Figure 1
Figure 2
![Principal component analysis (PCA) ordination plot of functional trait variables (leaf size [LS], specific leaf area [SLA], leaf thickness [LT], wood density [WD], and maximum plant height [Hmax]) indicating the tree species (Δ) in three forest sites growing along an altitudinal gradient on a limestone hill in Phrae Province, northern Thailand. Species abbreviations are listed in Appendix 1.](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/6471d9d7215d2f6c89db306c/j_fsmu-2019-0014_fig_002.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA6AP2G7AKOUXAVR44%2F20251209%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251209T134406Z&X-Amz-Expires=3600&X-Amz-Signature=2b3e07a3acd3176ad0549e9933c747a206ab094c2d2526adb5bb40fdfe8255d1&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Measurements of the environmental factors at each forest site_ Measurements were taken at the three study sites, i_e_, lower forest site (LFS), middle forest site (MFS), and upper forest site (UFS), along an altitudinal gradient on a limestone hill_ Different superscript letters within a row indicate significantly different means (ANOVA test, p < 0_05; n = 54)_ Values are mean ± standard deviation_
| Factors | LFS | MFS | UFS | p |
|---|---|---|---|---|
| Elevation (m) | 73.88 ± 13.53c | 145.90 ± 14.76b | 222 ± 10.80a | 0.0004 |
| PAR (μmol photons m−2 s−1) | 37.83 ± 6.78b | 109.17 ± 44.38b | 349 ± 73.81a | 0.0032 |
| Rocky outcroppings (%) | 75.33 ± 1.86b | 80.00 ± 1.08b | 87.57 ± 1.11a | 0.0041 |
| Soil moisture content (%) | 3.60 ± 0.30a | 2.90 ± 0.24ab | 2.60 ± 0.95b | 0.0025 |
| Nitrogen (%) | 60.63 ± 16.11ns | 61.29 ± 6.96ns | 59.62 ± 2.71ns | 0.1241 |
| Phosphorus (%) | 0.25 ± 0.01ns | 0.24 ± 0.01ns | 0.29 ± 0.02ns | 0.0723 |
| Potassium (%) | 0.42 ± 0.04a | 0.19 ± 0.02b | 0.019 ± 0.02b | 0.0251 |
Ecological characteristics of the three forest sites growing along an altitudinal gradient on a limestone hill in Phrae Province, northern Thailand_ The three study sites were lower forest sites (LFS), middle forest sites (MFS), and upper forest sites (UFS)_
| Ecological characteristics | Forest sites | ||
|---|---|---|---|
| LFS | MFS | UFS | |
| 1. Number of species | 21 | 21 | 16 |
| 2. Species diversity index (H′) | 2.04 | 2.43 | 1.40 |
| 3. Stand basal area (m2 ha−1) | 13.2 | 15.9 | 18.9 |
| 4. Stem density (stems ha−1) | 1556 | 1616 | 2175 |
Basal area (Ba, m2 ha−1) and stem density (D, stem ha−1) of the five prevalent species in each of the three forest sites growing along an altitudinal gradient on a limestone hill, ranked with the importance value index (IVI, sum of the relative basal area [RDo, %], relative density [RD, %], and relative frequency [RF, %]) of each species_
| Forest site | Species | Ba | D | RDo | RD | RF | IVI |
|---|---|---|---|---|---|---|---|
| Lower forest site | |||||||
| 1 | Streblus taxoides | 2.69 | 738.89 | 20.36 | 47.5 | 14.4 | 82.26 |
| 2 | Alphonsea siamensis | 2.11 | 211.11 | 15.96 | 13.57 | 12 | 41.53 |
| 3 | Parishia insignis | 1.36 | 61.11 | 10.27 | 3.93 | 8 | 22.2 |
| 4 | Aglaia edulis | 0.95 | 44.44 | 7.2 | 2.86 | 8.8 | 18.86 |
| 5 | Sterculia pexa | 1.03 | 61.11 | 7.79 | 3.93 | 4.8 | 16.52 |
| Middle forest site | |||||||
| 1 | Ficus macleilandii | 3.18 | 381.82 | 19.89 | 23.63 | 13.16 | 56.68 |
| 2 | Sterculia pexa | 2.02 | 202.27 | 12.64 | 12.52 | 9.87 | 35.02 |
| 3 | Dracaena cochinchinensis | 1.62 | 200.00 | 10.12 | 12.38 | 10.53 | 33.02 |
| 4 | Alphonsea siamensis | 2.52 | 81.82 | 15.76 | 5.06 | 10.53 | 31.35 |
| 5 | Parishia insignis | 1.37 | 168.18 | 8.59 | 10.41 | 7.89 | 26.89 |
| Upper forest site | |||||||
| 1 | Dracaena cochinchinensis | 10.51 | 1457.14 | 55.49 | 67 | 16.87 | 139.36 |
| 2 | Parishia insignis | 2.78 | 114.29 | 14.69 | 5.25 | 13.25 | 33.2 |
