Debarking damage by alien Pallas’s squirrel, <i>Callosciurus erythraeus</i>, in Argentina and its effects on tree growth

Abstract

Introduced squirrels threaten forest ecosystems by debarking, resulting in economic losses to the timber industry and additional damage mitigation and pest control costs. The Pallas’s squirrel, also called the red-bellied squirrel. (Callosciurus erythraeus), originally from Asia, is the first squirrel species introduced to South America. In Argentina, C. erythraeus causes bark stripping damage in several tree species but their impact on tree growth and wood quality has not been evaluated yet. Field work was undertaken during 2016 in a forest establishment in Lujan district, Buenos Aires Province, Argentina. Samples were taken in plantations of Pinus elliottii, Eucalyptus dunnii and Populus deltoides. For each tree species, we sampled two plantations (1–3 ha) that belonged to two age classes comprised of young and mature trees. Two or three transects, 50 m apart, were set up within each plantation and data collected from individual trees. We evaluated affected tissues, percentage of girdling (percentage of circumference of stem with damage), wood volume and stem defects on damaged and undamaged trees. Wounds damaged live tissues and reached the xylem, causing deformations in the growth rings of all the evaluated trees. Partial girdling was prevalent in younger P. elliottii and P. deltoides (more than 40% on average) and in both ages of E. dunnii (more than 50% on average). Minimum damage caused by squirrels was statistically significant among age classes for both P. elliottii and P. deltoides at 3 m and 6 m tree height. This is the section of the tree most relevant to the wood market. The damage resulted in wood-volume losses between 20% and 58% with diameter at breast height and/or height reduction in some plantations. In E. dunnii and P. deltoides the stem breaks were significant. The results of this study suggest that the Pallas’s squirrel may have an adverse impact on commercial forestry as a result of their continuous damage to trees, which leads to yield reduction and consequent economic losses.

Keywords: bark stripping; biological invasions; introduced squirrel; timber industry