The Environmental Change Network at Alice Holt Research Forest

Purple emperor butterfly Research Note The Environmental Change Network at Alice Holt Research Forest

Suzanne Benham June 2008

The Environmental Change Network (ECN) was established in 1992 to provide a framework for monitoring the effects of a range of environmental drivers on freshwater and terrestrial ecosystems. The Alice Holt ECN site represents the Forestry Commission’s commitment to this long-term collaborative programme. This Research Note reviews data collected at the Alice Holt site over 14 years of operation from 1992 –2006. Evidence of the impacts of climate change, pollution and their interaction with land management are explored. Monitoring of air quality has demonstrated a decline in the levels of some harmful pollutants and this is reflected in a reduction in soil acidity and resulting changes in plant communities. Meteorological data provide evidence that the climate is changing with significant trends in summer rainfall and winter cold days. Changes in moth populations have been linked to changes in climate while the decline in some butterfly species is identified as a possible consequence of reduction in open space. In contrast, this reduction has benefited several species of ground beetle, which prefer shady conditions. Bird surveys have enabled assessment and identification of possible causes of changes to the woodland bird populations, including those species subject to Biodiversity Action Plans. Similar trends are becoming apparent across the network, providing a robust early warning system for detecting changes in natural ecosystems as the effects of climate change set in.

FCRN001 1 Introduction The Alice Holt ECN site

It is now accepted that the climate is warming, largely as a result The Alice Holt Forest ECN site (latitude 0 °50’W; longitude 51 °10’N) of anthropogenic emissions of greenhouse gases into the occupies a gently sloping plateau on the Surrey–Hampshire atmosphere. Globally, temperatures have risen by 0.8 °C since border at an altitude of 70–125 m OD. The soils are heavy the late 19th century and in England 8 of the 12 warmest years surface-water gleys derived from drift. Gault clay dominates the on record have occurred since 1995. The Intergovernmental underlying geology, with some calcareous Upper Greensand Panel on Climate Change (IPCC, 2007) has concluded that the material. The forest probably originated during the Atlantic concentration of carbon dioxide in the atmosphere is likely to period ( c.7800–5700 BP) with pedunculate oak ( Quercus robur ) rise from the current of value of 383 parts per million (ppm) to emerging as the dominant tree species. In 1812 the Crown between 550 and 700 ppm by the end of the century, leading to enclosed the forest and undertook extensive replanting. In the a 3–5 °C rise in global temperature. The magnitude and rate of late 19th century, because of poor growth, oaks planted on these predicted changes are unprecedented since at least the areas of leached gravel soils were cleared and replanted with last glacial period and highlight the need to understand their coniferous species – primarily Scots pine, Norway spruce and likely impacts on natural ecosystems. Monitoring the impacts of Douglas fir. Ownership and management of the forest was climate change is an important element of a strategy to forecast transferred to the Forestry Commission in 1924. The forest is and adapt to the threats posed by global climate change. currently dominated by Corsican pine ( Pinus nigra var. maritima) However, climate change is not the only environmental pressure; but 140 ha of old-growth oak woodland remain and it is in this air pollution, habitat fragmentation and land management area that both extensive and intensive long-term environmental practices all affect the functioning of ecosystems. Identifying the monitoring are being carried out. cause and effect of individual drivers is a major challenge for environmental monitoring, as it requires that the effects of Figure 1 Map of Environmental Change Network sites in the UK. those drivers are distinguished from background variation. The Environmental Change Network

The Environmental Change Network (ECN) is a multi-agency, long-term monitoring programme funded by a consortium of sponsoring government departments and agencies. The network (Figure 1) was established in 1992 to provide a long- Cairngorms River sites term integrated monitoring platform that is more likely to detect Glensaugh change than several individual and unconnected components. Lake sites Existing monitoring methodology was adopted by ECN where Terrestrial sites feasible, enabling inclusion of existing sites, surveys and networks. In addition, ECN methodology has been integrated Sourhope into a number of new monitoring initiatives.

Alice Holt Forest is one of 12 terrestrial sites which operate to a Hillsborough Moor House and Upper Teesdale uniform system of core measurement protocols. Atmospheric, soil and water chemistry data provide information on abiotic drivers. Indicator species, representing all trophic levels

(herbivores, insectivores, decomposers, higher plants), provide Yr Wyddfa information on biotic impacts. The indicator species/genera (Snowdon) were selected as those most likely to show an early response to the effects of climate change . These biological indicators and Drayton the physical parameters outlined above are listed in Table 1. Wytham Rothamsted

Data collected at the ECN sites are available under licence for Porton Alice Holt research purposes and for teaching in schools and universities. North Wyke The ECN internet site is included in the National Grid for learning and, in 2000, ECN hosted a conference designed to promote the use of environmental data in teaching (www.ecn.ac.uk).

