Wildre Alters the Linkage Between Total and Available Soil C:N:P Ratios and the Stoichiometric Effects on Fine Root Growth in a Chinese Boreal Larch Forest

Background and aims Wildre is a primary driver of ecosystem functioning, and the re-induced changes in the cycling and balance of multiple nutrients may inuence the response of plant growth to burning. However, the relationships between total and available soil stoichiometry and stoichiometric effects on the growth of ne roots following re in forests remain unclear. Methods We measured the total and available soil C, N and P concentrations, their ratios and ne root biomass (FRB) at an unburned control, 1-year-postre and 11-year-postre sites in a Chinese boreal larch forest. The relationships between soil stoichiometry and FRB were analyzed. study suggest that available pools of soil C, N and P are more responsive to wildre than total pools, and soil C:N:P stoichiometry is more sensitive to wildre than individual elements in the boreal larch forest of the Great Xing’an Mountains. Additionally, wildres can exert a relatively long-term effect on soil stoichiometry. Our results also suggest that wildres strengthen the linkage between total and available soil C:N:P stoichiometry, as well as between FRB and soil C:N:P stoichiometry. Meanwhile, we found that ne root was by before this this effect little following re, suggesting that wildre could alleviate limitation by These ndings indicate that wildres can profoundly disrupt or even decouple the biogeochemical cycling of C, N and P in the soil and produce a more complex soil-plant interaction in the postre early succession stage of boreal larch forest. Future studies on the relationships between postre soil stoichiometry and forest ecosystem structure and function are needed to improve the understanding of the soil-plant interaction in response to wildre in boreal forest ecosystems.


Introduction
Wild re is a dominant natural disturbance in boreal forests, annually burning 1 % of the boreal forest area (Stocks et al. 1998) and in uencing the elemental cycling and balance within the forest ecosystems Compared to the effects of wild re on individual element C, N, and P cycling in the soil, its effect on their stoichiometric relationship, may be just as important as the changes in the absolute contents of C, N and P because soil C:N:P stoichiometry can in uence central ecosystem functioning such as optimal plant growth and biogeochemical processes (Creamer et al. 2014; Ren et al. 2016; Sophie et al. 2015).
The few prior studies have reported that total soil C:N:P stoichiometry increased following re and then decreased with post re stand age in a boreal forest (Hume et al. 2016) and that recent burning decreased soil labile C:P and N:P ratios (Butler et al. 2017), but increased total soil C:P and N:P ratios in tropical forest ecosystems (Butler et al. 2020). These studies, however, usually focused on the concentrations and stoichiometry of plant-available and total pools of element C, N and P and failed to investigate the wild re effects on the linkage between total and available soil nutrient pools even though their interactions greatly affect biogeochemical cycling (Baret et al. 2015;Cavard et al. 2019). For instance, the increased available soil N and P concentrations can stimulate microbial activity and subsequent mineralization of soil organic matter (Caldwell et al.), and thus affect the total soil C:N:P stoichiometry (Shen et al. 2018). A recent research showed that mineralization of SOM increased with available soil C:N and C:P ratios because available soil stoichiometry could shift microbial community composition by increasing organic matter mineralization to maintain the microbial stoichiometric homeostasis (Wei et al. 2020). Likewise, total soil C:N:P stoichiometry can regulate soil C, N, and P biogeochemical processes through directly affecting the genetic resistance of microbial groups which involved in C, N, and P cycling , and thus likely affect the supply of available soil N and P. Therefore, to fully appreciate the effects of wild re on biogeochemical processes, it is also vital to consider the relationships between total and available soil stoichiometry, which may provide new insight into re-induced ecological consequences.
