Mini-drone assisted tree canopy sampling: a low-cost and high-precision solution.

The collection of tree canopy samples in forest ecosystems has been challenging for researchers and managers during the past decades. Various methods, including pole pruner, tree climber, shooter, throw-line launcher, hydraulic lift (e.g., tower crane) and UAV (unmanned aerial vehicle)-based devices, have been used, however, they are limited by sampling height restrictions, safety hazards to a climber, low retrieving accuracy, high equipment costs, and transportation inconvenience. This study proposed a novel method for collecting tree canopy samples using a portable mini-drone. The mini-drone is operated to pull a traction line across the target branch, drag the retrieving rope to the selected cutting point of the branch, and carry the equipped wire saw or chain saw to cut the canopy sample off. Through on-site testing and field trials, this method was feasible for lower- and middle-canopy sampling (up to 30 meters tall) across most temperate broad-leaved and coniferous tree species. This technique would have great potential in plantation and old-growth forests. Adopting this low-cost mini-drone technique, researchers can collect tree canopy samples safely and efficiently, leading to improvements in relevant physiological and ecological studies focusing on functional traits of branches, leaves, and seeds.

Geographical variation of ecological stoichiometry and nutrient resorption in leaves of Pinus koraiensis and Fraxinus mandshurica.

In this study, we sampled leaves of coniferous species Pinus koraiensis and broad-leaved tree species Fraxinus mandshurica from four latitudes in northeastern China to investigate the carbon (C), nitrogen (N), phosphorus (P) stoichiometric characteristics and nutrient resorption efficiency and their potential relationships, as well as their responses to climatic and edaphic factors. The results showed that stoichiometric characteristics were species-specific, and that the C and N contents in leaves of F. mandshurica significantly increased with increasing latitude. The C:N of F. mandshurica and N:P of P. koraiensis were negatively correlated with latitude, but an inverse relationship was found for N:P of F. mandshurica. P resorption efficiency was significantly correlated with latitude in P. koraiensis. The spatial variation of ecological stoichiometry of these two species was mainly affected by climatic factors such as mean annual temperature and precipitation, while that of nutrient resorption was influenced by several soil factors such as soil pH and nitrogen content. Principal component analysis showed that P resorption efficiency of P. koraiensis and F. mandshurica was significantly negatively correlated with N:P, but positively correlated with P content. N resorption efficiency showed significantly positive correlation with P content but negative correlation with N:P in P. koraiensis. Compared with P. koraiensis, F. mandshurica was more inclined to fast investment and return in terms of leaf traits.