2 Table 1 Monitoring carried out by the ECN network at Alice Holt since 1994.

Surveys prior Parameter Measurements Survey method Frequency to 1994

Physical Meteorology Temperature, rain, sun, wind, soil wetness Manual and automatic Daily Since 1949 Precipitation pH, conductivity, alkalinity, N, P, K, Ca, Mg, Chemical analysis Weekly chemistry Na, Cl, Al, Fe, NO 3, SO 4, PO 4, TOC, Total N Ammonia Alpha sample, denuder tube Monthly Atmospheric Oxides of nitrogen Diffusion tubes Fortnightly chemistry Ozone Diffusion tubes Monthly Sulphur dioxide Diffusion tubes Monthly Soil survey Soil series Classification At start Soil chemistry Chemical and physical characteristics Various Every 5 and 20 years Soil solution pH, conductivity, alkalinity, N, P, K, Ca, Mg, Chemical analysis Fortnightly chemistry Na, Cl, Al, Fe, NO 3, SO 4, PO 4, TOC, Total N Biological Canopy structure, vascular plants, seedlings Plot and quadrat counts Every 9 years NVC monitoring of vascular plants Plot and quadrat counts Every 3 years Vegetation Since 1987 Mensuration Heights and diameters Every 3 years Forest Health Survey Annual Moths Rothamsted Insect Survey Daily Butterflies National Butterfly Monitoring Scheme Annually (Mar–Oct) Invertebrates Since 1966 Spittle bugs† Quadrat counts Twice yearly (Jun, Aug) Ground beetles Pitfall traps Annually (Apr–Oct) Birds CBS and BBS Annually Deer Dung counts, infrared counts Twice yearly (Mar, Sep) Vertebrates Bats Activity Annually (Jun–Sep) Rabbits† Dung counts Twice yearly (Mar, Sep) † Data collected at Alice Holt not represented in this Research Note.

Drivers of ecosystem function such as ‘active woods’, ‘nature’s health service’ (O’Brien, 2005) and ‘forest schools’ (O’Brien, 2006). Sixteen hectares of Alice Holt Forest Woodland management are devoted solely to recreational use and numerous new footpaths and cycle paths have been established in recent years. This has led The Forestry Commission is committed to sustainable forest to an increase in people using the forest from 197 000 visitors in management and this requires an understanding of the effects 2001 to over 250 000 in 2006 – a trend that is likely to continue. of management practice on woodland ecosystem function, associated biodiversity and the environment. Social and Climate biodiversity objectives are now key priorities for woodland management, and in many cases these have replaced The climate at Alice Holt Forest is characteristic of southeast economics and timber production as the principal objectives. England, with the growing season typically extending from mid- These changes in approach to management place different March to November. Average annual (1994–2006) temperature is pressures on forests. Integrated monitoring provides the 10.1 °C with January normally the coldest month (4 ºC) and July contextual detail that can help to explain the large variations usually the hottest month (19 ºC). Mean annual rainfall is 803 mm found in biological data and help to interpret interactions with November usually the wettest month (85 mm) and July the between management and a range of environmental drivers, driest month (56 mm). such as climate and atmospheric chemistry. There is already evidence of a systematic change in seasonality of Recreation and education precipitation in Alice Holt Forest, with wetter winters and drier summers in recent years. The summers of 1995, 1996 and 2003 Well-managed forests can enhance quality of life; woodlands were some of the driest on record, while 2005 was the driest year are now promoted for their contribution to a healthy lifestyle, since records began at Alice Holt in 1949. Average air temperatures and this requires additional infrastructure and increases visitor are rising and the number of cold days (mean temperature <0 ºC) pressure. This trend is likely to continue in response to initiatives in winter has decreased significantly (Figure 2a and b).

3 pr co v of lead rai and summ er 20 Impa cts Tyn H ni b a Figure dioxid Power Ni Atmospheric Clima te am mo biolo E demand gr to recive aci av etvationeg Ni ut r olt tro o

oblem Number of cold days Number of hot days a t n a fro ica tion. dif 10 20 30 40 50 60 10 15 20 25 30 trog ica tion rif wth ilabil dal er op fall 0 0 5 1 ch 6 1950 s en g to ). 950 gical st ince º an e h l ni 2 ang stat ions T C (up more and of da m m icat i (NO hese en it e chan g in a Pr d temp Tren depo h for y ore 1947 (N g pla nts , igher p e ogram relativ (fr co to on roces dioxi H s e, ag 2 in of nu H pecis d om ) 1 1 scena rio More frequ mm th an adle 50% eratu 960 960 si an 3 . i gr (e and am tr ient n ) ti than s e xc emi ound dis d on. me t ses both cenar ios bu unity he de y mon ia hum ess less) ent y th e n re i tran spo eas e Cent res (se mp t at ss num are Nit rog (the por the can chemistry s in and ur nitrogen ions 1 1 NO and v idity i structu 970 970 ort ant ly co ndica te ned , e tationeg al the m section an d 194–206 ber UK to ha ve mbined 2 for sou inor comm unit ies vse r from rt en am and ar and nit rat sou CIP0 2 of ins ect are the e ma king rces re is d det r in (a monia 1 1 pred for theas t that N eposi e on 980 980 p an agr is ) t e U he co ublish ed to H per hot w su ch af imen tal scena rios: in K fo at tack ess entia l veg icul 3 wards mp ith by icted fected ) main a ha rest io tion ) soil and and pl v coul d etation, tu re e ds the higher ar ison. v an ts as su ch r 1990 1 e ag ec osyst em 990 al to (b) (NEGT of videne c i more sources ben irf es, s by eff 208 by so e. can a more declin e. be nu dr cold Hu ects as Lower pa the co ntrib utes tempera tures nitr In o 0s es pag tr ient betwen ligh tnin g do p . ught hea thl nitrenog rt AP, lme ru r rep 002010 2000 2000 days e nog av ereag icul a U when tiblesu scep of min ate K is 20 al f su ared et un ction, for nitrenog Cl 6–7). Cl emer rl y at areas , 01 an d. mmer al imate oud yth e th e Alice 3 ). an d ., seriou s by 2010 to º ging C will soil the 4 Fi of exp The Oz Ozo Fi 20 ha v hav i the NO the low com m chem me an cont year va oz pr

-3 n g 3 g 2 o

ecur NH (µg m )

