Climate Variation

Details: Written by: Dustin Rocksvold

Redwood enthusiasts who are lucky enough to know where these elusive albino redwoods reside have discovered that some of these peculiar trees tend to dieback and regrow in cyclical patterns. Some basal albino redwoods exhibit large amounts of leaf litter accumulation while others show very little accumulation. As if the albino redwood mystery wasn’t complex enough, some experts have suggested that this dieback & regrowth pattern occurs because the mutations are easily prone to environmental stresses. Specifically: heat, cold, and drought conditions appear to play a role in albino redwood mortality. Research at UC Santa Cruz has shown that albino redwoods do indeed transpire at much higher rates in summer compared to their green counterparts as seen here in this paper: <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0191836" target="_blank" rel="noopener">The water relations and xylem attributes of albino redwood shoots</a> These discoveries have led experts to speculate that albino redwoods overall may have inefficient stomatal control leading to excessive moisture loss and death within their needles. Stomata are pores on plant leaves that help regulate transpiration and water loss. In normal green redwoods, cool humid conditions will prompt stomata pores to open allowing for a greater surface area for transpiration to occur. Conversely, in warm weather accompanied by low humidity, stomata will close down to conserve water. The situation for albino redwoods is more problematic and appears to run counter to the normal function of the plant. In hot weather, if albino redwood stomatal cells don’t close down enough to limit moisture loss, the foliage will cavitate, wilt, and die. On the other hand, if temperature and humidity levels are ideal, but there isn’t a sufficient amount of sugars readily available from the parent tree, the mutation will dieback due to deprivation. This is a catch 22 situation that albino redwoods must face on a daily basis. Even when surviving in this precarious state, it’s not known if reliance on high transpiration rates is a definitive reason why there’s a tendency to see dieback on these trees. While it’s generally understood that all redwoods (whether albino or not) will experience some form of dieback under extreme moisture stress, it’s not known if the parent redwood is sacrificing the mutation at the expense of water or energy conservation.
Additionally, other seasonal factors like excessive heat, & freezing temperatures have led to further assumptions that albino redwoods may not have adequate coping mechanisms for extreme weather conditions.
 <img src="/images/DSCN9857_L.jpg" alt="DSCN9857 L" width="311" height="462" /><img src="/images/DSC09671_L.jpg" alt="DSC09671 L" width="259" height="462" style="float: left;" />
 Pictures of a basal albino redwood in the natural range. The photo on the left was taken in June 2012 while the one on the right was taken in June 2018. Notice how the albino redwood almost appears dead in 2012, only to return to a more vigorous state in 2018. Some may attribute this to the drought that was experienced between 2011-2016. If this is true, why do surrounding green shoots appear unaffected in both the 2012 & 2018 pictures?
 
