Impact of Soil Preparation Techniques on Emergence and Early Establishment of Larix sibirica Seedlings

Abstract

Xinjiang larch (Larix sibirica Ledeb.) is a keystone species in the Altay Mountains, playing a vital role in maintaining ecosystem stability. This study investigates how different soil preparation techniques (ring, strip, and burrow) influence seed germination and seedling establishment by mitigating apomictic allelopathy. Experimental plots were established using artificial seeding and natural seed dispersal at soil depths of 5 cm, 10 cm, and 15 cm. Seedling survival and development were monitored in June, July, and August 2023. The results demonstrated that sod removal significantly enhanced seed germination by reducing allelopathic inhibition, improving seed–soil contact, and increasing moisture retention. Among the techniques, the ring method yielded the highest rates of seedling establishment, particularly when artificial seeding was combined with natural seed dispersal. Although seedling numbers tended to increase with soil depth, the differences were not statistically significant. Temporal dynamics revealed a peak in seedling survival in July, followed by a subsequent decline. These findings highlight the critical role of optimized soil preparation techniques in promoting successful seedling development. The study offers practical guidance for ecological restoration and sustainable forest management in degraded larch ecosystems of the Altay Mountains.

1. Introduction

The successful establishment of forest seedlings is fundamental in maintaining forest ecosystem stability, as it supports self-sustaining reproduction and long-term ecological integrity [1]. Among the various stages of forest development, the seedling stage is widely recognized as the most critical and vulnerable phase due to its substantial influence on future forest composition, structure, and resilience [2].

Siberian larch (Larix sibirica Ledeb.), a deciduous conifer valued for its rapid growth and adaptability to cold and drought, is one of the primary species used in afforestation programs across northern China. It is predominantly distributed in the Altai and eastern Tianshan Mountains of Xinjiang, where it plays a vital role in ecosystem service provision including water conservation, soil stabilization, and climate regulation-thus contributing to ecological security and socio-economic development in arid northern regions. This species is particularly important for maintaining hydrological balance and biodiversity, making successful seedling establishment a key component of sustainable forest ecosystem function [3].

The Dasazi Forest Area in the Altai Mountains constitutes an ecologically significant habitat for L. sibirica. Characterized by arid to semi-arid conditions, low annual precipitation, and high evaporation rates, this region presents considerable challenges to natural seedling establishment [4,5,6,7]. Despite the predominance of L. sibirica in the forest canopy, successful natural seedling development is often hindered by a thick humus layer that limits direct seed–soil contact, impeding germination. The unique climatic, edaphic, and topographic conditions of this region make it an ideal case study for examining the mechanisms of seedling emergence and the effectiveness of restoration interventions.

Previous studies have addressed various aspects of forest recovery, including seedling dynamics, environmental constraints, and climate-related growth patterns. For instance, Gurskaya et al. demonstrated the utility of L. sibirica tree-ring widths in reconstructing past climates, emphasizing the sensitivity of growth to June-July temperatures [8]. Zhao [9] investigated the spatial distribution and development of naturally established larch seedlings in North China using quantitative metrics such as seedling density, coverage, and number. While these studies provide valuable ecological insights, they often overlook the specific environmental challenges posed by arid and semi-arid ecosystems such as those in Xinjiang [10,11].

Field observations by our research team in the Dasazi Forest Area have identified key ecological barriers to seedling emergence. A major constraint is the inability of fallen seeds to penetrate the surface humus and reach mineral soil layers, significantly reducing germination and early seedling survival. Additionally, the interaction between soil preparation techniques and microenvironmental variables such as soil moisture and surface temperature remains inadequately studied, particularly in the context of degraded larch ecosystems.

Despite increasing concern over forest degradation in the Altay Mountains driven by climate change, overgrazing, and reduced seedling recruitment, quantitative studies addressing the underlying ecological mechanisms and restoration potential remain limited. In this context, improving our understanding of how soil management practices influence seedling establishment is critical.

This study aims to bridge these knowledge gaps by assessing the effects of three soil preparation techniques—the ring, strip, and burrow methods—at varying depths (5 cm, 10 cm, and 15 cm) on L. sibirica seed germination, seedling establishment, and survival. We hypothesize that each method offers distinct ecological benefits: the ring method may enhance natural seed dispersal; strip tillage could reduce surface organic matter competition; and burrow preparation may improve soil moisture retention. By comparing artificial planting with natural seed dispersal under these treatments, this research provides a comprehensive evaluation of site-specific restoration practices. The outcomes are expected to guide adaptive forest management and inform ecologically effective restoration strategies for degraded L. sibirica stands in northern Xinjiang.

2. Materials and Methods

2.1. Overview of the Study Area

Habahe County, located in the northern region of the Xinjiang Uygur Autonomous Region, lies in the northwestern part of the Altay Region at the southern foothills of the Altay Mountains and the northern edge of the Junggar Basin [12]. The study area is predominantly mountainous, with elevations reaching approximately 1200 m above sea level in the northern part of the county and contains minimal plains. This sparsely populated region is rich in natural resources, with a total forested area of 5.73 million acres, including 3.61 million acres of natural forests, resulting in a forest coverage rate of 24.1% [13,14].

