  Climate change and the resulting increased drought frequencies pose
considerable threats to forest herb populations, especially when compounded by
additional environmental challenges. Specifically, habitat fragmentation may
disrupt climate adaptation and cause shifts in mating systems. To examine this,
we conducted a garden experiment with Primula elatior offspring from 24
populations across a climate and landscape fragmentation gradient. We evaluated
vegetative, regulatory, and reproductive traits under different soil moisture
regimes, assessing local adaptation and phenotypic plasticity. We also
conducted a field study in 60 populations along the same gradient to examine
potential breakdown of reciprocal herkogamy. Our results showed an evolutionary
shift from drought avoidance in southern populations to drought tolerance in
northern populations for large, connected populations. However, fragmentation
disrupted climate clines and adaptive responses to drought in key traits
related to growth, biomass allocation and water regulation. Our findings also
indicate the beginning of an evolutionary breakdown in reciprocal herkogamy.
These disruptions resulted in significantly reduced flowering investment,
especially in southern fragmented populations. These findings provide new
evidence of how habitat fragmentation disrupts climate adaptation and drought
tolerance in Primula elatior, emphasizing the need to account for habitat
fragmentation in conservation strategies to preserve resilient forest herb
populations amidst global changes.