NO concentration (ppb) r on the 8 on ure ure ia 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 ni o er e e 2 2.0 0 2 4 6 8 ear 0 U s ‘ in po µg cr bl s , e , co ne to i s K e ica u n at 9619 9819 0020 0220 0420 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 1996 a b u co l ue, i s e 3 4 t o vle re ti cr u (O r er r h bs ut ncent m m t 1 ed ng eci cal w l nd r nc en M M 997 ea s en t f r -3 el ospher equ 3 in r o i ba ea t ) o e e t , s at ter h s s o l cr d an an a ex as m oa v ed a ckgr cti i ra n es n o t 1 entl p eas A nd s m. i r 998 o an d har st ul a a z at o o ti l the si i n n o m ’ ce s l o e n t cl i o lu nce in ap ni nua nua F ra ne o y n s an n ed o a un or ea ta n g tr r s vi H at 1 t l i r p o nv i e 999 n nt s og fo l r at a o l l o d r o ow ni u by i wer en. ua oa nd nitr a s t f tha let o r l r emp l A m t tr i en A al 1 m a ve l s l lice H l v s al ch o us . l con m l 2 h Am oge 06 i r in ra n a i a y at ce g es ng 000 l ox ig v t t o en, ce d i E the i is o ri mo s er n o n u h µ C cen i m n H i al r l A olt hav a m des n ia er l us g a a t t N 1 ti dio he i o . on 2001 g l 9 s s thr a o 9 m o con denu U ed p t l o e tr at i 8 n s t ha e 96 f , n. her i r % a ia - n xid s -m (F d ca t the es 3 b o t t es s l to c n ecl i ra . I i i ig o p on con en n der sam s t ke en ho ta e C 2 e a an f a to a (F u w 0 i a r de on l c in ly ti d br hav s. lso l t 02 i re o l s onc i el ra s s sites d al , ent cent g sed ed ecosys tem e pher t H oad a cent an l ure her t v 4 v ions occurs va i e be l oweve 2 ola resul t a n lra pler ). e if b 0 d lue. n f b ra ri y 03 leav allen em etw 3). e p t ra o a y ti at ra a ti 1 oll ut re w l w s reas ti e o ion 97 tion i An 20 u Hvowe en on ssion ed of her Line r, n t or pr n n h i 04 s concentr at n l , nu a e c – s a ig e ga have wodla whe a e 196 n a ar 2 u di recn 1 are cr it . ht ser i nd n 06. al t s lpha sa ni r 2 it 9 s, (Alice H (Alice cted al 0 of wi er, c protect av 05 ic re ly oz Pea t hig es 4 – ben he ca t al the 2 e hsta t le i a on n ati 06. r of n to mpl 2 hly rbon n k l a vels 0 oa d t d olt) eg ons e 06 he nd i er s d n concentration has a close relationship with climate variables. and Scots pine plantations (Figure 6). Of this, approximately 450 Polluted, slow-moving air of continental origin can lead to very ha will be returned to native woodland over the next 100 years. high concentrations of ozone in the southeast of England.

Figure 6 Tree species composition of Alice Holt Forest (2003). High ozone concentrations affect the photosynthetic capability 300 of plants by damaging the internal leaf structure leading to leaf 270 tissue necrosis and early senescence. Accumulated O 3 exposure 250 over a threshold of 40 ppb (AOT40) is calculated as the product of 200 193 time and concentration (Figure 5). The critical level for forest trees ) a

h 150 (

has been set at 5 ppm h between April and September a e r 100 (Karlsson et al ., 2004), and this value is exceeded at the Alice A 50 45 Holt ECN site in some years. Predictions are for concentrations 50 35 24 21 13 12 11 7665 4 3 2 to continue to rise as a result of continuing precursor emissions, 0 s t s r k r r s e r h e e h h k i h s i r a u a a e s f c c c f c n n c l e e i r i v n d r e u f r i A o O s higher temperatures and reduced cloud cover (NEGTAP, 2001). p d t i l p a r p e a e p B a s o n n e l c p L s B y l e m n a P t s g o c r d h e a d c o u y a c e h G c C n i r o a r o s S o e r n r D w s n r h r b o r t e w o e r t C a t O

Figure 5 Ozone AOT40 values for each year at Alice Holt between s e N s L e h e 1994 and 2006; 2004 and 2005 values not available. t W W O 20

16 ) 1 - h Indicators of ecosystem function

m 12 p p ( 0

4 8

T Soil chemistry O A 4 –– The accumulation or loss of soil organic carbon and nitrogen is 0 0 9 8 6 5 5 3 7 4 6 4 1 2 dependent on complex climatic interactions. These can act 0 0 0 9 9 9 9 0 0 0 0 9 9 0 9 9 9 9 0 0 0 9 9 0 0 0 2 2 2 1 1 1 1 2 2 2 2 1 1 directly on soil processes such as decomposition and chemical transformation, and indirectly by affecting productivity and the input of litter to the soil . Increased nitrate leaching from forest Sulphur dioxide systems has been widely reported: signs of forest damage are linked to the input of atmospheric nitrogen. Nitrate is mobile in There has been a steady and marked decline in sulphur dioxide soil water and if present in excess of plant uptake can be

(SO 2) concentrations since the 1980s, initially achieved by emission leached out to surface waters, accompanied by aluminium on controls on the power industry and continuing through the acidic soils. At Alice Holt there is no evidence of these processes introduction of low-sulphur transport fuels. SO 2 levels occurring. Analysis of soil water chemistry has shown no measured at Alice Holt are usually close to the detection limits significant changes over time. Nitrate and aluminium of the instrumentation and are not considered to be a threat. concentrations have remained within a constant range, with no evidence of increased leaching. Sulphate levels in the deep (50 cm) Land use and land cover change soil solution samples indicate a slight downward trend.

