Regeneration and Early Tending of Black Locust (Robinia pseudoacacia L.) Stands in the North-West of Romania

Abstract

Background and Purpose: The aim of this study is to highlight the importance of black locust (Robinia pseudoacacia L.), a North American-originating tree species of major importance in Romania, in extreme site conditions such as sand dunes. In this respect, a Research and Development (R&D) project has been carried out in Carei-Valea lui Mihai Plain (north-west of Romania) since 2016. Materials and Methods: Three sub-compartments were selected in IV Valea lui Mihai Working Circle, Săcueni Forest District: two pure natural regenerations by root suckers of black locust at different ages (sub-compartments 3B and 52A%) and a mixed black locust - black cherry stand (sub-compartment 23D). Biometrical measurements and analyses as well as biomass estimations were performed. A thorough statistical analysis using the data on initial, extracted and residual trees/stands was also performed. Results: The main outputs of the project are as follows: (1) Black locust was established naturally by root suckers and the stocking of newly established stands can be as high as 50,000 suckers·ha-1; (2) The initial growth of black locust regeneration is quick and the young regeneration can close the canopy in 1-2 years, resulting in an appropriate dune fixation and wind erosion control; (3) The young pure or mixed black locust-dominated stands are left untended until the first cleaning-respacing (mean diameter 5-6 cm), when the stand shows high stocking/density and a wide variation in tree size. This intervention is from below, heavy (intensity over 25% by number of trees or basal area) and of negative selection type, removing mostly low Kraft’s class, dead or dying, and defective trees. Conclusions: This R&D project has shown the high potential of black locust to establish naturally by root suckers after a low coppice cut and stump removal, as well as the fast initial growth of regenerated black locust. The quick canopy closure of young regeneration results in an appropriate dune fixation and wind erosion control.

Does Black Locust Performs in Any Forest Sites?

“…A registration error or a particular case? It is well known that in our country this kind of regeneration was reported in very few cases (Negulescu and Săvulescu, 1957;Stănescu, 1979;Nicolescu et al, 2019).…”

Black Locust (Robinia pseudoacacia L.) in Romanian Forestry

“…Although black locust produces annually a very large number of seeds, because of their thick tegument, successful natural stand regeneration is missing almost completely [13]. Exceptionally isolated trees can be recognized as being from seeds in very particular sites, such as upper sides of river banks [14] or at pile burning sites where forest residues are burned [15].…”

“…While the harvesting technique is always clear cutting, stand regeneration occurs via sprouts on the aboveground part of the stump or suckers by mechanical stimulation of roots by: (a) ploughing of the soil among the stumps at 20 cm depth; or (b) digging out the stump together with the roots around it in a radius of 50 cm combined with additional ploughing. When regeneration targets root-suckers, the sprouts must be removed through early tending operations, so as to not overwhelm the slow growing root suckers [13]. After two cycles of vegetative regeneration from sprouts, the stumps weaken and lose their sprouting capacity (due to fungal impact and soil nutrient depletion); and by the third generation, the stand's productivity drops to 40% of that of plantations [16].…”

“…In any case, after the third generation of vegetative regeneration, all of the stumps must be removed from the harvested area and further regeneration is ensured via the planting of seedlings. Recent studies have showed that, after clearcutting and stump removal, the density of root suckers can reach 50,000 plants per hectare [13].…”

Ecology, growth and management of black locust (Robinia pseudoacacia L.), a non-native species integrated into European forests

“…These are produced abundantly even by trees over 70 years old (Vítková et al 2017) from superficial roots, particularly following mechanical damage to the root system (Boer 2013;Vítková et al 2016) or soil disturbance (Savill 2013). The number of suckers per tree can range from 1-2 up to 45-46 (Dimitrov 2001), so initial stocking after one growing season reach 40,000-60,000 suckers ha −1 (Pagès 1985, cited by Carbonnière et al 2007Nicolescu et al 2019). More suckers are produced in open, sunny areas, and on sandy loam than in shade, dense vegetation or on heavy soils (Converse 1984;Wieseler 2005, cited by Boer 2013Stone 2009).…”