Environmental factors related to community-level functional traits in limestone hill forests along an altitudinal gradient: a case study in northern Thailand

Figure 1

Figure 2

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