| 3 | Sterculia lanceolata | 1.09 | 107.14 | 5.73 | 4.93 | 10.84 | 21.5 |
| 4 | Meliosma pinnata | 0.93 | 121.43 | 4.93 | 5.58 | 9.64 | 20.15 |
| 5 | Ficus macleilandii | 0.66 | 107.14 | 3.47 | 4.93 | 9.64 | 18.03 |
Study area map depicting the three forest site plot numbers_ Site selection was based on elevation and the geomorphological features of the hill_
| Forest site | Descriptions | Number of plots |
|---|---|---|
| Lower forest site (LFS) | A forest community located at the base of the limestone hill, with rocky outcroppings covering >50% of the area. The site spanned elevations of 320–360 m a.s.l. | 18 |
| Middle forest site (MFS) | A forest stand located on a long narrow ridge on the high, steep slope of the limestone hill. The site spanned elevations of 370–400 m a.s.l. | 22 |
| Upper forest site (UFS) | A forest stand established on a rocky outcropping located at the summit of the limestone hill. The site spanned elevations of 410–460 m a.s.l. | 14 |
Selected factors from the generalized linear mixed models evaluating the community functional values (FD) of woody plants relating to the environmental variables_
| FD | Environmental variables | ||||||
|---|---|---|---|---|---|---|---|
| Elv | RC | PAR | SMC | N | P | K | |
| FDis | 0.026** | ||||||
| FRic | 0.021** | ||||||
| CWM | |||||||
| LS | 2.302*** | 7.856*** | 1.508*** | −3.137*** | −3.767*** | 2.535*** | −1.705*** |
| SLA | 1.372*** | 0.031*** | 0.001*** | −0.002*** | 0.853 | ||
| LT | 0.461*** | 1.003*** | 2.014*** | ||||
| WD | −1.241*** | −0.127*** | |||||
| Hmax | −0.006*** | −0.546*** | 0.151*** | ||||
Community-level weighted means (CWM) of leaf size (LS), specific leaf area (SLA), leaf thickness (LT), wood density (WD), maximum plant height (Hmax), functional richness (FRic), and functional dispersion (FDis) of woody tree species measured in the different forest sites, i_e_, lower forest site (LFS), middle forest site (MFS), and upper forest site (UFS), growing along an altitudinal gradient on a limestone hill_
| Functional trait | LFS | MFS | UFS | Sig. |
|---|---|---|---|---|
| CWM-LS | 133.80 ± 54.85b | 299.23 ± 52.07a | 253.42 ± 81.26a | ** |
| CWM-SLA | 16.34 ± 8.16b | 24.27 ± 11.22a | 14.88 ± 5.84b | ** |
| CWM-LT | 0.23 ± 0.02c | 0.26 ± 0.04b | 0.35 ± 0.03a | *** |
| CWM-WD | 1.88 ± 0.16a | 1.62 ± 0.39ab | 1.50 ± 0.22b | *** |
| CWM-Hmax | 15.84 ± 1.23a | 11.29 ± 21.79ab | 8.32 ± 0.48b | ** |
| FRic | 3.16 ± 2.72b | 6.66 ± 3.06a | 5.66 ± 3.98a | ** |
| FDis | 1.32 ± 0.32b | 2.12 ± 0.41a | 1.86 ± 0.44a | *** |
j_fsmu-2019-0014_tab_007_w2aab3b8c72b1b7b1ab2b2ab2Aa
| No. | Species | Code | LFS | MFS | UFS | Total |
|---|---|---|---|---|---|---|
| 1 | Dracaena cochinchinensis | DRCO | 20 | 168 | 408 | 596 |
| 2 | Streblus taxoides | STTA | 266 | 70 | 7 | 343 |
| 3 | Alphonsea siamensis | ALSI | 76 | 89 | 10 | 175 |
| 4 | Ficus macleilandii | FIMA | 14 | 88 | 30 | 132 |
| 5 | Sterculia pexa | STPE | 22 | 74 | 17 | 113 |
| 6 | Parishia insignis | PAIN | 22 | 36 | 32 | 90 |
| 7 | Sterculia lanceolata | STLA | - | 34 | 30 | 64 |
| 8 | Meliosma pinnata | MEPI | 6 | 24 | 34 | 64 |
| 9 | Drypetes hoaensis | DRHO | 24 | 29 | 7 | 60 |
| 10 | Ficus rumphiin | FIRU | 12 | 24 | 12 | 48 |
| 11 | Aglaia edulis | AGED | 16 | 17 | - | 33 |
| 12 | Sterculia villosa | STVI | 7 | 16 | 5 | 28 |
| 13 | Tarenna hoaensis | TAHO | 18 | 5 | 2 | 25 |
| 14 | Memecylon caeruleum | MECA | 9 | 14 | - | 23 |
| 15 | Putranjiva roxburghii | PURO | 16 | 2 | - | 18 |
| 16 | Mallotus peltatus | MAPE | 17 | - | - | 17 |
| 17 | Diospyros castanea | DICA | 4 | 6 | 1 | 11 |
| 18 | Ficus curtipes | FICU | 5 | 6 | - | 11 |
| 19 | Excoecari oppositifolia | EXOP | - | - | 10 | 10 |
| 20 | Firmiana colorata | FICO | - | 3 | 3 | 6 |
| 21 | Brucea javanica | BRJA | - | 3 | 1 | 4 |