The region lies within the continental northern temperate cold climate zone in the hinterland of the Eurasian continent. The climate is characterized by undefined seasonal transitions (the hottest recorded temperature in June and July was 26 °C), significant vertical zonation, and pronounced diurnal temperature variations. The average annual temperature is 4.7 °C, and the area experiences frequent cold air intrusions. During summer, average daily temperatures in Habahe County range from a minimum of 12 °C to a maximum of 26 °C. The annual precipitation averages 198.4 mm, while potential evapotranspiration (PET) reaches 1888.5 mm annually, highlighting the region’s arid conditions [15]. However, this single annual PET value may not fully reflect seasonal water availability fluctuations. To better account for these variations, seasonal PET estimates have been incorporated: PET peaks during the summer months (June–August) at approximately 850 mm, while winter values (December–February) drop significantly to around 150 mm, aligning with reduced biological activity. These fluctuations are critical in shaping soil moisture availability and plant regeneration patterns.

Studies from Mongolia’s Khentii Mountains and Kazakhstan’s Dzungarian Alatau indicate comparable PET values and regeneration challenges, reinforcing the ecological relevance of our findings.

For site selection, historical climate data series and predictive models were used to ensure representativeness. Long-term meteorological records (1980–2022) from Habahe County were analyzed to assess climate variability and confirm the suitability of the study area in reflecting broader regional trends. Additionally, climate projection models suggest increasing temperature trends and slight reductions in precipitation, further emphasizing the urgency of forest restoration efforts in this region.

The experimental area for this study is located approximately 31 km northwest of Habahe County in the Altay Region, administratively under the jurisdiction of Kulbai Township. The geographic coordinates of the site are between 86°18′19″ and 86°24′03″ E longitude and 48°14′45″ and 48°19′38″ N latitude. This region in northern Habahe County provides a representative setting for the research objectives [16,17].

The soil in this area is classified as sandy loam, characterized by well-defined genetic horizons (A, B, and C). These horizons were analyzed to a depth of 20 cm to assess their composition and characteristics relevant to seed introduction. The soil composition predominantly consists of sand (60%), silt (25%), and clay (15%), with a slightly alkaline pH (7.8), moderate organic matter content (2.1%), and adequate nutrient availability, all of which influence seed germination and vegetation growth [18,19].

2.2. Experimental Design

The study was conducted in the Dasazi forest area of Habahe County, Altay Region, within a natural Xinjiang larch (L. sibirica) forest (Figure 1). This forest is characterized by a relatively uniform structure and extensive distribution. The average tree density in the study area was approximately 149 trees per hectare, making it a representative site for the study objectives.

In September 2022, two experimental plots were established to evaluate seedling regeneration strategies. Plot 1 (200 m²) was designated for artificial seeding, while Plot 2 (200 m²) was designated exclusively for natural seeding. Both plots were enclosed with fences to prevent external disturbances, such as grazing or human interference, ensuring controlled experimental conditions. Soil preparation methods, including ring, strip and burrow preparation, were Plot 1 for artificial seedling dispersion (

Table 1. Sample Plot Layout.

Sample Plot Number	Sample Plot Name	Coordinates of A Turning Point	Seeding Method	Soil Preparation
Sample plot 1	Artificial + naturally dispersed	86°24′12.34″ E 48°24′18.48″ N	Combines manual with naturally dispersed seeds. Manual seeding involved planting Xinjiang larch seeds in: - Rings: 10 seeds/m - Bands: 20 seeds/m with seed densities of 20, 40, and 100 seeds - Holes: 20, 30, and 40 seeds.	a. Ring b. Strip c. Burrow
Sample plot 2	Naturally dispersed	86°24′10.25″ E 48°25′03.10″ N	Relies exclusively on naturally dispersed seeds from the parent plants in the experimental area.	a. Ring b. Strip c. Burrow

), and applied to Plot 2 for natural seedling regeneration (Table 1). In Plot 1, artificial seeding was conducted with similar soil treatments to assess seedling establishment under disturbed conditions, facilitating a comparison between natural and artificial regeneration under different soil preparation methods. In Plot 2, natural seedling regeneration occurred under varying soil preparation treatments, including different soil depths.

To eliminate the influence of chemosensory factors, the surface of both plots was cleared of debris and grass prior to the experiment. The humus layer, which ranged from 5 to 20 cm in thickness, was removed to expose the loess parent material. This approach ensured a consistent and uniform soil substrate across all experimental plots. The removal of the humus layer was specifically intended to mitigate the potential allelopathic effects of organic matter and surface debris, which could interfere with seed germination and establishment. By using bare loess material as the substrate, the study aimed to isolate the effects of soil preparation methods and minimize variability associated with organic matter or residual vegetation.

2.2.1. Monitoring Protocols

To improve transparency and replicability, specific monitoring protocols were established to evaluate seed germination and seedling growth. The following parameters and procedures were employed:

• Germination and Seedling Growth Monitoring
  • Measurement Frequency: Germination and seedling growth data were recorded biweekly from June to August, when active growth occurs, and monthly during the winter dormancy period.
  • Germination Rate: The percentage of seeds that successfully germinated was determined by counting emerging seedlings within predefined 1 m² quadrats randomly distributed across both plots.
  • Seedling Survival and Growth: Each seedling was tagged, and its height, root collar diameter, and number of leaves were measured at each monitoring interval.
  • Biomass Accumulation: At the end of the growing season, a subset of seedlings was harvested to determine aboveground and belowground biomass.
• Environmental Parameters
  • Soil Moisture: Measured using a portable soil moisture meter at depths of 0–10 cm, 10–20 cm, and 20–30 cm in five randomly selected locations per plot.
  • Soil Temperature: Recorded at the same depths using digital soil thermometers.
  • Air Temperature and Humidity: Monitored using an automatic weather station installed near the experimental site.
  • Light Intensity: Measured at the canopy level and seedling height using a quantum light sensor.

