Background

Identifying species that will grow effectively in forest restoration schemes often requires time-consuming and expensive field trials from which results are not available for several years (Elliott et al. 2002; Elliott et al. 2003). The Forest Restoration Research Unit (FORRU) of Chiang Mai University have been running nursery and field trials in the Doi Suthep-Pui National Park since 1997 (Elliott et al.

2002; Elliott et al. 2003) based around the Framework Species Approach to forest restoration. These have been very successful (Blakesley et al. 2002; Elliott et al.

2002; Elliott et al. 2003) but it has been suggested that these trials may be targeted more effectively by pre-assessing species using easily measured physical, chemical and life-history traits (Walters & Reich 1999; Poorter & Bongers 2006).

Functional traits have been found to be useful predictors of growth and survival (Westoby et al. 2002; Reich et al. 2003; Wright et al. 2010) and specifically in seasonally-dry tropical forest (Chaturvedi, Raghubanshi & Singh 2011) and restoration projects (Pywell et al. 2003). Species with low leaf specific area and denser wood have been found to grow slower than those with high specific leaf areas and less dense wood (Wright et al. 2010). Other authors however have found that hydraulic architecture is a better predictor of growth rates than robustness in the form of wood or leaf density (Zhang & Cao 2009; Fan et al. 2012).

A great deal of work has been done on identifying relationships between leaf traits and a number of key relationships and tradeoffs have been found (Wright et al.

2004). Increasingly, similar relationships between wood traits (Chave et al. 2009) have also been identified. Here, key leaf traits, (see Chapters 3) in the seasonally- dry tropical forest of northern Thailand have been found to correlate as predicted within a single leaf economic spectrum (Wright et al. 2004; Chave et al. 2009). Wood traits have been found to vary on three different axes (see chapter 4).

7.1.2. Hypotheses and aims

Here, the extent to which wood and leaf traits are linked to species growth rates is as yet unknown. The validity of using wood and leaf trait data to predict growth rates for plantation seedlings in the seasonally-dry, tropical forest of northern Thailand was tested , and models created that may be used as predictors of growth in the field. It was predicted that;

• Species with leaves at the “biomass retention” end of the leaf economic spectrum will grow more slowly than those at the “biomass gaining” end.

• Species with dense wood will grow more slowly than those with less dense wood

• Species with high levels of protective features, such as drought tolerance traits, in either wood or leaves. will grow slower than those with few protective features.

• Species with wide xylem vessels will grow faster than those with narrow xylem vessels

7.2. Methods

7.2.1. Doi Suthep-Pui National Park

The Doi Suthep-Pui National Park (created in 1981) is an area of approximately 260 km2 of seasonally-dry tropical forest near Chiang Mai in Northern Thailand

(18.83203°N / 98.88805°E) and ranges from 340 to 1680m a.s.l (Maxwell & Elliott 2001). Whilst annual rainfall is high, rainfall in January and February can be as low as 6 mm a month, rising after the start of the monsoon in April or May to a peak of 275mm in August before dropping swiftly from October. The dry season is sub- divided into the cool-dry season (November–January) where maximum

temperatures range from 30 oC to 32 oC and the hot-dry season (February– April), with a maximum temperature daily temperature of between 30 oC and 39 oC (Fig. 7.1.). Whilst previously fully forested, the area has experienced serious forest loss and degradation with approximately 50% of the park deforested in 1996 (Elliott et al. 2003)

Figure 7.1: Monthly (a) maximum and minimum daily temperature and (b) rainfall in the Chiang Mai area of northern Thailand. Based on records from between 1952 and 1997– (Maxwell & Elliott 2001)

7.2.2. Species selected

Species used here consisted of 45 species (Table 7.1) planted as part of a

restoration project in Doi Suthep-Pui National Park in northern Thailand in 1998, 1999 and 2001. Species planted only in 2000 were not used here due to unusual growth in that plot (see Chapter 5).

Table 7.1: The 45 species of tree and corresponding species code found in Doi Suthep-Pui National Park from which wood trait data and leaf trait data has been collected and which had been planted in the as part of a restoration trial in 1998, 1999 or 2000.