The Forestry Commission gave some woodlands in Britain Soil properties at the ECN plots have been extensively assessed special status in the late 1980s recognising that they were of and characterised every five years (1994, 1999 and 2004). Soils special interest. These included Alice Holt Forest as well as the have been sampled by both depth and horizon. Analysis suggests native broadleaved areas of the old inclosures of the Royal that the soil has become less acid as a result of the decrease in Forests. Ancient Semi-Natural Woodland (ASNW) is recognised deposition of acidifying compounds, reflecting the success of as being of significant value for biodiversity. In Britain, around emissions control measures for sulphur and nitrogen. This 300 000 ha of ASNWs still exist, although 44% are now planted reduction is consistent with the findings of Kirby et al . (2005) for with conifers, broadleaves or a mixture of the two (Pryor and 103 woodland plots in Britain over a period of 30 years. While Smith, 2002). The UK Forestry Standard (Forestry Commission, Bellamy et al . (2005) reported a loss of soil carbon from mineral 2004) sets out the Government’s commitment to the restoration soils under most land uses, including forestry, in England and Wales of planted ancient woodland sites (PAWS). Within Alice Holt over the past 25 years, Alice Holt soil data show no change in Forest there are 502 ha of PAWS consisting mainly of Corsican carbon when analysed by horizon (Figure 7a) or depth (Figure 7b).

5 Figure 7 Average organic carbon by (a) horizon and (b) depth. buffered systems. Woodland vegetation communities at upland a 7 sites, including some dominated by bracken, seem to show a 1994 1999 2004 6 decrease in southern components, while intensively managed

n grassland showed signs of an increase (Morecroft, 2004).

o 5 b r

a 4 c t

n Reanalysing the Alice Holt data using British adjusted Ellenberg

e 3 c r

e 2 indicator values (Hill et al ., 1999) allows assessment of plant P 1 requirement with age according to their habitat and 0 environmental requirements. Under this system each plant and Horizon 1 Horizon 2 Horizon 3 bryophyte recorded is assigned a score for light, water, nitrogen b 7 and pH preference. Corsican pine showed the greatest change 6 in age with significant differences detected for all indicators

n (Figure 8a–d). Oak showed significant differences in light, pH

o 5 b r

a and nitrogen levels (Figure 8e, g and h), though light and

c 4 t

n nitrogen are in the opposite direction to those seen in the pine.

e 3 c r

e 2 No change was seen in water requirement for oak (Figure 8f). P 1 Both woodland types showed a significant increase in nitrogen 0 levels with the age of the crop. This has implications for woodland 0–5 5–10 10–20 20–30 vegetation surveys as nitrogen increase in ageing stands may be Depth (cm) misinterpreted as being caused by nitrogen pollution. Carbon balance Field layer vegetation assessment Forest carbon sequestration is dependent on factors such as

The structure and composition of the ground flora dictate the tree species, stand density and age. Temperature, CO 2 levels, quality of the habitat for other trophic levels and are affected by nutrient availability and thinning can all have a positive a range of environmental drivers. Together they form a key influence on tree growth. Change in carbon stocks in Alice Holt component and indicator of ecological condition. The spatial Forest have been modelled over time (model: BSORT) by using distribution patterns of vegetation show a strong correlation with forest management records (Table 2). climate and the predicted increase in mean annual temperature of 2.0 ºC to 4.5 °C could substantially change the composition Increases of 9500 tonnes of carbon per year, equivalent to one of woodland ground flora. Climate and climate change can tonne per hectare per year, are in line with the national estimates impact on both individual plants/populations and communities. even after the loss of 38 hectares due to forest restructuring. Data collected within ECN can be used to identify these trends.

Table 2 Carbon stock change in Alice Holt Forest 1993–2002. At Alice Holt, by classifying data obtained from the vascular Above ground Lop & tC ha -1 plant surveys by the age of the canopy it is growing beneath Area Stem Branch Total tC ha -1 woody biomass top yr -1 (chronosequencing), an investigation into the effects of climate change on two major forest species Corsican pine ( Pinus nigra Biomass 1993 765.5 52 148 1648 20 789 74 585 49 var. maritima ) and oak ( Quercus robur) has been carried out. Using a system developed by Preston and Hill (1997), we have Biomass 2002 727.6 61 045 1457 21 572 84 074 58 examined whether the balances of northern/southern species Biomass change -37.9 8 897 -190 783 9 490 9.1 1.0 are changing in terms of continentality and temperature cline.

Corsican pine stands showed a slight but non-significant increase in continentality and temperature in mature trees with Tree growth a tendency towards plants associated with wetter conditions. No changes in ground vegetation associated with oak stands The majority of tree species native to the UK are tolerant of a were found. The lack of change is not surprising since understorey range of environmental conditions and are unlikely to disappear vegetation is well buffered by the canopy and climate effects from southern England: their European distribution is testament would have to be prolonged or severe to register. Changes to this. However, competition between species, their growth have, however, been observed at other ECN sites on less rates and distribution is likely to change as a result of climate

6 Figure 8 Ellenberg values on a chronosequence of Corsican pine (a –d) and oak (e –h); significance level is demonstrated by * ** ***. a. Light values under Corsican pine e. Light values under oak

6.0 6.0

Young–old *

e 5.5 u l

a 5.5 v g r

e 5.0

b * n e l

l 5.0 E E l l

4.5 e n b e r g

4.0 v 4.5 a l Thicket Mid-rotation Mature u Young oak Mid-rotation Old oak e b. Water values under Corsican pine f. Water values under oak

