Variation in Plant Functional Traits along Altitudinal Gradient and Land Use Types in Sagarmatha National Park and Buffer Zone, Nepal

Functional traits are predictors of plants in response to environmental stimuli. They represent specific functional adaptations to various environmental stresses. This study deals with the variation in plant functional traits along elevation gradient and land-use types in Sagarmatha National Park and Buffer Zone, Nepal. Two field investigations in April and September, 2011 were made to collect samples. Sampling was done from 2200 3800 m asl varying approx. 400 m. East and west facing aspects of each valley were chosen. In each aspect four land-use type categories including disturbed (cultivated land, exploited forest and meadow) and less disturbed natural forest were selected. A transect of 25 m long and 2.5 m wide was laid. Different eight traits of plants including lifeform, plant height, clonality, spinescence, leaf dry matter content, stem specific density, twig dry matter content and twig drying time were examined for 60 plant species belonging to 31 families, collected from 40 sampled plots. Nine different types of growth forms were recorded. Plant height of the investigated species ranged from 0.03 15 m. The stolon consisting species were dominant in exploited forests. Diversity of clonal species was more in meadow and non-clonal species were dominant in all the altitudes. Only eight species consisted of spines. In the disturbed land-use categories, we found high variation in a particular trait. Correlation analyses revealed the significant relationship (p < 0.01) among different traits. Herbs and shrubs were dominant at higher elevation and in disturbed land-use categories. Species from high altitude were mostly short basal herbs, while How to cite this paper: Shah, S., Shrestha, K.K. and Scheidegger, C. (2019) Variation in Plant Functional Traits along Altitudinal Gradient and Land Use Types in Sagarmatha National Park and Buffer Zone, Nepal. American Journal of Plant Sciences, 10, 595-614. https://doi.org/10.4236/ajps.2019.104043 Received: January 26, 2019 Accepted: April 23, 2019 Published: April 26, 2019 Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
Functional traits are those properties of an organism or a part of an organism which strongly influences fitness through their effects on growth, reproduction and survival [1]. They are biological attributes of a species that respond to the environmental conditions or processes in an ecosystem [2] [3]. Plant eco-physiological traits are clearly linked with biotic interactions involving plants, and ecosystem level properties and processes [4]. Traits are expressed in response to the influence of biotic and abiotic factors [1]. Plant functional trait (PFT) are therefore very useful in predicting changes in vegetation and biodiversity as an effect of environmental and disturbance changes and land-use shifts at regional and global scales [5]. The presence, abundance and diversity of PFT including morphological, eco-physiological and life history characteristics could be used for estimating particular components of biodiversity and together form a term called "functional indicators of biodiversity" [6]. Important questions can be answered effectively beginning with a thorough understanding of how and why key "functional" traits are related, and how these traits affect ecological outcomes such as where a species grows best and where it is most competitive [7]. Single traits cannot be the only basis for predicting vegetation changes. So, a functional analysis between key traits is necessary [8].

Species Traits and Elevation Gradient
Functional attributes including physiological, life history and ecological traits are directly related to variation in elevation that change with climatic factors as well as land area surface. Temperature, air pressure, and solar radiation are the climatic factors that vary with elevation influencing on the distribution of species [9]. Elevation, slope inclination and aspect exposition are the topographic factors playing an important role in determining the abundance of PFTs. Elevation is a complex combination of related climatic variables closely correlated with numerous other environmental properties like soil texture, nutrients, substrate stability and many more [10].

Species Traits and Land-Use Types
Land-use change includes modified and fragmented habitats, which are more  [11], land-use changes involve two main impacts on the biosphere: first, the conversion (i.e. natural habitats altered for human use) and second, intensification (e.g. greater intensity and frequency of disturbance, increased use of external inputs). Habitat loss and fragmentation are the major factors which cause biodiversity loss by decreasing suitable habitats of species and thereby forcing the species to extinction [12].
Land conversion for agricultural purposes, population growth, socio-economic conditions drive land cover changes.
The present study deals with the variation in plant functional traits along the different land-use types and altitudinal gradient in Sagarmatha National Park and Buffer Zone. Further, the study aims to know the major traits the dominant plant species present in the study area; to assess variation in the traits of dominant species among major land use types; and to identify the plant species best suited for specific altitude and land-use type.

Study Area
Sagarmatha National Park (SNP) is located in the north-eastern part of Nepal in  Meadows are open grasslands with less than 20% tree coverage. Cultivated lands are intensively managed, fertilized, sometimes irrigated and yearly ploughed areas.
For Laboratory techniques, the protocol for standardized and easy measurement of plant functional traits worldwide [15] was followed. Functional traits were either directly measured in the forest, at the research station in the evening after collecting, in the laboratory or deduced later from measured traits. were assigned as Non-clonal, clonal aboveground and clonal belowground.

2) Spinescence:
A spine is usually a pointed modified leaf, leaf part or stipule. The type, size and density of spines, thorns and/or prickles play an obvious role in antiherbivore defense.

