Tag Archives: redwood tree height

Canopy Height Distribution in Old Growth Redwood Forests

Methods

This article is related to an earlier article posted on this web site, “Distribution of Tree Height in An Old Growth Redwood Forest”.   An analysis of recent LiDAR data allows for confirmation and expansion of the analysis in that article.

LiDAR data includes first return and ground points.  From this information height above ground can be calculated, typically at the square meter level using average ground elevation and maximum first return elevation within the square meter.  From this, derivative products can be created, including color height maps and data tables. 

In order to use the LiDAR data for canopy height distribution, I aggregated the results to 20 m x 20 m (400 square meter) tiles.  This is used to approximate crown spacing in old growth redwood forests.  The maximum calculated height above ground within each 400 square meter area is used to create the distribution graphs.  In practice the number of tiles is slightly greater than the number of actual redwood trees, by about twenty percent.  This is due to the same tree being included in two tiles.

Overall Results

Most importantly, redwood groves have a variety of footprints but similar distributions of tree height beyond the median height for the grove.  Some groves are thin wisps along canyon bottoms (think Big Sur) versus others are broad forests filling both sides of large valleys (think Prairie Creek).  But for most groves the very tallest trees in the grove are much higher than average height and the number of trees drops markedly in each ten foot height increment beyond the grove median height.

Redwood forests are amazingly scarce and small.  Coming out of the latest glacial maximum redwoods were few in number, then filled in a shifting northward range that represented just 2,000,000 acres in a 500 miles long by average six miles wide thin rectangle just inland of the Pacific Ocean from southern Oregon to Big Sur. In this range the needed blend of rare winter freezes (as redwoods cannot propagate by seed in areas with regular winter freezes) and regular intraday offshore to onshore summer fog (as fog hydrates the tall crowns of redwoods but lots of sun is also needed) occurs. Today’s remaining 100,000 or so old growth acres cover about the same range but in remnant patches, almost all in parks. 

Second, redwoods grow tall in good habitat throughout their range. Three-hundred-foot redwoods can be found from Big Sur to southern Oregon, and 328-foot (100 meter) redwoods can be found from the Santa Cruz Mountains to the Smith River near Crescent City.  Then the 50 or so tallest, those over 360 feet, can be found in Humboldt Redwoods State Park (about 33), Redwood National Park (about 13), and Montgomery Woods Reserve (about 4).  Prairie Creek Redwoods State Park and Jedediah Smith Redwoods State Park may also each have one or so 360-foot trees.

Third, old growth redwoods follow similar height distributions beyond a midpoint which is much lower than the maximum height in any particular grove.  The median height in a grove is typically 250-275 feet tall, with 300-foot redwoods often common and redwoods over 340 feet relatively rare.  When reviewed at the hectare level, the tallest canopies are around 340 feet median height.

The shortest trees reaching the canopy may be about 150 feet tall, there is no zero point.  This makes the distribution a truncated normal distribution, not a normal distribution. The canopy height distribution does follow a near normal distribution to the right of the canopy height midpoint.

Fourth, the tallest redwoods tend to clump together within groves. Reasons could be local light advantage, a local underground water source, common genetic specificity, or exceptional local soil conditions. The majority of the tallest redwoods have locally tall trees adjacent or nearby. The tallest redwoods tend to grow in groups of two, three, or four, with their tops twenty to thirty feet above the other tree tops in the same area. This is especially true on flats where the canopies are continuous rather than on slopes where the canopies tend to be emergent.

Demonstrated Canopy Height Distribution

The first area assessed are the Bull Creek and Eel River groves in Humboldt Redwoods State Park.

Here the canopy is relatively continuous within groves (in other words very few canopy gaps) with the exception of a couple areas.   This is a LiDAR color height map along Bull Creek in the Tall Tree area (Tall Tree / Rockefeller Redwood is in upper right).  The area shown covers about 500m x 500m.  Yellow is over 80 meters, orange over 90 meters, and red over 100 meters.  Here you can see yellows and oranges dominate, with most tree heights in the 275-300-foot range.  Then here and there are taller trees, which tend to clump together.

HRSP Tall Tree Area Color Height Map of Canopy (Tall Tree is to Upper Right)

This same pattern is repeated over and over in these groves, resulting in this aggregate canopy height distribution map:

Humboldt Redwoods State Park Old Growth Eel River and Bull Creek Canopy Height Distribution

To highlight what is shown, this is the percent of the canopy over given heights:

Over 280 feet    51%

Over 300 feet    35%

Over 320 feet    16%

Over 330 feet    8.5%      

Over 340 feet    3.5%                                

Over 350 feet    1.1%

Over 360 feet    0.2%    

Over 370 feet    0.01%

A top five percent tree is 340 feet tall. 

Then the second area assessed is a drainage well north of Humboldt Redwoods State Park.  Here the canopy is emergent, there are large gaps with lower heights but certainly many areas with tall redwoods, typically following slopes along and above creeks, which provide good soil and some wind protection.  This is a LiDAR color height map of a portion of the valley, covering about a 500m x 500m area. Yellow is over 80 meters, orange over 90 meters, and red over 100 meters.  Here you can see yellows and oranges in groups separated by lower canopy, with most tree heights in the 250-260-foot range.  Then here and there are taller trees. The tall trees are less dense, more spread out, versus Humboldt Redwoods State Park.

