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