.. Larix occidentalis (western larch) Western larch is distributed over a relatively small range from southeastern British Columbia to Idaho and northern Oregon (Farrar ). It is a fast- growing deciduous conifer that typically regenerates disturbed areas, particularly after fire (USDA Forest Service ). Western larch can be found as high as _ m elevation; it is quite frost-tolerant but not very drought-tolerant. Its deciduous needles are very shade-intolerant and have high photosynthetic rates. Because of their short life, the needles require less of a carbon investment than do evergreen needles of other conifer species. We tested -year-old western larch seedlings from m elevation, and younger seedlings from , FIGURE Western larch seedlings grown with no UV-B , and m elevation seed sources. Growth was (left) had long, straight needles. Those reduced by increasing doses of UV-B radiation, and grown at high UV-B (12 kJ m-2 d -1 ) (right) needle morphology changed dramatically. Instead of had shorter, twisted needles. growing long, straight, and flat, the needles became shorter, twisted, and corkscrewed (Figure ). 60 Seedlings grown for months under the highest level a. of UV-B were % shorter than seedlings grown 50
without UV-B (Figure b). However, there was little o 40 change in height between seedlings grown without UV-B and those grown at twice the ambient levels. 30 In addition to their morphological changes, 20 seedlings also showed changes in stress physiology. Quantum yield Frost hardiness in mid-October increased with 10 after freezing to -9 C (%) increasing UV-B dose (Figure a). Seedlings grown 0 without any UV-B had about one-third more damage 04812 than those grown at the highest UV-B dose. This UV-B dose (kJ m-2 d -1 ) response was similar for seedlings from all three FIGURE a Frost hardiness of western larch seedlings after elevations. freezing to -9o C in early October. Each bar is Western larch may be considered sensitive to the mean of 54 seedlings, +_o ne standard UV-B because of its changes in morphology, height error. growth, and physiology. Because its needles are deciduous, there would be no direct cumulative effects on foliage productivity, but changes in carbon 20 b. allocation would be expected to affect stem and root biomass. Because there is significant genetic variation 15 among populations (Jaquish and El-Kassaby ), testing of more sources and trees in field situations is 10 needed to estimate the potential for future effects.
Shoot height (cm) 5
0 04812 UV-B dose (kJ m-2 d -1 )
FIGURE b Shoot height of western larch seedlings after 5 months of UV-B exposure. Each bar is the mean of 90 seedlings, +_o ne standard e rror.
.. Picea engelmannii (Engelmann spruce) Engelmann spruce is a high-elevation species ranging from northern British Columbia south through Idaho to Arizona, usually growing above m and up to treeline (Farrar ). Seedlings are very shade- and frost-tolerant and slow-growing in their natural environments. They do not compete well with faster- growing and less shade-tolerant associates when regenerating under open canopies or on disturbed sites (USDA Forest Service ). We tested Engelmann spruce seedlings from three seed sources covering a m range in elevation. High-elevation seedlings were very slow-growing under greenhouse conditions (Figure a), with a height of less than cm after months of growth. However, they did not appear to be negatively affected by increased doses of UV-B. FIGURE Young Engelmann spruce seedlings grown In contrast, low- and middle-elevation seedlings without any UV-B (on right) or at 12 kJ -2 -1 grew about three times as fast, but were affected by UV-B m d (three times ambient, on left). UV-B. They grew best at and ambient UV-B levels (Figures , , and a). At the highest level of UV-B, 14 a. they were about % shorter than at ambient UV. 12 Even with this decrease, they were still more than 10 double the size of the high-elevation seedlings. Along with decreased height, seedlings grown at 8 the higher UV-B levels also had smaller root collar 6 diameter, fewer branches, shorter needles, more 4 visible injury, and lower biomass. Seedling height (cm) As with several other species, Engelmann spruce 2 0 kJ UV-B 4 kJ UV-B 8 kJ UV-B 12 kJ UV-B seedlings showed increased stress resistance when 0 854 m 1220 m 1707 m exposed to increasing levels of UV-B. Frost hardiness Seed source elevation (m) in September increased by more than % for seedlings grown at the highest UV-B levels, relative to FIGURE a Shoot height of Engelmann spruce seedlings those grown without any UV-B (Figure b). This after 4 months of UV-B exposure. Each bar is happened for seedlings from all three elevations, with the mean of 45 seedlings, +_o ne standard the only notable difference being that high-elevation error. seedlings showed high levels of frost hardiness at all three UV-B levels_ only the seedlings grown without
o 80 UV-B were damaged. It seems that exposure to UV-B b. triggers metabolic and biochemical changes that 60 make photosynthetic and cellular membranes more resistant to disruption from freezing temperatures. Test results for this species again show that 40 generalizations for a species must be made cautiously. Engelmann spruce, being a high-elevation species, 20 would be expected to be very resistant to UV-B, but the resistance is affected by population source. There 0 0 kJ UV-B 4 kJ UV-B 8 kJ UV-B 12 kJ UV-B is likely also a difference in resistance between 854 m 1220 m 1707 m seedlings and mature trees, and between sun and Quantum yield after freezing to -13 C (%) Seed source elevation (m) shade foliage. Tests, including a larger combination of FIGURE b Frost hardiness of Engelmann spruce seedlings genetic and environmental treatments, are needed to after freezing to -13o C in September. Each bar establish a range of UV-B resistance in this species. is the mean of 15 seedlings, +_o ne standard e rror.
