Can intercropping with native trees enhance structural stability in young rubber (Hevea brasiliensis) agroforestry system?

Rubber (Hevea brasiliensis Müll. Arg.) trees have been commercialized for several decades in Asia, notably in China and form a typical plantation ecosystem in tropical areas. Although rubber trees have been planted successfully as commercial crops in many places, adapting rubber plantations to sub-optimal environments remains a challenge. Especially in young rubber plantations, populations are often not stable or sustainable because tree breakage and death are common due to frequent strong storms. Intercropping to optimize group structure has been proposed as a method to improve the overall stability of rubber plantations. The objective of our study is to explore the wind resistance and growth of individual rubber trees in an intercropped system that utilizes native tree species Michelia macclurei and Mytilaria laosensis. The density of rubber trees was the same in the monoculture and the intercrop, with additional native trees added in the intercrop. The effects of the wind resistance and growth of the system to three different planting patterns namely, the monoculture of Hevea brasiliensis, Hevea brasiliensis intercropping with Michelia macclurei, and Hevea brasiliensis intercropping with Mytilaria laosensis were analyzed using observation data from the field plots. The results show that both the maximum and average wind speeds were lower in intercropped rubber plantations than in monoculture rubber plantations, the average maximum wind speeds were lower in Hevea-Michelia and Hevea-Mytilaria intercropping systems than in the Hevea monocrop system by 8.4% and 19.6%, respectively. The average wind speeds were also lower in Hevea-Michelia and Hevea-Mytilaria intercropping systems than in the Hevea monocrop system, with daily average wind speeds 21.2% and 36.0% lower, respectively. The proportion of rubber trees showing Grade 6 wind damage in monoculture, intercropping with Michelia and intercropping with Mytilaria were 9.5%, 2.3% and 1.9%, respectively. There was a competition between the intercropping Michelia / macclurei and Hevea in soil nutrient absorption and utilization, and the competition of soil nutrient further decreased the height growth and formed small crown area opposing wind loading. This indicates that the pattern of intercropping rubber with native tree species may reduce wind speed and average wind speed in intercropped rubber systems, thereby reducing the wind damage on rubber trees and improving their health. The biomass of intercropping with Michelia and intercropping with Mytilaria systems is significantly higher than Hevea monocrop system. This result shows that the intercropping patterns of Hevea-Michelia and Hevea-Mytilaria enhance the total productivity. This indicates that intercropping rubber with native trees may construct an environment that buffers wind effects and benefits tree growth to the extent that it could also improve ecosystem stability in rubber plantations. Healthier and stronger rubber trees may lead to a more sustainable and possibly increased yield of rubber from plantations in the future. These results also enrich tropical protection science and provide a valuable reference for the sustainable management of agricultural system or other plantation.