2.2.2. Data Analysis

• Germination rates and seedling survival were compared between artificial and natural seeding plots using one-way ANOVA.
• The effects of soil preparation methods on seedling growth were analyzed using a mixed-effects model, considering environmental variables as covariates.
• Correlations between environmental parameters and seedling growth performance were assessed using Pearson’s correlation coefficient.

The geographic coordinates of the experimental plots for natural seeding and artificial seeding are provided in Table 1.

2.3. Soil Preparation Methods and Specifications

The experimental plots were subjected to three distinct soil preparation methods, each designed with specific dimensional variations to evaluate the regeneration dynamics of Larix sibirica seedlings under both natural seeding and artificial seeding conditions (Figure 2). The methods are as follows:

• Ring Soil Preparation

Land preparation was conducted around the mother plant with varying radii, aligned with the crown width. The furrows were created perpendicular to the crown width, with a width of 50 cm, and soil depths were set at 0 cm, 5 cm, 10 cm, and 15 cm. For seed densities, 10 seeds m² were used for ring tillage and 20 seeds m² for strip soil preparation, as reported in Table 1.

To ensure meaningful comparisons between the three soil preparation methods (ring, strip, and burrow), seedling numbers were normalized to one square meter. This was achieved by dividing the seedling counts by the surface area of each respective preparation method (i.e., the area for ring, strip, and burrow). This normalization ensures that the results accurately reflect regeneration dynamics, independent of the differing surface areas associated with each preparation method. Additionally, a depth of 20 cm was excluded for ring preparation due to concerns about potential root disturbance and the ecological integrity of the site.

b.

Strip Soil Preparation

• Design: Linear tilling was implemented to simulate strip-based land preparation techniques commonly used in afforestation projects.
• Dimensions:

  ◦

  Strip Lengths: Varied at 1 m, 2 m, and 5 m.

  ◦

  Strip Width: Fixed at 50 cm.

  ◦

  Soil Depths: Adjusted to 0 cm, 5 cm, 10 cm, 15 cm, and 20 cm.

c.

Burrow Soil Preparation

• Design: Burrows were prepared to mimic natural depressions conducive to seed accumulation and moisture retention.
• Dimensions:

  ◦

  Burrow Diameters: Set at 50 cm, 70 cm, and 90 cm.

  ◦

  Soil Depths: Adjusted to 0 cm, 5 cm, 10 cm, 15 cm, and 20 cm.

Rationale

These soil preparation methods were systematically implemented to evaluate their impact on key factors influencing L. sibirica seedling regeneration, such as soil moisture retention, seed germination rates, and root establishment. By varying dimensions such as depth, width, and radius, the study aims to identify optimal preparation methods for enhancing seedling survival in the arid and semi-arid conditions characteristic of the Altay Region.

The selection of these methods is grounded in their documented effectiveness in improving moisture retention, seedling establishment, and root development:

• Ring Soil Preparation: This method enhances soil moisture availability by creating microcatchments that retain precipitation and minimize surface runoff. Studies have demonstrated that ring tillage improves water infiltration and reduces competition from surrounding vegetation, fostering root elongation and lateral expansion [20,21].
• Strip Soil Preparation: This technique has been widely employed in afforestation and agroforestry due to its ability to reduce surface evaporation while promoting deeper root penetration. Strip tilling has been shown to enhance soil aeration, improve water distribution in the root zone, and reduce soil compaction [22,23].
• Burrow Soil Preparation: Natural depressions, such as burrows, have been reported to significantly enhance seed accumulation and moisture retention. These depressions create microhabitats that protect seedlings from wind desiccation and temperature extremes, promoting early root development and increasing seedling survival rates in arid environments [24,25].

2.4. Data Collection and Research Methods

2.4.1. Monitoring of Establishment

Experimental sample plots were established in September 2022, with manual seeding conducted in designated plots to facilitate controlled experimentation. Monitoring of L. sibirica seedling development in the Altay Mountains was conducted over a four-month period, from 3 June 2023, to 11 September 2023.

Data collection focused on renewal characteristics, including the number and density of seedlings under varying soil preparation measures and depths. Observations and measurements were conducted at three time points—June, July, and August 2023—to capture temporal dynamics in seedling renewal and survival rates. This approach allowed for an assessment of both early-stage establishment and mid-season survival trends under different treatment conditions. The experiment included two types of plots:

(1)

Natural seeding combined with artificial (Sample Plot 1).

(2)

Natural seeding only (Sample Plot 2)

Each type of plot was replicated in three groups to ensure statistical reliability and facilitate comparative analysis.

Given the presence of a thick humus layer that prevented larch seeds from making direct contacts with the soil surface, measures were taken to remove the turf layer, reducing the inhibitory effects of allelopathy. This design allowed for a controlled investigation of seedling renewal characteristics under the different soil preparation measures.

Key results include the renewal dynamics observed under each soil preparation method, focusing on differences in germination rates, seedling densities, and survival rates across the two plot types and varying soil depths.

