Herbivory has a greater impact in shade than in sun: response of Quercus pyrenaica seedlings to multifactorial environmental variation

Abstract

Many biotic and abiotic factors affect seedling establishment in woody plants. In Mediterranean environments, the major factors affecting tree regeneration are light, water, and herbivory. We investigated the response of some morphological and chemical traits of Quercus pyrenaica Willd. seedlings to simulated herbivory (hand removal of 50% of the aerial mass) and two levels of light (sun vs. shade) and water (one vs. two waterings). Water had no appreciable direct effect on morphological or chemical traits. Shaded seedlings grew less but had greater total leaf area. Simulated herbivory decreased the total leaf area, and root and aerial mass. Among the chemical characteristics, shaded seedlings had higher levels of nitrogen and lower levels of condensed tannins. In colorimetric assays of tannins, clipped seedlings had lower absorbances than did unclipped plants, and this effect was more pronounced in the sun than in the shade. Our experiment shows that light availability and herbivory affect the development and defence of Q. pyrenaica seedlings. Although Q. pyrenaica tolerated shade and simulated herbivory, both factors decreased biomass and chemical defence, which could affect the seedlings' future performance.Key words: environmental context, light, mammal herbivory, oak seedlings, Quercus pyrenaica, secondary compounds.

Influence of overstory density on understory light, soil moisture, and survival of two underplanted oak species in a Mediterranean montane Scots pine forest

“…Besides, the greater root to shoot ratio of seedlings of pyrenean oak, together with their higher resprouting ability (Rodríguez-Calcerrada et al, 2007b) could have enhanced their resistance to browsing damages over those of sessile oak. In line with this reasoning, despite browsing was similar among overstory treatments, different light availability for plants between treatments could have influenced resilience of seedlings of pyrenean oak to foliage removal (Baraza et al, 2004). Higher light in the thinned plots likely allowed for a higher leaf area re-development and carbon gain revenue with respect to the uncut plots, which could help to rebuild-up non-structural carbohydrate reserves in the root system and favour initial persistence, at least until reserves are depleted in repeatedly producing new shoots to compensate for the continued lost of foliage (Baraza et al, 2004;Landhäusser and Lieffers, 2002).…”

Does snail grazing affect growth of the old forest lichen Lobaria pulmonaria?

“…Accordingly, a combination of reduced growth and increased grazing with increasing proximity to the ground suggests that lichen-feeding invertebrates may play a significant role in shaping the lower distribution limit of epiphytic lichens within forest canopies. Grazing and shade adversely affect the performance of seedlings of plants (Baraza et al 2004). …”

Shedding light on shade: ecological perspectives of understorey plant life

“…Thus, for example, mortality due to resource limitation in the understorey can be balanced by mortality due to herbivory in gaps. In other cases, herbivores are more abundant, or exert greater feeding pressure in the understorey, so that the overall impact of herbivory can be greater in shade than in the open (Baraza et al 2004). Ultraviolet radiation, which varies in intensity with total irradiance along the gap-understorey gradient, has a significant impact on the interactions between plants and animals.…”

“…It may also be associated with increased herbivory (Baraza et al 2004) and greater competition for below-ground resources because dense above-ground vegetation also exploits below-ground space heavily (Valladares and Pearcy 2002). Reducing light intensity, damping temperature variation and ameliorating soil conditions under the canopy are some mechanisms by which established plants facilitate other plants (Valiente-Banuet and Ezcurra 1991; Pugnaire et al 2004), but in most cases facilitation effects are less significant as water and nutrient availabilities become lower (Maestre et al 2006).…”