Neighbourhood and stand structure affect stemflow generation in a heterogeneous deciduous temperate forest

Abstract

Abstract. Although stemflow oftentimes only represents a small portion of net precipitation in forests, it creates hot spots of water input that can affect subsurface storm-flow dynamics. The distribution of stemflow over different trees is assumed to be temporally stable, yet often unknown. Therefore, it is essential to know the systematic factors driving stemflow patterns. Several drivers have been identified in the past, mainly related to tree traits. However, less attention has been paid to tree neighbourhood interactions impacting stemflow generation and creating stand patches with enhanced or reduced stemflow. We recorded stemflow during 26 precipitation events on 65 trees, growing in 11 subplots (100 m2 each), in a temperate mixed beech forest in the Hainich National Park, Germany. We used linear mixed effects models to investigate how traits of individual trees (tree size, tree species, number of neighbouring trees, their basal area and their relative height) affect stemflow and how stemflow is affected by stand properties (stand, biomass and diversity metrics). As expected, stemflow increased with event and tree size. Stemflow was highly variable at both the tree and subplot scale. Especially in large rainfall events (>10 mm), the tree/subplot ranking was almost identical between events, probably due to fully developed flow paths bringing out the full stemflow potential of each tree. Neighbourhood and stand structure were increasingly important with event size (15 % of fixed effects on the tree scale and ca. 65 % on the subplot scale for large events). Subplot-scale stemflow was especially enhanced by a higher proportion of woody surface, expressed by a high number of trees, low leaf area and a large maximum tree size. The Simpson diversity index contributed positively to stemflow yield for large events, probably by allowing more efficient space occupation. Furthermore, our models suggest that the neighbourhood impacts individual tree morphology, which may additionally increase stemflow in dense, species diverse neighbourhoods. Unexpectedly, rain shading within the canopy had little impact on the stemflow spatial variation. Overall, we find a strong cross-scale temporal stability. Tree size and tree density were the main drivers, independently increasing stemflow, creating forest patches with strongly enhanced or reduced stemflow. Our results show that, besides tree metrics, forest structure and tree diversity also affect stemflow patterns and the potentially associated biogeochemical hot spots.

Exploring the stemflow dynamics and driving factors at both inter‐ and intra‐event scales in a typical subtropical deciduous forest

“…Some studies have suggested there is a threshold of rainfall amounts before initiating stemflow (Levia & Frost, 2003;Metzger et al, 2019;. In our study, Q. acutissima did not produce any stemflow in four rainfall events (G P < 4.4 mm), even though B. papyrifera generated stemflow in all events (n = 9) of rainfall type D. This result indicated stemflow from Q. acutissima trees had a higher threshold of rainfall amounts than B. papyrifera trees.…”

“…In addition, because stemflow has the ability to transport nutrients, "fertile islands" may form around tree boles (Imamura et al, 2017;Loffredo et al, 2014), which would affect the growth and distributions of understory vegetation (Andersson, 1991;Falkengren-Grerup, 1989). Therefore, it is important to investigate stemflow dynamics to gain a better understanding the hydrological and biogeochemical processes in forest ecosystems (Metzger et al, 2019).…”

“…Stemflow generation is determined by various meteorological factors, including rainfall amount, duration and intensity, vapour pressure deficit, wind condition (Cayuela et al, 2018;Metzger et al, 2019;Tanaka et al, 2017;Zhang et al, 2015). At the inter-event scale, studies have indicated that higher rainfall amount and longer rainfall duration can result in larger amount of stemflow (Tanaka et al, 2017;Van Stan et al, 2014), whereas increased vapour pressure deficit can reduce the contribution of rainfall to stemflow (Staelens et al, 2008).…”

“…For instance, tree species with smooth bark tend to produce more stemflow than tree species with rough and rugose bark (Certini et al, 1998;Su et al, 2016), and smaller trees would have higher stemflow funnelling ratios (González-Martínez et al, 2017;Siegert & Levia, 2014). In addition, neighbourhood properties (e.g., species composition, tree size heterogeneity) may affect tree traits related to stemflow (Metzger et al, 2019), and soil properties can affect stemflow by influencing tree morphology (Corti et al, 2019). Stemflow ratios and funnelling ratios have been documented to vary widely in relation to these aforementioned factors (Pryet et al, 2012;Xu et al, 2005;Zhang, Levia, et al, 2020), which presents a challenge to understand the causes of stemflow dynamics for different tree species under different meteorological conditions.…”

How Is Bark Absorbability and Wettability Related to Stemflow Yield? Observations From Isolated Trees in the Brazilian Cerrado

“…Secondly, the structure of canopies can influence how effectively individual trees drain this capture rainfall, and currently it is hypothesized that there may be an optimum branch inclination angle that most efficiently drains rainwater to the stem (Levia, 2003;Sadeghi et al, 2020). Third, the orientation of canopies within the "tree neighborhood" is believed to impact stemflow generation -some dominant canopies overshadow others (Metzger et al, 2019) or gather wind-driven rainfall (Herwitz and Slye, 1995;Levia and Herwitz, 2005;Van Stan et al, 2011). Finally, bark structure, being the surface over which stemflow must flow, is considered a master variable.…”