Impact of afforestation-induced grassland fragmentation on soil and microclimate in Groenvaly, South Africa

Afforestation is considered to be one of the leading land-use changes affecting ecosystem function and diversity. This study investigates the impact of pine afforestation on microclimate and soil in fragments of highly vulnerable Afromontane grassland at Groenvaly. Three major challenges for afforestation research are identified as (i) the range and intricacy of the impact of afforestation, (ii) differences in measurement and monitoring periods and (iii) a lack of focus on biomes adjacent to plantations. The approach here aimed to address these three areas. Air microclimate data were collected for 24 months within a plantation site, a control grassland site and a grassland fragment using three Davis Vantage Pro2 weather stations. Soil temperature data were logged on iButtonsTM for 18 months and soil samples from four seasons were analysed for moisture content, nitrogen (N), nitrate, ammonium, phosphorous (P), pH, sodium (Na), calcium (Ca), potassium (K), magnesium (Mg) and soil organic carbon (SOC). All data were statistically analysed at within-site, between-site, seasonal and mean scales and each analysis highlighted different conclusions. Results for the chemicals properties of the individual grassland fragments did not exhibit within-site variation except for K and P and between-site variation was only evident for N, nitrate, moisture and SOC. Solar irradiance was reduced in the fragments only during winter while SOC and P in the fragments only differed from the control grassland sites in summer and autumn respectively. Mean values for P, pH, Na, Ca, K, SOC and soil moisture within the fragments’ soil were between those of the control grassland and the plantation while N and Mg values were closer to the plantation than the control grassland. Mean values for air temperature, wind speed, solar irradiance and humidity within the fragment were closer to the control grassland than the plantation. Soil temperatures at 2cm in the fragments were similar to the control grassland, while temperatures at 10cm below the surface were lower than both the control grassland and the plantation sites in winter. Maximum air temperatures in the fragments were lowered in summer and raised in winter but minimum air temperatures were raised in the fragments across all seasons. Results of this study show that there are different impacts in different seasons while overall mean data indicate that the fragments’ soil is affected, and microclimate is unaffected, by the plantation. The impact of the change in soil and microclimate in grassland fragments requires more investigation to determine if grassland fragments are a suitable conservation strategy in pine plantations.