The manuscript compared temporal variation of LAI, as measured from the semi-direct benchmark littertrap method, with DHP, using different clumping corrections. The relative novelty of the study is to use temporal series, which allows to investigate how the accuracy between methods varied with canopy development (and thus LAI density). 

The study focused on beech forests, which are very dense, and where the recent LXG method can correct more for clumping index, compared with other approaches. The result agrees with previous finding indicating that LXG is more suited for nearly non-transparent crowns.

The main issues in my view are about

1) data collection. Fisheye photos are strongly influenced by sky condition and camera exposure. The authors collected data in direct sky conditions and likely automatic exposure. Both options greatly influence gap fraction retrieval, with generally increase the underestimation of LAI from DHP. This is apparent in the sample images in Fig2-Fig3 where the sky is likely saturating (clipping) and this can largely overestimate gap fraction (and thus underestimate LAI). Additionally, gamma correction is another factor required to provide linear relationship between image brightness and radiance.

There is a wide range of literature confirming this, and therefore the accuracy of the method can be biased compared to litter traps. This should be acknowledged and authors could try to find some solution to this issue. For example, if they collected RAW imagery, they can try to analyse raw images using the bRaw R package, https://www.biorxiv.org/content/10.1101/2022.10.25.513518v1, which resemble a method by Macfarlane et al. 2014, to linearly scale 12 to 8 bit raw blue imagery to reduce DHP sensitivity to camera exposure. 

2) The DHP invert LAI without requiring information on extinction coefficient by integrating multiple gap fraction (GF) measurements over the full zenith range, as the integral of G(theta) is 0.5 over 0-90°, as per the Miller 1967 theorem. By reducing the zenith angle view, the LAI inversion is not straightforward. Therefore, the higher correlation with LT at smaller VZA is in my view the results of higher clumping correction, as the inner rings could have more variability, which reduced the underestimation of DHP. Authors should de-structure their LAI component obtained from DHP, namely explore the variation in GF, CI  and G(theta) (here using LAI from LT) across VZA,  to explore how these three attributes varied with VZA. This would  shed some light on the different performance of canopy units like GF, G and CI to the resulting LAI estimation from DHP.

Specific comments:

Direct, semi-direct vs indirect methods

LT is typically considered a semi-direct method (Bréda 2003), in that the leaf area is directly measured, as for the allometry methods. No “fully” direct methods exist in forestry. Basically, the distinction is between those based on direct measurement, or contact-approaches (Jonckheere et al. 2004) and those based on optical theory. With “Indirect methods “ the literature consider all the methods based on optical theory, and particularly the Beer-Lambert law. Indirect methods in the field are based on both passive and active sensors. 

Importantly, authors should explain the difference between transmittance based and gap fraction based methods. The former requires measuring above and below (absolute or relative) light, and then calculate light transmittance accordingly. This comprises PAR ceptometers . Gap fraction based methods include LAI-2000, which estimate gap as the ratio of above to below canopy relative radiation, and DHP, which calculate gap fraction as the ratio of classified pixels gaps over total image pixels. With some assumption (e.g., leaves are homogeneous turbid medium) gap fraction and light transmittance equals, and then the Beer Lambert law is used on all these methods.

Finally, I would add in the intro the well-established Beer-law formula and explain differences between effective to true LAI in optical measurements. This will help introducing the importance of clumping index, its multi-scale spatial nature, and why different methods provide different clumping corrections, and finally, why effective LAI is the first step to know the true LAI, also compared with those from direct methods (which by definition ignore clumping)

L33 the litter traps is also labor intensive cause the litter should be separated, and the leaf component dried in forced-air stove, to determine the dry mass, which is combined with SLA.

L 60 here an example of continuous DHP measurements https://www.sciencedirect.com/science/article/pii/S0168192320300460 

L90. Timestemp/timestep -> sampling period

L90-120 From the best I can understand this approach foresee the indirect (i.e. scanning) measurements of all leaves in the traps. It is noticeably more time consuming than measuring a sample of leaves to determine SLA and then multiply with the total biomass. Authors should acknowledge this. Additionally, it is the very first time I see a litter trap laying at the floor - these baskets are typically set at 1 m height to reduce seed predation - how these traps be impacted by fauna, which can influence the leaf litter inside?

Lotz and others explore different methods of using canopy photography to estimate leaf area index measured using litter traps. The analysis was well-cited and carefully carried out,but should be improved in a number of ways.

Check wording and usage throughout the manuscript. One example is the verb in ' Uncertainties for individual litter traps attributed to varying site conditions, such as tree stem density or canopy coverage.’ Honestly some of the text reads like it was written or checked by a LLM including 'As leaves constitute the active surfaces for these mass and energy exchanges, the leaf area index (LAI) emerges as a fundamental biophysical parameter - quantifying canopy structural

complexity through its definition as half of the total intercepting area per unit ground surface area’. An additional careful round of editing would be beneficial.

On line 31 there are more fundamental references for litter traps. Somewhat disagree that litter traps can’t be used for evergreen species, one just has to correct for leaf geometry.

40: corrections for clumping can be applied although I guess this is still correct in that the fundamental equation is for a homogeneous medium

From figure 1d a bit surprised that the litter traps weren’t suspended above the ground to help dry material and prevent decay

Font sizes in Figure 2 are very small. It’s not entirely clear to me what LAI difference means as described.

Equation 1: don’t use the star for multiplication in formal mathematical equations. Use the multiplication symbol.

Figure 4: I question if this color scheme is adequate for people with red-green colorblindness. Different colors should be chosen.

As noted in other reviews, avoiding sunny conditions is key to not wash out canopy photos. What steps were taken to ensure consistent sky conditions either near dusk or with uniform cloudiness?