title: Lianas, trees and insect herbivory
Creators: name: Odell, Erica
Publisher: name: Griffith University
Year: 2018
Subjects: subject: Lianas
subject: Woody climbing plants
subject: Neotropical rainforest
subject: Herbivorous insects
subject: Tropical rainforests
subject: Herbivory
subject: Leaf traits

description: Insect herbivory is a key ecological process which mediates the structure, functioning and maintenance of forests. Studies of insect herbivory in tropical forests typically focus on trees whereas the contributions of other plant types, particularly climbing plants, remains undervalued and under studied. Lianas, or woody climbing plants, are important ecosystem contributors. Per unit basal area, lianas support substantially more leaves than trees and typically comprise 20-40% of the above ground leaf biomass in rainforests. This indicates a likely function in insect herbivory. Little data, however, exists which quantifies the importance of their contribution to overall ecosystem dynamics, particularly in contrast with trees. Information on the contributions of other plant types to herbivory are necessary if we are to fully appreciate the role of lianas in herbivory and understand the ways in which forests and associated processes may shift given anticipated environmental and vegetation changes. This thesis aims to address this knowledge gap and demonstrate the value of lianas in supporting herbivory and associated insect assemblages. I aim to establish the need for a better understanding of liana-supported insect herbivory, quantify the trophic link among different plant types and insects in two contrasting rainforests, and determined the influence of structural and chemical leaf traits. First, I determine the need for liana focussed herbivory research by providing a comprehensive review of the literature. Second, I examine the temporal changes in liana and tree communities over two decades in a 1 ha plot of Australian subtropical rainforest. It is firmly established that lianas are increasing in Neotropical rainforest. In other bioregions, however, the pattern is less clear and derived from few sources. In Australia, where the factors influencing vegetation dynamics may differ, no such studies exist. I found liana abundance and biomass increased substantially from 2005 to 2015 while tree abundance remained stable from 1995 to 2015. Tree biomass also rose considerably, but at approximately half the rate of lianas. Based on the structure of liana and tree communities, I suggest increasing atmospheric CO2 to be the most probable explanatory hypothesis over changes in rainfall or tree mortality. Given the results presented here and other documented increases in liana abundances globally, it is concerning we do not know more about the ecosystem services they provide. Third, theoretical and empirical evidence suggests lianas may be an important food source for phytophagous insects. I address this hypothesis by two methods. First, in a literature-based study I assess the relative use of lianas as host plants for Australian butterflies. Second I make quantitative assessments Insect herbivory is a key ecological process which mediates the structure, functioning and maintenance of forests. Studies of insect herbivory in tropical forests typically focus on trees whereas the contributions of other plant types, particularly climbing plants, remains undervalued and under studied. Lianas, or woody climbing plants, are important ecosystem contributors. Per unit basal area, lianas support substantially more leaves than trees and typically comprise 20-40% of the above ground leaf biomass in rainforests. This indicates a likely function in insect herbivory. Little data, however, exists which quantifies the importance of their contribution to overall ecosystem dynamics, particularly in contrast with trees. Information on the contributions of other plant types to herbivory are necessary if we are to fully appreciate the role of lianas in herbivory and understand the ways in which forests and associated processes may shift given anticipated environmental and vegetation changes. This thesis aims to address this knowledge gap and demonstrate the value of lianas in supporting herbivory and associated insect assemblages. I aim to establish the need for a better understanding of liana-supported insect herbivory, quantify the trophic link among different plant types and insects in two contrasting rainforests, and determined the influence of structural and chemical leaf traits. First, I determine the need for liana focussed herbivory research by providing a comprehensive review of the literature. Second, I examine the temporal changes in liana and tree communities over two decades in a 1 ha plot of Australian subtropical rainforest. It is firmly established that lianas are increasing in Neotropical rainforest. In other bioregions, however, the pattern is less clear and derived from few sources. In Australia, where the factors influencing vegetation dynamics may differ, no such studies exist. I found liana abundance and biomass increased substantially from 2005 to 2015 while tree abundance remained stable from 1995 to 2015. Tree biomass also rose considerably, but at approximately half the rate of lianas. Based on the structure of liana and tree communities, I suggest increasing atmospheric CO2 to be the most probable explanatory hypothesis over changes in rainfall or tree mortality. Given the results presented here and other documented increases in liana abundances globally, it is concerning