.. Picea glauca x engelmannii (interior spruce) a. In many parts of its range, Engelmann spruce hybridizes freely with other spruce species (Daubenmire ). Hybrids between Engelmann and white spruce are common throughout central British Columbia, mostly at lower elevations, where they are called interior spruce (Xie et al. ). These hybrids most closely resemble white spruce, but cannot be readily distinguished from Engelmann spruce. The most frequently planted seedlings in British Columbia are interior spruce, which have a large economic value (Xie et al. ). Because the hybrids include a range of characteristics of the two pure species, they might be expected to exhibit a range of responses to increased UV-B radiation. b. We tested -year-old seedlings from m elevation in northern British Columbia, and younger seedlings from three elevations in the southeastern part of the province. This last group suffered from water stress in the early part of the test, so here we present the results for the older seedlings. Interior spruce seedlings for the most part were fairly resistant to increases in UV-B levels. At the highest UV-B dose, some seedlings showed needle curling or changes in needle angle relative to seedlings grown at lower UV-B levels (Figure a, b). There did not appear to be notable changes in FIGURE a) Interior spruce seedlings grown at 0 (left) biomass. or 12 (right) kJ UV-B m-2 d -1 for 4 months. Unlike several other conifer species that we tested, b) Interior spruce shoots grown at high light interior spruce seedlings showed a decrease in frost and 4 (left) or 12 (right) kJ UV-B m-2 d -1 for hardiness with increasing UV-B exposure (Figure ). 5 weeks. Note the needle angles. Photos a This was found in early September, near the and b are from different studies with beginning of fall cold acclimation. Although the different seedlings. difference was not large, it was significant. Interior spruce populations probably have a fairly large range in UV-B sensitivity, depending on the 80 genetic makeup of the hybrids. Some populations are expected to be quite sensitive, others fairly resistant. o 60 Because this complex is so widely planted in the province, it would be advisable to check a range of 40 sources from wild stands and seed orchards for vulnerability to increased UV-B levels. Quantum yield 20 after freezing to -10 C (%) 0 04812 UV-B dose (kJ m-2 d -1 )
FIGURE Frost hardiness of interior spruce seedlings after freezing to -10o C in September. Each bar is the mean of 15 seedlings, +_o ne standard error.