If these reasons aren’t enough to show albino redwoods are at a real disadvantage, other factors such as fungal pathogens, insect damage, vandalism, and animal browsing can further add to the demise of these trees. Sudden oak death which has made headlines in the last couple of decades produces minor dieback on both green and white foliage. Various insects such as thrips and mites which are common in redwood forests attack redwood needles and discolor foliage. Visitors at times take albino foliage as souvenirs also adding to further losses. Deer which have been known at times to rub their antlers on young trees during the fall rut also contribute to additional damage. The culmination of these external causes doesn’t appear to add up to a cyclical pattern of dieback seen in albino redwoods, but can further contribute to their destruction.
 With the culmination of the above, albino redwoods are indeed in a precarious position and must find a balance to survive. These disadvantages alone, make researchers question how these anomalies of nature can survive in an environment where the deck seems stacked against them. But are albino redwoods truly fragile mutations or robust warriors? Some may indeed exhibit poor stomatal control, but are they really at the mercy of the weather, or is there another factor at play pointing to albino redwood mortality? What advantages do healthy-appearing albino redwoods have over their counterparts and what can their life cycles tell us about the overall health of the redwood forests? These questions may seem daunting as if one was to begin tackling a 10,000-piece jigsaw puzzle. It seems current research is only now starting to piece together the outer edges of the mystery.
<img src="/images/DSCN9947_L.jpg" alt="DSCN9947 L" />
 Cotati Tree Chimeric Albino redwood illustrating various mosaic patterns seen within these mutations.
To start putting the pieces into place, several key questions need to be asked and formed into a hypothesis.
Are albino redwoods fragile due to physiological, ecological, or environmental causes?
Specifically:
A) Are climate factors contributing to albino redwood dieback or longevity? B) Does temperature variation affect stomatal control? C) Can albino redwoods endure weather extremes? D) What implications will these results have on the species?
Because naturally occurring albino redwoods in the wild are very rare, studying various groups of trees in the natural setting was deemed impractical for logistical & ecological reasons. The concern was to conduct a study that would yield the best possible answers, yet not leave the human footprint within the forest. To achieve this, a group of 25 propagated chimeric albino redwoods was selected & planted a test plot within the Central Sierra spring of 2017. Ten trees were initially planted in the ground with the remaining planted out over the course of summer. Trees selected for the study exhibited traits that were morphologically very similar to albino redwoods in the wild and ranged from 3-8’ in height. Both the wild & planted albino redwoods exhibit sectors that had mutated foliage supported by healthy green foliage. Observing the growth patterns with propagated albino chimeric redwoods allowed researchers the opportunity to see daily changes in a controlled setting that otherwise wouldn’t be possible with albino redwoods in the wild. Various chimeric albino redwoods from different parts of the natural range were selected for the study to gain a wider genetic sampling on how these chlorophyll deficient mutations would respond.
<img src="/images/DSCN9879_LL.jpg" alt="DSCN9879 LL" width="656" height="875" />
 Seven-foot-tall chimeric albino redwood at the Sierra test site.
 The location chosen for the test plot was well removed from the native range of Coast Redwoods by more than 100 miles. The site was situated in a lower montane forest at an elevation of approximately 3500’ elevation. The test plot’s climate fell within USDA hardiness zone 9a which exhibits average winter low temps between 20 to 25°F. At this elevation, snow is frequent in winter adding an element of stress to the trees that otherwise would not be seen regularly in the natural range. Summers exhibit hot conditions with temperatures frequently running from the low 90’s to the low 100’s°F. Additionally, humidity ranged only between 13-60% during the summer months. Some might consider this a hostile environment well beyond the scope of what would be seen in the natural setting. Because of these climate extremes, all trees were given supplemental irrigation during the summer months so as not to induce water stress. The experiment was looking for stomata control correlating to heat & cold tolerance in albino redwoods & not the test subjects’ ability to withstand drought stress.
 During the summer of 2017, all subjects were exposed to temperatures of over 100°F. Daily temperature fluctuations averaged between 68-93°F per day and did not exceed a temperature swing of more than 30°F in a single day. By late fall of that year, remarkably only 5% of the albino foliage from the 2017 growth season exhibited some form of dieback. A modest 20% of dieback occurred on albino foliage that was two seasons or older.
 
 <img src="/images/IMG_1546_L.jpg" alt="IMG 1546 L" width="733" height="978" />
Tree #14 originating from Santa Cruz County endures the full afternoon sun on July 29th, 2017. A nearby weather station recorded the daily high temperature at 98°F. Note how a majority of the albino foliage appears healthy despite the intense heat. The all-time high for the year was recorded a month later on August 28th, 2017 at 104°F.
 
