities of 3 m on center. Thus, even with 100% survival assumed, cover is, at best, 45% for baldcypress, 60% for red maple, and 33% for longleaf pine. Although permits generally allow, in fact require, replant- ing to adjust for mortality, this practice leads to a tempo- ral lag in growth and further contributes to failure of meet- ing growth criteria within the designated five-year period. Possible solutions to bridging the gap between per- formance and requirements include: extending the five- year time frame, reducing the survival and cover require- ments, and planting at greater initial densities. In any case, the requirements should also allow for individu- al species variation (e.g., longleaf pine’s grass stage). If initial planting densities were increased to achieve 50% cover, the approximate densities and costs are exhib- ited in Table 2. Although this shows it may possibly be more advantageous to plant #1 sized containers instead of #3 for baldcypress and red maples with this strategy, the pos- sible effects of planting at increased densities are not known. The factors influencing growth and establishment of trans- planted trees, particularly in an ecological restoration or forest setting, are exceedingly numerous and in most cases difficult to control or even predict. One factor readily within the control of the project manager is the size of the trees to be installed; and under the conditions of this study, #3 container grown trees performed the best. There may be situations in which #1 container trees will have an advantage, but it appears that #7 container-grown trees are a poor choice with respect to both cost and performance. ©2010 International Society of Arboriculture
March 2010
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