6.0 5.7 5.6 5.5 e e u u 5.5 l l a a v v 5.0 *** g g 5.4 r r e e b b n n 5.3 e e 4.5 l l l l E E 5.2 4.0 5.1 3.5 5.0 Thicket Mid-rotation Mature Young oak Mid-rotation Old oak

c. pH values under Corsican pine g. pH values under oak

5.5 6.5

5.0 6.0 e e u u l l 4.5 a a 5.5 v v * *** g g r r ** *** e e 4.0 5.0 b b n n e e l l l l 3.5 E E 4.5

3.0 4.0

2.5 3.5 Thicket Mid-rotation Mature Young oak Mid-rotation Old oak d. Nitrogen values under Corsican pine h. Nitrogen values under oak

5.0 6.0

5.5 e u l 4.0 *** a *** v 5.0 g ** r e

b *** n

e 4.5 l

l 3.0 E E l l e

n 4.0 b e r g

2.0 v 3.5 a l Thicket Mid-rotation Mature u Young oak Mid-rotation Old oak e

7 change. Dendrochronological evidence from Alice Holt Forest temperature and precipitation (Turner et al ., 1987; Pollard, highlights the impact of summer drought on diameter growth 1988). Tracking trends in local species demography provides an of Scots pine and oak (Figure 9), with summers such as those of opportunity to relate community-wide changes to changes in 1976, 1984 and 1995 resulting in a decline in growth for 2–3 environmental conditions, and to assess the relative impact of years. A longer chronology for oak (Figure 10) again shows a habitat disturbance and climate change. high level of inter-annual variation but also an apparent increase in growth rate since the late 1970s, which may be a Moths result of rising levels of CO 2 in the atmosphere. As leaf flushing dates of trees and shrubs get earlier the moths that rely on these plants as a food source will need to modify Figure 9 Dendrochronological record for Scots pine and oak. their life cycle to survive. Records of moths and climate, Oak AH Scots pine AH Drought years collected over 36 years at the Alice Holt site, were summarised 2 ) and used to examine trends in species abundance and numbers m m

( of species occurring in relation to climatic data (Pitts et al., 2005). h t

w 1.5 o r

g The total number of moth species declined significantly during g n i

r the period 1966–2001 with an average loss of about two -

e 1 e r

t species per year (Figure 11). Examining the relationship between d e climate and moth abundance showed that summer temperature m r

o 0.5 f has a significant positive effect and winter precipitation a s n a

r negative effect. The results are in line with those of other studies t - Z 0 which indicate a general 60% decline in national 1970 1975 1980 1985 1990 1995 2000 2005 2010 macrolepidoptera numbers since 1930 (Woiwod, 2003).

Figure 10 Oak chronology from Alice Holt Forest showing an Figure 11 Variation in the total numbers of individuals and species increase in growth over the past two decades. of moths collected at Alice Holt, 1966–2001.

Number of species Number of individuals

1.5 300 6000

280 s l

5000 a

1.25 u d ) i

s 260 v r m i e d m b ( n

4000 i m h 240 f t u o n w 1.0 r o s e r e b i g 220

c 3000 m k e u a p n S O

200 l

0.75 a t

2000 o 180 T

0.5 160 1000 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020 1966 1971 1976 1981 1986 1991 1996 2001

Invertebrates Trees in the UK are defoliated by several species of moth . Particular attention has been given to species which are known to Some forest invertebrates damage trees and their impact is favour broadleaved trees, in order to identify how the health and dependent on their abundance. Warmer temperatures could productivity of these trees might be affected in the future. increase pest survival and the number of generations in a Among the key species showing a negative trend were winter season, while drought stress would reduce the ability of plants moth ( Operophtea brumata ) and mottled umber (Erannis to resist attack. Alternatively, higher temperatures may lead to defoliaria ), both known to be responsible for episodes of more rapid plant development, leaving less time for pests to broadleaved tree defoliation in the UK . The decline in abundance attack. Predictions about range expansions and migrant of these species suggests that there is likely to be a reduction in invasions are generally based on knowledge of the relationship risk of defoliation in the future. The decline in moth numbers at between species biology and climatic variables, particularly Alice Holt and the reasons for extinction of resident species

8 remain largely unknown. Research has shown that moths and Ground beetles oak trees use different temperature mechanisms to time life cycle events. This has led to a breakdown in the synchronisation Ground beetles ( Carabidae) are a predatory group and can respond of their life cycles with moths hatching up to three weeks before to changes in distribution of their prey. At Alice Holt, 97% of oak bud burst (Visser and Holleman, 2001). In isolation, climate beetles caught are of two species – Abax parallelepipedus and change would be expected to benefit winter moth, but the loss of Pterostichus madidus (Figure 12) . The latter is known to be sensitive synchrony between flushing of oak and caterpillar emergence to changes in temperature; Thiele (1977) demonstrated a morph- would have the opposite effect. Analysis of records from a nearby ological variation in colour of beetle legs over temperature clines. oak forest in Surrey shows that the flushing date of oak has advanced by two weeks since the 1950s (Sparks and Gill, 2002). Although very variable in number, most beetle populations at Alice Holt have remained stable over time (Figure 12). Three Butterflies species, Cychrus caraboides, Nebrai brevicollis and Notiophilus biguttatus have increased significantly in numbers in the past The trend towards warmer temperatures has favoured an increase ten years. C. caraboides and N. brevicollis prefer damp conditions in the number of butterfly species and an increase in population with the latter often found under dead bark. N. biguttatus has numbers. For example, the common blue ( Polyommatus icarus ) no particular habitat preference. There are a number of factors has shown an increased distribution across the UK in recent years. which could be responsible for the rise in numbers, including The large skipper ( Ochlodes sylvanus) was predicted by the an increase in food availability, decrease in predation or habitat MONARCH (Modelling Natural Resource Response to Climate change. The most likely reasons are the increase in litter Change) project to be a species likely to expand its range into accumulation (evident from the soil survey), dead wood higher altitudes (Harrison et al ., 2001). Although no evidence for associated with the natural stand ageing process and shade as this has yet been seen, ECN sites are well placed to identify this the canopy ages and the hazel understorey develops. change if it occurs. Migrant species such as the painted lady (Vanessa cardui ), red admiral ( Vanessa atalanta ) and clouded Figure 12 Trend in beetle populations at Alice Holt 1994 –2006. yellow ( Colias croceus ) may be expected to successfully overwinter as a result of climate warming. Analysis of the Alice Holt data set Other species Abax Pterostichus Number of species does not support this hypothesis. Apart from a ‘freak’ event in 14 7000 1996, which saw large numbers of painted ladies and red admirals blown in from the continent, numbers have remained constant. 12 6000

