Does replacement of a Pinus taeda L. man-made plantation with a Carpinus betulus L. natural stand alter the throughfall nutrient inputs and pH and EC values?

A key effect of reforestation is its impact on the hydrological cycle which can change the quantity and quality of rainfall. The aim of this research was to compare the nutrient elements, pH and EC of rainfall compared to TF of a natural stand of Carpinus betulus L. and a man-made Pinus taeda L. plantation located in the western Hyrcanian region, Astara, north of Iran.

Rainfall and throughfall samplings were done using nine and 18 man-made plastic collectors installed randomly under the canopy and open space of each stands, respectively,. The amounts of EC and pH were measured using EC meter and pH meter. The nutrient amounts of calcium (Ca++) and magnesium (Mg++) were measured by the Titration method and potassium (K+) and sodium (Na+) elements were measured by Flame photometer for three rainfall events during the summer season, 2022. Comparison of means was done by one-way ANOVA and LSD at 95% confidence level.

pH in TF of C. betulus stand was 7 and 6.8 and P. taeda 6.4 and 6.6 in two events which were significantly different from those measured for rainfall (6.6 and 7.1). EC of TF of C. betulus and P. taeda increased by 126.4 percent and 113.2 percent, respectively. The amounts of Ca++ in the TF of the C. betulus stand for three events were 24, 19.6 and 12.5 ppm (mean: 18.7 ppm), respectively, while for corresponding rainfall were measured 11.6, 6.7 and 6.2 (mean: 28.8 ppm), respectively, statically different for all events. Mg++ showed the least change compared to other nutrients elements. The K+ in TF of C. betulus in July rainfall (21.2 ppm) had increased by 11.9 ppm compared to rain (9.3 ppm). The amount of Na+ in TF of man-made P. taeda plantation in the first event (15.6) showed a significant difference with that of Na+ in rainfall (9.3 ppm).

When rainfall hits the canopy of the C. betulus natural stand, in 85 to 90% of the samples of TF, nutrients as well as the pH and EC were significantly changed compared to rainfall. However, this percentage of significant change was 70 to 75% for P. taeda man-mad plantation. In this way, replacement of C. betulus with P. taeda altered the nutrients elements of TF as well as pH and EC by 55%. Understanding the change in the amount of nutrients inputs to the forest ecosystems via TF is essential for choosing the appropriate species for the reforestation of degraded forests since planting new species in an area, in addition to changing the amount of rain that reaches the forest floor, it changes the quality of rainfall.