3) Leaf traits:
Leaf dry matter content (LDMC) is an estimate for plant tissue density. Fresh weight of each leaf was taken and tagged. And dried in an oven at 60˚C for 72 hrs and reweighted for dry mass. It was calculated by dividing Oven dry wt. of

Statistical Analyses
For analyses of quantitative traits, the overall data was divided into three growth forms (i.e. herb, shrub and tree). Each trait was then tested to find significant difference with land-use types and altitude for three growth forms. After a normality test (Shapiro Wilk), traits such as plant height, LDMC and SSD of herbs and shrubs were square root transformed to meet the normality assumption while the remaining data was considered normal and left untransformed.
One-way Analysis of Variance (ANOVA) was used to find the variability

Results
Sixty

Growth form along Land-Use Type and Altitude
Nine different types of growth forms were recorded from the study site.

Plant Height
Plant height of the investigated species ranged from 0.03 -15 m. Among the herb and shrub species, height showed highly significant difference with altitude.
Height of the tree species showed significant difference with land-use type and altitude (Table 1). From post hoc analysis, significant difference was observed between meadow and natural forest (p < 0.01). Outlier was observed at 3000 m showing the highest height of herb. Herb height showed the lowest value at 3800 m with outlier (Figure 3(a)). Shrub height showed the lowest value at 2600 m and the highest value at 3000 m and 3800 m (Figure 3(b)). Taller tree was present at natural forest and tree with less height were observed in meadows (Figure 3(c)).

Clonality
The stolon consisting species such as Anaphalis busua, Androsacae sarmentosa, Fragaria nubicola, and F. indica were dominant in exploited forest. Diversity of clonal species was more in meadow (Figure 4(a)). Non-clonal species were dominant in all the altitudes. At 3400 m, stolon, bulb and adventitious bud forming species were dominant. At 2200 m, non-clonal species were most dominant followed by stolon and vegetative bud forming species (Figure 4(b)). Species with vegetative buds were Arundinaria maling, Impatiens urticifolia and Rosa sericea; and others clonal belowground were Commelina maculata, Iris clarkei, Malaxis cylindristachya, Senecio diversifolius and Rumex nepalensis.

Spinescence
Among the investigated species, only eight consisted of spines. The species with longer spines were dominant mostly at the meadows ( Figure 5(a)). In comparison to lower altitude, spine consisting species decreased at highest altitude ( Figure   5(b)). Spinescence was observed in Berberis aristata, Cotoneaster microphyllus, Dipsacus inermis, Rosa sericea, and Zanthoxylum armatum, occurring at the meadow whereas Rubus ellipticus and Quercus semecarpifolia were occurred at the natural forests.

Leaf Dry Matter Content (LDMC)
The highest LDMC was recorded in Rhododendron arboreum (736.360 mg/g) followed by Pinus wallichiana, Quercus semecarpifolia and Abies spectabilis American Journal of Plant Sciences   observed in natural forest (Figure 6(a)). Highest value of shrub LDMC was observed at 2600 m with outliers and the lowest value at 3400 m ( Figure 6(b)).
Highest value of herb LDMC was observed at 3400 m and lowest at 2200 m with outliers ( Figure 6(c)).

Stem Specific Density (SSD)
Altogether 27 trees and shrub species were collected and among them stem specific density of 15 shrubs were measured. The highest value of SSD was recorded in Rhododendron lepidotum (9.35 mg/mm 3 ) while the lowest value was observed in Anaphalis busua (0.19 mg/mm 3 ). Stem specific density for herbs showed significant difference with land-use type (Table 3). More difference was seen in between exploited forest and cultivated land (p < 0.001) as well as natural forest and exploited forest (p < 0.001) from post hoc analysis. Similar result was observed from boxplot showing lowest value of SSD at exploited and natural forest with presence of outliers and highest value at natural forest ( Figure 7).

Twig Dry Matter Content (TDMC)
Twig dry matter content was calculated for tree and shrubs. The highest value of TDMC was 875 mg/gm in Gaultheria fragrantissima, while the lowest was 251.57 mg/gm in Abies spectabilis. TDMC of shrub species was found significant with American Journal of Plant Sciences  land-use and altitude (Table 4). More difference was found between meadow and exploited forest. Similarly, twig dry matter content for trees showed significant difference with land-use type (Table 4). Outlier was present showing the highest value of tree TDMC at the natural forest and lowest mean value was observed at meadow (Figure 8).