we do not know more about the ecosystem services they provide. Third, theoretical and empirical evidence suggests lianas may be an important food source for phytophagous insects. I address this hypothesis by two methods. First, in a literature-based study I assess the relative use of lianas as host plants for Australian butterflies. Second I make quantitative assessments Insect herbivory is a key ecological process which mediates the structure, functioning and maintenance of forests. Studies of insect herbivory in tropical forests typically focus on trees whereas the contributions of other plant types, particularly climbing plants, remains undervalued and under studied. Lianas, or woody climbing plants, are important ecosystem contributors. Per unit basal area, lianas support substantially more leaves than trees and typically comprise 20-40% of the above ground leaf biomass in rainforests. This indicates a likely function in insect herbivory. Little data, however, exists which quantifies the importance of their contribution to overall ecosystem dynamics, particularly in contrast with trees. Information on the contributions of other plant types to herbivory are necessary if we are to fully appreciate the role of lianas in herbivory and understand the ways in which forests and associated processes may shift given anticipated environmental and vegetation changes. This thesis aims to address this knowledge gap and demonstrate the value of lianas in supporting herbivory and associated insect assemblages. I aim to establish the need for a better understanding of liana-supported insect herbivory, quantify the trophic link among different plant types and insects in two contrasting rainforests, and determined the influence of structural and chemical leaf traits. First, I determine the need for liana focussed herbivory research by providing a comprehensive review of the literature. Second, I examine the temporal changes in liana and tree communities over two decades in a 1 ha plot of Australian subtropical rainforest. It is firmly established that lianas are increasing in Neotropical rainforest. In other bioregions, however, the pattern is less clear and derived from few sources. In Australia, where the factors influencing vegetation dynamics may differ, no such studies exist. I found liana abundance and biomass increased substantially from 2005 to 2015 while tree abundance remained stable from 1995 to 2015. Tree biomass also rose considerably, but at approximately half the rate of lianas. Based on the structure of liana and tree communities, I suggest increasing atmospheric CO2 to be the most probable explanatory hypothesis over changes in rainfall or tree mortality. Given the results presented here and other documented increases in liana abundances globally, it is concerning we do not know more about the ecosystem services they provide. Third, theoretical and empirical evidence suggests lianas may be an important food source for phytophagous insects. I address this hypothesis by two methods. First, in a literature-based study I assess the relative use of lianas as host plants for Australian butterflies. Second I make quantitative assessments of herbivore damage in the canopy of a tropical Chinese rainforest and the understory of a subtropical Australian rainforest based on new, primary data. Lianas, and vines alike, are hypothesised to be important food plants for butterflies. This speculation, however, has never been formally tested. Based on available food plant information of Australian butterflies, I found lianas to be an important food source for butterfly caterpillars in rainforests and their use as host plants to be greater than what simple plant diversity would predict. Interestingly, butterflies feeding on climbing plants had significantly greater incidences of monophagy than those feeding on trees. The patterns of host plant use and specialisation on trees and lianas are similar to those found in phytophagous rainforest beetles elsewhere. If lianas support greater diversity and abundances of foliar feeding insects than trees, we would expect this to be reflected by asymmetrical incidences of herbivore damage across the two plant types. I found no overall significant difference across plant types in neither the canopy of a tropical Chinese rainforest or the understory of a subtropical Australian rainforest, providing further support for this hypothesis. I did however observe that; 1) lianas influence their host’s leaf traits, most likely through inputs of nitrogen rich leaf litter around the base of their hosts, 2) under drought conditions lianas may reduce the amount of herbivory occurring on their host trees, and 3) leaf traits important for predicting herbivory are not consistent across plant types. Through the combination of studies, I have shown that lianas are an important food source for herbivorous insects at least as much so as trees. The results of this thesis have helped close the knowledge gap in our understanding of herbivory and demonstrate the importance of lianas in supporting insect assemblages. Without understanding the contributions of other plant types to herbivory (and the associated insect faunas they support) we are unable to make accurate models and predictions about their future. Given lianas are increasing in many tropical rainforests, including those studied here, it is concerning that not more is known about their contributions to herbivory and their relationships with the insect herbivores they support – this thesis goes part way to allay this concern.