Impact of red deer (Cervus elaphus) on forage crops in a protected area

During the last decades in Italy red deer (Cervus elaphus) density has locally reached very high values, with consequent serious problems due to the interaction with human activities, especially in protected areas. This study aims at quantifying the impact of red deer on herbaceous crops for forage production in a protected area in Northern Italy, that has been recently colonized by this species. To this aim, 14 exclusion enclosures on maize destined for whole plant silage production and 24 exclusion enclosures (not grazed, NG) on permanent meadows were established. For each of these sample plots (2 × 2 m), an adjacent control plot of identical surface area was established, freely available to red deer (grazed, G). Maize was harvested in September, whereas three grass cuts were harvested on meadows (May, July and August) and biomass production was weighed. Grass samples were collected, both in NG and in G plots, for chemical analysis. Red deer number was monthly estimated by night counts along fixed paths, using spotlights. The analysis of deer distribution allowed the distinction between two areas: High Density (HD: Northern area, with lower human disturbance, abundance of sheltered areas and an estimated deer density of 14–30 heads/km2) and Low Density (LD: Central and Southern areas, with an estimated deer density of 0–1.6 heads/km2). The percentage of maize plots with deer damage was significantly higher in HD than in LD area (83.3 vs 12.5%, respectively; P < 0.05). In HD, red deer impact on maize crop was significant on plant height (NG = 250.75 ± 47.58 vs G = 136.87 ± 87.90 cm; P < 0.05) and biomass production/plant (NG = 0.87 ± 0.42 vs G = 0.37 ± 0.39 kg/4 m2; P < 0.05), whereas no significant effect was observed in LD. The percentage of plots of permanent meadows with deer damage did not differ between HD and LD areas. Significant losses were observed only in the second cut in the HD area for DM production, which was reduced by almost 14%. The chemical composition of the meadow forages showed only slight differences between G and NG plots (CP and NDF content significantly lower in G plots). The results obtained indicate that a high red deer density has an impact on the economic activity of farmers, particularly in term of maize losses (with estimated economic losses higher than € 20,000/farm/year), and suggest that appropriate management strategies, such as fencing of the crops at risk, are highly advisable.