Correlation between Traits
Spearman's Correlation Analysis revealed significant relationships among a number of traits (Table 5)

Growth form along Land-Use Type and Altitude
The result achieved shows variation in different traits along altitude as well as land-use types. Among the various growth forms, tree was dominant in natural forest while different categories of herbs were less dominant. This might be because herbs do not grow well under canopy due to difficulty in light intensity much reaching to the ground [16] [17]. Shrubs and erect leafy were found to be dominant at meadow and exploited forest which may be an adaptation to grazing. The height and positioning of the foliage may be both adaptations and responses to grazing by different herbivores [15]. Along the altitudinal gradient, tree and erect leafy herb species decreased in number whereas other herb and dwarf shrub species were found to be dominant along higher altitude. Similar result of increment in herbs at higher altitudes was found by Wana and Beierkuhnlein (2009) [18] in southwest Ethiopian highlands. The distinction of growth forms informs us about the specific adaptations to environmental conditions such as climate and wind [19] [20], solar energy partitioning [21], water use efficiency [22] and resource partitioning [23] in the ecosystem.

Plant Height
Herb and shrub height showed a significant difference with the altitude. A study by Bhattarai and Vetaas (2003) [24] in the Himalayan range indicates that woody species display a uni-modal pattern of diversity while herbaceous species do not show any relationship to altitude which is different from the result of present study. The reason behind it could possibly be the effect of an incomplete gradient length of the study ranging of 2200 -3800 m asl. Plant height in case of shrubs showed significant difference between natural forest and exploited forest as well as between meadow and exploited forest. Significant difference was observed with land-use types mainly between meadow and natural forest in case of tree height. It may be due to the presence of very few trees of short stature in meadow, and low disturbance such as grazing, mowing, firing, etc in natural forest in comparison to the meadow. Short plants were found most dominant in the meadows because they have higher quality and growth rate, and are more tolerant to herbivory than taller plants [25].

Clonality
Rhizomes and other clonal species were dominant in high altitudes for adaptation to chilling and grazing, similar to the finding of Wana and Beierkuhnlein (2009) [18]. Increase of clonal species in the colder sites was also found by [26] in East Ladakh, Western Himalayas. Diversity of clonal species was high in the meadows as they grow well in harsher environment [10] and nutrient-poor conditions [27]. In response to severe environments, plants either develop adaptations that enable protection of renewing buds or spread the risk of bud mortality by multiplying buds through clonal growth [28]. Clonal behavior may also be an effective means of short distance spread under circumstances of poor seed dispersal or seedling recruitment [15].

Spinescence
Plant species with spines were mostly shrubs and were dominant at the meadows as disturbance level is high due to grazing, trampling, etc. Another reason may be defense mechanism to protect them from herbivores. They can play an additional role in reducing heat or drought stress [15] by dissipating heat loading on the surface of the leaves and stems or absorbing solar radiation, in addition to their role as a mechanical deterrence against vertebrate herbivory [29]. Spines were found to be more abundant in lower altitudinal ranges in response to drought and grazing which is similar to the findings Wana and Beierkuhnlein (2009) [18] and Dalacho (2009) [20].

Leaf Dry Matter Content (LDMC)
Leaf dry matter content of tree varied significantly with land-use type and altitude. Significant differences were found between meadow and cultivated land as well as natural forest and cultivated land. In the natural forest, trees with high LDMC were present while in the cultivated and meadow more herbs with low LDMC were present. Species with low LDMC are associated with highly disturbed environments, intensive land-use and colder sites [30]. At higher altitude, fast-growing and shorter species also have low LDMC and lower toughness [31].

Stem Specific Density (SSD)
Stem specific density for herbs showed significant difference with land-use type.
More difference was observed between exploited forest and cultivated (p < 0.001) as well as natural forest and exploited (p < 0.001). Trees present in the natural forest had more stem specific density than the ones present in the ex-

Twig Dry Matter Content (TDMC)
Twig dry matter content of tree differed significantly with altitude and land-use type. High significance was between meadow and exploited forest. Low TDMC may be positively correlated with high potential relative growth rate. Twig drying time was positively correlated to twig dry matter content in case of trees.
Twigs with high dry matter are expected to dry out relatively quickly during the dry season in fire-prone regions [15]. Highest TDMC value in this study was recorded in Gaultheria fragrantissima which indicates that it has stronger

Conclusions
Both quantitative as well as qualitative traits show a great deal of variation among different environmental gradients (altitude and land-use types). Four different land-use types exhibited a significant relationship with traits. Plant traits were found to vary significantly between disturbed (i.e. cultivated land, meadow and exploited forest) and less disturbed (natural forest). Some contrasting results found in this study pave the way towards a better understanding of how species cope with varying habitat conditions. Both natural as well as anthropogenic disturbances are responsible for the shift of PFTs. The main disturbances were grazing, fire, trampling, litter collection, etc. Grazing favors species that are short-lived, herbaceous growth form and clonal. The study site being a Himalayan region, especially in the higher altitude a more harsher environment persist due to cold climate as well as other disturbance factors which cause less diversity of growth forms and more variation in traits. The variation in the abundance of certain plant functional traits at a particular habitat informs us about the strength of the dominant environmental constraint such as climate, resource availability and disturbance level in that ecosystem. Growth forms: T = Tree; S = Shrub; DS = Dwarf Shrub; H = Herb. Life forms: Th = Therophyte; He = Hemicryptophyte; P = Phanerophyte; C = Chameophyte; G = Geophyte.