Post-Fire Changes in Canopy Solute Leaching in Pinus densiflora Forests

Round 1

Reviewer 1 Report

The manuscript "Post-fire Changes in the Throughfall Quantity and Chemistry in Pinus densiflora Forests" evaluates the difference in throughfall deposition of TOC and Ca from burned and partially burned Pinus densiflora forests. The manuscript is clearly written and I think covers a bit of what is an important topic, but I came into it hoping for a little more description of how the results relate to baseline conditions to put them in better context. I think part of my problem here is that when I read the title, I think of throughfall of being molecules in the atmosphere that settle on canopy surfaces and then are washed to the forest floor with precipitation. As the authors say in their hypothesis/research statement, they mean to “examine the differences in solute concentrations leached according to crown damage”, and thus, I believe that should be reflected in the title to something like “Relative intensity of wildfire damage leads to changes in canopy solute-leaching in Pinus densiflora Forests”.

My biggest concern is that the study is missing both of two potential controls to put the measurements into context. One would be the rainwater capture and throughfall nutrient content under a fully canopy and the other is what nutrient content is in bulk samples outside of the canopy. From my perspective this would improve the paper in being clear how much has changed in what is getting to the forest floor. To me this reads more like a comparison about how residual Ca and TOC are leached off of differently burned materials. I understand that the intent of the study was to measure throughfall in a specific area that was similarly impacted by deposition/precipitation, and that adding a separate control of unburned forest would have added additional precipitation measurements, but as the world is experiencing more large scale wildfires, it would be valuable to know how throughfall measurements of precipitation and nutrients are changing in these areas. Thus, if the data is available even from within the forest, I think at minimum it would be worth including data on what the rainfall capture rate is and report it when comparing throughfall rates on lines 236-243.

Speaking of that section, I think it would be best moved somewhere near 324-335. It seems out of place in the early results as you are explaining them as if it was the discussion, where as everywhere else you are describing the results first and then describe the why later.

My recommendation is that the methods in section 2.2 be written a little bit clearer about how often the water was collected. I can’t tell if you collected each sample and measured throughfall after an event, or just measured from the bulk sample at periodic intervals.

Another recommendation is that within the results you should make a statement about the difference or similarity in values between the 1m and 2m distanced samplers. I think there is significance in your results being the same at the trunk as it is farther into the canopy, especially if they are similar with different canopy cover; which I would assume would be higher closer in to the partially burned trees.

I recommend that you remove Figure 4. I think that the relationship could be communicated with a combination of referencing Figure 5 and citing the regression &/or r^2 value in the text. If you choose to keep it, make the axes the same.

I lastly recommend making the x-axes on figure 6 & 7 to scale. For 6, I think it would be good to have a reference for the time between measurements. I also think there could be some value of having a bar graph for the amount of precipitation at each rainfall collection date that would link it better with Figure 7. The precipitation data would also make it easier to understand what the concentrations mean in terms of total TOC/Ca in each sample.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

The authors collected throughfall at two forest sites damaged by fire over a relatively short period of time (less than a year) and measured the amount and the chemical property of the throughfall, with rainfall collected at a nearby open area as the control group. In terms of throughfall volume, the authors found that the throughfall to gross rainfall ratio increases (in a insignificant manner) as the severity of vegetation damage increases. For total organic carbon (TOC) and calcium concentration, the authors found that both TOC and calcium concentration in the throughfall decreases over time and cumulative rainfall, and more severe vegetation damage results in higher TOC but lower calcium concentration.

Major comments:

1. On vegetation damage's effect on throughfall volume: the author showed that the throughfall to gross rainfall ratio increased as vegetation damage severity increased in Table 2, but such a change is not significant as shown in in Figure 4. However, the author concluded that there is an increase in the throughfall ratio with increased severity of vegetation damage at the end of the manuscript. This conclusion is not well supported by the results shown by the authors, especially the significance of the increase. The lack of significance should be noted in the conclusion.

2. The unburned control was missing in method and result sections but referred to in the conclusion section. The author wrote that "The maximum throughfall rate was attained in the following increasing order: unburned, foliage necrosis, and crown fuel consumption areas. " in the conclusion section. However, the unburned control was not shown in the method or result section. I understand that an unburned control with similar meteorological conditions may be difficult to find after the fire, so I assume that the unburned control may come from previous studies, but the data that supports the statement in the conclusion section should be included in the result section.

3. The TOC and calcium concentration of gross rainfall is not shown. According to the methods described by the authors, both the throughfall and the rainfall samples were collected and their chemical property analyzed. However, the baseline TOC and calcium concentration of the rainfall is not presented in the result section. The authors mentioned that a large amount of organic carbon can be released into the atmosphere after a wildfire and a significant proportion of them are water-soluble. The baseline TOC of the rainfall may help to evaluate the effect of these air-borne organic carbon on the TOC concentration of throughfall, partitioning the contribution between canopy leaching and air-adsorption of organic carbon, and consequently may help address the issue mentioned by the authors in line 305-307.

4. There is a seemingly conflicting statement in line 283: "However, there was no significant difference in dissolved calcium concentration with crown damage (p=0.2874; Figure 6)." while the authors just showed that "The average calcium concentration at the FN site was 54% lower than that at the CC site for all rainfall events (p<0.001)" in previously lines. It would be very helpful to readers to clarify the comparisons made here.

Minor

Line 209: the line reads "at the three sites" but only two sites were described in the table and the experimental design.

Line 228:  In Table 1, it does not make intuitive sense to me that the major axis is shorter than the minor axis. It would be helpful for readers to briefly describe how these axes are defined in the method section. 

Line 247: In Figure 4, is it possible to use square-root- or log-transformation to avoid clumping of data points near the lower half of the plot? 

Line 292,316: It would be helpful to add "cumulative" to the X-axis label of Figure 7 and 8 to clarify that it represents the cumulative rainfall instead of the rainfall in a single precipitation event (as in Figure 5).

Line 376: I fully agree that calcium is not a volatile element in natural environments but it does not make sense to me to use the boiling point of the calcium metal to support this claim, as we rarely see calcium element presents as metal in natural environments. I think a general statement here should suffice. 

Author Response

Please see the attachment

Author Response File: Author Response.docx