From facilitation to competition: the effect of black locust (Robinia pseudoacacia L.) on the growth performance of four poplar-hybrids (Populus spp.) in mixed short rotation coppice

Abstract

Short rotation coppices play an important role in providing biomass for energetic use. Mixing fast-growing tree species in short rotation coppices may show complementarity effects and increased yield. The aim of this study was to analyze the effect of species interaction in mixed short rotation coppices with fast-growing Populus spp.-hybrids and the N-fixing Robinia pseudoacacia. Four different Populus-hybrids (AF2, Fritzi Pauley, Hybride 275 and Max 1), planted alternately in pure and mixed stands with R. pseudoacacia were used for the analysis. Height and root collar diameter were measured once a year, over a period of four years (2014–2017). Additionally, in the third year, aboveground competition was surveyed with a terrestrial laser scanner and root biomass was analyzed to assess belowground competition. Soil nitrogen was also determined in order to verify enrichment properties of mixtures compared to pure stands. Populus-hybrids’ stem volume showed no significant differences between stand types in the first year after planting. In the second and third year, however, two Populus-hybrids (AF2 and Max 1) had a higher stem volume increment of up to 3.8 times than stem volume increment in pure stands. This may be related to the fact that soil nitrogen was 39% higher in the mixtures than in pure stands. However, in the 4th year after stand establishment, R. pseudoacacia’s crowns were so massive and broad, that this species was far more competitive than the Populus-hybrids. With the exception of P. ‘Fritzi Pauley’, which showed no significant differences between stand types, growth rates reversed for the other three Populus-hybrids. AF2, Max 1 and Hybride 275 showed up to 75% lower stem volume increment in mixtures compared to pure stands. We assume that, in spite of the initially observed facilitation between the species, the competition exerted by R. pseudoacacia started dominating after 4 years and began to surpass the benefits of facilitation.

Biomass production in mixed short rotation coppice with poplar‐hybrids (Populus spp.) and black locust (Robinia pseudoacacia L.)

“…pseudoacacia . In our previous work about mortality (Rebola‐Lichtenberg et al, 2019) and facilitation and competition (Rebola‐Lichtenberg et al, 2021) in mixed poplar‐black locust SRC, we came, however, to the conclusion that R . pseudoacacia affected the overall performance of poplar mostly negatively due to its advanced growth and dominance in the crown layer.…”

“…Even though poplar showed lower performance in mixed culture with black locust (Figure 2; Tables 4 and 5; Rebola‐Lichtenberg et al, 2019, 2021), a significant non‐transgressive overyielding was observed for two mixtures ( P . ‘AF2’/ R .…”

“…pseudoacacia took advantage of the rather narrow crowned poplar genotypes and was able to find the required space that they need for optimal growth (Nicolescu et al, 2020). The dominance of black locust in mixed stands had not only a positive effect on its own growth, but it was also the reason why poplars performed so poorly in mixture (Rebola‐Lichtenberg et al, 2021). A recent study did also find evidence of overyielding in mixtures of a poplar hybrid ( P .…”

“…Height and root collar diameter were measured for each tree at the field while in dormancy. Height (measured in cm) was measured using a measuring pole for bigger trees and a ruler for smaller (<200 cm) trees and root collar diameter (in mm) was measured at 3 cm above ground using a digital calliper (Rebola‐Lichtenberg et al, 2021). We used root collar diameter instead of dbh because most of the trees in the first 2 years were too small (<1.3 m).…”

Response of Poplar Leaf Transcriptome to Changed Management and Environmental Conditions in Pure and Mixed with Black Locust Stands

“…Mixed stands of poplar and black locust have already been tested in several recent studies [22,[24][25][26][27][28][29][30][31]. Black cottonwood (Populus trichocarpa Torr.…”