Furthermore, re-induced stoichiometric shifts in the balance of element C, N, and P in soils have the potential to in uence soil biotic processes (Butler et al. 2019;Toberman et al. 2014), plant nutritional status and forest productivity. Some studies have reported that prescribed-re could alter foliar N and P concentrations and N:P ratio through its effects on the amounts and balance of available soil nutrients in subtropical atwoods (Schafer and Mack 2014) and tropical forest ecosystems (Butler et al. 2016). In contrast, the meta-analysis study showed that re effects on plant N:P ratio were not related to the changes in available soil nutrients (Dijkstra and Adams 2015). However, these studies generally concentrated on the effects of soil nutrients status on aboveground plant tissues (i.e., leaf) and neglected the effects on belowground roots, particularly ne roots. In fact, ne roots (i.e., roots < 2 mm in diameter) are very important for C ow and biogeochemical cycling of terrestrial ecosystem (Matamala et al. 2003;Yuan and Chen 2010). For instance, ne roots are the primary organ for plants to absorb water and nutrients from the soil and serve as a major channel of C below ground (Kyaschenko et al. 2019). Fine root mortality and decomposition can release large nutrients to the soil due to fast turnover rates (Gill and Jackson 2000). Previous studies have shown that the amount of C and nutrients cycling to the soil from ne roots may equal or exceed those from above-ground litter (Norby, Fitter & Jackson 2000) although ne root biomass contributes only a small part of total forest biomass (Vogt et al. 1996). However, despite the close linkage between ne roots and soil environments, the response of ne root growth to re-induced stoichiometric shifts in soils remains unclear. Hence, a better understanding of how re-induced stoichiometric shifts in soil in uence ne root growth could help us fully unravel the re's ecological effects.
In this study, we examined the wild re effects on total and available soil C, N, and P concentrations and stoichiometry among three study sites (control, 1-year-post re, and 11-year-post re) in the Great Xing'an Mountains in China and determined the re-induced changes in soil stoichiometry on ne root biomass (FRB). The Great Xing'an Mountains are at the extreme southern boundary of the Eurasian boreal forests, and more than 70 % of the forested area is occupied by Dahurian larch (Larix gmelinii Rupr.) (Xu 1998). Wild re is the primary natural disturbance in these forests, and regulates the ecosystem structure and function (Cai et al. 2013 information about the relationships between total and available soil stoichiometry and stoichiometric effects on the growth of ne roots following re are unclear. Specially, we will focus on: (1) the dynamics of available and total soil C, N and P concentrations and their stoichiometry change along a temporal gradient of re history; (2) the relationships between total and available soil C:N:P stoichiometry; and (3) the response of ne root growth to the re-induced changes in soil C:N:P stoichiometry and nutrient supply. We expected that wild re would decrease soil C:N:P ratios due to more loss of C to the atmosphere and more release of N and P to the soil through burning fuels. Moreover, we also expected that the relationships between total and available soil C:N:P stoichiometry would be more closer due to the re-driven recycling of soil C, N and P and then would become weaker over time. Finally, given wild re would shift soil C:N:P stoichiometry, we expected that the ne root growth would be more responsive to the soil C:N:P stoichiometry compared to the individual changes in soil nutrient element immediately after the re.
The area has a terrestrial monsoon climate with a long and severe winter. The mean annual temperature is -4. To examine the post re changes in soil nutrient status and the effects of such changes on ne root growth along a temporal re history gradient, we selected sample plots based on re history. This study had one unburned control and two re history levels (i.e., 1-year-post re and 11-year-post re). An adjacent unburned area with similar pre-re vegetation, topography and soil properties as those of the two burned areas was selected as a control (Table 1). Unburned area is a mature larch forest without being affected by wild res in nearly 80 years according to records of the management committee of Huzhong National Natural Reserve. We collected a total of 60 soil samples (  Soil nutrient supply and ne root sampling The soil nutrient supply was measured using the Plant Root Simulator probes (PRS®, Western Ag Innovations, Saskatoon, SK, Canada) via in situ incubation. The PRS® probes can absorb ions from soil like plant uptake for nutrients. As a convenient and economical soil analysis tool, the PRS® technology has been widely applied in agronomic, forestry, and ecological research. Each pair of the probes consists of cation and anion exchange resin membranes, which concurrently adsorb cations (e.g., NH 4 + ) and anions (e.g., NO 3 − , PO 4 3− ). The cation probes are saturated with Na + and the anion probes are saturated with HCO 3 − . Values are µg element 10-cm − 2 per 15-cm depth.
In each plot, we randomly selected two of ve soil sampling points as in situ measurement locations ( Fig. 1). At each in situ location, we buried a sharpened open PVC (polyvinyl chloride plastic) tube (10-cm diameter, 20-cm long) into the soil (20-cm depth) as an external root exclusion cylinder (Fig. 1). Then, we vertically inserted one pair of PRS® probes in each PVC tube. The 60 pairs of probes were kept for three weeks in situ locations during the growing season. Then, all probes were removed, washed immediately with distilled water, and placed in zipseal plastic bags. Lastly, all probes were shipped to Western Ag Innovations, Saskatoon, SK, Canada on ice for analysis; the two pairs of probes from the same plot were pooled for elution and analysis.
