Effects of climate change and forest management on wood mass loss in southeastern US loblolly pine forests
Wood debris is an important C pool in forest ecosystems. Understanding the response of wood decomposition to climate change is necessary for studying forest ecosystem and soil carbon cycling. The productivity of managed pine forests in the southeastern US has been improved through nutrient management. Although uncertainty exists, climate change may drive a reduction of rainfall of 10%-30% by 2080 for the region. In managed forests that undergo periodic harvesting, the forest can become a source of C when decomposer activity increases C loss from residual wood. Two questions motivated this research. How does reduced precipitation, interacting with fertilization, affect wood decomposition in managed pine forests? And how does wood decomposition vary across climatic regions and within forest ecosystems? To address these questions, we analyzed the mass loss of southern pine wood substrates under a factorial combination of two treatments: soil moisture (30% throughfall removal) and nutrient addition (224 kg/ha N, 64 kg/ha P and 67 kg/ha K). The experiment sites were located in Oklahoma (OK), Florida (FL), Georgia (GA), and Virginal (VA). To assess the response of decomposition to treatments and spatial variation, common substrates (southern pine wood sticks with the dimension of 6 × 1.8 × 0.6 cm) were placed in 16 plots in each site in August of 2013 and collected after 0.5, 1 and 1.5 year. Four trees were randomly selected in each plot and the substrates were set close, middle and far from the tree.
We analyzed wood decomposition in response to fertilization, rainout, location, time, and sites. Our early results showed that higher woody mass loss in FL compared to OK, GA and VA (P<0.001), which maybe explained by higher temperature and precipitation. In FL and OK, wood mass loss by Macro-invertebrates was much higher compared to GA and VA. Interestingly, we found fertilization reduced mass loss of wood with macro-invertebrates’ tunnels in FL (P=0.009) but increased mass loss of those wood in OK (P<0.001). Our data indicated that in OK future drought would cause slower substrate decomposition but higher substrate mass loss by fertilization. In FL, fertilization may cause lower substrate mass loss. Decomposition also showed a spatial pattern where wood substrate close to the tree decayed faster than wood far from the tree both in OK (P<0.001) and FL (P<0.001). High spatial variability exists among or within sites, indicating the complexity of wood decomposition at both macro and micro scales.