.. Picea sitchensis (Sitka spruce) Sitka spruce is a low-elevation coastal species ranging from Alaska to Northern California, in many places growing in the fog belt (Farrar ). It prefers cool, moist summers and does best in areas of high precipitation. This long-lived species is the world's tallest spruce (USDA Forest Service ). Sitka spruce is shade-intolerant, and is both a pioneer and a climax species. In a previous study, we tested Sitka spruce 04 812 seedlings from , , and m elevation by FIGURE Shoot tips of Sitka spruce seedlings grown growing them for months in late winter in a with increasing UV-B. From left to right, glasshouse. Height growth was strongly affected by -2 -1 0, 4, 8, 12 kJ UV-B m d . both seed source elevation and UV-B dose (Figure a). Seedlings from the low and middle elevation 12 were taller at all UV-B doses than those from the a. high-elevation source. Increasing UV-B had only 10 small effects on seedling height as it increased from zero to ambient and double ambient, but, at three 8 times ambient, many seedlings were killed and height 6 growth dropped by more than half. In this study, the effects of high UV-B may have been exaggerated 4 because ambient levels of visible light were relatively Seedling height (cm) 2 low from late winter to early spring. 0 kJ UV-B 4 kJ UV-B 8 kJ UV-B 14 kJ UV-B 0 Subsequent work with Sitka spruce used -year- 127 m 305 m 488m old seedlings, which showed few effects on needle Seed source elevation (m) morphology (Figure ). Needles seemed to be more angled upward in the presence of UV-B, but showed FIGURE a Shoot height of Sitka spruce seedlings after no signs of curling. However, shoot growth decreased 4 months of UV-B exposure. Each bar is the by % between the and kJ UV-B treatments, and mean of 30 seedlings, +_o ne standard error. stress resistance changed as well. Several heat stress tests found that Sitka spruce seedlings were more 80 heat-tolerant when UV-B levels were above zero b. (Figure b). 60 Because Sitka spruce is a shade-intolerant species, o it may be fairly resistant to UV-B when visible light 40 levels are also high enough to facilitate repair processes. It also seems to increase in heat resistance Quantum yield when grown under increasing UV-B levels. Given the 20 wide latitudinal range of this species, further tests of after heating to 38 C (%) populations from the north and south extremes, and 0 04812 of hybrids with other spruce species, would be useful UV-B dose (kJ m-2 d -1 ) for predicting variation in UV-B resistance levels. FIGURE b Heat resistance of Sitka spruce seedlings after heating to 38o C for 30 minutes. Needles from 1-year-old seedlings from an 84-m seed source were tested. Each bar is the mean of 15 seedlings, +_o ne standard error.
.. Pinus contorta var. latifolia (interior lodgepole pine) One of the most common conifers in the interior of British Columbia is the interior variety of lodgepole pine. In North America, it ranges from the Yukon to Colorado, often in even-aged stands that arise after forest fires (Farrar ). It can be found at low elevations on relatively warm, dry sites through a range of site conditions to cool and moist at high elevations, with strong genetic variation among populations (Rehfeldt et al. ). This generally short-lived (less than years) species is found growing as high as m in some parts of its range (USDA Forest Service ). FIGURE Shoots of interior lodgepole pine seedlings Being a shade-intolerant pioneer species, lodgepole grown with increasing UV-B. From left to right, pine might be expected to be fairly resistant to UV-B 0, 4, 8, and 12 kJ UV-B m-2 d -1 . radiation. However, there is considerable variation among and within populations in growth potential and stress (cold, drought, etc.) resistance, so similar 20 a. variation would be expected in UV-B resistance. In our study we tested lodgepole pine seedlings 15 from the southern interior of British Columbia, from three elevations up to m, and -year-old seedlings 10 from m elevation (Figure ). As expected, there were no obvious visible changes in the foliage (Figure 5 ), and no indication of needle curling or pigment Seedling height (cm) 0 kJ UV-B 4 kJ UV-B 8 kJ UV-B 12 kJ UV-B breakdown even at triple the ambient dose of UV-B. 0 At the morphological level, the populations we tested 700 m 1080 m 1720 m seemed to be very resistant to increased levels of UV-B. Seed source elevation (m) For young seedlings from low elevation ( m), FIGURE a Shoot height of lodgepole pine seedlings height growth was positively affected by moderate after 5 months of UV-B exposure. Each bar is levels of UV-B, increasing by % as dose increased the mean of 45 seedlings, +_o ne standard from to kJ (Figure a). Growth then decreased error. slightly at the highest UV level. For seedlings from middle and high elevation, UV-B levels above zero had no effect or a small positive effect. 30 b. Increased exposure to UV-B increased stress 25 resistance in seedlings from all elevations. Frost o hardiness in early fall increased with increasing UV-B 20 dose (Figure b), and heat resistance also increased 15 slightly (Figure ). From these results, it seems that 10 some UV-B radiation is beneficial to growth and Quantum yield survival of this species. 5 At the population level, growth potential of after freezing to -13 C (%) 0 lodgepole pine is negatively correlated with stress 04812 resistance (faster growth associated with lower stress UV-B dose (kJ m-2 d -1 ) resistance) (Rehfeldt et al. ). However, owing to the large amount of variation within populations, it FIGURE b Frost hardiness of lodgepole pine seedlings o may be possible to find parents with both high growth after freezing to -13 C in early September. potential and high resistance to UV-B and other Each bar is the mean of 45 seedlings, +_o ne stresses. standard error.
