Cambridge Sapling Planting and Removal 2016-2022

Author

Kent S Johnson

Introduction

This report summarizes sapling plantings and subsequent removals for the City of Cambridge in the years 2016 to 2022. The focus is on the number of saplings planted in this period, number removed after planting (mortality), the time between planting and removal, and factors affecting removal.

The analysis is based on tree data available from Cambridge GIS as of January 9, 2023.

Note: the status of saplings that have not been removed is not known. They may be healthy, ailing, or dead and awaiting removal.

Summary

Number planted and removed

In this period, 5,361 saplings were planted in all locations; 3,971 of these were street trees.

In the three years since the Urban Forest Master Plan was released, 2,027 new street trees have been planted, an average of 676 plantings per year. To date, 297 of these have been removed, giving an average of 577 successful new street trees per year for these three years. These numbers will change as more of these trees are removed in the next few years.

Overall mortality

12% of saplings planted were removed within the first year; 20% were removed within three years and 23% were removed within five years.

More recent planting years have a higher percentage of removals. This may be due to the planting of smaller saplings in recent years.

Saplings larger than 2” diameter have dramatically improved removal rates

39% of saplings less than 2” diameter were removed within three years. Only 9% of saplings greater than 2” diameter were removed within three years.

48% of bare root saplings smaller than 1” were removed within one year.

Planting method

Bare root saplings were removed more frequently than ball & burlap. This may be due to learning pains in the bare root program, or the generally smaller size of bare root saplings.

Planting location

There is little difference in removal by planting location except that saplings planted at public schools seem to do better than saplings in other locations.

Planting by an organization

Data on the planting organization is incomplete. DPW is listed as the planting organization for 10% of plantings.

The best performance is for the 38% of saplings planted by an unknown organization.

The worst performance is for saplings planted by DPW. This may be due to the high removal rate of saplings planted by DPW in 2021 and the limited number of DPW-planted saplings.

Sapling species

Mortality of the most-planted species seems to fall in three tiers.

Honeylocust, cherry, elm, red maple and Kentucky coffeetree have relatively few removals after three years.

Oak, London planetree, sweetgum and serviceberry have substantially higher mortality at one and three years.

Tulip tree is in a class by itself, with high mortality at both one and three years.

Yearly planting and removal

Of the 5,361 saplings planted in this period, 923 were subsequently removed (17%) and 4,438 remain.

This table and chart show removals by planting year as of January 9, 2023. These numbers will change over time. They count removals against the planting year; the removal numbers for recent years will increase over time as more trees are removed.

Saplings planted and subsequently removed 2016-2022
Year Total Removed Remaining
Pct Count Count
2016 400 13% 53 347
2017 789 18% 142 647
2018 488 21% 102 386
2019 898 26% 231 667
2020 565 19% 107 458
2021 1239 21% 266 973
2022 982 2% 22 960
Total 5361 17% 923 4438
Data: Cambridge GIS | Analysis: Kent S Johnson

Net new saplings by year

This table shows the number of saplings planted each year and the number of recently-planted saplings removed in the same year. The difference is the net number of new saplings each year.

These numbers will not change over time; they count removals in the year they occur.

Net new saplings planted, 2016-2022
Saplings planted minus saplings removed after less than three years
Year Planted Removed Net planted
2016 400 0 400
2017 789 47 742
2018 488 85 403
2019 898 140 758
2020 565 170 395
2021 1239 211 1028
2022 982 212 770
Total 5361 865 4496
Data: Cambridge GIS | Analysis: Kent S Johnson

Sapling size

The diameter (caliper) of saplings planted varies considerably, from less than one inch up to six inches. There is a clear trend toward planting smaller saplings in more recent years; 89% of saplings planted in 2022 were two inches or smaller.

Size of saplings planted 2016-2022
Year Size in inches
0-1 1-2 2-3 3-4 4-5 5-6 Unknown
2016 1 73 136 93 68 24 5
2017 2 193 323 191 55 9 16
2018 10 161 221 83 9 1 3
2019 27 333 349 135 29 19 6
2020 12 345 192 13 1 0 2
2021 201 728 256 33 5 4 12
2022 85 785 106 1 2 0 3
Total 338 2618 1583 549 169 57 47
Data: Cambridge GIS | Analysis: Kent S Johnson

Planting technique

A bare root planting program was started in 2017 and expanded in 2020. 42% of the saplings planted since 2020 have been bare root.

Sapling planting technique 2016-2022
Year Total Bare root Ball & burlap
Count Pct Count Pct
2016 400 0 0% 400 100%
2017 789 58 7% 731 93%
2018 488 17 3% 471 97%
2019 898 69 8% 829 92%
2020 565 230 41% 335 59%
2021 1239 556 45% 683 55%
2022 982 379 39% 603 61%
Total 5361 1309 24% 4052 76%
Data: Cambridge GIS | Analysis: Kent S Johnson

Size of bare root vs ball & burlap

Most of the bare root saplings planted were less than 2” diameter. Many ball & burlap saplings were larger than 2”.

