Assessing the Impact of Native and Plantation Forests on Catchment Water Yield in Tropical Regions: A meta-analysis

Afforestation and reforestation using native and exotic tree species in degraded land are considered to be one of the popular suggestive measures for carbon storage and potential flood magnitude reduction. However, oftentimes, it ignores quantitative evaluation of their impacts on catchment hydrology, specially in water-limited regions with consequences for downstream users. Though the science of the effect of plantations on catchment water yield is well established and understood, understanding changes in water yield or stream flow pattern following plantation activities is crucial for developing plans for water resources management. This review is an attempt to address this issue by comparing the effect of native forest and plantation forest on the water yield of forested catchments conducted on tropical climate condition. A rigorous database developed by Hua et al. (2022) was used for this review. This database considered catchment studies comprising native and plantation forest from 1960-2021. Primary forest, secondary forest and generic forests were considered as “native” forest whereas mixed-plantation, mono-plantation and abandoned plantation were considered as “plantation” forest. The amount of water discharge or draining annually from forested catchments/plots, expressed as % of rainfall is considered as water yield of a catchment or plot. The results revealed that native forest water yield is 4% higher (37±19%) when it was compared with plantations (33±20%). In case of various types of plantations, catchment with mono-plantation has yielded more water (35%) compared to mixed (26%) and abandoned plantations (10%). In contrast, among native forest types, secondary forest has yielded more water (41%) compared to generic native (38%) and primary forest (34%). Native forests age and plantation forest age does not have significant effect on water yield. When native forest water yield was compared with plantation it was found that water yield has decreased up to of 2.30%. Both mono-plantation and mixed plantation methods showed a negative log response ratio indicates water yield decreased because of plantation intervention. Temperature and rainfall doesn’t have significant impact on both native and plantation forest water yield. Overall, this review suggests that native forests are much more productive in terms of catchment water yield compared to catchments with plantations. Therefore, policy makers need to take more measures to protect mature native forests from human disturbances.