DOI: 10.5061/dryad.8931zcrx4
title: Effects of experimental warming on oak defenses and herbivory across latitudes

description: Forest microclimatic variation can result in substantial temperature
 differences at local scales with concomitant impacts on plant defences and
 herbivory. Such microclimatic effects, however, may differ across
 abiotically contrasting sites depending on background environmental
 differences. To test these cross-scale effects shaping species'
 ecological and evolutionary responses, we experimentally tested the
 effects of aboveground microhabitat warming on insect leaf herbivory and
 leaf defences (toughness, phenolic compounds) for saplings of sessile oak
 (Quercus petraea) across two abiotically contrasting sites spanning 9°
 latitude. We found higher levels of herbivory at the low-latitude site,
 but leaf traits showed mixed patterns across sites. Toughness and
 condensed tannins were higher at the high-latitude site, whereas
 hydrolysable tannins and hydroxycinnamic acids were higher at the
 low-latitude site. At the microhabitat scale, experimental warming
 increased herbivory but did not affect any of the measured leaf traits.
 Condensed tannins were negatively correlated with herbivory, suggesting
 that they drive variation in leaf damage at both scales. Moreover, the
 effects of microhabitat warming on herbivory and leaf traits were
 consistent across sites, i.e., effects at the microhabitat scale play out
 similarly despite variation in factors acting at broader scales. These
 findings together suggest that herbivory responds to both microhabitat
 (warming) and broad-scale environmental factors, whereas leaf traits
 appear to respond more to environmental factors operating at broad scales
 (e.g., macroclimatic factors) than to warming at the microhabitat scale.
 In turn, leaf secondary chemistry (tannins) appears to drive both
 broad-scale and microhabitat-scale variation in herbivory. Further studies
 are needed using reciprocal transplants with more populations across a
 greater number of sites to tease apart plant plasticity from genetic
 differences contributing to leaf trait and associated herbivory responses
 across scales and, in doing so, better understand the potential for
 dynamics such as local adaptation and range expansion or contraction under
 shifting climatic regimes.
description: # Oak warming treatment
 [https://doi.org/10.5061/dryad.8931zcrx4](https://doi.org/10.5061/dryad.8931zcrx4) We conducted a manipulative field study testing for the effects of experimental warming at the microhabitat-scale on insect leaf herbivory and leaf traits associated with herbivory across two sites with contrasting (e.g., macroclimatic) conditions using sessile oak (*Quercus petraea*) as model species, a common tree species in many Western European broadleaf forests (Supporting Information). Specifically, we established two field sites spanning two thirds of this species’ latitudinal range, one in Spain (42°N) and one in Belgium (51°N), using three-year-old saplings local to each site. We imposed microhabitat-level warming for half of the saplings at each site using infrared heater arrays. After a full growing season (March to September 2022), we collected leaves to measure insect leaf herbivory and to quantify physical (specific leaf area, correlated with leaf thickness or toughness) and chemical (phenolic compounds) traits known to affect herbivory in oak species. ## Description of the data and file structure | Block | experimental blocks | | ----- | ------------------- | | site | high-latitude in Belgium and low-latitude in Spain | | Treatment | control (ambient temperature) or aboveground warming | | SLA | in cm<sup>2 </sup>g<sup>-1</sup> | | Herbivory | in % | | flavonoids | in mg g<sup>-1</sup> d.w. | | Hydroxicinnamic\_acids | in mg g<sup>-1</sup> d.w. | | Condensed\_tannins | in mg g<sup>-1</sup> d.w. | | Hydrolysable\_tannins | in mg g<sup>-1</sup> d.w. | ## Code/Software We ran general linear mixed models testing for the effect of site (two levels: high- vs. low-latitude), microhabitat-level warming (two levels: control or ambient temperature vs. experimental warming) and their interaction on four different response variables: phenolic compounds (separately for each group of compounds), SLA and insect leaf herbivory. We performed all analyses with PROC MIXED in SAS ver. 9.4. We log-transformed herbivory, condensed and hydrolysable tannins, flavonoids, and plant relative growth rate to achieve normality of the residuals, and report model least-squares means and standard errors as descriptive statistics.