STUDY OF SEASONAL BIOMASS PRODUCTIVITY AND NUTRITIONAL QUALITY OF MAJOR FORAGE SPECIES IN SUBTROPICAL SUB HUMID RANGELANDS OF DISTRICT CHAKWAL

Abstract

Forage biomass is generally the most important resource for animal production in scrubby ecosystems that is rapidly being depleted due to heavy grazing over vast areas of rangelands. Overoptimistic stocking rates in Chakwal have been attributed to the leading cause of rangeland degradation. Moreover, uneven distribution of animal impact had been due to differentially preferred and quality areas in the range landscape. Deterioration in range conditions continues due to over stocking while vegetative cover and species diversity is decreasing. It is evident that successful range management and improvement requires knowledge of forage calendar, nutritional value of range plants species (both qualitative and quantitative) and forage palatability and preferences of the flock in the region. A comprehensive study was conducted to determinate the comparative nutrient value of available forage resources during the various seasons and the ability of these resources to meet the animal requirements for optimum livestock production. In the first part of study, relative species composition and seasonal biomass productivity of major forage species in three representative rangelands of District Chakwal were assessed during 2004-05. Sixty nine plant species, all native, distributed among 29 families, were recorded on the vegetation transects in four sites of each rangeland. These included 20 species of grasses, 12 of trees, 31 of shrubs and 6 of undershrubs and herbs. Plant species composition studied in three consecutive seasons indicated that average density of plants was 33165, 15848 and 17442 plants/ha in Nurpur Reserved Forest (RF), Mari Dharnal RF and Ara RF respectively. Flat areas (17971 plants/ha) and sloping areas (15763 plants/ha) were similar to each other but different as compared to nullah i beds/channels (7858 plants/ha) and exposed sandstone areas (2675 plants/ha) in Nurpur RF. In Mari Dharnal RF, flat areas (7204 plants/ha), sloping areas (6666 plants/ha) and nullah beds/channels (5835 plants/ha) were similar to each other but different as compared to exposed sandstone areas (1426 plants/ha). In Ara RF, sloping areas (8386 plants/ha) were different as compared to flat areas (6644 plants/ha) and nullah beds/channels (6680 plants/ha), which were similar to each other but different from exposed sandstone areas (1546 plants/ha). In Nurpur RF and Ara RF respectively, shrubs were greater (20309, 9694 plants/ha) as compared to grasses (12208, 7610 plants/ha) and trees (648, 138 plants/ha) while grasses (9922 plants/ha) were more as compared to trees (116 plants/ha) and shrubs (5810 plants/ha) in Mari Dharnal RF. Grass composition increased as the season advanced from fall to summer. Plant frequency varied among grasses, trees and shrubs across the three growth seasons. In winter in all the three rangelands, shrubs contributed maximum to the vegetation cover followed by trees while grasses contributed the least. In Nurpur Reserved Forest, grass cover was 2.11 and 29.52%, tree cover was 1.18 and 1.17%, and shrub cover was 1.86 and 1.87% in spring and summer 2005 respectively. In Mari Dharnal RF, grass cover was 2.34 and 38.592%, tree cover was 1.32 and 1.82%, and shrub cover was 1.75 and 0.72 % in spring and summer 2005 respectively. In Ara RF, grass cover was 3.77 and 35.68%, tree cover was 1.82 and 2.29%, and shrub cover was 1.44 and 2.2 % in spring and summer 2005 respectively. Based on the importance value (IV) of plant species, vegetation communities for each site of the rangelands across three growth seasons in Chakwal were identified, characterized and established. In all, 36 vegetation communities were recognized and described. Above ground dry forage production of grasses, trees and shrubs was recorded across the three grazing seasons under grazing field conditions. In winter 2004, maximum above ground dry forage production was recorded from shrubs and trees and the lowest from grasses in all the three rangelands. The average forage production recorded from all range sites was greater in Ara RF (168.77, 894.83, 2222.79 kg/ha) followed by Mari Dharnal RF (150.97, 368.38, 1340.86 kg/ha) and the lowest was in Nurpur RF (90.34, 355.15, 1367.23 kg/ha) for winter 2004, spring and summer 2005 respectively. Maximum forage production was recorded in flat areas followed by sloping areas and nullah beds/channels and the lowest was recorded from exposed sandstone areas in all the rangelands across the three growing seasons. Summer 2005 season was the most productive season followed by spring 2005 season whereas winter 2004 season was the least productive. The average carrying capacity (CC) differed from (107.60, 64.39, 57.26 ha/AU/Y) in winter, (27.37, 26.39, 11.96 ha/AU/Y) in spring to (7.11, 7.25, 4.38 ha/AU/Y) in summer 2005 in Nurpur RF, Mari Dharnal RF and Ara RF respectively. Among the range sites, flat areas showed greater potential in terms of carrying capacity to support animal production followed by sloping areas and nullah beds/channels whereas exposed sandstone areas exhibited lowest potential across the three seasons in all rangelands. Relative preference of range grasses and other forages (graze-able and browse- able vegetation) by grazing goats and sheep was analyzed for their preference of selection and grazing. Goats were found to prefer more browse (trees and shrubs) as compared to grasses (P < 0.01). For goats, the overall (highest to least) order of iii preference was trees>shrubs>grasses. Sheep were found to prefer more grasses as compared to shrubs and trees (P < 0.01) and the overall rank order of preference for sheep was grasses>shrub>trees (P < 0.01). The data analysis indicated that plants preferences and forage selection shifted with the progress of season from spring to summer. The preference for herbaceous species increased in spring and summer and number of bites also increased whereas the preference of browse declined in the same grazing periods with the availability of grasses. The nutritive value of grasses, shrub and trees at 3 phonological stages, revealed that mean values of dry matter (DM) percent in all plant species varied significantly from each other at three phonological stages of growth. Crude protein (CP) percent varied from 3.8 to 9.6 in grasses and from 5.36 to 24.47 in trees and shrub. Minimum CP% was observed in winter when the grasses reached maturity and maximum CP% was observed in the current growth material in spring when grasses were in vegetative stage. In trees and shrub, minimum CP% was observed in summer and maximum CP% in spring. The overall effect of three growth stages on the CP% content was highly significant. Neutral Detergent Fiber (NDF) varied from 24.80 to 44.47% in grasses and from 16.90 to 82.20% in trees and shrub. Acid Detergent Fiber (ADF) varied from 9.5 to 22.3% in grasses and from 11.8 to 50.1% in trees and shrub. Minimum ADF among plants was observed in winter and maximum ADF in summer. In winter, when grasses were at maturity stage, forage (herbage and browse) quality was fair. In spring and summer 2005, forage quality of tested grasses and browse were highly nutritious and profoundly supportive to livestock production.