Root architecture, early development and basal sweep in containerized and bare-rooted Douglas fir (Pseudotsuga menziesii)

Seedlings grown in containers often have deformed, spiralling, kinking root systems (reported especially in pine growing in colder climates like Fenno -Scandinavia). The current study examines the effect of containers on the r oot systems of Douglas fir planted in Ireland. A sample of sixteen 10-year- old Douglas fir trees, planted as either bare-rooted transplants (2/1) or c ontainerized seedlings (Paperpot 610 (2/0)) on an acid brown earth site in Ireland, were excavated for root achitectural studies. In addition to thoro ugh above-ground measurements, an assessment of basal sweep was also carrie d out. Root systems were systematically described and horizontal angles, cr oss-sectional areas (CSA), and maximum depths of all roots >5 mm in diamete r were recorded. Various biomass ratios and estimates for dominant roots we re also calculated. Symmetry of the root systems, max. and min. numbers, an d CSA of roots for sectors of various sizes were compared for the two plant types. The initially (when planted) bigger bare-rooted transplants were st ill larger than the container-planted trees after ten years. Of the total a bove-ground fresh weight, the container stock had allocated more to the cro wn and less to the stem compared to bare-roots. The difference in root weig hts between stock types was small. Basal sweep occurred on average in 50% o f the bare-roots and 35% of the container trees. The direction of the basal sweep leaning was concentrated to the NE, which coincided with the directi on of the slope and the prevailing wind direction. No effect of planting po sition in relation to the direction of site preparation was found for basal sweep. The size of the root system, fresh weight and total cross-sectional area was on average for all trees correlated to both DBH and shoot fresh w eights. For containers separately, however, only root area was correlated t o DBH and stem fresh weight. In spite of the difference in the above-ground size, there were no significant differences in root numbers and root area (CSA) between the two plant types. No difference in rooting depth between p lant types was found. When splitting the root system into 120 degrees horiz ontal sectors (1/3 of the root system) the highest numbers of roots were co ncentrated in the NW direction. The highest amount of root area tended to b e concentrated along a NW-SE diagonal, with a dominance for the latter (SE) . Sectors without dominant roots (expected to be the future main structural , stabilizing roots), varied in size (94-178 degrees) but were on average w ider in bare-roots and on average concentrated in the NE direction and the downhill side of the slope.