Tag Archives: redwood tree height

Increased Atmospheric CO2 Is Increasing the Maximum Height of Old Growth Redwood Trees in Northern California

Note the information and assessments made herein are those of the author.  Some statements of facts and forecasts involve a degree of conjecture.

1       Increase in Atmospheric CO2 Since 1900

Atmospheric carbon dioxide (CO2) has increased since 1900 at an increasing rate.   This is due to the burning of fossil fuels to support industrialization, transportation, and home comfort.  Before 1900 the concentration of atmospheric CO2 was about 285 ppm and holding steady.  Now it is 415 ppm, increasing at an increasing rate, and will likely be around 500 ppm by 2050. 

For plants, CO2 provides energy for photosynthesis.  For humans, CO2 is a product of cellular respiration and must be released by breathing.  Increasing CO2 from the background level of 285 ppm up to about 1,000 ppm enables faster plant growth.  This is commonly done in indoor green houses.

However we humans have evolved over the past 200,000 years with CO2 at 285 ppm, now it is much higher.  In the same way increased CO2 supports increased plant growth, it is possible increased CO2 creates adverse issues for human cellular functioning.  Indoor CO2 levels over 1,000 ppm cause people to start to feel drowsy, an indicator of impeded brain function.

Plants:  Carbon dioxide + water + light YIELDS glucose + oxygen + water

Humans and other mammals:    Glucose + oxygen YIELDS carbon dioxide + water

2       Increase in Redwood Tree Growth Rates Since 1950

Studies of tree rings have shown redwood trees in the northern redwood parks have increased their growth rates markedly, especially since 1950.  Tree ring width since 1950 can average 50% per year more than what was experienced on average in the tree’s 1,000 to 2,000 years of life before 1950.

The northern redwood parks have not experienced adverse climate change like the southern redwood parks.  The recent droughts in the Humboldt and Del Norte county redwood parks were not as severe as those further south and there were no major fire events within these parks.   The increased CO2 has not led to substantial adverse climate events in the northern redwood parks and the redwood trees are increasing their growth rates in response to the CO2 increase.

3       Height Changes in very Tall Redwood Trees Since 2000

The increased growth rate in redwood trees is also expressed in increased crown growth, leading to increased tree height. It is documented theoretical tree height is limited to 425 feet or so due to how far ground nutrients can be pulled upward by adhesion versus the effect of gravity. For tall redwood trees this is partially offset by fog absorption but the demonstrated current height limit is 381 feet, with an historic height limit of maybe 400 feet. But for most of their lifespans the tallest redwood trees dealt with CO2 at 285 ppm, now it is 415 and going to 500.  So they may be able to get taller, all other things being equal.

To assess this, here are height changes in the tallest redwood trees by park that were measured somewhere around 2000 and then again somewhere around 2013.  So the height changes are over a 13 year period on average.

If redwood trees were experiencing their maximum heights then it would be expected the tallest trees in 2000 would grow less in the next thirteen years than trees that were a bit shorter. 

For RNP and HRSP this is not the case, the tallest trees grew just as much as other slightly shorter trees during the thirteen year period.   For MWP the tallest trees were suppressed, this is in line with the drought and fire conditions experienced by that redwoods reserve.

Humboldt redwoods 25 tallest trees measured in 2000 and 2013. Ordered left to right by descending height. Note tallest trees continued to grow at rate of less tall trees.

Humboldt Redwoods 93 tallest trees measured in both 2000 and 2013. Ordered left to right by descending height. Note tallest trees continued to grow at rate similar to less tall trees.

Redwood National Park tallest trees mesured in both 2000 and 2013. Ordered left to right by descending height Note tallest trees continued to grow at rate of less tall trees. Also note many current RNP tall trees were unknown in 2000.

Montgomery Woods Reserve tallest trees measured in both 2000 and 2013, ordered left to right by descending height. Note max height has been reached as tallest trees grew less than less tall trees. Park was subject to drought and fire during the 2000-2013 time period.

4       Tallest trees in 2050

It is likely the tallest redwood trees in the northern redwood parks will continue to grow, at an increasing rate, at least to the year 2050.  By 2050 the tallest trees, and the entire redwood canopy, are likely to be six or more feet higher than they are now.

So at least in part of their range, the redwood trees are benefitting from increased CO2.  As for people, the benefits are less certain.

Thanks for reading.