Fine roots were sampled using the soil-coring method (inside diameter 10-cm PVC tube). In this study, the probe pair and soil core were incubated together in the same PVC tube. After the incubation, one pair of probes was removed, then the PVC tubes were pulled out by carefully digging the soil and nally root sample was collected from each tube. The ne root samples from the same plot were mixed as one sample. On the same day, we carefully washed the roots in the water to eliminate the adherent soil. The living ne roots (< 2 mm in diameter) were separated by hand from the samples and the dead roots were discarded. The sorting of dead and living roots was based on root color, where living roots are white and dead roots are dark (Brassard et al. 2011). Then, the root samples were oven-dried at 70°C for 48 h and weighed them.

Lab methods
The soil samples were screened over a 2-mm sieve and then divided into two parts: one part was stored at 4°C for the extractable N and soil dissolved organic carbon (DOC) analysis; the other was air-dried and then nely ground for the analysis of total soil carbon (TC), phosphorus (TP), nitrogen (TN) and available phosphorus (AP). Soil TP was determined using the perchloric/sulfuric acid digestion method and the Mo-Sb anti-spectrophotography method (Lu, 2000

Calculations and statistical analysis
On a mass basis, we calculated total soil C:N:P ratios using TC, TN and TP concentrations, as well as got available soil C:N:P ratios using DOC, AN and AP concentrations. We checked the data for normality and homogeneity of variance. One-way ANOVA was used to determine how wild re affected the soil C, N and P concentrations and their stoichiometry, and ne root biomass (FRB). A Games-Howell post hoc test was used to identify differences in the soil C, N and P concentrations, C:N:P ratios and FRB among the control, 1-year-post re and 11-year-post re sites. Spearman rank-order correlation analysis was used to identify the correlations between total and available soil C, N and P concentrations. The relationships between total and available soil C:N:P stoichiometry, and between FRB and soil C:N:P stoichiometry and the supplies of soil N and P for each study site were re ected through simple linear regression analysis. In this study, all statistical analyses were conducted with the R statistical package (version 3.2.4; R Core Team 2016), and the signi cance level was α < 0.05.

Results
The effects of wild re on soil C, N, and P concentrations and their stoichiometric ratios Wild re had different effects on the soil C, N and P concentrations ( Table 2). Compared to the control, wild res showed little effects on the soil TC and TN concentrations at either the 1-year-post re or the 11year-post re sites. Soil TP concentration was 82 % and 50% higher than the control at the 1-year-post re and 11-year-post re sites, respectively. Soil DOC concentration was 34 % and 22 % lower than the control at the 1-year-post re and 11-year-post re sites, respectively. However, wild re signi cantly increased soil AN and AP concentrations by 59 % and 26 %, respectively, at the 1-year-post re site, and these two indicators recovered to the control levels at the 11-year-post re site. Table 2 Total and available soil C, N, and P concentrations, and their ratios at the control (n = 12 plots), 1-yearpost-re (1-YPF, n = 24 plots), and 11-year-post-re (11-YPF, n = 24 plots) sites. Wild re had numerous signi cant effects on the soil C:N:P stoichiometry at the two burned sites relative to the control (Table 2). At the 1-year-post re site, wild re greatly reduced the total soil C:N, N:P and C:P ratios, by 14 %, 57 % and 49 %, respectively. Eleven years post re, total soil C:N ratio recovered to pre-re control level. In addition, total soil N:P and C:P ratios increased over time, but were still signi cantly lower at the 11-year-post re site than those at the control site. Similarly, at the 1-year-post re site, available soil C:N and C:P ratios were 60 % and 50 % lower than the control, respectively. At the 11-year-post re site, available soil C:N ratio was still signi cantly lower than the control, whereas available soil C:P ratio recovered to the control level. Additionally, wild re showed little effect on the available soil N:P ratio at the two burned sites.
Relationships between total and available soil C:N:P stoichiometry Wild re signi cantly affected the correlations between available and total soil nutrient pools (Fig. 2). The soil TC and TN concentrations were signi cantly correlated positively between each other at the two burned and control sites. Soil TC was correlated negatively with DOC concentration at the control site, and positively related to AN concentration at the 11-year-post re site. There was no signi cant correlations between soil TC and TP and DOC concentrations at the control and 1-year-post re site.
