Abstract
Herbivores modulate the structure and composition of plant communities, including plant invasions. This is conditioned by plant palatability which can be reduced by its chemical or physical traits. The effects that ungulates browsing has on pine invasions are variable and the empirical evidence on the causes of this variability is scarce. We experimentally explored how sheep browsing preference varies between seedlings of pine species with different invasiveness; Pinus contorta (high invasiveness), P. ponderosa (medium invasiveness), P. radiata (medium invasiveness) and P. jeffreyi (low invasiveness). Secondly, we quantified anti-herbivory chemical compounds and physical traits of these species and related them with sheep preference observed. The browsing incidence of P. contorta was 68%, P. ponderosa 58%, P. radiata 29%, and P. jeffreyi 84%. Among anti-herbivory traits analyzed, α-pinene concentration had a negative effect on the probability of a terminal bud being browsed and on browsing intensity. Meanwhile, foliar toughness was negatively related to browsing intensity and water concentration was positively related to browsing intensity. Also, the most invasive species, P. contorta, was highly damaged. Thus, sheep herbivory could be slowing pine invasion rate; suggesting that could be considered a tool to control early invasions, especially for this particular species.
Highlights
Herbivores modulate the structure and composition of plant communities, including plant invasions
Pinus radiata seedlings were significantly less browsed than the seedlings of the other three pine species, while P. jeffreyi seedlings were significantly more browsed than the seedlings of the other species (Fig. 1a, results of post-hoc comparisons can be found as Supplementary Table S2.1 online)
The relative reduction in P. contorta, P. ponderosa, P. radiata, and P. jeffreyi seedling height estimated by the model was 27%, 24%, 23%, and 18% respectively (Table 1) with the reduction in height of P. contorta seedlings significantly higher than the reductions in height of P. radiata and P. jeffreyi seedlings; and reductions in height of P. ponderosa seedlings were significantly greater than the reduction in height of P. jeffreyi seedlings (Fig. 1b; results of post-hoc comparisons can be found as Supplementary Table S2.1 online)
Summary
Herbivores modulate the structure and composition of plant communities, including plant invasions This is conditioned by plant palatability which can be reduced by its chemical or physical traits. We experimentally explored how sheep browsing preference varies between seedlings of pine species with different invasiveness; Pinus contorta (high invasiveness), P. ponderosa (medium invasiveness), P. radiata (medium invasiveness) and P. jeffreyi (low invasiveness). It was suggested that exotic vertebrates herbivores negatively affected Pinus radiata survival in Mediterranean areas of Chile[30] These opposing results may be due to distinctive characteristics of ungulates; such as its behavior, physiology, habits, and origin; as well as intrinsic characteristics of the plant such as phenology, plant morphology, and p alatability[32,33,34,35,36]. Chemical defenses vary greatly between different conifer species and even between genotypes within a species, causing palatability to differ[45, 46]
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