Abstract
Abstract. Evaluating the interactions of woody plants has been a major research topic of ecological investigations in arid ecosystems. Plant-plant interactions can shift from positive (facilitation) to negative (competition) depending on levels of environmental stress and determine the spatial pattern of plants. The spatial distribution analysis of plants via different summary statistics can reveal the interactions of plants and how they influence one another. An aggregated distribution indicates facilitative interactions among plants, while dispersion of species reflects their competition for scarce resources. This study was aimed to explore the intraspecific interactions of eshnan (Seidlitzia rosmarinus) shrubs in arid lands, central Iran, using different summary statistics (i.e., pair correlation function g(r), O-ring function O(r), nearest neighbour distribution function D(r), spherical contact distribution function Hs(r)). The observed pattern of shrubs showed significant spatial heterogeneity as compared to inhomogeneous Poisson process (α=0.05). The results of g(r) and O(r) revealed the significant aggregation of eshnan shrubs up to scale of 3 m (α=0.05). The results of D(r) and Hs(r) also showed that maximum distance to nearest shrub was 6 m and the distribution of the sizes of gaps was significantly different from random distribution up to this spatial scale. In general, it was concluded that there were positive interactions between eshnan shrubs at small scales and they were aggregated due to their intraspecific facilitation effects in the study area.
Highlights
Arid and semi-arid ecosystems seem to be very simple biotic communities, while there are complicated ecological interactions between woody plants with each other and with their environment
A 160 m × 160 m plot with density of 386.3 shrub per hectare and mean elevation of 1549.2± 0.44 m above sea level was selected in Qehi protected area and all 989 eshnan shrubs were precisely mapped by Trimble R8 differential global positioning system (DGPS)
The spatial distribution of eshnan shrubs was compared to the null model of homogeneous Poisson process which has been increasingly applied in the literature (e.g., Getzin et al, 2008; Cisz et al, 2013; Nguyen et al, 2014) and Kolmogorov-Smirnov nonparametric goodness-of-fit test was used to analyse the significance of differences
Summary
Arid and semi-arid ecosystems seem to be very simple biotic communities, while there are complicated ecological interactions between woody plants with each other and with their environment Investigation of these complicated ecological interactions that can be performed by spatial pattern analysis of plants has an important role in understanding the structure of these ecosystems (Lopez et al, 2010; Navarro-Cerrillo et al, 2013). The spatial distribution modeling of plants via different summary statistics is very useful to recognize horizontal structure of plant communities and understand how they are related to each other The results of this analysis can provide information in little known regions and for the management objectives of other regions (Wiegand and Moloney, 2004; Lopez et al, 2010; Carrer et al, 2013). A majority of studies have been focused on the characteristics of this important species and impacts of environmental factors on its growth (Kurkova et al, 2002; Jafari et al, 2004; Abdollahi et al, 2006; Baghestani Maybodi and Zare, 2009; Zare Chahouki et al, 2010), its effects on soil and sand dunes stabilization (Amiraslani and Dragovich, 2011; Mahdavi Ardakani et al, 2011; Mahmoodi et al, 2013), as well as anatomical, physical and chemical properties of its wood (Safdari, 2012)
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