3.1. Health
There were significant differences in health of the 2017 buffer group trees (HEALTH
2017) among buffer and clone main effects for the first, second, and third year of growth (
P2017,2018,2019 < 0.0001), yet the buffer × clone interaction governed health for all three years (
P2017 < 0.0001;
P2018 < 0.0001;
P2019 = 0.0152) (
Table S2). HEALTH
2017 of trees measured in 2017 (i.e., HEALTH
2017(2017)) ranged from 1.0 ± 0.0 (‘NM2’ and ‘NM5’ at Menomonee Falls (East); ‘NM2’ at Whitelaw; most healthy] to 1.6 ± 0.1 (‘DM114’ at Caledonia (East); least healthy), with an overall mean of 1.1 ± 0.1 (
Figure 2). Thus, all trees were of optimal health (i.e., health index ranging from 1 to 2). The healthiest trees were grown at Whitelaw, which had 14.1% better HEALTH
2017(2017) than at Caledonia (East), the buffer with trees exhibiting the poorest health. The range in health scores was broader for clones, with ‘NM5’ having 37.0% healthier trees than ‘DM114’. Common clones had the healthiest and Experimental clones the least-healthiest trees, with NRRI genotypes being intermediate for HEALTH
2017(2017). Seven buffer × clone interactions resulted in HEALTH
2017(2017) values that were significantly greater than the overall mean [‘DM114’, ‘DN177’, and ‘NC14106’ at Caledonia (East); ‘DM114’ and ‘NC14106’ at Menomonee Falls (East); ‘DM114’ at Menomonee Falls (West); ‘DM114’ at Slinger]. With the exception of ‘DM114’ and ‘DN177’, all clones were generalists for HEALTH
2017(2017), with health index scores not varying by more than 0.3 for any buffer × clone combinations. Trees grown at Bellevue (West) and Whitelaw were 38.4% healthier than those at Menomonee Falls (East) and Caledonia (East) for ‘DM114’. Similarly, for ‘DN177’, trees at Whitelaw were 32.2% healthier than at Caledonia (East) (
Figure 2). Trends in second- (HEALTH
2017(2018)) and third-year (HEALTH
2017(2019)) health of the 2017 buffer group trees were similar to HEALTH
2017(2017) (
Figures S1 and S2).
Differences among buffer and clone main effects were significant for first- (HEALTH
2018(2018)) and second-year (HEALTH
2018(2019)] health of the 2018 buffer group trees (
P2018 = 0.0009 for Clone;
P2018,2019 < 0.0001 for all other main effects), yet the buffer × clone interaction governed health for both years (
P2018 = 0.0029;
P2019 < 0.0001) (
Table S2). HEALTH
2018(2018) ranged from 1.0 ± 0.0 (‘9732-11’, ‘9732-24’, ‘DM114’, ‘DN2’, ‘NM2’, ‘NM5’, ‘NM6’ at Bellevue (East); ‘9732-11’, ‘DN2’ at Bellevue (Central); most healthy) to 1.5 ± 0.1 (‘DM114’ at Manitowoc; least healthy), with an overall mean of 1.1 ± 0.1 (
Figure 3). Similar to HEALTH
2017(2017) above, all trees were of optimal health. The healthiest trees were grown at Marquette and Bellevue (East), which had 25.5 % better HEALTH
2018(2018) than at Manitowoc that exhibited the poorest health. The range in health scores was narrower for clones, with ‘NM5’ having 12.9 % healthier trees than ‘DM114’ that had the poorest health. Common and NRRI clones had the best overall health scores that were similar to one another yet better than Experimental genotypes. Seven buffer × clone interactions resulted in HEALTH
2018(2018) values there were significantly greater (i.e., of poorer health) than the overall mean, with all occurring at Manitowoc: ‘9732-11’, ‘9732-24’, ‘9732-31’, ‘9732-36’, ‘7300502’, ‘DM114’, ‘DN2’, and ‘DN5’. With the exception of ‘7300502’ and ‘DM114’, all clones were classified as generalists for HEALTH
2018(2018). Trees grown at Bellevue (East) and Marquette were 52.5% healthier than those at Manitowoc for ‘7300502’, while those at Bellevue (East), Bellevue (Central), and Marquette were 48.8% healthier than at Manitowoc (
Figure 3). Trends in second-year health of the 2018 buffer group trees (HEALTH
2018(2019)) were similar to HEALTH
2018(2018) (
Figure S3).
