Forest canopy restoration has indirect effects on litter decomposition and no effect on denitrification

Abstract

Forest restoration has potential to recover degraded ecosystem functions in disturbed environments. Decomposition and denitrification are two critical functions involved in forest nutrient cycling that are often compromised in degraded ecosystems. As forest canopy structure develops following initial plantings, it may indirectly impact ecosystem functions by altering abiotic conditions. It is likely, however, that there are other abiotic factors that affect decomposition and denitrification that are unrelated to forest canopy structure. Here, we aimed to determine whether forest canopy openness, topography, and soil sand content would affect litter decomposition and denitrification by regulating the microclimate, the herbaceous plant layer, soil chemistry, and soil moisture. Research occurred in restored native temperate rainforest patches in two New Zealand cities. Urban forests are an excellent context for measuring impact of canopy restoration on ecosystem properties such as microclimate due to the extreme swings in city conditions (e.g., urban heat island). Decomposition rates were determined using leaf litter bags and denitrification rates through denitrification enzyme activity assays. We used structural equation modeling to quantify the direct and indirect drivers of these ecosystem functions. Results indicated that decomposition rates were positively related to soil moisture, relative humidity, and herbaceous plant cover. Interestingly, forest canopy openness indirectly affected decomposition through counteracting forces, meaning greater canopy openness in young forests permitted dense herbaceous plant growth which enhanced decomposition, while less canopy openness in older forests enhanced humidity levels which increased decomposition. Denitrification was negatively related to soil pH and positively related to soil moisture, but these abiotic factors were unrelated to the forest canopy. Discovering drivers of ecosystem functions can improve approaches to the restoration of degraded ecosystems, especially in disturbed urban areas. Identifying counteracting effects on ecosystem functions could improve management by focusing restoration actions on specific drivers to elicit desired changes. Some ecosystem processes, like denitrification, are not affected by forest canopy restoration or management, but are instead driven by edaphic and landscape factors.

Seed bank analysis and species similarity in the Air Force Base of Pirassununga (São Paulo State, Brazil)

“…The largest number of pioneer individuals cataloged was in plots R, that is, the largest seed bank in this ecological group was cataloged at the edge of the fragment, which borders the Mogi Guaçu River. Forest areas adjacent to the watercourse have greater stratification of vegetation, allowing direct light to enter the area (Wallace et al 2018), providing subsidy for the germination of species of this ecological group (Pereira et al 2010;Correia & Martins 2015), which justifies the data obtained here. On the contrary, in plots I (farthest from the river), most nonpioneer species were cataloged.…”

Trophic selectivity of litter saprophages (Diplopoda, Isopoda) in natural forests in the steppe conditions

“…Накопичення маси листяного опаду в природних і штучних лісових екосистемах залежить не тільки від видового складу, але й від зімкнутості деревного ярусу та водно-теплового режиму під пологом лісу. Склад, вік та зімкнутість деревостану мають вирішальний вплив на масу листяного опаду, яка протягом життя одного покоління лісу змінюється в декілька разів (Martinovich et al, 1998;Brygadyrenko, 2016;Wallace et al, 2018). У листях всіх деревних порід, що опадають, у порівнянні із зеленим листям спостерігається збільшення загальної кількості всіх елементів, у підстилці відбувається подальше збільшення загальної суми елементів за рахунок підвищення вмісту кремнію, магнію, алюмінію, заліза, іноді кальцію, азоту, сірки, маргану й зменшення вмісту калію, хлору, натрію, іноді фосфору (Dubovskaya, 1984).…”

Climate, Soil, and Plant Controls on Early-Stage Litter Decomposition in Moso Bamboo Stands at a Regional Scale

“…In addition, canopy coverage can influence soil moisture conditions through rainfall interception or by decreasing the rate of evaporation from the soil through decreased sunlight (Prescott, 2002). Previous studies have shown that canopy structure is an important indirect driver of decomposition in regional and large-scale analyses (Joly et al, 2017;Wallace et al, 2018;Zhang et al, 2019). However, the overall contribution of stand structure and organic matter input can be masked by considering only their direct effects on litter decomposition (Wallace et al, 2018).…”

“…Previous studies have shown that canopy structure is an important indirect driver of decomposition in regional and large-scale analyses (Joly et al, 2017;Wallace et al, 2018;Zhang et al, 2019). However, the overall contribution of stand structure and organic matter input can be masked by considering only their direct effects on litter decomposition (Wallace et al, 2018). As several factors within the decomposition system often affect each other, evaluating their direct and indirect effects could help elucidate the underlying mechanisms that simultaneously control the decomposition process.…”