Planting size by technique
Less than 2" 2" or more
Ball & burlap 1243 2771
Bare root 1215 85

Planting location

The saplings planted are predominantly street trees (74%) and park trees (17%) with 9% in other locations.

Sapling planting locations 2016-2022
Year Street Tree Park Tree Back of Sidewalk Public School Planting Strip Golf Course City Building Other
2016 343 42 10 2 0 0 0 3
2017 633 63 62 1 8 0 1 21
2018 364 82 4 8 21 0 1 8
2019 604 174 15 58 19 0 26 2
2020 386 155 15 1 2 1 3 2
2021 819 274 25 16 18 65 8 14
2022 822 96 5 21 16 14 0 8
Total 3971 886 136 107 84 80 39 58
Data: Cambridge GIS | Analysis: Kent S Johnson

Planting by an organization

Data on the planting organization is incomplete, for 38% of plantings the organization is not recorded.

Planting organization 2016-2022
Year Total Unknown Leahy DPW
Count Pct Count Pct Count Pct
2016 400 400 100% 0 - 0 -
2017 789 412 52% 377 48% 0 -
2018 488 486 100% 2 0% 0 -
2019 898 403 45% 490 55% 5 1%
2020 565 22 4% 543 96% 0 -
2021 1239 275 22% 809 65% 155 13%
2022 982 13 1% 591 60% 378 38%
Total 0 2011 38% 2812 52% 538 10%
Data: Cambridge GIS | Analysis: Kent S Johnson

Top tree species

Tree species planted 2016-2022
Top ten species overall
Year Elm Oak Serviceberry London Planetree Tulip Tree Sweetgum Kentucky Coffeetree Cherry Red Maple Honeylocust
2016 61 8 26 24 0 0 1 1 67 19
2017 70 69 56 57 1 9 32 113 8 20
2018 57 63 48 36 10 33 26 10 24 8
2019 105 81 133 69 83 71 7 19 17 37
2020 53 51 35 50 43 33 35 8 2 16
2021 91 127 73 62 66 25 43 2 18 25
2022 47 73 56 63 47 27 50 11 9 19
Total 484 472 427 361 250 198 194 164 145 144
Data: Cambridge GIS | Analysis: Kent S Johnson

Mortality analysis

Mortality analysis attempts to estimate the probability of survival over time from observations of actual survival and death. It takes into account that some individuals are still alive when measurements end. Kaplan-Meier curves show the estimated probability of survival over time.

What is survival?

For this analysis, removal of a sapling is treated as “death” and non-removal is treated as “survival”. Because the status of non-removed saplings is uncertain, this analysis may over-estimate the true survival percentages.

Overall mortality

12% of saplings planted were removed within the first year, 20% were removed within three years and 23% were removed within five years.

This plot shows the probability of non-removal for all saplings planted since 2016.

Mortality by planting size

Saplings less than two inches in diameter have dramatically higher removal rates than larger saplings.

After three years, 39% of saplings less than two inches have been removed. Only 9% of saplings greater than two inches have been removed.

Removal percent at one and three years by sapling size
Diameter One year Three years
0-1 40% 49%
1-2 20% 36%
2-3 3% 7%
3-4 1% 2%
4-5 1% 2%
5-6 0% 0%
Data: Cambridge GIS | Analysis: Kent S Johnson

Mortality by planting year

More recent planting years have a higher percentage of removals.

This may be due to the smaller planting sizes in recent years.

Removal percent at one and three years by planting year
PlantYear One year Three years
2016 2% 9%
2017 4% 13%
2018 10% 19%
2019 18% 25%
2020 12% 20%
2021 19% 23%
2022 5% 5%
Data: Cambridge GIS | Analysis: Kent S Johnson

Saplings 2” and larger have similar mortality for all planting years.

Mortality by planting technique

Bare root saplings are removed more frequently than ball & burlap. This may be due to learning pains in the bare root program, or the generally smaller size of bare root saplings.

Removal percent at one and three years by planting technique
Technique One year Three years
Ball & burlap 10% 17%
Bare root 21% 34%
Data: Cambridge GIS | Analysis: Kent S Johnson

Which is more important–planting technique or size?

Both bare root and ball & burlap plantings show significantly better results for larger saplings.

Bare root

Ball & burlap

For the smallest saplings (less than 1”), ball & burlap is much more successful.

For 2-3” saplings, the difference in mortality is not significant.

Mortality by planting location

There is little difference in mortality by planting location except that saplings planted at public schools seem to do better than saplings in other locations.

