Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Resumen:

Litterfall is the most easily and most frequently measured part of net primary productivity (NPP) of forests. It has been shown that litterfall accounts for about one third of total NPP and thus serves as a proxy for the total productivity of forests. Moreover, litterfall carries nutrients from the forest canopy to the soil and therefore is also a major vector of nutrient cycling. I reviewed the published literature about litterfall rates and chemical properties in Andean forests and found reports from 44 forest sites, which I evaluated together with unpublished data from 12 sites in a lower montane forest in Ecuador. I found many more reports from tropical (52 sites) than from temperate Andean forests (4 sites). In the humid tropical north Andes, litterfall showed a hump-shaped elevational distribution. It increased from premontane to lower montane forests and decreased to upper montane forests. The tropical lower montane forest had a similar productivity than tropical lowland forests. The litterfall of the temperate southern beech forests was similar to that of the tropical upper montane forests. The C/N and C/P ratios of litterfall decreased with increasing elevation, while the N/P ratios were not correlated with elevation. This illustrates that the forests become increasingly nutrient efficient with increasing elevation, while there is no indication of a general change in the kind of nutrient limitation. There was a negative correlation between litterfall and soil organic layer thickness (r = −0.61, p < 0.001) illustrating that the organic matter input via litterfall is a less important driver of organic matter accumulation on top of the mineral soil than other, mainly abiotic properties including temperature and soil waterlogging. My evaluation suggests that there are systematic relationships between abiotic conditions and litterfall, which could be used to predict litterfall in the Andes. However, the data coverage particularly of the southern Andes (Bolivia, Chile, Argentina), the Andean dry forests, and the widespread tree plantations is poor. The observed elevational influence on litterfall in the humid tropical Andes suggests that the forest productivity will likely respond to climate change driving the vegetation belts to higher elevation with an unknown overall effect on C sequestration of these forests.

Resumen:

We quantified the changes in macronutrient storages of the soil in a remote Andean tropical montane rain forest on the rim of the Amazon basin from 1998 to 2013. In the studied 15 years, the N, P, and S fluxes in throughfall+stemflow increased significantly, while those of Ca decreased and of Mg and K remained unchanged. The main reasons for increasing nutrient inputs were Amazonian forest fires. Ca inputs decreased because of a particularly strong Sahara dust deposition event in 1999/2000. On average of the 15 budgeted years, P and K accumulated in the organic layer at a rate doubling their current storages in 197 and 27 years, respectively. The other macronutrients were on average leached from the organic layer, depleting it in 38 (Mg) to 281 years (N). Nutrient leaching was likely favored by enhanced mineralization driven by climate warming. In the upper 30 cm of the mineral soil, all macronutrients accumulated at rates doubling their storages in 57 (Ca) to 601 years (P). Our results demonstrate that the current environmental change increased the nutrient supply of the studied ecosystem. Increased nutrient supply might shift the ecosystem to a new state and change the chemistry of headwater streams.