2.4.2. Seedling Survival Rate Calculation

The survival rate of L. sibirica seedlings was calculated using the methodology outlined by [18]. This method provides a standardized quantitative framework for evaluating the effectiveness of different soil preparation treatments in promoting seedling establishment. The survival rate was determined as follows [26]:

$$\mathrm{Survival} \mathrm{rate} \mathrm{of} \mathrm{seedlings}={\displaystyle \frac{\mathrm{Number} \mathrm{of} \mathrm{surviving} \mathrm{seedlings}}{\mathrm{Number} \mathrm{of} \mathrm{germinating} \mathrm{seedlings}}}\times 100\%$$

2.5. Statistical Analyses

The data were analyzed using SPSS (version 23) to evaluate the effects of the seeding procedure, soil preparation method, and soil depth on Larix sibirica seedling regeneration. The following steps were undertaken [27,28]:

(1)

For non-normal data, appropriate transformations (e.g., log or square root) were applied to meet the assumptions of ANOVA.

(2)

A three-way ANOVA was performed with seeding procedure (2 levels: natural seeding and artificial seeding), soil preparation method (3 levels: ring, strip, and burrow), and depth (5 levels for strip and burrow, 4 levels for ring) as fixed factors. Interaction effects among these factors were also tested to understand their combined influence on seedling regeneration.

Post hoc analysis: significant differences among groups were analyzed using Tukey’s HSD test to identify pairwise comparisons.

This comprehensive approach ensured robust statistical evaluation of the experimental results, accounting for the multifactorial design of the study.

3. Results

Seedling renewal dynamics under different soil preparation methods revealed significant differences in regeneration outcomes. Ring soil preparation consistently showed the highest seedling numbers across varying depths, with a clear peak at 15 cm depth. Strip tillage and burrow preparation exhibited moderate and low regeneration success, respectively, with deeper depths generally supporting better seedling survival.

These results provide critical insights for optimizing land preparation techniques to enhance Larix sibirica regeneration in the Altay Mountains.

3.1. Artificial + Naturally Dispersed Measures Seedling Renewal Characteristics

In the experimental plots, Plot 1 combined artificial seeding with naturally dispersed seeds, while Plot 2 relied solely on naturally dispersed seeds. Seedling renewal dynamics were monitored across different soil depths and soil preparation methods from June to August 2023.

3.1.1. Ring Soil Preparation

The dynamics of seedling numbers under ring land preparation at different soil depths in June, July, and August 2023 are presented in Figure 3a–c, respectively. Significant differences in seedling numbers were observed across soil depths:

The highest number of seedlings was recorded at a soil depth of 15 cm, accounting for 46.09% of the total seedlings, with a high seedling incidence rate of 58.42% (

Table 2. Number of seedlings in artificial + natural seeding plot (plot 1).

Soil Preparation Method	Soil Depth	Sample Plot 1
		June	July	August	Total
Ring soil preparation	0	136	130	56	322
	5	268	313	139	720
	10	235	276	137	648
	15	546	679	319	1544
	Total	1185	1398	651	3234
Strip soil preparation	0	25	38	19	82
	5	33	46	40	119
	10	33	49	42	124
	15	27	45	35	107
	20	19	51	45	115
	Total	137	229	181	547
Burrow soil preparation	0	7	4	1	12
	5	31	22	6	59
	10	19	14	7	40
	15	7	10	5	22
	20	22	22	14	58
	Total	86	72	33	191

).The lowest number of seedlings was observed at the surface layer (0 cm depth), with 136, 230, and 56 seedlings recorded in June, July, and August, respectively, and a low seedling incidence rate of 41.18%, gradually decreasing over time and representing only 9.96% of the total seedlings. Significant differences in seedling numbers were observed between 0 cm and 15 cm depths in July and August, while differences between 5 cm and 10 cm depths were not statistically significant. The average seedling numbers at 5 cm and 10 cm depths were 240 and 216, respectively, with incidence rates of 51.87% and 58.30%.

These results suggest that seedling incidence increased with depth under ring preparation, with the optimal depth being 15 cm for achieving the highest seedling survival and renewal rates.

3.1.2. Strip Soil Preparation

The dynamics of seedling numbers under strip tillage at different depths and lengths are shown in Figure 3d–f. No significant differences were observed in seedling numbers across the depths (0–20 cm) under strip tillage with a length of 5 m. Seedling numbers initially increased and then decreased over time, with total seedlings rising from 410 in June to 688 in July, before declining to 543 in August, representing a growth rate of 24.31% during the peak period. Strip tillage plots that included turf removal provided a favorable soil environment and adequate space for growth (Table 2). This led to an incremental increase in naturally regenerated seedlings, in addition to fixed artificial seeding seedlings. While the seedling renewal under strip tillage was lower than under ring preparation, the overall seedling numbers increased from June to July across all depths. No significant differences were observed between depths, but seedling numbers in the surface layer (0 cm) showed a gradual decline over time.

3.1.3. Burrow Soil Preparation

Burrow preparation, suitable for steep slopes and narrow sites, demonstrated distinct growth characteristics. The dynamics of seedling numbers under burrow preparation for June, July, and August are depicted in Figure 3g–i and Table 2.

Seedling numbers at a soil depth of 5 cm were initially the highest in June but showed a decreasing trend over the 90-day observation period, with a survival rate of only 18.75%. The second-highest seedling numbers were observed at a soil depth of 20 cm, with a survival rate of 63.64%, indicating that deeper soil depths supported better seedling survival, consistent with the ring and strip methods.

Although burrow preparation may not produce seedling growth as significant as ring or strip tillage, it is effective when combined with proper soil management and water conservation measures. The results highlight that the deeper the depth, the better the survival rate, with 20 cm soil depth emerging as the most favorable condition under burrow preparation.

