Clustered root distribution in mature stands of Fagus sylvatica and Picea abies

Abstract

Distribution of small roots (diameter between 2 mm and 5 mm) was studied in 19 pits with a total of 72 m(2) trench profile walls in pure stands of Fagus sylvatica and Picea abies. Root positions within the walls were marked and transformed into x-coordinates and y-coordinates. In a GIS-based evaluation, zones of potential influence around each root were calculated. The total potential influence produced isoline maps of relative root influence zones, thus indicating small root clustering. The questions studied were (1) whether there were marked clusters of small roots in the soil and (2) whether trees surrounding the pit (defined as tree density) correlate with the root abundance and distribution on the trench profile walls. Small roots of both species showed maximum abundance in the top 20 cm of the soil, where pronounced root clusters occurred next to areas with only low root accumulation. The area of root clusters did not differ significantly between the two stands. Weighted clumping, WC, calculated as a product of root class, and its area was used as an index of root clustering, which again did not differ between beech and spruce stands. However, evaluations on a single root level showed that beech achieved the same degree of clustering with lower number of roots. Regardless of soil properties related to root clusters, a significantly higher clustering acquired per root for beech than for spruce suggests beech to be more efficient in belowground acquisition of space. Because none of the parameters describing root clustering were correlated with tree density around the investigated soil profiles, clusters of small roots are inherently present within the tree stands.

Analysis of Spatial Point Patterns in Microscopic and Macroscopic Biological Image Data

“…The results show for spruces a stronger clustering in a smaller range of attraction ( R spruce = 4.9 cm), while the clustering is weaker for beeches, but the range of attraction ( R beech = 7.4 cm) seems to be slightly larger. This finding is in accordance with another investigation ( [42]) calculating influence areas for each root. Their results indicated that the root system of spruce requires more roots to achieve a similar degree of space acquisition and thus beech exploits patchily distributed soil resources at lower root numbers.…”

“…The previous GIS-based investigation of root distribution ( [42]) was not able to quantify the differences of clustering between the two species so precisely as the applied modelling by point processes. Finally a non-homogeneous Matern-cluster model has been constructed by a retransformation of the homogeneous model, thereby reflecting the observed depth distribution of the tree roots.…”

“…Thus, clusters of small roots reflect the presence of nutrient patches or zones of better water availability ( [19], [34], [39]). As the number of small roots and their clustering was independent of the distance to the surrounding trees and of their diameter ( [42]), the root clusters are suggested as an inherent property of below-ground space acquisition.…”

“…In summary there is a combination of two effects, the depth distribution already described in [41] and the cluster effects analyzed in the present paper. Structural differences between spruce and beech indicated in [42] have been mathematically described. Stronger clustering in the case of spruce than in the case of beech can be seen also regarding the characteristics mentioned above as well as by a comparison of the estimated parameters for the homogeneous model λ t spruce = 0.00774 vs. λ t beech = 0.00253, keeping in mind that the estimated parent intensities are almost equal ( λ p spruce = 0.00690 vs.…”

“…While the point patterns regarded in the first application are three dimensional, the second application reveals planar point patterns having a vertically inhomogeneous structure. For a more extensive description of the studied cases, the reader is referred to [4], [5], and [16], [41], [42], respectively.…”