Elevated atmospheric CO2 and humidity delay leaf fall in Betula pendula, but not in Alnus glutinosa or Populus tremula × tremuloides

Table 2 Environmental variables and the lifespan of the leaf canopy (bud burst to final leaf fall) at FAHM throughout the 5 years of relative humidity (RH) manipulation

Year	T_min (°C)	T_max (°C)	GDD (base 10 °C)	Rain (May–Oct) (mm)	^aTotal precipitation (mm)	Ambient RH canopy lifespan (days)		Elevated RH canopy lifespan (days)
Year	T_min (°C)	T_max (°C)	GDD (base 10 °C)	Rain (May–Oct) (mm)	^aTotal precipitation (mm)	50 % fallen	100 % fallen	50 % fallen	100 % fallen
2008	−17.1	30.8	619	502	853	Aspen: 156	170	156 (+0)	170 (+0)
2008	−17.1	30.8	619	502	853	Birch: 168	205	177 (+9)	205 (+0)
2009	−20.7	30.7	1,015	468	696	Aspen: 160	190	160 (+0)	190 (+0)
2009	−20.7	30.7	1,015	468	696	Birch: 145	211	166 (+21)	211 (+0)
2010	−27.6	36.9	1,321	387	828	Aspen: 151	193	137 (−14)	193 (+0)
2010	−27.6	36.9	1,321	387	828	Birch: 123	205	163 (+40)	205 (+0)
2011	−28.8	32	1,043	261	669	Aspen: 154	178	154 (+0)	178 (+0)
2011	−28.8	32	1,043	261	669	Birch: 141	192	153 (+12)	192 (+0)
2012	−31.3	32.9	753	339	756	Aspen: 140	171	140 (+0)	171 (+0)
2012	−31.3	32.9	753	339	756	Birch:−^b	−^b	−^b	−^b

The effect of FAHM on canopy lifespan is shown in parenthesis in days. T_min and T_max are based on the average annual minimum and maximum temperatures
GDD growing degree days
\( \mathrm{GDD}=\left(\frac{T_{\min }+{T}_{\max }}{2}\right)-10 \)
^aTotal annual precipitation recorded by the Estonian Environment Agency’s weather station, situated ca. 70 km from FAHM
^bBirches were harvested in dormant season of 2011/2012

ISSN: 1297-966X