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          Poplars around car parks at Stanborough Park


Author:   Colin Last, Bsc (Hons), F. Arbor A.
          Arboricultural Advisor
Date:     3rd August 2006
1. Summary

   1.1. When Stanborough Park was created 35 years ago, over 700 Lombardy
        Poplars were planted around the car park areas. They quickly provided
        an effective screen. Now however they have outlived their usefulness;
        they have reached a stage where loss or breakage of stems can be

   1.2. The problems have arisen due to Lombardy Poplars not being very long
        lived trees; to being planted close together; and to the hostile rooting
        environment of the tarmac car park. Poplars in South car park were
        ‘topped’ in the past, and this has added to the current problems.

   1.3. As long as the trees remain there is a high risk of damage to property or
        people, mainly from the breakage of stems in high winds. It is
        recommended that all the Lombardy Poplars are removed in the next few

2. Introduction

   2.1. The North and South car parks in Stanborough Park were created when
        the Park was opened in 1971, and planted up with over 700 Lombardy

   2.2. Trees in the main South car park were ‘topped’ (severely reduced in
        height) about 20 years ago.

   2.3. Some new planting has occurred in the North car park, as replacement of
        lost trees.

   2.4. No other work has been undertaken. This report is to considered how
        best to manage the trees in the future.

                  ACF/CRL/   Stanborough Park     3rd August 2006
3. Location and Layout

   3.1. A sketch map showing the position of the trees on both the North and
        South car parks is shown on page ---.

   3.2. The trees have been planted in single lines, to divide up the car parks into
        parking bays. There are 466 Lombardy Poplars on North car park, and
        244 on South car park.

   3.3. Note that there are other trees around the periphery of the car park, which
        have not been included in this report. Some work may need to be
        undertaken on these trees on safety grounds. Refer to ----- for details.

4. Condition of Trees

   4.1. The trees were inspected from ground level only using a visual tree
        inspection (VTA) method. See tree schedule.

       Some general facts about Lombardy Poplar

   4.2. Lombardy Poplar originated from the Lombardy region of northern Italy,
        probably as a variety of Black Poplar. It has a distinctive ‘fastigiate’ or
        very narrow crown, which even in maturity is less than 5 metres across. It
        can grow up to 25 metres or more in height.

   4.3. There are only a few varieties of Lombardy Poplars, which differ slightly in
        their branching habit, some being narrower than others. They propagate
        very easily, from cuttings planted directly into the ground. All cuttings are
        genetically similar. In this country virtually all Lombardy Poplars are
        males, and originate from a very small number of parent trees.

   4.4. It was introduced into Britain in the late 1700’s. The timber is worthless
        but the tree is frequently planted in landscaping because of its distinctive

   4.5. They grow very rapidly in the early years, and there has been a tendency
        in the past to plant them to produce a quick screen. This has often proved
        to be ill advised as the trees are not long lived, and loss or breakage can
        occur sooner than expected. A life span of only 50 years is quite typical.

                 ACF/CRL/     Stanborough Park     3rd August 2006
4.6. Unlike some other trees Poplars are very prone to breakage. In
     evolutionary terms they are basically pioneer species, quickly taking
     advantage of colonising open ground. They are adapted for a strategy of
     rapid growth, at the partial expense of wood strength. This means they
     are more likely to fail in high winds than other trees.

4.7. Because they have a low wood density, Poplars are more rapidly
     decayed by fungi than other trees. They are ineffective at forming barriers
     to isolate any decay that develops. This means that any injuries to the
     tree, which exposes the xylem, can be readily exploited by decay fungi.

4.8. In practical terms a large injury to a tree, such as produced by ‘topping’,
     allows easy access for decay fungi to enter. Once decay fungi get in, they
     effectively cannot be stopped, and the tree is likely to become hazardous.

   Picture 1.    Damaged tree in smaller area, South car park.

                ACF/CRL/   Stanborough Park    3rd August 2006
ACF/CRL/   Stanborough Park   3rd August 2006
5. Discussion

  5.1. ‘Topped’ trees in South car park. All the trees in the main car park
       area have been topped about 20 years ago. There is cause for concern
       about failure of the trees, as described below:

        Picture 2.   Close up of ‘topped’ tree

                ACF/CRL/    Stanborough Park     3rd August 2006
5.2. The trees are 35 years old. They do not have long before the end of their
     life span, which is possibly 50 years. There is evidence already of branch

5.3. There is a high risk of stems breaking and causing damage to property or
     people if nothing is done. This is a high usage site and measures should
     be taken to reduce or eliminate the risk of stem failure in the trees.

5.4. This can be achieved by: 1) Felling,
       or 2) Reducing the trees back to where previously cut, at a height of
       around 5 to 6 metres.