Differences among buffer and clone main effects were significant for first-year health of the 2019 buffer group trees (HEALTH
2019(2019)) (
PBuffer < 0.0001;
PClone = 0.0159), yet the buffer × clone interaction governed health (
P = 0.0036) (
Table S2). HEALTH
2019(2019) ranged from 1.0 ± 0.0 [‘9732-24’, ‘DM114’, ‘DN2’, ‘NM2’, ‘NM6’ at Munising; ‘9732-31’ at Ontonagon (North); ‘99038022’, ‘9732-11’, ‘DM114’, ‘DN2’, ‘NM6’ at Ontonagon (South); most healthy] to 1.3 ± 0.0 [‘DM114’, ‘DN2’ Escanaba (West); least healthy], with an overall mean of 1.1 ± 0.0 (
Figure 4). All trees were of optimal health. The healthiest trees were grown at Ontonagon (South), which had 13.7% better HEALTH
2019(2019) than at Escanaba (West) where trees had the poorest health. The range in health scores was narrower for clones, with 7.2% separating the healthiest trees of ‘NM2’ from the least healthy trees of ‘DN2’, ‘DN34’, and ‘DN177’. Similar to HEALTH
2017(2017), Common clones had the healthiest and Experimental clones the least-healthiest trees, with NRRI genotypes being intermediate for HEALTH
2019(2019). Two buffer × clone interactions resulted in HEALTH
2019(2019) values there were significantly greater than the overall mean (‘DM114’and ‘DN2’ at Escanaba (West)). No clones varied by more than 0.3 health index points for any buffer × clone combinations, thus indicating that all had generalist health performance. The largest variation in clonal responses to specific buffers was where trees were 21.7% healthier at all buffers relative to Escanaba (West) for ‘DM114’, and where trees were 26.3% healthier at Munising and Ontonagon (South) than Escanaba (West) for ‘DN2’ (
Figure 4).
3.2. Biomass and Growth
Differences for buffer and clone main effects were significant for fourth-year mean annual increment of the 2017 buffer group trees (MAI
2017(2020)) (
P < 0.0001), yet the buffer × clone interaction governed MAI
2017(2020) (
P < 0.0001) (
Table S2). MAI
2017(2020) ranged from 1.10 ± 0.73 (‘7300502’ at Whitelaw) to 7.67 ± 0.5 Mg ha
−1 yr
−1 (‘NM5’ at Menomonee Falls (East)), with an overall mean of 3.20 ± 0.51 Mg ha
−1 yr
−1 (
Figure 5). The largest trees were grown at Menomonee Falls (West), which had 55.4% greater MAI
2017(2020) than at Whitelaw, the buffer with the smallest trees. The range in MAI
2017(2020) was broader for clones, with ‘NM5’ exhibiting 69.8% more biomass than ‘NC14106’ that had the smallest trees of any genotype. While MAI
2017(2020) varied across genotypes, trends across clone groups were non-existent, with Common, Experimental, and NRRI clones performing similarly across buffer × clone combinations. Many buffer × clone interactions resulted in MAI
2017(2020) values that were significantly greater than the overall mean, with the most notable being ‘NM5’ outperforming the mean at four of the six buffers: Caledonia (East), Menomonee Falls (East), Menomonee Falls (West), and Slinger. In contrast, ‘NC14106’ had significantly less MAI
2017(2020) than the overall mean at three buffers: Bellevue (West), Menomonee Falls (East), and Whitelaw.
In addition to these changes in magnitude, there were distinct changes in MAI
2017(2020) ranks that defined the genotypes as generalists or specialists. In particular, clones exhibited generalist MAI
2017(2020), with four exceptions (
Table 4). First, ‘99059016’ had stable performance across five of the six buffers, with Whitelaw (i.e., the buffer with its lowest rank of eleventh) having 60.9% less MAI
2017(2020) than Bellevue (West), where ‘99059016’ ranked fifth. Second, ‘7300502’ had broad variation in MAI
2017(2020) across all six buffers, with a 75.3% reduction in MAI
2017(2020) at Whitelaw (rank = 12) versus Bellevue (West) (rank = 3). Third, ‘DN177’ was a specialist because of its high MAI
2017(2020) at Slinger (where it ranked fourth), which was 36.7% greater than Menomonee Falls (East) (rank = 9). Fourth, despite higher ranking (rank = 7) at Whitelaw relative to other buffers for ‘DN34’, MAI
2017(2020) at Whitelaw was 60.6% less than that of Caledonia (East) (rank = 11), resulting in its specialist response (
Table 4). However, this classification for ‘DN34’ should be interpreted with caution, especially given that ‘DN34’ ranked tenth at four buffers and eleventh at one buffer, indicating stable performance across buffers.