Northern redwood park Color Height Map of canopy in creek valley

A dozen similar areas were then aggregated to create this height distribution chart:

Area of Northern Redwood Park Canopy Height Distribution

To highlight what is shown, here is the percent of canopy above certain heights:

Over 260 feet    54%

Over 280 feet    25%

Over 300 feet      7%

Over 310 feet      3%

Over 320 feet    1.2%

Over 330 feet    0.3%      

Over 340 feet    .07%                                

Over 350 feet    .03%

A top five percent tree is 310 feet tall.

Putting HRSP and the northern redwood park area together in a graph of ten-foot height intervals above median height, it is evident both follow a similar distribution up to the tallest trees.  This is likely true when reviewing other old growth redwood areas. 

Height Distribution Ten Foot Intervals Right of Median

Finally this is a chart showing the canopy cross section in the three tallest 100m x 100m (hectares) in Humboldt Redwoods State Park. As noted earlier, the tallest trees tend to grow adjacently and are twenty to thirty feet above the average height in the local (one hectare) area.

Height Distribution HRSP Tallest Hectares

Redwoods became rare coming out of the latest ice age, then old growth redwoods became much, much rarer after commercial harvest.  Then within remaining old growth areas, the tree heights follow a truncated normal distribution, with decreasing numbers of trees for each ten foot increment above the local median. Then the tallest trees, those over 340 feet, are very uncommon and tend to clump together in very specific areas having the most optimal growing conditions.

Thanks for reading.

How Fast Do Growing Redwoods Reach Exceptional Heights

 

1       Redwood Tree Height

 Redwood trees are noted for reaching exceptional heights.  This is the only species of tree that currently has numerous individual trees over 100 meters in height.  But even for redwoods, 100-meter trees are relatively uncommon, with about 1,900 individual trees exceeding this height.  Then there are only 40 or so redwoods over 110 meters in height, with the current demonstrated maximum height about 116 meters.

This table recaps the counts for tall redwood trees by Park and Area.

Summary 100 Meter Redwood Trees

2       Redwood Tree Height vs Age In Old Growth Forests

In 2009 and 2010 redwood research plots were established in old growth forests across the current redwood range, sixteen in all.  Each plot is one hectare (10,000 square meters) and is shaped in a long narrow 10-meter X 100-meter rectangle, with two tall redwoods near each end.   These plots were put in to monitor redwood tree and redwood tree forest health over time.  As part of this research, the tree heights are measured every so often, and the tree ages were established by core samples up the trunk to allow the thin increment borer to reach the center of the trunk if possible.  A few redwoods outside the plots are also included in the longitudinal study.

All of this is detailed in the research paper: 

Carroll AL, Sillett SC, Kramer RD (2014) Millennium-Scale Crossdating and Inter-Annual Climate Sensitivities of Standing California Redwoods. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0102545

and then recently updated in this paper:

Stephen C. Sillett, Robert Van Pelt, Allyson L. Carroll, Jim Campbell-Spickler, Marie E. Antoine (2020) Aboveground biomass dynamics and growth efficiency of Sequoia sempervirens forests
https://doi.org/10.1016/j.foreco.2019.117740

From Appendix F in the updated research paper, the tree heights and ages can be plotted.  I have generated this plot and table from the information in Appendix F.

SESE Study Age vs Height

From this graph we can see the youngest 100-meter redwood from the study is a little over 300 years old.  Then the tallest redwoods cover a broad age range, from about 630 years old to about 2,000 years old.  Some of the older trees lost some height but then grew tall again, this is termed reiterated growth.   Then other trees have continued to grow without much crown breakage.  The very oldest trees tend to be a little shorter and include many reiterations. 

Note there is a 120 or so year old tree that is 82 meters in height. The young redwoods in old growth areas, if they have sufficient access to light, may grow more quickly than young redwoods in second growth forests, as the young redwoods in old growth forests can tap into the underground root network put out by other old growth trees and acquire shared nutrients from the existing old growth trees.

3       Redwood Tree Height vs Age in Second Growth Forests

Redwood tree forests were timbered starting around 1850.  After timber operations left an area the redwoods began to grow again from the ground up, either as new growth from stump roots or growth from seedling sprouts.  These second growth forests are in both managed timber lands and in parks and reserves.  In parks and reserves the second growth redwoods have been thinned over time to help the forests more quickly mature.  The tallest second growth redwoods are about 285 feet tall and about 160 years old.  How long will it be before these trees reach 100 meters in height?  It is likely much sooner than 500 years.

Navarro North Fork Tallest Tree (LiDAR indicated height 275 feet, age about 160 years. From Google Earth Street View.

For example, in Navarro Redwoods the tallest trees are 250-275 feet tall and growing on average eight inches per year.

Tall Navarro trees with LiDAR indicated growth rates. Trees are approximately 160 years old.

This is an estimate of growth curves for second growth redwoods in optimal habitats.  It is predicted 160 year old second growth redwoods in optimal growing areas will on average reach 100 meters in height at age 400 years (240 years from now).  There will likely be a few very fast-growing second growth trees that reach 300 feet 30 years from now and 328 feet (100 meters) 100 years from now.

Estimated Height Growth Curve for Second Growth Redwoods in Optimal Habitats

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.