Plots for multi-temporal data collection

Five locations were identified within Delamere forest at which data collection took place, referred to as plots. The location of the site and selected plots is shown in Figure 3.2. Several preliminary visits to the study site were undertaken in order to identify the site for each plot and a number of factors were taken into account including species composition, topography, understorey and ground vegetation, size and age of trees, access, and

proximity to one another. Common UK broadleaf deciduous species are represented in

Plots 1, 2, and 3. The relatively small number of key plots meant that they could all be scanned consecutively in a single field day, prioritising frequency and resolution of data acquisition over number of sites. Plot 4 comprises evergreen conifer species which provides an opportunity to assess seasonal changes in the UK’s most widely planted conifer forest type. Finally, Plot 5 contains Japanese larch (Larix kaempferi), a deciduous conifer. This choice of data collection sites allows analysis and comparison of broadleaf

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and needle-leaf species, and the presence of oak (Quercus petraea) in Plot 1 provides a link between the destructive sampling conducted at Alice Holt. A basic overview of the characteristics of each plot is shown in Figure 3.3.

Figure 3.2. Site Location maps, showing: a) location of Delamere Forest within England, b) location of study site within Delamere Forest, and c) location of the five plots chosen for multi-temporal sampling (labelled 1-5). The red rectangles in a) and b) show the graphical

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Plot Ground/understorey Canopy Description

1 Broadleaf deciduous

Tree species: Sessile oak (Quercus petraea; common), Silver birch (Betula pendula; common), sweet chestnut (Castanea sativa; rare), ash (Fraxinus; rare). Ferns, bracken, leaf litter, moss. Near to road.

2 Broadleaf deciduous

Tree species: Sweet chestnut (Castanea sativa; abundant),

Rowan (Sorbus; rare).

Multilayered canopy. Some young samplings. Slightly sloping to two sides. Dry soils.

3 Broadleaf deciduous

Tree species: Common beech (Fagus; abundant), sweet

chestnut (Castanea sativa;

rare). Mostly bare ground, some small grasses patches. Open on West side and path to East.

4 Conifer evergreen

Tree species: Corsican pine (Pinus nigra; common),

Weymouth pine (Pinus

strobes; common), Scots pine (Pinus sylvestris; common) Dense ferns, scrub. Damp. Slightly undulating ground.

5 Conifer deciduous

Tree species: Japanese larch (Larix kaempferi; abundant) Sparse understorey and ground vegetation, mixture of bare ground and low laying vegetation.

Figure 3.3. Site description of plots, including the tree species present (Latin name, abundance).

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3.3.2 Experimental design

The multi-temporal field campaign at Delamere forest was carried out during a full annual seasonal cycle between March 2014 and April 2015. The frequency of visits varied

according to the amount of growth activity in the canopy. In spring (April through to June) visits were made around twice a week in order to capture budburst, leaf development, and leaf growth. In summer (July through to September) full leaf is reached in the canopy, during this time green leaf area stays relatively constant (Peñuelas & Filella, 2001) and therefore visits were scaled back to around twice per month. On each field visit visual phenological observations, hemispherical photographs, and TLS measurements were acquired according to the relevant data acquisition protocols described in the following sections. Thirty five field visits were carried out and the plots surveyed at each visit are shown in Figure 3.4. A revised optical filter combination was installed to the TLS instrument prior to 1st April, therefore the TLS data collected before this date (hashed areas; Figure 3.4) were not used as the output laser power differences mean that they are not comparable.

Due to the nature of TLS data collection, the weather can pose a significant limitation. Adverse weather conditions such as wind, rain, or fog, may reduce data quality

considerably. For instance, the laser beam can be scattered by falling raindrops or

suspended fog particles triggering a false return. Furthermore, the TLS instrument used is not fully watertight and any rain droplets that land on the external filter could also create erroneous returns. Therefore efforts were made to avoid adverse weather conditions by planning according to the Met Office weather forecast. However, weather patterns do change and rain can occur unexpectedly: if adverse weather was encountered in the field, TLS scanning was aborted and all electronic equipment covered. It is worth noting that due to the amount and weight of equipment involved in field scanning activity, a fieldwork assistant was required to accompany all of the field visits. These constraints on weather and resource availability did occasionally limit the frequency of visits. Furthermore, as Delamere Forest is actively managed as a timber resource by the Forestry Commission forestry works are routinely carried out throughout different areas of the forest. As a result, some plots were inaccessible during certain periods due to machinery present for thinning works and timber collection. This was the case for plot 5 and prevented visits to this plot during springtime. As a consequence, this plot was scanned once in summer and again the following winter to provide a leaf-on and leaf-off dataset.

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Visit Data visited Plot number Notes

1 2 3 4 5

X1 10 March Generator broke – no scanning

X2 12 March

X3 13 March Equipment failure – no scanning

X4 17 March

X5 24 March Equipment failure – no scanning

1 01 April New optical filter combination

2 02 April

3 08 April Very windy so re-scanned on 9th April

4 09 April 5 15 April 6 17 April 7 24 April 8 28 April 9 02 May

10 07 May Scan at plot 3 aborted before

completion due to adverse weather

11 13 May 12 14 May 13 18 May 14 19 May 15 26 May 16 30 May 17 03 June 18 13 June 19 19 June 20 26 June

21 04 July Scan at plot 2 aborted before

completion due to adverse weather

22 17 July 23 31 July 24 07 August 25 21 August 26 02 September 27 11 September 28 27 October 29 09 April 2015 30 21 April 2015

Figure 3.4. Details of fieldwork visits. The hatched areas (12th March and 17th March)

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