A detailed time series of hourly circumference variations in Pinuspinea L. in Chile

The dataset provides digital dendrometer measurements on stem circumference of irrigated and non-irrigated Pinus pinea trees. Data were obtained in a xeric non-native habitat of central Chile. Forest mensuration was hourly collected from six adult trees during a growth year. This data can be re-used to perform different studies, including growth and tree water status temporal correlations, climate-growth relationships, and to compare stone pine stands growing in native and non-native habitats. Such studies could facilitate decisions for the species management and contribute to the understanding of its growth dynamics in a climate change context, providing valuable information for a climate-smart forestry. Dataset access is at https://doi.org/10.5281/zenodo.6010567. Associated metadata are available at metadata-afs.nancy.inra.fr/geonetwork/srv/fre/catalog.search#/metadata/bcea7f69-2cf1-444b-8e5b-e9feb23683db


Background
This dataset was recorded during the FONDEF D11I1134 project (http://repositorio.conicyt.cl/handle/ 10533/108139/browse?type=folio&value=D11I1134) and developed during the Development and contributions for the use of high value forest and fruit-forest species for Chile program (Ministry of Agriculture). Its aims are to identify, to study, and to propose productive alternatives feasible to be established in the country with social, environmental and economic benefits, especially in the context of forecasted warming (IPCC 2021) that makes important the knowledge of forest species growth and its response to hydric deficit.
This tree-level dataset was used to evaluate short-term stem diameter variations (Loewe-Muñoz et al. 2021) at different temporal scales under irrigation and non-irrigation over a 1-year period to answer the scientific question of how the dynamics of seasonal growth and tree water status change in response to environmental factors in a xeric non-native environment (Fig. 1). This study showed that irrigation, besides increasing productivity, also decreased tree sensitivity to temperatures, evapotranspiration and rainfall variability, contributing to the prediction of responses to environmental changes.

Methods
Dendrometer data represent a high level of information for research activities on this emergent species in Chile. To evaluate the effect of irrigation on a stone pine plantation, one experimental field trial of 2 ha was designed and realized in the coast of central Chile; 6 plots of 25 trees were established. Between 2014 and 2015, one tree per plot was monitored with high-resolution dendrometers, to characterize seasonal growth dynamics, relevant for forest management purposes (van der Maaten et al. 2018;Zalloni et al. 2018).
We collected hourly stem circumference changes in irrigated and non-irrigated 31-year-old stone pine trees in the 2014/2015 growing year. During this year, below average precipitation for central coastal Chile was recorded (annual hydric deficit (rainfall minus potential evapotranspiration) close to 1000 mm) ( Table 1). The dataset contains stem circumference values recorded with high-resolution dendrometers at each hour during 365 days. The time series from each tree are indexed as irrigated or non-irrigated. The generated dataset includes six time series of stem circumference along with air temperature; variables are described in Table 2.

Site description and experimental design
The study was conducted in a 31-year-old stone pine plantation located in Cáhuil (34°30′ S, 71°59′ W), central Chile, on smooth hills at 125 m a.s.l. The climate is typically Mediterranean, with long dry summers and short intense winter rainfall, with maritime influence of the Pacific Ocean. Average annual climate data indicate annual rainfall of 641 mm, annual evapotranspiration of 1177 mm (estimated from automatically collected average, minimum, and maximum temperatures from dendrometers, with extra-terrestrial radiation values taken from FAO (www.fao.org/3/X0490E/x04 90e0j.htm), following Hargreaves and Samani 1985), 6 dry  months year −1 and annual average temperature of 13.2°C (Santibáñez 2017). Drought was recorded during the study period (Table 1). Further climate data can be accessed from DGA Pichilemu (snia.mop.gob.cl/BNAConsultas/reportes). Soil is silty clay loam, granitic, slightly acid (pH = 5.9), with medium organic matter content (3.6%), not salty (E.C. 0.11 mmho cm −1 ). The plantation was established on a 30-ha area in winter 1983. A first thinning was applied 20 years after establishment, when 50% of trees were extracted; the first pruning and a second thinning (extraction of 65% of trees, resulting in 285 trees ha −1 ) were conducted 1 year before establishing the experimental trial in 2014. It involves two treatments, irrigation and control (non-irrigation). Treatments were arranged in a randomized complete block design with three blocks (n = 3). Each plot within blocks had 25 trees. At the beginning of the study (age 31), trees measured on average 5.7 ± 0.35 m, 16.0 ± 1.32 cm, and 3.6 ± 0.34 m for height, DBH, and crown diameter, respectively, with no significant differences among treatments. One representative, regarding growth, central tree per plot was selected to install at breast height (DBH, c. 1.3 m) stem digital band dendrometers (EMS DLR26A with resolution < 1 μm, Environmental Measuring Systems, Czech Republic).
Daily irrigation was provided from spring (September) to autumn (April) using a drip irrigation system. The amount of irrigation was defined as 10% of the expected hydric deficit for the study period, which was calculated in terms of monthly air temperature, precipitation and potential evapotranspiration (PET) of the previous 1year period (Table 1). Daily irrigation increased from 1.9 L tree −1 in September to a maximum of 5.0 L tree −1 in January, and then decreased to 2.7 L tree −1 in April, totalling 753 L tree −1 year −1 .

Measurements of short-term stem circumference changes
Stem circumference variations were recorded daily at 1-h intervals (00:00 to 24:00 h) from June 2014 to May 2015 using the software EMS Mini32. The temperature in the data logger of the sensor was obtained at 1-h intervals from each dendrometer (Loewe-Muñoz et al. 2022).

Data access and metadata description
A dataset was generated in csv format, including six time series of stem circumference along with air temperature. The database includes 52,560 measurements (lines) and 6 columns (variables). Mensurational parameter attributes are presented in Table 2.

Technical validation
Each dendrometer has been carefully checked before publication, avoiding misspelling or errors. The database has been compiled in metric units using the dot as decimal value. The dataset was used in a study conducted in an adult stone pine plantation located in a droughtprone environment in Chile to establish a better understanding of the effect of irrigation on short-term stem diameter changes, and on the sensitivity of the species to weather conditions (Loewe-Muñoz et al. 2021).

Reuse potential and limits
This original dataset includes forest circumference values of irrigated and non-irrigated P. pinea trees along with air temperature, in a xeric environment in central Chile. This dataset has already been used to analyze short-term stem diameter variations, useful to carry out sustainable forest management.
Regarding the potential use and limits of the dataset, even if the monitored trees were six, the sampling design and the number of repetitions in each treatment may allow the calculation of several forestry-related indices regarding growth and tree water status within and between days, by removing the fitted long-term trend from the stem diameter variations (SDVs) through standardization, including temporal autocorrelations. This dataset is a unique opportunity to develop other research studies, including climate-growth relationships in different environments (Lamas and Rozas 2007); stone pine productivity under different water availability scenarios, useful to study climate change impacts; and to compare Chilean stone pine stands with stands located in the species native habitat and other zones in which P. pinea has been widely introduced (Akyol et al. 2020).