   For reduction, it should be noted that the same problems will occur in the
   future. For safety reasons the trees would need to be reduced regularly
   every 2 or 3 years.

5.5. All trees in South and North car parks:     There is an urgent need to
     consider the future management of even those trees where there appears
     to be no problem at the moment.

   Picture 3.    North car park

5.6. As mentioned before, Lombardy Poplar have a relatively short life span.
     Problems with decay and stem breakage will be expected to occur to
     many trees within the next few years.

                ACF/CRL/   Stanborough Park    3rd August 2006
5.7. There are other factors which contribute to shortening this life span to
     even fewer years.

5.8. Most of the trees have roots growing in the hostile environment of a
     tarmac car park, with only a very narrow strip of earth in which to gain
     essential water and nutrients. This is compounded by the trees growing
     very close together, so their roots are competing with each other and
     restricting the development of a stable root system. See picture below.

       Picture 4.   South car park, showing rooting area of trees

5.9. There is an option to remove those trees showing signs of basal decay or
     other defects, and replanting.

5.10.There is however a recognised problem in removing trees where they
    are growing close together. The remaining trees are exposed to winds
    they are not used to, and they are more likely to fail too.

5.11.Within the next few years there is a high risk of failure in high winds.
    Once gaps appear within the line of trees, this will make it more likely that
    other trees will fail too.

5.12.The safest option is to remove all of the trees at the same time.
    Otherwise there is a high risk that any remaining trees will fail and
    damage property or people.

              ACF/CRL/     Stanborough Park     3rd August 2006
6. Conclusion

  6.1. In hindsight Lombardy Poplar were perhaps unsuitable trees to plant
       around a high usage car park. It is unfortunate that there are so many
       trees of the same age, which have come to maturity at the same time.

  6.2. For reasons I have outlined above there is a high risk of failure of the
       trees, and for public safety the trees need to be dealt with soon.

  6.3. All of the Lombardy Poplars need to be removed.

  6.4. This may seem drastic, but failure to do so could result in a greater risk of
       failure of the remaining trees, which are exposed to winds they were
       previously sheltered from.

  6.5. However removing all the trees does provide an opportunity to redesign
       the landscaping of the car park areas. Thought should be given to any
       replanting in the future to ensure a better age class balance.

7. Recommendations

  7.1. 210 Lombardy Poplars in main area of South car park (trees that have
       been ‘topped’ in past).
                                                 Priority – within 2 years.
                                                 Fell to ground level.

  7.2. 34 Lombardy Poplars in smaller area of South car park.
                                                    Priority – within 3 years
                                                    Fell to ground level.

  7.3. 466 Lombardy Poplars in North car park.
                                                       Priority – within 3 years
                                                       Fell to ground level.

                ACF/CRL/     Stanborough Park     3rd August 2006
ACF/CRL/   Stanborough Park   3rd August 2006
SKETCH PLAN (Not to scale) of Stanborough Park – South Car Park

             ACF/CRL/   Stanborough Park   3rd August 2006
SKETCH PLAN (Not to scale) of Stanborough Park – North Car Park

             ACF/CRL/   Stanborough Park   3rd August 2006
        Tree Schedule

 Location                        Height
                  Species                  Spread     DBH (mm)                                   Condition
(see map)                         (m)
                                                                      Trees planted in lines. Spacing approximately 1.5 m apart.
   1.         Lombardy Poplar   18 to 20   2 to 4       Mainly        All trees reduced in past to a height of 5 to 6 m.
 South        (Populus nigra                          200 to 400      Some trees with basal decay.
car park.     ‘Italica’)                                              Trees planted in narrow strip of earth, between tarmac car park
Main area                                                              area.

(210 trees)

                                                                      Tree planted in lines. Spacing approximately 1.5 m apart.
    2.        Lombardy Poplar   22 to 24   2 to 4       Mainly        Trees have not been reduced, or pruned.
   South      (Populus nigra                          200 to 400      4 trees have extensive wounds with decay at base.
 car park.    ‘Italica’)                                              Trees planted in small groups, in small grass areas, within
  Smaller                                                              stoned car park area.

(34 trees)

                                                        Mainly        Trees planted in lines. Spacing approximately 1.5 m apart.
    3.        Lombardy Poplar   Mainly     2 to 4     200 to 400      Trees have not been reduced or pruned.
  North       (Populus nigra    22 to 24                              Basal decay in some trees. A few with extensive decay.
 car park     ‘Italica’)                                              First 3 lines, at northern end of car park, are very varied in age
                                                                       and size, with some new planting. Gaps have been replaced
(466 trees)                                                            over the years. Other lines are fairly uniform, with few
                                                                      Larger trees at southern end, by pond. (Up to 600mm DBH)
                                                                      Trees planted in narrow strip of earth, between tarmac car park

                                           ACF/CRL/     Stanborough Park      3rd August 2006

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