Trait records of marked Salvia nemorosa L. individuals censused annually between 2021-2023 in 13 localities of the Great Hungarian Plain

Predicting how changes in weather patterns and land use jointly impact populations is a pressing task in ecology. Microclimate may play a key role in species’ local persistence by modulating regional weather effects. We lack sufficient empirical evidence to understand the relative effects of landscape structure and habitat conditions on intraspecific trait variation. We used this spatially and temporally replicated dataset to test the relative effect of landscape structure (area and connectivity of remnant habitat fragments), microclimate (heat load), and fluctuation in weather conditions (study year) on intraspecific plant trait variation, and we investigated whether the local heat load modulated the weather effects on the studied traits.

Methods
The study was located in the Great Hungarian Plain in Eastern Hungary, Europe. We worked on 13 sites (11 kurgans and two reference flat grasslands) where Salvia nemorosa was present, spanning across 135 km (E - W) and 79 km (N - S). Kurgans were selected to represent different habitat area (basal area ranged between 528 - 4,321 m2) and connectivity (Hanski connectivity index ranged between 0 - 338.4). S. nemorosa grew in remnant grassland patches dominated by Festuca rupicola. 

Data was collected at peak flowering of S. nemorosa in June-July, over three consecutive years between 2021-2023. Eight sites were censused each year throughout the length of the study, further four sites were censused only twice as new sites were added to the study between 2022-2023, while one site was only censused once in 2021 due to subsequent census difficulties. We established up to four permanent transects of varying lengths (4-10 m), depending on the area of the habitat patch, where the number of individuals was representative of the habitat. On kurgans, S. nemorosa individuals were often limited to only one side of the kurgan (typically on South-Southwestern slopes or on the top), but on three kurgans a larger number of individuals allowed setting up transects on two contrasting slopes. Along each transect, we laid down permanent contiguous plots of 0.5 x 0.5 m, within which we permanently marked all S. nemorosa individuals with a numbered linoleum tag, including new individuals each consecutive year. For each plant, we recorded in-situ three vegetative traits: height of the tallest stem, number of stems, length and width of two biggest leaves forming a leaf pair, and two reproductive traits: inflorescence length and number of primary side inflorescence pairs. To calculate mean leaf area, we approximated the measured leaf shapes to a triangle, and we multiplied the leaf length and width, which we averaged across the two measured leaves. In this study, we narrowed our analyses only to mature plants, to capture maximum attainable growth responses that can be related to the reproductive effort of same individuals. We defined mature individuals as plants that had a flowering probability (i.e., the likelihood that a plant develops inflorescence) higher than 50%.