Broussonetia papyrifera (L.) L'Hér. ex vent.: an environmental constraint on the Himalayan Foothills vegetation.
The effects of B. papyrifera on the native scrub forest at the Himalayan Foothills, Islamabad, Pakistan, and its relationship with ecological gradients that are important in terms of its spatial distribution were studied. Field work was carried out in April, May and June 2005. Floristic species composition and environmental factors were measured from 77 plots from 2 sites of the scrub forest at the lower elevation of Margalla Hills National Park Islamabad. Agglomerative hierarchical cluster analysis (CA) was used for species assemblage pattern and ordination analyses. Detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used to establish the relationship with the underlying ecological gradients. CA divided the plots into 3 vegetation zones: a vegetation zone consisting of species in the native scrub forest dominated by Acacia modesta; a transition vegetation zone where B. papyrifera was present either in scattered form among the scrub forest species or in a patchy distribution; and an invasive vegetation zone dominated by B. papyrifera. Man Whitney U-test was used to determine if the vegetation zones identified by CA could be significantly different from each other based on the measured environmental factors. Factor analysis (FA)/principal component analysis (PCA) were used to identify a set of environmental factors/predictors that can best discriminate vegetation zones. FA/PCA (raw varimax rotated) on the environmental factors resulted in 3 varifactors with eigenvalues greater than 1.0, accounting for more than 72% of the total variance. Multivariate analyses indicated that the spatial distribution of B. papyrifera is related to edaphic factors, such as soil texture, and organic matter and moisture contents. The distribution was not sensitive to the topographic factors. The probable consequences of B. papyrifera invasion for future scrub forest composition and plant species diversity are discussed.