Dataaset for No effect of invasive tree species on aboveground biomass increments of oaks and pines in temperate forests

Dataset for article about increments of native tree species (https://www.sciencedirect.com/science/article/pii/S219756202400037X).In September of 2021 and 2022, we measured the DBH of all of the living specimens of each species that were >1.3 m tall. We used these measurements to calculate the total aboveground biomass, absolute invasive species biomass, and proportion of total aboveground biomass accounted for by invasive species. In January 2023, we used a Haglöf increment borer to collect wood core samples at a height of 1.3 m from five trees per plot (pines or oaks) facing two directions (north and east). We sampled only dominant trees. It certainly would have been interesting to also examine the impact on pines and oaks growing in the lower levels of the stand. However, in many of our plots, we did not observe pine or oak trees in the lower forest strata. In particular, pine and young oak stands were quite uniform in terms of DBH distributions. Moreover, many studies examining tree growth sample only dominant trees (Ruiz-Peinado et al., 2021; Vospernik et al., 2023). When selecting trees to sample to determine the distribution of the DBH of the dominant tree in the area, we focused on the health and condition of the individuals. Since we did not define the competition conditions separately for each sample tree, we ensured that the cover of invasive species was evenly dispersed within plots and their surroundings by establishing study plots within homogenous forest patches. In total, we collected 720 wood core samples. The core increment samples were sanded and then scanned at 1200 dpi resolution. We used CooRecorder and CDendro (Cybis software) to measure average annual growth of studied native trees on each plot over the last five years (2018–2022) and to cross-validate samples for the same trees. During data processing, we rejected three oaks and three pines from formal analysis due to poor visibility of annual rings after preparation or serious damage or defects in samples that could have negatively affected the precision of measurements.To define different metrics of species abundance, we used DBH measurements to calculate basal area, density, and aboveground biomass of the studied species. Moreover, we calculated stand aboveground biomass to express the proportion of it accounted for by the studied species. The aboveground biomass for each of the species within the plots was calculated using the allometric equations published in different studies (Alberti et al., 2005; Brown, 1976; Dyderski and Jagodziński, 2019a; Forrester et al., 2017; Jagodziński et al., 2018, 2019; Zasada, 2017). We assigned species not assessed by these authors to other generic groups (see Tables S1 and S2 for details). Then, we calculated the proportion of total aboveground biomass accounted for by P. serotina and R. pseudoacacia for each study plot (invader proportion). The abundance of trees in an ecosystem can be determined in many ways. Canopy cover helped us differentiate the invasion gradient during the selection of study plots before their establishment. However, it does not fully capture differences when comparing P. serotina and R. pseudoacacia. The canopy cover does not fully reflect the actual state of the gradient that occurs in the forests, but it was helpful in our initial search for study plots and was carefully recorded. In addition to the canopy cover, we paid attention to the size of the invasive trees. In our opinion, cover does not account for the vertical stratification of the forest, and, as an estimate, it is highly biased by observer effects. Biomass was determined from detailed measurements of DBH. Typically, it was not difficult to find P. serotina stands in the early stages of invasion, so we dedicated substantial effort to looking for stands with larger P. serotina trees. A much larger problem was finding pine or oak stands with R. pseudoacacia and without a large proportion of P. serotina. Both of these mentioned limitations affected the final gradient we achieved, which was generally low for P. serotina and was hardly representative for R. pseudoacacia, which had a larger gradient. For that reason, we decided to use the proportion of total aboveground biomass accounted for by invasive species and invasive species absolute aboveground biomass as independent variables in our models. For different quantitative indicators, we obtained slightly different gradients. The canopy cover of P. serotina ranged from 5–80% with an average of 27.8 ± 23.1%. For R. pseudoacacia, canopy cover had a similar range, from 4–72% with an average of 34.8 ± 24.5%. However, if we considered the number of individuals, basal area, and aboveground biomass, the differences were much more distinct. The density of P. serotina ranged from 180–6180 ind. ha−1 with an average of 1793 ± 1722 ind. ha−1. The density of R. pseudoacacia ranged from 80–4400 ind. ha−1 with an average of 789 ± 928 ind. ha−1. The average basal area for P. serotina ranged from 0.01–3.30 m2 ha−1 with an average of 0.98 ± 0.10 m2 ha−1, while for R. pseudoacacia it ranged from 0.35–27.47 m2 ha−1 with an average of 6.38 ± 7.93 m2 ha−1. Aboveground biomass of P. serotina ranged from 0.18–17.03 Mg ha−1 with an average of 4.39 ± 4.34 Mg ha−1. For R. pseudoacacia, aboveground biomass ranged from 0.83–264.45 Mg ha−1 with an average of 48.86 ± 75.90 Mg ha−1 (Fig. 2).The difference in the biomass of pines and oaks between 2018 and 2022, relative to the biomass in 2022 (relative aboveground biomass increment, relABinc), was calculated at the tree level and at the stand level. We calculated relABinc as: where relABinc is the relative aboveground biomass increment (dimensionless), AB2022 is the aboveground biomass of individual pines/oaks in 2022 (Mg), and AB2018 is the aboveground biomass of individual pines/oaks in 2018 (Mg). The aboveground biomass of sample trees after late (summer) growth in 2017 (or before early (spring) growth in 2018), designated AB2018, and after late (summer) growth in 2022, designated AB2022, were calculated using previous allometric models published by Forrester et al. (2017) for oaks and Jagodziński et al. (2019) for Scots pine (Table S2). This period is hereafter referred to as the period from 2018–2022. At the stand level, the growth of the remaining trees from which no core samples were taken was estimated based on the growth of the sample trees and their DBH. Finally, the relative increase in biomass for pines and oaks at the stand level was calculated from the sum of the aboveground biomass of all pines and oaks and the sum of their increments using a formula analogous to that for relABinc for individual trees.