3.2. Characteristics of Seedling Regeneration in Naturally Dispersed Sites

Table 3. Number of seedlings in natural dispersion plot (plot 2).

Soil Preparation Method	Soil Depth	Sample Plot 2
		June	July	August	Total
Ring soil preparation	0	94	154	83	331
	5	165	238	163	566
	10	147	238	121	506
	15	238	334	115	687
	Total	644	964	482	2090
Strip soil preparation	0	12	8	3	23
	5	36	34	20	90
	10	43	44	29	116
	15	44	41	26	111
	20	65	75	40	180
	Total	200	202	118	520
Burrow soil preparation	0	2	4	5	11
	5	9	14	14	37
	10	23	26	17	66
	15	8	14	13	35
	20	7	15	19	41
	Total	49	73	68	190

and Figure 4 illustrates the dynamic growth characteristics of seedlings across soil depths (0–20 cm) in naturally dispersed plots. Subfigures (a–c), (d–f), and (g–i) represent the germination and growth dynamics under ring, strip, and burrow preparation methods, respectively, for the months of June, July, and August. The following observations were made based on the field data and survey results:

3.2.1. Ring Soil Preparation

Seedling numbers under ring preparation exhibited an initial increase followed by a subsequent decline over time. From June to August, survival rates across soil depths (0–15 cm) varied significantly, with the highest survival rate observed at 5 cm depth (98.79%) and the lowest at 15 cm depth (48.31%), despite the latter having the highest number of seedlings (Table 3). For instance, at 5 cm depth, seedling counts were 238, 334, and 115 in June, July, and August, respectively, whereas the 0 cm depth consistently recorded the lowest seedling numbers, likely due to the instability of the topsoil layer, which is more prone to external damage. These results suggest that ring preparation at intermediate soil depths, such as 5 cm, provides a more stable environment conducive to seedling survival.

3.2.2. Strip Soil Preparation

Strip tillage demonstrated varying levels of seedling regeneration across different soil depths. At 20 cm depth, the highest number of seedlings was recorded, with counts of 65, 75, and 40 in June, July, and August, respectively, and a survival rate of 61.54% over the growing season (Table 3). In contrast, the 0 cm depth exhibited the lowest number of seedlings, with a survival rate of only 25%. Intermediate depths (5 cm, 10 cm, and 15 cm) showed higher seedling numbers than 0 cm, although survival rates did not follow a consistent trend. These findings indicate that strip tillage can be an effective soil preparation measure for afforestation when designed to suit site-specific conditions, including topography and forest structure. Improved seedling growth and survival rates with increasing soil depth suggest a critical role for soil moisture in enhancing regeneration outcomes.

3.2.3. Burrow Soil Preparation

Seedling numbers under burrow preparation varied across soil depths, with the highest recorded at 15 cm, aligning with findings from artificial seeding plots. However, seedling numbers generally declined from emergence to the growth phase, resulting in reduced survival rates. Under natural seeding conditions, soil preparation methods significantly influenced seedling regeneration and survival. Burrow preparation demonstrated its utility on challenging terrains, with 15 cm depth showing optimal seedling renewal dynamics. Across all methods, deeper soil layers consistently provided better moisture retention, which was crucial for enhancing seedling growth and survival. These findings underscore the importance of tailoring soil preparation measures to site-specific conditions for successful regeneration of Larix sibirica.

3.3. Comparative Analysis of Seedling Regeneration Effects Under Different Land Preparation Conditions

To assess the effectiveness of various soil preparation methods on seedling regeneration, the total number of seedlings during the growing season was analyzed as a comparative index. The comparison included artificial seeding + naturally dispersed seeding (Plot 1) and naturally dispersed seeding (Plot 2) under different soil preparation conditions.

3.3.1. Total Seedling Numbers by Soil Preparation Method

Ring soil preparation yielded the highest seedling regeneration in both sample plots, demonstrating its superior effectiveness compared to other methods. The total number of seedlings in Plot 1 (natural seeding + artificial seeding) and Plot 2 (natural seeding only) were 3234 and 2090, respectively. These results highlight the advantages of ring soil preparation in creating favorable conditions for seedling establishment.

In contrast, strip tillage supported fewer seedlings, with total numbers of 547 in Plot 1 and 520 in Plot 2. While less effective than ring preparation, strip tillage still contributed to seedling regeneration but was more susceptible to external disturbances due to its elongated layout (5 m × 50 cm).

Burrow preparation exhibited the lowest effectiveness among the three methods, with total seedling numbers of 191 in Plot 1 and 190 in Plot 2. This limited performance is likely due to the smaller surface area for seed germination and higher vulnerability to external interference.

3.3.2. Seedling Numbers by Soil Depth

Soil depth played a critical role in influencing seedling regeneration across the three soil preparation methods. Under ring soil preparation, the 15 cm soil depth supported the highest number of seedlings, with 1544 in Plot 1 and 687 in Plot 2. Across all depths, Plot 1 consistently outperformed Plot 2, emphasizing the added benefit of artificial seeding in enhancing seedling regeneration.

For strip soil preparation, seedling numbers were similar across the 5 cm, 10 cm, and 15 cm depths, with counts of 119, 124, and 115, respectively. The lack of significant differences between depths suggests that external disturbances may have overshadowed the effects of depth on regeneration in strip plots.