Comparatively, soil TN concentration was not related to available and total soil C and P concentrations at the two burned and control sites, but positively correlated with soil AN concentration only at the 11-yearpost re site. Soil TP concentration was strongly correlated with soil AP and DOC concentrations at the 1year-post re site, but was not correlated with other soil indicators at the control and 11-year-post re sites. Soil AP concentration was signi cantly correlated negatively with soil DOC concentration at the control site.
Wild re greatly altered the relationships between total and available soil C:N:P ratios (Fig. 3). At the control site, total soil C:N ratio was marginally correlated negatively with the available soil C:N ratio (n = 12, R 2 = 0.317, p = 0.056; Fig. 3A) and signi cantly correlated positively with the available C:N ratio at the 1-year-post re (Fig. 3D) and 11-year-post re sites (Fig. 3G). Total soil C:P ratio was not correlated with the available soil C:P ratio at the control site (Fig. 3B), but signi cantly correlated positively with the available soil C:P ratio at the 1-year-post re site (Fig. 3E). Eleven years post re, the relationships between total and available soil C:P ratios recovered to the control levels (Fig. 3H). Similarly, the correlations between total and available soil N:P ratios were not signi cant at the control site (Fig. 3C), but signi cantly positive at the 1-year-post re site (Fig. 3F). However, there was no signi cant correlations between total and available soil N:P ratios at the 11-year-post re site (Fig. 3I).
Response of ne root biomass to the re-induced changes in soil nutrient supply and C:N:P stoichiometry Wild re greatly affected the soil nutrient supply (Fig. 4). At the 1-year-post re site, soil N and P supplies were 210 % and 157 % higher than the control, respectively. Then, soil N and P supplies signi cantly declined to the control levels at the 11-year-post re site. Fine root biomass (FRB) at the 1-year-post re and 11-year-post re sites was 67 % and 58 % lower than the control, respectively (Fig. 5).
Wild re affected the relationships between ne root growth and soil nutrient status (Fig. 6, 7). At the control site, FRB was signi cantly correlated positively with soil N supply but not correlated with soil P supply (Fig. 6). In contrast, FRB was not correlated with soil N and P supplies at the two burned sites (Fig. 6). Fine root growth showed different responses to the soil C:N:P stoichiometry at the control and burned sites (Fig. 7). At the control site, FRB was strongly correlated positively with the total soil C:N ratios (Fig. 7A), but not related to the total soil C:P and N:P ratios, and available C:N:P stoichiometry. At the 1-year-post re site, FRB was signi cantly correlated positively with the total soil C:N:P stoichiometry, available C:N and C:P ratios (Fig. 7A-E). However, there were no signi cant correlations between FRB and available N:P ratio (Fig. 7F). At the 11-year-post re site, FRB was signi cantly correlated negatively with the total soil C:N ratio (Fig. 7A). Comparatively, there were no signi cant correlations between FRB, total soil C:P and N:P ratios, and available C:N:P stoichiometry (Fig. 7B-F). Totally, the correlations between ne root growth and soil C:N:P stoichiometry were stronger at the 1-year-post re site than those at the 11year-post re and control sites.

Discussion
The effects of wild re on soil C, N, and P concentrations and their stoichiometric ratios In this study, total soil C and N concentrations were not signi cantly different at the control and two burned sites (Table 2) Wirth et al. 2002). However, soil TC loss was higher than soil TN loss immediately after the re (Table 2), because a large portion of soil organic N survives following low intensity re (Certini 2005). Thus such more decrease in soil TC than TN immediately following the re resulted in the signi cant reduction in total soil C:N ratio ( Table 2). Then total soil C:N ratio increased to the pre-re level with time since re due to inputs of C and N from the return of understory vegetation (e.g., herbaceous annual plants), litterfall and vegetation root turnover from the regenerating stands (Alexander et al. 2018;De Long et al. 2016;Yuan and Chen 2013), and biological xation (Harden et al. 2003). However, in a boreal Jack pine forest of central Canada, Hume et al. (2016) reported that post re total soil C:N ratio in the mineral layer exerted no signi cant changes with time since re but that in the forest oor increased with the stand age because substantial litter was accumulated on the forest oor and provided organic matter for the soil.
