PJB-2007-119
BROUSSONETIA PAPYRIFERA (L.) L'HÉR. EX VENT.: AN ENVIRONMENTAL CONSTRAINT ON THE HIMALAYAN FOOTHILLS VEGETATION
RIFFAT NASEEM MALIK1 AND SYED ZAHOOR HUSAIN2
Abstract
Biological invasion caused by the non-indigenous plant species have been considered as one of the major threat to the native vegetation and its diversity at local, regional and global level and its effect on native forest ecosystem is regarded as one of the most critical issues confronting environmental conservationists. This study addresses the influence of Broussonetia papyrifera on the native scrub forest at the Himalayan Foothills, Islamabad, Pakistan and its relationship with ecological gradients which are important in terms of its spatial distribution. Floristic species composition and environmental factors were measured from 77 plots from two 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 patterns and ordination analyses such as Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA) was used to establish the relationship with the underlying ecological gradients. CA divided the plots into three vegetation zones: a vegetation zone comprised of species of native scrub forest dominated by Acacia modesta; a transition vegetation zone where B. papyrifera was present either in scattered form amongst the scrub forest species or showed patchy distribution and invasive vegetation zone dominated by B. papyrifera. Man Whitney U-test was used to find out if vegetation zones identified by CA could be significantly different from each other based on the measured environmental factors. Factor Analysis (FA)/Principal Components Analysis (PCA) were used to identify set of environmental factors/predictors, which can best discriminate vegetation zones. FA/PCA (raw varimax rotated) on the environmental factors renders three varifactors with eigenvalues higher than 1.0 accounting for over 72% of total variance. Multivariate analyses indicated that the spatial distribution of B. papyrifera is related to edaphic factors such as the soil texture, organic matter and moisture contents. The distribution was insensitive to the topographic factors. The probable consequences of B. papyrifera invasion for future scrub forest composition and plant species diversity are also discussed. The findings of this research will be used in formulating scientifically sound management and conservation strategy for the forest ecosystems of the Margalla Hills National Park Islamabad.
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