.. Pseudotsuga menziesii var. menziesii a. (coastal Douglas-fir) Coastal Douglas-fir is an economically valuable tree species along the west coast, ranging from mid- British Columbia to central California (Farrar ). This dominant long-lived species is a pioneer with moderate shade tolerance in its first year, thereafter requiring full sunlight (USDA Forest Service ). b. Damage from UV-B is most likely to occur in the first year where seedlings are growing on exposed sites. The needles last _ years, so although mature needles are well-adapted to high light conditions, there may be potential for cumulative UV-B damage as surface layers change over time. We tested young seedlings of coastal Douglas-fir in a preliminary study done in . Seedlings from three elevations (_ m) on Vancouver Island were used. To stress seedlings when they were potentially most sensitive, we began UV-B exposure week after germination. There were four doses of supplemental UV-B (, , , and kJ m-2 d -1 ), with FIGURE a) Seedlings of mid-elevation coastal Douglas- the highest dose slightly higher than that used in our fir grown with increasing UV-B (seedling at 14 -2 -1 other experiments. Exposure began in February is dead). Units for UV-B are kJ m d . in a heated glasshouse. b) High-elevation seedling grown at highest Within days, seedlings at the highest dose UV-B level. showed needle curling, and in less than a week, about % of the Douglas-fir seedlings at that dose were dead (Figure a,b). Seedlings at the lower UV-B 20 doses also showed morphological changes; after weeks there was a strong effect of UV-B on height 15 (Figure ), root collar diameter, and dry weight. Dry weights of Douglas-fir seedlings decreased as much 10 as % as UV-B increased from to kJ m-2 d -1 . There was no overall effect of elevation on these responses 5 to UV-B, possibly because the range in elevation was Seedling height (cm) 0 kJ UV-B 4 kJ UV-B 8 kJ UV-B 14 kJ UV-B not wide enough. 0 Light quality and balance (ratio of UV-B to 150 m 525 m 970 m visible) may have been confounding factors in this Seed source elevation (m) experiment because the test was done during the grey days of winter in Victoria, when ambient visible light FIGURE Shoot height of coastal Douglas-fir seedlings levels are usually less than half of summer levels. after 4 months of UV-B exposure in a This may have made the seedlings more vulnerable to glasshouse. Each bar is the mean of 30 seedlings, +_o ne standard error, except for UV-B, with less ability to undergo light-dependent the 14 kJ treatment in which most seedlings repair processes. died. Further testing is needed to reliably establish the sensitivity of this species to UV-B under ambient visible light levels.
.. Pseudotsuga menziesii var. glauca (interior Douglas-fir) Interior or Rocky Mountain Douglas-fir ranges from the interior mountains of the Pacific Northwest south through the Rocky Mountains to Mexico (Farrar ), at elevations up to m. It is more cold- and drought-tolerant than the coastal variety, with which it hybridizes freely in areas of overlapping range. There is a considerable amount of genetic variation among populations following gradients of elevation and latitude (Rehfeldt ), with strong differences in frost hardiness and growth potential. The interior variety of Douglas-fir grows more slowly than the coastal variety and has a shorter lifespan (USDA Forest Service ). Seedlings regenerate best in moderate shade, where they would be exposed to FIGURE Seedlings of mid-elevation interior Douglas-fir less UV-B. grown at 0 (left) or 12 (right) kJ UV-B m-2 d -1 . We tested young seedlings of interior Douglas-fir There were no striking morphological changes from three elevations (, , and m). For the in interior Douglas-fir seedlings. most part, seedlings grew normally and showed little evidence of UV-B_ induced changes in morphology 25 (Figure ). Low-elevation seedlings showed greater a. height growth than mid- and high-elevation seed- 20 lings (Figure a), but were not strongly affected by increased UV-B. Height growth did not decrease 15 significantly with increased UV-B for any of the 10 elevations. Similar to several other species, interior Douglas- Seedling height (cm) 5 fir seedlings showed increased frost hardiness with 0 kJ UV-B 4 kJ UV-B 8 kJ UV-B 12 kJ UV-B increased UV-B up to a point. Seedlings grown 0 488 m 826m 1223 m without any UV-B were the most damaged by Seed source elevation (m) freezing (Figure b), while those grown at kJ (double ambient levels) were the most frost hardy. FIGURE a Shoot height of interior Douglas-fir seedlings Frost hardiness was similar at and kJ. after 5 months of UV-B exposure. Each bar is Based on our preliminary results, we suggest that the mean of 45 seedlings, +_o ne standard interior Douglas-fir is more resistant to UV-B than error. the coastal variety. Because there are known patterns of genetic variation in other adaptive traits, it is expected that there will also be patterns of variation b. in UV-B resistance. Testing of a wider range of seed 60 sources, using seedlings and mature trees under field o conditions, would be needed to describe these 40 patterns.
