Plant Population Structure and Species Diversity Status at Two Disturbance Regimes Within Mixed Forests and Sal Forests of Gorakhpur, India

Abstract

This study of plant population structure and regeneration strategy of various woody species of mixed forests and sal forests compares the effect of disturbance on the status of species population especially with reference to ramet vs. genet. The less disturbed forests were more dominated by sprouters and ramet producing species as compared to highly disturbed ones. Analysis of variance among the number of species falling under different regeneration categories, i.e., OS (Regenerating only through seeds), FS (Facultative sprouters), OR (Obligate sprouter), RP (Ramet producers) and SR (Storage roots) showed significant differences (F 4, 3 = 5.31) at  p < 0.01.   A total of 166 species was recorded in less disturbed mixed forest and only 48 species in highly disturbed sal forest stand. At low disturbance, the trees like Mallotus philippensis, Holarrhena antidysenterica, Ficus glomerulata, Careya arborea and Pongamia pinnata  showed quite stable population structure. On the other hand, trees like Flacourtia indica, Carissa spinarum, Casearia tomentosa, Putranjiva roxburghii, Antidesma ghaesembilla and Cassia fistula, at high disturbance, were quite frequent as sprouts in mixed forests as compared to sal stands. In presence of recurrent disturbance, the common undertrees and lianas readily acquired shrubby habit. Most of the obligate sprouter and ramet producers formed several sub-populations or meta-populations (patronized by a single genet).  Population structure for tree species was stable in less disturbed forest stands having large number of individuals of lower girth classes. Except for sal, most of the tree species showed reverse J-shaped population structure. The ramet and genet density, along the age series, was positively correlated in sal forests and negatively correlated in mixed forests. Proportion of obligate sprouters was quite similar for less disturbed sal and mixed forests when the whole complex of a single genet was treated as only one individual. The diversity index (H) was always greater when a genet complex was treated as single individual than in case when each ramet, distinct at soil surface, were treated as separate individuals irrespective of the forest type and degree of disturbance. Further, this index was always greater for forest communities facing low disturbance. The similarity index values ranged between 0.46 to 0.84 for any two forest stands. The information on the impact of disturbance and heat stress of different degrees on the regeneration strategy and population structure of woody plants may be helpful for adapting conservation and diversity maintenance strategy within the regional tropical forest ecosystem.