10 5000 s e r l t e

The first appearance of orange tips ( Anthocharis cardamines ) has e b e m 8 4000 b f been adopted as a UK government indicator of climate change u o n r s e e (Defra, 2003). Analysis of first appearance and peak flight data i 6 3000 b c e m p should show an advance with warming temperatures. The data u S from the Alice Holt ECN site do not support these findings. The 4 2000 N orange tip has shown a significant decline in numbers ( p=0.05) 2 1000 over the survey period with peak flight times becoming later 0 0 1 4 5 7 8 9 0 2 3 4 5 6 6

rather than earlier at the site. Five other species: comma 0 9 9 9 9 9 0 0 0 0 0 0 9 0 9 9 9 9 9 0 0 0 0 0 0 9 2 1 1 1 1 1 2 2 2 2 2 2 (Polygonia c-album ), small skipper ( Thymelicus sylvestris ), large 1 skipper, purple hairstreak ( Neozephyrus quercus ) and white admiral ( Limenitis camilla ) also showed significant declines (p=0.05) . This indicates that at the ECN site other factors are Vertebrates overriding the positive effects of temperature. Changing agricultural practices, habitat management and loss of habitat Birds have been implicated as factors in the decline of moths and butterflies in the UK (Asher et al ., 2001). At a broad scale, Bird populations are recognised as good indicators of the habitats in Alice Holt Forest have changed little over the past 40 general environmental status of the countryside on account of years, but reduction in ride management and ageing of the crop their varied ecology and widespread distribution across the UK. has led to many rides becoming overgrown and has The Woodland Bird Index for the UK, which relies on data from consequently reduced the number of open spaces available. the Common Bird Survey (CBS) and Breeding Bird Survey (BBS), Changes in land use in the area surrounding the forest may also showed a 20% decrease in the population of woodland birds be having an effect on butterfly populations. from 1970 to 2002. The main casualties were specialists such as

9 the lesser-spotted woodpecker ( Dendrocopos minor ) and migrants across the country have shown a serious 56% decline in cuckoo such as the spotted flycatcher ( Muscicapa striata ) and willow numbers since 1977. The reasons are complex and include a warbler ( Phylloscopus trochilus ). Nationally, the more generalist shortage of hairy caterpillars, a major part of their diet (Glue, woodland birds such as chaffinch ( Fringilla coelebs ) and robin 2006). The goldcrest ( Regulus regulus ) and dunnock ( Prunella (Erithacus rubecula ) are maintaining stable populations. Species modularis ) have shown an increase in population size. such as the wren ( Troglodytes troglodytes ) and long-tailed tit (Aegithalos caudatus ) have increased in numbers, benefiting from Changes in forest practice, including non-removal of deadwood, the milder winters and warmer spring conditions leading to more are likely to have had a positive effect on bird populations, successful reproduction. Migrant species such as the black cap while predation of eggs by grey squirrels and removal of the (Sylvia atricapilla ) and chiffchaff ( Phylloscopus collybita ) are doing shrub layer due to grazing by deer have been shown to have a well and many are now overwintering in our warmer climate. significant negative effect. Climatic factors also play a major role. Recent mild winters increase the survival chances of small The most bird-diverse woodlands in the UK tend to be the birds, and have allowed previously migrant species to Ancient Woodland sites. Much of this woodland is identified in overwinter. Species susceptible to cold weather are benefiting the UK Biodiversity Action Plan (BAP; GB Parliament, 1994). The from climate warming, although early nesting could increase BAP lists bird species according to three levels. Red list species mortality when late frosts occur. Milder winters and warmer are those showing a decline in population >50% in the past 25 springs may lead to an increase in food availability or a decline years; amber species have suffered a 20–50% loss; and green list as pest emergence/egg hatching move out of synchronisation. species are considered to be at no significant risk. The type of monitoring carried out at ECN sites is well placed to evaluate Deer population dynamics and also to identify possible causal factors. Browsing mammals such as deer and rabbits have a significant In general, woodland bird populations are increasing at Alice effect on their environment and deer numbers have been Holt (Figure 13). Of the 26 woodland bird species recorded shown to have a dramatic effect on woodland structure. It is between 1994 and 2006, five are red listed and seven are therefore important to know numbers in order to estimate any amber. Of the red list species, lesser-spotted woodpeckers have effect on vegetation caused by populations, rather than, or even not been recorded since 1994 while marsh tits ( Poecile palustris ) as a result of, the effects of climate change. Monitoring of deer and bullfinch ( Pyrrhula pyrrhula ) disappeared between 1998 and numbers has shown a significant decline in deer densities at the 1999 respectively. Spotted flycatchers have not been seen since ECN site since 1995 (Table 3). Grazing by deer is known to have 2001. Willow tits ( Poecile montanus ) were last seen in 2003. a significant effect on some bird species populations; overgrazing Song thrush ( Turdus philomelos ) showed a steady increase until can reduce the amount of shrub layer and hence nesting sites. 2000, and numbers have since stabilised across the forest. However, at Alice Holt, both seedling survival and shrub layer On the amber list, the cuckoo ( Cuculus canorus ), green wood- have increased since 1994 as deer densities have fallen (Figure peckers ( Picus viridis ), willow warblers and woodcock ( Scolopax 14a and b). This is reflected by the general increase in woodland rusticola ) have all maintained small populations. Recent surveys bird populations observed as previously mentioned.