The buffer × clone × year interaction was significant for height (
P = 0.0483), diameter (
P = 0.0018), and volume (
P = 0.0001) of the 2017 buffer group trees (
Table S3). VOLUME
2017 of trees measured in 2017 (VOLUME
2017(2017)) ranged from 3.1 ± 54.4 (‘7300502’ at Whitelaw) to 459.6 ± 22.6 cm
3 (‘7300502’ at Slinger), with an overall mean of 132.0 ± 38.7 cm
3, while VOLUME
2017(2018) (i.e., 2017 buffer group trees measured in 2018) ranged from 503.5 ± 1619.6 (‘7300502’ at Whitelaw) to 13,027.0 ± 1402.6 cm
3 (‘NM2’ at Slinger), with an overall mean of 5765.2 ± 1132.3 cm
3 (
Table 5). VOLUME
2017(2019) ranged from 1668.7 ± 3018.1 (‘7300502’ at Whitelaw) to 26,652.0 ± 1848.0 cm
3 (‘NM5’ at Menomonee Falls (East)), with an overall mean of 10,530.6 ± 2109.5 cm
3 (
Table 5). Across all buffer × clone × year combinations, volume increased 43.7-fold from the first year to the second year after planting, and then 1.8-fold from the second year to the third year. After the first and second growing seasons, the largest trees were grown at Slinger, which had 1301 and 268% greater volume than the buffer with the smallest trees (Whitelaw), respectively. For the third growing season, trees at Menomonee Falls (East) were largest, with VOLUME
2017(2019) being 338% greater than Whitelaw, which had the smallest trees.
The range in volume was narrower for clones, with ‘DN5’ having 204% greater volume than the least productive clone (‘99059016’) for VOLUME
2017(2017), ‘NM5’ being 86% greater than ‘7300502’ for VOLUME
2017(2018), and ‘NM5’ being 114% greater than ‘NC14106’ for VOLUME
2017(2019). With the exception of the first growing season where NRRI clones exhibited the least overall volume followed by Experimental and Common (most volume) genotypes, Common clones had the largest and Experimental clones the smallest trees, with NRRI genotypes being intermediate for VOLUME
2017(2018) and VOLUME
2017(2019). Trends in height and diameter of the 2017 buffer group trees were similar to volume (
Tables S4 and S5). Furthermore, in addition to the broad variability in the magnitude of differences among buffer × clone × year combinations, the frequency and magnitude of changes in rank within and across years defined genotypes as generalists (i.e., minimal rank changes) or specialists (i.e., broad variation resulting in ≥5 rank changes for at least one buffer × clone × year pair) (
Table S6). In particular, the NRRI clones (‘99038022’, ‘99059016’, ‘9732-36’) were high-level generalists characterized by nearly universal stability in ranks across buffers within measurement years, less than three substantial (i.e., >5 ranks) rank changes across all three-way combinations, and moderate to high rank stability over time. Clones ‘DM114’ and ‘NC14106’ were also generalists, exhibiting moderate rank stability within years and consistent ranks over time. The remaining genotypes were specialists. Clone ‘7300502’ had the most variability in early ranks of all clones, followed by high rank stability in later years that were not consistent over time. For example, ‘7300502’ ranked first at Slinger in 2017 but then twelfth at this buffer in 2018 and 2019. Clones ‘NM2’, ‘NM5’, and ‘NM6’ were high-level specialists characterized by broad variability in ranks across buffers within measurement years, frequent substantial rank changes across all three-way combinations, and moderate stability over time. Similarly, ‘DN5’, ‘DN34’, and ‘DN177’ were specialists, albeit with more moderate rank variation than the ‘NMx’ genotypes (
Table S6).