Quantum yield 20 after freezing to -13 C (%) 0 04812 UV-B dose (kJ m-2 d -1 )
FIGURE b Frost hardiness of interior Douglas-fir seedlings after freezing to -13o C in early September. Each bar is the mean of 45 seedlings, +_o ne standard error.
.. Thuja plicata (western redcedar) Ranging from the Pacific coast of northern British Columbia south to northern California and east through the west slopes of the Rocky Mountains, western redcedar grows to large sizes and may live for more than years (USDA Forest Service ). This valuable species regenerates best in partial shade; seedlings often succumb to drought and high temperature stresses in full sunlight. Although it is found at elevations up to m or more farther south, in British Columbia it is usually found at less 0 4 812 than m elevation, with a preference for moist sites. Because seedlings are very shade-tolerant, and FIGURE Shoots of western redcedar grown at (left to susceptible to drought and heat stress, we expected -2 -1 right) 0, 4, 8, and 12 kJ UV-B m d . There that they might also be sensitive to UV-B radiation. appeared to be changes in branchlet angle as We tested several seed sources of young seedlings UV-B levels increased. and a single source of -year-old seedlings from m elevation. Our test with young seedlings was somewhat compromised by taking place during the 70 time of an unusually large blizzard in early , 60 during which the greenhouse nearly collapsed. We o 50 will present results here for the -year-old seedlings, 40 grown the following summer. As UV-B levels increased, there were no marked 30
changes in the scale-like leaves, but there appeared to Quantum yield 20 be small changes in the angle of branchlets (Figure 10 ). There was also a reduction in height growth (data after freezing to -13 C (%) 0 not shown). 04812 In addition to these changes, western redcedar UV-B dose (kJ m-2 d -1 ) seedlings showed strong changes in frost hardiness as UV-B dose increased (Figure ). Seedlings grown FIGURE Frost hardiness of western redcedar seedlings without any UV-B were less hardy than those grown after freezing to -13o C in September. Each bar is at ambient levels, but, as UV-B increased beyond the mean of 15 seedlings, +_o ne standard error. ambient, frost hardiness decreased. Seedlings grown at the highest UV-B level were very sensitive to freezing. The responses of the western redcedar seedlings in our test suggest that at least some populations of this species may be sensitive to increases in UV-B radi- ation. Because there is moderate genetic variation in other adaptive traits in western redcedar, it would be useful to expand testing to include more populations from across its natural range.
