96 Lambert et al.: Effect of Container Size at Time of Planting on Tree Growth Rates Table 2. Planting densities and estimated costs per hect- are (per acre values in parentheses), listed by species and planting container size required to achieve theoretical 50% canopy cover in five years based on observed survival rates and canopy diameters. All costs listed in U.S. dollars. Species Longleaf Pine #3 Longleaf Pine #1 Red Maple #7 Size Planting Density Unit Cost Total Cost 843 (2,108/ac) 4919 (12,297/ac) 676 (1,690/ac) Red Maple #3 278 (695/ac) #7 371 (928/ac) Baldcypress #3 260 (649/ac) Baldcypress #1 380 (948/ac) $10 $5 $35 $10 Red Maple #1 524 (1,310/ac) $5 Baldcypress $35 $10 $5 $8,432 ($21,080/ac) $24,594 ($61,485/ac) $23,664 ($59,161/ac) $2,781 ($6,953/ac) $2,621 ($6,552/ac) $12,994 ($32,485/ac) $2,597 ($6,491/ac) $1,897 ($4,743/ac) Figure 2. Canopy diameter (mean ± SE) of baldcypress, red maple and longleaf pine trees in #1, #3, and #7 container sizes at time of initial planting and five years later. Shaded base is canopy diam- eter at time of planting, nonshaded top section reflects five-year change in canopy diameter; bar total represents cumulative five- year canopy diameter. Reference value shown of 2.4 m represents the canopy diameter required to achieve theoretical 50% cover assuming 100% survival and an initial tree planting density of 174/ha. DISCUSSION Baldcypress Growth rates of cypress vary considerably in the landscape, with competition for nutrients a major determining factor. In this study, increase in height over five years ranged from 2.2 m for the #7 trees, to 3.2 m for the #1 and #3 trees, similar to results in a previous study for cypress in a weed-controlled environment (Wilhite and Toliver 1990). A factor that may have influenced the relative height growth of both the baldcypress and the red maple in the #7 containers was their frequent use as a perch by birds in the early years when they were the tallest trees; this caused the apical stem to break off in many cases, resulting in stunted vertical growth. Additionally, although competition with weeds for nutrients can deter growth, tall weedy species can potentially convey nurse crop benefits (Richardson and Kluson 2000), which the initially taller #7 trees would not have received. While the #1 trees were comparable in height to the #3 trees, they lagged behind with regard to canopy diameter. This could be explained by the lack of shade tolerance of this species and the primary al- location of resources to reach sunlight at the top of the canopy. ©2010 International Society of Arboriculture If this is the case, then the #1 trees would likely equal the #3 trees with respect to other growth measurements in the future. Survival rates have a tendency to be low in large scale restora- tion plantings (Morgan and Roberts 1999; Gamble and Mitsch 2005), as compared to what would be expected for trees planted in a landscape or nursery setting. The most likely cause is drought stress (Ferrini et al. 2000), brought on by the higher transpira- tion rates of container grown trees (Harris and Bassuk 1993), in combination with the frequent absence of any irrigation or post- planting watering regime in many mitigation plantings. Poor ini- tial soil conditions, the emphasis on speed during planting with- out regard to proper planting procedures, and the low standard of post-transplant care, all associated with restoration plantings, would also affect longer-term survival and are all generally det- rimental to tree establishment and growth (Harris and Bassuk 1993; Gilman et al. 2009). The particularly poor survival rate of cypress grown in the #1 containers, in comparison to the #3 and #7 sizes, is most likely explained by their small size, making the trees most susceptible entanglement by vines or obscured by tall grasses and other components of the weedy landscape. Once ob- scured they could easily be trampled or suffer collateral herbicide or mechanical damage during nuisance species control efforts. They would also be more prone to damage by Florida wildlife, such as alligators and river otters observed utilizing the area. Studies involving larger sizes of trees did not show a dif- ference in growth rate between sizes (Gilman et al. 2008b; Struve 2009). This contrasts with results for the sizes used in this study, for which there were significant differences be- tween sizes in each of the three species. The #3 cypress had the overall best growth rate and the highest survival rate five years post-planting. The trees may have been large enough to be recognizable and thus not subject to trampling and collateral damage, yet small enough to not suffer from transplant shock. Anecdotal information was collected for the presence of cones and cypress twig gall midge (Taxodiomyia cupressiananassa), and revealed some patterns that bear further investigation. The pres- ence of cones was not affected by height or container size, where- as the presence of galls was not affected by height but did increase with container size. For the final year only, those trees with galls were less likely to have cones, indicating the pattern may develop further as the trees continue to mature. Research that includes the quantity of galls or cones and which looks at this trend over a greater span of time would add additional insight into these relationships. Red Maple Heat stress may have been a major detriment to growth and survival of red maples in the study area, which may have been intensified by soil conditions and hydrology. Red maples may become less efficient in absorbing certain nutrients as soil fer- tility increases (Platt and Schwartz 1990); conversely, greater efficiency in less fertile soils may be offset by other effects of more stressful conditions. Under favorable conditions, red ma- ple seedlings increase in height up to 0.3 m the first year, and 0.6 m or more annually for the next several years (Walters and Yawney 1990). The #1 and #3 red maples in this study both in- creased in height 3.6 m five years post-planting, while the #7 trees averaged 2.4 m increase over five years. A similar trend of larger trees having a slower growth rate has been noted for red maples planted into a nursery setting (Gilman et al. 2008a).
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