Open top chamber climate impact studies - Results from the Headley IV experiment

Results after one year of exposure

Six lowland UK forest tree species, including candidates for future afforestation policies were planted in March 2000, followed by daily watering during April and May to encourage establishment. Irrigation was limited during the summer months (June – August) to 0.98 mm per day, delivered as 2 mm every second day, corresponding to the UKCIP98 medium high scenario for the 10 km grid-square centred on Headley (1.4 mm per day; 36% wet day frequency), assuming 30% interception loss. Outside these periods, experimental (factorial) treatments of elevated CO2 (ambient and 600 ppm) and elevated ozone (ambient and 80 ppb peak concentration) were maintained throughout. Preliminary data for growth effects after one growing season in the experimental treatments are summarised in the table below.

The effect of treatment on height, diameter and estimated volume growth of six UK forest tree species after one years growth in open top chambers.
Volume is estimated as the volume of a cone (1/3pr2h)
Species
Corsican pine Douglas fir Beech Oak Sycamore Nothofagus Total
Height (%) ambient

100

100

100

100

100

100

100

O3

94.4

98.6

100.7

96.0

83.3

104.6

94.9

CO2+O3

112.9

103.3

131.5

87.4

103.3

141.8

115.5

CO2

118.5

113.2

148.7

97.9

108.9

129.6

117.9

Total

106.7

103.8

120.2

95.3

99.2

119.0

107.1

Diameter (%) ambient

100

100

100

100

100

100

100

O3

91.6

95.2

95.7

104.5

105.0

106.1

100.0

CO2+O3

108.5

104.7

120.5

104.4

118.1

130.8

115.0

CO2

116.6

114.6

127.4

107.3

117.2

126.6

118.2

Total

104.4

103.6

110.9

104.1

110.2

115.9

108.4

Volume (%) ambient

100

100

100

100

100

100

100

O3

76.6

87.7

86.5

111.4

99.7

135.1

109.2

CO2+O3

136.6

113.1

180.3

100.9

143.8

227.1

167.0

CO2

166.9

143.7

234.0

113.4

150.1

209.7

170.8

Total

120.7

111.1

150.2

106.4

123.9

168.0

137.0

Corsican pine exhibited the classic responses of a decrease in both height and diameter growth in response to ozone (~5-10%) and an increase in response to elevated CO2 (~20%). The combined treatment was intermediate. The responses of Douglas fir were similar, although the magnitude of these responses was smaller. Beech again showed similar responses, although the height growth response to ozone was minimal, and that to CO2 was enhanced (~50%). The growth of oak was largely unaffected by any treatment, although the combined treatment did result in a small reduction in height growth. Sycamore showed the largest reduction in height growth in response to ozone (18%), whilst the growth of Nothofagus was enhanced in both ozone and elevated CO, leading to the combined treatment having the largest growth increment. In terms of volume growth (estimated as that of a cone), there was variation in both the direction and magnitude of responses. Corsican pine showed the largest growth reduction in response to ozone (-22%), sycamore was unaffected, whilst the growth of Nothofagus increased by 35%. Oak was largely unaffected by any treatment, and the largest responses to elevated CO2 was seen in beech (CO2 alone) and Nothofagus (combined treatment), in both of which, a doubling of growth increment was observed.

A number of underlying processes may explain these differing responses, including establishment success, root allocation (which has not been assessed to date), susceptibility of the photosynthetic apparatus to ozone damage and differing responses to water availability. In addition, long-term growth responses may not be evident after only a single growing season of the experimental treatments being imposed.

Results after two years of exposure

In the second year of growth, differences in responses between the species became further apparent, and these are discussed in detail, together with details of fumigation in the 2002-3 progress report (PDF-248K). This report also details results of the limited harvest carried out during the winter of 2001-2, regrowth of coppiced southern beech and sycamore and the programme of stomatal conductance measurements on the broadleaf species.