Dynamics of tree stems and biomass in old‐growth and secondary forests along gradients in liana dominance, elevation and soil

• Published in: The Journal of ecology Vol. 112; no. 7; pp. 1638 - 1654
• Main Authors: Ngute, Alain Senghor K., Pfeifer, Marion, Schoeman, David S., Gereau, Roy E., Mnendendo, Hamidu R., Lyatuu, Herman M., Seki, Hamidu A., Shirima, Deo D., Marshall, Andrew R.
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.07.2024
• Subjects: Biomass; carbon; Cation exchange; Cation exchanging; Cations; disturbance; Dominance; Dynamics; Ecological succession; Ecosystem recovery; Ecosystems; Elevation; Environmental gradient; Environmental restoration; Exchange capacity; Forest ecosystems; Forest management; Forests; Gradients; landscape ecology; Lianas; Mortality; Mountains; Organic carbon; Organic soils; plant–climate interactions; plant–plant interactions; plant–soil interactions; Recovery; Recruitment; Regeneration; Regeneration (biological); restoration; Soil properties; Stems; Terrestrial ecosystems; topography; Trees; Tropical forests; vines; Tanzania
• ISSN: 0022-0477; 1365-2745
• DOI: 10.1111/1365-2745.14347

Lianas, or woody vines, are key components of many tropical forests and can have substantial impacts on the dynamics and functioning of these important ecosystems. Their competition with trees for resources, in particular light, can hamper the recovery of forests from disturbances. Yet, it is unclear how forest disturbance interacts with liana–tree ratio (LTR), topography and soil properties to shape tree dynamics and the trajectories of forest succession. Using temporal data from the Kilombero Valley and the Udzungwa Mountains of Tanzania, we demonstrate how the dynamics of tree stems and biomass vary between secondary and old‐growth forests with changes in the dominance of lianas and environmental gradients. Greater tree recruitment and mortality in secondary forests compared with old‐growth forests suggested rapid regeneration processes and faster turnover. However, no significant differences were found in the net annual changes in the number or biomass of trees between secondary and old‐growth forests. Our findings also showed that higher LTRs were positively associated with stem mortality but also with tree biomass growth, indicating a nuanced ecological role of lianas in forest ecosystems, which warrants further investigation to fully understand the causal factors at play. Net changes in tree stem numbers decreased significantly with elevation, implying climatic constraints on forest regeneration at higher elevations. Soil cation exchange capacity and organic carbon were found to significantly influence tree stem recruitment and net change in abundance, although their effects on biomass remained unclear. Synthesis: Our findings indicate that the recovery of tropical forests from disturbance in terms of the number and biomass of tree stems may be predictable along environmental gradients. These insights have the potential to broaden our capacity to develop more nuanced strategies that identify when and where tropical forests may require restoration interventions, with a focus on structural recovery. Muhtasari Lianas, au kamba za miti, ni mimea muhimu katika misitu mingi ya kitropiki ambayo inaweza kuwa na athari kubwa kwenye mienendo na utendaji wa mifumo hii muhimu ya ikolojia. Ushindani wao na miti kwa rasilimali, hasa mwanga, unaweza kuzuia urejesho wa misitu kutokana na kuvurugika kimazingira. Hata hivyo, haijulikani ni jinsi gani kuvurugika kwa misitu kunavyoingiliana na uwiano wa liana‐miti, topografia, na sifa za udongo, ili kushape mienendo ya miti na mwelekeo wa mafanikio ya misitu baada ya kuvurugika. Kwa kutumia data ya muda kutoka Bonde la Kilombero na Milima ya Udzungwa nchini Tanzania, tunaonyesha jinsi mienendo ya shina la miti na biomasi inavyotofautiana kwenye misitu ya sekondari na misitu ya kale kutokana na mabadiliko katika utawala wa liana na gradi za kimazingira. Uajiri mkubwa wa miti na vifo vyao katika misitu ya sekondari ikilinganishwa na misitu ya kale vimependekeza mchakato wa ukuaji haraka na mzunguko wa haraka. Hata hivyo, hakukuwa na tofauti kubwa katika idadi ya miti kwa mwaka au mabadiliko ya biomasi kati ya misitu ya sekondari na misitu ya kale. Matokeo yetu pia yalionyesha kuwa uwiano wa juu wa liana‐miti ulikuwa una uhusiano chanya na vifo vya shina lakini pia na ukuaji wa biomasi ya miti, ikionyesha jukumu tata la ikolojia la lianas katika mifumo ya misitu, ambayo inahitaji uchunguzi zaidi ili kuelewa kikamilifu sababu za kisababishi zinazocheza. Mabadiliko ya jumla katika idadi ya shina la miti yalipungua sana na mwinuko, ikimaanisha vikwazo vya hali ya hewa kwenye urejesho wa misitu katika viwango vya juu. Uwezo wa udongo kubadilishana kationi na wingi wa kaboni ya kikaboni ulionekana kuwa na athari kubwa katika uajiri wa shina la miti na mabadiliko ya jumla katika wingi, ingawa athari zao kwenye biomasi bado hazikuwa wazi. Usanisi: Matokeo yetu yanaonyesha kuwa urejesho wa misitu ya kitropiki kutokana na usumbufu kwa suala la idadi na biomasi ya shina la miti inaweza kutabirika kando ya gradi za kimazingira. Maarifa haya yanatoa mwanga katika kuendeleza mikakati ya kutambua ni lini na mahali gani urejesho wa misitu ya kitropiki unahitajika. Secondary tropical forests can show resilience, maintaining carbon storage and ecological functions despite disturbances. Tree dynamics are influenced by elevation, soil properties and complex interactions with lianas, which can have both positive and negative impacts, depending on the context. These insights can guide ecosystem restoration strategies, considering environmental gradients and forest structure, in the context of global climate change mitigation.