Dendroecology as a tool for evaluating past ungulate activity in forest stands
The wild ungulates, at high densities, can pose a problem for forest regeneration and mountain forests are more exposed to damage owing to the long periods needed for the regeneration processes. The use of dendroecological methods could be a useful tool to study present and past injuries and to support forest and wildlife management. Ungulates cause damage in forest regeneration and influence forest succession by browsing, bark stripping and fraying.
Browsing damages have only indirect effects on ring width so a careful observation is necessary to characterize the interaction between browsing and ring features. A severe browsing induce a strong ring width reduction. Browsing marks on the stem axis can be used to determinate the past browsing under particular conditions.
Fraying and bark stripping causes a scar on the tree. A scar is defined as the portion of the cambial zone where the cambium is killed by an injury. The tree reacts to this scar by compartmentalisation.
According to SHIGO, healing is a restoration or regenerative process by which injuries and infected cells are repaired and replaced in the same spatial position, whereas the concept of compartmentalisation identifies a different process namely the formation of boundaries to isolate the injured tissues and thus contain the spread of pathogens. Trees close wounds on the outside and compartmentalise pathogens on the inside. This type of defence allows the year in which damage occurred to be identified using dendroecological analysis. Dendroecology has been used in the study of a variety of scars on forest trees caused by both animals and other biological or physical causes, in particular scars caused by the passage of fire. Scars on trees may generally be dated either by simply counting the tree rings between the cambium and the scar-ring, or by cross-dating the rings prior to the scar. In some instances scars can be dated, in a less destructive way, from cores removed from the tree.
Red deer and rod deer fraying scars were studied in the forest of Paneveggio (Trento, Italy). The fraying caused by red deer was distinguished from that caused by roe deer according to the diameter of the tree at the moment of damage, the height from the ground, the overall extent of the damage and the position of the scar in the ring. The presence of red deer has been documented back to 1961 onwards, a finding which corresponds relatively well to data available on the reintroduction of red deer in Paneveggio. The presence of roe deer has been documented back to 1910.
Bark stripping scars caused by red deer were studied in the "Gran Bosco di Salbertrand" Natural Park (Susa Valley, Piedmont, Italy). Scars were dated by counting the rings between the scar-ring and the cambium. In Silver fir the ring widths in the cross sections with pre-scar ring growth of at least 20 years rings were measured and the scar-ring was dated using cross-dating by comparing these series with the silver fir site chronology. Cross-dating was only possible in 44.2% of cases given that these were very young and suppressed specimens. In all cases in which it was possible, the results confirmed the dating made by counting rings between the scar-ring and cambium. A bark stripping scar chronology (1964-1994) was constructed and confronted with the deer density.