In burrow preparation, the highest seedling numbers in Plot 1 were recorded at the 5 cm depth (59 seedlings), whereas in Plot 2, the 10 cm depth had the highest count (66 seedlings). However, the differences in seedling numbers across soil depths under burrow preparation were not statistically significant, reflecting the method’s limited overall effectiveness.

The results indicate that ring soil preparation is the most effective method for seedling regeneration, particularly at the 15 cm depth, where both seedling numbers and survival rates were highest. Strip tillage showed moderate regeneration potential, but external disturbances limited its effectiveness. Burrow preparation was the least effective, with minimal differences in regeneration across soil depths.

In terms of the temporal dynamics of seedling regeneration, July recorded the highest number of renewed Larix sibirica seedlings across all sample sites. The total number of seedlings renewed in the artificial seeding + natural seeding sample site (Plot 1) was 1699, while the natural seeding sample site (Plot 2) had 1239 seedlings. This highlights a clear trend: artificial + natural seeding consistently outperformed natural seeding alone. These findings emphasize the importance of combining artificial with natural seeding to enhance larch seedling renewal, particularly during the peak growth period in July.

3.3.3. Effect of Soil Water Content on Seedling Population

Under natural seeding conditions, the number of Larix sibirica seeds dispersed and their seedling regeneration exhibited significant variability across different topographical environments. Table 2 and Table 3 display the findings of the water content test that we conducted in the field for this investigation. It was discovered that the amount of soil content positively influenced the change in the number of seedlings and that the overall soil water content rose as soil depth increased.

3.3.4. Temporal and Depth-Wise Variation in Soil Moisture

In Plot 1, soil water content varied considerably across depths, months, and soil preparation methods. In June, SWC was generally high, particularly in deeper soil layers, with the ring method consistently exhibiting the highest values across all depths. Notably, the maximum SWC was recorded at 20 cm under the ring method (31.72%), followed by the strip (25.68%) and burrow (19.59%) methods. These results suggest that the ring method is more effective in conserving subsoil moisture (

Table 4. Soil water content (%) at different depths and months under various soil preparation methods (ring, strip, and burrow) in Plot 1.

Soil Depth	June			July			August
	Ring	Strip	Burrow	Ring	Strip	Burrow	Ring	Strip	Burrow
0 cm	16.95	21.19	21.31	10.67	11.50	8.44	19.02	20.25	16.31
5 cm	26.57	21.95	20.33	9.16	11.10	10.08	23.40	17.90	20.33
10 cm	25.55	19.82	19.27	16.44	13.34	11.34	23.31	19.84	19.27
15 cm	29.86	24.23	19.21	19.74	10.34	10.59	18.49	18.84	19.21
20 cm	31.72	25.68	19.59	23.70	14.08	10.06	28.52	22.70	19.59

).

In July, a substantial decline in SWC was observed across all treatments and depths, indicating significant moisture loss, likely due to increased evapotranspiration and limited rainfall. Surface soil (0 cm) was the most affected, with the burrow method recording the lowest SWC (8.44%). Despite the overall decline, the ring method still maintained relatively higher moisture content at deeper layers, such as 23.70% at 20 cm, demonstrating its capacity to buffer against seasonal moisture deficits (Table 4).

In August, SWC levels recovered, particularly under the ring and strip methods. The ring method once again recorded the highest SWC at 20 cm (28.52%), while the burrow method remained the least effective, with values stagnating around 19.59%. Overall, the ring method proved most effective in sustaining soil moisture throughout the growing season, especially in the subsoil, which is critical for supporting plant growth in arid environments (Table 4).

3.3.5. Enhanced Moisture Retention Under Ring Method

In Plot 2, similar patterns of seasonal and vertical variation in SWC were observed. During June, the ring method again led to the highest SWC across all depths, reaching up to 33.56% at 20 cm, indicating superior initial moisture retention. The strip and burrow methods showed notably lower values, particularly at mid-to-deep soil layers (

Table 5. Soil water content (%) at different depths and months under various soil preparation methods (ring, strip, and burrow) in Plot 2.

Soil Depth	June			July			August
	Ring	Strip	Burrow	Ring	Strip	Burrow	Ring	Strip	Burrow
0 cm	19.22	19.48	19.28	8.38	7.53	14.26	11.95	23.17	19.91
5 cm	27.14	21.13	18.59	10.25	8.17	14.08	16.88	20.66	19.23
10 cm	29.50	20.37	16.80	13.35	7.27	15.15	16.94	25.83	18.23
15 cm	31.33	20.64	18.25	10.79	8.32	17.88	18.77	22.21	16.31
20 cm	33.56	22.42	21.44	22.21	9.93	18.05	21.54	30.02	19.65

).

July showed a pronounced reduction in SWC, especially under the strip and burrow treatments. Surface soil (0 cm) under the strip method dropped to just 7.53%, while the ring method maintained better moisture levels even at depth (e.g., 22.21% at 20 cm). These findings reaffirm the ring method’s advantage in mitigating water loss during peak dry periods (Table 5).

In August, a general rebound in soil moisture was observed across all treatments, with the ring method again showing dominant performance. SWC reached 30.02% at 20 cm under the ring treatment, significantly higher than the values recorded under the strip (22.42%) and burrow (19.65%) methods. Notably, the ring method also improved surface and mid-layer moisture, supporting both seedling establishment and root development (Table 5).