... Tsuga heterophylla (western hemlock) a. b. From Alaska to northern California, western hemlock stands are found on moist sites along the coast and also inland west of the Rocky Mountains (Farrar ). This fast-growing species is usually found at low to mid elevations, although farther south it grows as high as about m (USDA Forest Service ). The highly shade-tolerant seedlings are susceptible to frost, heat, drought, and sunscald, but mature trees can grow in high light conditions, provided there is adequate moisture. Seedlings might be expected to 0 4 812 be relatively sensitive to increased UV-B radiation, particularly in the presence of other environmental FIGURE a) Shoots of western hemlock grown at (left stresses. to right) 0, 4, 8, and 12 kJ UV-B m-2 d -1 . Note We tested young western hemlock seedlings from _ the needle curling as UV-B levels increased. a range of elevations ( m) and -year-old b) Bronzing on needles of western hemlock seedlings from a source at m elevation. Seedlings grown at the highest UV-B dose. showed typical morphological symptoms of UV-B damage early in the treatments (Figure , and a,b). 20 Needles grown without any UV-B were straight and 18 a. flat, while those grown at higher levels of UV were 16 curled and twisted, and often showed bronzing 14 (Figure b) or chlorosis. Height growth was also 12 reduced by _ % as UV-B dose increased from to 10 kJ (Figure a). High-elevation seedlings were less 8 affected than low- or mid-elevation ones, but they 6
Seedling height (cm) 4 also grew less at all UV-B doses. 2 0 kJ UV-B 4 kJ UV-B 8 kJ UV-B 12 kJ UV-B Growth under higher levels of UV-B increased 0 the heat resistance of young and older seedlings. 100 m 350 m 600 m Seedlings grown with no UV-B suffered two to three Seed source elevation (m) times as much damage from heat as seedlings grown FIGURE a Shoot height of western hemlock seedlings at kJ UV-B (see Figure ). Frost hardiness, after 4 months of UV-B exposure. Each bar is however, did not always increase with UV-B the mean of 45 seedlings, +_o ne standard exposure_ in early September, it decreased for error. seedlings grown at higher levels of UV-B. Hemlock seedlings showed pronounced changes 1600 in pigment and flavonoid content in their foliage as b. exposure to UV-B increased. Chlorophyll levels 1400 tended to decrease with increasing UV-B (data not -1 1200 shown), but flavonoids increased (Figure b). 1000 Averaged over all elevations, there was a % increase 800 in flavonoid absorbance at nm between and 600 kJ UV-B. 400 These tests indicate that seedlings of western Flavonoid content 200
hemlock from British Columbia are potentially 0 kJ UV-B 4 kJ UV-B 8 kJ UV-B 12 kJ UV-B 0 sensitive to increasing levels of UV-B radiation. (absorbance at 280 nm g tissue) 183 m 460 m 670 m Comparison with populations from farther south Seed source elevation (m) and higher elevations would be useful. FIGURE b Flavonoid content of western hemlock seedlings after 5 months of UV-B exposure. Each bar is the mean of nine seedlings, +_o ne standard error.
. Ranking of Species by Risk of Damage 012
Of the dozen species and four dozen seed sources that we tested in our UV-B chambers, several showed pronounced changes in morphology, growth, and stress tolerance, while others appeared to be resistant, showing few changes (Figure ). UV-B exposure, in general, had more effect on low- than high-elevation seed sources. The sensitive conifers developed external changes such as curled and twisted needles, changes in needle or branchlet angle, and reduced growth. The lone hardwood tested, paper birch, showed large reductions in leaf size and changes in leaf surface morphology under high UV-B levels. FIGURE Lodgepole pine, interior Douglas-fir, western The resistant species showed few obvious external hemlock, and Engelmann spruce grown at 0 changes, but they did show increased resistance to -2 -1 (four seedlings on left) or 12 kJ UV-B m d . other stresses such as freezing and heat. In fact, most The hemlock and spruce showed strong of the species tested, whether UV-B sensitive or morphological changes with increased UV-B, resistant, were more resistant to high temperatures while the pine and Douglas-fir did not. when grown with supplemental UV-B radiation (Figure ). This suggests that acclimation to increased UV-B triggers metabolic changes that are 70 also involved in resistance to high temperatures, no UV-B with UV-B likely by increasing the ability to dissipate excess 60 energy. o 50 Our tests were done in greenhouse conditions with seedlings, so we cannot accurately extrapolate to 40 field conditions with mature trees. We cannot, 30
therefore, provide a definitive prediction about the Quantum yield effects of long-term UV-B radiation increases on 20 overall growth and yield of the species tested. But we after heating to 38 C (%) 10 can provide a relative ranking of species for seedlings, and have done so in Figure . In the first year or two 0 of growth, it is probable that this ranking gives a Cwr Cy Hw Ss Fdi Pli Se reasonable general estimate of how these species will FIGURE Heat resistance of conifer species grown with or respond to increasing levels of UV-B. However, there without UV-B. Cwr = western redcedar, will be a wide range of sensitivity within most Cy = yellow-cedar, Hw = western hemlock, species, because populations are strongly differen- Ss = Sitka spruce, Fdi = interior Douglas-fir, tiated in adaptive traits. The sensitivity will also Pli = interior lodgepole pine, Se = Engelmann depend on other environmental conditions at the spruce. The "with UV-B" column is the mean of growing site, and whether or not planted seedlings the 4, 8, and 12 kJ UV-B treatments. have been pre-conditioned by exposure to UV-B during early growth. This variety of responses among and within species will help researchers and forest managers in developing solutions to deal with increased UV-B levels and their impacts on forest ecosystems.
