Stand characteristics
Stand characteristics of four sites showed a notable variation (Table 1). A total of 10 woody species (≥ 1cm dbh) were recorded. The woody species richness ranged from 03 at OG to 07 at the MF site. 40% species were common between MF and OP, 30% between MF and YP, 20% between MF and OG, 40% between OP and YP, 10% between MP and OG and 30% between YP and OG (Fig. 2). The total density of woody species (≥ 1 cm dbh) ranged from 156 individuals ha− 1 at OG to 852 individuals ha− 1 at MF. Based on density, Cedrus deodara at MF (density = 416 individual’s ha− 1), Pinus wallichiana at OP and YP (296 and 84 individual’s ha− 1 respectively) and Berberis lyceum at OG (96 individual’s ha− 1) were the dominant species. While moving from the sites with no plantation through young plantations towards the mature forest, an increase in the basal area was observed. The total stand basal area ranged from 0.12 m2ha1 at OG to 76.28 m2ha1 at MF (Table 1). A significant difference (p < 0.05) was observed between the sites with respect to both density and basal area.
Table 1
Stand characteristics of woody species (≥ 1cm DBH) in different study sites
Site | Total basal area (m2 ha1) | Total density (ha− 1) | Average canopy cover (%) | Average tree height (m) |
OG | 0.12 | 156 | 1.80 | 0.41 |
YP | 0.32 | 292 | 6.00 | 1.40 |
OP | 2.17 | 576 | 21.72 | 5.74 |
MF | 76.28 | 852 | 49.96 | 24.76 |
The height of woody species ranged from 0.1–1.5m at OG, 0.3–3.4m at YP, 0.6–9.6m at OP and 12.6–34.2m at MF. The canopy cover was highest in MF (Mean = 49.9%), followed by OP (21.72%), YP (6.0%) and OG (1.8%) (Table 1). Based on the plant height and canopy cover, the sites varied significantly with each other except OG and YP where it was not significant (p > 0.05). Based on stand characteristics the site combinations OG:YP, OG:OP, OG:MF, YP:OP, YP:MF and OP:MF showed 69%, 41%, 27%, 66%, 46% and 75% similarity respectively.
Soil properties
Soil properties varied between the sites (Fig. 3). The pH ranged from 5.01 at MF to 6.05 at OG and varied significantly (p < 0.05) across the sites. OG had the highest content of organic carbon (3.35%) and available phosphorus (5.48 µg g− 1) whereas MF had the highest concentration of total nitrogen (0.36%). Soil organic carbon ranged from 2.23 to 3.52%, total nitrogen from 0.21 to 0.38% and available phosphorus from 3.22 to 5.56 (µg g− 1) across all sites. Based on organic carbon and total nitrogen there was no significant difference (p > 0.05) between sites, however, the sites differed significantly (p < 0.05) with each other based on values of available phosphorus.
Community characteristics of G. kurroo
The community characteristics of G. kurroo are shown in Table 2. The density of the species ranged from 320 individuals ha− 1 at MF to 8532 individuals ha− 1 at OG. The species was frequently and abundantly found in OG while it was very rare in MF (Table 2). A high importance value index was recorded at OG followed by YP, OP and MF. The species covered the largest area (41.6%) in OG, which was lowest in MF (1.22%) (Table 2). Based on the community characteristics, all the sites showed a significant difference from each other. The individual pattern of height class distributions of the species at different sites showed a varied trend (Fig. 4). At all the sites (except MF) an inverse J-shaped curve was observed having many small individuals but a smaller number of big individuals. Of all the sites, OG had the highest proportion of bigger height class individuals (16–20 cm) followed by YP and OP. The individuals in the lowest (< 4 cm) and highest (16–20 cm) classes were completely absent in MF (Fig. 4).
Table 2
Community characteristics of G. kurroo at different sites
Site | Density (individuals ha− 1) | Frequency (%) | Abundance (%) | Cover (%) | IVI |
OG | 8532 | 84 | 100.0 | 41.46 | 96.39 |
YP | 4424 | 64 | 69.1 | 28.21 | 60.00 |
OP | 2176 | 40 | 54.4 | 15.23 | 33.69 |
MF | 320 | 16 | 20.0 | 1.22 | 9.91 |
Population structure and regeneration
A total of 3863 individuals including seedling, sapling and adult individuals of G. kurroo were recorded at all the sites. The highest population was observed at OG (2133 individuals), followed by YP (1106 individuals), OP (544 individuals) and MF (80 individuals). Of all the sites, OG had highest population of seedlings (44.1%), saplings (29%) and adults (26.9%), followed by YP (37.7, 29.7 and 32.6% respectively), OP (30.0, 31.1 and 39.0% respectively) and MF (0, 42.5 and 57.5% respectively) (Fig. 5). Based on the number of seedlings, saplings and adults, the regeneration of G. kurroo was poor at MF and MP, fair at YP and good at OG (Fig. 5). There was a significant difference between the sites based on the number of regenerating individuals (seedlings and saplings).
The regeneration status of G. kurroo was negatively correlated with tree density (r = − 0.73) and litter depth (r = − 0.78). With an increase in canopy openness, the number of regenerating individuals increased indicating a negative effect of canopy cover on regeneration (Fig. 5). There was no linear correlation between canopy openness and the number of regenerating individuals. Conversely, a quadratic relationship between the two was apparent (Fig. 6), where test for polynomial trends showed a significant quadratic relationship for OG (F = 15.24, P = 0.02), YP (F = 19.61, P = 0.03), OP (F = 60.25, P = 0.01) and MF (F = 1.087, P = 0.001) (Fig. 6).
Woody species composition seems to have exerted a considerable influence over the population of G. kurroo. Significant (p = 0.042) and a negative relation (r= -0.737) was found between the density of G. kurroo with woody species density (Fig. 7). Similar, but the non-significant trend was observed between G. kurroo density with litter depth (r= -0.782, p = 0.71) (Fig. 7).
Ordination analysis between different sites depicted the levels of influence by various variables on the density of G. kurroo. In ordination space, the overlap of the studied species in different plots showed that the density of G. kurroo responds negatively with the stand basal area, litter depth, tree density, canopy cover, tree height and total nitrogen in the soil, but responds positively with soil organic carbon, available phosphorus, and reduction in plantation intensity (Fig. 8). The first axis of canonical correspondence analysis (CCA) explained 44.26% of data variance, while the second axis explained 36.99%. At 999 permutation value, the Eigenvalue for both the axis was 0.3 but the p-value was higher (0.41) in first and lower (0.16) in second. The first axis was mainly related to soil properties, while the second axis was mostly determined by a combination of community characteristics and total nitrogen (Fig. 8).