Adaptation in Montane Plants

Science Center Objects

Montane plant communities in widely separated intact natural environments of the world have responded to changes in precipitation and temperature regimes by shifting both margins and core distributional ranges upward in elevation.  Reduced evapotranspiration rates in cooler climate zones at higher elevation may compensate for less precipitation and higher temperatures within species’ former ranges.  Plants with short generation times and faster population turnover, such as grasses, may be able to quickly disperse upward; however, longer-lived plants that disperse more slowly may consequently adapt poorly to rising elevation of climate zones.

Iliahi leaves
Native ‘iliahi plant. Photo: S. Hess

Overview:

Montane plant communities in widely separated intact natural environments of the world have responded to changes in precipitation and temperature regimes by shifting both margins and core distributional ranges upward in elevation.  Reduced evapotranspiration rates in cooler climate zones at higher elevation may compensate for less precipitation and higher temperatures within species’ former ranges.  Plants with short generation times and faster population turnover, such as grasses, may be able to quickly disperse upward; however, longer-lived plants that disperse more slowly may consequently adapt poorly to rising elevation of climate zones.

Several studies have reported warmer and drier climate conditions in Hawai‘i consistent with climate change reported in other environments throughout the world, including a rapid rise in surface temperature since about 1975, downward trends in annual precipitation since 1905, upward trends in drought indexes since the 1950s, and long-term (1913–2008) downward trends in streamflow and groundwater discharge to streams.  Moreover, changes in the trade wind inversion that limit upward movement of prevailing moisture-laden trade winds indicate a long-term shift toward drier conditions for high-elevation areas in Hawai‘i, and long-term drought has occurred since 2008.

Mountain parklands are among the most degraded ecosystems in Hawai‘i.  Centuries of adverse land use practices have caused deforestation, fragmentation, and genetic isolation in montane plants, disrupting biological connectivity between high-elevation subalpine woodlands and lower-elevation montane wet and mesic forests. The loss of montane forest cover also breaks an important positive feedback mechanism by interrupting fog-drip interception whereby convection commonly delivers additional precipitation to higher-elevation forests.

Koa flowers
Koa flowers. Photo: S. Hess

There is now substantial evidence that non-native ungulates have degraded native ecosystems throughout Hawai‘i, and that recovery of native plant communities cannot occur in the continued presence of ungulates. Several species of non-native ungulates are known to directly inhibit regeneration and cause mortality in many native tree and understory plant species through herbivory, digging, and bark stripping. To date, ungulates have been completely excluded or removed from roughly 750 km2 of important terrestrial ecosystems throughout the Hawaiian Islands, including the Kanakaleonui Bird Corridor (KBC) of windward Mauna Kea.  Although these management actions have demonstrated beneficial effects for native ecosystems, some areas like KBC may require intensive restoration efforts to recover ecological integrity and ecosystem function, particularly during a regime of changing climate.

Organisms that cannot disperse or adapt biologically in situ to rapid environmental changes may decrease in distributional range and abundance, thereby diminishing ecosystem resilience.  Moreover, fragmented forest habitats may have little gene flow due to limited seed dispersal, further reducing species’ ability to adapt naturally.  Several native plant species in mountain parkland ecosystems are found naturally over a broad range of elevation, but may become range-restricted if environmental conditions shift rapidly as a consequence of climate change.  Remaining plant populations may now be poorly-suited for natural recovery within mountain parklands; however, conspecifics from more distant seed sources may grow more vigorously and have greater survival at higher elevation if altitudinal climate zones have shifted upward.  Genetic enrichment from more appropriate elevation climate zones may benefit such species.  Transplanting conspecifics from low-elevation locations to small fragmented populations in higher-elevation zones is a potential management approach that encourages evolutionary change by moving climate compatible variants to more appropriate zones faster than they can disperse naturally.

USGS personnel and cooperators plant native plants
USGS personnel and cooperators plant native Hawaiian plants on Mauna Kea. Photo: S. Hess

Project Objectives:

The primary focus of this work is to determine if montane plants may be able to adapt to the ecological effects of climate change by facilitating their movement to more favorable environments.  This experimental research will determine if genetic enrichment may enhance survival, growth, and adaptation of important native montane plant species subject to changing precipitation patterns in Hawai‘i.  We propose to collect seeds of montane plants from low- and high-elevation sources, conduct outplanting trials in common locations along an elevation gradient, and monitor survival, growth, and vigor.  We will test the hypothesis that moving the distributional ranges of montane plants upward in elevation can facilitate adaptation to climate change.  This work will identify sources of plant seeds from appropriate climate zones to restore mountain parkland ecosystems, thereby increasing ecosystem resilience and tolerance to contemporary and future climate conditions.  This proposed research addresses an important gap in knowledge for bridging plant vulnerability assessment efforts by PICCC and others that have not been explicitly addressed elsewhere (Fortini et al. 2013).  Differences in plasticity and population-based environmental tolerances could have important effects on species’ responses to climate change and thus will help inform current estimates of vulnerabilities in Hawaiian plant species.

Highlights and Key Findings:

PIERC cooperators plant native Hawaiian plants
USGS personnel and cooperators plant native Hawaiian plants on Mauna Kea. Photo: S. Hess

Forests throughout the world have been moving higher in elevation as a response to climate change over the past several decades.  Higher-elevation areas may offer more favorable, cooler environments than the former ranges of these forests. The culturally-rich forests of Mauna Kea volcano on Hawai‘i Island, however, cannot move upslope because they are blocked by an unsuitable zone. Centuries of habitat degradation have virtually eliminated the mountain parkland forest, which has been replaced by non-native grasses.  These grasses compete with tree seedlings for water and nutrients, and increase the likelihood of destructive fires, preventing the natural regeneration of trees and plants. The inability to extend into higher elevation environments may restrict forest species to increasingly smaller ranges.  Restoration of mountain parkland forests may therefore need to accommodate for a changing climate by assisting the gradual upslope movement of plants and trees. To determine if upslope movement is necessary for Hawaiian forest plants to adapt to climate change, we are conducting research by experimentally moving seedlings of eight culturally important Hawaiian forest species to higher elevation sites, and comparing survival and growth to the same species which will be moved downslope. The outcome of this experimental research will be used to guide restoration strategies for mountain forests.