MOST MOST SENSITIVE RESISTANT
fir pine Sitka larch birch cedar Paper Grand spruce spruce spruce Yellow- Interior Interior Interior Coastal Western Western Western Western Western Western hemlock redcedar lodgepole Douglas-fir Douglas-fir Engelmann
FIGURE Predicted ranking of some British Columbia tree species for resistance to increased UV-B, based on greenhouse testing.
4 OBSERVATIONS AND RECOMMENDATIONS FOR FUTURE WORK
There were many challenges on the way to completing avoided when handling seedlings. For high-elevation this project in a fairly new research area. We designed or high-UV-B sites, the seed sources used should and built innovative UV-B chambers, and developed combine reasonable levels of UV-B tolerance and and applied fresh methods of testing seedling growth potential. Lodgepole pine seedlings appear to responses to UV-B. We dealt with the vagaries of be well adapted to current levels of UV-B, and will Victoria weather (Figure )and obstinate irrigation likely continue to do well under moderate future systems. We gathered a truckload of data and climbed increases. a mountain of analyses. The decrease in ozone levels over Canada From all of this, benefits have emerged. We met (relative to pre-) was _ % over the past decade, our objectives of ) determining the effects of and may continue for at least a few decades. This increased UV-B levels on tree seedlings, ) looking for translates into UV-B increases of _ %, with a geographic variation in responses, and ) estimating doubling of UV-B possible in British Columbia for the risk of damage to various species. We provided some periods during the growing season. Given these information and education to interested audiences, changes, and that there are many unknowns (such as raising the awareness of ozone and UV-B in British the interactions between UV-B and climate change), Columbia. Our methods, hardware, and instrument calibrations have become a reference for new studies on the effects of UV-B in forestry and agriculture. There is now enough information available on UV-B effects on British Columbia trees to help in choices for seedling management and deployment to planting sites, at least for some of the major species. We know that UV-B sensitivity is generally higher for low- versus high-elevation seed sources, for decidu- ous versus evergreen species, and for shade-tolerant versus shade-intolerant species. We recommend that seedlings of shade-tolerant species (e.g., western hemlock) be protected from full sun at the planting site, or gradually conditioned to UV-B in the nursery. Sharp increases in UV-B and visible light should be FIGURE UV-B greenhouse with a snowfall.
this issue cannot be considered resolved. With this additional information, managers will It is our hope that others will continue the work be able to make appropriate choices using genecology that we began. From the modest start made here, and silviculture to minimize the risk of UV-B damage more extensive testing and monitoring projects in the to future forest productivity. field will determine the cumulative effects of elevated UV-B on forest productivity and sustainability in British Columbia. Our recommendations for future studies are based on our results and priorities from other scientists (de Fabo ; Farrell ). Ideally, further research and monitoring of UV-B effects on forest species in British Columbia should include the following: Multi-year growth studies in field conditions Tests of seedlings and mature trees from a wide range of species and populations Use of several populations for each species, and families within populations Identification of sensitive species and populations, not just in trees (indicators) Use of at least two levels of increased UV-B, preferably with modulating exposure systems Field sites covering gradients of latitude and elevation (range of UV-B doses) c Sven Kohle, www.allthesky.de Measurement of effects on carbon allocation and secondary chemistry FIGURE Rainbows are natural examples of the Identification of key symptoms of UV-B damage spectral qualities of sunlight. Interaction between UV-B and other stresses Modelling of growth processes and competitive interactions Testing of effects on reproductive physiology Evaluation of implications of UV-B_ induced changes on insect and disease resistance Genetic selection of UV-B_ resistant, productive populations and families
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