Above‐ground net primary productivity in regenerating seasonally dry tropical forest: Contributions of rainfall, forest age and soil

Abstract

Identifying factors controlling forest productivity is critical to understanding forest‐climate change feedbacks, modelling vegetation dynamics and carbon finance schemes. However, little research has focused on productivity in regenerating tropical forests which are expanding in their fraction of global area have an order of magnitude larger carbon uptake rates relative to older forest. We examined above‐ground net primary productivity (ANPP) and its components (wood production and litterfall) over 10 years in forest plots that vary in successional age, soil characteristics and species composition using band dendrometers and litterfall traps in regenerating seasonally dry tropical forests in northwestern Costa Rica. We show that the components of ANPP are differentially driven by age and annual rainfall and that local soil variation is important. Total ANPP was explained by a combination of age, annual rainfall and soil variation. Wood production comprised 35% of ANPP on average across sites and years, and was explained by annual rainfall but not forest age. Conversely, litterfall increased with forest age and soil fertility yet was not affected by annual rainfall. In this region, edaphic variability is highly correlated with plant community composition. Thus, variation in ecosystem processes explained by soil may also be partially explained by species composition. These results suggest that future changes in annual rainfall can alter the secondary forest carbon sink, but this effect will be buffered by the litterfall flux which varies little among years. In determining the long‐term strength of the secondary forest carbon sink, both rainfall and forest age will be critical variables to track. We also conclude that detailed understanding of local site variation in soils and plant community may be required to accurately predict the impact of changing rainfall on forest carbon uptake. Synthesis. We show that in seasonally dry tropical forest, annual rainfall has a positive relationship with the growth of above‐ground woody tissues of trees and that droughts lead to significant reductions in above‐ground productivity. These results provide evidence for climate change—carbon cycle feedbacks in the seasonal tropics and highlight the value of longitudinal data on forest regeneration.

Throughfall exclusion and fertilization effects on tropical dry forest tree plantations, a large-scale experiment

“…Moreover, the increase in productivity as a function of fertilization depended on the presence of throughfall structures with non-drought showing the greatest increase (Figure 5, panel b). This confirms the colimitation of water availability and soil fertility on TDF productivity, where forests in fertile soils are more responsive to increases in rainfall than forests in infertile soils (Becknell et al, 2021). At the same time, our results are comparable to other throughfall exclusion experiments in which fine litter production was not affected by the drought treatment in a consistent manner (Nepstad et al, 2002;Brando et al, 2006;Schwendenmann et al, 2010), with a lot of its variation possibly linked to climatic variability (Brando et al, 2008).…”

“…Contrary to tropical rain forests, carbon cycling in TDFs is likely limited by both water and nutrient availability (Lugo and Murphy, 1986;Castro et al, 2018;Medvigy et al, 2019;Becknell et al, 2021). This colimitation of resources highlights the importance of quantifying the individual and interactive roles of these two https://doi.org/10.5194/bg-2022-203 Preprint.…”

Lianas, Ecosystems, and Global Change

“…The other twelve sites represented the more common diverse and majority deciduous SDTF in the lowlands of Santa Rosa and Palo Verde. These same plots have been described in several other studies of succession, ecosystem function, and drought disturbance (Powers and Peréz-Aviles, 2013;Schilling et al, 2016;Becknell et al, 2021).…”

Increasing Liana Abundance and Associated Reductions in Tree Growth in Secondary Seasonally Dry Tropical Forest

“…Our study was conducted in seasonally dry tropical forests (SDTF) of Guanacaste Province, Costa Rica. In 2008, 18 permanent research plots (0.1 ha each) were established in Área de Conservación Guanacaste, Sector Santa Rosa (Santa Rosa National Park) and Área de Conservación Arenal Tempisque (Palo Verde National Park; Becknell et al, 2021). Both of these parks are a patchwork of forests in different successional stages recovering from agricultural abandonment at different times over the past century (Powers et al, 2009).…”