In contrast to little changes in soil TC and TN after re, soil TP concentration greatly increased at the 1year-post re site ( Table 2), suggesting that wild res promote the P cycling by burning vegetation and forest oor, as found by Schaller et al. (2015). This con rms that previous work showing the mature or old boreal forests may not be able to keep a positive P balance because P is derived mainly from the geochemical weathering of bedrock and over time becomes increasingly bound in more stable forms by calcite minerals (Buendía et al. 2014;Huang et al. 2017;Walker et al. 1983). Such non-proportional changes in total soil C, N and P resulted in signi cant reductions in the total soil C:P and N:P ratios immediately after re (Table 2). Over time, total soil C:P and N:P ratios signi cantly increased but still were lower in the 11-year-post re stand than the control, suggesting that long-term effects of wild re on the balance of soil C, N and P cycling. Similarly, Hume et al. (2016) reported that the 15-year-post re stand had lower total soil C:P and N:P ratios than the mature stands in the boreal forest of central Canada, and attributed the reductions to the increase in soil TP. In this study, soil TP concentration at the 11-year-post re site was signi cantly lower than that in the 1-year-post re site, suggesting substantial P losses at the burned area. Several studies considered that the post re P loss could be related to the surface runoff or erosion (Blake et al. 2010;Bodí et al. 2012) because most re-increased P accumulates in the surface soils (Certini 2005;Lagerström et al. 2009). Another possible explanation is that part of available P in soil could be utilized by regeneration plants and bound in plant tissues. These processes could be responsible for the P losses with time since re in this study. Our results indicate that wild re could not only greatly release P into the soil through burning plant biomass and forest oor but also lead to substantial P losses because the re-caused removal of most the forest oor may be vulnerable to runoff or erosion (Pereira et al. 2016). Therefore, post re engineering measures such as mulching forest residues may be needed to reduce and even stop soil erosion and ensure soil recovery (Fernández 2016).
Compared to the changes in total soil C, N, and P pools after re, wild res exerted greater effects on their available pools in the Great Xing'an Mountains, suggesting that available pools of soil C, N, and P were more responsive to wild re that total pools. In fact, re-produced ash with abundant available nutrients manly deposits on the surface soil and thus replenishs soil nutrients (Bodí et al. 2012). As a consequence, available soil N and P greatly increased immediately after re ( Table 2), but most C in biomass and litter could be volatized into atmosphere during burning except for pyrogenic carbon left on the surface soil (Kane et al. 2010). In this study, we found soil DOC in the 1-year-post re site was signi cantly lower than that at the control site. Such non-proportional changes in available soil C, N, and P concentrations resulted in great reductions in available soil C:N and C:P ratios, which may promote microbial growth and activities, and thus increase mineralization of SOM (Wei et al. 2020). However, the change in available soil N:P ratio in the 1-year-post re site was little relative to the control, which may be related to the concurrently substantial increases in AN and AP in the recently burned soils (Kong et al. 2018). This was not consistent with Butler et al. (2017) who found recent burned soils had signi cantly lower labile soil N:P ratio in Australian eucalypt forests. This discrepancy may be related to the differences in measurement method and ecosystem type. Butler et al. (2017) used water-hot-extractable C, N and P as labile soil pools of these elements, whereas soil AN and AP in our study were extracted by 2 M KCL and 0.1 M NaHCO 3 , respectively. Additionally, soils in Australian eucalypt forests are low-P and thus have high N:P ratios in unburned areas, while burning increased labile soil P and decreased labile N resulting in lower soil labile N:P ratios (Butler et al. 2017). Eleven years post re, available soil C:P ratio recovered to the pre re level, whereas available soil C:N ratio was still signi cantly lower than the control, suggesting that wild re would exert a relatively long-term effect on available soil stoichiometry. The changes in available soil C:P and C:N ratios may be attributed to the slow recovery rate of soil DOC and large declines in AN and AP (Table 2). We found soil AN and AP decreased to the pre re levels Eleven years post re, suggesting burned soils lost substantial N and P possibly because of leaching, erosion and plant uptake (Durán et al. 2008). Compared to the AN, AP losses was greater because biological xation can replenish some available N for soil (De Long et al. 2016;DeLuca et al. 2008). These results indicates that wild re could exert greater effects on available soil stoichiometry, which may produce profound effects mineralization of soil organic C (Shuman et al.) and plant growth.