Distribution of Tree Height in an Old Growth Redwood Forest

1      Old Growth Redwoods


Old growth redwoods – that phrase invokes a lot of different feelings in people. Certainly in the present the phrase describes the large never cut forests in the redwood parks. Forests full of giant trees, some by rivers or streams and others along hillsides. Forests covered with needles and sorrel and forests covered with ferns. Forests with deer moving through them to reach the creeks, all the while shadowed by mountain lions. Forests with black bear dens. Remote and rugged but never more than a few miles from a highway.

Two parks with many acres of old growth redwoods as well as the ten tallest trees in the world are Humboldt Redwoods State Park and Redwood National Park.   Each parks contains hundreds of thousands of old growth redwood trees.   Here is the math:

Park Acres Old Growth Redwoods # Redwood Trees > 100 cm per Hectare # Acres per Hectare # Old Growth Redwood Trees
HRSP                    17,000 50 2.47                            344,130
RNP                    19,640 50 2.47                            397,571


The redwood density figure is a general rounding of the findings in a redwood plots study underway at Humboldt State University.

If that number seems too high, well…. Here are two pictures.   These are from the Redwood Creek Overlook on Bald Hills Road in Redwood National Park.   The old growth forests and patches are very distinctive.   If you go to that overlook and put a strong pair of binoculars on those forests it is an impressive site.   Many big and tall trees all growing along Redwood Creek and the surrounding feeder creeks and hillsides. I can’t imagine a more spectacular forest. It is kind of intimidating.

Redwood Creek Overlook looking west northwest.
Redwood Creek Overlook looking west northwest.


Redwood Creek Overlook west southwest view
Redwood Creek Overlook west southwest view


2      Height Distribution for the Tallest Trees


Thorough ground based searches combined with LiDAR technology have given a pretty complete picture of tree height in all parks with the exception of the Headwaters Reserve. The tallest redwoods, those over 365 feet, are all in Humboldt Redwoods State Park and Redwood National Park, with the exception of two trees in the exceptional Montgomery Woods Reserve. Then all the trees over 370 feet (there are only ten or so) are in Humboldt Redwoods State Park and Redwood National Park.


Trees over 350 feet.  Each line represents a tree.
Trees over 350 feet. Each line represents a tree.


There are two things that are apparent when viewing these graphs. First, the distribution patterns are very similar between the parks. And second, there are a lot more tall trees in HRSP than in RNP. Based on this data paired with the history of each park the explanation is certainly this: In Humboldt most of the forests with the tallest trees are intact. In Redwood National Park most of the forests with the tallest trees have been thinned or removed.


3      Height Distribution for Old Growth Redwood Trees


Noting the steepness of the curve on the tall trees graph it is evident there is some type of “bell shaped” distribution where there are many trees of a certain height, say 350 feet, then the trees get fewer and fewer at 360 feet and even more scarce at 370 feet.

Using this information and the total number of old growth redwoods we can infer the number of trees of certain heights:

Std Deviations Expected Pct of Trees Less Than HRSP Expected Trees RNP Expected Trees HRSP + RNP Expected Trees
2 97.725%                      7,829                      9,045                              16,874
3 99.865%                          465                          537                                1,001
4 99.997%                            11                            13                                      23
4.5 99.99966%                              1                              1                                        3
5 99.99997% 0.0981 0.1133 0.21

Looking at the results of expected trees versus actual tree populations, it is evident four standard deviations describes 368 feet or so redwoods, while 4.5 standard deviations describes the very tallest redwoods (380 feet).

Then with some calculations and interpolation, we can arrive at three standard deviations corresponding to a 338 foot redwood tree.   This then results with the following very approximate distribution of tree height in old growth redwood forests in Humboldt Redwoods State Park and Redwood National Park.

Std Dev Height Feet
4.5 383
4 368
3 338
2 308
1 278
0 248
-1 218
-2 188
-3 158
-4 128
-4.5 113


So the average old growth redwood in Humboldt and Redwood NP is 250 feet tall.  Remember this covers all old growth trees at all elevations that are at least 3.28 feet in diameter.

Then there are 1,000 trees over 338 feet in height.

What do you think?


4      Old Growth Redwood Groves Close Ups


For some closer in views of old growth, here are pictures from two of my favorite areas in the redwood parks.   There are views like this all over the redwood parks.


Humboldt Bull Creek outflow
Humboldt Bull Creek outflow


Redwood NP Lost Man Creek area
Redwood NP Lost Man Creek area


Thanks for viewing and reading.