Reactions to gap emergence: Norway spruce increases growth while European beech features horizontal space occupation – evidence by repeated 3D TLS measurements

Abstract

Highlights• Analysis of the closure dynamics of a Norway spruce, a European beech and a mixed forest gap by repeated TLS measurements.• Norway spruce allocated additional resources predominantly into DBH growth and displayed stronger resilience against mechanical crown damage.• European beech allocated resources towards space occupation and displayed higher crown plasticity.• Species mixture had no significant effect. AbstractThe reach of different tree species' crowns and the velocity of gap closure during the occupation of canopy gaps resulting from mortality and thinning during stand development determine species-specific competition and productivity within forest stands. However, classical dendrometric methods are rather inaccurate or even incapable of time-and cost-effectively measuring 3D tree structure, crown dynamics and space occupation non-destructively. Therefore, we applied terrestrial laser scanning (TLS) in order to measure the structural dynamics at tree and stand level from gap cutting in 2006 until 2012 in pure and mixed stands of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.). In conclusion, our results suggest that Norway spruce invests newly available above-ground resources primarily into DBH as well as biomass growth and indicate a stronger resilience against loss of crown mass induced by mechanical damage. European beech showed a vastly different reaction, investing gains from additional above-ground resources primarily into faster occupation of canopy space. Whether our sample trees were located in pure or mixed groups around the gaps had no significant impact on their behavior during the years after gap cutting.

Assessing transformation scenarios from pure Norway spruce to mixed uneven-aged forests in mountain areas

“…Moreover, in mixed mountain forests spruce and fir are typically higher than beech and can pre-empt the light due to their occupation of the upper canopy layer (Pretzsch et al 2015). On the other hand, the high morphological plasticity enables beech to more quickly occupy the empty space in case of disturbances (Bayer and Pretzsch 2017).…”

Application of Terrestrial Laser Scanner to Evaluate the Influence of Root Collar Geometry on Stump Height after Mechanized Forest Operations

“…Initially developed to address issues in the industrial building sector, the use of TLS in forestry settings is increasing in frequency. TLS data have already been used to estimate forest structures such as sub-canopy architecture [6], leaf area index [7][8][9], tree height, diameter and diameter at breast height [10][11][12][13][14][15], and specific tree properties, such as stem volume [14] and crown characteristics [16][17][18][19]. Regarding stump measurements, TLS was used to assess above-ground stump biomass and the associated indirect emission of bioenergy [20].…”