In this study we aimed to show whether plant communities in areas of woodland enclosed by pheasant release pens were different to those found in other parts of the same woodland. We did the study in the southern half of England and confined it to ancient semi-natural woodland sites. These woodlands are valuable habitats for wildlife and an important part of our cultural heritage.
We used replicated quadrat surveys of ground flora species and structure in a sample of 43 release pens in ancient semi-natural woodland and 43 (paired) control plots. We did this in spring/early summer, to ensure that any changes detected were not just seasonal (ie. just following release). We also investigated the extent to which any effect might be related to the stocking density of the pen, pen size or pen age.
We did the original field work back in 1988 and wrote it up in a report for English Nature and an article for our own Review of 1988. Since then, the work has become increasingly topical as part of our programme of research on effects of pheasant releasing (see Review of 2002). An inspection of the original field sheets suggested that there may be more to the data than originally thought, so in 2003 we did a more sophisticated analysis of the 1988 data, which has revealed some important new relationships for the first time.
The sample of 43 release pens ranged from one to 20 years in age. The average pen size was 0.5 hectares and the average stocking density was 2,100 pheasants per hectare of pen. Since 1988 pen sizes may have increased and densities decreased. Overall, the release pens had more bare ground and less vegetative cover from 0 to 10 centimetres off the ground in the spring than the control areas. Bare ground was most evident in smaller pens (see top left graph in Figure 1).
Top left:Amount of bare ground in relation to pen size
|Note: each point represents a separate site. For each graph the vertical axis is the percentage difference between the pen plot and the control plot at a particular site, so positive values mean more of that measure of the ground flora in the pen than in the control and vice versa. Regression lines are all statistically significant at P<0.05.|
Overall, plants of fertile or disturbed ground (see Table 1) were significantly more common in release pens than control plots. However, these species only increased in percentage cover as stocking density increased above a certain level. At densities below around 1,000 birds per hectare, the establishment of these (sometimes undesirable) species will not occur (see top right graph in Figure 1).
The release pens, however, had fewer species overall and this was due to a reduction in the percentage cover of shade-tolerant perennials characteristic of old woodland sites (see Table 1). The number of these important woodland plants reduced further as stocking densities went up. At densities below around 1,000 birds per hectare, these effects are minimised, but still occur (see bottom left graph in Figure 1).
Tree and shrub seedlings were not common in most of the pen or control sites in the study. This a problem for many lowland woods, particularly where deer are numerous. Where these seedlings did occur, their abundance was further reduced by the presence of a release pen. This time the reduction was related to the age of the pen (see bottom right graph in Figure 1). Bramble, the most abundant species in the study, was also less common in release pens.
We have documented many of the benefits to woodlands of releasing pheasants in cases where a principal aim of the game manager is to encourage shrubby cover and open areas for pheasants through coppicing, skylighting, ride widening and so on. Although we have identified release pens as a possible source of conflict which, when managed badly, can negate the benefits in sensitive woodlands, the work also indicates that by implementing good practice these conflicts can be avoided.
In particular, we believe it is best to avoid areas of ancient semi-natural woodland containing a valuable native shade-tolerant woodland flora when considering a new pen site. We recommend maintaining stocking densities at recommended levels by restricting the number of birds released, maximising the pen size, or both. We are currently expanding our research to produce detailed recommendations.
Common Plants in Pens
|Preferring fertile or disturbed ground||Preferring shady conditions|
|Creeping thistle||4||2||Wood anemone||11||13|
|Cocksfoot||11||6||Lord and Ladies||9||4|
|Yorkshire fog||7||3||Wood avens||6||21|
|Annual meadow grass||14||3||Ground ivy||8||22|
|Common nettle||27||22||Wood melick||5||5|
|Lords and ladies||9||14||Dogs mercury||29||30|
|Yellow archangel||9||18||Wood millet||2||9|
|Wood millet||2||9||Wood sorrel||3||7|
|Rough meadow grass||35||30||Lesser celandine||5||6|
The numbers are sites from the sample of 43 at which species were recorded in the pen or control area.