Mortality by planting organization

The best performance is for the 38% of saplings planted by an unknown organization

The worst performance is for saplings planted by DPW. This may be due to the high removal rate of saplings planted by DPW in 2021 and the limited number of DPW-planted saplings.

Mortality by tree species

Mortality of the most-planted species seems to fall in three tiers.

Honeylocust, cherry, elm, red maple and Kentucky coffeetree have relatively few removals after three years.

Oak, London planetree, sweetgum and serviceberry have substantially higher mortality at one and three years.

Tulip tree is in a class by itself, with high mortality at both one and three years.

Removal percent at one and three years by tree species
Common name One year Three years
Honeylocust 2% 6%
Cherry 3% 7%
Elm 4% 7%
Red Maple 4% 7%
Kentucky Coffeetree 9% 9%
Oak 13% 25%
London Planetree 17% 28%
Sweetgum 18% 29%
Serviceberry 26% 32%
Tulip Tree 41% 53%
Data: Cambridge GIS | Analysis: Kent S Johnson

Detailed yearly removal data

These tables show the cumulative yearly percent of saplings removed for each planting year and each stratification of the data.

Cumulative yearly sapling removal, saplings planted in 2016
Planted Cumulative Percent Removed
Year 1 Year 2 Year 3 Year 4 Year 5 Year 6
Technique Ball & burlap 400 2% 7% 8% 12% 12% 13%
Diameter 0-1 1 0% 0% 0% 0% 0% 0%
1-2 73 4% 30% 34% 44% 44% 44%
2-3 136 3% 5% 7% 12% 12% 13%
3-4 93 0% 0% 0% 0% 1% 2%
4-5 68 0% 0% 0% 0% 0% 0%
5-6 24 0% 0% 0% 0% 0% 4%
Unknown 5 0% 0% 0% 0% 0% 0%
Company Unknown 400 2% 7% 8% 12% 12% 13%
Location Back of Sidewalk 10 0% 0% 0% 0% 0% 0%
Park Tree 42 7% 7% 10% 17% 19% 24%
Public School 2 0% 0% 0% 0% 0% 0%
Street Tree 343 1% 8% 9% 12% 12% 13%
Unknown 3 0% 0% 0% 0% 0% 0%
Total Total Planted 400 2% 7% 8% 12% 12% 13%
Data: Cambridge GIS | Analysis: Kent S Johnson
Cumulative yearly sapling removal, saplings planted in 2017
Planted Cumulative Percent Removed
Year 1 Year 2 Year 3 Year 4 Year 5 Year 6
Technique Ball & burlap 731 4% 10% 12% 14% 16% 16%
Bare root 58 3% 26% 36% 40% 41% 43%
Diameter 0-1 2 0% 0% 0% 0% 0% 0%
1-2 193 14% 36% 41% 46% 48% 49%
2-3 323 1% 4% 7% 10% 11% 12%
3-4 191 0% 1% 1% 1% 2% 3%
4-5 55 2% 2% 2% 2% 2% 2%
5-6 9 0% 0% 0% 0% 0% 0%
Unknown 16 6% 19% 19% 25% 25% 25%
Company Leahy 377 3% 12% 16% 20% 22% 23%
Unknown 412 5% 11% 11% 12% 14% 14%
Location Back of Sidewalk 62 13% 16% 19% 19% 21% 21%
City Building 1 0% 0% 0% 0% 0% 0%
Former Tree 7 0% 0% 0% 0% 0% 0%
Park Tree 63 2% 5% 5% 14% 17% 17%
Planting Strip 8 12% 25% 25% 38% 38% 38%
Public School 1 0% 0% 0% 0% 0% 0%
Street Tree 633 3% 11% 14% 16% 17% 18%
Unknown 14 7% 21% 21% 21% 21% 21%
Total Total Planted 789 4% 11% 13% 16% 18% 18%
Data: Cambridge GIS | Analysis: Kent S Johnson
Cumulative yearly sapling removal, saplings planted in 2018
Planted Cumulative Percent Removed
Year 1 Year 2 Year 3 Year 4 Year 5
Technique Ball & burlap 471 10% 17% 19% 20% 21%
Bare root 17 18% 29% 29% 29% 29%
Diameter 0-1 10 10% 30% 30% 30% 30%
1-2 161 25% 42% 44% 46% 47%
2-3 221 4% 6% 7% 9% 9%
3-4 83 1% 1% 2% 2% 2%
4-5 9 0% 0% 11% 11% 11%
5-6 1 0% 0% 0% 0% 0%
Unknown 3 0% 33% 33% 33% 33%