<img src="/images/DSCN0012_L.jpg" alt="DSCN0012 L" width="735" height="981" />
 This picture was taken after the trees were planted on Nov 3rd, 2017. Notice how little albino foliage has died back on tree #14 during the summer months despite days of temperatures over 100°F.
As winter approached, it was not known if the albino foliage would be as resilient to cold weather as it had with coping in the summer heat. February daily winter temperatures averaged between 55°F -35°F per day with humidity ranging between 35% & 85%. As with the summer results, the albino foliage on 90% of the test subjects exhibited cold tolerant characteristics unseen before in albino redwoods. 
<img src="/images/DSCN9809_LL.jpg" alt="DSCN9809 LL" width="734" height="979" />
 In the dead of winter, albino foliage appears mangy on Tree #14 but is otherwise healthy under the snow. The picture was taken on February 21st, 2018. Two days later on the 23rd, the lowest temperature of the year was recorded at 18.7°F.
 <img src="/images/DSCN9812_L.jpg" alt="DSCN9812 L" width="728" height="971" />
 Tree #8 originating from Sonoma County shows the contrast of albino & green foliage in the snow. At times, these trees were covered in over a foot of snow during the winter of 2017/2018. The picture was taken on February 18th, 2018.
 
<img src="/images/DSCN9825_L.jpg" alt="DSCN9825 L" width="727" height="969" />
 The following spring, albino foliage on tree #14 survived remarkably well over winter with minimal dieback. The picture was taken on April 1st, 2018.
 
 <img src="/images/DSCN9832_L.jpg" alt="DSCN9832 L" width="725" height="544" />
 Close up of tree #14 in April 2018 showing foliage in excellent condition after enduring winter snow and ice. The picture was taken on April 1st, 2018.
 
<img src="/images/DSCN9863_L.jpg" alt="DSCN9863 L" width="729" height="972" />
 A closeup of Tree #8 April 2018 exhibiting albino redwood foliage after surviving the winter of 2017 & 2018. Like tree #14, albino foliage shows almost no dieback after winter.
By spring of 2018, only 10% of year-old albino foliage exhibited some form of dieback from either heat or cold stresses on all test subjects. A more modest 30% dieback occurred on albino foliage that was at least two seasons or older.
 If the weather environment at the Sierra test pot site exhibited temperature extremes higher and lower than what’s normally seen in the natural range, then why did these test subjects perform remarkably well during the heat of summer and cold of winter compared to their wild counterparts? One would assume that more needle dieback on the Sierra test subjects should have been seen compared to the naturally occurring albino redwoods along the coast. Another could argue that the test plot trees were given ample irrigation compared to the albino redwoods in the natural range which relies solely on fog drip and groundwater. If this truly was an unfair advantage, then why does normal green foliage on the parent trees to albino redwoods appear healthy when albino foliage started to dieback? The answer appears to indicate that redwoods may not exclusively be dependent on how much water is readily available, but how they respond & adapt to rapidly changing weather patterns.
 To test the hypothesis that rapidly changing weather patterns are influencing albino redwood dieback, a comparison was made between the weather patterns at the Sierra test plot site to two locations within the natural redwood range. Specifically, the weather patterns at Guerneville in Sonoma County and Felton in Santa Cruz County were used in the study. The hottest three consecutive days in July 2017 were plotted and compared at all three sites.
<img src="/images/Chart_1L.PNG" alt="Chart 1L" />
 Data courtesy of Weather Underground.
<img src="/images/Chart_2.PNG" alt="Chart 2" />
What's remarkable was the huge 24-hour variation in temperature and humidity reported by the Guerneville and Felton weather stations compared to the Sierra site. The trees within the Sierra test plot rarely experienced temperature shifts greater than 30°F per day and humidity changes of 33%. In contrast, the Guerneville and Felton sites exhibited temperature shifts greater than 51 degrees °F in a single day, accompanied by humidity swings exceeding 90% according to Weather Underground data. Cool onshore winds carrying low temperatures and high humidity during summer can quickly reverse to an off-shore weather pattern bringing low humidity and hot dry winds within a matter of hours. This yoyo weather effect induces stress on the native trees that otherwise would not be as pronounced in California’s interior. It’s plausible that in some individuals, the stomata within natural albino redwoods become overwhelmed in these conditions, leading to higher transpiration rates, cavitation, and eventual dieback. In comparison, the relatively dry Sierra Nevada test site provided a more stable temperature and humidity environment allowing for more efficient stomatal control in coast redwood albino chimeras.
A second temperature & humidity comparison was made for winter 2018 between the Sierra test plot site and the Guerneville & Felton locations. The coldest three consecutive days in February were plotted and compared at all three sites.
 <img src="/images/Chart_4.PNG" alt="Chart 4" width="931" height="661" />
 The winter trend lines for temperature and humidity appeared to follow a little more closely between all three sites compared to summer. Temperature fluctuations were less severe averaging a modest 32-degree °F swing at the Sierra site, 20-degree °F swing at Guerneville, & 21-degree °F swing at Felton. As expected, the Sierra site exhibited lower temperatures and humidity levels compared to the coastal locations. The humidity results showed a reversal in winter between the Sierra and coastal locations. The Sierra site showed the largest humidity swing of approximately 71% when compared to Guerneville’s 64%, & Felton’s 58% respectively. It’s speculated that the winter dormancy period combined with a lower variation of temperature and humidity may help preserve albino redwood foliage.
Stepping back and looking at the history of the Felton and Guerneville sites before the old-growth forests were removed; temperature and humidity changes most likely were more moderate during times of hot and cold weather periods compared to today. The dense stands of trees acted as a temperature and humidity buffer when rapidly changing weather patterns descended upon the forests. Because of these insulating properties, the trees created their own protective weather bubble by limiting moisture loss which is not seen at these sites today. Without the support of large tree stands, it’s assumed that the genetics of these individuals may not be as adaptive or tolerant to rapidly changing weather conditions as redwoods growing in more interior locations. Field observations have shown that albino redwoods growing in the natural range which exhibits fewer signs of cyclical dieback are most likely to be found growing in isolated interior groves. These trees are far more likely to be subject to weather extremes than their coastal brothers. These redwoods exhibit better stomatal control than trees near the coast & may be better adapted to coping with rapidly changing weather environments. In the broader sense, these implications may have a larger impact on the redwoods species as scientists delve into the questions of climate change. The answer may not lie with redwoods just adapting to new climates, but one that offers adequate moisture and a minimal shift in daily temperature & humidly variations. Redwood trees that can withstand large temperature and humidity shifts may be better suited to planting in new environments.
<img src="/images/DSCN0060_LL.jpg" alt="DSCN0060 LL" width="935" height="701" />
 The Amador Sentinel growing high above the banks of the Mokelumne River & Highway 49 is a normal green coast redwood located in the Sierra foothills. The tree is situated on a dry south-facing slope surrounded by grasslands. How this tree survives hot scorching summers may be in its ability to conserve water through strong stomatal control and adaptation to an environment that favors lower variation in temperature & humidity.
 
