Analysis of Plants Blooming on the Santa Rosa Plateau Vs. Time in 2001

Number Of Species Beginning And Ending Bloom Vs. Time
Bloom Duration
Showiness of the Bloom vs. Time


This page contains plots of the number of plants in bloom and the showiness of the bloom for the entire calendar year 2001, but contains an analysis of that data set only up to 6/21/01.

With the data set I've accumulated for the bloom at the Santa Rosa Plateau in the year 2001, I can compute detailed statistics on the bloom as it has progressed so far this year. This includes the number of plants that have begun blooming by a given date, the number that have ended blooming by a given date, the total number that are blooming vs. time, and the bloom duration of each species. In addition, I can estimate how "showy" the bloom is vs. time, using several different measures.

The data set is as follows. Beginning on 2/14/01, I have hiked 2-10 miles every 2-4 days, recorded which species are blooming, and estimated how full the bloom is for each common species. Because of the difficulty in hiking every trail and road, it is not always possible to produce regular estimates for species that bloom only in one location, or that bloom only on one trail that I do not hike as frequently. Thus the analysis here is confined only to those species for which I have accurately recorded the beginning and ending of their bloom, as well as producing accurate estimates of the percentage of bloom between those times.

The fullness of the bloom refers to how good the display is in the Reserve, either considering the Reserve as a whole or, in the case of spectacular displays in a given location, how good the display is in that location. Another way to think of it is in terms of this question: If I come to the Reserve at a given time, are there places I can go to see spectacular blooms, and if not, how will I rate the overall general bloom for a given species? In particular, it is not the fullness of bloom for a single plant or a single location, although it is usually similar due to the small range in altitude and environment at the Reserve. The most noticeable dissimilarities so far this year were for the chocolate lilies and the blue dicks:

Keep in mind that such species are the exceptions. For most species, all the plants come into bloom at about the same time at the Reserve, go out of bloom at the same time, and their fullness of bloom is the same wherever they are found on the Reserve.

This analysis is a work in progress, with some of the plots below confined to dates prior to 6/21. (Three of the plots are updated regularly, with the other three updated only infrequently.)

As of 6/21, there are 156 species in my data set, compared to 66 species that were too rare to be adequately followed.

Number Of Species Blooming, Beginning And Ending Bloom Vs. Time

Number Of Species Beginning Their Bloom Vs. Time:

Surprisingly, the number of species that have begun their bloom vs. time is almost exactly constant in time from mid-March through mid-June (the latest date analyzed), equal to 1.1 species beginning their bloom every day (a line with this slope is shown on the plot). Even the earliest bloomers, from mid-February through mid-March, have numbers that are quite similar, 1.2 species beginning their bloom every day.

Thus, in particular, there is no evidence of a "Spring Bloom" in the number of species beginning their bloom!

Number Of Species Ending Their Bloom Vs. Time:

Similarly, the number of species that have ended their bloom vs. time is almost exactly constant from late April through mid-June (the latest date analyzed), equal to 1.3 species ending their bloom every day. Thus again there is no evidence for a spring peak in these end numbers alone.

However, many species follow a pattern of coming in and out of full bloom quickly, but then declining to zero bloom very slowly. For example, species such as blue dicks, bush monkeyflower, owl's clover and California buttercup had a small population that continued to bloom for about a month after 95% of the population had finished blooming.

In the plot above, the end date is when it is not possible to find a given species blooming anywhere. If one defines the beginning and ending of bloom by the time at which 10% of the peak bloom is reached, the beginning plot would be roughly unchanged, whereas the ending plot would have significantly higher rates of around 2.1 species per day ending their bloom.

Number Of Species Blooming Vs. Time:

The total number of species blooming increased by the 1.1 species per day until the first flowers ended their bloom. At that point, there were ~80 species in bloom on any given day, which stayed roughly constant from the end of April to mid-May. After that time, the net of 1.1 species coming into bloom each day and 1.3 species ending their bloom each day results in a slow decline of 0.2 species per day that are in bloom.

Thus according to the number of species in bloom, the peak bloom is of very long duration. Typically, peaks are defined by their width at half-height, which means the peak bloom began in mid-April and the end hasn't been sighted yet!

With my estimates of how full the bloom is for each species, I can calculate a sum over all species of blooms of {the estimated percentage of full bloom for each species}. The variation of this number with time is plotted below:

This plot shows a definite shorter peak, the two weeks from mid-April to the beginning of May. (Although the half-height measurement would still result in a very long peak bloom interval.) It showed a sharper decline than the total number of species blooming, primarily because of the number of species had some individuals that lingered on well past the time when most of the species had finished blooming.

Bloom Duration

I calculate two measures of the bloom duration for each species. The first is a simple measure of time between the end date and the beginning date. The second is the time between the "10%" points, at which the species is in bloom at more than 10% of its peak.