Figure 13 Bird population trends at Alice Holt between 1997 and 2006 (Common Bird Survey).

30 Greater spotted woodpecker Wren 25 Robin Blackbird s r i

a 20 Song thrush p

g Black cap n i

d Chiffchaff e 15 e r Willow warbler b f

o Goldcrest e

t 10

a Blue tit m i t

s Great tit E 5 Nuthatch Jay 0 Chaffinch 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Spotted flycatcher

10 Table 3 Decline in deer densities in Alice Holt Forest. In the UK bats hibernate throughout the winter to avoid food Year Density (deer per km 2) shortages, emerging in spring to feed and breed. Changes in the 1995 20.9 internal temperature of roost sites as the climate warms may 1998 16.4 force bats to abandon traditional hibernaculars and attempt to 2003 14.0 find new sites. Warmer winters and milder springs could lead to alterations in hibernation patterns. Pipistrelle bats take advantage of warm winter evenings (over 10 °C) to emerge and Figure 14 General increase in (a) seedling survival and (b) shrub feed, leading to reduced risk of winter fatality. However, layer since 1994 as deer densities have fallen. increased precipitation in spring may make it difficult for the a 1994 2002 newly emerged bats to find food and, because of their low

) 298 0 300 5 reproductive rate, individual populations are highly vulnerable. = n ( 247 s

t 250 o l

p At the Alice Holt ECN site, the most common bat species is the

n 200 i

s common pipistrelle ( Pipistrellus pipistrellus ), considered to be the g n i l 150 most widespread and abundant bat in Europe, including the UK d e e s 93 (Stebbing and Griffiths, 1986). Other bats recorded at the site f 100 o

r are the soprano pipistrelle ( Pipistrellus pygmaeus ), serotine e

b 50 26 27 m 18 17 17 (Eptesicus serotinus ) and the noctule ( Nyctalus noctula ). The years u 11 9 11 9 6 1 1 1 2 2 3 1 221 5 N 1

0 l t e t k

e since 1999 have been some of the warmest on record with k n n y e n n y h l h h e l r w r c r u e r r a l a n s r c c p i r e e r o o n o o o o u t e A i l O a l w e t P l h s h higher summer temperatures and a decrease in cold days in a w i e s B o H m h t t e m m L S e B a k R C e W w h c c d W a l h winter. Analysis of the bat data shows a significant increase in c y a l e S H i B F activity measured by the number of observations made; this is b 1996 2002 associated with an increase in bat numbers at the site (Figure 15).

) 80 0 5

= 70 n

( Although the overall habitat of Alice Holt Forest has not s t 60 o l changed over the sampling period, localised activities have p 50 n i affected bat activity in specific areas. In 2000/2001, thinning s

b 40 u

r was carried out in the compartments adjacent to the h

s 30 f monitoring transect. A corresponding increase in bat activity in o

r 20 e

b this area was recorded in the years following this work. It was

m 10

u noticeable, however, that despite the increase in activity, there N l t n y 0 n e n e l r m n r s

l was a decrease in feeding in this area in the year following the z o e o o o r o o a r h o h r d R t H r H t u n thinning. In 2003, forest operations in the area led to a k B w e C c a d a l H o

B corresponding drop in bat numbers immediately following this d o

h work, probably as a result of disturbance. By the following year, R numbers had returned to previously observed levels.

Bats Figure 15 Bat activity at Alice Holt between 1994 and 2006; no data recorded for 1996 and 1997. Bats are sensitive to alterations to their environment such as habitat loss, changes to commuting routes, roost destruction, 25 pesticide poisoning and changes in climate. In examining the s n

o 20 effects of environmental change, both large-scale change and i t a v small modifications to habitat will have a significant impact. r e s

b 15

Bats rely on trees as roosting sites, changing sites as temperature o t a and humidity vary in order to maintain suitable environmental b f

o 10 conditions. Geographical features such as rides and hedgerows r e b are used to navigate between roost sites and feeding grounds. m u 5 Warmer temperatures are expected to lead to a movement in N the northern limits of some bat species, but this effect may be 0 1 5 4 6 7 0 3 9 6 5 2 4 8 0 9 0 9 9 0 0 9 0 0 0 9 9 complicated by such factors as loss of roost sites, flight line 0 9 0 9 9 0 0 9 0 0 0 9 9 2 1 2 1 1 2 2 1 2 2 2 features and feeding habitats. 1 1

