DOI: 10.5061/dryad.70rxwdbxv
title: Tropical montane forest in South Asia: Composition, structure and dieback in relation to soils and topography

description: We evaluated the composition, structure and dieback of a montane forest in
 relation to soils and physiography of an important biogeographic region
 that has been sparsely studied. Our objectives were to: 1. Describe the
 forest composition and structure; 2. Assess the current extent of dieback;
 and 3. Relate tree composition, structure, and dieback proneness to
 edaphic and physiographic measures. We enumerated all live and dead
 standing plants ≥ 3 cm diameter at breast height (DBH), in thirty 20×15 m2
 over story plots. We measured all regeneration &lt; 1m height in
 subplots, sampled soils and measures of physiography, and visually rated
 the proportion of crown die-back, and recorded standing dead trees.
description: Our study was conducted in the tropical montane cloud forests at
 Horton Plains National Park (HPNP), situated in the Nuwaraeliya District
 of the central province of Sri Lanka (6’ 47<sup>o </sup>N to
 6’ 50<sup>o </sup>N and 80’46<sup>o </sup>E to
 80’51<sup>o </sup>E). The condition and successional
 development of the forest would be considered primary, undisturbed forest
 with no known impact by humans from timber or fuelwood harvest, livestock
 grazing or collection of non-timber forest products. The park is managed
 under the jurisdiction of the Department of Wildlife Conservation, Sri
 Lanka. It is situated on the highest plateau land of Sri Lanka and is
 characterized by undulating valleys and rolling hills (Fig. 1). The Park
 extends over an area of 3160 ha. Mean annual
 temperature of HPNP is 15<sup>o </sup>C (DWC, 2007), with an
 annual precipitation of 2150 mm (DWC, 2007), and a minimum monthly
 precipitation of 100 mm (Bruijnzeel and Scatena, 2011). Southwest monsoons
 bring more rains to the study site during May-July, than northeast
 monsoons (October-November) with drier inter-monsoonal periods in August
 and January to March (DWC, 2007). Frequent mist occurs during early
 afternoons and may continue throughout the whole night, especially during
 the southwest monsoon period. Cloud deposition contributes significantly
 to total precipitation especially during the southwest monsoon when
 gale-strength winds can also occur (DWC, 2007). Most of
 the park area is covered with<em> </em>tropical montane cloud
 forests (70.4 %) at elevations between 2100 m to 2300 m. Grasslands
 defined by tall tussock grass (18.4 %) and carpet grasses (2 %) occupy
 most of the remaining lower slopes and hollows of the park (see Fig. 2).
 In addition, some riparian areas comprise dwarf bamboo,
 <em>Arundinaria densifolia</em> (Ediriweera<em> et
 al.</em>, 2008). When forest die-back was first noticed to actually
 start remains unknown but it was first reported in 1970s (Perera, 1978)
 and has been observed to continue over time, largely reported in the
 non-peer reviewed gray literature (Werner, 1988; Mahaliyanage <em>et
 al</em>., 1999; Ediriweera <em>et al</em>., 2008;
 Chandrajith <em>et al</em>., 2009; Kotinkaduwa <em>et
 al</em>. 2011). Thirty plots for the study were
 chosen randomly on a 1:50,000 map of HPNP with the aid of Hawth's
 Tools in ArcGIS software. One restriction imposed by the National Park
 Service was that all plots had to be placed within 200 m of a trail to
 enable access and to prevent any new trail being created within areas
 deemed wilderness. Plots were selected in forest between the 2100 m to
 2300 m altitudinal range. This range represented where the forest was
 present across the undulating park plateau. For each 20 m×15 m plot we
 measured all live and standing dead woody plants in which the diameter at
 breast height (DBH) ≥ 3 cm was tagged and enumerated between December 2016
 and December 2017. Where plants were of uncertain taxonomy, voucher
 specimens were collected and verified by comparing with samples from the
 National Herbarium of the Royal Botanical Garden, Peradeniya. Crowns of
 each tagged tree was observed using Nikon® binoculars. Dieback status was
 recorded as described by a die-back scale (McLaughlin <em>et
 al</em>., 1992) with some modifications. Bark damage (both signs of
 browse and fraying) from sambar deer (<em>Rusa unicolor</em>)
 was visually estimated on all trees and shrubs (DBH≥3 cm) using a
 generated scale (See Table 1b). Seedlings &lt; 1 m
 in height were enumerated in two, 2 m × 2 m quadrats that were established
 in each overstory plot. Based on the characteristics of cotyledons and
 other morphological features, seedlings were identified to the species
 level where possible or at least to genus. A compass
 and clinometer was used to record the aspect and the slope of each plot.
 An altimeter was used to record altitude to the nearest meter. Canpy
 openness was calculated for each plot by taking hemispherical photographs
 using Nikon Coolpix 5400® digital camera fixed into the FC-E9 fisheye
 converter lens®. Photographs were captured from the plot center at 1.3 m
 above the ground surface during relatively uniform overcast skies. Soils
 were collected from at least three randomly located places within each
 plot for the first 15 cm of mineral top soil immediately beneath the
 organic horizon. Samples for each plot were mixed together to make a
 single composite sample. Soil samples were then air dried and sieved
 &lt; 2mm to remove stones. Soil pH was measured with
 H<sub>2</sub>O extraction. Cation exchange capacity (CEC),
 conductivity, phosphorus (P), magnesium (Mg), potassium (K), calcium (Ca)
 nitrogen (N), carbon (C), iron (Fe), Aluminum (Al) and a variety of
 micro-nutrients and metals (manganese (Mn); nickel (Ni); sodium (Na); lead
 (Pb)) were determined at Uva Wellassa University and the soil laboratory
 of the Coconut Research Institute of Sri Lanka. Available nutrients and
 organic carbon were extracted to 1 M (mol/L) ammonium acetate buffered to
 pH 7 by using Kjeldahl digest according to Walkley and Black
 (1934).
description: There are six excel data files:1. HPNP_DBH; 2. HPNP_Environmental
 data; 3. HPNP_Canpy openness data; 4. HPNP_species list; 5.
 HPNP_Vegetation data; and 6. HPNP_Mortality data See
 the meta data file for further information