The buffer × clone × year interaction was significant for height, diameter, and volume (
P < 0.0001) of the 2018 buffer group trees (
Table S3). VOLUME
2018(2018) ranged from 12.2 ± 38.4 (‘DN5’ at Marquette) to 185.7 ± 25.3 cm
3 (‘NM2’ at Manitowoc), with an overall mean of 71.2 ± 26.3 cm
3, while VOLUME
2018(2019) ranged from 287.8 ± 1518.7 (‘DN5’ at Marquette) to 11,085.0 ± 930.0 cm
3 (‘NM2’ at Manitowoc), with an overall mean of 3418.4 ± 1035.2 cm
3 (
Table 6). VOLUME
2018(2020) ranged from 261.0 ± 3882.2 (‘DN5’ at Marquette) to 27,220.0 ± 2377.4 cm
3 (‘NM5’ at Manitowoc), with an overall mean of 8826.0 ± 2646.2 cm
3 (
Table 6). Across all buffer × clone × year combinations, volume increased 48-fold from the first year to the second year after planting, and then 2.6-fold from the second year to the third year. After the first growing season, the largest trees were grown at Caledonia (West), which had 529% greater volume than Marquette, the buffer with the smallest trees. During the second and third growing seasons, the largest trees were from Manitowoc, which had 1079 and 1744% greater volume than the buffer with the smallest trees (Marquette), respectively. As with volume for the 2017 buffer group trees, there was less variability among clones than buffers, with ‘9732-31’ having 156% greater volume than the least productive clone (‘7300502’) for VOLUME
2018(2018), ‘NM5’ being 163% greater than ‘7300502’ for VOLUME
2018(2018), and ‘NM5’ being 143% greater than ‘DM114’ for VOLUME
2018(2018). During the first growing season, NRRI clones had the greatest overall volume, while Common clones exhibited the largest trees at two and three years after planting. For all three years, Experimental clones had the least volume. Trends in height and diameter of the 2018 buffer group trees were similar to volume (
Tables S7 and S8). Moreover, as with 2017 buffer group trees, changes in magnitude and rank of 2018 buffer group clones across buffer × year combinations defined them as generalists or specialists (defined as for
Table S6 above) (
Table S9). Similar to 2017, the NRRI clones (‘9732-11’, ‘9732-24’, ‘9732-31’, ‘9732-36’) were high-level generalists with universal stability in ranks, few rank changes greater than five ranks, and high rank stability over time. Clone ‘DM114’ was also a generalist, having only two substantial rank changes and nearly identical ranks from 2017 to 2019. All other genotypes were specialists. As in 2017, clone ‘7300502’ had a high level of early rank variability and low to moderate rank consistency over time; clones ‘NM2’, ‘NM5’, and ‘NM6’ were high-level specialists with broad rank variability, numerous substantial rank changes, and moderate stability as trees aged; ‘DN2’, ‘DN5’, and ‘DN34’ were consistent specialists with moderate levels of rank changes and age-dependent stability (
Table S9).
The buffer × clone × year interaction was significant for height (
P = 0.0079), diameter (
P < 0.0001), and volume (
P < 0.0001) of the 2019 buffer group trees (
Table S3). VOLUME
2019(2019) ranged from 8.6 ± 26.9 (‘DN177’ at Ontonagon (North)) to 396. ± 26.7 cm
3 (‘99038022’ at Escanaba (West)), with an overall mean of 88.7 ± 26.7 cm
3, while VOLUME
2019(2020) ranged from 92.6 ± 612.7 (‘NM5’ at Ontonagon (North)) to 8909.6 ± 573.1 cm
3 (‘NM2’ at Escanaba (West)), with an overall mean of 1440.4 ± 575.1 cm
3 (
Table 7). Across all buffer × clone × year combinations, volume increased 16.2-fold from the first year to the second year after planting. After the first and second growing seasons, the largest trees were grown at Escanaba (West), which had 1008 and 1066% greater volume than the buffer with the smallest trees (Ontonagon (North)), respectively. For VOLUME
2019(2019), ‘99038022’ had 101% greater volume than the least productive clone (‘DN177’), while ‘NM2’ was 164% greater than ‘9732-11’ for VOLUME
2019(2020). NRRI clones exhibited the greatest first-year volume, followed by Common and Experimental genotypes. For VOLUME
2019(2020), ranks of NRRI, Experimental, and Common clones changed, with Common genotypes having the most VOLUME
2019(2020) followed by Experimental and NRRI (least volume) clones. Trends in height and diameter of the 2019 buffer group trees were similar to volume (
Tables S10 and S11). Furthermore, 2019 clones were classified as generalists or specialists (defined as for
Table S6 above) (
Table S12).
As in previous buffer groups, ‘DM114’ was a high-level generalist. With the exception of ‘99038022’ that was a high-level generalist with nearly universal rank stability, only two substantial rank changes across all three-way combinations, and moderate stability over time, the NRRI clones were specialists for the 2019 buffer group. In particular, ‘9732-11’, ‘9732-24’, ‘9732-31’, and ‘9732-36’ were moderate- to high-level specialists characterized by broad rank variability, substantial rank changes, and moderate stability over time. Similarly, the performance of ‘DN2’ as a generalist in the 2019 buffer group was different relative to its specialist volume in the 2018 buffer group. Across 2019 phyto buffers, ‘DN2’ exhibited moderate rank stability within years and consistent ranks over time. All remaining clones were moderate- (‘DN34’, ‘DN177’) and high-level (‘NM2’, ‘NM5’, ‘NM6’) specialists with trends for changes in magnitude and rank similar to their performance in 2017 and 2018 buffer groups (
Table S12).