11 HULME, M., JENKINS, G., LU, X., TURNPENNY, J.R., MITCHELL, T.D., Conclusions JONES, R.G., LOWE, J., MURPHY, J.M., HASSELL, D., BOORMAN, P., MCDONALD, R. and HILL, S. (2002). Climate change scenarios for The detection and monitoring of environmental change requires the United Kingdom: the UKCIP02 scientific report . Tyndall Centre for Climate Change Research, UEA, Norwich. intensive monitoring of whole ecosystems. The ECN enables us IPCC (2007). Climate change 2007: the physical science basis, eds S to identify change within this context. Its use of common protocol s Solomon, D Qin, M Manning, Z Chen, M Marquis, K B Averyt, M provides links with other national, European and worldwide Tignor, and H L Miller. Contribution of Working Group 1 to the Fourth Assessment Report of the IPCC. Cambridge University Press, Cambridge. networks. The ECN site at Alice Holt provides ecological records KARLSSON, P.E., UDDLING, J., BRAUN, S., BROADMEADOW, M., to aid interpretation of interactions within the forest environment. ELVIRA, S., GIMENO, B.S., LE THIEC, D., OKSANEN, E., It is relevant to sustainable forest management, the scientific VANDERMEIREN, K., WILKINSON, M., CEULEMANS, R. and EMBERSON, L. (2004). Dose–response relationships for ozone impact community, forest managers and the wider public. It allows us to on the biomass accumulation of young trees based on cumulative focus on the effects of both pollution and climate change and leaf ozone uptake. Atmospheric Environment 38 , 2283–2294. their interactions with biodiversity, soil and air quality; and it KIRBY, K.J., SMART, S.M., BLACK, H.I.J., BUNCE, R.G.H., CORNEY, P.M. and SMITHERS, R.J. (2005). Long term ecological change in British provides input to UK forestry policy. Initial findings of this short woodland (1971–2001) . English Nature Research Reports 653. data set have proven the effectiveness of ECN. Some of the main English Nature, Peterborough. causes and effects of change both to the forest structure and its MORECROFT, M. (2004). Plotting change. Vegetation change at ECN sites from 1993 – 2002. ECN News 16 , 6–7. associated biodiversity have been identified. ECN is proving itself NEGTAP (2001). Transboundary air pollution: acidification, eutrophication to be an effective early warning system for environmental and ground level ozone in the UK. Report of the National Group on change effects and a comprehensive way of gaining information Transboundary Air Pollution. Defra, London. O’BRIEN, L. (2005). Trees and woodlands: nature’s health service . Forest on the effect of management practices and land use changes. Research, Farnham. O’BRIEN, L. (2006). A marvellous opportunity for children to learn. A participatory evaluation of Forest School in England and Wales . Forest References Research, Farnham. PITTS, A., BENHAM, S., STRAW, N.A. and MOFFAT, A.J. (2005). ASHER, J., WARREN, M., FOX, R., HARDING, P., JEFFCOATE, G. and Evaluation of moth-trap data from Alice Holt Forest, Hampshire, JEFFCOATE, S., EDS (2001). The millennium atlas of butterflies in 1966–2001: possible effects of changing climate on Britain and Ireland . Oxford University Press, Oxford. Macrolepidoptera. Entomologist’s Gazette 56 , 237–247. BELLAMY, P.H., LOVELAND, P.J., BRADLEY, R.I., LARK, R.M. and KIRK, POLLARD, E. (1988). Temperature, rainfall and butterfly numbers. Journal G.J.D. (2005). Carbon losses from all soils across England and Wales of Applied Ecology 25 , 819–828. 1978–2003. Nature 437 , 245–248. PRESTON, C.D. and HILL, M.O. (1997). The geographical relationship of DEFRA (2003). Review of UK climate change indicators (revised 2004). British and Irish vascular plants. Botanical Journal of the Linnean Contract EPG 1/1/158. Department for Environment, Food and Society 124 , 1–120. Rural Affairs, London. www.ecn.ac.uk/iccuk PRYOR, S.N. and SMITH, S. (2002). The area and composition of FORESTRY COMMISSION (2004). The UK forestry standard: the government’s plantations on ancient woodland sites . The Woodland Trust, Grantham. approach to sustainable forestry . Forestry Commission, Edinburgh. SPARKS, T. and GILL, R. (2002). Climate change and the seasonality of GB PARLIAMENT (1994). Biodiversity: the UK Action Plan . Summary woodland flora and fauna. In: Climate change: impacts on UK forests , Report. HMSO, London. ed. M. Broadmeadow. Forestry Commission, Edinburgh, 69 –82. GLUE, D.E. (2006). Cuckoos in crisis. BTO News 263 , 22–23. STEBBING, R.E. and GRIFFITHS, F. (1986). Distribution and status of bats HARRISON, P.A., BERRY, P.M. and DAWSON, T.P., EDS (2001). Climate in Europe . Institute of Terrestrial Ecology, Huntingdon. change and nature conservation in Britain and Ireland: modelling THIELE, H.U. (1977). Carabid beetles in their environments . Springer- natural resources response to climate change (the MONARCH project). Verlag, Berlin. UKCIP Technical Report, Oxford. VISSER, M.E. and HOLLEMAN, L.J.M. (2001). Warmer springs disrupt the HILL, M.O., MOUNTFORD, J.O., ROY, D.B. and BUNCE, R.G.H. (1999). synchrony of oak and winter moth phenology. Proceedings of the Ellenberg’s indicator values for British plants. ECOFACT volume 2 , Royal Society B 268 , 289–294. technical annex . ITE Monkswood, Huntingdon. Department of the WOIWOD, I.P. (2003). Are common moths in trouble? Butterfly Environment, Transport and the Regions, London. Conservation News 82 , 9–11.

The ECN is a long-term, integrated Enquiries relating to this publication should be addressed to: environmental monitoring and research programme sponsored by a consortium Suzanne Benham of UK government departments and Environmental and Human Sciences Division agencies, including the Forestry Commission. It is co- Forest Research ordinated on their behalf by the NERC Centre for Ecology Alice Holt Lodge and Hydrology. For more information visit: www.ecn.ac.uk . Farnham F

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