The following histogram shows both measures:

The median bloom duration for all species is 52 days, with 38 days spent at greater than 10% of bloom.

Showiness of the Bloom vs. Time

Many people want to know when the peak bloom occurs for wildflowers. For example, Anza-Borrego State Park will send you a postcard approximately two weeks before they estimate that peak bloom will occur, and many people use that service.

The Showiness of the bloom is of course a quite subjective term. Some people are ecstatic to see the chocolate lilies in bloom because they are a rare species with a pretty bloom, whereas others may pass a field of chocolate lilies in full bloom and not even notice them since they do not create a large display of bright color. In the measures below, in general (but not always!) I ignore the rareness of the species or delicateness of the bloom, since these are very specific to an individual person. This is not to say that these factors are not important, just that they are difficult to quantify for a large number of people.

I concentrate on measures that would match most people's Wow! factor in judging how spectacular the bloom is. This involves how many species are blooming, how full the bloom for each species is, how spectacular each species is by itself, and how widespread the display is. Hence I define the showiness of the bloom as follows:

The showiness factor I use is a scale of 1-10, and is specific to this year. Flowers vary in their show from year to year, so the factor for a given species may be different in other years.

The factor of 10 is assigned to those flowers that create stunning visual displays, or that are of widespread interest. The flowers with a factor of 10 this year as of mid-May are:

Flowers with a factor of 8 are johnny-jump-up and California buttercup, which are sprinkled extensively throughout the Reserve, producing fields of yellow splashes of color. But these never produce the spectacular displays of the flowers with a factor of 10.

Flowers with a factor of 7 are ground pinks, California poppy, lupine and checkerbloom. Ground pinks produce a few patches of beautiful color, but this year their displays are small in number. Fields of California poppy reach a factor of 10 in many areas of California, but not here this year. Similarly, lupines are spectacular individual plants, but their bushes are not found extensively in the Reserve, nor are there many stunning collections of them. They tend to be in a few patches, with bushes here and there.

At the other extreme, factors of 1 are plants that many people wouldn't even notice are blooming, such as lomatium, miner's lettuce and pineapple weed, all of which have a not-particularly showy bloom on a plant which is typically only inches in height. Detailed factors are given in the table below for those species with showiness factors above three as of mid-May.

The value of showiness gives an indication of how showy the bloom is at a given time, but does not reveal how that showiness is derived. For example, a value of 50 could be achieved by five different extremely showy species being in 100% full bloom, each with a showiness factor of 10. Alternatively, a value of 50 could be achieved by ten different moderately showy species being in 100% full bloom, each with a showiness factor of 5. Either way, however, a value of 50 indicates that there are a lot of flowers to be seen!

In contrast, if the showiness is small, ten or less, it is unlikely that anyone will "ooh" and "aah" over the bloom.

A rough idea of how many species contribute significantly to the showiness can be obtained by plotting the species with the {1, 3, 5, and 7}-ranked top showiness vs. time.

It is also of interest to compare this measure to two other plots shown previously. Eliminating the showiness factor in the sum gives the plot shown earlier of total number of species blooming times the fullness of the bloom for each species. A comparison of the showiness plot to this plot will reveal whether a few spectacular species are responsible for most of the showiness.

The other comparison is simply the total number of species in bloom at any given point, regardless of whether 1% or 100% of the plants are blooming. People who come to see the largest number of different species only care about this measure of the bloom.

The four plots are given together below:

The three different total measures agreed surprisingly well in how rapidly the bloom increased this year up to the beginning of April. However, they then diverged significantly:

The showiness of the top species may perhaps give the clearest sense of what most observers might define as the peak bloom. At the beginning of April, there were seven species that each had a showiness of 8 or better. In contrast, shortly after the beginning of May, there were at most two species that exceeded a showiness of 5. For many people, no combination of species with showiness of 5 or less could equal having seven showy species in bloom at the same time.

If you would like to compute your own overall showiness plots, you can download my spreadsheet with the basic data and assign your own showiness factors to individual species. The data contain the bloom percentage for each species vs. time, and can be used to find how long your favorite species bloomed this year. Let me know if your showiness plot looks qualitatively different than mine!

Right click on the following link to save the files on your computer: Excel 97.

PlantShowiness Factor
blue dicks10
blue-eyed grass10
California buttercup10
chocolate lilies10
hoaryleaf ceanothus10
shooting star10
bush lupine7
California poppy7
ground pinks7
bush monkeyflower5
chaparral yucca (Our Lord's Candle)5
mission manzanita (berries)5
prickly pear5
purple nightshade5
Ramona lilac5
wild pea5
yerba santa5
redstem filaree4
short popcorn flower4
sun cup4
tall popcorn flower4
wild cucumber4

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Copyright © 2001-2003 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Updated 28 January 2003.