<img src="/images/DSC09328_L.jpg" alt="DSC09328 L" width="930" height="698" />
Can you spot the redwoods growing in this picture? Believe it or not, these coast redwoods are thriving amongst Ponderosa, Gray, & Knob Cone Pines which are species specifically adapted to drier environments. The trees are growing in an isolated interior grove within Pope Valley in Napa County. These redwoods endure colder winters, hotter summers, and drier conditions compared to trees near the coast. What’s remarkable is these redwoods have adapted to survive in this difficult environment.
In conclusion, the foliage in albino redwoods has shown remarkable resiliency to survive the harsh weather extremes of the Sierra Nevada Mountains. The results were quite astonishing for a mutation that once was considered quite fragile. This study demonstrated that albino redwood foliage does have adequate stomata control within a certain temperature & humidity band. It also shows that albino foliage does have the ability to adapt to weather extremes so long as the changes are gradual. Looking at the species as a whole, the key to redwood endurance may not hinge on a gradually warming climate, but an environment that lends itself to where trees can readily adjust to rapidly changing weather conditions. Whether the climate is hot or cold, it appears an environment that offers a lower variation of temperature & humidity may favor long-term survival for coast redwoods. The implications of these results may lend to normal green redwoods being genetically selected for more efficient water conservation qualities. This in turn could lead to trees that are better adapted to shifting weather patterns and drier conditions as the species faces the challenges of climate change. Individuals that exhibit robust stomatal control may be key in preserving the species into the new millennium.

Albino Redwoods Point to Resiliency Within The Species

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