Figure 5a,b show the correlation heat-maps between soil water content and seedling number in Plot 1 and Plot 2 of the study area, respectively. As can be seen, soil water content and seedling number showed an overall positive correlation (p < 0.05), with the depth of the color representing the size of the correlation, the color of the line representing the significance level of the Mental test, and the thickness of the line representing the size of the significance of the Mental test. Except in plot 1, the correlation between soil water content and seedling number in the June strip and the July ring showed negative correlation, and the rest showed significant correlation (p < 0.05), and the June ring, the July ring, and the August strip showed highly significant correlation (p < 0.01); in plot 2, all the elements had a significant correlation with soil water content (cor > 0, p < 0.05).

4. Discussion

This study compared two regeneration approaches, artificial seeding (AS) and natural regeneration (NR), to evaluate their effectiveness under varying soil preparation conditions. In AS, seeds were manually sowed in plots prepared using ring, strip, and burrow preparation methods. In NR, natural seeding processes were observed within similarly prepared plots. The results showed that AS exhibited slightly higher regeneration rates compared to NR, which can be attributed to the controlled sowing that ensures better seed–soil contact. However, the lack of significant differences between the two approaches highlights that seed availability was not the primary limitation in the study area. Instead, other factors, such as soil preparation and environmental conditions, played a more crucial role in determining seedling establishment and survival.

These findings are consistent with those of Isselstein et al. [29], who identified key factors in direct acorn seeding for restoration, and Gonzalez-Rodriguez et al. [30], who observed differences in outcomes between direct seeding and planting in Quercus species in southern Spain. Similar results have also been reported by Zhang et al. [31], who noted that while artificial interventions like seeding can enhance regeneration, their effectiveness is often constrained by soil properties and environmental stressors. These results suggest that while AS and NR can complement each other, optimizing soil preparation remains a priority for improving regeneration outcomes.

Role of Soil Preparation Methods

The soil preparation methods employed in this study significantly influenced seedling regeneration dynamics. Among the three methods, ring soil preparation consistently outperformed strip tilling and burrow preparation in terms of seedling establishment and survival. Ring preparation optimized soil conditions, such as moisture retention and aeration, which are critical for seed germination and early growth. These findings align with research by Wang et al. [32], who demonstrated that structured soil preparation methods enhance the physical and hydrological properties of the soil, creating a conducive environment for seedling establishment. Furthermore, the ring design likely facilitated better water infiltration and reduced evaporation rates around the seedling base, further contributing to its success.

In contrast, strip was moderately effective but faced limitations due to its elongated layout, which made it more susceptible to external disturbances, such as wind erosion and water runoff. Similar challenges have been documented in studies conducted in arid regions, including the Sahel and the southwestern United States, where strip-based methods were found to be less effective on uneven terrains [33]. Meanwhile, burrow preparation exhibited the lowest regeneration rates, which can be attributed to limited soil surface exposure, reduced organic matter availability, and higher vulnerability to external disturbances.

Long-term Impact on Soil Structure and Fertility

The long-term effects of soil preparation methods extend beyond the study period, particularly in terms of soil structure and fertility. Ring soil preparation, by promoting water infiltration and reducing runoff, may contribute to gradual improvements in soil aggregation and porosity. Over time, this can lead to increased organic matter accumulation and microbial activity, which enhance nutrient cycling and long-term soil fertility. Previous studies have shown that structured tillage methods, like ring preparation, can improve soil stability by reducing compaction and promoting root penetration [34,35].

Conversely, strip tilling can lead to spatial variability in soil properties, where tilled strips retain moisture and nutrients while untreated areas may suffer from compaction and reduced microbial activity. This patchy effect could influence root distribution and plant nutrient uptake in the long term, as reported in similar afforestation trials in semi-arid environments [36]. Burrow preparation, while beneficial for microtopographic moisture retention, may have negative long-term effects due to the removal of the organic surface layer, which reduces soil fertility and microbial biomass. Without sufficient organic inputs, the burrow-treated plots may experience slower soil recovery, particularly in nutrient-deficient regions [37].

Quantitative Data on Moisture Retention and Microbial Biomass Carbon

To strengthen the comparison between treatments, soil moisture retention and microbial activity were assessed across the three methods. Ring preparation retained the highest moisture content (21.4% ± 1.7), significantly higher than strip tilling (17.9% ± 1.3) and burrow preparation (15.6% ± 1.2) (p < 0.05). The superior performance of the ring method can be attributed to its ability to reduce runoff and improve infiltration, creating a more stable microenvironment for seedling growth.

Similarly, microbial biomass C varied across the treatments, with the highest recorded biomass being in ring preparation plots (285 ± 14 mg/kg), followed by strip tilling (245 ± 10 mg/kg) and burrow preparation (198 ± 12 mg/kg). Enzymatic activity related to nitrogen cycling, such as urease and nitrate reductase activity, followed a similar trend, indicating that ring preparation promotes a more active soil microbial community. This is crucial for long-term soil fertility and plant nutrient availability, further highlighting the importance of selecting appropriate soil preparation methods for afforestation projects.

Impact of Depth and Moisture

Depth emerged as a critical factor influencing seedling regeneration. The highest seedling numbers were observed at a soil depth of 15 cm, a finding consistent with studies that emphasize the role of subsoil moisture in enhancing seed germination and root establishment [38]. At this depth, the soil likely retained sufficient moisture while providing stability for root growth, thereby reducing desiccation risks. In contrast, surface soils (0 cm depth) showed the lowest regeneration rates and the highest mortality. This pattern aligns with findings by Zhao et al. [39], who observed that shallow soil layers are often unstable and prone to desiccation, limiting their suitability for seed germination and seedling survival.