Company Leahy 2 0% 0% 0% 0% 0%
Unknown 486 10% 18% 19% 21% 21%
Location Back of Sidewalk 4 25% 25% 25% 25% 25%
Cemetery Tree 1 0% 0% 0% 0% 0%
City Building 1 0% 0% 0% 0% 0%
Park Tree 82 5% 16% 20% 20% 20%
Planting Strip 21 10% 10% 10% 10% 10%
Public School 8 0% 0% 0% 0% 0%
Street Tree 364 12% 19% 21% 23% 23%
Unknown 7 0% 0% 0% 0% 0%
Total Total Planted 488 10% 18% 19% 21% 21%
Data: Cambridge GIS | Analysis: Kent S Johnson
Cumulative yearly sapling removal, saplings planted in 2019
Planted Cumulative Percent Removed
Year 1 Year 2 Year 3 Year 4
Technique Ball & burlap 829 19% 22% 25% 26%
Bare root 69 7% 19% 26% 26%
Diameter 0-1 27 26% 33% 33% 33%
1-2 333 43% 52% 56% 58%
2-3 349 3% 4% 7% 7%
3-4 135 0% 0% 1% 1%
4-5 29 0% 0% 3% 3%
5-6 19 0% 0% 0% 0%
Unknown 6 33% 50% 50% 50%
Company DPW 5 20% 40% 40% 40%
Leahy 490 22% 25% 27% 28%
Unknown 403 14% 18% 22% 23%
Location Back of Sidewalk 15 27% 27% 27% 27%
City Building 26 12% 12% 12% 12%
Park Tree 174 9% 16% 23% 24%
Planting Strip 19 32% 32% 32% 32%
Public School 58 3% 5% 5% 5%
Street Tree 604 22% 25% 28% 28%
Unknown 2 50% 50% 50% 50%
Total Total Planted 898 18% 22% 25% 26%
Data: Cambridge GIS | Analysis: Kent S Johnson
Cumulative yearly sapling removal, saplings planted in 2020
Planted Cumulative Percent Removed
Year 1 Year 2 Year 3
Technique Ball & burlap 335 11% 17% 19%
Bare root 230 14% 19% 19%
Diameter 0-1 12 50% 75% 75%
1-2 345 15% 23% 23%
2-3 192 4% 5% 7%
3-4 13 15% 23% 23%
4-5 1 0% 0% 0%
5-6 NA NA NA NA
Unknown 2 0% 0% 0%
Company Leahy 543 12% 18% 20%
Unknown 22 5% 5% 5%
Location Back of Sidewalk 15 7% 7% 7%
Cemetery Tree 2 50% 50% 50%
City Building 3 0% 0% 0%
Golf Course 1 0% 0% 0%
Park Tree 155 14% 20% 20%
Planting Strip 2 50% 50% 50%
Public School 1 0% 0% 0%
Street Tree 386 11% 17% 19%
Total Total Planted 565 12% 18% 19%
Data: Cambridge GIS | Analysis: Kent S Johnson
Cumulative yearly sapling removal, saplings planted in 2021
Planted Cumulative Percent Removed
Year 1 Year 2
Technique Ball & burlap 683 9% 10%
Bare root 556 32% 36%
Diameter 0-1 201 48% 51%
1-2 728 18% 20%
2-3 256 4% 4%
3-4 33 0% 6%
4-5 5 0% 0%
5-6 4 0% 0%
Unknown 12 33% 33%
Company DPW 155 42% 43%
Leahy 809 20% 23%
Unknown 275 6% 6%
Location Back of Sidewalk 25 16% 20%
Cemetery Tree 9 0% 0%
City Building 8 0% 0%
Fresh Pond Reservation 4 0% 0%
Golf Course 65 25% 26%
Park Tree 274 12% 12%
Planting Strip 18 11% 11%
Public School 16 6% 25%
Street Tree 819 23% 25%
Unknown 1 0% 0%
Total Total Planted 1239 19% 21%
Data: Cambridge GIS | Analysis: Kent S Johnson
Cumulative yearly sapling removal, saplings planted in 2022
Planted Cumulative Percent Removed
Year 1
Technique Ball & burlap 603 3%
Bare root 379 2%
Diameter 0-1 85 1%
1-2 785 2%
2-3 106 2%
3-4 1 0%
4-5 2 0%
5-6 NA NA
Unknown 3 0%
Company DPW 378 2%
Leahy 591 3%
Unknown 13 0%
Location Back of Sidewalk 5 0%
Cemetery Tree 8 25%
Golf Course 14 0%
Park Tree 96 0%
Planting Strip 16 0%
Public School 21 0%
Street Tree 822 2%
Total Total Planted 982 2%
Data: Cambridge GIS | Analysis: Kent S Johnson

Sources

Tree planting and removal data from Cambridge GIS as of January 9, 2023.

Copyright 2023 Kent S Johnson Creative Commons License 2023-01-18