Insect herbivory is thought to favour carbon allocation to storage in juveniles of shade-tolerant trees. This argument assumes that insect herbivory in the understorey is sufficiently intense as to select for storage; however, understoreys might be less attractive to insect herbivores than canopy gaps, because of low resource availability and -at temperate latitudes -low temperatures. Although empirical studies show that shade-tolerant species in tropical forests do allocate more photosynthate to storage than their light-demanding associates, the same pattern has not been consistently observed in temperate forests. Does this reflect a latitudinal trend in the relative activity of insect herbivory in gap versus understorey environments? To date there has been no global review of the effect of light environment on insect herbivory in forests. We postulated that if temperature is the primary factor limiting insect herbivory, the effect of gaps on rates of insect herbivory should be more evident in temperate than in tropical forests; due to low growing season temperatures in the oceanic temperate forests of the Southern Hemisphere, the effect of gaps on insect herbivory rates should in turn be stronger there than in the more continental temperate climates of the Northern Hemisphere. We examined global patterns of insect herbivory in gaps versus understories through meta-analysis of 87 conspecific comparisons of leaf damage in contrasting light environments. Overall, insect herbivory in gaps was significantly higher than in the understorey; insect herbivory was 50% higher in gaps than in understoreys of tropical forests but did not differ significantly between gaps and understories in temperate forests of either hemisphere. Results are consistent with the idea that low resource availability -and not temperature -limits insect herbivore activity in forest understoreys, especially in the tropics, and suggest the selective influence of insect herbivory on late-successional tree species may have been over-estimated.

SUMMARYThis work examined the utility of multispectral remote sensing to recognize the effects produced by infestation of the cypress aphid (Cinara cupressi) in the sanitary condition of the cordillera cypress (Austrocedrus chilensis). The study area is Fundo Los Cipreses, located in the foothills sector of the San Fernando County, Maule Region of Chile. Procedures focused on the recognition of variations in foliage vigor and turgidity of infested A. chilensis using ASTER images acquired at periods of preinfestation (March, 2003) and infestation (March, 2008). Both parameters were measured by the normalized difference vegetation index (NDVI) and the normalized difference water index (NDWI), respectively, for a set of geographic points corresponding to two main damage categories detected in the field (moderate and severe). In the study period a clear decrease in the NDVI and NDWI of the severely damaged individuals was evidenced, while those individuals that present a moderate damage did not show important differences for both indices. Results suggest that multispectral images are useful to detect severe damage in a stand. In the future it is expected that further development of the capacities of this type of product, complemented with hyperspectral images, allow for effective monitoring of C. cupressi infestation in other areas of the country.

We explore the suitability of vegetation indices derived from satellite hyperspectral data for identifying stress symptoms induced by the invasion of cypress aphid (Cinara cupressi Buckton complex) in a Cipre´s de La Cordillera (Austrocedrus chilensis (D. Don) Pic.Serm. & M.P. Bizzarri) forest, located in the Andes mountain range of central Chile. A set of 11 indices related to leaf physiology was retrieved from the processing of a Hyperion image of the study area. The indicies were correlated with the percentage of chlorosis and necrosis of the crown foliage of infested trees estimated visually in the field. The strongest correlations were recorded for two anthocyanin reflectance indices and the photochemical reflectance index. Vegetation indices sensitive to foliage quantity were weakly correlated with field data, likely due to the influence of wind-induced defoliation. Even when tree stands presented fairly similar levels of chlorosis and necrosis, as well as moderate vegetation cover, the results indicate that vegetation indices derived from hyperspectral images are potentially very useful in the detection, assessment and monitoring of the damage caused by the aphid.

An understanding of the spatial and temporal patterns of insect abundance and plant damage across altitudinal gradients and the mechanisms driving them is limited. Importantly, little is known in this area in relation to specific Mediterranean climate ecosystems. Insect abundance and plant damage in these environments may be closely related to air temperature, since it contributes to insect performance, length of growing season and tree growth, which is hypothesised to be negatively related to host plant defences against herbivory. In this study, we examined general insect abundance (across all taxa) and associated leaf damage, plant growth and leaf defences in the tree Nothofagus macrocarpa along an altitudinal gradient in the Mediterranean climate zone of Chile. Sampling was conducted in spring and summer at 'El Roble' mountain at three elevations (masl): low (1100-1200), medium (1600-1700) and high . Foliar insect abundance in both seasons was twofold higher at high vs. low altitude, and in summer leaf area damage increased with altitude. Twig growth was highest at high altitude, whereas leaf total polyphenols in both seasons were also relatively high at this altitude. Results indicate that in this climate, higher overall insect abundance and damage in a plant species can be found at higher altitudes and that air temperature does not limit insect presence. Moreover, total leaf polyphenols were not negatively related to this pattern or to plant growth. Among the possible explanations, we suggest that climate change is creating unfavourable conditions for insects at lower altitudes, resulting in an altitudinal shift.

An understanding of the impact that climate change will have on dominant plant species is important given the central role of these species in ecosystem functioning. Southern beech (Nothofagus Blume) is a central genus in the forests of the southern cone of South America, with Nothofagus glauca (Phil.) Krasser a dominant, at-risk tree inhabiting the drought-prone region of central Chile. The present study explored the relationships among several environmental variables that may be critical to understanding the impact of climate change on N. glauca, most importantly crown condition, plant water availability, insect leaf damage and landscape features. Furthermore, the study examined whether these variables differed between individuals from drier or wetter stands distributed within a north–south geographic area. Multiple regression modelling detected important relationships for the dependent variable crown condition with branch midday water potential, N. glauca diameter at breast height and vegetative cover, as well as with landscape variables in interaction with different plant vigour and water availability measures. Negative correlations between insect damage and plant water availability measures were observed at two field sites. Overall, crown condition and water availability were higher, and insect damage was lower, in wetter stands. The results of the present study have important negative implications for the species in terms of climate change and can be applied to future investigations.