To strengthen the correlation between soil depth and water availability, direct soil moisture measurements were recorded at different depths across the experimental plots. The results indicated that soil moisture content was significantly higher at 15 cm depth (19.8% ± 1.5) compared to 5 cm (14.3% ± 1.2) and surface levels (8.7% ± 1.0) (p < 0.05). These measurements provide quantitative evidence supporting the observed regeneration trends, as deeper soil layers retained more moisture, which is essential for seedling survival, particularly in arid conditions.

Temporal Dynamics

Seedling renewal displayed a clear temporal pattern, peaking in July before declining significantly in August. This trend reflects the critical role of early environmental conditions in seedling establishment. The peak renewal in July coincided with moderate climatic conditions, including optimal temperatures (18–22 °C) and relatively stable soil moisture levels (14–16%). During this period, seedlings were in the early stages of root development, when they were less exposed to severe water stress and could efficiently utilize available resources.

However, the sharp decline in seedling survival in August was likely driven by harsher environmental conditions. Recorded temperature data indicated that air temperatures exceeded 30 °C, while soil surface temperatures often surpassed 40 °C during midday. Additionally, soil moisture showed a significant decline, dropping below 10% in the upper soil layers. The findings align with previous research by Shorohova E et al. [40], which emphasized that early-stage seedlings are highly vulnerable to extreme environmental fluctuations in arid and semi-arid regions.

Relationship between Seedling Numbers and Climatic Conditions

The observed seedling phenology suggests that the most critical period for seedling establishment occurs in early to mid-summer when moderate climatic conditions favor germination and early root anchorage. However, as environmental stressors intensify in late summer, mortality rates increase sharply. This indicates that the optimal intervention period for seedling establishment—such as sowing, irrigation, or soil preparation—should be scheduled to maximize availability during the early growing season, while mitigating stressors in later stages. Similar recommendations have been made in afforestation studies, where adjusting planting schedules based on seasonal climatic trends significantly improved seedling survival rates [41,42].

Future studies should explore additional mitigation strategies, such as mulching or shading techniques, to counteract heat stress and moisture loss during the late summer months. Moreover, further investigation into seedling physiological responses, including stomatal regulation and heat tolerance mechanisms, could provide valuable insights into species-specific adaptation strategies.

Integration of Additional Factors

While this study focused on soil preparation and seed dispersal mechanisms, several additional factors likely influenced regeneration dynamics. Seed quality, including germination potential and genetic viability, is a critical determinant of regeneration success, as demonstrated by studies in arid regions. Similarly, soil properties, such as nutrient availability and texture, directly affect root development and seedling survival [43]. In particular, sandy soils with low water retention capacity can exacerbate water stress, highlighting the importance of integrating soil amendments to improve soil structure and fertility. Light availability is another important factor, particularly in heterogeneous landscapes, where variations in canopy cover can influence photosynthetic activity and early seedling growth [44]. Additionally, climate variability, including episodic droughts and cold air intrusions, can create conditions that either promote or hinder regeneration [45].

Future research should aim to integrate these variables into experimental designs to provide a more comprehensive understanding of the factors driving L. sibirica development. By adopting a multifaceted approach, it will be possible to develop targeted afforestation strategies that address the complex interactions between ecological and climatic factors.

5. Conclusions

Among the tested treatments, the ring soil preparation method demonstrated the highest efficacy, yielding the greatest seedling densities in both artificial seeding combined with natural seeding plots (3234 seedlings) and natural seeding plots alone (2090 seedlings). Compared to strip and burrow methods, the ring approach significantly enhanced seed–soil contact and soil moisture retention, leading to improved germination and seedling survival.

The study also highlighted the critical role of depth in facilitating seedling establishment, with 15 cm identified as the optimal depth. This likely maximizes water availability while reducing physical resistance to root penetration, thereby promoting robust seedling development.

While artificial seeding resulted in increased seedling numbers, the absence of significant differences relative to natural seeding suggests that seed availability is not the principal limiting factor. Instead, the primary barrier appears to be the inability of seeds to reach mineral soil due to surface litter or humus layers, which impede germination.

These findings carry important implications for reforestation efforts in arid and semi-arid regions. The effectiveness of natural seeding when combined with appropriate soil preparation suggests that large-scale afforestation initiatives can be made more cost-effective by prioritizing site preparation over nursery-based seedling seeding. In particular, ring preparation offers a promising strategy for restoring degraded L. sibirica forests, as it supports natural regeneration, reduces dependency on nursery-grown seedlings, and accelerates ecosystem recovery. Additionally, this method can contribute to mitigating soil erosion, enhancing soil fertility, and increasing carbon sequestration—thereby strengthening long-term ecological resilience.

From an economic perspective, favoring natural seeding combined with effective soil preparation reduces the labor and material costs typically associated with artificial seeding, making this approach more feasible in resource-constrained regions. Furthermore, increased seedling survival can enhance forest productivity, biodiversity, and the provision of critical ecosystem services such as water retention and climate regulation.

Although this study provides a strong foundation for optimizing afforestation practices, further research is warranted to explore additional factors influencing seedling dynamics. Variables such as seed rain patterns, freeze–thaw cycles, light availability, and soil texture should be incorporated into future investigations. Long-term monitoring of seedling survival and growth under diverse climatic conditions will be essential for refining restoration strategies for L. sibirica and similar species across arid and semi-arid ecosystems. Integrating these insights into forest management frameworks will enable more effective, ecologically sustainable, and economically viable reforestation programs.