Relationships between total and available soil C:N:P stoichiometry In the three re history site, the correlations between total and available soil C:N:P stoichiometry was the strongest at the 1-year-post re site (Fig. 5), consistent with our expectation that wild re could strengthen the relationship between available and total soil stoichiometry. This supports the idea that burning forest oor not only in uences balances of soil C, N and P, but also their biogeochemical cycling site, there were lower available soil C:N:P ratios, suggesting a su cient nutrient supply which could satisfy the microbial demand of optimum available C, N, and P ratios, and thus promote recovery of bacterial community (Wei et al. 2020). Our previous study in Great Xing'an Mountains has also shown that bacterial community structure could rapidly recover to the pre-re levels because burned soils had higher pH, AN and suitable moisture (Xiang et al. 2014), which may create bene cial conditions for SOC decomposition. And the bare surface soils at the 1-year-post re site had lower total C:N:P ratios, indicating SOC may be vulnerable to microbial decomposition (Sistla and Schimel 2012). These processes can be responsible for the closer link between available and total soil C:N:P stoichiometry. As far as we know, this is the rst study to show that the effects of wild re on the relationships between total and available soil stoichiometry in boreal forest ecosystems. The novelty is critical for our in-depth understanding consequences of wild re biogeochemical effects.
Responses of ne roots growth to soil N and P supply and C:N:P stoichiometry following re In this study, ne root biomass was signi cantly correlated positively with soil N supply at the control site but was not correlated with soil N and P supply at the two burned sites (Fig. 6). This was because a large amount of available N and P can be released into the soil through burning vegetation biomass and forest oor (Certini 2005). Another possible explanation was reduced plant uptake after re because we observed almost all vegetation was killed by burning and regenerated vegetation was small in the two burned sites. Thus, re fertilization effect can not only alleviate N limitation but also supply enough N and P for regeneration plant growth in the Great Xing'an Mountains. Dijkstra and Adams (2015) also found that re had the potential to enhance or alleviate the magnitude of N and P limitation in plants.
Despite no signi cant correlations between FRB and soil nutrient supply after re, FRB was signi cantly correlated positively with soil C:N:P stoichiometry at the recently burned site relative to the control and 11year-post re sites, suggesting that FRB was more responsive to the re-caused changes in soil resource stoichiometry than the increases in their absolute amounts. This supports the idea that soil C forest soils. Therefore, these processes may lead to a stronger association between ne root growth and soil stoichiometry immediately after re. Assuming that the interaction between ne roots and soil stoichiometry increases following re in boreal forests, additional research should focus on the post re relationships between the soil stoichiometry and ne root turnover and stoichiometry.

Conclusions
Our study suggest that available pools of soil C, N and P are more responsive to wild re than total pools, and soil C:N:P stoichiometry is more sensitive to wild re than individual elements in the boreal larch forest of the Great Xing'an Mountains. Additionally, wild res can exert a relatively long-term effect on soil stoichiometry. Our results also suggest that wild res strengthen the linkage between total and available soil C:N:P stoichiometry, as well as between FRB and soil C:N:P stoichiometry. Meanwhile, we found that ne root growth was controlled by soil N supply before re in this forest ecosystem, whereas this effect was little following re, suggesting that wild re could alleviate N limitation by burning fuels. These ndings indicate that wild res can profoundly disrupt or even decouple the biogeochemical cycling of C, N and P in the soil and produce a more complex soil-plant interaction in the post re early succession stage of boreal larch forest. Future studies on the relationships between post re soil stoichiometry and forest ecosystem structure and function are needed to improve the understanding of the soil-plant interaction in response to wild re in boreal forest ecosystems.
Declarations Figure 1 Study area and sampling plots (little yellow square) of Great Xing'an Mountains in northeastern China and the sampling process. Polygon A represents the 11-year-post-re site appearing bright pink color due to the vegetation recovery and black carbon erosion, polygon B represents the1-year-post-re site appearing fresh red due to high black carbon coverage and high vegetation mortality, polygon C represents the unburned control site which is green due to vegetation cover. The false color Landsat TM images (NASA Landsat Program, 2010, Landsat TM scene LT51210242010254IKR02, L1T, USGS, Sioux Falls, 09/11/2010) were obtained from USGS GLOVIS (https://glovis.usgs.gov/).