Species_Name Code Species_Name Code Species_Name Code Aglaia lawii S123 Ficus heteropleura S372 Machilus bombycina S163 Alseodaphne andersonii S101 Ficus hispida S380 Manglietia garrettii S007 Aphanamixis polystachya S060 Ficus racemosa S365 Markhamia

stipulata S204 Balakata baccata S015 Ficus subulata S039 Melia toosendan S005 Betula alnoides S048 Garcinia mckeaniana S128 Michelia baillonii S138 Bischofia javanica S004 Glochidion kerrii S179 Nyssa javanica S146 Castanopsis

acuminatissima S270 Gmelina arborea S078 Phoebe cathia S379 Castanopsis calathiformis S335 Helicia nilagirica S104 Phoebe lanceolata S268 Cinnamomum caudatum S207 Heynea trijuga S157 Prunus cerasoides S071 Cinnamomum iners S218 Horsfieldia

amygdalina S119

Pterocarpus

macrocarpus S092 Diospyros glandulosa S012 Horsfieldia thorelii S236 Quercus semiserrata S062 Erythrina subumbrans S317 Hovenia dulcis S018 Rhus rhetsoides S019 Eugenia albiflora S325 Lithocarpus elegans S280 Sapindus rarak S013 Ficus benjamina S029 Lithocarpus

fenestratus S337

Sarcosperma

arboreum S105 Ficus glaberrima S361 Macaranga

denticulata S009 Spondias axillaris S066

Leaf and wood samples were collected during the 2011 wet season from the 1998 and 1999 plots only and were not collected from coppiced regrowth to ensure that samples were from saplings of equal age, grown in simialr conditions and were exposed to similar environmental conditions.

7.2.3. Leaf trait data collection

Measurements, key ratios and derived fields identified by literature search were calculated and included in the analysis. Phenological leafing strategy data (deciduous, evergreen or intermediate) were collated from the Chiang Mai University Herbarium and refers to leafing patterns within the Doi Suthep-Pui National Park itself. Other sources such as the Flora of China (Zhengyi, Raven & Deyuan 1994+) and Flora of Thailand (Flora.of.Thailand.Editorial.Board 1970+) often suggest different strategies to those displayed within Doi Suthep-Pui National Park, suggesting that a number of species identified as either evergreen or deciduous may actually be facultative deciduous species (Table 7.2, see Chapter 3 for details)

Table 7.2: Leaf-trait measurements collected from 45 species of trees within the Doi Suthep-Pui National Park in Northern Thailand that have been planted as part of a restoration scheme managed by the Forest Restoration Research Unit (FORRU).

Descriptive variables (values)

Continuous variables (units) Derived continuous variables (Calculation;Units) Phenological leafing strategy (Evergreen, Intermediate, Deciduous)

Area (mm2) Specific Leaf Area (SLA)

(Leaf Area/Leaf Dry Mass; mm2 g-1) Wet Mass (g) Dry Mass (g) Leaf Density (Dry Mass/area*thickness; g mm3) Blade Length (mm) Blade Width (mm)

Petiole length (mm) Petiole_Ratio

(Petiole length/Blade length; ratio) Glabrescence

(Glabrous, Glabrescent, Hairy)

Leaf Thickness (µm)

Cuticle thickness (µm) Blade_Ratio

(Blade width/Blade length; ratio) Nmass (mg g-1); Narea (mg mm-2)

Cmass (mg g-1); Carea (mg mm-2) DryWetRatio

(Dry weight/Wet weight; ratio) Pmass (mg g-1); Parea (mg mm-2)

Leaf Type (Simple, Compound)

Kmass (mg g-1); Karea (mg mm-2) Nitrogen to carbon ratio (N:C Ratio)

(Nmass/Cmass; ratio)

Namass (mg g-1); Naarea (mg mm-2)

Camass (mg g-1); Caarea (mg mm-2) P:N Ratio

(Pmass/Nmass; ratio)

Mgmass (mg g-1); Mgarea (mg mm-2) Leaf Margin (Entire, Partially- Toothed, Full Toothed)

Femass (mg g-1); Fearea (mg mm-2) Stomatal cross-sectional area

((Stomatal Diameter/2)2*pi; mm2) Mnmass (mg g-1);Mnarea (mg mm-2)

Stomatal Proportion

(Stomatal Count*Stomatal cross- sectional area; proportion)

Stomatal Diameter (µm) Stomatal Count (mm-2)

Leaf breaking point (LBP) (g) Leaf Tensile strength (LTS) (LBP /leaf thickness;g mm-1 Leaf Strength per Unit Mass (SPUM) (LBP*SLA; g g-1)